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1
Forcolin, Matia <1984>. « Preparazione e reattività di diazoalcano complessi di rutenio ed osmio ». Master's Degree Thesis, Università Ca' Foscari Venezia, 2013. http://hdl.handle.net/10579/3472.
Texte intégralRésumé :
In questo lavoro di tesi sono state realizzate sintesi di nuovi diazoalcano complessi di rutenio ed osmio con tris-pirazoil-borato e areni, stabilizzati da leganti fosfinici e fosfitici. Di alcuni di questi è stata successivamente studiata la reattività chimica.
2
Comparin, Giulia <1988>. « Reazioni di diazoalcani coordinati ad un frammento di rutenio con alcheni ed alchini ». Master's Degree Thesis, Università Ca' Foscari Venezia, 2013. http://hdl.handle.net/10579/2586.
Texte intégralRésumé :
In questo lavoro di tesi sono stati coordinati diversi diazoalcani a complessi "half-sandwich" di rutenio. I complessi di rutenio sono stati sintetizzati variando il legante coordinato (Cp, indene, Tp) e i leganti spettatori (fosfiti). E' stata dunque studiata la reattività di questi complessi con alcheni ed alchini. I risultati di queste prove hanno portato alla sintesi, nei complessi contenenti il legante ciclopentadienilico, di 4,5-diidro-3H-pirazoli.
3
Agostinis, Lodovico <1989>. « Sintesi e luminescenza di complessi eteropolimetallici di elementi dei blocci d ed f ». Master's Degree Thesis, Università Ca' Foscari Venezia, 2014. http://hdl.handle.net/10579/5404.
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Valente, Giorgia <1994>. « Sintesi ed attività antiproliferativa di nuovi composti olefinici di Pd (o) e Pt (o) ». Master's Degree Thesis, Università Ca' Foscari Venezia, 2020. http://hdl.handle.net/10579/16604.
Texte intégralRésumé :
In questo lavoro di tesi sono stati sintetizzati ed esaustivamente caratterizzati cinque nuovi complessi olefinici di Pt(0) contenenti come legante spettatore l'1,3,5-triaza-7-fosfaadamantano (PTA). Tali composti, insieme ad altri sintetizzati in precedenza dal gruppo di ricerca presso il quale è stata svolta la prima parte del tirocinio, sono stati successivamente testati su tre diverse linee cellulari tumorali (A2780, A2780cis e K562) e su una linea di cellule sane (Ha-Cat).
I valori di IC50 ottenuti presso il gruppo di ricerca di biologia molecolare dell'Università degli Studi di Ferrara (referente: prof.ssa Ilaria Lampronti) hanno evidenziato una buona attività antiproliferativa e proapoptotica sulle due linee di carcinoma ovarico (A2780 e A2780cis) per tutti i composti testati. Alcuni composti inoltre hanno evidenziato una marcata selettività verso le cellule tumorali in virtù della bassa citotossicità registrata sulle cellule sane Ha-Cat.
Inoltre, a differenza del cisplatino ed in generale dei complessi di Pt(II), i complessi di Pt(0) in esame sono risultati generalmente poco attivi nei confronti della linea tumorale K562 (leucemia mieloide cronica).
In conclusione, in questo lavoro di tesi viene quindi riportato il primo studio sistematico dell'attività antitumorale di complessi di platino in stato d'ossidazione zero.
5
Palu', Alberto <1994>. « Sintesi di complessi luminescenti di manganese(II) ed europio(III) con fosfonati nella sfera di coordinazione ». Master's Degree Thesis, Università Ca' Foscari Venezia, 2021. http://hdl.handle.net/10579/19123.
Texte intégralRésumé :
Composti di tipo fosfonato sono stati sintetizzati per reazione di sostituzione a partire da opportuni precursori contenenti il legame P-Cl. La strategia di sintesi adottata ha permesso di isolare specie contenenti frammenti aromatici e, in alcuni casi, gruppi chirali derivanti da molecole quali borneolo, idrobenzoino e binaftolo.
Le molecole isolate sono state indagate quali potenziali leganti O-donatori nei confronti di manganese(II) ed europio(III), con l’obiettivo di isolare nuovi composti di coordinazione ed investigarne le proprietà fotoluminescenti. I precursori metallici utilizzati sono stati alogenuri di Mn(II) e beta-dichetonato-complessi di Eu(III). I complessi sono stati caratterizzati spettroscopicamente e mediante misure di magnetismo.
Nel caso dei derivati di manganese è stata osservata in diversi casi luminescenza attribuibile a transizioni del centro metallico. La lunghezza d’onda dell’emissione e l’intensità sono risultate fortemente dipendenti dalla natura dell’alogenuro coordinato, oltre che dalla scelta del legante O-donatore. Per i complessi di europio sono state sempre osservate le tipiche transizioni f-f del centro metallico, con notevole effetto-antenna da parte dei leganti coordinati e tempi di vita dell’ordine delle centinaia di microsecondi. La presenza di porzioni chirali in alcuni complessi potrebbe consentire una futura estensione degli studi, al fine di verificare la possibilità di emissione luminescente polarizzata circolarmente.
6
Baggio, Filippo <1996>. « Sintesi e caratterizzazione di complessi luminescenti di centri metallici d10 con leganti azoto- ed ossigeno-donatori ». Master's Degree Thesis, Università Ca' Foscari Venezia, 2022. http://hdl.handle.net/10579/21436.
Texte intégralRésumé :
In questo lavoro di tesi sono stati sintetizzati e caratterizzati nuovi complessi di Cu(I) e Zn(II) con leganti N- e O-donatori nella sfera di coordinazione. Partendo da CuCl sono stati ottenuti complessi eterolettici con leganti eterociclici aromatici, quali il benzoxazolo e il benzofurazano, in combinazione con leganti P-donatori come la trifenilfosfina. Alogenuri di zinco(II), acetato di zinco(II) e Zn(NCS)2 sono stati impiegati come precursori in reazione con leganti eterociclici aromatici, quali benzotiazolo, benzotiadiazolo e benzoxazolo, e [O=P]-donatori, come il trifenilfosfinossido e la N,N,N’,N’-tetrametil-P-indol-1-il diammide fosfonica. In alcuni casi è stata osservata luminescenza nella regione del visibile. Le formulazioni proposte sono state confermate mediante spettroscopia NMR eteronucleare e IR e misure di conducibilità. Le proprietà fotofisiche dei complessi di zinco(II) sono state investigate tramite spettroscopia di assorbimento UV-vis e misure di emissione (PL), eccitazione (PLE) e decadimento luminescente. I dati ottenuti sono stati razionalizzati tramite calcoli di tipo DFT, in alcuni casi supportati anche da misure elettrochimiche.
7
Muzzioli, Sara <1983>. « Sintesi e studio delle proprietà fotofisiche ed elettrochimiche di nuovi composti di coordinazione con leganti aromatici azotati ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3872/1/muzzioli_sara_tesi.pdf.
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Muzzioli, Sara <1983>. « Sintesi e studio delle proprietà fotofisiche ed elettrochimiche di nuovi composti di coordinazione con leganti aromatici azotati ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3872/.
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9
Locatelli, D. « Nano-organizzazione di molecole organiche ed ibride inorganiche/organiche con proprietà NLO e di rettificazione molecolare ». Doctoral thesis, Università degli Studi di Milano, 2006. http://hdl.handle.net/2434/67254.
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PINA, C. DELLA. « Catalizzatori a base di oro : preparazione, caratterizzazione ed applicazione nell'ossidazione di composti organici ». Doctoral thesis, Università degli Studi di Milano, 2006. http://hdl.handle.net/2434/196577.
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The PhD thesis deals with the preparation, characterization and application of gold based catalysts in the oxidation of organic compounds, both in liquid and gaseous phase.
The application of mono- and bimetallic gold nanoparticles as an aid for organic synthesis has been mainly devoted to the aerobic oxidation of alcohols and aldehydes, as well as to VOCs (volatile organic compounds), thus demonstrating the superior performance of gold in terms of activity, selectivity and durability in comparison with traditional Pd and Pt catalysts. Starting from the observation that oxygen activation towards organic compounds occurs mainly in the presence of nanometric gold clusters, the outstanding properties of colloidal “naked” particles were also discovered. Thorough kinetic studies suggested models for interpreting the aerobic oxidation of glucose, performed either by gold catalysis or the enzyme thereby shedding light on the molecular mechanism.
11
ALIOTTA, Chiara. « Studio di materiali avanzati per celle a combustibile ad ossidi solidi : influenza dei droganti e delle tecniche di sintesi sulle proprietà di anodi ed elettroliti ». Doctoral thesis, Università degli Studi di Palermo, 2014. http://hdl.handle.net/10447/90937.
Texte intégralRésumé :
Today fuel cell (FC) technology is envisaged as a strategic alternative for providing clean energy through the exploitation of renewable sources; FC research is substantially funded by governments as a mean to meet the global market demand of zero environmental impact. Due to the high level of efficiency, FC devices are already able to compete with the existing power generation technologies and, in particular, solid oxide fuel cells (SOFCs) plants for stationary application constitute one the most efficient way to produce electric power and heat. Nowadays, the main challenges for SOFC research activity are: i) improving costs and durability, by reducing the operating temperature from ∼1000°C (HT) to ~500-800°C (IT); and ii) using renewable fuels such as hydrogen and biofuels obtained by industrial and municipal wastes or energy crops. To achieve these purposes, it is essential to seek new materials characterized by suitable ionic conductivity for electrolytes and high electrocatalytic activity for electrodes. The electrolyte material must ensure high ionic conductivity, low electronic conductivity and very low permeability to both fuel and air in the operative temperature range. On the other hand, the anode material must be a mixed ionic-electronic conductor in the same temperature range, an efficient oxidation electrocatalyst and, finally, ensure good chemical and structural compatibility with the electrolyte.
In this light, the present study focuses on exploring electrolyte and anode materials for IT-SOFCs fuelled with H2 and, as a reference for carbonaceous streams, with CH4.
Electrolyte materials based on CeO2 doped with samarium or gadolinium are the most promising ion oxide (O2-) conductors in the intermediate range. The research activity concerning these compounds is mainly addressed to achieve the best performances in dependence of the doping amount and preparation routes. In this thesis the study of doped-CeO2 has been divided in two different parts. In the former part, the influence of different preparation routes on the ionic conductivity of Ce0.8Sm0.2O2-x has been evaluated. In the latter, a detailed investigation on local structure in Er-, Yb- and Sm-doped ceria has been carried out, aiming at elucidating the role of different dopants on the mechanism of ionic conduction.
Concerning the anode materials, the issues of resistance towards poisoning originated by “dirty” fuels and compatibility with the electrolyte focused the research activity on the development of new oxide materials alternative to cermets. Among other candidates, it has been recently observed that La1-xSrxCr1-yFeyO3-δ has suitable properties as potential anode for IT-SOFCs. In this thesis LaCrO3-based anode materials have been investigated relative to the issues of optimal composition, structure, mixed ionic-electronic conductivity, catalytic activity towards fuel oxidation, also with consideration for the aspect of resistance to poisoning by carbonaceous fuel.
12
TIBERTI, MATTEO. « Computational investigation of structure-function relationship in metalloenzymes ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2014. http://hdl.handle.net/10281/53873.
Texte intégralRésumé :
Important processes such as carbon dioxide capture, hydrogen evolution and oxidation as well as bioremediation are of paramount importance for the development of an environmental-friendly economy. In nature, the reactions underlying these processes are naturally performed by metalloenzymes.
The understanding of how they work will ease the development of important technological and biotechnological applications, such as bioinspired inorganic catalysts or more effective enzymes. In the present work, we have used computational methods to study structure-function relationships in metalloenzymes which catalyze important reactions involved in environment-friendly processes. In particular, we selected three cases of study; the formate dehydrogenase (FDH) from Escherichia coli, which catalyzes the conversion between carbon dioxide and formate, the [NiFe]-hydrogenase from Allochromatium vinosum, which performs hydrogen oxidation, and the phosphotriesterase (PTE) from Agrobacterium radiobacter that is able to hydrolyse organophosphates. Since the study of structure-function relationship in enzymes generally requires both a
view on the reaction mechanism and on the functional dynamics, we had to employ different levels of theory. At first, we focused on the study of metallo-enzymes for which the catalytic mechanisms still have to be clarified in details, as FDH and a [NiFe]-hydrogenase. In particular, we studied the oxidation of formate to carbon dioxide at the Mo-binding cofactor in the active site of FDH, using Density Functional Theory (DFT).
