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1
Labidi, Olfa. "RELATIONS STRUCTURES-PROPRIETES DANS LE SYSTEME Bi2O3-PbO-V2O5 : SURSTRUCTURES, POLYMORPHISME, INCOMMENSURABILITE et CONDUCTIVITE." Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2006. http://tel.archives-ouvertes.fr/tel-00199221.
Abstract:
Ce travail concerne la recherche de nouveaux matériaux à base de bismuth à propriétés spécifiques plus performantes, ou l'amélioration de propriétés de matériaux connus telles que la conduction ionique pour leur intérêt, en particulier dans le domaine énergétique. Dans le système Bi2O3-PbO-V2O5, notre travail a porté tout d'abord sur le domaine riche en bismuth. La structure du composé PbBi6V2O15 a été déterminée. Le problème de discernement par diffraction X de Bi3+ et de Pb2+ a été abordé par le remplacement du plomb par d'autres cations M2+ tels que Sr2+, Ca2+ et Cd2+. Les déterminations structurales sur monocristaux ont révélé des solutions solides. Partant de la structure connue Pb5Bi18V4O42, le remplacement du Pb par Sr, Ca et Cd a abouti à de nouvelles phases cristallines non stoechiométriques. Il s'agit dans ces différents cas de surstructures dérivées de Bi2O3-δ.L'étude s'est prolongée au sein du binaire BiVO4-nPbO. Une transition de phase α→β a été caractérisée pour le terme n=1, PbBiVO5. Les structures des cristaux «maclés» ont été résolues à l'ambiante et à 530°C. PbBiPO5 subit une transition analogue. PbBiAsO5 cristallise dès l'ambiante dans la forme β.
Pb2BiVO6 (n=2) subit plusieurs transitions structurales α, β et δ. Les structures des formes α et β ont été déterminées sur monocristal ; la résolution de la structure de β a nécessité l'emploi d'un formalisme 4D. Deux nouvelles formes α' et δ' ont été obtenues par substitution du V par Mn ou P. Leurs structures découlent des phases α à l'ambiante, et δ à 680°C. La conductivité électrique des matériaux a été étudiée et des corrélations propriétés de conduction - caractéristiques structurales proposées.
2
Chaghi, Radhouane. "ETUDE DE LA SOLUBILISATION DES PRODUITS ORGANIQUES A FAIBLE MASSE MOLECULAIRE DANS UN SYSTEME MICELLAIRE." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2007. http://tel.archives-ouvertes.fr/tel-00196348.
Abstract:
Le but de ce travail est la compréhension du mécanisme de la solubilisation micellaire de molécules organiques modèle de faible masse moléculaire et d'une solubilité limitée dans l'eau. Les interactions entre ces molécules organiques(Phénol, butanol, heptanol et acide heptanoïque) et les micelles du tensioactif cationique le bromure d'hexadécyltriméthylammonium (CTAB) au voisinage de la concentration micellaire critique et à de faibles concentrations en solutés ont été caractérisées avec différentes techniques expérimentales : La RMN du 1H, la microcalorimétrie de titration, la conductivité spécifique et la spectroscopie UV. La localisation et l'orientation des solutés modèle dans la micelle ont été déterminées.
La solubilisation de ces molécules dans un système micellaire varie selon la composition du mélange. En effet, les interactions tensioactif-soluté, qui sont très faibles et difficiles à détecter, nécessitent pour être étudiées des techniques expérimentales sensibles et précises (RMN 1H et microcalorimétrie de titration).
L'exploitation des résultats obtenus a fourni des indications sur la localisation et l'orientation du Phénol à l'intérieur de la micelle. Ces résultats confirment que le Phénol, pour de faibles molalités, se solubilise principalement dans la couronne micellaire et la couche de palissade. A cause de l'aspect compétitif entre le Phénol, le NaBr et les alcools résulte que à faibles molalités en solutés, le Phénol est contraint à quitter la micelle. Le butanol et l'acide favorisent la solubilisation du Phénol dans le coeur de la micelle.
3
Olivieri, Enzo. "Application de la catalyse pour l'alimentation de systèmes chimiques sans déchet." Electronic Thesis or Diss., Aix-Marseille, 2021. http://theses.univ-amu.fr.lama.univ-amu.fr/211216_OLIVIERI_825ir382ikksw374agndg983uvnl_TH.pdf.
Abstract:
Au cours de cette thèse nous avons pris avantage de la catalyse pour le développement de nouveaux carburants, limitant l’accumulation de déchets lors de l’activation sélective de nouveaux systèmes chimiques. Dans une première partie, nous avons transposé le principe de réactions d’hydrogénations réversibles au domaine des machines moléculaires. Cette approche a permis l’élaboration d’un interrupteur moléculaire de type tolane fonctionnant lors de deux cycles consécutifs de dés/hydrogénation. Celui-ci représente le premier système alimenté par carburant chimique sans aucune production de déchet. Nous avons aussi étendu l’utilisation de l’acide trichloracétique (TCA), pour le développement de nouveaux systèmes d’autoassemblages et notamment d’organogels contrôlés dans le temps. Ainsi à partir d’un dérivé d’aminoacide naturel (O-tert-Butyl-L-tyrosine), nous avons pu mettre au point deux systèmes complémentaires permettant une transition gel-sol-gel ou sol-gel-sol. Nous avons ainsi pu réaliser 11 cycles gel-sol-gel consécutifs, et plus 25 cycles sol-gel-sol consécutifs avant de devoir régénérer le système par une simple évaporation. Cette stratégie a pu être étendue à l’octadécylamine avec laquelle nous avons réalisés 12 cycles gel-sol-gel consécutifs. Il est important de noter que les deux systèmes gel-sol-gel et sol-gel-sol à base de O-tert-Butyl-L-tyrosine, possèdent des propriétés chiroptiques uniques. Finalement, nous nous sommes attelés au développement de systèmes hybrides capables de répondre à deux stimuli différents, l’hydrogène et le TCA. Basés sur des squelettes de type phénanthridines, ils permettent une rotation contrôlée en réponse à ces deux types de stimuliIn this thesis we have taken advantage of catalysis for the development of new fuels, limiting the accumulation of waste during the selective activation of new chemical systems. In a first part, we transposed the principle of reversible hydrogenation reactions to the field of molecular machines. This approach has allowed the development of a tolane-type molecular switch operating during two consecutive de/hydrogenation cycles. This represents the first system powered by chemical fuel without any waste production. We have also extended the use of trichloroacetic acid (TCA), for the development of new self-assembly systems and in particular time-controlled organogels. Thus, starting from a natural amino acid derivative (O-tert-Butyl-L-tyrosine), we were able to develop two complementary systems allowing a gel-sol-gel or sol-gel-sol transition. We were able to perform 11 consecutive gel-sol-gel cycles, and more than 25 consecutive sol-gel-sol cycles before having to regenerate the system by simple evaporation. This strategy could be extended to octadecylamine with which we performed 12 consecutive gel-sol-gel cycles. It is important to note that both gel-sol-gel and sol-gel-sol systems based on O-tert-Butyl-L-tyrosine, have unique chiroptical properties. Finally, we set out to develop hybrid systems capable of responding to two different stimuli, hydrogen and TCA. Based on phenanthridine backbones, they allow a controlled rotation in response to these two types of stimuli
4
Zavoiura, Oleksandr. "Quantum Dot-basierte FRET Systeme zur Templat-vermittelten Detektion von RNA." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19614.
Abstract:
Die Detektion von Nukleinsäuren ist eine der am häufigsten verwendeten Methoden zur Erkennung von viralen und bakteriellen Spezies in biologischen Proben. Oligonukleotid-vermittelte Reaktionen (OVR), die die Zielsequenz als Katalysator der chemischen Reaktion zwischen reaktiven Sonden verwenden, bieten gegenüber den enzymatischen Methoden viele Vorteile, wie z.B. Simplizität und Kosteneffizienz. Normalerweise besitzt das Produkt der OVR deutliche fluoreszierende Eigenschaften, die durch Fluoreszenzspektroskopie gemessen werden können. Die Haupteinschränkung solcher Systeme ist die nur moderate Helligkeit von organischen Farbstoffen, die meistens zur Markierung von reaktiven Sonden genutzt werden. Um dieses Problem zu lösen, sind Fluorophore mit höherer Helligkeit erforderlich.
Die vorliegende Arbeit beschreibt die Entwicklung einer Methode zur Detektion von RNA durch Templat-vermittelten Transfer des Fluorophors auf den Quantum Dot (QD). Das System besteht aus zwei reaktiven Peptide Nucleic Acid (PNA)-basierten Antisense-Sonden. Die Label Akzeptor PNA (LAPNA) Sonde ist auf dem QD immobilisiert und enthält eine Cysteineinheit am N-terminus. Die Label Donor PNA (LDPNA) Sonde trägt eine Cy5-Einheit, die als Thioester gebunden ist. Durch die benachbarte Hybridisierung der Sonden am RNA-Templat nimmt die effektive Molarität der reaktiven Gruppen zu, und führt somit durch das Prinzip von Native Chemical Ligation zum Transfer des Cy5 auf den QD. Dies resultiert in Förster−Resonanzenergietransfer (FRET) zwischen dem QD und den Cy5-Molekülen, der durch die Löschung der Emission des QDs sowie die Verstärkung der Fluoreszenz des Cy5 beobachtet werden kann. Die Verwendung von sehr hellen QDs als FRET-Donor ermöglicht die Umsetzung von Sonden bei geringen Konzentrationen und ermöglicht die Erkennung von RNA mit Nachweisgrenzen im Bereich von weniger pikomolar.Detection of nucleic acids is one of the most reliable methods for the identification of bacterial and viral species in biological samples. Oligonucleotide-templated reactions (OTRs) that exploit an RNA or DNA target to catalyze a chemical reaction hold great promise for the development of enzyme-free and low-cost detection schemes. Commonly, these strategies rely on organic dyes and are designed so that the product of OTR exhibits distinct fluorogenic properties. The main constraint of such schemes is the moderate brightness of organic fluorophores, which limits the read-out when the probes are used at low concentrations. To tackle this obstacle, significantly brighter fluorophores are needed. This work describes the development of an RNA detection scheme that relies on target-templated fluorophore transfer onto a semiconductor quantum dot (QD). The approach uses two reactive peptide nucleic acid (PNA) antisense probes. Label acceptor peptide nucleic acid (LAPNA) probe is immobilized on a QD and bears a cysteine at the N-terminus; label donor peptide nucleic acid (LDPNA) probe is equipped with a Cy5 dye, attached as a thioester. The adjacent annealing of these recognition elements following binding to target RNA triggers the transfer of Cy5 onto a QD in a native chemical ligation manner. This leads to a detectable fluorescence signal brought about by FRET from QD to the Cy5. The use of unprecedentedly bright QDs that can act as FRET donors for several Cy5 functionalities allows application of probes at very low concentrations (pM range) and achieves enhanced sensitivity of target-templated RNA detection. The method enabled RNA detection in the low pM range using a conventional microtiter plate reader.
