In this thesis, we investigate the entanglement and magnetic properties of frustrated spin systems and correlated electronic properties of conjugated carbon systems. In chapter 1, we present different approaches to solve the time-independent, nonrelativistic Schr¨odinger equation for a many-body system. We start with the full non-relativistic Hamiltonian of a multi nuclear system to describe the Born - Oppenheimer approximation which allows the study of electronic Hamiltonian which treats nuclear positions parametrically. We then also describe ab initio techniques such as the Hartree-Fock Method and density functional theories. We then introduce model Hamiltonians for strongly correlated systems such as the Hubbard, Pariser-Parr-Pople and Heisenberg models, and show how they result from the noninteracting one-band tight-binding model. In chapter 2, we discuss various numerical techniques like the exact diagonalization methods and density matrix renormalization group (DMRG) method. We also discuss quantum entanglement and the success of DMRG which can be attributed to the area law of entanglement entropy. In chapter 3, we study here different regions in phase diagrams of the spin-1/2, spin-1 and spin-3/2 one-dimensional antiferromagnetic Heisenberg systems with nearest-neighbor (J1) and next-nearest-neighbor (J2) interactions and dimerization (d ). Frustration arises for specific relative signs of the interactions J1 and J2. In particular, we analyze the behavior of the bipartite entanglement entropy and fidelity at the gapless to gapped phase transitions and across the lines separating different phases in the J2−d plane. All the calculations in this work are based on exact diagonalizations of finite systems. In chapter 4, we study Heisenberg spin-1/2 and spin-1 chains with alternating ferromagnetic (JF 1 ) and antiferromagnetic (JA 1 ) nearest-neighbor interactions and a ferromagnetic next-nearest-neighbor interaction (JF 2 ). In this model frustration is present due to non-zero JF 2 . The model with site spin s behaves like a Haldane spin chain with site spin 2s in the limit of vanishing JF 2 and large JF 1 /JA 1 . We show that the exact ground state of the model can be found along a line in the parameter space. For fixed JF 1 , the phase diagram in the space of JA 1 −JF 2 is determined using numerical techniques complemented by analytical calculations. A number of quantities, including the structure factor, energy gap, entanglement entropy and zero temperature magnetization, are studied to understand the complete phase diagram. An interesting and potentially important feature of this model is that it can exhibit a macroscopic magnetization jump in the presence of a magnetic field; we study this using an effective Hamiltonian. In chapter 5, we study correlated electronic properties of zigzag and armchair fused naphthalenes and polyperylene systems in the presence of long-range electronelectron interactions. We find that the ground state of zigzag fused naphthalene system is a higher spin state, while the ground state of armchair fused naphthalene is a singlet. The spin gap of polyperylene is unusually small and the ground state is a singlet. Our calculations of optical gap and two-photon gap suggest that polyperylene should exhibit fluorescence. From the charge gap calculation, we predict that in zigzag fused naphthalene and polyperylene systems, excitons are weakly binding. Peierls type of distortion is negligible in zigzag fused naphthalene and polyperylene systems, however, in armchair fused naphthalene system, interior bonds have tendency to distort in low-lying excited states. In chapter 6, we study the ground state spin of the Heisenberg spin-1/2 nearestneighboring antiferromagnetic exchange models of systems with fused odd member rings. In particular, we compute the ground state spin of fused three and five membered rings as well as fused five membered rings. In the thermodynamic limit, the ground state of the fused three and five membered system is a higher spin state, while fused five membered system shows a singlet ground state, for all system sizes.