We employed for the first time a cluster model for the molybdopterin cofactor which is meant to best reproduce the stereoelectronic properties of the whole moiety. By testing several reaction pathways for the ratedetermining step of FDH catalytic cycle, we were able to propose a novel reaction mechanism which includes a β-hydride elimination step with a metal hydride intermediate. We then employed similar methods to study hydrogen oxidation in [NiFe]-hydrogenase. We have investigated the dihydrogen
coordination mode and subsequent oxidation, using model clusters of different sizes. It turned out that the spin state and the distorted seesaw coordination geometry of the Ni ion are two crucial factors that tune the energetics and regiochemistry of H2 binding. We were able to propose a reaction pathway involving the oxidative addition of H2 followed by proton transfer to the sulfur atom of one of the terminally coordinated cysteines as the lowest energy one. We then focused on another metalloenzyme, in which experimental evidences support a role of conformational dynamics for the catalysis, PTE. In this enzyme, it has been shown that the substrate hydrolysis can occur on fast time-scales, whereas one of the rate limiting steps seems to be the transition between so-called "open" and "closed" conformations with respect to the metal-binding site.
Indeed, in PTE mutations of residues, which are not directly involved in the active site, are known to affect the population of the closed and open states, as well as to alter the kcat. We thus studied this enzyme by atomistic Molecular Dynamics (MD) simulations to investigate the long-range structural communication routes between mutation sites and active site residues. We did so by considering both wild-type PTE (arPTE-WT) and a multiple mutant (arPTE-8M) in which mutations alter the equilibrium between the “closed” and “open” populations. By employing both freely available and in-house produced MD trajectories analysis tools, we were able to identify the major communication routes in the enzymes as well as to point out which mutation sites are more likely to be involved in the transmission of structural information. Comparing the communication
pathways in the two variants allowed us to investigate how the presence of mutations influence the communication pathways in the protein and to relate them to the effects induce by the mutations on protein function.
In conclusion, we have studied function-structure relationships in three different metalloenzymes, FDH, [NiFe] hydrogenase and PTE, by using high level DFT.
13
ARRIGONI, FEDERICA. « Chemistry and renewable energy : DFT investigation on CO2 reduction and H2 oxidation/production catalyzed by transition metal biomimics ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2017. http://hdl.handle.net/10281/153273.
Texte intégralRésumé :
My PhD research has been devoted to the investigation of diiron dithiolate compounds, that are structurally and functionally related to [FeFe]-hydrogenase and nitrogenase active sites. DFT computations provided relevant insights for a better comprehension of the chemistry of these systems, at the same time posing new questions and hints for future prospects.
The core of the thesis is dedicated to [FeFe]-hydrogenase biomimics, whose structures and reactivity have been theoretically addressed by various standpoints. Several gaps concerning the activity of these systems still need to be filled. Indeed, besides catalyzing proton reduction at moderate rates (usually accompanied to high overpotentials), synthetic analogues of [FeFe]-hydrogenases are not reversible catalysts, i.e. they cannot oxidize dihydrogen catalytically (except very few examples).
Some of the most puzzling issues in the field of hydrogenase biomimic have been computationally addressed, such as the oxidative behavior of biomimic compounds, as well as their role in H2 binding and activation (one of the most problematic yet less explored topics in this research area).
Then, also the effect on the variation of Fe’s coordination sphere on H2 production catalysis has been investigated. In particular, we studied the catalytic behavior of an hexacarbonyl model compound, in which a highly protophilic bridge-head pendant has proved to play a crucial role in the hindering of bridging hydride formation, a well-known obstacle for catalysis.
An alternative strategy to the hindering of bridging hydride formation is increasing its reactivity towards H2 formation. This aspect has been theoretically unraveled, and key information, regarding the stereoelectronic ingredients necessary to achieve this reactivity, has been provided.
DFT has been also used to perform the rational design of a hydrogenase biomimic with the so called “rotated” conformation (usually achieved only transiently in biomimics), which is considered one of the most relevant active site features, necessary to entail a hydrogenase-like reactivity. The proposed system thus represents the first example of biomimic compound which is theoretically predicted to resemble the actual Fe’s coordination geometry of the natural system.
The last period of my PhD research has been instead devoted to the study of compounds featuring a Fe2S2 scaffold, proposed nitrogenase biomimics. The aim of the work was to verify if the substrate promiscuity shown by the enzyme active site e.g. towards CO2 activation, could also be preserved in biomimic compounds. Thus, we made a preliminary study regarding the role of Fe2S2 biomimics in CO2 activation and conversion. Our results provided some useful general information about theirreactivity towards CO2, as well as some clues to favor CO2 binding and activation.La mia ricerca di dottorato è stata focalizzata sull’indagine di composti Fe2S2, strutturalmente e funzionalmente correlati al sito attivo di [FeFe[-idrogenasi e nitrogenasi. I metodi computazionali , in particolare la Teoria del Funzionale della Densità (DFT), hanno permesso di ottenere informazioni utili riguardo al funzionamento di questi sistemi, in luce del loro impiego come catalizzarori per la produzione di bio fuels. Il cuore della tesi è costituito dallo studio delle [FeFe]-idrogenasi e dei loro complessi biomimetici, la cui struttura e reattività è stata investigata in dettaglio secondo differenti punti di vista. L’attività dei sistemi biomimetici (in contrasto a quello naturale) è affetta da parecchie problematiche, che li rende poco attivi e non reversibili. Infatti, essi catalizzano (con bassi turnover e alte sovratensioni) la reazione di produzione di H2 da protoni ed elettroni, ma sono incapaci (a parte poche eccezioni) di ossidarlo. Alcuni degli aspetti problematici relativi a questi sistemi sono stati quindi investigati per mezzo del DFT. Innanzitutto ne è stato indagato il comportamento ossidativo, la cui conoscenza e controllo sono fondamentali per poter performare efficientemente l’ossidazione di H2. Questa tematica, sebbene la più problematica in quest’ ambito di ricerca, è anche la meno investigata. In particolare si è scoperto che la natura del ponte ditiolato contenuto in questi sistemi è fondamentale per modulare le proprietà redox di questi sistemi, mediante la formazione di interazioni deboli formatesi durante il processo ossidativo. Tuttavia una buona conoscenza delle proprietà redox di questi sistemi non è sufficiente a garantire un buon funzionamento nei confronti dell’ossidazione di idrogeno. Per questo sono stati studiati i quattro step fondamentali del ciclo catalitico, sia prendendo in esame il sito attivo enzimatico sia i suoi biomimetici. Da una comparazione accurata dei risultati ottenute sono emerse differenze che evidenziano il ruolo chiave di alcuni fattori stereo-elettronici, mancanti nei sistemi sintetici. Per quanto riguarda la riduzione protonica invece, a dare H2, una delle cause principali della scarsa efficienza è la formazione di un idruro a ponte come intermedio di protonazione (estremamente stabile) nel ciclo catalitico, il quale non si forma invece nel sistema naturale. Il DFT ha permesso di evidenziare che l’aumento di protofilicità della funzione contenuta nel pendant ditiolato impedisce (rallenta) la formazione di questo intermedio stabile. Inoltre è stato sviluppato un protocollo per rendere questo intermedio (notoriamente poco reattivo) più reattivo rispetto alla sua controparte terminale. Una delle features più importanti del sito attivo è la cosiddetta conformazione “ruotata”, in cui uno dei due Fe espone un sito di coordinazione vacante per il substrato. Questa conformazione è stata ottenuta finora solo transientemente in sistemi biomimetici, per mezzo di trucchi sterici. Durante il mio progetto di dottorato abbiamo progettato razionalmente un sistema biomimetico che (in linea di principio) ha un ground state con conformazione ruotata. Infine, l’ultima parte di dottorato è stata dedicata allo studio delle nitrogenasi, le quali hanno mostrato una rilevante promiscuità di substrato, catalizzando anche la riduzione di CO2 a idrocarburi. Abbiamo quindi studiato l’attivazione di CO2 da parte di biomimetici del tipo F2S2 di nitrogenasi, per verificare se questa promiscuità sia mantenuta anche a livello sintetico.
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RONCHI, COSTANZA. « Ab initio study of ground and excited state properties of dopamine-functionalized TiO2 : from flat surfaces to realistic spherical nanoparticles ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/263109.
Texte intégralRésumé :
I nanocompositi ibridi bioinorganici, costruiti collegando nanostrutture inorganiche, come le nanoparticelle di TiO2 (NP), a molecole bioattive (ad esempio farmaci, proteine, frammenti di DNA), sono stati recentemente utilizzati per diverse applicazioni biomediche, grazie alla loro biocompatibilità e alla possibilità di effettuare il targeting di cellule specifiche o il rilascio controllato di farmaci.
Lo scopo del mio progetto è studiare, attraverso calcoli basati sulla Teoria del Funzionale della Densità (DFT), l'interazione tra le superfici di TiO2 e un linker bifunzionale (dopamina, DA), che può ancorare efficacemente la superficie dell'ossido metallico e, allo stesso tempo, agganciare biomolecole.
Durante il primo anno di dottorato di ricerca, abbiamo simulato l'adsorbimento di DA sulla superficie piana (101) di anatasio TiO2, che è un modello semplificato per NP sfaccettate, utilizzando calcoli DFT ibridi. Abbiamo studiato diverse modalità di adsorbimento e abbiamo aumentato i regimi di copertura per esplorare il processo di autoassemblaggio sia in condizioni cinetiche che termodinamiche. Abbiamo scoperto che il gruppo funzionale etil-ammino della DA svolge un ruolo cruciale, interagendo con la superficie nel regime a bassa copertura e governando l'organizzazione del monostrato autoassemblato nel caso ad alta copertura, quando osserviamo trasferimenti inattesi di protoni tra la superficie protonata di TiO2 e le molecole DA.
Durante il secondo anno, abbiamo studiato il comportamento di DA su un modello più complesso, ma più realistico, di TiO2, cioè la superficie curva di una NP sferica. Innanzitutto, abbiamo studiato le possibili configurazioni di adsorbimento di una molecola DA isolata. Per le più stabili, abbiamo studiato l'effetto dell'irradiazione della luce, considerando la formazione di eccitoni, la separazione di buche ed elettroni fotoeccitati, il loro eventuale intrappolamento o ricombinazione. Quindi, abbiamo costruito un modello ad alta copertura, assorbendo un numero progressivamente crescente di DA e, infine, considerando gli effetti della temperatura attraverso la dinamica molecolare (DM) con il metodo tight binding density functional theory (DM-DFTB). Abbiamo chiarito l'effetto del numero di molecole adsorbite sull'energia di legame e sulla struttura elettronica del sistema. A questo scopo, abbiamo valutato la validità di un calcolo di energia DFT sulla geometria DFTB per riprodurre correttamente le proprietà elettroniche a un costo computazionale accettabile.
Durante il terzo anno, abbiamo studiato tramite time-dependent DFT (TDDFT) le proprietà ottiche del DA adsorbito sulla superficie piana di TiO2 dell'anatasio. In primo luogo, abbiamo confrontato lo spettro ottico di una molecola DA nel vuoto e dell’anatasio TiO2 massivo (bulk) con precedenti dati sperimentali. Quindi, dallo spettro di assorbimento elettronico di diverse configurazioni di adsorbimento di DA sulle superfici dell'anatasio abbiamo potuto determinare il meccanismo dettagliato del trasferimento di carica tra la molecola e la superficie di TiO2, sia ne caso a bassa che ad alta copertura.
