Tesi sul tema "Carbon"

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007.
Vita.
Includes bibliographical references.
This thesis presents work towards the development of a new catalytic C-C bond forming reaction. Alkynes and olefins insert into [(IPr)CuH]2 (IPr = N,N-bis-(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene) to give copper vinyl and copper alkyl complexes. These copper complexes insert CO2 into the Cu-C bond to form copper acrylate and copper carboxylate complexes. Acrylic and carboxylic acids can be isolated by hydrolysis. A catalytic cycle based on (IPr)copper(I) was developed. Alkynes undergo reductive carboxylation to give acrylic acids in moderate yields. Unexpected interactions between several components of the catalytic system led to a number of side reaction, most importantly between [(IPr)CuH]2 and the product silyl acrylate. The use of silylcarbonate salts to desylilate the product enhanced yield. In addition, silylcarbonates can also serve as a source of CO2.
by Gergely Sirokman.
Ph.D.

El balanç entre l´entrada de C (dels residus vegetals) i sortides de C (principalment com CO2 de la descomposició del carboni orgànic del sòl -SOC-), determina el contingut de SOC, que és el depòsit de C més voluminós a la superfície terrestre. Als agroecosistemes semiàrids Mediterránis, l’aigua és el principal factor limitant del creixement del cultiu i de l´entrada de residus al sòl. Les pràctiques agronòmiques alternatives poden millorar el creixement vegetal i augmentar la quantitat de residus (entrada de C) en aquestos sistemes. No obstant això la resposta del contingut de SOC dependrà del balanç de les entrades amb les sortides de C. Aquest treball estudia els efectes de l’adopció a llarg termini de sistemes de conreu (NT, sembra directa; MT, mínim conreu CT, conreu convencional) i del nivell de fertilizació nitrogenada (zero; mitjà, 60 kg N ha-1; alt, 120 kg N ha-1) al balanç de C del sòl i el contingut de SOC. El contingut de SOC augmentà finalment 4.3 i 3.9 Mg C ha-1 sota NT repecte a MT i CT. Nivells mitjans i alts de fertilització nitrogenada augmentaren el contingut de SOC en 3.4 i 4.5 Mg C ha-1 respecte al contingut a les parcel•les no fertilitzades. L´adopció a llarg termini de pràctiques de conreu de conservació (sembra directa), juntament amb l’ús adequat de la fertilització nitrogenada van demostrar ser eines per a millorar la sostenibilitat dels nostres secans i emmagatzemar C al sòl.
El balance entre la entrada de C (de los residuos vegetales) y salidas de C (principalmente como CO2 de la descomposición del carbono orgánico del suelo -SOC-), determina el contenido de SOC, que es el mayor depósito terrestre de C. En agroecosistemas semiáridos Mediterráneos, el agua es el principal factor limitante del crecimiento del cultivo y de la entrada de residuos en el suelo. Las prácticas agronómicas alternativas pueden mejorar el crecimiento vegetal y aumentar la cantidad de residuos (entrada de C) en estos sistemas. Este trabajo estudió los efectos de la adopción a largo plazo de sistemas de laboreo (NT, no-laboreo; MT, laboreo minimo; CT, laboreo convencional) y del nivel de fertilización nitrogenada (cero; medio, 60 kg N ha-1; alto, 120 kg N ha-1) en el balance de C del suelo y el contenido de SOC. El contenido de SOC aumentó en 4.3 y 3.9 Mg C ha-1 bajo NT con respecto a MT y CT. Niveles medios y altos de fertilización nitrogenada aumentaron el contenido de SOC en 3.4 y 4.5 Mg C ha-1 con respecto al contenido en las parcelas no fertilizadas. La adopción a largo plazo de prácticas de laboreo de conservación (no-laboreo o siembra directa), junto con el uso adecuado de la fertilitzación nitrogenada demostraron ser herramientas para mejorar la sostenibilidad de los secanos semiáridos Mediterráneos y almacenar C en el suelo.
The balance between C inputs (from plant residues) and C outputs (mainly as CO2 from soil organic carbon -SOC- decomposition) determines the content of SOC which is is the largest terrestrial reservoir of carbon. Under semiarid Mediterranean agroecosystems, water limitation restrains plant growth and the return of crop residues to the soil. Alternative agronomical practices may improve crop growth and increase return of crop residue (C inputs) under these systems. This work studied the effects of long term adoption of tillage practices (NT, no-tillage; MT, minimum tillage; CT, conventional tillage) and nitrogen (N) fertilization level (zero; medium, 60 kg N ha-1; high, 120 kg N ha-1) on the SOC balance and the content of SOC. The stock of SOC was increased by 4.3 and 3.9 Mg C ha-1 under NT in comparison to MT and CT respectively. Long-term medium and high N fertilization increased the stock of SOC by 3.4 and 4.5 Mg C ha-1 in contrast to unfertilized plots. Long-term adoption of conservation tillage practices (no-tillage) together with adequate N fertilizer use, proved to be effective tools to improve sustainability of semiarid Mediterranean drylands and to store C in the soil.

Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Dr. Christopher Jones; Committee Co-Chair: Dr. Pradeep Agrawal; Committee Member: Dr. Sujit Banerjee; Committee Member: Dr. Tom Fuller. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The thesis is composed of two parts. Part I presents catalytic C-C, C-N, C-O bond formation: a series of dienylethers, 2,5-disubstituted furans, allylketones, γ-functionalized ketones, multisubstituted quinolines were made starting from terminal alkynes with the initial help of a ruthenium catalyst. Part II presents C-C, C-N, C-O bond formation reactions: a variety of tetrahydropyrimidines, and 1,3-oxazines were synthesized starting from electron-deficient alkynes via multiple component reactions
La thèse est composée de deux parties. La partie I présente la formation catalytique de liaisons C-C, C-N et C-O : une série d’ethers, de diényle, furanes 2,5-disubstitués, cétones allyliques et γ-fonctionalisées et quinolines polysubstituées ont été préparées à partir d’alcynes avec l’aide initiale d’un catalyseur de ruthenium. La partie II présente la formation de liaisons C-C, C-N, C-O: une variété de tetrahydropyridines, et de 1,3-oxazines ont été synthétisées à partir d’alcynes electrophiles via des réactions à composants multiples

Ce travail de thèse présente le développement de nouvelles réactions de formation de liaisons carbone-carbone. Le premier chapitre décrit la cyanation d’arylzinciques par catalyse au cobalt à partir d’une source non toxique et bénigne, le N-cyano-N-phenyl-p-methylbenzenesulfonamide (NCTS), et conduit à de bons rendements en benzonitriles correspondants. Dans cette réaction, le cobalt sert de catalyseur non seulement pour la formation des arylzinciques mais aussi pour la formation de liaisons C-CN. Les groupements fonctionnels, cétone et nitrile, sont permis lorsque le complexe de cobalt associé au ligand bipyridine est utilisé. Le deuxième chapitre porte sur l’homocouplage Csp3-Csp3. Un simple halogénure de cobalt permet de catalyser la dimérisation des halogénures d’alkyles et des acétates d’allyles avec de bons à d’excellents rendements. L’ajout d’iodure de sodium permet d’étendre cette réaction aux chlorures et tosylates d’alkyles. Le couplage croisé entre 2 halogénures d’alkyle différents a également été testé mais les conditions doivent être optimisées. Dans le troisième chapitre, le couplage croisé catalysé au cobalt entre des bromures vinyliques et des chlorures benzyliques est présenté. Des halogénures de vinyles et de benzyles porteurs de groupements electrodonneurs ou electroattrateurs peuvent ainsi être couplés efficacement avec rétention de la configuration de la double liaison. Un mécanisme radicalaire semble être impliqué. Enfin, le dernier chapitre décrit l’arylation d’une 2-phenylpyridine avec un arylzincique par catalyse au cobalt par activation d’une liaison C-H et conduit à de premiers résultats encourageants
This thesis presents the development of cobalt-catalyzed carbon-carbon bonds formation. The first chapter describes a novel cobalt-catalyzed electrophilic cyanation of arylzinc species, employing benign and non-toxic N-cyano-N-phenyl-p-methylbenzenesulfonamide (NCTS) as the cyano source. In this reaction, cobalt catalyzes both the formation of arylzinc species and the cyanation reaction. Various benzonitriles are synthesized affording good to excellent yields. Using cobalt-bipyridine complexes instead of CoBr2, ketone and nitrile groups can be tolerated. The second chapter reports cobalt-catalyzed Csp3-Csp3 homocoupling reaction. A simple catalytic system could deliver dimers of a number of alkyl halides/pseudohalides and allylic acetates. Sodium iodide is crucial for the homocoupling of unactivated alkyl chlorides and tosylates. This method is extended to alkyl-alkyl cross-coupling; however, the conditions still need to be optimized. The third chapter describes a cobalt-catalyzed vinyl-benzyl cross-coupling. A variety of functionalized vinyl bromides and benzyl chlorides are efficiently coupled under mild conditions in good to excellent yields, with retention of Z/E configuration. A few mechanistic experiments indicate a single electron transfer involved. The last chapter discusses the progress on the cobalt-catalyzed arylation of 2-phenylpyridine with an arylzinc species by C-H activation and promising results are obtained