<p align="justify">Plusieurs métaux de notre vie courante sont obtenus industriellement au moyen de procédés électrolytiques. Un des procédés les plus communs est l’électro-obtention de cuivre, dans lequel le métal est déposé à la cathode tandis que l'oxygène se dégage à l'anode. Généralement, en usine, plusieurs anodes et cathodes, ayant une surface de 1 m2 et séparées par plus ou moins 10 cm sont alternées dans une cellule contenant une solution d'acide sulfurique riche en sulfate de cuivre. En fonction des conditions d'utilisation, les cathodes sont remplacées, après un certain temps, par des nouvelles de façon à récupérer le cuivre déposé. De ce fait, les anodes doivent être capables de résister sans se corroder, se déformer ou perdre leurs propriétés électrocatalytiques pendant de longues périodes. Au début, des alliages en Pb (pb-Ag, Pb-Ca-Sn,) ont été utilisés comme anodes. Malheureusement, malgré leur faible prix, ces anodes présentent des surtensions élevées et une faible résistance à la corrosion et au fluage. Par conséquent, une alternative aux anodes traditionnelles en 1 développée. Ce nouveau type d'anode, connu sous le nom d’anode dimensionnellement stable (DSA) est fabriquée à partir d'une tôle en Ti recouverte par un mélange d'oxydes de métaux nobles catalysant la réaction de dégagement d'oxygène. Différentes techniques peuvent être utilisées pour préparer la couche d'oxyde. La technique la plus souvent employée consiste à décomposer thermiquement une solution de chlorures contenant un ou plusieurs nobles. Malheureusement, ce type d'anode est cher et a tendance à perdre son activité électrocatalytique avec le temps.</p><p><p align="justify">Dans le but de produire une DSA à faible prix, pouvant résister de longues périodes sans se passiver, un nouveau type de DSA a été développé dans le présent travail. Cette anode est produite par électrodépôt d'un métal noble dans les pores d'un substrat microporeux en Ti/TiO2.</p><p><p align="justify">Ce travail a permis de démontrer qu'une DSA avec une concentration en métal noble peut être obtenue par la voie proposée. Il a été montré que les propriétés électriques et électrochimiques de ces DSAs sont directement liées aux caractéristiques morphologiques et structurales du en Ti/TiO2. Lorsque la couche barrière existant au fond des pores est suffisamment fine et que le film présente des défauts, la résistance me l'interface Ti/métal noble est faible. Ceci abouti à des DSAs possédant d'excellentes propriétés électrocatalytiques. Les DSAs optimales sont capables de résister à des conditions similaires à celles employées en industrie avec des surtensions de ~ 0.4 V, ce qui représente un gain de 50% par rapport aux surtensions normalement atteintes par les anodes traditionnelles en Pb.</p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Quantum mechanics became a foundation for incessant development of versatile computational methods for analysis of chemical and physical properties of molecules and crystals. A huge progress has been made in the fifield of density functional theory, since nowadays this theory offers the best compromise between precision of results and efficiency fiof computation. The chemical bonding analysis can be easily performed with real space methods based on chemical concepts introduced via partitioning of real space into chemically meaningful domains, since the orbital based approach is not well applicable due to the delocalized nature of plane waves. However the practical usage of those methods often requires a signifificant amount of computational resources. Some methods require the evaluation of so called domain overlap matrices, that is a formidable task for complex and low-symmetry systems. In the present research the author enables the investigation of complex solid compounds with real space chemical bonding indicators by introducing the derivation of the expression for the evaluation of the domain overlap matrix elements from the projected-augmented wave method. The corresponding program module was developed, which is capable to perform the real space chemical bonding analysis with a number of methods, like electron localizability indicators, electron localization function, localization/delocalization indices and domain averaged Fermi hole orbitals. The efficiency and the accuracy of the developed implementation is demonstrated by the comparison with the domain overlap matrix elements evaluation from the full-potential linearized augmented plane wave method on a set of simple compounds with three atoms per primitive cell at most. A set of complex periodic structures is analyzed and the capability of the present implementation to unravel intricate chemical bonding patterns is demonstrated.

