Dissertations / Theses on the topic 'Bio-inorganic chemistry'

A wide range of metals are transported in the body by the protein transferrin, including both essential metal ions and probably also metals used in therapeutic agents. The metal binding sites on transferrin contain tyrosine, histidine and aspartate ligands. This thesis is concerned with studies of the essential metal ion manganese, and with titanium, which is used in anticancer agents. In order to aid the characterisation of Mn(III) and Ti(IV) transferrins, the Mn(III) and Ti(IV) complexes with the model ligand ethylenebis[(a-hydroxyphenyl)glycine](H₄EHPG) have been studied. The Mn(III) complexes rac-Na[Mn(EHPG)].3H₂0 (1) and rac,mesoNa[Mn(EHPG)].H₂0 (2), have been prepared and their X-ray crystal structures determined. Complex 1 contains N(S,S)C(R,R) configurations at the N and C stereogenic centres, whilst in the unit cell of complex 2 there are two independent molecules, 2a (mesa) and 2b (rac), with N(R,R)C(S,R) and N(R,R)C(S,S) configurations, respectively. Enantiomers of each complex are also present. The Mn(III) centres have Jahn-Teller-distorted octahedral geometry, with two long bonds and four short bonds. ¹H NMR spectra of these high-spin d⁴ paramagnetic complexes are reported. These complexes give rise to similar ligand (phenolate)-tometal charge-transfer bands as Mn(III)-transferrin. Dissociation of Mn(III) from EHPG occurs below pH 3.4. The Ti(IV) complex of rac-[Ti(EHPG)(H₂0)].1113H₂0 (3) has also been prepared and the X-ray crystal structure determined. All previously-reported crystalline racEHPG metal complexes contain N(S,S)C(R,R), or N(R,R)C(S,S) isomers, whereas 3 unexpectedly contains the N(S,S)C(S,S) and N(R,R)C(R,R) forms. 2D NMR studies indicate that 3 has a similar structure in solution to that in the solid state. A ligand (phenolate)-to-metal charge transfer band was observed at 386 nm, similar to that seen for Ti(IV)-transferrin. Ti(IV)EHPG was stable at pH values down to 1, however, the complex decomposed above pH 7. Mn(III)-transferrin complexes were prepared by air oxidation of Mn(II) in the presence of transferrin. The oxidation state of manganese bound to transferrin was Abstract confirmed by K edge EXAFS. Analysis of the EXAFS data revealed that the metal centre is also Jahn-Teller distorted but with four long bonds and two short bonds, i.e. an inverse distortion to that seen in the Mn(III)EHPG model complexes. Attempts to prepare other Mn(III) complexes which might be suitable for studies of Mn transfer to proteins are described and include cyclam and bicyclam as ligands. The crystal structure of [Mn(cyclam)Ch]Cl₂H₂0 was determined, and contained two long axial Mn-Cl bonds of 2.5249 Å. This complex was shown by electronic absorption spectroscopy to undergo a complicated series of reactions in aqueous solution. K edge EXAFS measurements suggested that at least one Cl ligand dissociated from the complex in aqueous solution. The hydrolysis was shown to be inhibited by the presence of fluoride.

L’un des principaux verrous scientifique rencontré au cours du développement de catalyseurs d’oxydation bio-inspirés concerne l’étape de réduction du métal pour permettre l’activation du dioxygène. Pour essayer de lever ce verrou, nous avons développé un système macromoléculaire composé d’un polymère hydrosoluble dans lequel deux types de cofacteurs sont incorporés ; (1) des cofacteurs redox capables de collecter des électrons issus d’un réducteur en solution, et (2) des cofacteurs catalytiques capables d’activer le dioxygène. De façon à permettre l’incorporation de ces cofacteurs au sein du polymère, ce dernier a été modifié avec différents groupement chimiques qui ont étés quantifiés par RMN du proton dans l’eau. Par ailleurs, la synthèse de différents complexes métalliques, connus pour être de bons catalyseurs d’oxydation, tels que des métalloporphyrines ou des complexes mononucléaire et binucléaire de fer et de cuivre, a été réalisée. Ces catalyseurs ont d’abord été étudiés avec H2O2 dans l’eau en présence ou en absence de polymère. En parallèle, l’incorporation de la FMN par interactions électrostatiques au sein du polymère a permis de générer un système capable de collecter les électrons de NADH en solution. Cette réduction s’est avérée 4 000 fois plus rapide que la réduction sans polymère modifié. Cette réductase artificielle (FMN+ PEI modifié) a ensuite été démontrée capable de réduire très efficacement les porphyrines de manganèse (III) ainsi que d’autres complexes métalliques. Au cours de l’étude, la capacité de ce système à séparer les électrons provenant de NADH a également été mis en avant. Finalement, cette réductase artificielle a été associée à différents catalyseurs métalliques afin d’étudier leur activité sur la réaction d’oxydation du thioanisole, ou d’autres substrats, par activation réductrice du dioxygène
A major scientific lock encountered during the development of bio-inspired oxidation catalysts is the metal reduction step to allow activation of dioxygen. In this optic, we have developped a macromolecular system composed of a water-soluble polymer in which two kinds of cofactors are incorporated; (1) redox cofactors capable of collecting electrons from a reducing agent in solution, and (2) catalytic cofactors capable of activating oxygen. In order to allow the incorporation of these co-factors within the polymer, the latter one has been modified by various chemical groups which have been quantified by proton NMR in water. Furthermore, the synthesis of various metal complexes, known as good oxidation catalysts, such as metalloporphyrins or mononuclear and dinuclear complexes of iron and copper was performed.These catalysts were first studied with H2O2 in water in the presence or the absence of polymer. In parallel, the incorporation of FMN by electrostatic interactions within the polymer has generated a system capable of collecting the electrons of NADH in solution. This reduction was found 4 000 times faster than the reduction without modified polymer. This artificial reductase (FMN + PEI modified) was then demonstrated to very efficiently reduce manganese porphyrins as well as other metal complexes. During this study, the ability of the system to split electron pairs collected from NADH has also been demonstrated. Finally, this artificial reductase has been associated with various metal catalysts in order to study their catalytic activity for various oxidation reaction using dioxygen