Nel complesso, lo studio condotto chiarisce vari aspetti dell'interfaccia tra DA e le superfici di TiO2 piane o curve, compresa la risposta di tali sistemi rispetto alla luce. I risultati di questo studio rappresentano la base per investigazioni future in cui i linker legano le biomolecole.Bioinorganic hybrid nanocomposites, built by connecting inorganic nanostructures, such as TiO2 nanoparticles (NPs), to bioactive molecules (e.g. drugs, proteins, DNA fragments), have been recently used for several biomedical applications, due to their biocompatibility and the possibility of targeting specific cells or of drug delivery. The aim of my project is to study, through density functional theory (DFT) calculations, the interplay between TiO2 surfaces and a bifunctional linker (dopamine, DA), which can efficiently anchor the metal oxide surface but also attach biomolecules. During the first year of PhD, we simulated the adsorption of DA on the flat anatase (101) TiO2 surface, which is a simplified model for faceted NPs, using hybrid DFT calculations. We investigated several adsorption modes and increasing coverage regimes to explore the process of self-assembling both under kinetic and thermodynamic conditions. We found out that the DA ethyl-amino functional group plays a crucial role, interacting with the surface at low coverage and ruling the organization of the self-assembled monolayer at high coverage, when unexpected proton transfers between the protonated TiO2 surface and the DA molecules are observed. During the second year, we investigated the behavior of DA on a more complex, but more realistic, model of TiO2, i.e. the curved surface of a spherical NP. First, we studied the possible adsorption configurations of an isolated DA molecule. For the most stable, we investigated the effect of light irradiation, considering the formation of excitons, the separation of photoexcited holes and electrons, their trapping or recombination. Then, we built a high-coverage model, adsorbing a gradually increasing number of DA and, finally, considering temperature effects through molecular dynamics density functional tight-binding (MD-DFTB). We clarified the effect of the number of adsorbed molecules on the binding energy and on the electronic structure of the system. To this aim, we assessed the validity of a single point DFT calculation on the DFTB geometry to correctly reproduce electronic properties at an acceptable computational cost. In the third year, we studied, through real-time time dependent DFT (TDDFT), the optical properties of DA adsorbed on the flat anatase TiO2 surface. First, we compared the optical spectrum of a DA molecule in vacuum and of bulk TiO2 anatase with previous experimental data. , Then, from the electronic absorption spectrum of different adsorption configurations of DA on the anatase surfaces, at both low and full coverage regimes, we could determine the detailed mechanism of the charge transfer between the molecule and TiO2. Overall, the performed study clarifies various aspects of the interface between DA and the flat or curved TiO2 surfaces, and on its response to light, which will be the basis for future studies where the linkers tether biomolecules.
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CIPRIANO, MARCOS LUIS ANTONIO. « Theoretical study of semiconductor heterojunctions for photo-and electro-catalysis ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2022. http://hdl.handle.net/10281/374415.
Texte intégralRésumé :
La presente tesi è centrata sul trattamento computazionale di ossidi di metalli di transizione e semiconduttori classici. L'interesse per questi materiali è dovuto alle loro proprietà elettroniche, ottiche e magnetiche e alla loro vasta gamma di applicazioni nella catalisi, nei dispositivi elettronici e nella foto ed elettrocatalisi. Una delle proprietà fondamentali di questi materiali è il gap di banda, che determina le proprietà ottiche, elettriche e chimiche. Da un punto di vista teorico, la metodologia più utilizzata per descrivere il gap di banda di questi materiali è la teoria funzionale della densità (DFT). La stima del gap di banda mediante DFT con l'approccio GGA o funzionali ibridi è giustificata per materiali non altamente correlati come semiconduttori TiO2, ZnO, V2O5, III-V, ecc. Tuttavia, quando si tratta di materiali altamente correlati, si è necessario introdurre metodi che includano effetti a molti corpi (saltellamento di elettroni), come il GW, e la teoria dinamica del campo medio (DMFT).
Per risolvere il problema della descrizione di materiali altamente correlati, abbiamo iniziato questa tesi con lo studio degli ossidi di metalli di transizione con carattere di Mott Hubbard utilizzando l'approccio Charge Transition Level (CTL). Da questa ricerca, è emerso che l'approccio CTL fornisce una migliore descrizione del gap di banda di materiali altamente correlati rispetto a quelli ottenuti con funzionali ibridi e metodi teorici di alto livello come GW e DMFT, in cui i valori calcolati vengono confrontati con misurazioni sperimentali. Successivamente, è stata studiata la descrizione e la razionalizzazione del ruolo del confinamento quantistico sui semiconduttori III-V attraverso la considerazione di (110) superfici con spessori diversi. I risultati del confinamento quantistico indicano che esistono due gruppi di semiconduttori, il primo corrisponde ai semiconduttori meno colpiti come il gruppo Al-V e il secondo ai semiconduttori fortemente interessati come il gruppo In-V.
Poi siamo passati al trattamento computazionale dei materiali compositi per applicazioni fotocatalitiche come le eterogiunzioni. In un capitolo dedicato sono stati forniti alcuni aspetti metodologici che devono essere considerati nella progettazione di eterogiunzioni binarie e ternarie. In particolare, viene fornita la descrizione delle eterogiunzioni di tipo II poiché questi tipi di interfacce sono le più interessanti per le applicazioni di fotocatalisi.
In questo ultimo capitolo della tesi vengono descritti due casi di co-catalizzatori, entrambi basati su catalizzatori ad atomi singoli (SAC) per la reazione di evoluzione dell'idrogeno (HER). In primo luogo, viene discusso l'effetto delle diverse dimensioni delle nanoparticelle d'oro (atomi singoli, nanocluster e nanoparticelle) supportate sul grafene drogato con azoto. In secondo luogo, viene descritta la formazione di due intermedi (MH e HMH) in metalli di transizione adsorbiti su diversi supporti di grafene drogati con azoto e bisolfuro di molibdeno (MoS2).The present thesis is focused on the computational treatment of transition metal oxides and classical semiconductors. The interest in these materials is due to their electronic, optical, and magnetic properties, and their wide range of applications in catalysis, electronic devices, and photo-and electro-catalysis. One of the fundamental properties of these materials is the band gap, which determines the optical, electrical, and chemical properties. From a theoretical perspective, the most widely employed methodology to describe the band gap of these materials is the Density Functional Theory (DFT). The estimation of the band gap by DFT with the GGA approach or hybrid functionals is justified for materials that are not highly correlated such as TiO2, ZnO, V2O5, III-V semiconductors, etc. However, when one deals with highly correlated materials, it is necessary to introduce methods that include many-body effects (electron hopping), such as the GW, and the dynamical mean-field theory (DMFT). In order to solve the problem of the description of highly correlated materials, we started this thesis with the study of transition metal oxides with Mott Hubbard character by using the Charge Transition Level approach (CTLs). From this research, it was found that CTLs approach provides a better description of the band gap of highly correlated materials than those obtained with hybrid functionals and high level of theory methods such as GW and DMFT, where the computed values are compared with experimental measurements. Next, the description and rationalization of the role of quantum confinement on III-V semiconductors through the consideration of (110) surfaces with different thicknesses was studied. The results from quantum confinement indicate that there are two groups of semiconductors, the first one corresponds to semiconductors that are less affected such as the Al-V group, and the second one to semiconductors that are strongly affected such as the In-V group. Then we moved to the computational treatment of composite materials for photocatalytic applications such as the heterojunctions. In a dedicated chapter, some methodological aspects that need to be considered in the design of binary and ternary heterojunctions were provided. In particular, the description of type-II heterojunctions is given since these kinds of interfaces are the most interesting for photocatalysis applications. In this last chapter of the thesis two cases of co-catalysts are described, both based on single atoms catalysts (SACs) for the hydrogen evolution reaction (HER). First, the effect of different gold nanoparticles size (Single atoms, Nanoclusters, and Nanoparticles) supported on nitrogen-doped graphene is discussed. Second, the formation of two intermediates (MH and HMH) in transition metal oxides adsorbed on different nitrogen-doped graphene supports and molybdenum disulfide (MoS2) is described.
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MIRIZZI, LORENZO. « Novel filler to enhance thermal condcutivity of rubber nanocomposites ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2023. https://hdl.handle.net/10281/403915.
Texte intégralRésumé :
I nanocompositi di gomma mostrano generalmente una scarsa conduttività termica, che può essere parzialmente migliorata dall'aggiunta di riempitivi termicamente conduttivi, ad esempio grafite, nerofumo, fibre di carbonio, particelle di ceramica o di metallo. Per raggiungere questo obiettivo sono in genere necessari concentrazioni di riempimento elevate; tuttavia, ciò altera notevolmente il comportamento meccanico e la densità di reticolazione dei materiali finali. Inoltre, i sistemi di riempimento attualmente impiegati non sono in grado di soddisfare contemporaneamente i requisiti chiave di elevata conducibilità termica e prestazioni meccaniche. In questo contesto, l'attività di ricerca del dottorato mira a progettare nuovi riempitivi adatti allo sviluppo di nanocompositi di gomma con elevata conducibilità termica e prestazioni meccaniche soddisfacenti. Sarà condotta un'indagine su diversi nano-riempitivi termicamente conduttivi, studiando in profondità le correlazioni tra struttura, morfologia, dispersione e distribuzione delle nanoparticelle nella matrice polimerica e proprietà finali dei compositi. Le migliori formulazioni verranno selezionate ed eventualmente scalate al fine di fornire reali applicazioni tecnologiche.Rubber nanocomposites generally exhibit poor thermal conductivity, which has been partially enhanced by the addition of thermally conductive fillers, i.e. graphite, carbon black, carbon fibres, ceramic or metal particles. High filler loadings are typically necessary to achieve this target; however, this dramatically alters the mechanical behaviour and the cross-linking density of the final materials. Further, the filler systems currently employed are not able to fulfil the key requirements of high thermal conductivity and remarkable performances, simultaneously. In this context, the PhD research activity aims at design novel fillers suitable for developing rubber nanocomposites with high thermal conductivity and satisfactory mechanical performances. A survey of different conductive nanofillers will be carried out, by investigating in depth the correlations between nanoparticles structure, morphology, dispersion and distribution in the polymer matrix, and final composites properties. The best formulations will be selected and possibly up-scaled in order to provide real technological applications.
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DATTEO, MARTINA. « Quantum Chemical modelling of physical and chemical properties of TiO2 hybrid interfaces between a semiconducting oxide surface and carbon-based layer ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/263111.
Texte intégralRésumé :
I materiali compositi hanno suscitato un notevole interesse nella comunità scientifica grazie alle loro eccezionali proprietà e alle loro promettenti applicazioni. Infatti, i materiali interfacciati hanno un ruolo cruciale in innumerevoli applicazioni. Nel presente lavoro di tesi, diversi tipi di interfacce ossido/strato di carbonio sono state considerate per svolgere un’indagine chimica quantistica. La superficie del biossido di titanio è stata interfacciata con monostrati a base di carbonio, che può essere sia bidimensionale ed inorganico (grafene), sia uno strato denso di molecole organiche (enedioli e silani).
Il lavoro mira a rivelare i fenomeni peculiari che si verificano all’interfaccia, dovuti delle proprietà complementari delle due componenti, che potrebbero essere interessanti per la catalisi e la bio-funzionalizzazione.
L’indagine teorica si basa su due livelli di teoria: self-consistent charge density-functional tight-binding (SCC-DFTB) e la teoria del funzionale della densità (DFT). Il metodo SCCF-DFTB approssimativo consente di studiare le proprietà dinamiche e strutturali di questi sistemi complessi, mente i calcoli DFT più accurati permettono di raffinare i modelli e studiare le loro proprietà elettroniche.
La prima parte del lavoro è stata dedicata alla modellizzazione dell’interfaccia tra TiO2 in fase anatasio e il grafene, in presenza di difetti. Oltre a ciò, si è considerata la reattività di molecole d’acqua all’interfaccia per proporre possibili percorsi di reazioni e studiare gli effetti del ricoprimento dovuti al confinamento della reattività.
La seconda parte del lavoro presenta lo studio del modello di nanoparticella sferica di TiO2 decorata con un monostrato denso di molecole organiche: l’enediolo DOPAC e l’organosilano TETT, che sono eccellenti linker.
Il DOPAC è un derivato catecolico che presenta un gruppo carbossilico aggiuntivo. È stata studiata un’ampia gamma di modalità di adsorbimento sulla superficie curva di TiO2. Inoltre, sono state eseguite simulazioni di dinamica molecolare per elucidare l’affinità dei gruppi carbossilici rispetto alla superficie di TiO2 e per studiare l’effetto termico sulla conformazione strutturale del sistema ibrido inorganico/organico. Poiché la TiO2 è un eccellente assorbitore di luce, è stata studiata anche la fotoeccitazione del sistema TiO2/DOPAC.
Il TETT è un organosilano con una catena propilica recante un’etilendiammina, ulteriormente funzionalizzata con tre gruppi carbossilici. A causa delle dimensioni e della complessità delle nanoparticelle di TiO2 completamente decorate con il TETT, si è campionato la spazio configurazionale attraverso diverse serie di dinamiche molecolari.