Transition metals (TMs) are ‘elements whose atoms have partially filled d-shell, or which can give rise to cations with an incomplete d-shell’. In TMs, the d-shell overlaps with next higher s-shell. Most of the TMs exhibit more than one (multiple) oxidation states. Some TMs, such as silver and gold, occur naturally in their metallic state but, most of the TM minerals are generally oxides. Most of the minerals on the planet earth are metal oxides, because of large free energies of formation for the oxides. The thermodynamic stability of the oxides is determined from the Ellingham diagram. Ellingham diagram shows the temperature dependence of the stability (free energy) for binaries such as metal oxides. Ellingham diagram also shows the ease of reducibility of metal oxides. TM oxides of general formulas MO, M2O3, MO2, M2O5, MO3 are known to exist, many of them being the ultimate products of oxidation in air in their highest oxidation states. In addition, TM oxides also exist in lower oxidation states which are prepared under controlled conditions. The nature of bonding in these oxides varies from mainly ionic (e.g. NiO, CoO) to mainly covalent (e.g. OsO4). Simple binary oxides of the compositions, MO, generally possess the rock salt structure (e.g. NiO), while the dioxides, MO2, possess the rutile structure (e.g. TiO2); many sesquioxides, M2O3, possess the corundum structure (e.g. Cr2O3). TMs form important ternary oxides like perovskites (e.g. CaTiO3), spinels (e.g. MgFe2O4) and so on. In TM oxides, the valence (outer) d-shell could be empty, d0 (e. g. TiO2), partially filled, dn (1≤ n≤ 9) (e.g. TiO, VO, NiO etc.) or completely filled, d10 (e.g. ZnO, CdO, Cu2O etc.). The outer d electrons in TM oxides could be localized or delocalized. Localized outer d electrons give insulators/semiconductors, while delocalized/itinerant d electrons make the TM oxide ‘metallic’ (e.g. ReO3, RuO2). Partially filled dn states are normally expected to give rise to itinerant (metallic) electron behaviour. But most of TM oxides with partially filled d shell are insulators because of special electronic energy (correlation energy) involved in d electron transfer to adjacent sites. Such insulating TM oxides are known as Mott insulators (e. g. NiO, CoO etc.). Certain TM oxides are known to exhibit both localized (insulating) and itinerant (metallic) behaviour as a function of temperature or pressure. For example, VO2 shows a insulator–metal transition at ~340K. Similar transitions are also known for V2O3, metal-rich EuO and so on. The chemical composition and bonding of TM oxides, which determine the crystal and electronic structures, give rise to functional properties. Table 1 gives representative examples. Properties like ionic conductivity and diffusion are governed by both the crystal structure and the defect structure (point defects), whereas properties such as magnetism and electron transport mainly arise from the electronic structures of the materials. Accordingly, TM oxides provide a platform for exploring functional materials properties. Among the various functional materials properties exhibited by transition metal oxides, the present thesis is devoted to investigations of lithium ion battery cathodes, inorganic pigments and magnetic perovskites. Over the years, most of the lithium containing first row transition metal oxides of rock salt derived structure have been investigated for possible application as cathode materials in lithium ion batteries (LIBs). First major breakthrough in LIBs research was achieved by electrochemically deinserting and inserting lithium in LiCoO2. A new series of cathode materials for LIBs were prepared by incorporating excess lithium into the transition metal containing layered lithium oxides through solid solution formation between Li2MnO3–LiMO2 (M = Cr, Mn, Fe, Co, Ni), known as lithium-rich layered oxides (LLOs). LLOs exhibit improved electrochemical performance as compared to the corresponding end members and hence received significant attention as a potential next generation cathode materials for LIBs in recent times. LiCoO2 (R-3m) crystallizes in the layered α-NaFeO2 structure with the oxygens in a ccp arrangement. Li+ and Co3+ ions almost perfectly order in the octahedral sites (3a and 3b) to