2013/2014
La nanotecnologia è chiamata a rivoluzionare molti settori della nostra vita. Tra tutti i campi in cui è convolta, la ricerca delle energie rinnovabili, la possibilità di ottenere acqua pulita in tutte le parti del mondo, il miglioramento della salute e l’aumento dell’aspettativa di vita e lo sviluppo di sistemi informatici, sono gli obiettivi che si distinguono. Le nanostrutture di carbonio sono materiali promettenti che possono aiutare a raggiungere questi obiettivi: includono fullereni, grafene, nanotubi e nanohorns di carbonio. Tutti hanno proprietà interessanti e offrono nuovi vantaggi per le applicazioni in chimica dei materiali e nella medicina. Il nostro gruppo di ricerca ha sviluppato interessanti metodi per modificare queste nanostrutture per poterli applicare nei campi sopra menzionate. In questo contesto, lo scopo generale di questa tesi è il disegno di sistemi multifunzionali basati su nanostrutture di carbonio destinati ai sensori e alle applicazioni biologiche. Nel capitolo 1, viene fatta una breve panoramica dei nanotubi e i nanohorns di carbonio, spiegando la loro struttura, le loro proprietà e le loro applicazioni. Inoltre, vengono descritte le diverse strategie per la loro funzionalizzazione. Il riconoscimento molecolare gioca un ruolo importante in molti sistemi biologici. In flavoproteine, l'interazione specifica tra il cofattore flavina e l’apoenzima determina la reattività della proteina. Di conseguenza, la modulazione dell'ambiente delle flavine può essere utilizzata come strumento per determinare il loro comportamento e anche per comprendere i processi molecolari negli enzimi. Con questi obiettivi in mente, nel capitolo 2 è descritta la sintesi di differenti derivati basati sul sistema nanotubi di carbonio-triazina per l’uso come ricevitori di riboflavina. In primo luogo, la sintesi e la caratterizzazione di diverse 1,3,5-triazine sono riportate. In una seconda fase, viene descritta la funzionalizzazione di nanotubi di carbonio a parete singola e a parete multipla con le differenti triazine e anche con catene di p-tolil, impiegando le radiazioni microonde. Dopo, si riporta la caratterizzazione completa di questi derivati con varie tecniche. L’auto-assemblaggio degli ibridi è stato analizzato con microscopia elettronica a trasmissione, osservando come i funzionalizzati con 1,3,5-triazine formano buone dispersioni in acqua, mentre loro si auto-assemblano in solventi non polari a causa del riconoscimento di legami d’idrogeno complementari. Tuttavia, derivati funzionalizzati con p-tolil formano migliori dispersioni in solventi organici ed invece si auto-assemblano in acqua. Viene poi studiata la capacità dei nanotubi di carbonio funzionalizzati a parete multipla di riconoscere la riboflavina con la spettroscopia di fluorescenza e ultravioletta visibile, analizzando la grandezza delle interazioni non-covalenti. Si vede come la funzionalizzazione covalente dei nanotubi di carbonio diminuisce la loro capacità di formare interazioni  mentre le interazioni di legame d’idrogeno giocano un ruolo fondamentale nel processo di riconoscimento tra i membri del sistema. Inoltre, si è demostrata l’influenza dei tipi di triazine nel comportamento della riboflavina. In questo modo, è dimostrata la modulazione del riconoscimento molecolare della riboflavina attraverso i diversi nanotubi. Così, recettori artificiali in processi di catalisi possono essere specificamente disegnati per ottenere il controllo delle interazioni tra i nanotubi di carbonio funzionalizzati e la riboflavina, modificando il suo comportamento. Inoltre, le dimensioni e le eccellenti proprietà di nanotubi permettono di utilizzarli come strumento nella progettazione di sensori per la rivelazione di singole molecole. Nel capitolo 3 si riporta la modifica di nanohorn di carbonio per l'impiego come farmaci selettivi nella terapia del cancro è rapportata. Prima, si mostra la sintesi e la caratterizzazione di diversi ibridi di nanohorn: Antibody-CNH, Drug-CNH, Antibody-Drug-CNH e Double Functionalized-CNH. In particolare vengono usati cisplatino, come profarmaco, ed un anticorpo specifico per le cellule che mostrano l’antigene PSMA (Prostate-specific membrane antigen). Di seguito, vengono presentati diversi esperimenti biologici sviluppati in collaborazione con il professor Marco Colombatti dell’Università degli Studi di Verona (Italia). L’ibrido Antibody-Drug-CNH possiede una migliore capacità di uccidere selettivamente le cellule che presentano l'antigene PSMA, rispetto ad altri derivati di nanohorns. Il nuovo sistema progettato offre un grande potenziale dato dalla possibilità di modificare il tipo e il grado di funzionalizzazione. Questo permette di variare la quantità di farmaco o di anticorpo nelle nanostrutture con lo scopo di migliorare l’efficienza dei nuovi derivati. Inoltre, questo metodo può incorporare altri farmaci o anticorpi al sistema, aprendo la porta al trattamento di altre malattie. Il capitolo 4 descrive l'applicazione di diverse nanostrutture di carbonio nella terapia genica. Prima, si mostra la funzionalizzazione di nanohorns di carbonio con gruppi amminici, impiegando diversi metodi che utilizzano le radiazioni a microonde (cicloaddizione 1,3-dipolare e addizione radicalica). In seguito, viene presentato il lavoro svolto in "the Nanomedicine Lab" (Università di Manchester), sotto la supervisione del Prof. Kostas Kostarelos. L'efficacia dei nanohorns di carbonio funzionalizzati per formare complessi con siRNA è comparata con quella dei nanotubi di carbonio forniti dal gruppo del professor Kostarelos. Si è visto come i nanohorn di carbonio formino complessi con siRNA a differenza dei nanotubi. I complessi siRNA/nanohorn si caratterizzano utilizzando varie tecniche e viene analizzata la loro capacità di rilasciare il siRNA. Sebbene nanohorn di carbonio funzionalizzati con l’addizione radicalica mostrano una forte interazione con il materiale genetico, i derivati funzionalizzati con la cicloaddizione 1,3-dipolare lo rilasciano più facilmente. I risultati suggeriscono che, per conseguire il miglior carrier, la complessazione totale del siRNA con le nanostrutture dovrebbe essere evitato. Tuttavia, gli ibridi devono essere analizzati in vitro per garantire la migliore scelta. Questo studio contribuisce alla comprensione dell’uso di nanohorn di carbonio come vettori per terapia genica; ma, un maggior numero di derivati deve essere analizzato per un confronto completo con i nanotubi di carbonio.
La nanotecnología se presenta como una nueva ciencia que podrá revolucionar multiples aspectos de nuestras vidas. Entre los numerosos campos en los que la nanotecnología está centrada, la búsqueda de energías renovables, la posibilidad de obtener agua limpia en cualquier parte del mundo, la mejora de la salud y la longevidad de las personas así como el avance de los sistemas informáticos, son los objetivos que más destacan. Las nanoestructuras de carbon son nanomateriales prometedores que pueden ayudar a lograr esas metas. Estos materiales incluyen fullerenos, grafeno, nanohorns y nanotubos de carbono, entre otros. Todos ellos presentan propiedades interesantes y ofrecen nuevas ventajas para aplicaciones en química de materiales y medicina. Nuestro grupo de investigación ha desarrollado metodologías interesantes para la modificación de esas nanoestructuras con el objeto de que puedan ser útiles en las aplicaciones citadas anteriormente. En ese contexto, el objetivo general de esta tesis es el diseño de sistemas multifuncionales basados en nanoestructuras de carbono para ser usados en sensores y en aplicaciones biológicas. En el capítulo 1 se detallan la estructura y las propiedades de los nanohorns y los nanotubos de carbono junto a sus aplicaciones. Además, se muestra un resumen de las diferentes metodologías usadas para su funcionalización. El reconocimiento molecular juega un papel importante en numerosos sistemas biológicos. En flavoproteinas, la interacción específica entre el cofactor flavina y la apoenzima determina la reactividad total de la proteina. De este modo, la modulación del entorno de la flavina puede usarse como herramienta para determinar su comportamiento y, además, para entender los procesos moleculares en las enzimas. Con esos objetivos en mente, en el capítulo 2 se describe la síntesis de diferentes derivados basados en el sistema nanotubo de carbono-triazina para usarlos como receptores múltiples de riboflavina. En primer lugar, se sintentizan y caracterizan distintas 1,3,5-triazinas. En un segundo paso, se funcionalizan nanotubos de carbono tanto de pared simple como de pared multiple con las diferentes triazinas así como con cadenas de p-tolilo usando radiación microondas, y esos derivados se caracterizan completamente mediante diversas técnicas. El autoensamblaje de los híbridos se analiza mediante microscopía de transmisión electrónica observando como los derivados de 1,3,5-triazinas forman buenas dispersiones en agua y se autoensamblan en disolventes no polares debido al reconocimiento mediante enlaces de hidrógeno complementarios. Sin embargo, los derivados de p-tolilo forman mejores dispersiones en disolventes orgánicos y se agregan en agua. Finalmente, la habilidad de los nanotubos de carbono de pared múltiple funcionalizados para reconocer la riboflavina se estudia mediante fluorescencia y espectrocopía ultravioleta visible, analizando el alcance de las interacciones no covalentes. La funcionalización covalente de nanotubos de carbono disminuye su habilidad para formar interacciones  mientras que las interacciones mediante enlaces de hidrógeno juegan un papel fundamental en el proceso de reconocimiento entre los componentes del sistema. También se estudia la infuencia de las diferentes triazinas en el comportamiento de los complejos. De esta manera, se demuestra la modulación del reconocimiento de la riboflavina por medio de los diversos híbridos de nanotubos de carbono. Así, los receptores artificiales en procesos de catálisis pueden ser específicamente diseñados para lograr control de la interacción entre los nanotubos de carbono funcionalizados y la riboflavina, modificando así su comportamiento. En el capítulo 3 se describe la modificación de nanohorns de carbon para ser usados como fármacos selectivos en la terapia contra el cancer. En primer lugar se muestra la síntesis y caracterización de diferentes híbridos de nanohorns: Antibody-CNH, Drug-CNH, Antibody-Drug-CNH and Double Functionalized-CNH. En particular se usan cisplatino en forma de prodroga y un anticuerpo específico (D2B) para células de próstata que muestran el antígeno PSMA. Finalmente se presentan diferentes experimentos biológicos desarrollados en colaboración con el profesor Marco Colombatti, de la Universidad de Verona (Italia). Se demuestra la mejor habilidad del híbrido Antibody-Drug-CNH para matar selectivamente células que muestran el antígeno PSMA en comparación con los otros derivados de nanohorns. El nuevo sistema diseñado ofrece gran potencial debido la la posibilidad de modificar tanto el tipo como el grado de funcionalización. Esto permite variar la cantidad de fármaco o anticuerpo en la nanoestructura con el objetivo de conseguir una mejor eficacia del derivado. Además, con este método se pueden incorporar otros fármacos o anticuerpos al sistema, lo que abre la puerta al tratamiento de otras enfermedades. El capítulo 4 describe la aplicación de distintas nanoestructuras de carbono en terapia génica. Primero se muestra la funcionalización de nanohorns de carbono con grupos amino mediante diferentes metodologías usando radiación microondas (cicloadición 1,3-dipolar y adición radicálica). Después, se presenta el trabajo desarrollado en “the Nanomedicine Lab” (Universidad de Manchester) bajo la supervision del profesor Kostas Kostarelos. Se compara la eficacia de los nanohorns de carbono funcionalizados para formar complejos con siRNA con la de una serie de nanotubos de carbono aportados por el grupo del profesor Kostarelos. En nuestros experimentos, los nanohorns de carbon forman complejos mejor que los nanotubos. Los complejos siRNA/nanohorns se caracterizan mediante diversas técnicas y se analiza su capacidad de liberar el siRNA. Aunque los nanohorns de carbono funcionalizados mediante adición radicálica muestran una interacción más fuerte con el material genético, los derivados funcionalizados mediante cicloadición 1,3-dipolar lo liberan de manera más fácil. Los resultados sugieren que la complejación total entre el siRNA y la nanoestructura debe ser evitada para lograr más fácilmente el posterior desplazamiento de este dentro de la célula. Sin embargo, para garantizar la elección del híbrido más eficaz, los complejos deben ser analizados in vitro. Por tanto, este estudio contribuye al entendimiento de los nanohorns de carbono como vectores en terapia génica. No obstante, un mayor número de derivados deben ser analizados para lograr una comparación completa con los nanotubos de carbono.
Nanotechnology is claimed to revolutionize every aspect of our life. Among the large number of fields in which nanotechnology is involved; finding renewable clean energy, obtaining clean water for all, improving health and longevity and enhancing computing power are the most noteworthy. Carbon nanostructures are promising nanomaterials that can help to achieve these objectives. Fullerenes, graphene, nanohorns and nanotubes are including within these materials. All of them exhibit interesting properties and offer new opportunities for applications in material chemistry and medicine. Our research group has developed interesting methodologies for modifying these nanostructures in order to be used in the aforementioned applications. In this context, the objective of this thesis is the design of multifunctional systems based on carbon nanomaterials to be applied in sensors and in biological applications. Chapter 1 explains the structure, properties and applications of carbon nanohorns and carbon nanotubes, together with their applications. In addition, it provides an overview of the different methodologies to functionalize them. Molecular recognition plays an important role in numerous biological systems. In flavoproteins, the specific interaction between the flavin cofactor and the apoenzyme determines the reactivity of the entire protein. Therefore, the modulation of the environment of flavins can be used as a tool to set their behaviour and to understand the molecular processes in enzymes. With these aims, chapter 2 describes the synthesis of different carbon nanotubes-triazine derivatives to be used as multi-receptors of riboflavin. Firstly, different triazines are synthesized and characterized. In a second step, both single-walled and multi-walled carbon nanotubes are functionalized with different 1,3,5-triazine and p-tolyl chains using radical addition under microwave irradiation and these derivatives are characterized by different techniques. The self-assembly of these hybrids is analysed by transmission electron microscopy, observing how the 1,3,5-triazines derivatives form good dispersions in water and self-assemble in non-polar solvents due to the DAD-ADA hydrogen bonding recognition, while the p-tolyl derivatives show better dispersability in organic solvents and aggregate in polar solvents. Finally, the ability of the functionalized multi-walled carbon nanotubes to recognize riboflavin is studied by fluorescence and UV spectroscopy, analysing the scope of the different non-covalent interactions. It is shown that the functionalization of nanotubes by covalent approach decreases the ability of them to form  stacking and also that the hydrogen bond interactions play an important role in the recognition processes between the components. The influence of the different triazines in the complexes is also shown. Thus, the modulation of the molecular recognition of riboflavin by the diverse nanotubes hybrids is demonstrated. Therefore, our study clarifies the understanding of non-covalent interactions in biological systems. In this way, artificial receptors in catalystic processes could be designed through a specific control of the interaction between functionalized carbon nanotubes and riboflavin. Additionally, the size and the excellent properties of carbon nanotubes will permit to use them as the building blocks in the design of sensors for single-molecule detection. In chapter 3, the modification of carbon nanohorns to be applied as new selective drugs in cancer therapy is shown. Firstly, the synthesis and characterization of different conjugates by the functionalization of carbon nanohorns with orthogonal chains is reported: Antibody-CNH, Drug-CNH, Antibody-Drug-CNH and Double Functionalized-CNH. In particular, cisplatin in a prodrug form and a specific D2B antibody for PSMA+ prostate cancer cells are attached. In collaboration with the group of Professor Marco Colombatti, different biological experiments are reported. The better ability of Antibody-Drug-CNH to selectively kill PSMA+ cancer cells in comparison with the other synthesized CNHs hybrids is demonstrated. This new system offers great potentiality due to the possibility of modifying the type and degree of functionalization. This allows the variation of the quantity of drug or antibody attached to the nanostructure in order to play with the killing efficacy. Similarly, the method is useful to attach different drugs or antibodies opening the way to the treatment of other diseases. Chapter 4 describes the application of different carbon nanostructures in gene delivery. Firstly, the functionalization of carbon nanohorns with amino moieties by different methodologies (1,3-dipolar cycloaddition and radical addition) under microwave irradiation and their characterization is shown. Then, the work developed at the Nanomedicine Lab (University of Manchester) under the supervision of Professor Kostas Kostarelos is reported. The efficacy of the functionalized carbon nanohorns to form complexes with siRNA is compared with the one of functionalized carbon nanotubes provides by Prof. Kostarelos’s group. In our experiments, carbon nanohorns form complexes better than nanotubes. The nanohors complexes are characterized by different techniques and their capability to release siRNA is analysed. Although the carbon nanohorns functionalized by radical addition showed the strongest complexation of siRNA, the derivatives functionalized by 1,3-dipolar cycloaddition showed its easiest release. The results suggest that, in order to obtain the best candidate, a complete complexation of siRNA with the carrier should be avoided. However, the analysis of the cellular uptake should be evaluated in the future to assess the greatest candidate. These outcomes contribute to the understanding of the role of carbon nanohorns as gene delivery vectors. Nevertheless, additional derivatives should be tested for a fully comparison with carbon nanotubes.
XXVII Ciclo
1986