Per concludere, lo studio di differenti sistemi ibridi (ossido metallico/monostrato a base di carbonio) svolto in questo lavoro ha permesso, da un lato, di razionalizzare la reattività all’interfaccia TiO2/grafene e, dall’altro, di eseguire un’analisi comparativa tra due diversi tipi di monostati organici (enedioli o silani) su TiO2 per poter valutare il loro potenziale come linker per l’attacco e il trasporto di biomolecole.Composite materials have attracted the attention of the scientific community due to their outstanding properties and promising applications. Materials interfaces play a crucial role in many of these applications. In the present work of thesis, different types of oxide/C-based layer interfaces have been considered for a quantum chemical investigation. The titanium dioxide surface has been interfaced with both inorganic bidimensional (graphene) and densely packed organic (enediols and silanes) C-based monolayers. The work aims at revealing the peculiar phenomena that occur at the interface, due to the complementary properties of the two components, that might be relevant for catalysis and bio-functionalization. The theoretical investigation is based on two levels of theory: self-consistent charge density-functional tight-binding (SCC-DFTB) and density functional theory (DFT) The approximate SCC-DFTB method allows to investigate the dynamical and structural properties of the complex systems, while the most accurate DFT calculations enable to refine the models and study their electronic properties. The first part of the work is devoted to the modelling of the interface between TiO2 anatase (101) surface and graphene with defects, since they are often observed in real samples. Furthermore, we have considered the presence of water molecules and their reactivity at the interface to propose possible reaction paths and to investigate the undercover effects due to the reaction confinement. The second part of the work presents the study on a model of spherical TiO2 nanoparticle decorated with a densely packed monolayer of two organic molecules: the enediol DOPAC and the organosilane TETT, that are excellent linkers. DOPAC is a catechol derivative bearing an extra carboxylic group. An extensive set of adsorption modes on the TiO2 curved surface have been investigated. Molecular dynamics (MD) simulations have also been performed to elucidate the affinity of the carboxylic groups toward the TiO2 surface and to investigate the thermal effect on the structural conformation of the hybrid inorganic/organic system. Since TiO2 is an excellent UV light absorbant, we have studied the TiO2/DOPAC system photoexcitation. TETT is an organosilane molecule with a propyl chain bearing an ethylenediamine group, further functionalized with three carboxylic groups. Due to the size and complexity of TETT fully-decorated TiO2 nanoparticle, we have sampled the configurational space through several MD runs. To conclude, the investigation of different hybrid (metal oxide/C-based layer) systems performed in this works has allowed, on one side, to rationalize the reactivity at the TiO2/graphene interface, and, on the other side, to perform a comparative analysis between two different types of organic monolayers (by enediols or silanes) on TiO2 and to assess their potential as linkers for biomolecules attachment and transport
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FATEHBASHARZAD, PARISA. « Functionalized Concave Cube Gold Nanoparticles as Dual probe for Magnetic Resonance Imaging and Surface Enhanced Raman Scattering ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/273768.
Texte intégralRésumé :
An innovative class of MRI CAs is represented by Gd-loaded gold nanoparticles. Differently from other nano-sized systems, the size, shape and chemical functionalization appear to affect the observed relaxation enhancement of water protons in their suspensions. The herein reported results shed more light on the determinants of the relaxation enhancement brought by Gd-loaded concave cube gold nanoparticles. It has been found that the role of the concave surface of these nanoparticles in the relaxivity is remarkable and it provides high contribution of second sphere water molecules. The specific shape of concave cube nanoparticles increases the relaxivity from 20.9 mM-1S-1 for spherical nanoparticles to 36.3 mM-1S-1.
On the other hand, our studies prove that this special shape gold nanoparticles show high efficiency as a SERS probe. In the single-particle surface-enhanced Raman spectroscopy, the use of tunable plasmonic nanoparticles, having tipped surface structures, as being substrates revealed a highly feasible and promising approach to optimize SERS-based imaging and sensing applications. The concave cubic morphology has shown a remarkable plasmonic response, representing high sensitivity to the concavity degree. hence they can provide strong Raman signal which can be use in Raman imaging.
Magnetic resonance and optical imaging are complementary techniques. By applying same nanoparticles as a contrast agent for both methods simultaniusly, screening total body with very clear identification become possible. This progress in imaging technologies associated with the advance of nanotechnology makes feasible the cancer detection and localization in its early stage.An innovative class of MRI CAs is represented by Gd-loaded gold nanoparticles. Differently from other nano-sized systems, the size, shape and chemical functionalization appear to affect the observed relaxation enhancement of water protons in their suspensions. The herein reported results shed more light on the determinants of the relaxation enhancement brought by Gd-loaded concave cube gold nanoparticles. It has been found that the role of the concave surface of these nanoparticles in the relaxivity is remarkable and it provides high contribution of second sphere water molecules. The specific shape of concave cube nanoparticles increases the relaxivity from 20.9 mM-1S-1 for spherical nanoparticles to 36.3 mM-1S-1. On the other hand, our studies prove that this special shape gold nanoparticles show high efficiency as a SERS probe. In the single-particle surface-enhanced Raman spectroscopy, the use of tunable plasmonic nanoparticles, having tipped surface structures, as being substrates revealed a highly feasible and promising approach to optimize SERS-based imaging and sensing applications. The concave cubic morphology has shown a remarkable plasmonic response, representing high sensitivity to the concavity degree. hence they can provide strong Raman signal which can be use in Raman imaging. Magnetic resonance and optical imaging are complementary techniques. By applying same nanoparticles as a contrast agent for both methods simultaniusly, screening total body with very clear identification become possible. This progress in imaging technologies associated with the advance of nanotechnology makes feasible the cancer detection and localization in its early stage.
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PERILLI, DANIELE. « Quantum Mechanical Modeling of Chemical Activated 2D-Materials for Electrocatalysis and Sensing ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2021. http://hdl.handle.net/10281/307660.
Texte intégralRésumé :
I materiali bidimensionali hanno suscitato grande interesse da parte della comunità scientifica grazie alle loro eccezionali proprietà fisiche e le loro promettenti applicazioni in molti campi di interesse tecnologico. In particolare, negli ultimi anni, la frontiera della ricerca si è spostata dallo studio delle loro proprietà di base a sistemi 2D modificati chimicamente, quali materiali drogati, e alla loro interazione con altri sistemi, come nanoparticelle o superfici.
In questo contesto, le superfici metalliche sono spesso impiegate come catalizzatori eterogenei per la crescita mediante CVD di materiali 2D, sebbene il loro ruolo sia spesso relegato a mero materiale di supporto, con scarsa attenzione al potenziale che queste interfacce ibride offrono.
Questo lavoro di tesi presenta un’analisi di interfacce complesse tra materiali bidimensionali e superfici metalliche, sia dal punto della loro comprensione di base che alla loro applicazione in elettrocatalisi e nella sensoristica. In particolare, il lavoro è principalmente indirizzato alla comprensione del ruolo sinergico del substrato metallico sottostante e di difetti come vacanze o droganti sulle proprietà chimiche e fisiche dello strato bidimensionale supportato.
Metodi computazionali all'avanguardia sono stati impiegati per modellizzare sistemi quanto più realistici. Tutti i calcoli sono stati eseguiti attraverso la teoria del funzionale della densità (DFT), utilizzando funzionali corretti per le forze di dispersione.
L'idea principale di questo lavoro è quella di sfruttare l'elevata area superficiale che i materiali bidimensionali offrono per intrappolare oggetti quali atomi o cluster metallici. Tali oggetti possono essere usati come siti catalitici per molte reazioni di grande interesse o favorire l’interazione di questi sistemi con gas molecolari.Two-dimensional materials have aroused great interest among the scientific community thanks to their exceptional properties and promising applications in many technological fields. Nevertheless, over the last years, the frontline of research has moved from the study of basic properties of pure 2D crystals to chemical modified forms, i.e. doped 2D materials, and their interaction with other systems, such as nanoparticles, or surfaces. Within this frame, metal substrates are often employed as heterogeneous catalysts for the growth of 2D materials, although their role is often relegated to mere supporting materials, with a little attention to the potential that these hybrid interfaces (two-dimensional materials/metal surfaces) offer. This work investigates complex interfaces between two-dimensional materials and metal surfaces, both from the point of view of basic understanding of such systems and application in electrocatalysis and sensing. In particular, the thesis is mainly addressed to the understanding of the synergistic role of the underlying metal substrate and defects like vacancies or dopants on the chemical and physical properties of the two-dimensional adlayer. We employed state-of-the-art computational methods to model systems that are as realistic as possible. All calculations have been performed through density functional theory (DFT), using dispersion-corrected functionals. The main idea of this work is to exploit the high surface area of two-dimensional materials to trap objects that can be atoms or metal clusters, as well as molecules. Such objects can be used as catalytic sites for many reactions of great interest or induce some modification in the 2D material, making it suitable as a sensor.
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Veclani, Daniele <1985>. « STUDI COMPUTAZIONALI SULLA CHIMICA DI COORDINAZIONE DELLO IONE TRIMETILSOLFONIO ». Master's Degree Thesis, Università Ca' Foscari Venezia, 2013. http://hdl.handle.net/10579/3133.
Texte intégral
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Bergamini, Giacomo <1979>. « Photo-and redox-active supramolecular systems ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/475/1/GBergaminiTesiXIXcicl.pdf.
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Bergamini, Giacomo <1979>. « Photo-and redox-active supramolecular systems ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/475/.
Texte intégral
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Giaffreda, Stefano Luca <1977>. « Preparazione e caratterizzazione di nuovi materiali mediante metodi "solvent-free" ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/478/1/Dottorato_XIX_Ciclo_-_Giaffreda_Stefano_Luca.pdf.
Texte intégral
24
Giaffreda, Stefano Luca <1977>. « Preparazione e caratterizzazione di nuovi materiali mediante metodi "solvent-free" ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/478/.
Texte intégral
25
Battistini, Gionata <1977>. « Sensori chimici basati su molecole e nanoparticelle ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1037/1/Tesi_Battistini_Gionata.pdf.
Texte intégralRésumé :
Con questo lavoro di tesi si è cercato da un lato di dare un contributo al settore dei
sensori chimici, caratterizzando e sviluppando diversi sistemi che presentano
promettenti proprietà per l’utilizzo nella realizzazione di sensori luminescenti, e
dall’altro di studiare sistemi di nanoparticelle di oro per identificarne e
caratterizzarne i processi che portano all’interazione con un’unità fluorescente di
riferimento, il pirene.
Quest’ultima parte della tesi, sviluppata nel capitolo 4, sebbene possa apparire
“slegata” dall’ambito della sensoristica, in realtà non lo è in quanto il lavoro di
ricerca svolto rappresenta una buona base di partenza per lo sviluppo di sistemi di
nanoparticelle metalliche con un possibile impiego in campo biomedico e
diagnostico.
Tutte le specie studiate, seppur molto diverse tra loro, posseggono quindi buone
caratteristiche di luminescenza ed interessanti capacità di riconoscimento, più o
meno selettivo, di specie in soluzione o allo stato gassoso.
L’approccio generale che è stato adottato comporta una iniziale caratterizzazione
in soluzione ed una susseguente ottimizzazione del sistema mirata a passare al
fissaggio su supporti solidi in vista di possibili applicazioni pratiche.
A tal proposito, nel capitolo 3 è stato possibile ottenere un monostrato organico
costituito da un recettore (un cavitando), dotato di una parte fluorescente le cui
proprietà di luminescenza sono sensibili alla presenza di una funzione chimica che
caratterizza una classe di analiti, gli alcoli. E’ interessante sottolineare come lo
stesso sistema in soluzione si comporti in maniera sostanzialmente differente,
mostrando una capacità di segnalare l’analita molto meno efficiente, anche in
funzione di una diversa orientazione della parte fluorescente. All’interfaccia
solido-gas invece, l’orientamento del fluoroforo gioca un ruolo chiave nel processo
di riconoscimento, e ottimizzando ulteriormente il setup sperimentale e la
composizione dello strato, sarà possibile arrivare a segnalare quantità di analita
sempre più basse.
Nel capitolo 5 invece, è stato preso in esame un sistema le cui potenzialità, per un
utilizzo come sonda fluorescente nel campo delle superfici di silicio, sembra
promettere molto bene. A tal proposito sono stati discussi anche i risultati del
lavoro che ha fornito l’idea per la concezione di questo sistema che, a breve, verrà
implementato a sua volta su superficie solida.