give alternating (111) planes of LiO6 and CoO6 octahedra. Table 1. Materials properties exhibited by representative TM oxides. Property Example(s) Ferroelectricity BaTiO3, PbTiO3, Bi4Ti3O12 Nonlinear Optical Response LiNbO3 Multiferroic response BiFeO3, TbMnO3 Microwave dielectric properties Ba3ZnTa2O9 Relaxor Dielectric Properties Pb3MgNb2O9, Colossal Magnetoresistance Tl2Mn2O7 Metallic ‘Ferroelectricity’ Cd2Re2O7 Superconductivity AOs2O6(A = K, Rb, Cs) Redox deinsertion/insertion of LiCoO2 lithium Photocatalysis/water splitting TiO2 Pigment Ca(1-x)LaxTaO(2-x)N1+x (yellow-red), YIn1-xMnxO3 (blue) Metallic Ferromagnetism CrO2 Antiferromagnetism NiO, LaFeO3 Zero thermal expansion ZrW2O8 The reversible capacity of LiCoO2 in common LIBs is relatively low at around 140 mA h g-1 (half of theoretical capacity), corresponding to: LiCo3+O2 → Li0.5Co3+0.5Co4+0.5O2 + 0.5Li+ + 0.5e– . Substitution of one or more transition metal ions in LiCOO2 has been explored to improve the electrochemical performance. The structure of LLOs is described as a solid solution or nano composite of Li2MnO3 (C2/m) and LiMO2 (R-3m). The electrochemical deinsertion/insertion behaviour of LLOs is complex and also not yet understood completely. The present thesis consists of four parts. After a brief introduction (Part 1), Part 2 is devoted to materials for Li-ion battery cathode, consisting of three Chapters 2.1, 2.2 and 2.3. In Chapter 2.1, we describe the synthesis, crystal structure, magnetic and electrochemical characterization of new LiCoO2 type rock salt oxides of formula, Li3M2RuO6 (M = Co, Ni). The M =Co oxide adopts the LiCoO2 (R-3m) structure, whereas the M = Ni oxide also adopts a similar layered structure related to Li2TiO3. Magnetic susceptibility measurements reveal that in Li3Co2RuO6, the oxidation states of transition metal ions are Co3+, Co2+ and Ru4+, whereas in Li3Ni2RuO6, the oxidation states are Ni2+ and Ru5+. Li3Co2RuO6 orders antiferromagnetically at ~10K. On the other hand, Li3Ni2RuO6 presents a ferrimagnetic behaviour with a Curie temperature of ~100K. Electrochemical Li-deinsertion/insertion studies show that high first charge capacities (between ca.160 and 180 mA h g−1) corresponding to ca.2/3 of theoretical capacity are reached albeit, in both cases, capacity retention and cyclability are not satisfactory. Chapter 2.2 presents a study of new ruthenium containing LLOs, Li3MRuO5 (M = Co and Ni). Both the oxides crystallize in the layered LLO type LiCoO2 (α-NaFeO2) structure consisting of Li[Li0.2M0.4Ru0.4]O2 layers. Magnetic susceptibility data suggest that the oxidation states of transition metals are Li3Co3+Ru4+O5 for the M = Co compound and Li3Ni2+Ru5+O5 for the M = Ni compound. Electrochemical investigations of lithium deintercalation–intercalation behaviour reveal that both Co and Ni phases exhibit attractive specific capacities of ca. 200 mA h g-1 at an average voltage of 4 V, that has been interpreted as due to the oxidation of Co3+ and Ru4+ in Li3CoRuO5 and Ni2+ to Ni4+ in the case of Li3NiRuO5. Thus, we find that ruthenium plays a favourable role in LLOs than in non-LLOs in stabilizing higher reversible electrochemical capacities. In Chapter 2.3, we describe the synthesis, crystal structure and lithium deinsertion–insertion electrochemistry of two new LLOs, Li3MRuO5 (M=Mn, Fe) which are analogs of the oxides described in Chapter 2.2. The Li3MnRuO5 oxide adopts a structure related to Li2MnO3 (C2/m), while the Li3FeRuO5 oxide adopts a near-perfect LiCoO2 (R-3m) structure. Lithium electrochemistry shows typical behaviour of LLOs for both oxides, where participation of oxide ions in the electrochemical processes is observed. A long first charge process with capacities of 240 mA h g-1 (2.3 Li per f.u.) and 144 mA h g-1 (1.38 Li per f.u.) is observed for Li3MnRuO5 and Li3FeRuO5, respectively. Further discharge–charge cycling points to partial reversibility. X-ray photoelectron spectroscopy (XPS) characterisation of both pristine and electrochemically oxidized Li3MRuO5 reveals that in the Li3MnRuO5 oxide, Mn3+ and Ru4+ are partially oxidized to Mn4+ and Ru5+ in the sloping region at low voltage, while in the long plateau, O2- is also oxidized. In the Li3FeRuO5 oxide, the oxidation process appears to affect only Ru (4+ to 5+ in the sloping region) and O2- (plateau), while Fe seems to retain its 3+ state. Another characteristic feature of TMs is formation of several coloured solid materials where d–d transitions, band gap transitions and charge transfer transitions are involved in the colouration mechanism. Coloured TM oxides absorbing visible light find important applications as visible light photocatalyst (for example, yellow BiVO4 for solar water splitting and red Sr1-xNbO3 for oxidation of methylene blue) and inorganic pigments [for example, Egyptian blue (CaCuSi4O10), Malachite green (Cu2CO3(OH)2), Ochre red (Fe2O3)]. Pigments are applied as colouring materials in inks, dyes, paints, plastics, ceramic glazers, enamels and textiles. In this thesis, we have focused on the coloured TM oxides for possible application as inorganic pigments. Generally, colours arise from electronic transitions that absorb visible light. Colours of the inorganic pigments arise mainly from electronic transitions involving TM ions in various ligand fields and charge transfer transitions governed by different selection rules. The ligand field d–d transitions are parity forbidden but are relaxed due to various reasons, such as distortion (absence of center of inversion) and vibronic coupling. The d-electrons can be excited by light absorption in the visible region of the spectrum imparting colour to the material. Charge transfer transitions in the visible region are not restricted by the parity selection rules and therefore give intense colours. Here we have investigated the colours of manganese in unusual oxidation state (Mn5+) as well as the colours of different 3d-TM ions in distorted octahedral and trigonal prismatic sites in appropriate colourless crystalline host oxides. These results are discussed in Part 3 of the thesis. In Chapter 3.1, we describe a blue/green inorganic material, Ba3(P1−xMnxO4)2 (I) based on tetrahedral Mn5+O4 :3d2 chromophore. The solid solutions (I) which are sky-blue and turquoise-blue for x ≤ 0•25 and dark green for x ≥ 0•50, are readily synthesized in air from commonly available starting materials, stabilizing the Mn5+O4 chromophore in an isostructural phosphate host. We suggest that the covalency/ionicity of P–O/Mn–O bonds in the solid solutions tunes the crystal field strength around Mn(V) such that a blue colour results for materials with small values of x. The material could serve as a nontoxic blue/green inorganic pigment. In Chapter 3.2, an experimental investigation of the stabilization of the turquoise-coloured Mn5+O4 chromophore in various oxide hosts, viz., A3(VO4)2 (A = Ba, Sr, Ca), YVO4, and Ba2MO4 (M = Ti, Si), has been carried out. The results reveal that substitution of Mn5+O4 occurs in Ba3(VO4)2 forming the entire solid solution series Ba3(V1−xMnxO4)2 (0 < x ≤ 1.0), while, with the corresponding strontium derivative, only up to about 10% of Mn5+O4 substitution is possible. Ca3(VO4)2 and YVO4 do not stabilize Mn5+O4 at all. With Ba2MO4 (M = Ti, Si), we could prepare only partially substituted materials, Ba2M1−xMn5+xO4+x/2 for x up to 0.15, that are turquoise-coloured. We rationalize the results that a large stabilization of the O 2p-valence band states occurs in the presence of the electropositive barium that renders the Mn5+ oxidation state accessible in oxoanion compounds containing PO43−, VO43−, etc. By way of proof-of-concept, we synthesized new turquoise-coloured Mn5+O4 materials, Ba5(BO3)(MnO4)2Cl and Ba5(BO3)(PO4)(MnO4)Cl, based on the apatite – Ba5(PO4)3Cl – structure. Chapter 3.3 discusses crystal structures, and optical absorption spectra/colours of 3d-transition metal substituted lyonsite type oxides, Li3Al1-xMIIIx(MoO4)3 (0< x ≤1.0) (MIII = Cr, Fe) and Li3-xAl1-xMII2x(MoO4)3 (0< x ≤1.0) (MII = Co, Ni, Cu). Crystal structures determined from Rietveld refinement of PXRD data reveal that in the smaller trivalent metal substituted lyonsite oxides, MIII ions occupy the octahedral (8d, 4c) sites and the lithium ions exclusively occur at the trigonal prismatic (4c) site in the orthorhombic (Pnma) structure; on the other hand, larger divalent cations (CoII/CuII) substituted derivatives show occupancy of CoII/CuII ions at both the octahedral and trigonal prismatic sites. We have investigated the colours