Thesis: Ph. D. in Organic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Chapter 1. Palladium-Catalyzed Fluorination of Cyclic Vinyl Triflates: Dramatic Effect of TESCF₃ as an Additive A method for the synthesis of cyclic vinyl fluorides with high levels of regiochemical fidelity has been achieved by Pd-catalysis employing a new biarylphosphine ligand and TESCF₃ as a crucial additive. Five, six, and seven-membered vinyl triflate substrates, as well as a few acyclic substrates undergo the transformation successfully. The intriguing "TESCF₃ effect" provided a new tool for addressing the problem of the formation of regioisomers in Pd-catalyzed fluorination reactions. Chapter 2. Mechanistic Studies on Pd-Catalyzed Fluorination of Cyclic Vinyl Triflates: Evidence for in situ Ligand Modification by TESC₃ as an additive. A detailed mechanistic hypothesis for the Pd-catalyzed fluorination of cyclic vinyl triflates, and the unusual effect of TESCF₃ as an additive has been developed by combined experimental and computational studies. The preference of conducting [beta]-hydrogen elimination rather than reductive elimination from the trans-LPd(vinyl)F complex, which is generated predominantly due to the trans-effect, caused the poor regioselectivity of the fluorination reaction under TESCF₃-free conditions. An in situ ligand modification by trifluoromethyl anion, leading to the generation of the cis-LPd(vinyl)F complex which prefers reductive elimination rather than Phydrogen elimination, is proposed to be responsible for the improved regioselectivity of the fluorination reaction when TESCF₃ was used as an additive. Chapter 3. CuH-Catalyzed Enantioselective Alkylation of Indoles with Ligand-Controlled Regiodivergence A method for the enantioselective synthesis of either NI- and C3-chiral indoles by CuH-catalysis, depending on the choice of ligand, was developed. In contrast to conventional indole functionalization in which indoles are used as nucleophiles, hydroxyindole derivatives are employed as electrophiles in this method. DFT calculations indicated that the extent to which the Cu-P bonds of the alkylcopper intermediate distort, determines the regioselectivity of the reaction.
by Yuxuan Ye.
Ph. D. in Organic Chemistry

This thesis documents the development of synthetic methodologies utilising rhodium catalysis for the formation of carbon-carbon bonds and the functionalisation of carbon-sulfur bonds. Chapter 1 provides an overview of the two main areas of research discussed in this thesis that include the key developments in the field of intra- and intermolecular rhodium-catalysed hydroacylation, and the major advances in cross-coupling reactions via the catalytic cleavage of carbon-sulfur bonds. Chapter 2 details the development of a tandem rhodium-catalysed hydroacylation, sulfide elimination and subsequent enantioselective 1,4-conjugate addition sequence allowing the preparation of stereodefined β-substituted ketones. This process enables the formation of two carbon-carbon bonds and offers a general method to access highly functionalised traceless hydroacylation products. Chapter 3 describes the development of a rhodium-catalysed alkyne hydroacylation, thio-Michael addition sequence in a one-pot fashion. This methodology enables the synthesis of a variety of sulfur-containing heterocycles. Chapter 4 documents the efforts towards the development of a rhodium-catalysed cross-coupling reaction with alkenyl sulfides and boronic acids via C-S bond activation. This study explores both a tether-free and a traceless tether approach. Chapter 5 summarises the research and the potential future work. Chapter 6 provides experimental details and data.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007.
Additional advisors: Krishan K. Chawla, Derrick Dean, Yogesh Vohra, Mark Weaver. Description based on contents viewed Feb. 13, 2009; title from PDF t.p. Includes bibliographical references (p. 174-186).

This dissertation mainly contains two parts: one is C-X (C, O, S) bond formation through gold(I) catalysis, one is new applications via gold(I/III) redox catalysis. In first part, gold(I) catalysts would be introduced and their general applications, then the TA-Au species will be emphasized including the design, synthesis, characters and their application in catalysis. The applications are well developed during the past decade in our group, but here only involves three examples regarding C-C, C-O and C-S bond formations. From these effective applications, the unique stability and reactivity of TA-Au will be studied and explained, which is the reason and value of TA-Au discovery. In second part, gold(I/III) redox catalysis will be presented through two application examples: cross-coupling of terminal alkynes, multiple bond di-functionalization. The most challenging part for coupling reactions is the competition between homo-coupling and cross-coupling products, while in our project, we have successfully developed a new method to selectively obtain cross-coupling as major product to homo-coupling product (ratio 12:1). Later on, we found a new method to achieve gold (I/III) redox cycle by using mild oxidant diazonium salt instead of PIDA or Selectfluor strong oxidant. The new mild and efficient method have largely extended the application of gold(I/III) redox catalysis into organic synthesis. In sum, the new gold catalysts and catalysis methods reported here are important to the development of gold catalysis field, which are critical and useful to help people understand the reason of applying noble gold species as catalysts, and the advantages that other metals do not have.

The thesis mainly deals with the explorations of homogeneous palladium and heterogeneous Ruthenium catalyzed Carbon–Nitrogen bond forming reaction of aryl halide with amine and alkyne with sodium azide and benzyl bromide. Heterogeneous palladium, Gold and Brønsted acid catalysed C-C bond forming reaction is investigated by using cross coupling and Michael addition reaction of p-Quinone methide with nucleophile. The work demonstrated in this thesis has been divided into three chapters
CSIR HRDG for fellowship
AcSIR

Aquesta tesi doctoral es basa principalment amb la síntesis de molècules petites potencialment útils per investigacions avançades. S'han utilitzat diferents metodologies per obtenir-les: 1) Cicloaddicions intramoleculars entre un alkí i una azida lliures de coure per l'obtenció de derivats de benzodiazepines. Obtenint-se una gran varietat de triazols fusionats a heterocicles de set membres. Posteriorment, s'han dut a terme proves d'activitat biològica. 2) a) Trencament d'enllaços carboni-carboni no activats d'amino alcohols i utilització d'aquest com a nucleòfil juntament amb bromurs d'aril en una reacció d'acoplament catalitzada per pal.ladi per l'obtenció de dibenzil amines. S'ha dut a terme una gran optimització dels diferents paràmetres de reacció; base, dissolvent, electròfil, temperatura, catalitzador i lligand. b) Trencament d'enllaços carboni-carboni no activats de N-alil amino alcohols i utilització d'aquest com a nucleòfil juntament amb bromurs d'aril en una reacció d'acoplament catalitzada per pal.ladi per l'obtenció d'aldehids arilats en la posició beta. S'ha dut a terme la síntesis d'un gran nombre d' amino alcohols nous i aquests han estat sotmesos a les condicions optimitzades de reacció. Demostrant que aquest transformació és útil per un gran ventall de substrats (bromurs d'aril i amino alcohols).L'enamina resultant de la reacció d'acoplament s'ha aconseguit alquilar amb vinil metil cetona amb bons rendiments però pobres diastereoselectivitats tot i així s'ha demostrant que la reacció és factible. Per finalitzar, s'ha aconseguit desenvolupar la versió enantioselectiva de l’anterior transformació obtenint bons excessos enantiomerics tot i que baixos rendiments.
Ésta tesis doctoral está basada principalmente en la síntesis de moléculas pequeñas potencialmente útiles para investigaciones avanzadas. Se han empleado diferentes metodologías para obtenerlas: 1) Cicloadiciones intramoleculares entre un alkino y una azida libres de cobre para la obtención de derivados de benzodiazepinas. Se han obtenido una gran variedad de triazoles fusionados a heterociclos de siete miembros. Posteriormente se han realizado pruebas de actividad biológica de las moléculas resultantes. 2) a) Escisión de enlaces carbono-carbono no activados de amino alcoholes y utilitzación de éstos como nucleófilos conjuntamente con bromuros de arilo para una reacción de acoplamiento catalizada por paladio para la obtención de derivados de dibenzil aminas. Se ha realizado una gran optimización de las condiciones de reacción; base, disolvente, electrófilo, temperatura, catalizador y ligando. b) Escisión de enlaces carbono-carbono no activados de N-alilo amino alcoholes y la utilización de éste como nucleófilo conjuntamente con bromuros de arilo en una reacción de acoplamiento catalizada por paladio para la obtención de aldehídos arilados en posición beta. Se ha realizado la síntesis de un gran numero de amino alcoholes nuevos y éstos se han sometido a las condiciones optimizadas de reacción. Demostrando que ésta transformación es útil para una gran variedad de sustratos (bromuros de arilo y amino alcoholes). La enamina resultante de la reacción de acoplamiento se ha alquilado con vinil metil cetona con buenos rendimientos pero pobres diastereoselectividades aunque se ha demostrado que la reacción es factible. Para finalizar, se ha desarrollado la versión enantioselectiva de la anterior transformación obteniendo buenos excesos enantioméricos aunque con bajos rendimientos.
This PhD thesis is based basically on synthesis of small molecules potentially useful for further investigations. Different strategies have been used to obtain them; 1) Copper free intramolecular cycloadditions between an azide and an akyne for the obtention of benzodiazepine derivatives. A wide range of triazoles fused to seven membered heterocycles rings have been obtained. Later, biological studies have been carried out. 2)a) Carbon-carbon bond cleavage of amino alcohols has been carried out with the subsequent use of them as a nucleophile together with aryl bromides to develop a cross-coupling reaction for the obtention of dibenzyl amines. A wide optimization of the reaction parameters was carried out; base, ligand, catalyst, electrophile, temperatura, and solent. b) Carbon-carbon bond cleavage of N- allyl amino alcohols has been carried out with the subsequent use of them as a nucleophile together with aryl bromides to develop a cross-coupling reaction for the obtention of beta arylated aldehydes. An important number of new amino alcohols have been synthesized and these have been subjected to the optimized reaction conditions. It has been demonstrated that this transformation is useful for a wide range of substrates (amino alcohols and aryl bromides). The resultant enamine has been alkylated with methyl vinyl ketone with good yields but poor diastereoselectivity. To finish the enantioselective version of beta functionalization of aldehydes has been developed obtaining good enantioselectivity but poor yields

Coal-tar pitch is a promising carbon matrix precursor for carbon-carbon composites. It has a suitable viscosity, high carbon yield, and it forms graphitic structures. In addition, pitch is a relatively cheap raw material. This thesis is a study on the use of coal-tar pitch as carbon matrix precursor in carbon–carbon composites.

2011 - 2012
This PhD work describes the development of different Michael and Michael type processes employing different bifunctional organocatalysts. All the processes studied involved a non-covalent activation of the substrates provided by the organic promoters. An asymmetric epoxidation of electron-poor trisubstituted olefins has been developed by employing the commercially available diphenyl prolinol which afforded the epoxides in high yield, complete diastereocontrol and good enantioselectivity. Diaryl prolinols were found to promote a Michael addition of -ketoesters to nitroalkenes. An unexpected high efficiency and stereocontrol was observed with hexafluorobenzene as unconventional solvent, but also employed as an additive. A convenient tandem double Michael addition process was developed to access symmetrically and unsymmetrically 3,5-diaryl substituted cyclohexanones by using quinine as catalyst. An aziridination reaction of terminal electron-poor olefins has been disclosed by using a commercially available aminothiourea catalyst. The desired aziridines, bearing a quaternary stereocenter, were isolated in good yield and enantiocontrol. These compounds, were regioselectively ring-opened to access valuable ,-disubstituted -amino ester derivatives. Finally an asymmetric Fischer indolization to produce helical molecules was investigated employing a chiral phosphoric acid as promoter and an ion-exchange polymer as ammonia scavenger. [edited by author]
XI n.s.

La croissance de nanotubes de carbone (NTC) sur particules micrometriques d'alumine (Al2O3) permet d'obtenir une dispersion uniforme des NTC dans des matrices sans enchevêtrement de NTC. Ce type de structure hybride NTC-Al2O3 fournit également une solution prometteuse au problème de sécurité de NTC car ils intègrent NTC avec des particules micrométriques, étendant la dimension des NTC à partir de nano-échelle au micro-échelle. Cependant, l'adhérence entre les NTC et les Al2O3 particules ne permet pas de fixer efficacement les NTC. Par ailleurs, une autre préoccupation essentielle de NTC est de savoir comment créer une forte adhésion interfaciale entre les NTC et les matrices polymères pour obtenir de bonnes propriétés mécaniques et de ne pas diminuer la conductivité électrique de NTC. Motivé par ces considérations, cette thèse vise à proposer plusieurs techniques concernant le dépôt d'une nano-couche conductrice sur la surface des structures hybrides NTC-Al2O3. De plus, les impacts de la nano-couche déposée sur la fixation des NTC à la surface d’Al2O3, sur la conductivité électrique des hybrides NTC-Al2O3, et sur l'adhésion interfaciale des systèmes NTC-Al2O3/epoxy composites sont étudiés en détail
Growth of carbon nanotubes (CNTs) on micro-sized alumina (Al2O3) particles helps to achieve a uniform dispersion of CNTs in matrices without CNT entanglement. This kind of CNT-Al2O3 hybrids also provides a promising solution to the CNT safety problem since they integrate CNTs with micrometric particles, extending dimension of CNT fillers from nano-scale to micro-scale. However, the adhesion between the CNTs and the Al2O3 particles doesn’t sufficiently enable to fix the CNTs firmly and stably. Besides, another crucial concern of CNTs is how to create a strong interfacial adhesion between CNTs and polymer matrices for good mechanical properties and meanwhile not to degrade CNTs’ electrical conductivity. Motivated by these considerations, this PhD thesis aims to establishing several techniques for deposition of an electrically conductive nano-layer on the surface of CNT-Al2O3 hybrids. And the impacts of the deposited nano-layer on the fixing the CNTs on the Al2O3 surface, on bulk electrical conductivity of the CNT-Al2O3 hybrids, and on the interfacial adhesion of CNT-Al2O3/epoxy composite systems are investigated in detail