In conclusione, le ricerche descritte in questa tesi hanno quindi contribuito allo
sviluppo di nuovi chemosensori, cercando di migliorare sia le proprietà fotofisiche
dell’unità attiva, sia quelle dell’unità recettrice, sia, infine, l’efficienza del
processo di traduzione del segnale. I risultati ottenuti hanno inoltre permesso di
realizzare alcuni prototipi di dispositivi sensoriali aventi caratteristiche molto
promettenti e di ottenere informazioni utili per la progettazione di nuovi dispositivi
(ora in fase di sviluppo nei laboratori di ricerca) sempre più efficienti, rispondendo
in tal modo alle aspettative con cui questo lavoro di dottorato era stato intrapreso.
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Battistini, Gionata <1977>. « Sensori chimici basati su molecole e nanoparticelle ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1037/.
Texte intégralRésumé :
Con questo lavoro di tesi si è cercato da un lato di dare un contributo al settore dei
sensori chimici, caratterizzando e sviluppando diversi sistemi che presentano
promettenti proprietà per l’utilizzo nella realizzazione di sensori luminescenti, e
dall’altro di studiare sistemi di nanoparticelle di oro per identificarne e
caratterizzarne i processi che portano all’interazione con un’unità fluorescente di
riferimento, il pirene.
Quest’ultima parte della tesi, sviluppata nel capitolo 4, sebbene possa apparire
“slegata” dall’ambito della sensoristica, in realtà non lo è in quanto il lavoro di
ricerca svolto rappresenta una buona base di partenza per lo sviluppo di sistemi di
nanoparticelle metalliche con un possibile impiego in campo biomedico e
diagnostico.
Tutte le specie studiate, seppur molto diverse tra loro, posseggono quindi buone
caratteristiche di luminescenza ed interessanti capacità di riconoscimento, più o
meno selettivo, di specie in soluzione o allo stato gassoso.
L’approccio generale che è stato adottato comporta una iniziale caratterizzazione
in soluzione ed una susseguente ottimizzazione del sistema mirata a passare al
fissaggio su supporti solidi in vista di possibili applicazioni pratiche.
A tal proposito, nel capitolo 3 è stato possibile ottenere un monostrato organico
costituito da un recettore (un cavitando), dotato di una parte fluorescente le cui
proprietà di luminescenza sono sensibili alla presenza di una funzione chimica che
caratterizza una classe di analiti, gli alcoli. E’ interessante sottolineare come lo
stesso sistema in soluzione si comporti in maniera sostanzialmente differente,
mostrando una capacità di segnalare l’analita molto meno efficiente, anche in
funzione di una diversa orientazione della parte fluorescente. All’interfaccia
solido-gas invece, l’orientamento del fluoroforo gioca un ruolo chiave nel processo
di riconoscimento, e ottimizzando ulteriormente il setup sperimentale e la
composizione dello strato, sarà possibile arrivare a segnalare quantità di analita
sempre più basse.
Nel capitolo 5 invece, è stato preso in esame un sistema le cui potenzialità, per un
utilizzo come sonda fluorescente nel campo delle superfici di silicio, sembra
promettere molto bene. A tal proposito sono stati discussi anche i risultati del
lavoro che ha fornito l’idea per la concezione di questo sistema che, a breve, verrà
implementato a sua volta su superficie solida.
In conclusione, le ricerche descritte in questa tesi hanno quindi contribuito allo
sviluppo di nuovi chemosensori, cercando di migliorare sia le proprietà fotofisiche
dell’unità attiva, sia quelle dell’unità recettrice, sia, infine, l’efficienza del
processo di traduzione del segnale. I risultati ottenuti hanno inoltre permesso di
realizzare alcuni prototipi di dispositivi sensoriali aventi caratteristiche molto
promettenti e di ottenere informazioni utili per la progettazione di nuovi dispositivi
(ora in fase di sviluppo nei laboratori di ricerca) sempre più efficienti, rispondendo
in tal modo alle aspettative con cui questo lavoro di dottorato era stato intrapreso.
27
Kaswalder, Francesco <1980>. « Cluster metallo carbonilici funzionali ad elettronica molecolare ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1041/1/Tesi_Kaswalder_Francesco.pdf.
Texte intégral
28
Kaswalder, Francesco <1980>. « Cluster metallo carbonilici funzionali ad elettronica molecolare ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1041/.
Texte intégral
29
Natanti, Paolo <1979>. « Sintesi e coordinazione di leganti Ciclopentadienilici O-Multifunzionalizzati ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1044/1/Tesi_Natanti_Paolo.pdf.
Texte intégralRésumé :
The introduction of hydroxyl groups into ligands is able to transfer high hydrophilic features to the related
metal systems. The atom-economy synthetic procedure adopted which consists in the one-step
Cyclopentene-oxide ring opening, quantitatitatively affords stereoselective formation of the multi-hydroxyl
rac-1,2,4- C5H2[CH(CH2)3CHOH]3 Cpººº ligand1. Rh complexation of Cpººº gives rise to a novel class of
water-soluble complexes (L,L)RhCpººº (LL=NBD 1, COD 2, CH2CH2 3, CO 4) (Scheme 1) characterized
by their spectroscopic features (ESI-MS, IR, 2D NMR, n.O.e.).
The X-ray diffraction studies of 1a reveal the occurrence of one couple of enantiomeric pairs in the crystal
structure, whilst the crystal packing shows an interesting self-organization in chains of dimeric units of 1a,
promoted by strong intermolecular hydroxyl H-bonding. This effect has been exploited by performing VT
NMR experiments in different solvents (CDCl3, Py, DMSO). Unpredictably, in the absence of chiral tag, 1
exhibits solvent-dependent chiroptical properties (CD, αD^
25), which are correlated to UV transitions and DFT
calculations. The intra/inter molecular H-binding is crucial in driving the equilibrium between the observed
atropisomers 1a and 1b, by varying the planar chirality on the two π-complexes.
30
Natanti, Paolo <1979>. « Sintesi e coordinazione di leganti Ciclopentadienilici O-Multifunzionalizzati ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1044/.
Texte intégralRésumé :
The introduction of hydroxyl groups into ligands is able to transfer high hydrophilic features to the related
metal systems. The atom-economy synthetic procedure adopted which consists in the one-step
Cyclopentene-oxide ring opening, quantitatitatively affords stereoselective formation of the multi-hydroxyl
rac-1,2,4- C5H2[CH(CH2)3CHOH]3 Cpººº ligand1. Rh complexation of Cpººº gives rise to a novel class of
water-soluble complexes (L,L)RhCpººº (LL=NBD 1, COD 2, CH2CH2 3, CO 4) (Scheme 1) characterized
by their spectroscopic features (ESI-MS, IR, 2D NMR, n.O.e.).
The X-ray diffraction studies of 1a reveal the occurrence of one couple of enantiomeric pairs in the crystal
structure, whilst the crystal packing shows an interesting self-organization in chains of dimeric units of 1a,
promoted by strong intermolecular hydroxyl H-bonding. This effect has been exploited by performing VT
NMR experiments in different solvents (CDCl3, Py, DMSO). Unpredictably, in the absence of chiral tag, 1
exhibits solvent-dependent chiroptical properties (CD, αD^
25), which are correlated to UV transitions and DFT
calculations. The intra/inter molecular H-binding is crucial in driving the equilibrium between the observed
atropisomers 1a and 1b, by varying the planar chirality on the two π-complexes.
31
Giansante, Carlo <1978>. « Supramolecular photoactive systems ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1045/1/Tesi_Giansante_Carlo.pdf.
Texte intégral
32
Giansante, Carlo <1978>. « Supramolecular photoactive systems ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1045/.
Texte intégral
33
Sprio, Simone <1970>. « Synthesis and characterization of implants for bone substitutions made of biomedical apatites containing silicon ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1049/1/Tesi_Sprio_Simone.pdf.
Texte intégralRésumé :
In the last decades the development of bone substitutes characterized by a superior biomimetism has become of particular interest, owing to the increasing economic and societal impact of the bone diseases.
In the present work of research the development of bone substitutes characterized by improved biomimetism, has been faced in a chemical, structural and morphological perspective.
From a chemical point of view, it has been developed the synthesis of hydroxyapatite powders, exhibiting multiple ionic substitutions in both cationic and anionic sites, so to simulate the chemical composition of the natural bone. Particular emphasis has been given to the effect of silicon on the chemical-physical and solubility properties of the obtained hydroxyapatites.
From a structural point of view, it has been developed the synthesis of ceramic composite materials, based on hydroxyapatite and calcium silicates, employed both as a reinforcing phase, to raise the mechanical strength of the composite compared to hydroxyapatite, and as a bioactive phase, able to increase the bioactivity properties of the whole ceramic.
Finally the unique morphological features of the bone were mimicked by taking inspiration by Nature, so that native wood structures were treated in chemical and thermal way to obtain hydroxyapatite porous materials characterized by the same morphology as the native wood.
The results obtained in the present work were positive in all the three different areas of investigation, so to cover the three different aspects of biomimetism, chemical, structural and morphological. Anyway, only at the convergence of the three different fields it is possible to find out the best solutions to develop the ideal bone-like scaffold. Thus, the future activity should be devoted to solve the problems at the borderline between the different research lines, which hamper this convergence and in consequence, the achievement of a bone scaffold able to mimic the various aspects exhibited by the bone tissue
34
Sprio, Simone <1970>. « Synthesis and characterization of implants for bone substitutions made of biomedical apatites containing silicon ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/1049/.
Texte intégralRésumé :
In the last decades the development of bone substitutes characterized by a superior biomimetism has become of particular interest, owing to the increasing economic and societal impact of the bone diseases.
In the present work of research the development of bone substitutes characterized by improved biomimetism, has been faced in a chemical, structural and morphological perspective.
From a chemical point of view, it has been developed the synthesis of hydroxyapatite powders, exhibiting multiple ionic substitutions in both cationic and anionic sites, so to simulate the chemical composition of the natural bone. Particular emphasis has been given to the effect of silicon on the chemical-physical and solubility properties of the obtained hydroxyapatites.
From a structural point of view, it has been developed the synthesis of ceramic composite materials, based on hydroxyapatite and calcium silicates, employed both as a reinforcing phase, to raise the mechanical strength of the composite compared to hydroxyapatite, and as a bioactive phase, able to increase the bioactivity properties of the whole ceramic.
Finally the unique morphological features of the bone were mimicked by taking inspiration by Nature, so that native wood structures were treated in chemical and thermal way to obtain hydroxyapatite porous materials characterized by the same morphology as the native wood.
The results obtained in the present work were positive in all the three different areas of investigation, so to cover the three different aspects of biomimetism, chemical, structural and morphological. Anyway, only at the convergence of the three different fields it is possible to find out the best solutions to develop the ideal bone-like scaffold. Thus, the future activity should be devoted to solve the problems at the borderline between the different research lines, which hamper this convergence and in consequence, the achievement of a bone scaffold able to mimic the various aspects exhibited by the bone tissue
35
Marzocchi, Ettore <1981>. « Luminescent Systems for Genomics and Proteomics ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1371/1/Marzocchi_Ettore_Tesi.pdf.
Texte intégralRésumé :
The present PhD project was focused on the development of new tools and methods for luminescence-based techniques. In particular, the ultimate goal was to present substantial improvements to the currently available technologies for both research and diagnostic in the fields of biology, proteomics and genomics.
Different aspects and problems were investigated, requiring different strategies and approaches. The whole work was thus divided into separate chapters, each based on the study of one specific aspect of luminescence: Chemiluminescence, Fluorescence and Electrochemiluminescence.
CHAPTER 1, Chemiluminescence
The work on luminol-enhancer solution lead to a new luminol solution formulation with 1 order of magnitude lower detection limit for HRP. This technology was patented with Cyanagen brand and is now sold worldwide for Western Blot and ELISA applications.
CHAPTER 2, Fluorescescence
The work on dyed-doped silica nanoparticles is marking a new milestone in the development of nanotechnologies for biological applications. While the project is still in progress, preliminary studies on model structures are leading to very promising results. The improved brightness of these nano-sized objects, their simple synthesis and handling, their low toxicity will soon turn them, we strongly believe, into a new generation of fluorescent labels for many applications.