5
Haefner, Sebastian, Philipp Frank, Martin Elstner, Johannes Nowak, Stefan Odenbach, and Andreas Richter. "Smart hydrogels as storage elements with dispensing functionality in discontinuous microfluidic systems." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-222778.
Abstract:
Smart hydrogels are useful elements in microfluidic systems because they respond to environmental stimuli and are capable of storing reagents. We present here a concept of using hydrogels (poly(N-isopropylacrylamide)) as an interface between continuous and discontinuous microfluidics. Their swelling and shrinking capabilities allow them to act as storage elements for reagents absorbed in the swelling process. When the swollen hydrogel collapses in an oil-filled channel, the incorporated water and molecules are expelled from the hydrogel and form a water reservoir. Water-in-oil droplets can be released from the reservoir generating different sized droplets depending on the flow regime at various oil flow rates (dispensing functionality). Different hydrogel sizes and microfluidic structures are discussed in terms of their storage and droplet formation capabilities. The time behaviour of the hydrogel element is investigated by dynamic swelling experiments and computational fluid dynamics simulations. By precise temperature control, the device acts as an active droplet generator and converts continuous to discontinuous flows.
6
Kahle, Ingolf. "Wirt-Gast-Systeme - optische Eigenschaften von Farbstoffen und Metall-Nanopartikel in mikro- und mesoporösen Alumosilikaten." Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-149319.
Abstract:
Die vorliegende Arbeit beinhaltet die Synthese neuartiger Hybridmaterialien basierend auf der Einlagerung optischer Materialien, wie Farbstoffmoleküle und Metallnanopartikel, in anorganische Wirtsmaterialien mit definierten Porenstrukturen. Hierfür wurden mikro- und mesoporöse alumosilikatische Verbindungen, wie z.B. Zeolithe und Vertreter aus der Familie der sogenannten „Mobile Composition of Matter“ (MCM), verwendet. Mit Hilfe dieses Konzeptes konnte z.B. der Einfluss der Wirtsmaterialien hinsichtlich ihrer Porengrößen und inneren Polarität auf die optischen Eigenschaften von photochromen Naphthopyranfarbstoffen untersucht werden. Neue photochrome Kompositmaterialien, welche sich durch einfache industrielle Prozesse, wie z.B. der Extrusion in eine Polymermatrix, weiterverarbeiten lassen, wurden auf diesem Wege synthetisiert. Durch die Einkapselung eines solvatochromen Spiropyranderivats innerhalb der Superkäfige von Faujasiten konnten Rückschlüsse auf die Polaritätsparameter der äußeren und inneren Oberfläche der Molekularsiebe gewonnen werden.
Zudem wurde ein neues Synthesekonzept zur Herstellung fluoreszierender Silbernanopartikel innerhalb eines Zeolith Y entwickelt, um auf sehr einfachem Weg ein stabiles Material mit interessanten Fluoreszenzeigenschaften zu erhalten. Der Einfluss der Wirtsoberfläche auf fluoreszierende Farbstoffe wurde des Weiteren an Benzylidenketonfarbstoffen untersucht, die mittels „Ship in a Bottle reaction“ in Zeolith Y eingekapselt wurden. Um das Konzept zur Synthese optischer Effektpigmente zu erweitern, wurden neue photochrome Naphthopyrane, welche in Konjugation zu fluoreszierenden Farbstoffen stehen, synthetisiert und untersucht.
7
Haefner, Sebastian, Philipp Frank, Martin Elstner, Johannes Nowak, Stefan Odenbach, and Andreas Richter. "Smart hydrogels as storage elements with dispensing functionality in discontinuous microfluidic systems." Royal Society of Chemistry, 2016. https://tud.qucosa.de/id/qucosa%3A30257.
Abstract:
Smart hydrogels are useful elements in microfluidic systems because they respond to environmental stimuli and are capable of storing reagents. We present here a concept of using hydrogels (poly(N-isopropylacrylamide)) as an interface between continuous and discontinuous microfluidics. Their swelling and shrinking capabilities allow them to act as storage elements for reagents absorbed in the swelling process. When the swollen hydrogel collapses in an oil-filled channel, the incorporated water and molecules are expelled from the hydrogel and form a water reservoir. Water-in-oil droplets can be released from the reservoir generating different sized droplets depending on the flow regime at various oil flow rates (dispensing functionality). Different hydrogel sizes and microfluidic structures are discussed in terms of their storage and droplet formation capabilities. The time behaviour of the hydrogel element is investigated by dynamic swelling experiments and computational fluid dynamics simulations. By precise temperature control, the device acts as an active droplet generator and converts continuous to discontinuous flows.
8
Duchesne, Claire. "Etude des proprietes optiques non lineaires dans les verres. Cas du systeme NA2O-TIO2-P2O5." Phd thesis, Université Sciences et Technologies - Bordeaux I, 1993. http://tel.archives-ouvertes.fr/tel-00136123.
Abstract:
L' acces aux proprietes optiques non lineaires de materiaux tels que les verres mineraux ouvre de nouvelles perspectives dans le domaine du transport de l' information par fibre optique, voire dans celui de la commutation optique fonctionnant avec des temps de reponse tres brefs (domaine de la subpicoseconde). Concretement, leur potentialite peut etre estimee par une figure de merite F, expression d' un compromis qui doit etre trouve entre la necessite d' accroitre la vitesse et l' amplitude de changement d' indice de refraction et l' obligation d' attenuer la variation thermique de l' indice due a l' echauffement du materiau que provoque l' intensite du faisceau lumineux. Une analyse des criteres de choix des materiaux nous a conduit a centrer cette premiere etude sur des verres du systeme Na2O-TiO2-P2O5. Les resultats peuvent s' analyser en terme de reconnaissance des entites structurales se formant dans les verres et de performances obtenues sur le plan des non linearites optiques: l' analyse structurale des verres effectuee essentiellement par spectroscopie d' absorption des rayons X a conduit a l' identification des entites hyperpolarisables a l' origine des proprietes non lineaires, a savoir les groupements TiO5; les valeurs des indices non lineaires se situent un peu au-dessous de celles des verres contenant des ions lourds. En revanche, l' absence de tels constituants a permis d' accroitre considerablement les facteurs de merite. De ce point de vue, ces phosphates se placent sans doute en tete par rapport a tous les resultats publies a ce jour. Enfin, la pertinence des valeurs experimentales des indices lineaires et non lineaires a pu etre mise en evidence par une tentative de modelisation. Cette approche repose sur le modele de M. E. Lines qui a decrit la reponse electronique d' un cristal sous l' effet d' une perturbation electromagnetique en terme de processus interionique par une analyse de la liaison anion-cation.
9
Sato, Hiroki. "Chemistry /." Online version of thesis, 2008. http://hdl.handle.net/1850/7747.
10
Kristen, Juliane Ute. "Amphiphilic BAB-triblock copolymers bearing fluorocarbon groups : synthesis and self-organization in aqueous media." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2012/6178/.
Abstract:
In this work new fluorinated and non-fluorinated mono- and bifunctional trithiocarbonates of the structure Z-C(=S)-S-R and Z-C(=S)-S-R-S-C(=S)-Z were synthesized for the use as chain transfer agents (CTAs) in the RAFT-process. All newly synthesized CTAs were tested for their efficiency to moderate the free radical polymerization process by polymerizing styrene (M3). Besides characterization of the homopolymers by GPC measurements, end- group analysis of the synthesized block copolymers via 1H-, 19F-NMR, and in some cases also UV-vis spectroscopy, were performed attaching suitable fluorinated moieties to the Z- and/or R-groups of the CTAs.
Symmetric triblock copolymers of type BAB and non-symmetric fluorine end- capped polymers were accessible using the RAFT process in just two or one polymerization step. In particular, the RAFT-process enabled the controlled polymerization of hydrophilic monomers such as N-isopropylacrylamide (NIPAM) (M1) as well as N-acryloylpyrrolidine (NAP) (M2) for the A-blocks and of the hydrophobic monomers styrene (M3), 2-fluorostyrene (M4), 3-fluorostyrene (M5), 4-fluorostyrene (M6) and 2,3,4,5,6-pentafluorostyrene (M7) for the B-blocks.
The properties of the BAB-triblock copolymers were investigated in dilute, concentrated and highly concentrated aqueous solutions using DLS, turbidimetry, 1H- and 19F-NMR, rheology, determination of the CMC, foam height- and surface tension measurements and microscopy. Furthermore, their ability to stabilize emulsions and microemulsions and the wetting behaviour of their aqueous solutions on different substrates was investigated. The behaviour of the fluorine end-functionalized polymers to form micelles was studied applying DLS measurements in diluted organic solution.
All investigated BAB-triblock copolymers were able to form micelles and show surface activity at room temperature in dilute aqueous solution. The aqueous solutions displayed moderate foam formation. With different types and concentrations of oils, the formation of emulsions could be detected using a light microscope. A boosting effect in microemulsions could not be found adding BAB-triblock copolymers. At elevated polymer concentrations, the formation of hydrogels was proved applying rheology measurements.Im Rahmen dieser Arbeit wurden neue fluorierte und unfluorierte mono- und bifunktionelle Trithiocarbonate der Typen Z-C(=S)-S-R und Z-C(=S)-S-R-S-C(=S)-Z zur Anwendung als CTAs (chain- transfer agents) im RAFT-Polymerisationsverfahren hergestellt. Alle CTAs wurden erfolgreich auf ihre Effizienz zur Steuerung des radikalischen Polymerisationsverfahrens hin durch Polymerisation von Styrol (M3) getestet. Neben GPC-Messungen wurden Endgruppenanalysen der synthetisierten Blockcopolymere mittels 1H-, 19F-NMR und in manchen Fällen auch UV-Vis Spektroskopie durchgeführt. Dazu wurden die Z- und/oder R-Gruppen der CTAs mit geeigneten fluorierten Gruppen versehen. Durch Anwendung des RAFT Verfahrens konnten symmetrische Triblockcopolymere vom Typ BAB bzw. mit einer Fluoralkylgruppe endgecappte unsymmetrische Polymere in nur zwei bzw. einem Polymerisationsschritt hergestellt werden. Das RAFT- Polymerisationsverfahren ermöglicht sowohl die Polymerisation hydrophiler Monomere wie N-Isopropylacrylamid (NIPAM) (M1) oder N-Acryloylpyrrolidin (NAP) (M2) für die A-Blöcke als auch der hydropoben Monomere Styrol (M3), 2-Fluorostyrol (M4), 3-Fluorostyrol (M5), 4- Fluorostyrol (M6) und 2,3,4,5,6- Pentafluorostyrol (M7) für die B-Blöcke. Die Eigenschaften der Blockcopolymere in verdünnten, konzentrierten und hochkonzentrierten wässrigen Lösungen wurden mittels DLS, Trübungsphotometrie, 1H- und 19F-NMR, Rheologie, CMC- sowie Schaumhöhen- und Oberflächenspannungsmessungen und Lichtmikroskopie untersucht. Weiterhin wurden ihre Eigenschaften als Emulgatoren und in Mikroemulsion untersucht. Das Micellbildungsverhalten der hydrophob endfunktionalisierten Polymere wurde mittels DLS Messungen in verdünnter organischer Lösung untersucht. Alle untersuchten BAB-Triblöcke bildeten Micellen und zeigten Oberflächenaktivität bei Raumtemperatur in verdünnter, wässriger Lösung. Weiterhin zeigen die wässrigen Lösungen der Polymere mäßige Schaumbildung. Mit verschiedenen Öltypen und Ölkonzentrationen wurden Emulsionen bzw. Mikroemulsionen gebildet. In Mikroemulsion wurde durch Zugabe von BAB-Triblockopolymeren kein Boosting-Effekt erzielt werden. Bei Untersuchung höherer Polymerkonzentrationen wurde die Bildung von Hydrogelen mittels rheologischer Messungen nachgewiesen. Verschiedene Substrate konnten benetzt werden. Die hydrophob endgecappten Polymere bilden in verdünnter organischer Lösung Micellen, die mittels DLS untersucht wurden, und zeigen somit Tensidverhalten in nichtwässriger Lösung.