and optical absorption spectra of Li3Al1-xMIIIx(MoO4)3 (MIII = Cr, Fe) and Li3-xAl1-xMII2x(MoO4)3 (MII = Co, Ni, Cu) and interpreted the results in terms of average crystal field strengths experienced by MIII/MII ions at multiple coordination geometries. We have also identified the role of metal-to-metal charge transfer (MMCT) from the partially filled transition metal 3d orbitals to the empty Mo – 4d orbitals in the resulting colours of these oxides. B The ABO3 perovskite structure consists of a three dimensional framework of corner shared BO6 octahedra in which large A cation occupies dodecahedral site, surrounded by twelve oxide ions. The ideal cubic structure occurs when the Goldschmidt’s tolerance factor, t = (rA + rO)/{√2(rB + rO)}, adopts a value of unity and the A–O and B–O bond distances are perfectly matched. The BO6 octahedra tilt and bend the B – O – B bridges co-operatively to adjust for the non-ideal size of A cations, resulting deviation from ideal cubic structure to lower symmetries. Ordering of cations at the A and B sites of perovskite structure is an important phenomenon. Ordering of site cations in double (A2BB'O6) and multiple (A3BB'2O9) perovskites give rise to newer and interesting materials properties. Depending upon the constituent transition metals and ordering, double perovskite oxides exhibit a variety of magnetic behaviour such as ferromagnetism, ferrimagnetism, antiferromagnetism, spin-glass magnetism and so on. We also have coupled magnetic properties such as magnetoresistance (Sr2FeMoO6), magnetodielectric (La2NiMnO6) and magnetooptic (Sr2CrWO6) behaviour. Here we have investigated new magnetically frustrated double perovskite oxides of the formula Ln3B2RuO9(B = Co, Ni and Ln = La, Nd). The Chapter 4.1 describes Ln3B2RuO9 (B = Co, Ni and Ln = La, Nd) oxides (prepared by a solid state metathesis route) which adopt a monoclinic (P21/n) A2BB'O6 double perovskite structure, wherein the two independent octahedral 2c and 2d sites are occupied by B2+ and (B2+1/3Ru5+2/3) atoms, respectively. Temperature dependence of the molar magnetic susceptibility plots obtained under zero field cooled (ZFC) condition exhibit maxima in the temperature range 25–35K, suggesting an antiferromagnetic interaction in all these oxides. Ln3B2RuO9 oxides show spin-glass behavior and no long-range magnetic order is found down to 2 K. The results reveal the importance of competing nearest neighbour (NN), next nearest neighbor (NNN) and third nearest neighbour (third NN) interactions between the magnetic Ni2+/Co2+ and Ru5+ atoms in the partially ordered double perovskite structure that conspire to thwart the expected ferromagnetic order in these materials.

My thesis is divided into five chapters, starting with a general introduction in first chapter and sample preparation and protein-NMR assignment techniques in second chapter. The remaining three chapters focus on three different areas/projects that I have worked on. Chapter 1: Introduction to nanomaterials and all the experimental techniques This chapter reviews different kinds of nanomaterials and their application utilized for protein-nanomaterial interaction in our study, along with the introduction to different spectroscopy and microscopy techniques used for the interaction studies. Starting with introduction of nanomaterials and all the experimental techniques, which constitute the arsenal for structural studies of the protein-nanomaterial interaction, different steps enroute to structural and dynamic interaction are outlined in detail. Chapter 2: Preparation and Characterization of Proteins used for nanomaterial interaction studies Proteins are generally of three kinds- globular (structured), intrinsically disordered and membrane bound. These proteins have different functions in living organisms and play a major role to maintain metabolism and other important factors. To probe protein-nanomaterial interactions, we have chosen different protein/peptides. This chapter describes the protocol/procedure used for purifying the proteins. For studying a globular protein, ubiquitin was chosen. Nanomaterial-IDP interaction was investigated using the intrinsically disordered central linker domain of human insulin like growth factor binding protein-2 (L-hIGFBP2). The