N2O est le troisième plus important gaz à effet de serre ainsi qu’un des principaux gaz responsables de la dégradation de la couche d’ozone. Une approche bio-inspirée de la N2Oréductase (N2Or), enzyme réduisant N2O via un site actif comportant quatre ions cuivre pontés par un atome de soufre, aide au design de nouveaux systèmes. Six complexes à valences mixtes comportant un motif Cu2(µ-S) considéré comme minimum pour avoir une activité ont alors été synthétisés. Il a été démontré que la structure de ces centres métalliques est affectée par le solvant utilisé. Dans un solvant non coordinant comme l’acétone, tous les complexes possèdent une liaison intermétallique et une valence délocalisée à température ambiante. En revanche en solvant coordinant, la coordination de molécules d’acétonitrile rend impossible la formation de liaison intermétallique et localise la valence.Pour tester l’activité N2Or de ces complexes, un prototype permettant un bullage constant en cuve UV a été conçu. L’objectif est de mettre au point une réduction catalytique de N2O en utilisant un réducteur sacrificiel et une source de proton. Le gaz utilisé lors des tests semble cependant contenir une faible quantité de O2 empêchant la caractérisation des activités. Une optimisation visant à purifier N2O avant les tests est en cours.Par ailleurs, les réductions de O2 à deux électrons pour former H2O2 (un oxydant doux) et à quatre électrons pour former H2O (réaction utilisée dans les piles à combustibles) en font un domaine attractif. Il a été démontré que tous les complexes synthétisés lors de ces travaux sont capables de réduire catalytiquement O2 dans l’acétone et que seulement celui sans position échangeable est actif dans l’acétonitrile. Ce dernier a de plus montré une capacité à changer de sélectivité (H2O2 vs H2O) en fonction de la concentration en réducteur sacrificiel utilisé
N2O is the third most important global warming gas and one of the most aggressive gas against ozone layer. A bio-inspired approach from N2Oreductase (N2Or), enzyme catalysing the two electron reduction of N2O with a four sulfur-bridged copper ions centre, helps for the design of new systems. Six mixed valent copper complexes containing the minimum Cu2(µ-S) core were then synthetized. It has been shown that these structures are affected by solvents in solution. Indeed, in a non-coordinating solvent like acetone, all these complexes have an intermetallic bond and a delocalized valence at room temperature. However in a coordinating solvent, the acetonitrile coordination makes it impossible to form a Cu-Cu bond and localize the valences.To test the N2Or activity, a prototype allowing a constant N2O bubbling in a UV cuve using a closed system was designed. The aim is to develop a catalytic reduction using sacrificial reductant and proton source. However, the gas bottle used for activity tests seems to contain a small amounts of O2 preventing results interpretation. The aim is now to optimize the prototype by adding a system that can purify N2O before activity tests.In a second time, the O2 reduction using two electrons to produce H2O2 (a soft oxidant) or four electron to produce H2O (useful in fuel cells) are of interest. It has been shown that all these new complexes are capable of catalytically reducing O2 in acetone and that only the one without exchangeable position can do it in acetonitrile. The latter has also demonstrate its ability to change its selectivity to produce H2O2 or H2O by changing the sacrificial reductant concentration. These results bring interesting insights for O2 activation with bio-inspired copper complexes

Biomimetic chemistry is directed towards the simulation of enzymatic reactivity with synthetic analogues. In this thesis a quantum chemical method has been employed to study the mechanism of highly reactive iron-oxo complexes involved in oxygenation and chlorination of organic substrates. The aim of this research is to gain greater understanding for the reactivity paradigm of the iron-oxo group. One reaction deals with the conversion of cyclohexane into adipic acid, a key chemical in industrial chemistry, catalyzed by an iron(II)-porphyrin complex in the presence of dioxygen. This process constitutes a ’green’ alternative to conventional adipic acid production, and is thus of great interest to synthetic chemistry. Another reaction investigated herein regards the selective chlorination observed for a new group of non-heme iron enzymes. With help of theoretical modeling it was possible to propose a mechanism that explains the observed selectivity. It is furthermore demonstrated how a biomimetic iron complex simulates the enzymatic reactivity by a different mechanism. Other topics covered in this thesis regard the structure-reactivity relationship of a binuclear iron complex and the intradiol C-C bond cleavage of catechol catalyzed by an iron(III) complex.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Submitted. Paper 2: Accepted. Paper 3: Submitted.