Orientador: Francisco das Chagas Marques
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
Made available in DSpace on 2018-08-14T14:37:10Z (GMT). No. of bitstreams: 1 OliveiraJunior_MyrianoHenriquesde_D.pdf: 13534676 bytes, checksum: 4da81eaf9a2b22721528c9804801a446 (MD5) Previous issue date: 2009
Resumo: Neste trabalho desenvolvemos um sistema de deposição de filmes finos pela técnica de arco catódico filtrado (FCVA- Filtered Cathodic Vacuum Arc), que possibilita o desenvolvimento de ligas metálicas e, sobretudo, a deposição de filmes de carbono amorfo altamente tetraédrico. Utilizando este sistema desenvolvemos filmes de carbono amorfo (a-C) com elevada dureza (estimado em cerca de 50 a 60GPa) e alta concentração de ligações sp3 C-C em função da polarização do substrato. Estudamos as propriedades ópticas, mecânicas (stress e dureza), estruturais (Raman e RBS) e a estabilidade térmica (efusão de gases) destes filmes em função da energia de deposição. Também desenvolvemos e caracterizamos filmes de carbono crescidos por FCVA assistido por um feixe de íons secundário de Ar e Kr com diferentes energias, onde analisamos os efeitos da energia deste feixe sobre as propriedades físicas do material resultante. Além das estruturas de carbono intrínseco realizamos um estudo sobre filmes de carbono amorfo hidrogenado depositados por PECVD (plasma enhanced chemical vapor deposition) com diferentes tensões de bias (de 60 à 550V) e atmosferas mistas de CH4/Kr, onde variamos a pressão parcial deste gás nobre entre 0 e 50%. Estudamos a influência deste gás nobre sobre as propriedades estruturais do material assim como a forma como os átomos deste elemento se distribuem dentro da rede amorfa. Esta última análise foi baseada em estudos conduzidos a partir da absorção de raios-x na borda K do átomo de criptônio, onde verificamos a aglomeração destes átomos na forma de estruturas solidas. Também investigamos os processos de transformações estruturais ocorridas em estruturas a-C:H e ta-C com a temperatura baseadas na efusão de gases. Para este estudo construímos um sistema que funciona em ultra-alto vácuo, com temperatura controlada variando de ambiente até cerca de 1000 graus. Os estudos sobre as propriedades estruturais foram baseados, sobretudo, em medidas de espectroscopia de espalhamento Raman com radiação de excitação na região do visível e do ultravioleta, o que possibilita a obtenção de informações mais detalhadas sobre a forma como os átomos sp2 e sp3 distribuem-se no material. Por fim, exploramos o potencial de aplicação de três tipos de carbono amorfo; tipo polimérico (PLC), tipo diamante (DLC) e tetraédrico (ta-C) como monocamadas antirefletoras para células solares de silício cristalino e comparamos com o desempenho obtido com camadas fabricadas com materiais usualmente empregados na indústria para tal aplicação. Os resultados mostraram que filmes de carbono amorfo podem ser utilizados como camada anti-refletora. Os filmes de carbono tipo polimérico apresentaram resultados muito semelhantes aos obtidos com camadas convencionais de dióxido de estanho
Abstract: In this work we designed, manufactured and characterized a Filtered Cathodic Vacuum Arc (FCVA) deposition system. This technique is usually applied in the preparation of metallic alloys and highly sp3 - hybridized amorphous carbon thin films. By using this system we prepared a series of amorphous carbon films (a-C) with high hardness (up to ~60GPa) and high concentration of sp3 C-C bonds varying the deposition energy of the C+ ions. Mechanical (hardness and intrinsic stress) and structural (Raman, RBS and gas effusion) were investigated. Another series of a-C was developed by FCVA, but using an assisted beam of Ar or Kr as a function of the ion energy. The main purpose of this work is to understand of the effects of the bombardment of an energetic ion beam on the physical properties of the films. Another study performed on hydrogenated amorphous carbon films (a-C:H) were carried out on samples deposited by plasma enhanced chemical vapor deposition (PECVD). The films were prepared with different self-bias, varying from 60 up to 550V, and different mixed atmospheres of methane and krypton gases, varying the partial pressure of krypton from 0 to 50%. Films prepared at low bias are polymeric-like (PLC), while films prepared at high bias are diamond-like (DLC). We had performed investigations on the influence of this noble gas on the structural properties of the a-C:H films and how the Kr atoms are arranged within the amorphous matrix. The distribution of Kr atoms was studied mainly by x-ray absorption on the krypton absorption K-edge. Due to the absence of EXAFS oscillations the spectra were interpreted using the XANES region, which gave us evidences of clustering of Kr atoms. The processes involved in the a-C:H nd ta-C structural transformations during the thermal annealing were analyzed by means of thermal gas effusion measurements (using a quadrupole spectrometer) in a system developed in our laboratory. Raman scattering spectroscopy measurements were carried out with excitation radiation in the visible and ultraviolet ranges. This choice is justified due to the more detailed information obtained by multiwavelength Raman spectroscopy on the distribution of sp2and sp3sites within the amorphous carbon matrix. Finally, we had evaluated the possibility of the application of three types of amorphous carbon structures, the diamond-like and polymeric-like carbon, and the ta-C as antireflective coating on crystalline silicon solar cells. We observed that all amorphous carbon structures (DLC, PLC and ta-C) increase the short-circuit current of the solar cells. In the case of PLC films, the result is comparable to that obtained with conventional antireflective coating such as tin dioxide (SnO2)
Doutorado
Física da Matéria Condensada
Doutor em Ciências

Um dos grandes desafios a ser vencido para a utilização em larga escala das células a combustível de eletrólito polimérico alimentada com H2 obtido por reforma é a contaminação da superfície do eletrocatalisador de Pt, usualmente utilizado no ânodo,pelos gases CO e CO2 presentes no combustível. Neste trabalho é apresentado o estudo dos mecanismos de tolerância de materiais formados por Pt e Mo (Pt/C, Pt3Mo2/C e Pt1Mo1/C) aos contaminadores CO e CO2 e a influência da temperatura nesses processos. Os estudos foram realizados por meio de curvas de polarização com medidas de espectrometria de massas (EM) on line, experimentos de EM em circuito aberto e voltametria linear de remoção de CO adsorvido no catalisador em diferentes temperaturas. Para os catalisadores Pt/C e Pt3 Mo2 /C os resultados mostraram um aumento em 10 vezes na tolerância ao CO quando a temperatura de operação da célula é elevada em 20°C (de 85°C a 105°C) e uma tolerância significativamente superior do Pt3Mo2/C em relação à Pt/C. A ocorrência do mecanismo bifuncional, do mecanismo Eley-Rideal e da reação de Troca Gás-Água (do inglês Water Gas Shift - WGS) foi confirmada apenas para PtMo/C; porém, a diminuição do sobrepotencial de oxidação do CO com o aumento da temperatura foi notada para ambos os catalisadores. A reação de WGS é acelerada com a elevação da temperatura, confirmando que a cinética é a determinante da reação.Também foi realizada a quantificação do cruzamento do O2 do cátodo para o ânodo, sua participação na eliminação do CO e a influência da temperatura nesse processo. Observou-se que a oxidação parcial do CO pelo O2 efetivamente ocorre, aumenta com a temperatura, porém pouco contribui no processo global de tolerância dos catalisadores Pt/C e PtMo/C. Em relação ao contaminante CO3, confirmou-se a ocorrência da reação RWGS (WGS reversa) para ambos os catalisadores, assim como a reação RWGS eletroquímica. Em termos de desempenho de célula,excelentes resultados foram obtidos com a mesma operando a 105°C - para Pt3Mo2/C e utilizando uma mistura de H2/CO(75 ppm)/CO2(25%), observando-se sobrepotencial anódico de apenas 40 mV em relação ao hidrogênio puro em densidade de corrente de 1 Acm-2.
One of the biggest challenges to be overcome for the widespread use of polymer electrolye fuel cellsfueled with H2 obtained by reform is the surface contamination of the Pt electrocatalyst, usually used in the anode, by CO and CO2 present in the fuel stream. This work presents a study of the tolerance mechanisms of CO and CO2 contaminants on electrode materials formed by Pt and Mo (Pt /C, Pt3Mo2 /C, and Pt1Mo1/C) and the influence of temperature on these processes. The studies were performed using polarization curves with on line mass spectrometry measurements (MS), MS experiments at open circuit, and linear sweep CO stripping at different temperatures. For Pt/C and Pt3Mo2/C catalysts, results showed a 10 fold increase in the CO tolerance when the fuel cell operating temperature is raised by 20°C (85°C to 105°C) and a significantly higher tolerance of Pt3Mo2/C compared to Pt/C. The occurrence of the so called bifunctional mechanism, Eley-Rideal mecanism and the Water Gas Shift (WGS) reaction was confirmed only for PtMo/C, but the decrease in the CO oxidation overpotential with the increase of temperature was noted for both catalysts. Also a quantification of O2 crossover from the cathode to the anode was carried out, together with an evaluation of its participation in the elimination of CO and the characterization of influence of temperature in this process. It was observed that the partial oxidation of CO by O2 does occur, increases with temperature, but it has little effect in the overall tolerance of Pt/C and PtMo/Ccatalysts. The WGS reaction is accelerated by increasing the temperature, confirming that the kinetics of the reaction is rate determinant. Regarding CO2 contaminant, the occurrence of the RWGS reaction (reverse WGS) and the electrochemical RWGS were confirmed for both catalysts. In terms of cell performance, excellent results were obtained with the cell operating at 105°C for Pt3Mo2/C and using a mixture of H2/CO (75 ppm)/CO2 (25%), observing an anodic overpotential of only 40 mVcompared to pure hydrogen was observed at a current density of 1 Acm-2.

Les bis-ylures sont des espèces carbonées divalentes dans lesquelles un atome de carbone central porte deux charges négatives, chacune d’elles étant stabilisée par un hétéroatome chargé positivement en α du carbone. Transférer sélectivement l’atome de carbone central en se servant des deux fonctions ylures simultanément représente un grand intérêt pour les chimistes de synthèse. De telles sources atomiques de carbone restent toutefois rares, le carbone de la plupart des bis-ylures développés jusqu’à présent étant trop étroitement liées avec les deux ligands adjacent. Dans ce contexte, cette thèse se concentre sur le développement de bis-ylures et autres espèces réactives comprenant un ligand iodonium, fragment d’une extrême labilité qui permettrait une libération efficace du carbone central. Le premier chapitre est consacré à l’état de l’art des composés « carbone(0) » et à leur application en tant que source de carbone atomique, ainsi qu’à la structure et la réactivité de composés iodés hypervalents. Un second chapitre traite du relargage de bis-ylures après la rupture d’une liaison covalente, soit une liaison P–C d’ylures mixtes de phospho-iodonium stabilisés par une phosphine oxydée, soit une liaison Si–C d’ylures mixtes de phospho-iodonium stabilisés par un silane. Le troisième chapitre reporte nos tentatives d’obtenir des précurseurs de bis-ylures d’iodonium par iodation direct d’ylures de phosphonium ou de sulfoxonium nucléophiles. Le dernier chapitre concerne notre tentative de développer un yldiure d’iodonium, espèce pour laquelle seule une des deux charges négatives portées par le carbone est adjacente à un atome chargé positivement, l’autre n’étant stabilisé que par les effets inductifs et mésomères d’un groupement sulfonyle électroattracteur. Les résultats de ces tentatives nous ont permis d’identifier un nouvel ylure d’iodonium mono-stabilisé nucléophile, dont la réactivité avec des aldéhydes est décrite en fin de chapitre
Bis ylides are divalent carbonated s pecies on which a central carbon atom bears two negative charges, both stabilized by two α, positively charged heteroatoms. Selectively transferring the central carbon atom, using both ylides simultaneously is of great interest for synthetic chemists. Such atomic carbon sources are scarce, as most of the bis ylides developed until now were too tightly bind to his ligands. With this in mind, this thesis ambitions to develop bis ylides and other reactive species containing an iodonium ligand, an extremely labile fragment which could allowed an efficient liberation of the central carbon atom. The first chapter is dedicated to the state of the art of “carbon(0)” compounds and their application as atomic carbon sources, as well as the structure and reactivity of hypervalent iodine compounds. The second chapter is about releasing bis ylides by cleaving a covalent bond, either a P C bond from a phosphine oxide stabilized mixt phospho iodonium ylide, or a Si C bond from a silane stabilized mixt phospho iodonium ylide. A third chapter explains our attempts to obtain bis ylides precursor by direct iodination of nucleophilic phosphonium or sulfoxonium ylides. The last chapter is dedicated to our attempt to develop an iodonium yldiide, in which only one of the two negative charges borne by the central carbon is next to a positively charged heteroatom, the other being stabilized by a sulfonyl mesomeric and inductive effects. The results of those attempts allowed us to describe the reactivity of a new nucleophilic, mono stabilized iodonium ylide towards aldehydes

Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) have attracted intense research efforts with the expectation that these materials may have many unique properties and potential applications. The most promising way for large-scale synthesis of CNFs and CNTs is chemical vapor deposition (CVD).