CHAPTER 3, Electrochemiluminescence
The work on electrochemiluminescence produced interesting results that can potentially turn into great improvements from an analytical point of view. Ru(bpy)3 derivatives were employed both for on-chip microarray (Chapter 3.1) and for microscopic imaging applications (Chapter 3.2). The development of these new techniques is still under investigation, but the obtained results confirm the possibility to achieve the final goal. Furthermore the development of new ECL-active species (Chapter 3.3, 3.4, 3.5) and their use in these applications can significantly improve overall performances, thus helping to spread ECL as powerful analytical tool for routinary techniques.
To conclude, the results obtained are of strong value to largely increase the sensitivity of luminescence techniques, thus fulfilling the expectation we had at the beginning of this research work.
36
Marzocchi, Ettore <1981>. « Luminescent Systems for Genomics and Proteomics ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1371/.
Texte intégralRésumé :
The present PhD project was focused on the development of new tools and methods for luminescence-based techniques. In particular, the ultimate goal was to present substantial improvements to the currently available technologies for both research and diagnostic in the fields of biology, proteomics and genomics.
Different aspects and problems were investigated, requiring different strategies and approaches. The whole work was thus divided into separate chapters, each based on the study of one specific aspect of luminescence: Chemiluminescence, Fluorescence and Electrochemiluminescence.
CHAPTER 1, Chemiluminescence
The work on luminol-enhancer solution lead to a new luminol solution formulation with 1 order of magnitude lower detection limit for HRP. This technology was patented with Cyanagen brand and is now sold worldwide for Western Blot and ELISA applications.
CHAPTER 2, Fluorescescence
The work on dyed-doped silica nanoparticles is marking a new milestone in the development of nanotechnologies for biological applications. While the project is still in progress, preliminary studies on model structures are leading to very promising results. The improved brightness of these nano-sized objects, their simple synthesis and handling, their low toxicity will soon turn them, we strongly believe, into a new generation of fluorescent labels for many applications.
CHAPTER 3, Electrochemiluminescence
The work on electrochemiluminescence produced interesting results that can potentially turn into great improvements from an analytical point of view. Ru(bpy)3 derivatives were employed both for on-chip microarray (Chapter 3.1) and for microscopic imaging applications (Chapter 3.2). The development of these new techniques is still under investigation, but the obtained results confirm the possibility to achieve the final goal. Furthermore the development of new ECL-active species (Chapter 3.3, 3.4, 3.5) and their use in these applications can significantly improve overall performances, thus helping to spread ECL as powerful analytical tool for routinary techniques.
To conclude, the results obtained are of strong value to largely increase the sensitivity of luminescence techniques, thus fulfilling the expectation we had at the beginning of this research work.
37
Capuccini, Chiara <1979>. « Biomimetic Materials for Biomedical Applications ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1447/1/chiara_capuccini_tesi.pdf.
Texte intégralRésumé :
Objects with complex shape and functions have always attracted attention and interest. The morphological diversity and complexity of naturally occurring forms and patterns have been a motivation for humans to copy and adopt ideas from Nature to achieve functional, aesthetic and social value.
Biomimetics is addressed to the design and development of new synthetic materials using strategies adopted by living organisms to produce biological materials. In particular, biomineralized tissues are often sophisticate composite materials, in which the components and the interfaces between them have been defined and optimized, and that present unusual and optimal chemical-physical, morphological and mechanical properties. Moreover, biominerals are generally produced by easily traceable raw materials, in aqueous media and at room pressure and temperature, that is through cheap process and materials. Thus, it is not surprising that the idea to mimic those strategies proper of Nature has been employed in several areas of applied sciences, such as for the preparation of liquid crystals, ceramic thin films computer switches and many other advanced materials.
On this basis, this PhD thesis is focused on the investigation of the interaction of biologically active ions and molecules with calcium phosphates with the aim to develop new materials for the substitution and repair of skeletal tissue, according to the following lines:
I. Modified calcium phosphates.
A relevant part of this PhD thesis has been addressed to study the interaction of Strontium with calcium phosphates. It was demonstrated that strontium ion can substitute for calcium into hydroxyapatite, causing appreciable structural and morphological modifications. The detailed structural analysis carried out on the nanocrystals at different strontium content provided new insight into its interaction with the structure of hydroxyapatite.
At variance with the behaviour of Sr towards HA, it was found that this ion inhibits the synthesis of octacalcium phosphate. However, it can substitute for calcium in this structure up to 15 atom %, in agreement with the increase of the cell parameters observed on increasing ion concentration. A similar behaviour was found for Magnesium ion, whereas Manganese inhibits the synthesis of octacalcium phosphate and it promotes the precipitation of dicalcium phosphate dehydrate.
It was also found that Strontium affects the kinetics of the reaction of hydrolysis of α-TCP. It inhibits the conversion from α-TCP to hydroxyapatite. However, the resulting apatitic phase contains significant amounts of Sr2+ suggesting that the addition of Sr2+ to the composition of α-TCP bone cements could be successfully exploited for its local delivery in bone defects.
The hydrolysis of α-TCP has been investigated also in the presence of increasing amounts of gelatin: the results indicated that this biopolymer accelerates the hydrolysis reaction and promotes the conversion of α-TCP into OCP, suggesting that its addition in the composition of calcium phosphate cements can be employed to modulate the OCP/HA ratio, and as a consequence the solubility, of the set cement.
II. Deposition of modified calcium phosphates on metallic substrates.
Coating with a thin film of calcium phosphates is frequently applied on the surface of metallic implants in order to combine the high mechanical strength of the metal with the excellent bioactivity of the calcium phosphates surface layers. During this PhD thesis, thank to the collaboration with prof. I.N. Mihailescu, head of the Laser-Surface-Plasma Interactions Laboratory (National Institute for Lasers, Plasma and Radiation Physics – Laser Department, Bucharest) Pulsed Laser Deposition has been successfully applied to deposit thin films of Sr substituted HA on Titanium substrates. The synthesized coatings displayed a uniform Sr distribution, a granular surface and a good degree of crystallinity which slightly decreased on increasing Sr content. The results of in vitro tests carried out on osteoblast-like and osteoclast cells suggested that the presence of Sr in HA thin films can enhance the positive effect of HA coatings on osteointegration and bone regeneration, and prevent undesirable bone resorption.
The possibility to introduce an active molecule in the implant site was explored using Matrix Assisted Pulsed Laser Evaporation to deposit hydroxyapatite nanocrystals at different content of alendronate, a bisphosphonate widely employed in the treatments of pathological diseases associated to bone loss. The coatings displayed a good degree of crystallinity, and the results of in vitro tests indicated that alendronate promotes proliferation and differentiation of osteoblasts even when incorporated into hydroxyapatite.
III. Synthesis of drug carriers with a delayed release modulated by a calcium phosphate coating.
A core-shell system for modulated drug delivery and release has been developed through optimization of the experimental conditions to cover gelatin microspheres with a uniform layer of calcium phosphate. The kinetics of the release from uncoated and coated microspheres was investigated using aspirin as a model drug. It was shown that the presence of the calcium phosphate shell delays the release of aspirin and allows to modulate its action.
38
Capuccini, Chiara <1979>. « Biomimetic Materials for Biomedical Applications ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1447/.
Texte intégralRésumé :
Objects with complex shape and functions have always attracted attention and interest. The morphological diversity and complexity of naturally occurring forms and patterns have been a motivation for humans to copy and adopt ideas from Nature to achieve functional, aesthetic and social value.
Biomimetics is addressed to the design and development of new synthetic materials using strategies adopted by living organisms to produce biological materials. In particular, biomineralized tissues are often sophisticate composite materials, in which the components and the interfaces between them have been defined and optimized, and that present unusual and optimal chemical-physical, morphological and mechanical properties. Moreover, biominerals are generally produced by easily traceable raw materials, in aqueous media and at room pressure and temperature, that is through cheap process and materials. Thus, it is not surprising that the idea to mimic those strategies proper of Nature has been employed in several areas of applied sciences, such as for the preparation of liquid crystals, ceramic thin films computer switches and many other advanced materials.
On this basis, this PhD thesis is focused on the investigation of the interaction of biologically active ions and molecules with calcium phosphates with the aim to develop new materials for the substitution and repair of skeletal tissue, according to the following lines:
I. Modified calcium phosphates.
A relevant part of this PhD thesis has been addressed to study the interaction of Strontium with calcium phosphates. It was demonstrated that strontium ion can substitute for calcium into hydroxyapatite, causing appreciable structural and morphological modifications. The detailed structural analysis carried out on the nanocrystals at different strontium content provided new insight into its interaction with the structure of hydroxyapatite.
At variance with the behaviour of Sr towards HA, it was found that this ion inhibits the synthesis of octacalcium phosphate. However, it can substitute for calcium in this structure up to 15 atom %, in agreement with the increase of the cell parameters observed on increasing ion concentration. A similar behaviour was found for Magnesium ion, whereas Manganese inhibits the synthesis of octacalcium phosphate and it promotes the precipitation of dicalcium phosphate dehydrate.
It was also found that Strontium affects the kinetics of the reaction of hydrolysis of α-TCP. It inhibits the conversion from α-TCP to hydroxyapatite. However, the resulting apatitic phase contains significant amounts of Sr2+ suggesting that the addition of Sr2+ to the composition of α-TCP bone cements could be successfully exploited for its local delivery in bone defects.
The hydrolysis of α-TCP has been investigated also in the presence of increasing amounts of gelatin: the results indicated that this biopolymer accelerates the hydrolysis reaction and promotes the conversion of α-TCP into OCP, suggesting that its addition in the composition of calcium phosphate cements can be employed to modulate the OCP/HA ratio, and as a consequence the solubility, of the set cement.
II. Deposition of modified calcium phosphates on metallic substrates.
Coating with a thin film of calcium phosphates is frequently applied on the surface of metallic implants in order to combine the high mechanical strength of the metal with the excellent bioactivity of the calcium phosphates surface layers. During this PhD thesis, thank to the collaboration with prof. I.N. Mihailescu, head of the Laser-Surface-Plasma Interactions Laboratory (National Institute for Lasers, Plasma and Radiation Physics – Laser Department, Bucharest) Pulsed Laser Deposition has been successfully applied to deposit thin films of Sr substituted HA on Titanium substrates. The synthesized coatings displayed a uniform Sr distribution, a granular surface and a good degree of crystallinity which slightly decreased on increasing Sr content. The results of in vitro tests carried out on osteoblast-like and osteoclast cells suggested that the presence of Sr in HA thin films can enhance the positive effect of HA coatings on osteointegration and bone regeneration, and prevent undesirable bone resorption.
The possibility to introduce an active molecule in the implant site was explored using Matrix Assisted Pulsed Laser Evaporation to deposit hydroxyapatite nanocrystals at different content of alendronate, a bisphosphonate widely employed in the treatments of pathological diseases associated to bone loss. The coatings displayed a good degree of crystallinity, and the results of in vitro tests indicated that alendronate promotes proliferation and differentiation of osteoblasts even when incorporated into hydroxyapatite.
III. Synthesis of drug carriers with a delayed release modulated by a calcium phosphate coating.
A core-shell system for modulated drug delivery and release has been developed through optimization of the experimental conditions to cover gelatin microspheres with a uniform layer of calcium phosphate. The kinetics of the release from uncoated and coated microspheres was investigated using aspirin as a model drug. It was shown that the presence of the calcium phosphate shell delays the release of aspirin and allows to modulate its action.
39
Salmi, Mauro <1980>. « Transformations of bridging ligands in diiron complexes : unconventional routes to new functionalized multisite bound organic frames ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1480/1/salmi_mauro_tesi.pdf.
Texte intégralRésumé :
The main scope of this Ph.D. thesis has concerned the possible transformations of bridging ligands in diiron complexes, in order to explore unconventional routes to the synthesis of new functionalized multisite bound organic frames.
The results achieved during the Ph.D. can be summarized in the following points:
1) We have extended the assembling between small unsaturated molecules and bridging carbyne ligands in diiron complexes to other species. In particular, we have investigated the coupling between olefins and thiocarbyne, leading to the synthesis of thioallylidene bridging diiron complexes. Then, we have extended the study to the coupling between olefins and aminocarbyne. This result shows that the coupling between activated olefins and heteroatom substituted bridging carbynes has a general character.
2) As we have shown, the coupling of bridging alkylidyne ligands with alkynes and alkenes provides excellent routes to the synthesis of bridging C3 hydrocarbyl ligands. As a possible extension of these results we have examined the synthesis of C4 bridging frames through the combination of bridging alkylidynes with allenes. Also in this case the reaction has a general character.