Material science is an interdisciplinary area of research, which in part, designs and characterizes new materials. Research is concerned with synthesis, structure, properties, and performance of materials. Discoveries in materials science have significant impact on future technologies, especially in nano-scale applications where the physical properties of nanomaterials are significantly different than their bulk counterparts. The work presented here discusses the use of ferritin, a hollow sphere-like biomolecule, which forms metal oxo-hydride nanoparticles inside its protein shell for uses as a bio-inorganic material.Ferritin is capable of forming and sequestering 8 nm metal-oxide nanoparticles within its 2 nm thick protein shell. A variety of metal-oxide nanoparticles have been synthesized inside ferritin. The work herein focuses on three distinct areas:1) Ferritin's light harvesting properties: namely band gaps. Discrepancies in the band gap energies for ferritin's native ferrihydrite mineral and non-native minerals have been previously reported. Through the use of optical absorption spectroscopy, I resolved the types of band gaps as well as the energy of these band gaps. I show that metal oxides in ferritin are indirect band gap semiconductors which also contain a direct transition. Modifications to the ferrihydrite mineral's band gaps are measured as a result of co-depositing anions into ferritin during iron loading. I demonstrate that these band gaps can be used to photocatalytically reduce gold ions in solution with titanium oxide nanoparticles in ferritin. 2) A new method for manganese mineral synthesis inside ferritin: Comproportionation between permanganate and Mn(II) forms new manganese oxide minerals inside ferritin that are different than traditional manganese oxide mineral synthesis. This reaction creates a MnO2, Mn2O3, or Mn3O4 mineral inside ferritin, depending on the synthesis conditions. 3) Ferritin as an energetic material: Ferritin is capable of sequestering various metals and anions into its interior. Perchlorate, an energetic anion, is sequestered through a co-deposition process during iron loading and is tested with energetic binding materials. Peroxide, which can be used as an oxidant, is also shown to be sequestered within apoferritin and combined with an aluminum based fuel for solid rocket propellants.

Les adduits cuivre-oxygène dans les métallo-enzymes ont été proposés comme étant responsables de l'activation de liaisons C-H, processus qui ont un intérêt pour des applications industrielles potentielles. La première partie de ce travail est consacrée à une présentation de différentes mono-oxygénases à cuivre et de leurs complexes modèles. Récemment, des intermédiaires réactionnels ont émergé et parmi ceux-ci, des espèces de valence mixte CuIICuIII ont été proposées comme étant des espèces réactives clés pour l'activation de liaisons C-H fortes.Dans ce travail, à partir de ligands binucléants basés sur un espaceur 1,8-naphtyridine, la stabilisation et les caractérisations spectroscopiques de ce type d’intermédiaires à haut degré d’oxydation sont explorées. La préparation d’espèces Cu2:O2 à partir de l'activation du dioxygène par les complexes CuI2 est discutée. Deux complexes µ-ɳ2:ɳ2-peroxo-CuII2 ont été préparés à -80°C et caractérisés par différentes méthodes spectroscopiques associées à des calculs par la théorie de la fonctionnelle de la densité (DFT). A partir de nouveaux ligands dissymétriques possédant une fonction amide, nos tentatives pour contrôler la préparation des complexes binucléaires associés sont également présentées. Puis, les caractérisations des espèces à valence mixte CuIICuIII obtenues par mono-oxydation électronique des complexes CuII2 sont décrites (voltammétrie cyclique, résonance paramagnétique électronique, UV-visible, proche infrarouge et DFT).Enfin, ce travail est complété par l’étude de la réactivité des espèces CuIICuIII, pour lesquelles la littérature est presque inexistante. Lorsque des ligands stériquement encombrés sont utilisés dans les espèces à valence mixte, des oxydations intramoléculaires sont observées, alors que l’espèce CuIICuIII possédant un ligand moins encombré oxyde le toluène. Il est à noter que l'ajout d'une base rend le système catalytique
Copper-oxygen adducts in enzymes have been proposed to be responsible for the activation of C-H bonds, a process that has industrial applications. The first part of this thesis is therefore dedicated to a discussion on various copper oxygenases and their model complexes. Recently, key reactive intermediates have emerged and among them mixed valent CuIICuIII species have been proposed to be responsible for strong C-H bond activation.In this work the stabilisation and spectroscopic characterisation of high valent intermediates using dinucleating ligands based on a 1,8-naphthyridine spacer are explored. The generation of Cu2:O2 species from the activation of O2 by CuI2 complexes is discussed. Two µ-ɳ2:ɳ2-peroxo-CuII2 complexes have been prepared at -80°C and characterised by spectroscopy and density functional theory (DFT). Our attempts at generating dinuclear systems using new dissymmetric ligands with an amide function are also discussed. Finally the successful characterisation of mixed valent CuIICuIII species by mono-electronic oxidation of CuII2 complexes is described (cyclic voltammetry, electron paramagnetic resonance, UV-visible, near infrared and DFT).The last part focusses on probing the reactivity of CuIICuIII species, for which the literature is almost inexistent. When sterically congested ligands are used to support the mixed valent system, intramolecular aliphatic C-H oxidation was observed, whether as the CuIICuIII species supported by a less bulky ligand was able to oxidise toluene. Interestingly the addition of a base made the system catalytic