11
Beyvers, Stephanie. "Selective excitation of adsorbate vibrations on dissipative surfaces." Phd thesis, Universität Potsdam, 2008. http://opus.kobv.de/ubp/volltexte/2008/2551/.
Abstract:
The selective infrared (IR) excitation of molecular vibrations is a powerful tool to control the photoreactivity prior to electronic excitation in the ultraviolet / visible (UV/Vis) light regime ("vibrationally mediated chemistry").
For adsorbates on surfaces it has been theoretically predicted that IR preexcitation will lead to higher UV/Vis photodesorption yields
and larger cross sections for other photoreactions.
In a recent experiment, IR-mediated desorption of molecular hydrogen from a Si(111) surface on which atomic hydrogen and deuterium were co-adsorbed was achieved, following a vibrational mechanism as indicated by the isotope-selectivity.
In the present work, selective vibrational IR excitation of adsorbate molecules, treated as multi-dimensional oscillators on dissipative surfaces,
has been simulated within the framework of open-system density matrix theory.
Not only potential-mediated, inter-mode coupling poses an obstacle to selective excitation but also the coupling of the adsorbate ("system") modes
to the electronic and phononic degrees of freedom of the surface ("bath") does.
Vibrational relaxation thereby takes place, depending on the availabilty of energetically fitting electron-hole (e/h) pairs and/or phonons (lattice vibrations) in the surface, on time-scales ranging from milliseconds to several hundreds of femtoseconds. On metal surfaces, where the relaxation process of the adsorbate via the e/h pair mechanism dominates, vibrational lifetimes are usually shorter than on insulator or semiconductor surfaces, in the range of picoseconds, being also the timescale of the IR pulses used here.
Further inhibiting factors for selectivity can be the harmonicity of a mode and weak dipole activities ("dark modes") rendering vibrational excitation with moderate field intensities difficult.
In addition to simple analytical pulses, optimal control theory (OCT) has been employed here to generate a suitable electric field to populate the target state/mode maximally.
The complex OCT fields were analyzed by Husimi transformation, resolving the control field in time and energy.
The adsorbate/surface systems investigated were CO/Cu(100), H/Si(100) and 2H/Ru(0001). These systems proved to be suitable models to study the above mentioned effects.
Further, effects of temperature, pure dephasing (elastic scattering processes), pulse duration and dimensionality (up to four degrees of freedom)
were studied. It was possible to selectively excite single vibrational modes, often even state-selective.
Special processes like hot-band excitation, vibrationally mediated desorption and the excitation of "dark modes" were simulated.
Finally, a novel OCT algorithm in density matrix representation has been developed which allows for time-dependent target operators
and thus enables to control the excitation mechanism instead of only the final state.
The algorithm is based on a combination of global (iterative) and local (non-iterative) OCT schemes, such that short, globally controlled time-intervals are coupled locally in time.
Its numerical performance and accuracy were tested and verified and it was successfully applied to stabilize a two-state linear-combination and to enforce a successive "ladder climbing" in a rather harmonic system, where monochromatic, analytical pulses simultaneously excited several states, leading to a population loss in the target state.Die selektive Anregung von Molekülschwingungen mittels Infrarotlicht (IR) ist vorteilhaft, um die Wirkungsquerschnitte nachfolgender photochemischer oder photophysikalischer Prozesse zu steigern, welche durch Elektronenanregung mittels ultraviolettem (UV) bzw. sichtbarem (Vis) Licht ausgelöst werden. Für Adsorbatmoleküle auf Oberflächen wurden theoretische Vorhersagen getroffen, dass eine kombinierte (IR plus UV)-Strategie ("schwingungsvermittelte Chemie") die Ausbeute bei Photodesorption und anderen Photoreaktionen deutlich zu erhöhen vermag. Kürzlich wurde im Experiment gezeigt, dass eine rein IR-vermittelte Desorption möglich ist, welche über einen schwingungsangeregten Mechanismus erfolgt. Hierbei wurde molekularer Wasserstoff von einer Si(111)-Oberfläche desorbiert, an der atomarer Wasserstoff und atomares Deuterium gebunden waren. Eine thermische Anregung, die zum Bindungsbruch führt, konnte hierbei wegen der Isotopenselektivität ausgeschlossen werden. In der vorliegenden Arbeit wurde die selektive IR-Schwingungsanregung von Adsorbaten, die als multidimensionale Oszillatoren auf dissipativen Oberflächen behandelt wurden, mit Hilfe der Dichtematrixtheorie für offene Systeme simuliert. Nicht nur die potentialvermittelte Kopplung zwischen den einzelnen Moden ist ein Hindernis für selektive Anregung, sondern auch die Kopplung der Moden des Adsorbats ("Systems") an elektronische und phononische Freiheitsgrade des Substrats ("Bades"). Die Schwingungsrelaxation verläuft hierbei auf Zeitskalen, die von Millisekunden bis hin zu wenigen hundert Femtosekunden reichen, je nach Verfügbarkeit energetisch geeigneter Elektron-Loch-Paar-Anregungen bzw. Phononen (Gitterschwingungen) in der Oberfläche. Auf Metalloberflächen, bei denen die Schwingungrelaxation des Adsorbats zumeist von einem Elektronen-Loch-Paar-Mechanismus dominiert wird, sind die Schwingungslebensdauern normalerweise kürzer als auf Isolator- oder Halbleiteroberflächen und betragen einige Picosekunden, ebenso wie die Zeitskala der hier gewählten IR-Pulse. Weitere Faktoren, die die selektive Anregung behindern können sind die Harmonizität einer Mode und die geringe Dipolaktivität sogenannter "dunkler Moden", die eine Anregung mit moderat intensiven Feldern erschweren. Zusätzlich zu einfachen analytischen Pulsen wurden Felder mittels Optimaler Kontrolltheorie (OCT) erzeugt, um eine(n) Zielzustand/-mode maximal zu populieren. Komplexe OCT Pulse wurden mit Hilfe der Husimi-Transformation analysiert, welche das Kontrollfeld im Zeit- und Energieraum aufzulösen vermag. Die in dieser Arbeit untersuchten Adsorbat/Oberflächen-Systeme waren CO/Cu(100), H/Si(100) und 2H/Ru(0001), die sich als passende Modelle erwiesen, um oben genannte Faktoren zu untersuchen. Desweiteren wurden die Auswirkungen von Temperatur, reiner Dephasierung (elastische Streuprozesse), Dauer des IR-Pulses und Systemdimensionalit"at (Behandlung von bis zu vier Freiheitsgraden) studiert. Einzelne Schwingungsmoden konnten angeregt werden, in vielen Fällen sogar zustandsselektiv. Spezielle Prozesse wie die Anregung "heißer Banden", Desorption via alleiniger Schwingungsanregung und die Anregung "dunkler Moden" wurden simuliert. Schließlich wurde ein neuer OCT-Algorithmus in Dichtematrixdarstellung entwickelt, der es erlaubt, zeitabhängige Zieloperatoren einzuführen, um nicht nur Kontrolle über den Endzustand einer Anregung, sondern auch über den Anregungsmechanismus zu erlangen. Der Algorithmus basiert auf einer Kombination von globaler (iterativer) und lokaler (nicht-iterativer) optimaler Kontrollschemata in der Art, dass kurze, global kontrollierte Intervalle zeitlich lokal miteinander gekoppelt werden. Nach numerischen Tests wurde der Algorithmus erfolgreich angewandt, um eine Linearkombination aus zwei Zuständen zu stabilisieren, sowie um eine schrittweise "Leiteranregung" in einem harmonischen System zu forcieren, bei dem monochromatische, analytische Pulse mehrere Zustände zugleich anregen und somit einen Populationsverlust im angestrebten Zielzustand zur Folge haben.
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Rudberg, Elias. "Quantum Chemistry for Large Systems." Doctoral thesis, Stockholm : Bioteknologi, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4561.
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Pappas, Charalampos. "Supramolecular systems chemistry using peptides." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=26621.