hydrophobic membrane interacting part of the prion protein was chosen as a representative membrane protein. The characterization of the proteins by NMR spectroscopy is also described. Chapter 3: A nanomaterial based novel macromolecular crowding agent Carbon quantum dots (CQD) are nanomaterials with size less than 10 nm, first obtained in 2004 during purification of single-walled carbon-nanotubes. Since then CQDs have been used in a wide range of applications due to their low cost of preparation and favorable properties such as chemical inertness, biocompatibility, non-toxicity and solubility in aqueous medium. One of the applications of CQDs has been their use for imaging and tracking proteins inside cells, based on their intrinsic fluorescence. Further, quantum dots exhibit concentration dependent aggregation while retaining their solubility. Fluorescent carbon quantum dots (CQD) induce macromolecular crowding making them suitable for probing the structure, function and dynamics of both hydrophilic and hydrophobic peptides/ proteins under near in-cell conditions. We have prepared hydrophilic and hydrophobic quantum dots to see the crowding effect. After characterization of CQD, we tested the property of proteins with CQD and found that CQD behaves as a macromolecular crowding agent by mimicking near in-cell conditions. In our study, we have chosen a globular protein, an intrinsically disordered protein (IDP) and one hydrophobic membrane peptide. We have also compared the crowding property of CQD with ficoll which is widely used commercial crowding agent. The overall study tells that the CQD acts like crowding agent and can be used for the study of macromolecular crowding effect. This makes them suitable for structural and functional studies of proteins in near in-cell conditions. Chapter 4: Ubiquitin-Graphene oxide interactions Described here is the interaction of human ubiquitin with GO using NMR spectroscopy and other techniques such as Fluorescence spectroscopy, isothermal titration calorimetry (ITC), UV-Visible spectroscopy, dynamic light scattering (DLS), zeta potential measurements and transmission electron microscopy (TEM). The globular protein ubiquitin interacts with GO and undergoes a dynamic and reversible association-dissociation in a fast exchange regimen as revealed by NMR spectroscopy. The conformation of the protein is not affected and the primary interaction is seen to be electrostatic in nature due to the polar functional groups present on the protein and GO sheet surface. For the first time we have shown that the interaction between ubiquitin and GO is dynamic in nature with fast and reversible adsorption/desorption of protein from the surface of GO. This insight will help in understanding the mechanistic aspects of interaction of GO with cellular proteins and will help in designing appropriate functionalized graphene oxide for its biological application. Chapter 5: Section A: Interaction of an intrinsically disordered protein (L-HIGFBP2) with graphene oxide The interaction between intrinsically disordered linker domain of human insulin-like growth factor binding protein-2 (L-hIGFBP2) with GO was studied using NMR spectroscopy and other techniques such as isothermal titration calorimetry (ITC), dynamic light scattering (DLS), zeta-potential measurements. The study revealed that the disordered protein L-hIGFBP2 interacts with GO through electrostatic interaction and undergoes a dynamic and reversible association-dissociation in a fast exchange regime. The conformation of the protein is not affected. Section B: Stability of an Intrinsically disordered protein through weak interaction with Silver nanoparticles Using NMR spectroscopy and other techniques we probed the mechanism of L-hIGFBP2–AgNP interactions which render the IDP stable. The study reveals a mechanism which involves a relatively fast and reversible association–dissociation of L-hIGFBP2 (dynamic exchange) from the surface of AgNP. The AgNP–L-hIGFBP2 complex remains stable for more than a month. The techniques employed in addition to NMR include UV-Visible spectroscopy, dynamic light scattering (DLS), zeta potential measurements and transmission electron microscopy (TEM) to probe the protein-AgNP interaction here in this section.