Le superoxyde O2●- est une espèce réactive de l’oxygène produite par de nombreux métabolismes chez les espèces vivant en condition aérobie. Ses propriétés radicalaires font de O2●- une espèce très réactive capable d’endommager les macromolécules présentes dans les cellules, conduisant entre autre au stress oxydant et à de possibles troubles neurodégénératifs. Pour se protéger, la Nature utilise des enzymes, appelées superoxydes dismutases (SOD), qui sont chargées de catalyser la dismutation du superoxyde en oxygène et peroxyde d’hydrogène. La dernière qui fut découverte est la NiSOD qui comporte un ion nickel dans son site actif. Contrairement aux autres types de SOD, celle-ci n’est pas présente chez l’homme et ne l’est que chez certaines bactéries comme Chlamydiae. Ainsi, cibler la NiSOD est une méthode prometteuse pour le développement de nouveaux antibiotiques. De même, le développement de nouveaux complexes biomimétiques des SOD peut conduire à de nouveaux agents thérapeutiques contre les maladies liées au stress oxydant. Notre projet consiste à développer de nouveaux modèles actifs de la NiSOD, avec comme stratégie l’utilisation de ligands peptidiques. Les deux principaux objectifs sont (1) de développer des catalyseurs de type SOD, actifs dans l’eau, mais aussi (2) d’acquérir des informations supplémentaires sur le mécanisme mis en jeu lors de la catalyse par la NiSOD, afin de mettre en évidence les intermédiaires clés et les différences majeures entre la NiSOD et les autres SODs présentes chez l’homme. Nos résultats montrent qu’une bonne activité catalytique peut être obtenue même avec une sphère de coordination différente de celle de l’enzyme, et mettent en évidence des facteurs clés pour l’activité. De plus, des études mécanistiques tendent à montrer un mécanisme en sphère interne pour la réduction du superoxyde
The superoxide radical anion, O2●-, is generated by many life processes. Its radical properties make it a highly reactive species able to damage all macromolecules contributing to the pathogenesis of many diseases including neurodegenerative disorders. In order to protect cells against O2●-, Nature uses superoxide dismutases (SODs) which catalyze the dismutation of O2●- into hydrogen peroxide and oxygen. The last discovered SOD contains a nickel cofactor. Importantly the NiSOD is found in several pathogenic bacteria but not in humans. Therefore targeting the NiSOD is a promising approach to develop antibiotics. Secondly, the development of novel SOD mimics may have potential uses as therapeutic agents in oxidative stress-related diseases. Our project aims at developing innovative active NiSOD mimics, based on the use of peptide-based ligands with two main objectives: (i) to develop efficient SOD like catalysts, active in water, displaying antioxidant properties for potential therapeutic applications and (ii) to contribute to the full understanding of the catalytic mechanism of the NiSOD to highlight the specific key elements that differentiate NiSOD from the human MnSOD for the design of potential antibiotics. Our results show that, even with a coordination sphere different from the one in the enzyme, a good catalytic activity can be obtained. Key elements for the activity are also determined. Moreover, mechanistic studies indicates an inner sphere mechanism for superoxide reduction

Mes travaux de thèse ont consisté en l'élaboration de nouveaux catalyseurs répondant aux critères de la “chimie verte” dans le but de réaliser la catalyse asymétrique d'oxygénation de molécules organiques telles que les thioéthers et les alcènes. Ces nouveaux catalyseurs sont des hybrides bioinorganiques résultant de l'association d'une protéine et d'un complexe de fer. Notre choix s'est porté sur la protéine bactérienne NikA qui est capable de reconnaître le complexe Fe(EDTA). Nous avons synthétisé des complexes de fer possédant des ligands de type N2Py2 (deux amines et deux pyridines), un environnement propice pour avoir une chimie centrée sur le métal. Sur les amines, ont été greffés un ou deux groupements carboxyle pour permettre la reconnaissance avec NikA. Les études catalytiques menées sur ces complexes en oxydation d'alcènes et de thioéthers ont montré que la présence d'un seul groupement carboxyle altère peu l'activité du catalyseur, mais deux groupements carboxyle inhibent totalement la réactivité du complexe. L'obtention de la structure de l'un d'entre eux, ainsi que les analyses spectroscopiques nous ont montré des aspects singuliers de ces complexes, comme la coordination sur l'ion Fe(II) des groupements carboxyle par le carbonyle, et la formation de l'espèce Fe(II)Cl42-, en contre-ion, lorsque les complexes sont préparés à partir de Fe(II)Cl2. Les hybrides ont été testés en catalyse de sulfoxydation montrant une activité accrue sans (ou très peu) de production de sulfone, contrairement aux complexes correspondants avec lesquels autant de sulfoxyde que de sulfone se forme. En outre, nous avons observé au niveau de la structure cristallographique de certains des hybrides des configurations inédites pour ce type de complexes. Malheureusement, nous n'avons obtenu que de très faibles énantiosélectivités (ee = 11%). Pour pallier à ce problème, des expériences de mutagenèse dirigée, basées sur la structure cristallographique des hybrides et des études de docking, sont envisagées. Pour conclure, de nouvelles métalloenzymes artificielles ont été élaborées. Elles serviront de base pour de nouveaux systèmes plus optimisés.