Abstract:
Living systems possess overwhelming molecular complexity that largely results from combinations of just twenty amino acids that are found across all life forms (the building blocks of life). Complexity of proteins arises from combinations of hundreds amino acid building blocks, where self-assembly dictates structure and functionality. Apart from their vital role on building living processes, short peptide sequences (minimalistic version of more complex biological machinery, consisted of 2-6 amino acids), appear to be ideal structural candidates for the fabrication of soft nanomaterials, with potential applications in food, cosmetics and nanomedicine. Supramolecular systems can be classified into three distinct types of self-assembly, based on the way that precursors and self-assembling building blocks relate in the free energy diagram. Thermodynamically driven supramolecular systems, resulting in the formation of permanent supramolecular assemblies, where the self-assembly pathway and the final supramolecular state is irrelevant. The self-assembly pathway becomes a crucial factor for kinetically controlled supramolecular systems, with the structures formed, representing local minima in the free energy landscapes. Finally, away-from-equilibrium chemical systems, systems that transiently exist only under the influence of constant chemical energy (fuel) and when the energy runs out, the system relaxes back to the initial unassembled state. In the first part of the thesis, we demonstrate the use of mechanical energy (high oscillating pressure waves-ultrasonic frequencies of 80.000 Hz) to trigger anisotropy and the formation of highly ordered supramolecular architectures. This is achieved by using tripeptide sequences with D-stereoisomer in the N-terminus of the sequence, where the use of ultrasound gives rise to the formation of gels with enhanced supramolecular properties, as evidenced using spectroscopic (FT-IR, CD, LD) and microscopic techniques (TEM, SEM). Subsequently, ultrasound was used to transiently affect supramolecular systems. In this case, the mechanical energy was used to trigger temporary supramolecular reconfiguration of aromatic dipeptide amphiphiles. The supramolecular transitions observed were due to an alter balance of hydrophobic and H-bonding type interactions that drive the assembly of aromatic peptide amphiphiles. Notably, a direct comparison between thermal heating and mechanical energy is also demonstrated, which relates the directional and oscillating characteristics of ultrasound, when it is used to locally deliver heat into a system. Responsiveness, functionality and adaptability are further demonstrated using different stimuli. Biocatalytic self-assembly has been utilised to direct supramolecular systems. Thermodynamically driven biocatalytic self-assembly is used to achieve morphological control (fibres, sheets and tubes) on aromatic dipeptide amphiphiles, via minimal stereo-electronic substitution on the para position of the phenylalaline amino acid residue. The control of the resultant supramolecular nanostructures and properties arises from the relative importance of stacking interactions among the aromatics and H-bonding between the dipeptide backbones. The concept of thermodynamically driven biocatalytic self-assembly is further utilised to direct the formation of Dynamic Peptide Libraries (DPLs). The amino acids within a dipeptide sequence are exchanged dynamically using in situ catalytic synthesis and hydrolysis of amide bonds, where the free energy involved in selfassembly of the nanostructure provides the driving force for its formation. The use of searchable dynamic peptide libraries gives rise to the ability to explore the structural sequences space of short peptides. Selective catalytic amplification is achieved through an interplay with environmental triggers. Differential formation of peptide subunits (library members), accompanied with structural reconfiguration is favored in the presence of different environment, such as solvents and salts. Additionally, a direct comparison between biocatalytically driven formation of different molecular species and chemically synthesized assemblies is used to show that shape control may be achieved. Biocatalytic self-assembly is also used to trigger the formation of non-equilibrium transient supramolecular systems. In this case, structural adaption is achieved based on biocatalytic formation and hydrolysis of self-assembling tripeptides, which catalyzed by chymotrypsin, starting from a simple dipeptide methyl ester, the wellknown sweetener, aspartame. The chemical design dictates the kinetics and the consequent lifetime of the nanostructures formed, which can be refueled several times by the addition of the fuel (aspartame), where the fibres are continuously forming and shortening, indicating a dynamically unstable system. This thesis ends with a small chapter, where we demonstrate the use of audible sound frequencies (<1000 Hz) to direct supramolecular reorganization on an aromatic dipeptide amphiphile. We sought to achieve the formation of larger aggregates as a result of aqueous vibrations, using a variety of spectroscopic (FT-IR, fluorescence, DLS, DOSY NMR) and microscopic techniques (AFM, TEM), investigating the effect of pressure waves on molecular self-assembly.
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Shah, Faiz Ullah. "Designed boron chemistry for tribological systems." Doctoral thesis, Luleå tekniska universitet, Industriell miljö- och processteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26383.
Abstract:
Boron compounds can be environmentally friendly alternatives for commercially available lubricant additives. Some boron compounds are already used as friction modifiers, corrosion inhibitors, antioxidants and antiwear additives in lubricants. The focus of the present work is on the development and tribological investigations of new boron compounds for these applications. In this work, boron compounds based on dithiophosphates (DTPs), dithiocarbamates (DTCs) and ionic liquids (ILs) were designed, synthesized and tribologically optimized. The work was carried out in the following steps: (1) Synthesis of novel boron based compounds and ionic liquids; (2) Characterization of the compounds with FTIR, liquid-state (1H, 13C, 31P, 11B) and solid-state magic-angle-spinning (MAS) NMR spectroscopy, electrospray ionization mass spectrometery (ESI-MS), elemental analysis, thermal analyses (TG/DTG, DTA, DSC and QMS), viscosity, density and conductivity; (3) Tribological evaluation using four ball and pin-on-disc tribometers; (4) Surface analysis using an optical profiler and Scanning Electron Microscopy coupled with X-ray Energy Dispersive Spectroscopy (SEM/EDS). (i) Antiwear performance of S-di-n-octoxyboron-O,O’-di-n-octyldithiophosphate (DOB-DTP) was found considerably better in comparison with O,O’-di-n-butyl-dithiophosphato-zinc(II) (ZnDTP). However, since DOB-DTP contains B─S bond, which is sensitive to moisture and may be hydrolyzed by water, a novel class of alkylborate-ethyl-dithiophosphates was synthesized, in which boron is covalently bonded to the dialkyldithiophosphate group through the ethyl linker in order to avoid hydrolysis. (ii) Antiwear performance of an alkylborate-ethyl-dithiophosphate with decyl substitutes at both DTP and the borate groups of the molecule (DDB-EDTP) was superior compared with that of the octyl (DOB-EDTP) and the pentyl (DDB-EDTP) analogues. Residues of one representative compound from this class, DPB-EDTP, after thermal analyses were characterized by multinuclear 13C, 31P and 11B MAS and 31P CP/MAS NMR spectroscopy. Solid-state NMR data suggest that a dominant part of the solid residue of DPB-EDTP consists of borophosphates. (iii) It was found that a novel class of compounds containing alkylborate and dithiocarbamate groups with alkyl or methylbenzyl- substitutes in one molecule provide better antiwear performance compared with commercially available packages of ZnDTPs. (iv) Eight compounds belonging to a novel class of halogen-free chelated orthoborate ionic liquids (hf-BILs) with different phosphonium cations were synthesized. Important physical properties of the ILs including glass transition temperatures, density, viscosity and ionic conductivity were measured. As lubricants, these hf-BILs exhibit considerably better antiwear and friction reducing properties under boundary lubrication conditions for steel-aluminum contacts as compared with fully formulated (15W-50 grade) engine oil. (v) Five compounds belonging to another class of hf-BILs comprised of two chelated orthoborate anions, bis(mandelato)borate and bis(salicylato)borate, and three different nitrile cations (cholinium, pyrrolidinium and imidazolium) were prepared. Solid-state NMR spectroscopy was employed to probe interactions between cations and anions in the salts, which are solid at room temperature. Solid-state NMR data suggested a strong interaction between BScB anions and cholinium cations [Chol]+. This interaction was further confirmed by the X-ray diffraction single crystal structure of this salt as hydrogen bonding between OH of [Chol]+ and the carbonyl group of [BScB]-. The [BScB]- exhibited a strong interaction with imidazolium cation [EMIm]+, whereas a weaker interaction was suggested between pyrrolidinium cation [EMPy]+ and [BScB]-. It was found that the novel boron based DTPs and DTCs have considerably better antiwear performance and higher stability of the coefficient of friction with time as compared with ZnDTP. They also have a high thermal stability, good miscibility with oils and positive environmental issues all that make them an attractive alternative to ZnDTPs and other commercial additives to lubricants. It was found that novel halogen-free boron based ionic liquids may be also potentially used as alternative lubricants for ferrous and non-ferrous contact.Godkänd; 2011; 20110512 (faisha); DISPUTATION Ämnesområde: Gränsytors kemi/Chemistry of Interfaces Opponent: Professor Jean Michel Martin, Ecole Centrale de Lyon, Frankrike Ordförande: Professor Oleg N. Antzutkin, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Onsdag den 15 juni 2011, kl 10.00 Plats: C305, Luleå tekniska universitet
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Bond, Jade. "The Chemistry of Extrasolar Planetary Systems." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/194946.
Abstract:
This work examines the chemical nature of extrasolar planetary systems, considering both the host star and any potential terrestrial planets located within the system. Extrasolar planetary host stars are found to be enriched over non-host stars in several r- and s-process elements. These enrichments, however, are in keeping with general galactic chemical evolution trends. This implies that host stars have not experienced any unusual chemical processing or pollution and that the observed enrichments are primordial in nature.When combined with detailed chemical models, the dynamical models of O'Brien et al. (2006) are found to produce terrestrial planets with bulk elemental abundances in excellent agreement with observed planetary values. This clearly indicates that the combination of dynamical and chemical modeling applied here is successfully reproducing the terrestrial planets of the Solar System to the first order. Furthermore, these planets are found to form with a considerable amount of water, negating the need for large amounts of exogenous delivery. Little dependence on the orbital properties of Jupiter and Saturn is observed for the main rock-forming elements due to the largely homogenous disk composition calculated.The same modeling approach is applied to known extrasolar planetary systems. Terrestrial planets were found to be ubiquitous, forming in all simulations. Generally, small (< 1ML) terrestrial planets are produced close to their host star with little radial mixing occurring. Planetary compositions are found to be diverse, ranging from Earth-like to refractory dominated and C-dominated, containing significant amounts of carbide material. Based on these simulations, stars with Solar elemental ratios are the best place to focus future Earth-like planet searches as these systems are found to produce the most Earthlike terrestrial planets which are located within the habitable zones of their systems and containing a significant amount of water. C-rich planets, although unusual, are expected to exist in >20% of known extrasolar planetary systems based on their host star photospheric compositions. These planets are unlike any body we have previously observed and provide an exciting avenue for future observation and simulation.
16
Nguyen, Minh-Chau. "Chemistry of individual nanoparticles : 3D tracking by holographic microscopy and dynamic spectroscopy." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7196.
Abstract:
Dans ce travail, nous avons développé un système de spectroscopie dynamique utilisant l'holographie afin de surmonter cette difficulté. Notre stratégie est de localiser la nanoparticule en 3D et en temps réel grâce à l’holographie, et d’utiliser la position mesurée afin d’asservir le mouvement de la zone de collection du spectromètre. Notre système est donc constitué de deux parties principales: un microscope holographique pour le suivi 3D de la nanoparticule et un système optique adaptatif pour le déplacement de la zone de mesure spectroscopique. Après validation, ce système a été appliqué à l’étude du changement spectral de nanoparticules soumises à un échange galvanique. Dans cette réaction, un métal (Ag) est réduit et dissous pour être remplacé par un métal plus noble (Au) présent en solution sous forme ionique. Pour appréhender ce type de réaction la solution d’ions Au3+ est produite par voie électrochimique. Ceci permet le contrôle du déclenchement de la modification profonde de la particule qui s’accompagne d’une modification de son spectre de diffusion, et nous a permis de suivre la cinétique de la réaction. Par ailleurs, le suivi holographique de la trajectoire permet une mesure du rayon hydrodynamique de la particule, donc de l’évolution de son volume. Ces mesures indépendantes fournissent un tableau complet et cohérent du déroulement de la réactionIn this work, we developed a holography-based dynamic spectroscopy system in order to localize the nanoparticle in 3D and in real time, and use this position to move the spectroscopic measurement zone. Therefore, it consists of two main parts: an off-axis holographic microscope for 3D nanoparticle localization, and (ii) an adaptive optical system to position the spectral collection zone in 3D. Using this system, we monitored nanoparticles undergoing a galvanic exchange, i.e. a redox reaction in which a metal (Ag) is reduced and dissolved, to be replaced by a more noble metal (Au) present in ionic form in the solution. This change in the particle composition is here triggered by an electrochemical generation of the Au3+ ions solution. It induces a dynamic spectral shift which provides a first insight into the kinetics of the reaction. In addition, 3D particle tracking provides a measurement of the hydrodynamic radius of the particle, which affects Brownian motion. Together, these independent measurements give a relatively complete and coherent picture of the transformation undergone by these nanoparticles
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Van, Veelen Arjen. "Uranium coordination chemistry in Mg-rich systems." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/uranium-coordination-chemistry-in-mgrich-systems(707b1576-699c-4f0a-b945-7482cfb7f51f).html.