CNFs were synthesized on a series of hydrotalcite (HT) derived 77 wt.% Ni-Fe/Al₂O₃ catalysts in order to achieve the optimization of productivity and quality. It was found that only the Fe catalyst was active in CO disproportionation and only the Ni catalyst was active in ethylene decomposition, whereas all catalysts were active in ethylene decomposition when the reactants were a mixture of C₂H₄/CO. More control over the structure and diameter of the CNFs has been realized with the HT catalysts. At the same time, a high yield can be obtained. The synthesis process has been further studied as a function of various process parameters. It turned out that high hydrogen concentration, space velocity, and reaction temperature would enhance the production of CNFs. However, a slightly lower quality was associated with the higher productivity. The optimum CNF yield of 128 gCNF/gcat could be reached within 8 h on the HT catalyst with a Ni/Fe ratio of 6:1. Therefore, HT derived catalysts present a new promising route to large-scale controlled synthesis of CNFs.

CNTs has been synthesized from CO disproportionation on Ni-Fe/Al₂O₃ supported catalysts with metal loadings of 20 and 40 wt.%. A high space velocity resulted in a high production rate but a short lifetime and a low carbon capacity. Increasing the metal loading to 40 wt.% significantly increased the reaction rate and productivity, and produced similarly uniform CNTs. Furthermore, H₂ was found to be necessary for a high productivity, and the H₂ partial pressure could be changed to adjust the orientation angle of the graphite sheets.

The effects of catalyst particle size and catalyst support on the CNT growth rate during CO disproportionation were studied over SiO₂ and Al₂O₃ supported Fe catalysts with varying particle sizes. It was found that there was an optimum particle size at around 13-15 nm for the maximum growth rate, and the growth rate was influenced both by the particle size and the support but the particle size was the dominating factor. The trends have been demonstrated at two different synthesis temperatures of 600 and 650°C. The effect of gas precursors on the yield and structure of carbon growth has been systematically investigated over powder Fe and Fe/Al₂O₃ catalysts. CO/H₂, CO, CH₄, and C₂H₆/H₂ were the gas precursors studied. The carbon yield was higher on powder Fe from CO, but the yield was higher on Fe/Al₂O₃ from hydrocarbons. Completely different or similar carbon nanostructures were synthesized, depending on the gas precursors. It was suggested that the reactivity of gas precursors and the structures of carbon deposits are determined by the size and crystallographic faces of the catalyst particles, which are dictated by the interactions among metal particles, support, and the reactants. Controlled synthesis of CNT, platelet nanofiber, fishbone-tubular nanofiber, and onion-like carbon with high selectivity and yield was realized. A mechanism was proposed to illustrate the growth of different carbon nanostructures.

The process of C-C bond formation via Directed ort/zo-Metalation (DoM) consists of two separate steps. Utilizing fractional equivalents of TMEDA in hydrocarbon solvents at 60°C, o-lithiation of anisole and dimethylaniline can be effected in >95% yields. The first step in the DoM process involves preparation of solid samples of these o-lithiointermediates. Completing the sequence, the second step concerns formation of a new arene-derivative bond at the reactive site. For this thesis the arene-derivative bond formed is to carbon. Various carbon electrophiles have been studied using different solvent systems, and results reveal a possible disconnect between the reaction conditions for the formation of the o-lithiointermediate and its subsequent derivatization. Simple additions to several ketones produce a wide variety of results when solvated in cyclohexane, THF, glyme, or diglyme. The use of CsF has provided questionable assistance to certain reaction conditions. Product distribution variations were seen in reactions of the o-lithioarenes with tetramethylurea and diethylcarbonate. Unsymmetric biphenyl derivatives are also produced via reaction of a benzyne intermediate with the olithioarenes. Some useful Buchwald catalysts can be made by this procedure. It is the use of pure o-lithioarenes that permits control of the solvent in various derivatization steps, therefore permitting further understanding and manipulation of the reaction conditions.

This thesis details the development of methods for and application of the synthesis of carbon carbon bonds using organic sulfur(IV) chemistry. More specifically, the formation of C(sp2) C(sp3) and C(sp3) C(sp3) bonds is explored in detail. The necessity for this research stems from a correlation between a high proportion of sp3 centres in drug candidates, and their success in clinical trials. By facilitating the synthesis of drug candidates with higher fractions of sp3 hybridised carbon atoms, it is hoped that the rate of candidates proceeding through clinical trials may increase. The first topic addressed is the ligand coupling reactions of sulfoxides. In such reactions, the treatment of appropriately substituted sulfoxides with organometallic reagents forms C(sp2) C(sp3) coupling products via σ sulfurane intermediates. These reactions have the ability to excel where transition metal catalysed cross couplings fail; in the coupling of electron deficient (hetero)aromatic groups and alkyl groups. Very few reports have been published detailing the scope and utility of this reaction. The application of this methodology to the synthesis of diarylmethanes is explored in detail. Diarylmethanes are designated as privileged structures for the presence of these moieties in a vast array of diversely functional drug products. Investigation of the scope of the ligand coupling reaction allows for the elucidation of (hetero)aromatic moieties which can undergo this reaction. The depth of analysis in which the scope of benzylic substituents is studied allowed for the elucidation of previously unreported trends, which have been assigned to steric and electronic characteristics of the σ sulfurane intermediates. This knowledge gained is applied to the synthesis of both enantiomerically enriched diarylmethanes and well known drug products. Further exploration of the scope of ligand coupling reactions focusses on the coupling of α functionalised alkyl groups. Remarkable success is found in this completely unexplored area. Benzylic ethers, carbamates and halides are synthesised through a combination of inter molecular and intra molecular ligand coupling reactions. It is proposed that these reactions would be suitable for use in the synthesis of natural products to prove their utility. A newly-discovered sulfoxide homologation is detailed, which occurs upon reaction of sulfenate by products with the aforementioned benzylic halides, both synthesised by a ligand coupling reaction. This is particularly interesting since a similar homologated sulfoxide is found in the substructure of omeprazole, a blockbuster proton pump inhibitor. The second topic addressed is the synthesis of (±)-TAN1251A. The envisaged route proceeds through a novel palladium catalysed [3+2] cycloaddition of sulfinimines, forming methylene pyrrolidines. Previous work focussed on the use of this methodology to produce a diamine, mono-protected as a sulfonamide. A key aspect of the research presented in this thesis is the formation of the C ring of the spiro fused 1,4 diazabicyclo[3.2.1]octane moiety. Initial investigations focus on the synthesis of a pyruvic acid fragment to react with the aforementioned diamine. This concept is developed into the use of pyruvic acid synthetic equivalents: azlactones. A late stage intermediate is produced, however formation of the C ring from this intermediate is not observed. Synthesis is hampered by the deprotection of the sulfonamide, which forms several by-products under the strongly acidic conditions required. A revised retrosynthesis proposes that early deprotection of the diamine sulfonamide would prevent complications. The use of a simplified fragment to facilitate C ring formation is devised, comprising of an α-haloketone. Synthesis of the unprotected diamine is accelerated by serendipity, where a reductive amination also effects the elimination of a sulfinyl group. Formation of an α haloketone fragment is found to be troublesome, however synthesis via the natural product chavicol provides the required functionality. A wide variety of conditions are examined to effect the combination of these fragments. While coupling of the fragments is successful in providing another late-stage intermediate of (±) TAN1251A, formation of the desired C ring is not achieved. Finally, the potential to effect an enantioselective synthesis of (±)-TAN1251A is confirmed using a chiral sulfinamide to direct diastereoselective ketone reduction.

Friction material properties are important to clutch and brake performance, when applying rubbing force on a rotating friction surfaces heat will be generated and the surface temperature will increase this change in temperature will change the properties of the material, coefficient of friction and wear mechanism will change. The objectives of this thesis are to investigate the friction performance of carbon-carbon clutch discs under different operating condition and the wear rate calculated under different applied pressure and temperature.

The work presented in this dissertation has focused on synthesizing complexes of relevance to dioxygenase enzymes that oxidatively cleave aliphatic carbon-carbon bonds. The goal of this research was to elucidate mechanistic aspects of the activation of aliphatic carbon-carbon bonds towards cleavage by reaction with oxygen, and also investigate the regioselectivity of these reactions. The oxidative cleavage of a variety of enolizable substrates has been explored by utilizing several transition metal complexes supported by an aryl-appended tris(pyridylmethyl)amine ligand. In order to probe the widely-accepted “chelate hypothesis” for how changes in regiospecificity are achieved as a function of metal ion, we synthesized the compound [(6Ph2TPA)Fe(PhC(O)COHC(O)Ph)]OTf. Based on UV-vis and IR spectroscopy, the acireductone enolate was found to bind via a six-membered chelate ring. By comparison with the reactivity of [(6Ph2TPA)Ni(PhC(O)COHC(O)Ph)]ClO4, we determined that the chelate hypothesis was an insufficient explanation of the observed regioselectivity. Rather, ferrous ion-mediated hydration of a vicinal triketone intermediate was the key factor in determining the regioselectivity of the C-C cleavage reaction. We have developed a high-yielding synthetic route to protected precursors of C(1)H acireductones. Preparation of the complexes [(6Ph2TPA)M(PhC(O)COCHOC(O)CH3)]ClO4 (M = Fe, Ni) followed by judicious choice of deprotecting conditions allowed us to investigate the oxygen reactivity of a mono-nuclear complex with a dianionic acireductone substrate for the first time. This provides a promising strategy to continue investigations of complexes of relevance to the enzyme- substrate adduct of the acireductone dioxygenases. Divalent late first-row transition metal complexes have been used to investigate some new strategies for the activation of dioxygen and subsequent cleavage of C-C bonds. We have utilized photoreduction of a Ni(II) center to generate a highly O2-reactive Ni(I) fragment that leads to cleavage of a chloro-diketonate substrate. Additionally, we have found a Cu(II)-mediated thermal cleavage of chloro-diketonate substrates at room temperature. This reaction is interestingly accelerated by the addition of a catalytic amount of chloride ion.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.
Vita.
Includes bibliographical references.
Chapter 1. Highly active and efficient catalyst systems derived from palladium precatalysts and monophosphine ligands for the Suzuki-Miyaura cross-coupling reaction of heteroaryl boronic acids and esters has been developed. This method allows for the preparation of a wide variety of heterobiaryls in good to excellent yields and displays a high level of activity for the coupling of heteroaryl chlorides as well as hindered aryl and heteroaryl halides. Specific factors that govern the efficacy of the transformation for certain heterocyclic motifs were also investigated. Chapter 2. A highly efficient method for the palladium-catalyzed Suzuki-Miyaura reaction of lithium triisopropyl 2-pyridylborates has been developed. Catalysts comprised of Pd2dba3 and either diaryl or dialkyl phosphine oxide supporting ligands were found to be ideal for the transformation. This report represents one of the most general systems for the cross-coupling of aryl and heteroaryl bromides and chlorides with 2-pyridyl-derived nucleophiles. Chapter 3. Catalysts comprised of Pd and dialkylmonophosphinobiaryl ligands provide highly active systems for the borylation of aryl and heteroaryl chlorides. The direct preparation of symmetrical and unsymmetrical biaryls from two aryl chlorides without the need to isolate the intermediate boronate esters is also described. Additionally, computational studies provide insight into the roles of the biaryl phosphine ligand as well as KOAc in the catalytic cycle. Chapter 4. A highly efficient method for the palladium-catalyzed borylation of aryl halides with an inexpensive and atom-economical boron source, pinacol borane, has been developed.
(cont.) This system allows for the conversion of aryl and heteroaryl iodides, bromides and several chlorides, containing a variety of functional groups, to the corresponding pinacol boronate esters. In addition to the increase in substrate scope, this is the first general method where relatively low quantities of catalyst and short reaction times can be employed.
by Kelvin L. Billingsley.
Ph.D.

Society’s efforts to ‘manage’ the problem of human-induced climate change – for example through setting targets, tracking progress, imposing sanctions and incentives, and creating markets in emission rights and offsets – have given rise to numerous calculation, measurement, attribution, monitoring, reporting and verification challenges, which are being addressed by many different communities (including scientists, governments, businesses and accountants) in many different ways. Carbon accounting – this diverse and ever-expanding assemblage of calculative practices – is a rapidly evolving phenomenon, which has only recently become a subject of academic accountancy-related research. This thesis explores what carbon accounting means, who it involves, and how different communities define and lay claim to competence in the field. It also examines, through case studies on the emergence of the Climate Disclosure Standards Board and the controversies around generating tradable carbon offsets from forestry projects in the UK, the immense technical, cognitive, social and political work required to make carbon measurable, commensurable and thereby amenable to various forms of management. The thesis contributes to both conceptual and practical understanding of carbon accounting as an emerging field of study. Bringing together a wide range of empirical examples of different types of carbon accounting practices, it proposes a unique definition of carbon accounting which expands the horizons of the field. It provides a conceptual basis for making sense of carbon accounting by considering it not as a unitary phenomenon but rather as a set of overlapping frames, each associated with different communities of practice. It shows that competence in carbon accounting is contested, particularly where these frames overlap, and that boundary organisations are emerging that offer the opportunity to negotiate such tensions and lead to more productive policy-making. Finally, it makes the case that engagement with the detail of the ‘nuts and bolts’ of carbon accounting is essential, as these apparently technical details can have major implications for the effectiveness of society’s response to climate change, and it is only by opening them up to rigorous scrutiny that we can make progress, both conceptually and practically.