Use of arsenic-rich groundwater for crop irrigation can increase the arsenic (As) content in food crops and act as a carcinogen, compromising human health. Using aquatic plant based phytofiltration is a potential eco-technique for removing arsenic from water. The aquatic moss species Warnstorfia fluitans grows naturally in mining areas in northern Sweden, where high concentrations of arsenic occur in lakes and rivers. This species was selected as a model for field, climate chamber and greenhouse studies on factors governing arsenic removal and arsenic phytofiltration of irrigation water. The arsenic and silicon (Si) concentrations in soil, water and plant samples were measured by AAS (atomic absorption spectrophotometry), while arsenite and arsenate species were determined using AAS combined with high pressure liquid chromatography (HPLC) with an anion exchange column. The arsenic content in grains of hybrid and local aromatic rice (Oryza sativa) cultivars with differing arsenic accumulation factor (AF) values was investigated in an arsenic hotspot in Bangladesh. The results showed that arsenic AF was important in identifying arsenic-safer rice cultivars for growing in an arsenic hotspot. The study based on silicon effect on arsenic uptake in lettuce showed that arsenic accumulation in lettuce (Lactuca sativa) could be reduced by silicon addition. The aquatic moss had good phytofiltration capacity, with fast arsenic removal of up to 82% from a medium with low arsenic concentration (1 µM). Extraction analysis showed that inorganic arsenic species were firmly bound inside moss tissue. Absorption of arsenic was relatively higher than adsorption in the moss. Regarding effects of different abiotic factors, plants were stressed at low pH (pH 2.5) and arsenic removal rate was lower from the medium, while arsenic efflux occurred in arsenate-treated medium at low (12°C) and high (30°C) temperature regimes. Besides these factors, low oxygenation increased the efficiency of arsenic removal from the medium. Finally, combining W. fluitans as a phytofilter with a lettuce crop on a constructed wetland significantly reduced the arsenic content in edible parts (leaves) of lettuce. Thus W. fluitans has great potential for use as an arsenic phytofilter in temperate regions.

QC 20170323

Asymmetric reductions are used to produce chiral molecules, which are important precursors for the pharmaceutical industry. Bio catalytic reductions often display high enantioselectivity without the cost and toxicity associated with metal catalysis. However, unlike metal catalysts which use H₂ directly, many useful redox-enzymes require the hydride donor NADH. NADH is expensive; therefore for a bio-catalytic process to be viable it must be recycled, usually by using a sacrificial carbon based substrate, generating super-stoichiometric amounts of waste. Two different methods for H₂-driven NADH recycling are explored in this project: using soluble hydrogenases (SH) and, carbon particles modified with a hydrogenase and an NAD⁺-reductase moiety. The conductive carbon particles allow electrons from H₂-oxidation to be channelled from the hydrogenase to the NAD⁺ reductase for reduction of NAD⁺. This project focuses on four main areas. The first looks at using the enzyme-modified particles for the production of high value chiral amines. A yield of >98% was achieved using the enzyme-modified particles with an L alanine dehydrogenase for H₂ driven conversion of pyruvate to L-alanine. Moreover, a faster rate of reaction was demonstrated with the L-alanine dehydrogenase immobilised on particles versus with the L-alanine dehydrogenase in solution. The second section focuses on elevated temperature NADH recycling: an SH and an NAD⁺-reductase from a thermophilic organism were characterised. The NAD+-reductase was subsequently used as part of a system for recycling NADH at >35 °C. When demonstrated in combination with an enoate-reductase a 62 % yield was obtained for the reduction of 2 methyl 2 cyclopentenone. In the third strand SHs and enzyme-modified particles were investigated as recycling systems for NADH analogues. In summary, this thesis expands the scope for application of H₂-driven biocatalytic reduction reactions.