Abstract:
In the UK, large quantities of intermediate level waste pose complex radiological remediation challenges. Chemical understanding of uranium in these Mg-rich sludges is vital. Previous studies have examined uranium uptake by calcium carbonate minerals (calcite and aragonite) under conditions pertinent to both natural and anthropogenically perturbed systems. However, research on uranyl uptake by magnesium-rich minerals such as magnesite [MgCO3], brucite [Mg(OH)2], nesquehonite [MgCO3·3H2O] and hydromagnesite-[Mg5(CO3)4(OH)2·4H2O] has not, to the best of our knowledge, been previously conducted. Such experiments will improve our understanding of the mobility of uranium and other actinides in natural lithologies such as dolomitic limestones or mafic igneous emplacements, as well as provide key information applicable to nuclear waste repository strategies involving Mg-rich phases. By two EXAFS techniques, we determined: (1) where uranyl (UO22+) is adsorbed, and (2) how uranyl is attached to the mineral surface. Therefore powder experiments of U(VI) were performed with magnesite, brucite, nesquehonite and hydromagnesite. The second experiment (GIXAFS) consisted of single crystals of magnesite (10.4) and brucite (0001). The powders were reacted in solution pH ~8.5 with U(VI)nitrate for 48 hrs. under ambient PCO2 = -3.5. The single crystals were reacted under ambient and reduced PCO2 ~ -4.5 for 48 hrs. with concentrations of U(VI)chlroride above (500; 50 ppm) and below (5 ppm) solubility of schoepite [UO2(OH)2·H2O]. The GIXAFS measurements were made at χ = 0˚ and χ = 90˚ relative to the synchrotron beam polarisation to uequivocally determine the adsorbate structures. Kd values for Mg-carbonate phases were comparable to or exceeded those published for calcium carbonates. GIXAFS results clearly showed polarisation for both ambient and reduced PCO2. XANES results showed uranyl is oriented with the axial oxygens perpendicular to the mineral surface. This implies, using also X-ray reflectivity and diffuse scatter, local hydrated bayleyite [Mg2(UO2)(CO3)3∙18H2O] and possible rutherfordine-like [UO2CO3] regions, which will be useful to predict uranium behaviour in various remediation processes.
18
Shimizu, Kyoko. "The interfacial chemistry of isocyanate/metal systems." Thesis, University of Surrey, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.549654.
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Lukkari, Ingrid. "Flow injection systems for process analytical chemistry." Doctoral thesis, Umeå universitet, Kemiska institutionen, 1995. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-114755.
Abstract:
Flow injection systems have great potential for sample handling and analysis in process analytical chemistry. The flexibility and versatility of flow injection manifolds can he utilized in specific applications of sample conditioning and analysis. An overview of various flow injection methods, including flow reversals, double injection, and sequential injection is given, as well as different clean-up methods, such as gas diffusion, solid phase extraction, dialysis, and solvent extraction. Calibration techniques, such as single standard and multivariate calibration are also discussed. In addition, different aspects of process analytical chemistry, in particular sampling and sample handling, are discussed. The papers in this thesis describe a number of flow systems, where gradient-, gas diffusion-, and solid phase extraction- methodologies are applied, all of which have potential use in process analytical chemistry. Paper I is focused on multicomponent analysis of mixtures of organic acids by mathematically extracting information from complex spectra. The selectivity is improved by generating pH-gradients in the flow system. In paper II, the methodology of sensor injection is described and electrochemical and spectroscopic sensors are implemented in a sequential injection system. The method is illustrated by using pH sensors and a glucose electrode. Ammonia and ammonium ions are determined on-line to a bioprocess by gas diffusion in paper III. The benefit of frequent re-calibrations and in-line cleaning sequences are demonstrated. Finally a method for on-line determination of o-diphenols in the kraft process has been developed (paper IV). The o-diphenols are isolated from black liquor samples by solid phase extraction and thereafter transferred to a high performance liquid chromatography system for separation and quantification.Diss. (sammanfattning) Umeå : Umeå universitet, 1996, Härtill 4 uppsatser
digitalisering@umu
20
Duran-Frigola, Miquel 1985. "Blending biology and chemistry to enable systems pharmacology." Doctoral thesis, Universitat Pompeu Fabra, 2016. http://hdl.handle.net/10803/459111.
Abstract:
The avalanche of data that followed the sequencing of the human genome has revealed an overwhelming biological complexity. No simple molecular explanation exists for most of the diseases and, in consequence, simple therapies have low probability of success. The emerging field of systems pharmacology seeks drugs of broad impact on molecular networks. To achieve so, it is necessary to integrate heterogeneous data, at different levels of complexity, and find correlations between them. This translational exercise is, perhaps, the major concern of current biomedical research.
In this Thesis we undertake part of this challenge through cases that orbit the drug discovery endeavor. Using computational methods in various areas of bioinformatics and chemoinformatics, we link chemical, biomolecular and phenotypic data to provide a more holistic view of pharmacology.L’allau de dades que ha seguit la seqüenciació del genoma humà està revelant una increïble complexitat biològica. No existeix una explicació simple per a la majoria de les malalties i, en conseqüència, les teràpies simples tenen baixes probabilitats d’èxit. L’emergent camp de la farmacologia de sistemes busca medicaments d’ampli impacte en les xarxes moleculars. Per a aconseguir-ho, és necessària la integració de dades heterogènies, a diferents nivells de complexitat, i la capacitat de trobar correlacions entre elles. Aquest exercici translacional és, probablement, la major preocupació de la recerca biomèdica d’avui. En aquesta Tesi assumim part d’aquest repte a través de casos que orbiten el descobriment de fàrmacs. Mitjançant mètodes computacionals en àrees diverses de la bioinformàtica i la quimioinformàtica, connectem dades químiques, biomoleculars i fenotípiques per a facilitar una visió més holística de la farmacologia.
21
Bell, Douglas Hindmarsh. "Physical chemistry of liquid salt systems involving uranium." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/8248.
22
Roe, Gerard. "Surface and catalytic chemistry of Ni/Sm systems." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282064.
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Briscoe, Mark William. "Electrochemical reduction of fluorinated systems and derived chemistry." Thesis, Durham University, 1989. http://etheses.dur.ac.uk/6549/.
Abstract:
The work described in this thesis is divided into four sections: 1. The electrochemical reduction of fluorocarbon derivatives has been investigated. A number of systems have been studied analytically (using cyclic volt amine try) ; whilst preparatively a range of compounds have been synthesised, including semi-conducting polymers and four-membered perfluorocyclic products. 2. The use of sodium amalgam as an electromimetic medium to facilitate reduction of various fluorocarbon substrates has been studied. A series of volatile cyclic and acyclic F-dienes have been prepared from F-alkenes in good yield and conversion. The chemistry of these F-dienes is then described: 3. Both mono- and bi- functional nucleophiles have been reacted, giving a range of novel substitution products. 4. A number of free radical and cycloaddition reactions have been attempted without success. However, the complexation of decamethylferrocene as a metallocene one electron donor, with various F-alkenes of low reduction potential, has allowed a radical anion of a perfluorocyclic-diene to be stabilized and fully characterized for the first time.
24
Sagandira, Cloudius Ray. "Exploring acyl azides chemistry in continuous flow systems." Thesis, Nelson Mandela Metropolitan University, 2017. http://hdl.handle.net/10948/12065.
Abstract:
Organic azides are important in the synthesis of many target molecules of great use in fine chemical and pharmaceutical production. The use of this class of compounds is however limited due to their hazardous nature and many safety concerns, as they are highly exothermic. Micro reactors can handle exotherms extremely well, due to the inherent high surface area to volume ratio, unlike the conventional batch process. This dissertation therefore aims to investigate the safe application of micro reactors in acyl azide chemistry.With this in mind, Chapter 1 provides a comprehensive background on organic azides, reaction calorimetric studies, flow chemistry technology (micro reactors) and their theoretical advantages. This chapter also discusses the preparation of organic azides in continuous flow systems and scaling up in continuous flow systems. Chapter 2 illustrates and discusses multivariate optimisation of benzoyl azide synthesis as a model reaction, synthesis of other acyl azides using the model reaction optimised conditions and multistep synthesis of carbamates, amides and amines in continuous flow systems via the Curtius rearrangement of benzoyl azide formed in situ from benzoyl chloride and sodium azide. The chapter also discusses process hazards analysis and evaluation of benzoyl azide synthesis and decomposition using calorimetric studies. It also investigates and discusses the effects of different mixing regimes and channel sizes on scale up. Chapter 3 has comprehensive experimental details for the whole dissertation with Chapter 4 providing the concluding remarks and future work recommendations.
25
Alvarez, Silva Mayeli. "Surface chemistry study on the pentlandite- serpentine system." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97112.