3) Diiron complexes bearing bridging functionalized C3 organic frames display the presence of donor atoms, such as N and S, potentially able to coordinate unsaturated metal fragments. Thus, we have studied the possibility for these systems to act as ‘organometallic ligands’, in particular towards Pd and Rh.
4) The possibility of releasing the organic frame from the bridging coordination appears particularly appealing in the direction of a metal-assisted organic synthesis. Within this field, we have investigated the possibility of involving the C3 bridging ligand in cycloaddition reactions with alkynes, with the aim of generating variously functionalized five-membered cycles. The [3+2] cyclization does not lead to the complete release of the organic fragment but rather it produces its transformation into a cyclopentadienyl ring, which remains coordinated to one Fe atom. This result introduces a new approach to the formation of polyfunctionalised ferrocenes.
5) Furthermore, I have spent a research period of about six months at the Department of Inorganic Chemistry of the Barcelona University, under the supervision of Prof. Concepción López, with the aim of studying the chemistry of polydentate ferrocenyl ligands and their use in organometallic synthesis.
40
Salmi, Mauro <1980>. « Transformations of bridging ligands in diiron complexes : unconventional routes to new functionalized multisite bound organic frames ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1480/.
Texte intégralRésumé :
The main scope of this Ph.D. thesis has concerned the possible transformations of bridging ligands in diiron complexes, in order to explore unconventional routes to the synthesis of new functionalized multisite bound organic frames.
The results achieved during the Ph.D. can be summarized in the following points:
1) We have extended the assembling between small unsaturated molecules and bridging carbyne ligands in diiron complexes to other species. In particular, we have investigated the coupling between olefins and thiocarbyne, leading to the synthesis of thioallylidene bridging diiron complexes. Then, we have extended the study to the coupling between olefins and aminocarbyne. This result shows that the coupling between activated olefins and heteroatom substituted bridging carbynes has a general character.
2) As we have shown, the coupling of bridging alkylidyne ligands with alkynes and alkenes provides excellent routes to the synthesis of bridging C3 hydrocarbyl ligands. As a possible extension of these results we have examined the synthesis of C4 bridging frames through the combination of bridging alkylidynes with allenes. Also in this case the reaction has a general character.
3) Diiron complexes bearing bridging functionalized C3 organic frames display the presence of donor atoms, such as N and S, potentially able to coordinate unsaturated metal fragments. Thus, we have studied the possibility for these systems to act as ‘organometallic ligands’, in particular towards Pd and Rh.
4) The possibility of releasing the organic frame from the bridging coordination appears particularly appealing in the direction of a metal-assisted organic synthesis. Within this field, we have investigated the possibility of involving the C3 bridging ligand in cycloaddition reactions with alkynes, with the aim of generating variously functionalized five-membered cycles. The [3+2] cyclization does not lead to the complete release of the organic fragment but rather it produces its transformation into a cyclopentadienyl ring, which remains coordinated to one Fe atom. This result introduces a new approach to the formation of polyfunctionalised ferrocenes.
5) Furthermore, I have spent a research period of about six months at the Department of Inorganic Chemistry of the Barcelona University, under the supervision of Prof. Concepción López, with the aim of studying the chemistry of polydentate ferrocenyl ligands and their use in organometallic synthesis.
41
Tiozzo, Cristina <1980>. « New high nuclearity carbonyl clusters ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1507/1/Cristina_Tiozzo_Tesi.pdf.
Texte intégralRésumé :
The thesis reports the synthesis, and the chemical, structural and spectroscopic characterization of a series of new Rhodium and Au-Fe carbonyl clusters.
Most new high-nuclearity rhodium carbonyl clusters have been obtained by redox condensation of preformed rhodium clusters reacting with a species in a different oxidation state generated in situ by mild oxidation.
In particular the starting Rh carbonyl clusters is represented by the readily available [Rh7(CO)16]3- 9 compound. The oxidized species is generated in situ by reaction of the above with a stoichiometric defect of a mild oxidizing agents such as [M(H2O)x]n+ aquo complexes possessing different pKa’s and Mn+/M potentials. The experimental results are roughly in keeping with the conclusion that aquo complexes featuring E°(Mn+/M) < ca. -0.20 V do not lead to the formation of hetero-metallic Rh clusters, probably because of the inadequacy of their redox potentials relative to that of the [Rh7(CO)16]3-/2- redox couple. Only homometallic cluster s such as have been fairly selectively obtained.
As a fallout of the above investigations, also a convenient and reproducible synthesis of the ill-characterized species [HnRh22(CO)35]8-n has been discovered. The ready availability of the above compound triggered both its complete spectroscopic and chemical characterization. because it is the only example of Rhodium carbonyl clusters with two interstitial metal atoms. The presence of several hydride atoms, firstly suggested by chemical evidences, has been implemented by ESI-MS and 1H-NMR, as well as new structural characterization of its tetra- and penta-anion. All these species display redox behaviour and behave as molecular capacitors. Their chemical reactivity with CO gives rise to a new series of Rh22 clusters containing a different number of carbonyl groups, which have been likewise fully characterized.
Formation of hetero-metallic Rh clusters was only observed when using SnCl2H2O as oxidizing agent because. Quite all the Rh-Sn carbonyl clusters obtained have icosahedral geometry. The only previously reported example of an icosahedral Rh cluster with an interstitial atom is the [Rh12Sb(CO)27]3- trianion. They have very similar metal framework, as well as the same number of CO ligands and, consequently, cluster valence electrons (CVEs). .A first interesting aspect of the chemistry of the Rh-Sn system is that it also provides icosahedral clusters making exception to the cluster-borane analogy by showing electron counts from 166 to 171. As a result, the most electron-short species, namely [Rh12Sn(CO)25]4- displays redox propensity, even if disfavoured by the relatively high free negative charge of the starting anion and, moreover, behaves as a chloride scavenger.
The presence of these bulky interstitial atoms results in the metal framework adopting structures different from a close-packed metal lattice and, above all, imparts a notable stability to the resulting cluster.
An organometallic approach to a new kind of molecular ligand-stabilized gold nanoparticles, in which Fe(CO)x (x = 3,4) moieties protect and stabilize the gold kernel has also been undertaken. As a result, the new clusters [Au21{Fe(CO)4}10]5-, [Au22{Fe(CO)4}12]6-, Au28{Fe(CO)3}4{Fe(CO)4}10]8- and [Au34{Fe(CO)3}6{Fe(CO)4}8]6- have been isolated and characterized. As suggested by concepts of isolobal analogies, the Fe(CO)4 molecular fragment may display the same ligand capability of thiolates and go beyond. Indeed, the above clusters bring structural resemblance to the structurally characterized gold thiolates by showing Fe-Au-Fe, rather than S-Au-S, staple motives.
Staple motives, the oxidation state of surface gold atoms and the energy of Au atomic orbitals are likely to concur in delaying the insulator-to-metal transition as the nuclearity of gold thiolates increases, relative to the more compact transition-metal carbonyl clusters.
Finally, a few previously reported Au-Fe carbonyl clusters have been used as precursors in the preparation of supported gold catalysts. The catalysts obtained are active for toluene oxidation and the catalytic activity depends on the Fe/Au cluster loading over TiO2.
42
Tiozzo, Cristina <1980>. « New high nuclearity carbonyl clusters ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1507/.
Texte intégralRésumé :
The thesis reports the synthesis, and the chemical, structural and spectroscopic characterization of a series of new Rhodium and Au-Fe carbonyl clusters.
Most new high-nuclearity rhodium carbonyl clusters have been obtained by redox condensation of preformed rhodium clusters reacting with a species in a different oxidation state generated in situ by mild oxidation.
In particular the starting Rh carbonyl clusters is represented by the readily available [Rh7(CO)16]3- 9 compound. The oxidized species is generated in situ by reaction of the above with a stoichiometric defect of a mild oxidizing agents such as [M(H2O)x]n+ aquo complexes possessing different pKa’s and Mn+/M potentials. The experimental results are roughly in keeping with the conclusion that aquo complexes featuring E°(Mn+/M) < ca. -0.20 V do not lead to the formation of hetero-metallic Rh clusters, probably because of the inadequacy of their redox potentials relative to that of the [Rh7(CO)16]3-/2- redox couple. Only homometallic cluster s such as have been fairly selectively obtained.
As a fallout of the above investigations, also a convenient and reproducible synthesis of the ill-characterized species [HnRh22(CO)35]8-n has been discovered. The ready availability of the above compound triggered both its complete spectroscopic and chemical characterization. because it is the only example of Rhodium carbonyl clusters with two interstitial metal atoms. The presence of several hydride atoms, firstly suggested by chemical evidences, has been implemented by ESI-MS and 1H-NMR, as well as new structural characterization of its tetra- and penta-anion. All these species display redox behaviour and behave as molecular capacitors. Their chemical reactivity with CO gives rise to a new series of Rh22 clusters containing a different number of carbonyl groups, which have been likewise fully characterized.
Formation of hetero-metallic Rh clusters was only observed when using SnCl2H2O as oxidizing agent because. Quite all the Rh-Sn carbonyl clusters obtained have icosahedral geometry. The only previously reported example of an icosahedral Rh cluster with an interstitial atom is the [Rh12Sb(CO)27]3- trianion. They have very similar metal framework, as well as the same number of CO ligands and, consequently, cluster valence electrons (CVEs). .A first interesting aspect of the chemistry of the Rh-Sn system is that it also provides icosahedral clusters making exception to the cluster-borane analogy by showing electron counts from 166 to 171. As a result, the most electron-short species, namely [Rh12Sn(CO)25]4- displays redox propensity, even if disfavoured by the relatively high free negative charge of the starting anion and, moreover, behaves as a chloride scavenger.
The presence of these bulky interstitial atoms results in the metal framework adopting structures different from a close-packed metal lattice and, above all, imparts a notable stability to the resulting cluster.
An organometallic approach to a new kind of molecular ligand-stabilized gold nanoparticles, in which Fe(CO)x (x = 3,4) moieties protect and stabilize the gold kernel has also been undertaken. As a result, the new clusters [Au21{Fe(CO)4}10]5-, [Au22{Fe(CO)4}12]6-, Au28{Fe(CO)3}4{Fe(CO)4}10]8- and [Au34{Fe(CO)3}6{Fe(CO)4}8]6- have been isolated and characterized. As suggested by concepts of isolobal analogies, the Fe(CO)4 molecular fragment may display the same ligand capability of thiolates and go beyond. Indeed, the above clusters bring structural resemblance to the structurally characterized gold thiolates by showing Fe-Au-Fe, rather than S-Au-S, staple motives.
Staple motives, the oxidation state of surface gold atoms and the energy of Au atomic orbitals are likely to concur in delaying the insulator-to-metal transition as the nuclearity of gold thiolates increases, relative to the more compact transition-metal carbonyl clusters.
Finally, a few previously reported Au-Fe carbonyl clusters have been used as precursors in the preparation of supported gold catalysts. The catalysts obtained are active for toluene oxidation and the catalytic activity depends on the Fe/Au cluster loading over TiO2.
43
Bonacchi, Sara <1979>. « Design and Characterization of New Luminescent Sensors and Labels ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1610/1/Bonacchi_Sara_Tesi.pdf.
Texte intégralRésumé :
The aim of this Ph.D. project has been the design and characterization of new and more efficient luminescent tools, in particular sensors and labels, for analytical chemistry, medical diagnostics and imaging. Actually both the increasing temporal and spatial resolutions that are demanded by those branches, coupled to a sensitivity that is required to reach the single molecule resolution, can be provided by the wide range of techniques based on luminescence spectroscopy.
As far as the development of new chemical sensors is concerned, as chemists we were interested in the preparation of new, efficient, sensing materials. In this context, we kept developing new molecular chemosensors, by exploiting the supramolecular approach, for different classes of analytes. In particular we studied a family of luminescent tetrapodal-hosts based on aminopyridinium units with pyrenyl groups for the detection of anions. These systems exhibited noticeable changes in the photophysical properties, depending on the nature of the anion; in particular, addition of chloride resulted in a conformational change, giving an initial increase in excimeric emission. A good selectivity for dicarboxylic acid was also found.