The idea of utilizing nanomaterials in bio-related applications has been extensively practiced during the recent decades. Magnetic nanoparticles (MPs), especially superparamagnetic iron oxide nanoparticles have been demonstrated as promising candidates for biomedicine. A protective coating process with biocompatible materials is commonly performed on MPs to further enhance their colloidal and chemical stability in the physiological environment. Mesoporous hollow silica is another class of important nanomaterials that are extensively studied in drug delivery area for their ability to carry significant amount of guest molecules and release in a controlled manner. In this study, different synthetic approaches that are able to produce hybrid nanomaterials, constituting both mesoporous hollow silica and magnetite nanoparticles, are described. In a two-step approach, pre-synthesized magnetite nanoparticles are either covalently conjugated to the surface of polystyrene beads and coated with silica or embedded/enclosed in the porous shell during a nanosized CaCO3 templated condensation of silica precursors, followed by acid dissolution to generate the hollow structure. It was demonstrated that the hollow interior is able to load large amount of hydrophobic drugs such as ibuprofen while the mesoporous shell is capable of prolonged drug. In order to simplify the fabrication procedure, a novel in-situ method is developed to coat silica surface with magnetite nanoparticles. By refluxing the iron precursor with mesoporous hollow silica nanospheres in polyamine/polyalcohol mixed media, one is able to directly form a high density layer of magnetite nanoparticles on silica surface during the synthesis, leaving reactive amine groups for further surface functionalization such as fluorescence conjugation. This approach provides a convenient synthesis for silica nanostructures with promising potential for drug delivery and multimodal imaging. In addition to nanoparticles, nanowires also benefit the research and development of instruments in clinical diagnosis. Semiconductive nanowires have demonstrated their advantage in the fabrication of lab-on-a-chip devices to detect many charge carrying molecules such as antibody and DNA. In our study, In2O3 and silicon nanowire based field effect transistors were fabricated through bottom-up and top-down approaches, respectively, for ultrasensitive bio- detection of toxins such as ricin. The specific binding and non-specific interaction of nanowires with antibodies were also investigated.

Nanomaterials, typically less than 100 nm size in any direction have gained noteworthy interest from scientific community owing to their significantly different and often improved physical properties compared to their bulk counterparts. Semiconductor nanoparticles (NPs) are of great interest to study their tunable optical properties, primarily as a function of size and shape. Accordingly, there has been a lot of attention paid to synthesize discrete semiconducting nanoparticles, of where Group III-V and II-VI materials have been studied extensively. In contrast, Group IV and Group IV-V based nanocrystals as earth abundant and less-non-toxic semiconductors have not been studied thoroughly. From the class of Group IV, Ge1-xSnx alloys are prime candidates for the fabrication of Si-compatible applications in the field of electronic and photonic devices, transistors, and charge storage devices. In addition, Ge1-xSnx alloys are potentials candidates for bio-sensing applications as alternative to toxic materials. Tin phosphides, a class of Group IV-V materials with their promising applications in thermoelectric, photocatalytic, and charge storage devices. However, both aforementioned semiconductors have not been studied thoroughly for their full potential in visible (Vis) to near infrared (NIR) optoelectronic applications. In this dissertation research, we have successfully developed unique synthetic strategies to produce Ge1-xSnx alloy quantum dots (QDs) and tin phosphide (Sn3P4, SnP, and Sn4P3) nanoparticles with tunable physical properties and crystal structures for potential applications in IR technologies. Low-cost, less-non-toxic, and abundantly-produced Ge1-xSnx alloys are an interesting class of narrow energy-gap semiconductors that received noteworthy interest in optical technologies. Admixing of α-Sn into Ge results in an indirect-to-direct bandgap crossover significantly improving light absorption and emission relative to indirect-gap Ge. However, the narrow energy-gaps reported for bulk Ge1-xSnx alloys have become a major impediment for their widespread application in optoelectronics. Herein, we report the first colloidal synthesis of Ge1-xSnx alloy quantum dots (QDs) with narrow size dispersity (3.3±0.5 – 5.9±0.8 nm), wide range of Sn compositions (0–20.6%), and composition-tunable energy-gaps and near infrared (IR) photoluminescence (PL). The structural analysis of alloy QDs indicates linear expansion of cubic Ge lattice with increasing Sn, suggesting the formation of strain-free nanoalloys. The successful incorporation of α-Sn into crystalline Ge has been confirmed by electron microscopy, which suggests the homogeneous solid solution behavior of QDs. The quantum confinement effects have resulted in energy gaps that are significantly blue-shifted from bulk Ge for Ge1-xSnx alloy QDs with composition-tunable absorption onsets (1.72–0.84 eV for x=1.5–20.6%) and PL peaks (1.62–1.31 eV for x=1.5–5.6%). Time-resolved PL (TRPL) spectroscopy revealed microsecond and nanosecond timescale decays at 15 K and 295 K, respectively owing to radiative recombination of dark and bright excitons as well as the interplay of surface traps and core electronic states. Realization of low-to-non-toxic and silicon-compatible Ge1-xSnx QDs with composition-tunable near IR PL allows the unprecedented expansion of direct-gap Group IV semiconductors to a wide range of biomedical and advanced technological studies. Tin phosphides are a class of materials that received noteworthy interest in photocatalysis, charge storage and thermoelectric devices. Dual stable oxidation states of tin (Sn2+ and Sn4+) enable tin phosphides to exhibit different stoichiometries and crystal phases. However, the synthesis of such nanostructures with control over morphology and crystal structure has proven a challenging task. Herein, we report the first colloidal synthesis of size, shape, and phase controlled, narrowly disperse rhombohedral Sn4P3, hexagonal SnP, and amorphous tin phosphide nanoparticles (NPs) displaying tunable morphologies and size dependent physical properties. The control over NP morphology and crystal phase was achieved by tuning the nucleation/growth temperature, molar ratio of Sn/P, and incorporation of additional coordinating solvents (alkylphosphines). The absorption spectra of smaller NPs exhibit size-dependent blue shifts in energy gaps (0.88–1.38 eV) compared to the theoretical value of bulk Sn3P4 (0.83 eV), consistent with quantum confinement effects. The amorphous NPs adopt rhombohedral Sn4P3 and hexagonal SnP crystal structures at 180 and 250 °C, respectively. Structural and surface analysis indicates consistent bond energies for phosphorus across different crystal phases, whereas the rhombohedral Sn4P3 NPs demonstrate Sn oxidation states distinctive from those of the hexagonal and amorphous NPs owing to complex chemical structure. All phases exhibit N(1s) and ʋ(N-H) energies suggestive of alkylamine surface functionalization and are devoid of tetragonal Sn impurities.