La alta superficie y el hueco interior de los nanotubos de carbono (del inglés CNTs) los convierte en candidatos ideales para el desarrollo de nanovectores inteligentes para su aplicación en nanomedicina. Su cavidad interna puede emplearse para alojar compuestos seleccionados para propósitos de diagnóstico o terapéuticos, mientras que las paredes externas pueden modificarse para aumentar su biocompatibilidad e incluso para su direccionamiento. Un reto importante para trasladar los sistemas basados en CNT a su uso clínico es la reducción o eliminación de su toxicidad. Teniendo en cuenta la preocupación sobre salud y seguridad de nanomateriales, se han intensificado los esfuerzos de investigación para mejorar la biocompatibilidad de los CNTs, incluyendo el desarrollo de nuevas estrategias para el acortamiento y purificación de los mismos. La primera parte de esta tesis se enfoca en el estudio de la influencia del vapor de agua sobre la longitud, pureza y la integridad de las paredes de los nanotubos de carbono monocapa (del inglés SWCNTs) producidos tanto por deposición catalítica en fase de vapor (del inglés CVD ) como por descarga de arco. Para obtener nanotubos de carbono individualizados desarrollamos un protocolo que consiste en dispersar las muestras en orto-diclorobenceno y hemos empleado microscopía electrónica de barrido para adquirir las imágenes. CVD CNTs cortos con una longitud media de aprox. 200 nm se obtienen después de 10 h de tratamiento con vapor de agua, mientras que los CNT sintetizados por descarga de arco muestran una baja reactividad frente el vapor de agua. También se investigó la eficiencia de otros métodos de acortamiento comúnmente empleados, como son la molienda de bolas, una mezcla de ácido sulfúrico/nítrico y el tratamiento con piraña, tanto para SWCNTs como para CNTs multicapa (del inglés MWCNT) producidos por CVD. La combinación de piraña y vapor de agua resultó ser la más eficiente para el acortamiento de SWCNTs, y la combinación de ácido sulfúrico/nítrico con vapor de agua para MWCNTs. Estos protocolos proporcionan un buen equilibrio entre la obtención de nanotubos cortos con una distribución de longitud pequeña y la pureza de las muestras con un alto rendimiento de producción. En la segunda parte, estudiamos la encapsulación de distintos haluros metálicos, de interés tanto para imagen como para terapia, dentro de SWCNTs preparados por CVD y por descarga de arco. Se ha investigado el papel que juega la temperatura de calientamiento en el grado de cierre de las puntas de los nanotubos de carbono. Este estudio ha permitido la preparación de CNTs llenos con haluros metálicos de forma eficiente. El llenado de nanotubos de carbono da lugar a muestras que contienen una gran cantidad de material no encapsulado, externo a los nanotubos de carbono, que puede afectar e incluso dominar las propiedades de los nanotubos de carbono llenos. Por lo tanto, desarrollamos un protocolo que permite la eliminación de compuestos no encapsulados en poco tiempo y respetuoso con el medio ambiente, utilizando agua como solvente "verde" en un sistema Soxhlet, a la vez que se minimiza la cantidad de agua residual. La última parte de la tesis describe la modificación de las paredes externas de CNTs llenos. SWCNTs se han funcionalizado covalentemente a través de las reacciones de Tour y Prato, la primera resultando en un grado de funcionalización mayor. Para completar el estudio, las paredes externas de MWCNT llenos con cloruro de lutecio fueron decoradas con nanopartículas de oro. Estas nanocápsulas híbridas tienen interés para su uso como agentes duales para el diagnóstico y la terapia. En resumen, esta tesis aporta nuevos conocimientos sobre la preparación de nanocápsulas de carbono, para el desarrollo de la siguiente generación de agentes teranósticos.
The high surface area and hollow core of carbon nanotubes (CNTs) make them ideal candidates for the development of smart nanovectors in nanomedicine. Their inner cavity can be employed to host selected payloads for either diagnosis or therapeutic purposes while the external walls can be modified to increase their biocompatibility and even for targeting purposes. A major challenge to turn the potential of CNT based devices into customer applications is to reduce or eliminate their toxicity. Taking into account health and safety concerns, intensified research efforts are conducted to improve the biocompatibility of CNTs, including the development of new shortening and purification strategies. The first part of this thesis focused on the influence of steam on the length, purity, and sidewall integrity of chemical vapor deposition (CVD) and arc discharge single-walled carbon nanotubes (SWCNTs). In order to obtain individualized carbon nanotubes we developed a protocol that consisted of dispersing the samples in ortho-dichlorobenzene and employed scanning electron microscopy (SEM) to acquire the images. Short CVD CNTs with median length of ca. 200 nm can be obtained after 10 h of steam treatment, whereas arc discharged CNTs show low reactivity towards steam. The efficiency of other commonly employed shortening methods, namely ball milling, sulfuric/nitric acids, and piranha was also investigated for both SWCNT and multi-walled CNTs (MWCNTs) grown by CVD. A combination of piranha and steam turned out to be the most efficient for SWCNTs, and a combined sulfuric/nitric acids and steam for MWCNTs. These protocols provide a good balance between length distribution, sidewall integrity and purity of samples with a high yield of production. In the second part, we report on the encapsulation of selected metal halides, of interest for both imaging and therapy, inside CVD and arc discharge SWCNTs. The role of temperature on the degree of end-closing has been investigated, which has allowed the preparation of closed-ended metal halide filled CNTs. Bulk filling of carbon nanotubes results in samples that contain a large amount of non-encapsulated material, external to the carbon nanotubes, which can affect and even dominate the properties of filled carbon nanotubes. Therefore, we developed a straight forward approach that allows the removal of non-encapsulated compounds in a time efficient and environmentally friendly manner, using water as a “green” solvent in a Soxhlet setup, while minimizing the residual waste. The last part of the thesis describes the external modification of previously filled CNTs. SWCNTs have been covalently functionalized via Tour and Prato reactions, the former resulting in a higher degree of functionalization. To complete the study, lutetium chloride filled MWCNTs were externally decorated with gold nanoparticles. The developed hybrid nanocapsules hold potential to be employed as dual agents for diagnosis and therapy. To summarize, this thesis brings new insights in the preparation of carbon nanocapsules, i.e. close-ended filled carbon nanotubes with chosen payloads, for the development of the next generation of theranostic agents.

Los materiales compuestos por grafeno y nanotubos de carbono (CNTs) han despertado un amplio interés debido a sus propiedades excepcionales. La variación de éstas, empleando diversas técnicas de modificación aumentan sus aplicaciones potenciales en muchos campos. Ésta tesis describe la funcionalización de nanomateriales de carbono con nitrógeno y diversos haluros y óxidos. La modificación de la estructura de nanotubos de carbono multicapa (MWCNTs) y derivados de grafeno se llevó a cabo mediante reacciones sólido-gas y sólido-líquido. Hemos empleado diferentes métodos de funcionalización, que incluyen oxidación, funcionalización con nitrógeno y dopaje, así como modificaciones de las cavidades internas y superficies externas de los nanotubos de carbono, para modular las propiedades de las nanoestructuras preparadas. Mediante un estudio sistemático de las condiciones de tratamiento y una exhaustiva caracterización se determinaron las características estructurales de las muestras y se evaluaron algunas de sus propiedades fisicoquímicas. En ésta tesis proponemos un método simple, eficiente y reproducible para la síntesis de óxido de grafeno reducido (RGO) modificado con nitrógeno. La naturaleza de los átomos de nitrógeno dentro de la red del RGO se ha modulado mediante tratamientos de amonolísis de óxido de grafeno (GO) a temperaturas comprendidas entre 25 ˚C y 800 ˚C. El protocolo propuesto permite tanto la introducción de grupos funcionales alifáticos (funcionalización con N) como la de nitrógeno estructural (dopaje con N). Adicionalmente, la composición estructural de las muestras funcionalizadas y dopadas con nitrógeno se modificó mediante tratamientos posteriores empleando altas temperaturas y atmosferas no oxidantes. Éstos tratamientos provocan rearreglos internos que confieren mayor estabilidad térmica a los materiales. Por otro lado, se llevó a cabo el llenado de las cavidades y la decoración de las superficies externas de los MWCNTs con compuestos inorgánicos. Reportamos la formación de nanotubos inorgánicos monocapa dentro de los nanotubos de carbon empleando una técnica de capilaridad del material laminar en su fase fundida. Además, mediante la optimización de los parámetros experimentales conseguimos favorecer el crecimiento de éstos sistemas inorgánicos monocapa con respecto la formación de otras nanoestructuras, tales como, nanopartículas, nanobarras y nanoserpientes de los halogenuros empleados. Hemos descrito una nueva técnica para el aislamiento ó liberación de las sustancias previamente introducidas en las cavidades de los MWCNTs. Así, exploramos el uso potencial de los fulerenos como agentes aisladores o promotores de la liberación de estructuras huéspedes. Finalmente, hemos preparado MWCNTs decorados con óxidos de titanio reducidos empleando tratamientos a altas temperaturas. Mediante la oxidación de los nanotubos se obtuvieron “nanocollares” de titania libres de carbono. Los materiales soportados presentan una actividad fotocatalítica superior a la del material de referencia titania P25.
Graphene and carbon nanotubes (CNTs) are of wide interest in materials science due to their outstanding properties. Several approaches allow modulating their properties further expanding their potential applications in many fields. This thesis reports on the functionalization of carbon nanomaterials with nitrogen, halides and oxides. The modification of the structure of multiwalled carbon nanotubes (MWCNTs) and graphene derivatives has been carried out through solid-gas and solid-liquid reactions. Different methods of functionalization, which include oxidation, nitrogen functionalization and doping, as well as endohedral and exohedral modifications have been employed for tuning the properties of the prepared nanostructures. A systematic study of the conditions of treatment and an extensive characterization has allowed the determination of the structural characteristics of the samples and the evaluation of some of their physical and chemical properties. In this thesis we propose a simple, efficient and reproducible method for the synthesis of nitrogen-containing reduced graphene oxide (RGO). The nature of the nitrogen atoms within the RGO lattice has been tuned by ammonolysis treatments of graphene oxide (GO) in the range of 25 ˚C-800 ˚C. The reported protocol allows the introduction of aliphatic moieties (N-functionalization) and structural nitrogen (N-doping). Additionally, the structural composition of the N-containing RGO has been modified by post-annealing the material under non-oxidizing atmospheres. High temperature treatments induce internal rearrangements, leading to samples with an enhanced thermal stability. On the other hand, endohedral and exohedral functionalization of MWCNTs with inorganic materials have been carried out. We report on the formation of single-layered inorganic nanotubes within the cavities of MWCNTs through a molten phase capillary wetting technique. We have optimized the conditions of the synthesis to enhance the growth of the single-layered nanotubes, while decreasing the formation of other nanostructures (nanoparticles, nanorods and nanosnakes). A new technique for the confinement and/or release of the filled substances within the hollow cavity of the CNTs has also been developed. We have explored the potential of fullerenes as corking agents and as promoting species for the release of guest structures. Finally, we have prepared MWCNTs decorated with reduced titanium oxides employing high temperature treatments. By oxidation of MWCNTs self-standing titania “nano-necklaces” are formed. The photocatalytic performance of the carbon supported materials overpasses that of the reference material titania P25.