Abstract:
Interaction with MgO-minerals is one mechanism suspected to reduce selectivity in flotation of pentlandite from ultramafic ore. Understanding the surface chemistry of the minerals involved will lead to improved flotation conditions that maximize flotation selectivity. The first part of the thesis compares isoelectric point (i.e.p.) and point of zero charge (p.z.c.) determined using Mular-Roberts [M-R] titration technique of MgO-minerals chlorite, serpentine and talc. The M-R technique was unsuccessful with talc, attributed to Mg2+ acting as potential determining ion. For serpentine and chlorite, respectively, p.z.c. was pH 4.3 and 4.6 and i.e.p. pH 3.2 and <3. Dispersion index (DI) for chlorite suggested that aggregation/dispersion is controlled by both; serpentine remained dispersed, possibly due to hydration effects.The second part determines surface properties of pentlandite and serpentine isolated from an ultramafic ore. Zeta potential measurements were made on minerals alone and as mixtures with either indifferent electrolyte or supernatant derived from an ore suspension as background. Individual mineral results anticipated interaction due to electrostatic attraction. This was confirmed in the mixed mineral case, with Mg(OH)2 precipitate interaction as an additional factor. Scanning electron microscopy validated the findings.Aggregation/dispersion was determined by turbidimetry using a light scattering technique and optical microscopy. The effect of selected factors on aggregation/dispersion of pentlandite and serpentine was investigated by a design of experiment (DOE). Concentration of carboxymethyl cellulose, CMC, and the interaction between CMC and pH were the important factors. Contact angle measurements explored effects of several factors on pentlandite hydrophobicity and, using a DOE, small-scale flotation was used to investigate effects on pentlandite floatability. The pH was the most important factor, acidic pH increasing both hydrophobicity and floatability. Copper activation enhanced both properties, as well; magnesium affected hydrophobicity at alkaline pH, but it did not show significant effect on floatability; serpentine was detrimental to the process; and CMC was capable of partially restoring the hydrophobicity and floatability of pentlandite depressed with serpentine.L'interaction de la pentlandite avec des minéraux d'oxide de magnésium (MgO-) est soupçonnée d'être à l'origine de la sélectivité réduite de la pentlandite dans les procédés de flottation de minerais ultrabasiques. Une meilleure compréhension de la chimie de surface des minéraux impliqués devrait mener à l'amélioration des conditions de flottation qui en maximisent la sélectivité. La première partie de la thèse compare le point isoélectrique (p.i.e) et le point de charge nulle (p.c.n), déterminés à l'aide de la technique de titrage Mular-Roberts [M-R], de minéraux d'oxide de magnésium tels que la chlorite, la serpentine et le talc. Dans le cas du talc, la technique M-R a échoué, probablement dû aux ions Mg2+ qui jouent le rôle d'ions déterminateurs de potentiel. Dans le cas de la serpentine et de la chlorite, les p.c.n. ont été déterminés à pH 4,3 et 4,6 respectivement et les p.i.e à pH 3,2 et <3 respectivement. Des tests de décantations ont suggéré que l'agrégation/dispersion observée pour la chlorite était contrôlée à la fois par le p.c.n et le p.i.e ; la serpentine au contraire est restée dispersée, possiblement dû à des effets d'hydratation. La deuxième partie détermine les propriétés de surface de la pentlandite et de la serpentine isolées à partir d'un minerai ultrabasique. Des mesures du potentiel zêta ont été effectuées sur les minéraux seuls et mélangés en présence d'un électrolyte, indifférent dans un cas et surnageant dans l'autre cas, préparé à partir d'une suspension de minerai utilisée comme milieu d'étude. Les résultats relatifs aux minéraux individuels et en particulier les forces d'attraction électrostatique observables ont permis d'anticiper leur interaction. Cette hypothèse a été confirmée dans le cas des minéraux mélangés, étant après avoir pris en compte l'interaction de précipités de Mg(OH)2 comme facteur additionnel. Des observations au microscope électronique à balayage ont permis de valider les résultats. L'agrégation/dispersion a été déterminée par décantation en utilisant des techniques de lumière diffuse et de microscopie optique. L'effet de certains facteurs sur l'agrégation/dispersion de la pentlandite et de la serpentine a été étudié sur la base d'un plan d'expériences (PE). Entre autres, la concentration en carboxymethyl cellulose (CMC) et l'interaction entre le CMC et le pH ont été considérés comme des facteurs importants. Des mesures d'angle de contact ont permis d'explorer l'hydrophobicité de la pentlandite et, à l'aide d'un PE, une étude de flottation à petite échelle a été réalisée pour investiguer la flottabilité de la pentlandite. Les résultats ont montrés que le pH était le facteur le plus important, un pH acide ayant pour effet d'augmenter à la fois l'hydrophobicité et la flottabilité. L'ajout de cuivre a également permis de renforcer ces deux propriétés par un effet d'activation; la présence de magnésium au contraire a affecté l'hydrophobicité de la pentlandite à pH alcalin mais n'a pas eu d'effet significatif sur ses propriétés de flottabilité; la présence de serpentine s'est trouvée être préjudiciable au procédé mais l'utilisation de CMC a pu être utilisée afin de restaurer partiellement l'hydrophobicité et la flottabilité de la pentlandite diminuées par la présence de la serpentine.
26
Curley, John Joseph. "Dinitrogen fixation chemistry of a molybdenum trisanilide system." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/49549.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Vita.
Includes bibliographical references.
Dinitrogen cleavage by Mo(N[t-Bu]Ar)3 (Ar = 3,5-C6H3Me2) proceeds through the intermediate ([mu]-N2)[Mo(N[t-Bu]Ar)3]2 before forming N=Mo(N[t-Bu]Ar)3 as the product. Both the intermediate bridging N2 complex and the nitride product have been structurally characterized by single-crystal X-ray diffraction. The spectroscopic and structural features of this bridging N2 complex are discussed in comparison to its one- and two-electron oxidized congeners, [([mu]-N2)[Mo(N[t-Bu]Ar)3]2]n+, n = 1, 2. This series of three complexes share a common chromophore, the nature of which was identified with the aid of time-dependent density functional theory. A photochemical reaction of ([mu]-N2)[Mo(N[t-Bu]Ar)3]2 that forms both Mo(N[t-Bu]Ar)3 and N=Mo(N[t-Bu]Ar)3 is described. The dynamics of this photochemical reaction are explored by ultrafast transient absorbance spectroscopy. A synthetic scheme for nitrogen fixation in the form of organic nitriles is initiated from the product of dinitrogen cleavage, N=Mo(N[t-Bu]Ar)3. This synthetic scheme is a closed cycle that returns the molybdenum nitride starting material at the conclusion of the cycle. To achieve this synthetic goal, new methods were developed to form C-N bonds between organic electrophiles and the weakly nucleophilic terminal nitride. In a key reaction, Mo(IV) ketimide complexes, R'O(R)CNMo (N[t-Bu]Ar)3, were shown to react with either SnCl2 or ZnCl2 to afford the corresponding nitrile, RCN, and a ClMo(N[t-Bu]Ar)3 in essentially quantitative yields.
(cont.) The chloromolybdenum complex may be reductively recycled to yield Mo(N[t-Bu]Ar)3 for subsequent dinitrogen cleavage. A series of cationic diazoalkane complexes [4-RC6H4C(H)NNMo(N[t-Bu]Ar)3][AlCl4], R = NMe2, Me, H, Br, CN, have been prepared by treatment of the N2-derived diazenido complex Me3SiNNMo(N[t-Bu]Ar)3 with 4-RC6H4CHO and 2 equiv AlCl3. The physical properties of these complexes were determined by the use of X-ray crystallography, cyclic voltammetry, infrared, Raman, UV-vis, and 15N NMR spectroscopies. Electrochemical reduction of these cationic diazoalkane complexes forms the C-C bonded dimer, [mu]-(4-RC6H4C(H)NN)2[Mo(N[t-Bu]Ar)3]2, in a reaction that is proposed to proceed through the neutral, odd-electron complex 4-RC6H4C(H)NNMo(N[t-Bu]Ar)3. The structure of this odd-electron compound is described with the aid of density functional theory. The central C-C bond in [mu]-(4-RC6H4C(H)NN)2[Mo(N[t-Bu]Ar)3]2 is redox non-innocent, and oxidation of these compounds returns the cationic diazoalkane complex from which they were prepared.
by John Joseph Curley.
Ph.D.
27
Haley, Roger David. "Surface chemistry of the vinyl acetate catalytic system." Thesis, University of Cambridge, 1999. https://www.repository.cam.ac.uk/handle/1810/272089.
28
Jenkins, Dave A. "Teaching First-Semester General Chemistry Using 3D Video Games following an Atoms First Approach to Chemistry." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1248376/.
Abstract:
The unified learning model (ULM) focuses on students' engagement, motivation, prior knowledge, and working memory. This study employs the use of video games to assess students' learning through a 3D chemistry gaming environment. In this human-subjects research, students carried out missions and applied reasoning to solve problems appropriate for general chemistry content. For learning to occur, students must be engaged and motivated as stated in the ULM. Learning cannot necessarily be accomplished by experience alone, and critical thinking is required to turn the experience into learning. The interpretation of educational theory applied to video games and this proposed study are discussed. A moderately positive correlation was found between exam score and study time (playing the game). Essentially the more time spent playing the game or an online activity the higher the exam scores. There was an alpha level less than 0.05 (p < 0.05) between the experimental group and non-traditional group (no game or online activity). Supporting that there was a statistically significant difference between groups, the null hypothesis was accepted between the game and online activity. Furthermore, as stated under the ULM, engagement is necessary for optimal learning.
29
Hau, Lap Wing. "Electrokinetically-driven liquid flows in microchannels using surface-chemistry technology /." View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?MECH%202005%20HAU.
30
Hao, Jicheng. "An investigation of the inorganic chemistry of peat systems." Thesis, Liverpool John Moores University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337789.
31
Winbow, Howard David. "The chemistry and properties of magnesia-phosphate cement systems." Thesis, University of Sheffield, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249651.
32
Gregory, Robert John Hryntchyshyn. "Biocatalytic preparation and chemistry of some novel cyanohydrin systems." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365896.
33
Mathews, Sussen. "Study of systems relevant to combustion and atmospheric chemistry." Thesis, University of Aberdeen, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322537.
Abstract:
Two approaches have been used in this investigation. The first involved the employment of the technique of molecular modulation kinetic (MMK) spectroscopy in the study of reaction kinetics of transient species. Previous research at Aberdeen had established a systematic error in both the kinetic (kobs) and spectroscopic (σλ) parameters determined. Therefore it was intended to investigate the source of this error through the study of the kinetics of the association of the trichloromethyl radical with oxygen, producing the trichloromethyl peroxy (CCl3O2) radical. However, over a period of thirty-three months, no sensible results were obtained, as a result of severe instrumental component problems and the lack of in-house technical expertise. The project ultimately had to be abandoned. Since the kinetic investigation and the attempted rectification of the many problems encountered with the MMK spectrometer constituted a major portion of the allocated research time, they are reported in the final chapter of this thesis. In the second approach, two computational procedures, applying the Rice-Ramsperger-Kassel-Marcus (RRKM) theory of unimolecular reactions, have been used to evaluate kinetic parameters for the decomposition of two distinct chemical systems, namely tert-butoxy radical and peracetic acid. The programmes used are the Rabinovitch-RRKM programme and the programme UNIMOL (Gilbert et al), the latter of which is the more sophisticated. Fall-off data for the decomposition of tert-butoxy radical have been modelled over the temperature range 402-443 K relative to the experimental Arrhenius parameters, evaluated from both thermal and photolysis rate data obtained in previous investigations. The reaction was found to be pressure dependent over the range 1-1500 Torr. The refined high-pressure limit rate parameters obtained in this work are found to be in reasonable agreement with related rate constants reported from different laboratories. A value of the decomposition rate constant is extrapolated for atmospheric conditions. The efficiencies of energy transfer for three inert bath-gases, namely sulphur hexafluoride, carbon tetrafluoride and nitrogen, at 402 K, are examined using the weak collision model. RRKM modelling predicts very little difference in the efficiencies of these bath-gases - an unexpected result.
34
Merckel, Daniel Andrew Sturton. "The use of supramolecular chemistry in dye delivery systems." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246879.
35
Dong, Zhiming (Eric). "New Adventures in the Chemistry of Polycarboncyclic Ring Systems." Thesis, University of North Texas, 1997. https://digital.library.unt.edu/ark:/67531/metadc278356/.
Abstract:
I. Diels-Alder reactions of 1,2,3,4,9,9-hexachloro-1,4,4a,8a-tetrahydro-1,4-metha- nonaphthalene (16) and 1,2,3,4,9,9-hexachloro-1,4,6,7-tetrahydro-1,4-methanonaphthalene (17) toward dienophiles N-methyl-1,2,4-triazoline-3,5-dione (MTAD), N-phenyl-1,2,4-triazoline-3,5-dione (PTAD) and/or N-methylmaleimide (NMM) have been examined.