A l'heure actuelle la recherche de nouvelles ressources énergétiques est un domaine en plein développement. Dans ce cadre, l'hydrogène moléculaire y a toute sa place et sera un vecteur énergétique majeur du XXIème siècle en permettant le stockage des énergies renouvelables. Cependant son utilisation est pour l'instant limitée à cause du coût élevé de sa production, industriellement basée sur le platine comme catalyseur. Un des enjeux majeurs de ce siècle est donc de trouver de nouveaux catalyseurs performants pour la production d'hydrogène et dont le coût soit suffisamment faible pour permettre un développement industriel. Les hydrogénases sont des enzymes catalysant la réduction de protons en hydrogène avec une grande efficacité et en conditions douces. Leurs sites actifs sont basés sur des métaux abondants comme le nickel ou le fer et ont des activités similaires au platine dans certaines conditions. Cependant quelques inconvénients, comme leur inactivation par l'oxygène ou encore le fait qu'il soit assez difficile de les produire sous forme active, limitent leur utilisation technologique. Dans ce contexte, la chimie bio-inspirée et la chimie biomimétique sont particulièrement prometteuses : prenant exemple sur la nature et plus particulièrement sur les sites actifs enzymatiques, elles permettent de développer de nouvelles familles de catalyseurs. On a pu ainsi développer des complexes dinucléaire nickel-fer ou encore des complexes de cobalt ayant une activité dans la catalyse de réduction de protons. Certains complexes de cobalt, les cobaloximes et les complexes diimine dioxime de cobalt ont ainsi montré de bonnes activités dans la réduction de protons en milieux organiques ou mixtes organiques/eau. Jusqu'alors cependant peu d'études ont été effectuées en milieux complétement aqueux. Nous pouvons aller plus loin dans cette démarche via une approche dite biosynthétique, qui vise à incorporer des catalyseurs inorganiques dans des enveloppes protéiques. Ces enveloppes protéiques peuvent, par différentes interactions, potentiellement améliorer la solubilité et la stabilité dans l'eau des catalyseurs inorganiques. La thèse qui suit se concentre sur cette approche et plus particulièrement sur la production, la caractérisation et l'étude de nouveaux hybrides entre différentes hémoprotéines (myoglobine et hème oxygénase en particulier) et différents complexes de cobalt (cobaloximes et complexe diimine dioxime de cobalt). Après avoir mis au point un protocole pour la production et la purification de la myoglobine de cachalot sans son cofacteur héminique, nous nous sommes intéressés à préparer et caractériser différents hybrides. Nous avons pu montrer par ce travail que les hémoprotéines dépourvues de leur cofacteur biologique ont une affinité particulière pour les complexes de cobalt et que la coordination de ces complexes inorganiques se fait via une seule histidine de la protéine hôte. Les hybrides ainsi obtenus ont montré une grande stabilité en solution. En plus de l'ajout d'un ligand histidine en axial du cobalt, l'enveloppe protéique permet de moduler la seconde sphère de coordination. Nous avons pu montrer au cours de ce projet que la nature de la protéine hôte module les caractéristiques spectroscopiques et électrochimiques du complexe de cobalt. Enfin ces hybrides ont montré d'une manière générale une activité catalytique pour la production et la photoproduction d'hydrogène dans l'eau, là encore avec une nette influence de la protéine hôte sur l'activité du complexe. Nous avons donc au cours de cette thèse préparé et caractérisé des systèmes hybrides pouvant être qualifiés d'hydrogénases artificielles.