Compreender os ciclos de nutrientes e a dinâmica da matéria orgânica no ecossistema da Amazônia é essencial para o domínio do manejo eficiente da floresta e do solo. O desaparecimento de florestas tropicais, acompanhada de acelerados processos de perda de solo e de matéria orgânica, pelo desmatamento, queimadas e avanço da fronteira agrícola despertam preocupações. As características das substâncias húmicas remetem aos processos de gênese da matéria orgânica, à capacidade de sustentabilidade para os usos múltiplos em cultivos e aparece como indicador da qualidade do solo. O objetivo deste trabalho foi relacionar as características das substâncias húmicas do solo com o seqüestro de carbono em sítios de floresta em clímax, em área moderadamente e intensamente antropizada, ambientes de influência da Rodovia BR-163 - Cuiabá-Santarém, região que experimenta um incremento das ações antrópicas em função do anúncio da pavimentação desta rodovia. Foram determinadas as características das substâncias húmicas pelas técnicas de espectroscopia no infravermelho com transformada de Fourier (FTIR), análise elementar, espectroscopia de fluorescência de luz no UV/Visível, espectroscopia de absorção de luz no UV/Visível, espectroscopia de ressonância magnética nuclear (RMN) e espectroscopia de ressonância paramagnética eletrônica nuclear (EPR). Os resultados de infravermelho das substâncias húmicas do solo do sítio de floresta em clímax, indicam alta complexidade no arranjo conformacional, denotando-se a presença de elevada humificação do material orgânico, o que é corroborado pelos resultados de fluorescência, onde as características das substâncias húmicas deste ambiente apresentaram maior policondensação e grau de humificação. Utilizando-se a espectroscopia de absorção de luz no UV/Visível, constatou-se que a razão E4/E6 é de 2,27 para solo do ambiente de floresta em clímax. Esse é o menor valor das três frações, o que demonstra que as substâncias húmicas deste sítio estão em estágio elevado de policondensação e apresentam maior quantidade de estruturas aromáticas. Os resultados de RMN indicam que a maior percentagem de carbono aromático está exatamente nas substâncias húmicas do solo do sítio de floresta em clímax. Os resultados de EPR demonstram também que as substâncias húmicas dos solos dos sítios em clímax apresentam maiores números de radicais livres do tipo semiquinona (7,52) dos três ambientes estudados. As substâncias húmicas provenientes dos solos dos sítios com intensa atividade antrópica indicam a presença de menor grau de humificação, pelo número de radicais livres do tipo semiquinona (4,68), menor valor dos três ambientes estudados. Desta forma, as características das substâncias húmicas do solo de ambientes em clímax, pela elevada aromaticidade, policondensação e grau de humificação, proporcionam aumento da biodiversidade, incremento da produtividade, melhoria da estrutura deste solo, contribuindo junto à formação de fração húmica não lábil, bem como maior estabilidade dos complexos organominerais, condições favoráveis para o seqüestro de carbono e mitigação do aumento do efeito estufa.
Understanding the cycles of nutrients and organic matter dynamics in Amazons ecosystem is essential for the domain of efficient management of the forest and soil. The disappearance of tropical forests, accompanied by processes of accelerated loss of soil and organic matter, for the deforestation, forest fires and advancement of agricultural frontier arouse concerns. The characteristics of humic substances refer processes of genesis organic matter, capacity of sustainability for multiple uses in cultures appears as indicator the quality of the organic matter. The objective of this work was to relate the characteristics of humics substances in the soil, with the carbon sequestration in sites of forest in climax, in moderately and intensely area in humans use, environments in Influence of highway BR-163 - Cuiaba-Santarem, a region experiencing an increase in action of the human being according to the announcement of paving the road. There were certain characteristics of humic substances by the Fourier transform infrared (FTIR) spectroscopy, elemental analysis, ultraviolet-visible fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and electronic paramagnetic resonance (EPR) spectroscopy. The results of infrared of humic substances in soil site of a climax forest, show high complexity in conformal arrangement, showing up the presence of high humification of organic material, which is corroborated by the results of fluorescence, where the characteristics of humic substances this environment polycondensation and had greater degree of humification. Using ultraviolet-visible absorption spectroscopy, it was found that the reason E4/E6 is 2.27 for the environment of forest in climax. This is the lowest of the three fractions, which shows that the humic substances from this site are in high stage of polycondensation and the greatest amount of aromatic structures. The results of NMR indicate that the highest percentage of carbon aromatic is exactly humic substances in soil from site of forest in climax. The results of EPR also demonstrate that the soil humic substances in climax\'s sites show the highest numbers of free radicals semiquinonas type (7.52) in the three kinds of environments studied. The humic substances from the soil of sites with intense human activity indicate the lesser presence of degree humification, for the number of free radicals semiquinona\'s type (4.68), lower value of the three environments studied. Thus, the characteristics of humic substances in soil from environments in the climax for the high aromaticity, polycondensation and degree of humification, provide an increase of biodiversity, increasing productivity, improving the structure of the soil, contributing next to the formation of humic fraction not labile, greater stability of organic minerals complexes, favourable conditions for carbon sequestration and mitigation of increased greenhouse effect.

In the past decade, significant advances have been made in the formation of Csp2-Csp 2 bonds by direct arylation. However, this process generally requires the use of forcing conditions at temperatures typically above 100 °C, which limits the substrate compatibility as well as large-scale applications. Inspired by the recent advances in the development of milder reaction conditions for the arylation of electon-rich arenes in an aqueous medium, we describe that such reactivity is also possible with electron-deficient polyfluorinated arenes at room temperature under biphasic conditions. Several examples are included, highlighting the application of this method to the preparation of a variety of biaryls using iodides bearing electron-poor, electron-rich and sterically encumbering substituents. Several polyfluoroarenes with different substitution patterns are also tolerated. In addition, the method can be extended to the arylation of halogenated thiophenes in a regioselective fashion. However, direct arylation conditions that are general for a broad variety of heterocyclic coupling partners are only sparsely reported and the use of a different set of conditions for each type of substrate remains the norm. As part of a program dedicated to the study of the direct arylation mechanism and the development of broadly applicable reaction conditions, we became interested in investigating the effect of electron-deficient biaryl-type phosphine ligands on the C-H bond cleavage step of this process under Pd(0) catalysis. Inspired by previous reports validating the efficiency of these types of ligands in intramomecular direct arylation, we have developed a new electron-deficient fluoroarylphosphine ligand that promotes C-H bond functionalization of a broad variety of heterocycles. The demonstrated ability of these types of ligands to facilitate the C-H bond cleavage step of this process has been assessed and experimental evidence suggests a concerted metalation-deprotonation mechanism in the presence of an electrophilic metal center. Only recently, nonetheless, has attention been paid to the formation of Csp3-Csp2 bonds by the direct arylation strategy. As an alternative to the use of aliphatic halides as an entry point to a1kylpalladium(II) intermediates, we describe the use of a Heck-like cyclization of an aryl halide as a means of intercepting the key palladium(II) species, along with the first examples of domino Heck-arylation involving intermolecular capture with heterocyclic arenes via C-H bond cleavage. Several examples are presented, demonstrating the application of this method to the preparation of diverse dihydrobenzofurans, indolines and oxindoles substituted with sulfur-containing heterocycles such as thiazoles, thiophenes and benzothiophene.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2008.
Vita.
Includes bibliographical references.
Metal-catalyzed nucleophilic substitution reactions of aryl halides have become one of the most valuable and useful classes of reactions developed in the last 30 years. Foremost among these processes are the classes of palladium- and copper-catalyzed reactions, which employ heteroatom-based nucleophiles. Herein, newly designed catalyst systems are presented for the palladium- and/or copper-catalyzed nucleophilic substitution reactions of aryl halides with a variety of nucleophiles, including (benz)imidazoles, oxindoles, 2-, 3- and 4-hydroxypyridines, anilines, and aliphatic, benzylic, allylic and propargylic alcohols. In many cases, catalyst optimization and ligand structure are discussed and evaluated. Where applicable, the palladiumand copper-based catalyst systems are contrasted to demonstrate the complementary relationships between the employment of these two metals. Chapter One Chapter Two Chapter Three Chapter Four Chapter Five. Palladium- and Copper-catalyzed Reactions of Imidazoles and Benzimidazoles with Aryl Halides. Orthogonal Selectivity in Copper- and Palladium-catalyzed Reactions of Aryl Halides with Oxindoles. Copper-catalyzed Reactions of Hydroxypyridines and Related Compounds with Aryl Halides. Pyrrole-2-carboxylic Acid as a Ligand for the Copper-catalyzed Reactions of Primary Anilines with Aryl Halides. An Improved Copper-based Catalyst System for the Reactions of Aryl Halides with Aliphatic Alcohols.
y Ryan A. Altman.
Ph.D.

The controlled formation of carbon-carbon bonds is the bedrock of organic chemistry, with the asymmetric construction of stereogenic carbon-carbon bonds remaining a key motivation for the development of novel synthetic methodologies. Transition metal catalysis provides an important strategy in the arsenal of the modern synthetic chemist. While there is a plethora of transition metal-catalysed cross-couplings for the formation of sp2-sp2 and achiral sp2-sp3 carbon bonds, there are relatively few methodologies for the selective formation of stereogenic sp-sp3, sp2-sp3 and sp3-sp3 carbon-carbon bonds, the number of which that involve highly reactive organometallic reagents are fewer still. Two methodologies that can enable this asymmetric coupling are copper-catalysed SN2’ allylic alkylation and transition metal-catalysed allylic substitution. The overall utility of both these methods is described in the introductory review, which seeks to compare and contrast the relative advantages and disadvantage of both approaches. The asymmetric formation of carbon-carbon bonds utilising unstabilised carbon nucleophiles is generally dominated by the copper-catalysed SN2’ allylic alkylation. However, the copper-catalysed reaction suffers from poor substrate scope, in which electronically biased or symmetrical substrates are required in order to ensure favourable regioselectivities. Another restriction is that, for the formation of a stereocenter, the reaction is mechanistically limited to disubstituted allylic substrates. These linear substrates often require a multistep synthesis which involves a selective olefination, as an isomeric mixture of alkenes would result in the erosion of asymmetric induction. In contrast, there has been very little development of the analogous transition metal-catalysed allylic substitution utilising unstabilised carbon nucleophiles, especially in comparison to the analogous methodologies utilising stabilised carbon and heteroatom nucleophiles. Despite the numerous potential advantages that are afforded by this approach, a general method for the regio- and stereoselective transition-metal catalysed allylic substitution utilising unstabilised carbon nucleophiles has yet to be reported. Chapter 2 describes the development of a novel regio- and stereoselective rhodium-catalysed allylic substitution reaction, which utilises benzyl magnesium bromide as an unstabilised carbon nucleophile. Following a brief introduction to the rhodium-catalysed allylic substitution reaction, this chapter is organised into four distinct sections. The first of these outlines the identification of a suitable nucleophile, and the subsequent development of reaction conditions for the regioselective alkylation of secondary allylic carbonates with a range of benzyl magnesium bromides transmetallated with zinc iodide. Then the next section will deal with studies toward the development of the stereospecific variant, these studies will highlight the main challenges of deploying a sp3-hybridised carbon nucleophile. This section will also determine the absolute stereochemical outcome of the reaction, thus confirming the inner sphere mechanism of the reaction. The third section will demonstrate that how the limitation of the stereospecific reaction, namely the fluxionality of the rhodium-enyl, can be utilised to develop a regio- and diastereoselective alkylation for the formation of 1,2-stereoarrays containing tertiary and quaternary carbon stereocenters. Finally, preliminary studies towards the expansion of this methodology to include an sp2-hybridised vinylic nucleophiles for the preparation of 1,4-skipped dienes will be detailed. Overall, we have developed a novel, highly regioselective rhodium-catalysed allylic substitution of secondary allylic carbonates utilising highly unstabilised carbon nucleophiles. We also have developed a highly diastereoselective allylic substitution for the construction of both tertiary and quaternary carbon stereocenters, which to best of our knowledge, has yet to be described in the context of rhodium-catalysed allylic substitution utilising an unstabilised carbon nucleophile. We have successfully carried out preliminary studies towards the development of a rhodium-catalysed allylic substitution utilising a vinyl organometallic reagent as nucleophile, as well.