II. Epoxides derived from functionalized 1,4,4a,9a-tetrahydro-9,10-dioxo-1,4-methanoanthracenes (1a and 1b) undergo acid- and base-promoted intramolecular nucleophilic ring-opening to form new polycyclic alcohols.
III. The title cycloalkylidenecarbene has been generated via reaction of 8-methylenepentacyclo[5.4.0.0^{2,6}.0^{3,10}. 0^{5.9}]undecan-11-one (44) with diethyl diazomethyl-phosphonate (DAMP). This species could be trapped in situ by cyclohexene, thereby affording the corresponding cycloadduct 46a and 46b.
36
Thorn, Angie Sue (Morris). "The impact of nanoparticle surface chemistry on biological systems." Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5659.
Abstract:
The unique properties of nanomaterials, such as their small size and large surface area-to-volume ratios, have attracted tremendous interest in the scientific community over the last few decades. Thus, the synthesis and characterization of many different types of nanoparticles has been well defined and reported on in the literature. Current research efforts have redirected from the basic study of nanomaterial synthesis and their properties to more application-based studies where the development of functionally active materials is necessary. Today such nanoparticle-based systems exist for a range of biomedical applications including imaging, drug delivery and sensors. The inherent properties of the nanomaterial, although important, aren’t always ideal for specific applications. In order to optimize nanoparticles for biomedical applications it is often desirable to tune their surface properties. Researchers have shown that these surface properties (such as charge, hydrophobicity, or reactivity) play a direct role in the interactions between nanoparticles and biological systems can be altered by attaching molecules to the surface of nanoparticles.
In this work, the effects of physicochemical properties of a wide variety of nanoparticles was investigated using in vitro and in vivo models. For example, copper oxide (CuO) nanoparticles were of interest due to their instability in biological media. These nanoparticles undergo dissolution when in an aqueous environment and tend to aggregate. Therefore, the cytotoxicity of two sizes of CuO NPs was evaluated in cultured cells to develop a better understanding of how these propertied effect toxicity outcomes in biological systems. From these studies, it was determined that CuO NPs are cytotoxic to lung cells in a size-dependent manner and that dissolved copper ions contribute to the cytotoxicity however it is not solely responsible for cell death. Moreover, silica nanoparticles are one of the most commonly used nanomaterials because they are easy to synthesize and their properties (such as size, porosity and surface chemistry) can be fine-tuned. Silica nanoparticles can be found in thousands of commercially available products such as toothpastes, cosmetics and detergents and are currently being developed for biomedical applications such as drug delivery and biomedical imaging. Our findings herein indicate that the surface chemistry of silica nanoparticles can have an effect on lung inflammation after exposure. Specifically, amine-modified silica NPs are considered to be less toxic compared to bare silica nanoparticles. Together, these studies provide insight into the role that material properties have on toxicity and allow for a better understanding of their impact on human and environmental health.
The final aim of this thesis was to develop surface-modified nanoparticles for drug delivery applications. For this, biodegradable, polymeric NPs were used due to their inert nature and biocompatibility. Furthermore, polymeric NPs are excellent for loading drugs and using them as drug delivery vehicles. In this work, poly (lactic-co-glycolic acid) (PLGA) NPs were loaded with a therapeutic peptide. These NPs were then coated with chitosan (a mucoadhesive polymer) for the treatment of allergic asthma or coated with a small cationic mitochondrial targeting agent for the treatment of ischemia/reperfusion injury.
Taken as a whole, this thesis sheds light on the impact of NPs on human health. First by providing useful toxological data for CuO and silica NPs as well as highlighting the potential of surface-modified polymeric NPs to be used in drug delivery-based applications.
37
Keatings, Kevin William. "The basis for ostracod shell chemistry in palaeoclimate reconstruction." Thesis, Kingston University, 1999. http://eprints.kingston.ac.uk/20651/.
Abstract:
This project examined the trace-element and stable-isotope composition of non-marine ostracod shells and their use in Holocene palaeoclimate reconstruction, with particular reference to mid-latitude shallow carbonate lakes. Controls on the chemical composition of shells from such environments were studied. Results were used to test the application of ostracod shell chemistry data to palaeoclimate reconstruction. Selected techniques were applied to a high resolution study of Holocene lake marl sequence. The project investigated influences on shell chemistry during formation, sedimentary deposition and extraction. A core covering approximately 9,450 to 5,800 Cal. Yr BP was taken from Cunswick Tarn, Cumbria, yielding ostracod faunal and shell chemistry data used to produce a palaeoclimate interpretation for the early Holocene. This interpretation agreed with studies showing a warm, dry early Holocene and a cooler, wetter mid-Holocene. Seasonal sampling of water and ostracods at Cunswick Tarn provided a modern analogue for the core material. Species-specific fractionations of stable isotopes were similar to findings from ponds in Greywell, Hampshire. There were seasonal variations in the trace-element composition of shells, which may reflect: seasonal fluctuations; shell growth following initial calcification; and cleaning problems. Monthly sampling of water and ostracods was performed at carbonate ponds near Greywell. Species-specific fractionations of oxygen isotopes were observed. Compared to theoretical equilibrium calcite, all species exhibit [delta][sup]18 O values more positive than expected, while [delta][sup]13 C values equal equilibrium values. Variations in shell trace-element composition was greater than that of the water. This result may be related to animal physiology and the water’s low trace-element content. Ostracods collected from additional sites with elevated Mg/Ca[sub](water) ratios showed the best correlation between the Sr/Ca ratio of the water and the Sr/Ca of the shell. Effects of established cleaning techniques on shell chemistry were investigated. Whenever possible, only brush cleaning with deionised water should be used. Sodium hypochlorite is recommended for any further cleaning. An investigation of the effect of partial dissolution on shell chemistry demonstrated that even extremely degraded Cypretta brevisaepta shells have similar trace-element and stable-isotope ratios to unaltered shalls. However, dissolution may alter shell chemistry, and whenever possible, pristine shells should be used. Pseudocandona rostrata specimens from Greywell were grown in vitro. Adults had low weight with low M/Ca ratios. The Sr/Ca[sub](ostracod) ratios were negatively correlated with weight, while M/Ca[sub](ostracod) ratios were weakly positively correlated with M/Ca[sub](water), Sr/Ca[sub](water), and temperature. The research shows that a knowledge of the life-history and ecology of ostracods, together with the chemical signals recorded in their shells, can provide an effective tool for the interpretation of palaeoclimatic events.
38
Diaz, Cachero M. C. "Control strategy for a flexible analytical chemistry robotics system." Thesis, Middlesex University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.568484.
39
Lewis, Gareth Peter. "Intelligent monitoring and control system for microwave assisted chemistry." Thesis, Liverpool John Moores University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438835.
40
Jackson, A. R. W. "The imidazolethione/copper system : Coordination chemistry and corrosion inhibition." Thesis, University of Newcastle Upon Tyne, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371068.
41
Floyd, Tamara M. (Tamara Michelle) 1974. "A novel microchemical system for rapid liquid-liquid chemistry." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8273.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2002.Includes bibliographical references (leaves 110-119).
Microchemical systems are sub-milliliter systems for chemical processes. They are constructed using microfabrication techniques originally developed for the fabrication of microelectronic circuits. The reduction in size, as compared to conventional systems, offers several advantages in improvement of heat and mass transfer and control of flow fields. In addition, microchemical systems are smaller, therefore inherently safer and capable of shorter thermal response times. The focus of this work has been a microchemical system with a multi-inlet contactor for liquid-liquid processes. The systems are fabricated using, primarily, silicon and glass in which feature sizes range from approximately 10 to 500 [mu]m. The multi-inlet contactor consists of 10 alternating inlets for two components. Fluids continuously enter the contactor, are focused by a converging channel, mix and react in a 50 m channel. The contactor is the central element in the microchemical system that also includes a parallel plate heat exchanger, infrared transmission detection capabilities and thin film metal temperature sensors. Quantitative data are obtained using on-chip optical detection methods, integrated thin film sensors, and off-chip pressure sensors. For microchemical systems, the length scales are short. Consequently, Reynolds numbers are small and the flow is laminar. When two or more streams are contacted in a homogeneous system, the flow is stable. The short length scales of the resulting lamellar stream enable rapid diffusion mixing for applications, such as kinetics studies or reaction-rate-limited operation of fast reactions.
(cont.) The mixing characteristics in the multi-inlet contactor are investigated through experiments and simulations. Without optimization, sub-second mixing times are achieved. By using experiments and simulations to gain a better understanding of diffusion mixing in the system, 99% mixing is achieved in less than 25 ms. Characterization of the microchemical system also includes determining the overall heat transfer coefficient for the parallel plate heat exchanger and demonstrating on-chip infrared transmission detection from 4000-1000 cm-1. Thus, these devices combine all the features necessary for kinetic studies, specifically control of residence time, control and monitoring of temperature, and concentration measurement by infrared spectroscopy. As a demonstration of microchemical systems as tools for kinetics studies, the microchemical mixer was used with in situ Fourier Transform infrared spectroscopy to monitor the alkaline hydrolysis of methyl formate. This reaction follows second order kinetics and is fast with a half life of 70 ms for the conditions used in this study. The rate constant that was extracted was in good agreement with the literature value. Moreover, in contrast to a previous study, no sample post processing was needed and the half-life of the reaction was reduced by an order of magnitude. Microchemical systems can also be useful tools in achieving and understanding heterogeneous fluid contacting. When an aqueous phase and organic phase are contacted in a 1:1 volumetric ratio, flow segregation can occur ...
by Tamara M. Floyd.
Ph.D.
42
Ritter, Halle (Halle Caitlan). "Nitrogen chemistry in an urban bioretention system in Singapore." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82824.
Abstract:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 35-37).
An investigation into the nitrogen chemistry of the anoxic layer of an urban constructed wetland in Singapore was conducted. This pilot-scale wetland treats stormwater runoff from the Balam Estate housing development for several water quality parameters of concern, including nitrate. Earlier sampling in the wetland had indicated that the concentration of nitrate was lower in the outflow from the rain garden than in its inflow, but no research had been done on other nitrogen species or transformation pathways. Preliminary analyses suggest that, although the saturated layer is sufficiently anoxic and denitrification is occurring as per performance objectives, organic nitrogen is being added to the infiltrating water throughout this layer, causing a net export of total nitrogen from the anoxic zone. This organic nitrogen could be either re-released from reserves adsorbed onto organic material during previous storm events, or leached directly from the anoxic layer material which includes wood chips and sand. Readings at outflow pipes indicate that a percentage of this nitrogen is likely re-mineralizing to ammonia upon exposure to more oxygen-rich conditions in the outflow pipes. Further study in the Balam Rain Garden using isotope labeling to more clearly delineate nitrogen fate and transport is suggested.
by Halle Ritter.
M.Eng.
43
Hurwitz, Margaret Mead. "Idealised numerical simulations of the stratospheric chemistry-climate system." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612249.
44
Goodyear, Michael Cooper. "Organic chemistry and mineral interactions in the solar system." Thesis, Open University, 2013. http://oro.open.ac.uk/54719/.