abstract: Understanding the mechanisms of metalloproteins at the level necessary to engineer new functionalities is complicated by the need to parse the complex overlapping functions played by each amino acid without negatively impacting the host organism. Artificial or designed metallopeptides offer a convenient and simpler platform to explore metal-ligand interactions in an aqueous, biologically relevant coordination context. In this dissertation, the peptide SODA (ACDLPCG), a synthetic derivative of the nickel-binding pocket of nickel superoxide dismutase, is used as a scaffold to construct a variety of novel metallopeptides and explore their reactivity. In Chapter 2, I show that SODA binds Co(II) and the resulting peptide, CoSODA, reacts with oxygen in an unexpected two step process that models the biosynthesis of Co nitrile hydratase. First, the thiolate sulfur is oxidized and then the metallocenter is oxidized to Co(III). In Chapter 3, I show that both CoSODA and CuSODA form CN- adducts. Spectroscopic investigations of these metallopeptides are compared with data from NiSODA and Ni(CN)SODA to show the remarkable geometric versatility of SODA with respect to interactions with metallocenters. In Chapter 4, exploiting the propensity of sulfur ligands to form bridging structures, NiSODA is used as a metallosynthon to direct synthesis of hetero bi- and tri-metallic peptides as models for [NiFe]-hydrogenases and the A cluster of acetyl-CoA synthase carbon monoxide dehydrogenase. Building on this synthetic strategy, in Chapter 5, I demonstrate synthesis of NiRu complexes including a Ru(bipyridine)2 moiety and characterize their photochemistry.
Dissertation/Thesis
Ph.D. Chemistry 2012

Evasion of the immune system is a key hallmark of cancer progression. Developing strategies that diagnose early the immune-cancer synapse may lead to long term cures from these aggressive cancers. We aimed to develop optical endoscopic Raman imaging methodology to identify specific regions in the cancer-immune synapse currently beyond detection in vivo and improve survival of cancer patients. When these methodologies are made simpler and direct, success of implementation increases. This early stage detection reduces burden on both patients and physicians for better treatment management. Chapter 6 aimed in designing antibodies for cancer detection which can be applied for Raman Imaging. Instead of designing complete antibodies we aimed in designing recombinant antibodies namely single chain variable Fragment (scFv) to target Agr2/3 on cancer cells. ScFv hold many advantages than the complete antibodies. The problem was addressed in two different ways. (i) Imaging of Agr2/3 using Recombinant Antibodies: GFP labeled recombinant antibodies (scFv4) against Ag2/3 were designed and expressed in breast cancer cell line. Fluorescence live cell imaging was performed. After expression it was blotted against CD20, GFP and Agr2 to access their affinity towards the target. (ii) Purification of scFv7 for Agr2 identification-Towards Dipstick technology: scFv7 was expressed in bacteria and purified from them to make it identify from body fluids. scFv7 binding with Agr2 was analyzed using Elisa. Chapter 7 summarizes the thesis and brings out the key concepts by which the current study can be extended to diverse applications. Identification of bacterial infection and cancer are few of the challenges the posted by health care sectors. We hope in the near future that the vibrational microspectroscopic techniques like IR and Raman may transcend the current diagnostic methods and emerge as a rapid, sensitive and specific tool. Moreover, with the advent of many machine learning methods these techniques can be close to complete automation in diagnosis and screening programs which reduces the burden on technicians and physicians who have to handle large amount of samples in countries like India

Interacting cellular systems with nano-interfaces has shown great promise in promoting differentiation, regeneration, and stimulation. Functionalized nanostructures can serve as topological cues to mimic the extracellular matrix network to support cellular growth. Nanostructures can also generate signals, such as thermal, electrical, and mechanical stimulus, to trigger cellular stimulation. At this stage, the main challenges of applying nanostructures with biological systems are: (1) how to mimic the hierarchical structure of the ECM network in a 3D format and (2) how to improve the efficiency of the nanostructures while decreasing its invasiveness. To enable functional neuron regeneration after injuries, we have developed a 2D nanoladder scaffold, composed of micron size fibers and nanoscale protrusions, to mimic the ECM in the spinal cord. We have demonstrated that directional guidance during neuronal regeneration is critical for functional reconnection. We further transferred the nanoladder pattern onto biocompatible silk films. We established a self-folding strategy to fabricate 3D silk rolls, which is an even closer system to mimic the ECM of the spinal cord. As demonstrated by in vitro and in vivo experiments, such a scaffold can serve as a grafting bridge to guide axonal regeneration to desired targets for functional reconnection after spinal cord injuries. Benefited from the robust self-folding techniques, silk rolls can also be used for heterogeneous cell culture, providing a potential therapeutic approach for multiple tissue regeneration directions, such as bones, muscles, and tendons. For achieving neurostimulation, we have developed photoacoustic nanotransducers (PANs), which generate ultrasound upon excitation of NIR II nanosecond laser light. By surface functionalize PAN to bind to neurons, we have achieved an optoacoustic neuron stimulation process with a high spatial and temporal resolution, proved by in-vitro and in-vivo experiments. Such an application can enable non-invasive, optogenetics free and MRI compatible neurostimulation, which provides a new direction of gene-transfection free neuromodulation. Collectively, in this thesis, we have developed two systems to promote functional regeneration after injuries and stimulate neurons in a minimally invasive manner. By integrating those two functions, a potential new generation of the bioengineered scaffold can be investigated to enable functional and programmable control during the regeneration process.