El canvi climàtic, produït per l’increment de la concentració de gasos d’efecte hivernacle a l’atmosfera, amenaça la integritat del nostre planeta. En aquestes circumstàncies el biochar, material obtingut a partir de biomassa pirolitzada, s’ha proposat com a una possible mesura per augmentar el segrest de carboni en sòls. L’aplicació de biochar en sòls pot servir com a magatzem de carboni a llarg termini compensant les emissions de CO2. No obstant, l’eficàcia del biochar depèn del tipus de biochar i sòl utilitzats. L’objectiu principal d’aquesta tesi és avaluar els efectes de l’aplicació de biochars de pi (PB) i de blat de moro (ZB) a una dosi de 6.5 g kg-1 en un sòl franco-arenós amb pH neutre i baix contingut de carboni orgànic (CO) en condicions de camp durant dos anys. Els objectius específics són els efectes de l’aplicació de biochar en : 1) la resistència termoquímica del CO del sòl (Capítol 1 i Capítol 2); 2) la disponibilitat del CO pels microorganismes (Capítol 3); 3) la protecció física del CO per oclusió en els agregats (Capítol 4). Els mètodes utilitzats per estudiar els efectes del biochar sobre la resistència del CO van ser: pèrdua de pes per ignició (LOI), combustió-seca (TOC), oxidació forta (sO) i feble (mO) amb dicromat-potàssic, hidròlisis-àcida (AH), oxidació amb peròxid d’hidrogen (PO) i anàlisis-isotòpic. A més, el CO-resistent del sòl i del biochar es va estimar mitjançant un balanç de masses. També, es van dur a terme dos mostrejos de sòl a curt i llarg termini (2 i 26 mesos), i es van incubar durant 250 dies. El dia 30 i 250 d’incubació va ser determinada la quantitat i la senyal isotòpica del CO2-C respirat. Addicionalment, es va mesurar el CO-dissolt en les mostres de sòl mitjançant el mètode d’extracció amb aigua-calenta. Les propietats físiques van ser avaluades quantificant el pes dels agregats estables amb aigua destil·lada i de la fracció en partícules amb hexametafosfat (per la disgregació dels agregats) utilitzant el wet-sieving apparatus. A més, el CO procedent del sòl natiu i del biochar dins i fora dels agregats es va estimar mitjançant un balanç de masses utilitzant el mO i el TOC. També es va estimar la contribució de CO del sòl i del biochar en els sòls esmenats amb ZB utilitzant el anàlisis-isotòpic. Es van trobar quantitats de ROC similars en els sòls controls estimats mitjançant mO i AH (5 g CO kg-1), mentre que més contingut de ROC es va observar en els sòls esmenats (6-12 g CO kg-1). La presencia de biochar es va detectar en els sòls esmenats mitjançant la comparació del δ13C en sòls esmenats i no-esmenats, independentment de l’origen del biochar. D’altra banda, el 35% del CO del biochar de ZB dels sòls esmenats es va perdre en dos anys com a resultat de la dissolució del biochar en el sòl. A curt termini, es va observar un priming-negatiu en sòls esmenats amb PB i el contrari en sòls esmenats amb ZB, en resposta al major contingut de CO-làbil del ZB. No obstant, un lleuger priming negatiu es va observar en els dos sòls esmenats a mig termini ja que augmenta la protecció física del CO. Mentre el PB tendeix a ser incorporat en els agregats, el ZB promou l’oclusió del CO natiu del sòl. Al esgotar-se el CO-làbil, el CO queda protegit dins dels agregats. Per tant, l’aplicació del biochar en sòls agrícoles mediterranis augmenta la persistència del CO en el sòl com a resultat de la resistència innata del CO del biochar i la protecció física augmentant el contingut de CO dins dels agregats.
El incremento de gases de efecto invernadero en la atmosfera puede tener consecuencias severas para nuestro planeta. El uso de biochar como enmienda, material obtenido a partir de biomasa pirolizada, se ha propuesto como estrategia para el secuestro de carbono en el suelo. Sin embargo, la efectividad del biochar varía mucho dependiendo del biochar y el tipo de suelo. El objetivo principal de esta tesis es evaluar los efectos de dos biochares, de restos de pino (PB) y mazorca de maíz (ZB), incorporados a una dosis de 6.5 g kg-1 en un suelo de viña franco-arenosa con pH neutro y bajo contenido de carbono orgánico (CO), en condiciones de campo durante dos años. Los objetivos específicos fueron la evaluación de: 1) la resistencia del CO en el suelo a los procesos termoquímicos (Capítulo 1 y Capítulo 2); 2) la disponibilidad de CO a ser mineralizada por microorganismos del suelo (Capítulo 3); y 3) protección física de CO por aumento de agregados (Capítulo 4). Los métodos analíticos utilizados para evaluar los efectos del biochar en el CO resistente del suelo fueron: pérdida de peso por ignición (LOI), combustión-seca (TOC), oxidación fuerte (sO) y suave (mO) con dicromato potásico, hidrólisis-ácida (AH), oxidación con peróxido de hidrogeno (PO) y análisis isotópico. Además, se estimó el CO-resistente del suelo y del biochar a través de un balance de masas. Por otro lado, el suelo se muestreó a corto y medio plazo (2 y 26 meses) y las muestras se incubaron en el laboratorio durante 250 días. Se determinó el CO2-C liberado durante la respiración del suelo y la señal isotópica del día 30 y 250 de incubación. Además, se cuantificó el CO disuelto mediante un extracto con agua caliente. Para evaluar las propiedades físicas, se determinaron los agregados estables en agua destilada y el peso de la fracción particulada con hexametafosfato para la disrupción de los agregados usando el wet-sieving apparatus. El CO oxidable del suelo nativo y del biochar dentro y fuera de los agregados se estimó a través de un balance de masas usando mO y TOC. Por otro lado, mediante el análisis isotópico se estimó la contribución de CO del suelo nativo y del biochar en suelos enmendados con ZB. Se cuantificaron valores similares de ROC en los suelos control mediante AH y mO (5 g C kg-1), mientras que se obtuvieron valores de ROC más altos en los suelos enmendados con biochar (6-12 g C kg-1). Además, la detección cualitativa de biochar se logró comparando δ13C en suelos enmendados y controles, independientemente del origen del biochar. Sin embargo, el 35% de ZB-CO se perdió durante los dos años de experimento por dilución del biochar en el suelo. A corto plazo se observó un priming-negativo en suelos enmendados con PB y al contrario en los suelos con ZB debido al mayor contenido de CO-lábil en ZB comparado con PB. Sin embargo, se encontró un priming ligeramente negativo a medio plazo en ambos suelos enmendados con biochar, como consecuencia de una mayor protección física del CO. Mayores cantidades de TOC y BOC se encontraron en los agregados de los suelos enmendados aunque tuvieron lugar dos procesos diferentes, mientras el PB tiende a incorporarse en agregados el ZB promueve la oclusión del CO del suelo nativo. Al agotarse el CO-lábil, el CO-ocluido queda protegido previniendo las pérdidas adicionales por degradación. Por lo tanto, la aplicación de biochar a un suelo agrícola mediterráneo aumenta la persistencia del CO del suelo debido a la resistencia innata al biochar-CO y la protección física del CO, que previene la degradación biótica o abiótica del CO.
The increment of global threats due to climate change, caused by an increase in atmospheric concentration of GHGs, is predicted to have a severe impact on our planet. The use of biochar, obtained from the thermochemical conversion of biomass in an oxygen-limited environment, as a soil amendment has been proposed as one strategy for C-sequestration. Many environmental benefits have been attributed to the application of biochar into soil, including long-term C-sequestration compensating for CO2 emissions. However, biochar effectiveness still remains under debate because effects can vary greatly depending on biochar and soil type. The main objective of this thesis was to assess the effects of two contrasting biochars, from pine wood (PB) and corn cob (ZB) remains, incorporated at a rate of 6.5 g kg-1 on a sandy loam vineyard soil with neutral pH and low organic carbon (OC) content, in field conditions over two years. Specifically, the aims were to evaluate the consequences of the addition of the different biochars on: 1) soil OC resistance to thermochemical processes (Chapter 1 and Chapter 2); 2) the potential OC availability to be mineralized by soil microorganisms (Chapter 3); and 3) physical OC protection by the promotion of aggregates (Chapter 4). The analytical methods used to evaluate the effects of biochar in soil OC-resistance were: weight loss-on-ignition (LOI), dry-combustion (TOC), strong (sO) and mild (mO) acid potassium dichromate oxidations, acid hydrolysis (AH), peroxide-oxidation (PO) and isotope analysis. Moreover, soil and biochar resistant-OC (ROC) was estimated through a mass balance. Also, soil field samples were collected at the short- and the medium-term (2 and 26 months after the application, respectively), and then incubated in the lab for 250 additional days. The CO2-C released as soil respiration and the CO2-C isotopic signature were assessed after 30 and 250 days of the incubation. Additionally, dissolved-OC was assessed in the field soil samples by hot-water extraction. Regarding physical properties, water-stable aggregates and particulate fraction weight were determined using a wet-sieving apparatus, using distilled water or hexametaphosphate for aggregates disruption. Oxidisable and resistant OC (attributed mainly to native soil and biochar, respectively) inside and outside of aggregates was estimated through a mass balance using mO and TOC. On the other hand, native soil and biochar-OC contribution in ZB biochar-amended soil was estimated by isotope analysis. The ROC estimated by AH and mO led to similar values in control soil (5 g C kg-1 soil), whereas higher ROC values were obtained in biochar-amended ones (6-12 g C kg-1 soil). Moreover, qualitative biochar detection was achieved by comparing δ13C in amended and non-amended soils regardless of the biochar feedstock origin. However, 35% of ZB biochar-OC was apparently lost over two years, which was attributed to biochar dilution into soil. In addition, in the short-term, negative-priming was observed in amended-soil with PB (made at high temperature) whereas positive-priming was seen in those amended with ZB (produced at lower temperatures) as a result of the highest labile-OC content in ZB biochar compared to PB. However, in the medium-term, slightly negative-priming effects in both biochar-amended soils were found. This could be explained by promotion of physical protection processes preventing priming. This fact was corroborated as higher TOC and BOC amount was observed inside of aggregates in biochar-amended soils compare to controls. It seems that PB tended to be incorporated into aggregates while ZB promoted native soil-OC occlusion. Then, after labile-OC has been exhausted, the promotion of OC occlusion prevented further losses. Therefore, the application of biochar to a Mediterranean agricultural soil increases soil-OC persistence due to innate biochar-OC resistance and OC physical protection, which decrease OC degradation by abiotic and biotic agents.

L’objectif de ce travail est d’étudier quantitativement l’évolution des propriétés de surface des matériaux carbonés et leur réactivité dans les conditions proches de celles rencontrées lors du taxiage des avions. Les essais de freinage ont été réalisés à l’aide d’un Banc d’Essai Tribométrique à Simulation Inertielle. Les composites C/C frottés et les débris d’usure sont caractérisés par des techniques non-conventionnelles multi-échelles. Les composites frottés (dans leur totalité) et les débris d’usure sont caractérisés par thermo-désorption programmée et chimisorption d’oxygène. Ces analyses permettent de déterminer la nature et la quantité de groupes fonctionnels et la teneur en sites actifs, caractéristique de la réactivité intrinsèque du carbone et responsable de l’interaction avec les espèces gazeuses de l’environnement. Ces caractérisations sont complétées par des analyses morphologiques, structurales et texturales par microscopies, diffractions des rayons X, adsorption de gaz. L’analyse des caractéristiques physico-chimiques des débris d’usure et des disques frottés permet de remonter aux réactions tribochimiques ayant eu lieu dans le contact : des réactions chimiques entre l’oxygène ou l’eau et les liaisons C-C rompues ont été mises en évidence. Un modèle permettant de justifier les différences de propriétés tribologiques lors des essais de taxiage a été proposé. Ce modèle, basé sur la réactivité du système et sur les propriétés de l’interface de frottement, permet d’élucider les problématiques liées à la température dans ce type de système
The objective of this work is to study quantitatively the evolution of carbon materials surface properties and reactivity under breaking conditions similar to those encountered during taxiing. The breaking tests were carried out using a Tribometric Test Bench. The rubbed C/C composites and the wear debris collected are then characterized by mutiscale unconventional techniques. The whole rubbed composites and the wear debris are characterized by Temperature-Programmed Desorption and by oxygen chemisorption. These analyzes are used to determine the nature and amount of functional groups and the content of active sites that is characteristic of the reactivity of the carbon material and also responsible of its interaction with the surrounding environment. The characterizations are completed by morphological, structural and textural analysis, such as Electron Microscopy, X-Ray Diffraction and gas adsorption. The analysis of the physic-chemical characteristics of wear debris and of the rubbed discs enables to evidence the tribochemical reactions occurring in the mechanical contact: chemical reactions between oxygen or water and the broken C-C bonds have been evidenced. A model is finally proposed, justifying the differences in the tribological properties during taxiing tests. The later is based on the carbon reactivity and on the interface properties and justify the temperature dependence of this system

La capacitat de generar intermedis radicalaris, sota condicions suaus, ha portat a l'emergent camp de la catàlisi fotoredox al desenvolupament de noves transformacions. Tradicionalment, aquesta es basa en l'ús d'un fotocatalitzador, que absorbeix eficientment llum i indueix una transferència simple d'electrons (SET). No obstant això, la reactivitat química de les molècules excitades electrònicament difereix fonamentalment de les que es troben en el seu estat fonamental. Una molècula en estat excitat és alhora una millor donant i acceptora d'electrons que en el seu estat fonamental i es comporta respectivament com una millor reductora i una millor oxidant. El principal objectiu científic d'aquesta tesi doctoral ha estat investigar i comprendre la reactivitat de l'estat excitat d'algunes molècules orgàniques per desenvolupar nous processos fotoquímics de formació d'enllaços C-C. Per aconseguir aquest objectiu, s'ha combinat diferents eines de la química orgànica. En els primers projectes (discutits en els capítols III i IV), la fusió de la organocatàlisi i la fotoquímica han permès la funcionalització asimètrica directa en la posició β d’enals, desencadenada per l'excitació amb llum visible de sals de Imini quirals formades in situ. A la segona part d'aquests estudis doctorals (discutit en el capítol V), s'ha explotat les propietats de l'estat excitat de 4-alquil-1,4-dihidropiridines (alquil-DHP) en combinació amb la catàlisi de metalls de transició pel desenvolupament de catalitzadors de níquel en reaccions radicalàries d'acoblament creuat.
La capacidad de generar intermedios radicalarios, bajo condiciones suaves, ha llevado al emergente campo de la catálisis fotoredox al desarrollo de nuevas transformaciones. Tradicionalmente, esta se basa en el uso de un fotocatalizador, que absorbe eficientemente luz e induce una transferencia simple de electrones (SET). Sin embargo, la reactividad química de las moléculas excitadas electrónicamente difiere fundamentalmente de las que se encuentran en su estado fundamental. Una molécula en estado excitado es a la vez una mejor donante y aceptora de electrones que en su estado fundamental y se comporta respectivamente como una mejor reductora y una mejor oxidante. El principal objetivo científico de esta tesis doctoral ha sido investigar y comprender la reactividad del estado excitado de algunas moléculas orgánicas para desarrollar nuevos procesos fotoquímicos de formación de enlaces C-C. Para lograr este objetivo, se han combinado diferentes herramientas de la química orgánica. En los primeros proyectos (discutidos en los Capítulos III y IV), la fusión de la organocatálisis y la fotoquímica han permitido la funcionalización asimétrica directa en la posición β de enales, desencadenada por la excitación con luz visible de sales de iminio quirales formadas in situ. En la segunda parte de estos estudios doctorales (discutido en el Capítulo V), se ha explotado las propiedades del estado excitado de 4-alquil-1,4-dihidropiridinas (alquil-DHP) en combinación con la catálisis de metales de transición para el desarrollo de catalizadores de níquel en reacciones radicalarias de acoplamiento cruzado.
The emerging field of photoredox catalysis has led to the development of new transformations due to the ability to generate radical intermediates under mild conditions. Traditionally, this relies on the use of a photocatalyst, which efficiently absorbs light and induces a single electron transfer (SET). However, the chemical reactivity of electronically excited molecules differs fundamentally from that in the ground state. An excited-state molecule is both a better electron donor and a better electron acceptor than in the ground state and behaves respectively as a better reductant and a better oxidant. The main scientific objective of this doctoral research was to investigate and understand the excited-state reactivity of some organic molecules to develop novel photochemical C–C bond-forming processes. In order to achieve this goal, different tools of organic chemistry were combined. In the first projects (discussed in Chapter III and IV), the merger of organocatalysis and photochemistry enabled the direct asymmetric β-functionalization of enals triggered by the visible-light excitation of in situ formed chiral iminium salts. In the second part of the PhD studies (discussed in Chapter V), the excited-state properties of 4-alkyl-1,4-dihydropyridines (alkyl-DHP) were exploited in combination with transition metal catalysis for the development of nickel-catalyzed radical cross-couplings.