Abstract:
The objective of this project was to develop methods to detect meteoritic organic compounds in situ, and to detelmine whether any associations exist between specific classes of compound and co-located minerals, thus indicating a possible common origin. Carbonaceous chondrites, (which comprise a small proportion of meteorites), contain a few per cent of organic material, heterogeneously distributed within their structure, the major part being macromolecular ("insoluble organic material", lOM). Model compounds were covalently bonded to "molecular tags", atoms or groups not normally present in meteorites, enabling easier detection against background signals when using analytical methods suitable for use in situ, such as Raman spectroscopy or SEM. Also, extra functionality was introduced to model compounds by ozone treatment, allowing a greater density of tags to be attached. Following development work with terrestrial models, meteorite samples were exposed to ozone, but oxalic acid was formed instead of the expected oxygenated IOM derivative. To determine if this result was due to an effect of the minerals present, whole rock samples and demineralised IOM were analysed, both before and after exposure to ozone. Isolated IOM behaved differently from that still in situ. Fresh samples ofIOM were isolated (using two literature methods), and their reactions and properties compared. The evidence obtained indicated that the structure of IOM had been modified on isolation, and that the modifications caused by the two methods were different. This shows that any data generated from isolated IOM does not necessarily directly relate to organic material still present within a meteorite. Using the data obtained in this study, and that previously reported, two-component models for the structure of lOM, and scenarios for its formation, were discussed.
45
Hamdi, Meshal. "E-Waste Recycling System for Computers and Mobile Devices Using Green Chemistry." Digital Commons at Loyola Marymount University and Loyola Law School, 2015. https://digitalcommons.lmu.edu/etd/390.
46
Kokhanenko, Pavlo. "Hydrodynamics and chemistry of silica scale formation in hydrogeothermal systems." Thesis, University of Canterbury. Mechanical Egineering, 2015. http://hdl.handle.net/10092/10247.
Abstract:
The extraction of geothermal heat can cause precipitation of the minerals dissolved in
geothermal fluid. Their deposition on the walls of wells and above-ground plant and in pores
near reinjection wells, also known as mineral scaling, is one of the main obstacles to
increasing the effectiveness of utilization of the limited geothermal resources. If not
controlled properly it can result in accumulation of a significant amount of scale which
obstructs pipes and reinjection wells and reduces the efficacy of heat exchangers.
The most abundant mineral in geothermal fluid is silica and thus its precipitation can cause
the highest scaling rate. While this dissertation is devoted to the study of silica scaling the
results obtained may be applicable to other minerals with similar deposition mechanism.
Oversaturated silica is known to precipitate from aqueous solution either by the direct
chemisorption of single silicic acid molecules (monomers) or by forming colloidal particles
suspended in the solution. These particles can subsequently be transported to, and attach onto,
a wall. This process of colloidal silica deposition was previously recognised to cause much
faster scaling than the direct deposition of silica monomers under typical geothermal plant
conditions.
While the chemical kinetics of silica polymerization and colloid formation are relatively well
understood, transport of these colloids and their stability, which control their aggregation and
attachment rates, on the other hand are not.
Previous studies of the silica scaling process have identified prominent effects of geothermal
brine hydrodynamics on the scaling rate. It was found to increase with the flow rate and
particle size, thus suggesting the dominance of the advective (inertial) deposition of colloidal
silica. However, this conclusion contradicted the present theory of particle transport in
turbulent flows which argues the dominance of the diffusive transport for the relevant range
of particle sizes (<1 μm).
The development and continuing improvement of the anti-scaling measures required deeper
understanding of the complex combination of the phenomena involved in the process of silica
scaling. This was pursued in the present study using theoretical and experimental methods.
First, the rate of colloidal silica transport from a turbulent flow onto the internal surface of a
circular pipe, a cylinder and a flat plate were calculated using available analytical and
numerical methods. The obtained theoretical transport rate was found to be about four orders
of magnitude higher than the corresponding experimental scaling rate. The latter was
determined in the previous studies to be 4.2·10-8 kg/s/m2 for silica colloids of 125 nm in
diameter which corresponded to the dimensionless deposition velocity (the dimensionless
deposition velocity is the scaling rate normalised by the particle mass concentration and
friction velocity) of 1.2·10-6 for the dimensionless particle relaxation time of 2·10-4.
Next, based on the standard DLVO theory of particle interactions and in the framework of the
Smoluchowski approach the probability of colloidal silica particle attachment to a wall was
found to be 10-6.
Therefore, the theoretical scaling rate, calculated as a product of this probability and the
above-mentioned transport rate was two orders of magnitude lower than the experimental
scaling rate. This suggested that the implemented theoretical approach either underestimated
particle transport rate or overestimated particle stability. Both possibilities are explored in
this dissertation.
In addition, the silica scaling rate was measured for a range of conditions: particle size from
20 to 60 nm, particle concentration 1600-10000 ppm, friction velocity from 0.09 to 0.18 m/s
(Re = 9-50·103) and ionic strength from 30 to 80 mM, pH 8.1-9.5 and temperature from 25 to
44 °C. For this, laboratory experiments were designed and progressively modified in order to
improve the repeatability of the results and to study the scaling process. In these experiments
colloidal silica deposition onto the walls of mild steel pipe sections was studied with a
recirculating flow rig with variable (but controllable) particle size, concentration, flow rate,
pH and ionic strength of the solution. In addition, a parallel plate flow test section was
designed and built which will provide better capabilities for the control over the
hydrodynamic and test surface conditions in future experiments.
The control over the chemical conditions was achieved by the use of the synthetic colloidal
solutions. Two methods of their production – hydrolysis of either sodium metasilicate or
active silicic acid – were employed. The influence of the synthesis conditions, ion content
and pH on the long term behaviour of these colloidal solutions was investigated. The particle
size data, obtained using dynamic light scattering (DLS) and verified by electron microscopy,
was analysed and compared against the predictions of the current models of nanoparticle
growth and stability. The kinetic aggregation was identified to be the dominant particle
growth mechanism.
Experimental data collected during the long-term observations of the particle growth allowed
relationships between the aggregative stability and such parameters as the particle size, ion
concentration and pH of the solution to be elucidated. In particular, the aggregative stability
of 10-20 nm particles was found to be 108-1010 which is 7-9 orders of magnitude higher than
the corresponding DLVO stability. It was also found to decrease with the increase of the
particle size. This agreed with the theory of the colloid stabilization by steric interactions.
Moreover, the model of the “gel” layer was used to explain the observed “anomalies” of the
colloidal silica behaviour. The deposition experiments conducted with these synthetic
colloidal solutions showed that the scaling rate increased with the particle size, flow rate and
ionic strength (IS) of the solution. Thus, it was measured to be 9.7·10-9 kg/s/m2 for the 45 nm
particles in a solution with IS = 0.05 M, which corresponded to the dimensionless deposition
velocity of 6.6·10-8 for a dimensionless particle relaxation time of 2.2·10-6.
The scaling rate was calculated for these conditions by multiplying the corresponding
transport rate and the actual attachment probability determined as an inverse of the
experimental stability. It was found to agree with the experimental value within an order of
magnitude. In addition, the observed increase of the scaling rate with the increase of particle
size was explained by the compensation of the decreased rate of the particle transport by
faster decrease of actual particle stability (increase in attachment probability). Therefore the
contradiction between the theory and the experiment was resolved for the particles of 20 to
60 nm in diameter.
Moreover, the observations of the dimensions and distribution of the scale elements formed
in some of the present experiments strongly suggested the significance of the advective
(inertial) mechanism of particle deposition. This and comparative analysis of other
experimental and theoretical data suggested that the present theory may underestimate the
convective transport of the particles onto a rough wall. Therefore, the hypothesis of the
parallel-to-wall advective deposition of the nanoparticles onto the roughness/scale elements
(not accounted in the current theory) was proposed. The corresponding mass transfer problem
was solved analytically using experimentally found dimensions of the scale elements. The
additional transport was found to decrease the above-stated discrepancy between the
theoretical and experimental scaling rate for large (125 nm) particles by one order of
magnitude. The remaining difference of one order of magnitude was speculated to be due to
the underestimation of these particles attachment probability derived with the standard
DLVO theory. The actual aggregative stability of the silica colloids larger than 60 nm in
diameter and for a wider range of IS values is of interest for future experimental studies.
An improved understanding of the interrelation between the chemical and hydrodynamic
phenomena in the process of silica scaling and its dominant mechanisms was achieved in this
dissertation. This allowed optimization of the present anti-scaling practices aimed to
minimize the negative effects of mineral scaling on the operation of geothermal power
stations. Besides the practical recommendations, which may ultimately help to increase the
efficiency of geothermal power stations, the results of the present study may be of value in
the fields of mass transfer and colloid science.
47
Hardacre, Christopher. "Surface chemistry and catalysis of novel Pt/CeOâ†2 systems." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282862.
48
Kim, Judy E. (Judy Eunhee). "Physical chemistry of acid systems relevant to stratospheric ozone depletion." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/54401.
49
McKie, Marion Catherine. "The chemistry of 1,3,4-oxathiazol-2-ones and related systems." Thesis, University of Edinburgh, 1988. http://hdl.handle.net/1842/12633.
50
Murphy, Paul. "Development and applications of quantum chemistry to open shell systems." Thesis, Heriot-Watt University, 2017. http://hdl.handle.net/10399/3355.
Abstract:
This thesis investigates the applicability of a range of computational techniques across a range of open shell chemical systems from the geometrically simple but electronically complex to the geometrically complex but electronically simple. Initially an investigation into a range of geometrically simple but electronically complicated systems is presented. The Monte Carlo Configuration Interaction method (MCCI) is applied to challenging transition metals dimers such as ScNi in order to establish the ground state potential energy surface, from equilibrium bond lengths through to dissociation using highly compact wavefunctions compared to Full Configuration Interaction (FCI). It shall be demonstrated that the ScNi dimer represents the current limit of this technique. Software development of MCCI is then undertaken in order to perform calculations of spin-orbit coupling interactions. Results on B, C, O, F, Si, S, F, Cl, OH, NO, CN and C2 species are shown to be comparable with other techniques using the one-electron Breit-Pauli Hamiltonian. The application of quantum chemistry to geometrically complex but electronically simple systems is then considered. Density Functional Theory (DFT) is used to investigate the mechanism and energetic barriers leading to ring inversion of the biscalix[4]arene supra-molecule. A minimum barrier height of 19.31 kcalmol−1 to inversion is elucidated along with details of the complete mechanistic pathway to inversion. The focus then moves to polymetallic clusters of calix[4]arene. A DFT study is made of the preferential binding of calix[4]arene towards first row transition metals of various oxidation and spin states. Results indicate that Cu3+ (singlet) species will preferentially bind to the lower rim over other metals in the study. The final DFT-related work presented is a study of the preferential binding at the upper rim of polymetallic calix[4]arene clusters towards a range of important small gas molecules. It was found that gases such as NH3 and SO2 bind most strongly to the upper rim with the inclusion of a transition metal at the lower rim providing strengthening of the host-guest binding.