In the search for higher sensitivities, we moved our attention also to systems able to perform amplification effects. In this context we described the metal ion binding properties of three photoactive poly-(arylene ethynylene) co-polymers with different complexing units and we highlighted, for one of them, a ten-fold amplification of the response in case of addition of Zn2+, Cu2+ and Hg2+ ions. In addition, we were able to demonstrate the formation of complexes with Yb3+ an Er3+ and an efficient sensitization of their typical metal centered NIR emission upon excitation of the polymer structure, this feature being of particular interest for their possible applications in optical imaging and in optical amplification for telecommunication purposes.
An amplification effect was also observed during this research in silica nanoparticles derivatized with a suitable zinc probe. In this case we were able to prove, for the first time, that nanoparticles can work as “off-on” chemosensors with signal amplification. Fluorescent silica nanoparticles can be thus seen as innovative multicomponent systems in which the organization of photophysically active units gives rise to fruitful collective effects. These precious effects can be exploited for biological imaging, medical diagnostic and therapeutics, as evidenced also by some results reported in this thesis. In particular, the observed amplification effect has been obtained thanks to a suitable organization of molecular probe units onto the surface of the nanoparticles.
In the effort of reaching a deeper inside in the mechanisms which lead to the final amplification effects, we also attempted to find a correlation between the synthetic route and the final organization of the active molecules in the silica network, and thus with those mutual interactions between one another which result in the emerging, collective behavior, responsible for the desired signal amplification.
In this context, we firstly investigated the process of formation of silica nanoparticles doped with pyrene derivative and we showed that the dyes are not uniformly dispersed inside the silica matrix; thus, core-shell structures can be formed spontaneously in a one step synthesis. Moreover, as far as the design of new labels is concerned, we reported a new synthetic approach to obtain a class of robust, biocompatible silica core-shell nanoparticles able to show a long-term stability. Taking advantage of this new approach we also showed the synthesis and photophysical properties of core-shell NIR absorbing and emitting materials that proved to be very valuable for in-vivo imaging. In general, the dye doped silica nanoparticles prepared in the framework of this project can conjugate unique properties, such as a very high brightness, due to the possibility to include many fluorophores per nanoparticle, high stability, because of the shielding effect of the silica matrix, and, to date, no toxicity, with a simple and low-cost preparation. All these features make these nanostructures suitable to reach the low detection limits that are nowadays required for effective clinical and environmental applications, fulfilling in this way the initial expectations of this research project.
44
Bonacchi, Sara <1979>. « Design and Characterization of New Luminescent Sensors and Labels ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1610/.
Texte intégralRésumé :
The aim of this Ph.D. project has been the design and characterization of new and more efficient luminescent tools, in particular sensors and labels, for analytical chemistry, medical diagnostics and imaging. Actually both the increasing temporal and spatial resolutions that are demanded by those branches, coupled to a sensitivity that is required to reach the single molecule resolution, can be provided by the wide range of techniques based on luminescence spectroscopy.
As far as the development of new chemical sensors is concerned, as chemists we were interested in the preparation of new, efficient, sensing materials. In this context, we kept developing new molecular chemosensors, by exploiting the supramolecular approach, for different classes of analytes. In particular we studied a family of luminescent tetrapodal-hosts based on aminopyridinium units with pyrenyl groups for the detection of anions. These systems exhibited noticeable changes in the photophysical properties, depending on the nature of the anion; in particular, addition of chloride resulted in a conformational change, giving an initial increase in excimeric emission. A good selectivity for dicarboxylic acid was also found.
In the search for higher sensitivities, we moved our attention also to systems able to perform amplification effects. In this context we described the metal ion binding properties of three photoactive poly-(arylene ethynylene) co-polymers with different complexing units and we highlighted, for one of them, a ten-fold amplification of the response in case of addition of Zn2+, Cu2+ and Hg2+ ions. In addition, we were able to demonstrate the formation of complexes with Yb3+ an Er3+ and an efficient sensitization of their typical metal centered NIR emission upon excitation of the polymer structure, this feature being of particular interest for their possible applications in optical imaging and in optical amplification for telecommunication purposes.
An amplification effect was also observed during this research in silica nanoparticles derivatized with a suitable zinc probe. In this case we were able to prove, for the first time, that nanoparticles can work as “off-on” chemosensors with signal amplification. Fluorescent silica nanoparticles can be thus seen as innovative multicomponent systems in which the organization of photophysically active units gives rise to fruitful collective effects. These precious effects can be exploited for biological imaging, medical diagnostic and therapeutics, as evidenced also by some results reported in this thesis. In particular, the observed amplification effect has been obtained thanks to a suitable organization of molecular probe units onto the surface of the nanoparticles.
In the effort of reaching a deeper inside in the mechanisms which lead to the final amplification effects, we also attempted to find a correlation between the synthetic route and the final organization of the active molecules in the silica network, and thus with those mutual interactions between one another which result in the emerging, collective behavior, responsible for the desired signal amplification.
In this context, we firstly investigated the process of formation of silica nanoparticles doped with pyrene derivative and we showed that the dyes are not uniformly dispersed inside the silica matrix; thus, core-shell structures can be formed spontaneously in a one step synthesis. Moreover, as far as the design of new labels is concerned, we reported a new synthetic approach to obtain a class of robust, biocompatible silica core-shell nanoparticles able to show a long-term stability. Taking advantage of this new approach we also showed the synthesis and photophysical properties of core-shell NIR absorbing and emitting materials that proved to be very valuable for in-vivo imaging. In general, the dye doped silica nanoparticles prepared in the framework of this project can conjugate unique properties, such as a very high brightness, due to the possibility to include many fluorophores per nanoparticle, high stability, because of the shielding effect of the silica matrix, and, to date, no toxicity, with a simple and low-cost preparation. All these features make these nanostructures suitable to reach the low detection limits that are nowadays required for effective clinical and environmental applications, fulfilling in this way the initial expectations of this research project.
45
Iafisco, Michele <1980>. « Interaction between biomimetic inorganic materials and biomolecules : towards nanotechnological applications ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1621/1/TESI_Michele_Iafisco.pdf.
Texte intégral
46
Iafisco, Michele <1980>. « Interaction between biomimetic inorganic materials and biomolecules : towards nanotechnological applications ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1621/.
Texte intégral
47
Tosi, Giovanna <1979>. « Macromolecular crystallography : crystallisation and structural determination ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1625/1/TESI_GT.pdf.
Texte intégral
48
Tosi, Giovanna <1979>. « Macromolecular crystallography : crystallisation and structural determination ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1625/.
Texte intégral
49
Picone, Gianfranco <1977>. « NMR, Metabonomics and Molecular Profiles : Applications to the Quality Assessment of Foodstuffs ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1648/1/Picone_Gianfranco_NMR%2C_Metabonomics_and_Molecular_Profiles_Applications_to_the_Quality_Assessment_of_Foodstuff.pdf.
Texte intégralRésumé :
Nuclear Magnetic Resonance (NMR) is a branch of spectroscopy that is based on the fact that many atomic nuclei may be oriented by a strong magnetic field and will absorb radiofrequency radiation at characteristic frequencies. The parameters that can be measured on the resulting spectral lines (line positions, intensities, line widths, multiplicities and transients in time-dependent experi-ments) can be interpreted in terms of molecular structure, conformation, molecular motion and other rate processes. In this way, high resolution (HR) NMR allows performing qualitative and quantitative analysis of samples in solution, in order to determine the structure of molecules in solution and not only. In the past, high-field NMR spectroscopy has mainly concerned with the elucidation of chemical structure in solution, but today is emerging as a powerful exploratory tool for probing biochemical and physical processes. It represents a versatile tool for the analysis of foods. In literature many NMR studies have been reported on different type of food such as wine, olive oil, coffee, fruit juices, milk, meat, egg, starch granules, flour, etc using different NMR techniques.
Traditionally, univariate analytical methods have been used to ex-plore spectroscopic data. This method is useful to measure or to se-lect a single descriptive variable from the whole spectrum and , at the end, only this variable is analyzed. This univariate methods ap-proach, applied to HR-NMR data, lead to different problems due especially to the complexity of an NMR spectrum. In fact, the lat-ter is composed of different signals belonging to different mole-cules, but it is also true that the same molecules can be represented by different signals, generally strongly correlated. The univariate methods, in this case, takes in account only one or a few variables, causing a loss of information.
Thus, when dealing with complex samples like foodstuff, univariate analysis of spectra data results not enough powerful. Spectra need to be considered in their wholeness and, for analysing them, it must be taken in consideration the whole data matrix: chemometric methods are designed to treat such multivariate data.
Multivariate data analysis is used for a number of distinct, differ-ent purposes and the aims can be divided into three main groups:
• data description (explorative data structure modelling of any ge-neric n-dimensional data matrix, PCA for example);
• regression and prediction (PLS);
• classification and prediction of class belongings for new samples (LDA and PLS-DA and ECVA).
The aim of this PhD thesis was to verify the possibility of identify-ing and classifying plants or foodstuffs, in different classes, based on the concerted variation in metabolite levels, detected by NMR spectra and using the multivariate data analysis as a tool to inter-pret NMR information.
It is important to underline that the results obtained are useful to point out the metabolic consequences of a specific modification on foodstuffs, avoiding the use of a targeted analysis for the different metabolites. The data analysis is performed by applying chemomet-ric multivariate techniques to the NMR dataset of spectra acquired. The research work presented in this thesis is the result of a three years PhD study. This thesis reports the main results obtained from these two main activities:
A1) Evaluation of a data pre-processing system in order to mini-mize unwanted sources of variations, due to different instrumental set up, manual spectra processing and to sample preparations arte-facts;
A2) Application of multivariate chemiometric models in data analy-sis.
50
Picone, Gianfranco <1977>. « NMR, Metabonomics and Molecular Profiles : Applications to the Quality Assessment of Foodstuffs ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1648/.
Texte intégralRésumé :
Nuclear Magnetic Resonance (NMR) is a branch of spectroscopy that is based on the fact that many atomic nuclei may be oriented by a strong magnetic field and will absorb radiofrequency radiation at characteristic frequencies. The parameters that can be measured on the resulting spectral lines (line positions, intensities, line widths, multiplicities and transients in time-dependent experi-ments) can be interpreted in terms of molecular structure, conformation, molecular motion and other rate processes. In this way, high resolution (HR) NMR allows performing qualitative and quantitative analysis of samples in solution, in order to determine the structure of molecules in solution and not only. In the past, high-field NMR spectroscopy has mainly concerned with the elucidation of chemical structure in solution, but today is emerging as a powerful exploratory tool for probing biochemical and physical processes. It represents a versatile tool for the analysis of foods. In literature many NMR studies have been reported on different type of food such as wine, olive oil, coffee, fruit juices, milk, meat, egg, starch granules, flour, etc using different NMR techniques.
Traditionally, univariate analytical methods have been used to ex-plore spectroscopic data. This method is useful to measure or to se-lect a single descriptive variable from the whole spectrum and , at the end, only this variable is analyzed. This univariate methods ap-proach, applied to HR-NMR data, lead to different problems due especially to the complexity of an NMR spectrum. In fact, the lat-ter is composed of different signals belonging to different mole-cules, but it is also true that the same molecules can be represented by different signals, generally strongly correlated. The univariate methods, in this case, takes in account only one or a few variables, causing a loss of information.
Thus, when dealing with complex samples like foodstuff, univariate analysis of spectra data results not enough powerful. Spectra need to be considered in their wholeness and, for analysing them, it must be taken in consideration the whole data matrix: chemometric methods are designed to treat such multivariate data.
Multivariate data analysis is used for a number of distinct, differ-ent purposes and the aims can be divided into three main groups:
• data description (explorative data structure modelling of any ge-neric n-dimensional data matrix, PCA for example);
• regression and prediction (PLS);
• classification and prediction of class belongings for new samples (LDA and PLS-DA and ECVA).
The aim of this PhD thesis was to verify the possibility of identify-ing and classifying plants or foodstuffs, in different classes, based on the concerted variation in metabolite levels, detected by NMR spectra and using the multivariate data analysis as a tool to inter-pret NMR information.
It is important to underline that the results obtained are useful to point out the metabolic consequences of a specific modification on foodstuffs, avoiding the use of a targeted analysis for the different metabolites. The data analysis is performed by applying chemomet-ric multivariate techniques to the NMR dataset of spectra acquired. The research work presented in this thesis is the result of a three years PhD study. This thesis reports the main results obtained from these two main activities:
A1) Evaluation of a data pre-processing system in order to mini-mize unwanted sources of variations, due to different instrumental set up, manual spectra processing and to sample preparations arte-facts;
A2) Application of multivariate chemiometric models in data analy-sis.