Highly selective and sensitive phosphate sensors have been fabricated by constructing a solid membrane disk consisting of variable mixtures of aluminium powder (Al), aluminium phosphate (AlPO4) and powdered copper (Cu). Both binary and ternary electrode systems are produced depending on their composition. The ternary membranes exhibit greater selectivity over a wide range of concentrations. The ternary electrode with the composition 25% AlPO4, 25% Cu and 50% Al was selected as our preferred electrode. The newly fabricated ternary membrane phosphate selective electrodes exhibited linear potential response in the concentration range of 1.0 × 10−6 to 1.0 × 10−1 mol L−1. The electrodes also exhibit a fast response time of <60 s. Their detection limit is 1.0 × 10−6 mol L−1. The unique feature of the described electrodes is their ability to maintain a steady and reproducible response in the absence of an ionic strength control. The electrodes have a long lifetime and can be stored in air when not in use. The selectivity of the new phosphate selective electrodes with respect to other common ions is excellent. The results obtained provide further insight into the working principles of the newly fabricated phosphate selective electrodes. Dephosphorylation and phosphorylation reactions were monitored using the preferred phosphate selective electrode. The following reactions were studied and inferences drawn; (a) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[OH(PO2O)]2- for 1:1, 2:1 and 3:1 *[{CoN4(OH)(OH2)}]2+ to *[OH(PO2O)]2- ratios.(b) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[O2NC6H4PO2(O)(OH)]- for 1:1, 2:1 and 3:1 *[{CoN4(OH)(OH2)}]2+ to *[O2NC6H4PO2(O)(OH)]- ratios. (c) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[(OH)2(PO2)2O]2- for 1:1, 2:1 and 3:1 [{CoN4(OH)(OH2)}]2+ to *[(OH)2(PO2)2O]2- ratios, and (d) the reactions between *[{CoN4(OH)(OH2)}]2+ and *[(OH)2(PO2)3O2]3- for the 1:1, 2:1 and 3:1 [{CoN4(OH)(OH2)}]2+ to *[(OH)2(PO2)3O2]3- ratios. Further insight into dephosphorylation and phosphorylation reactions is unravelled by the novel phosphate selective electrode monitoring. *For clarity of the complexes utilized, see chapter 4, table 4.1. KEY WORDS; Dephosphorylation, phosphorylation, ion selective electrodes, phosphate ion selective electrode, decontamination, electromotive force, potential difference, activity, concentration, selectivity coefficient, calibration, ionic strength, hydrolysis, inorganic phosphates, nitrophenylphosphate, pyrophosphate, tripolyphosphate, organophosphate esters. / Chemistry / D. Phil (Chemistry)

<div>The global demand for energy of mankind, the ever-increasing cost of energy, and the expected depletion of fossil energy carriers within the next centuries urge the exploration of alternative and more sustainable ways to provide energy. The current quest for energy-efficient technologies for the replacement of existing cooling devices has made the magnetocaloric effect a field of current scientific interest. Cooling technologies based on magnetic refrigerants are expected to have a better environmental impact compared with those based on the gas compression-expansion cycle. This technology provides an alternative for refrigeration applications with advantages, such as high energy efficiency, environmental friendliness, and low power consumption. In search of promising magnetocaloric materials, several rare earth-depleted transition metal-based materials were designed and investigated.</div><div>In this work, RCrxAl2-x and RZnAl (R = Gd, Tb, Dy, Ho) belonging to the ternary rare-earth transition-metal Laves phases, were chosen as the starting point to establish the effect of valence electron concentration (VEC) on the magnetic behavior and magnetocaloric effect. Our result and the results from the previously studied RTAl phases (T = Cu, Ni, Co, Fe, Mn) shows that the perturbation of the valence electron concentration at the Fermi level is found to be the driving force that dictates the crystal structure, magnetocaloric and magnetic properties of these systems. Most notably, the decrease in the valence electron concentration at the Fermi level leads to an increase in the curie temperature.</div><div>In addition, we have further extended this theory to GdNiAl2 systems. GdNiAl2 is a known magnetocaloric material which exhibits an isothermal magnetic entropy change of ΔSM = 16.0 Jkg-1K-1 at TC = 28K under a magnetic field change from 0-5T. However, the low TC limits its application as a room temperature refrigerant. We, therefore, substituted Co for (Ni/Al) in the structure of GdNiAl2, intending to substantially perturb the position of the Fermi level of Ni since that will lead to a decrease in the VEC and hence elevate the TC. The study was also extended to another Icosagenides (Ga,), which saw the substitution of Ga for Al in GdNiAl2 and its Co substituted analogs. The Ga analogs exhibit complex magnetic behavior with a cascade (multiple) of magnetic transitions, as opposed to the rather simple magnetism of their Al congeners.</div>

Quantum mechanics became a foundation for incessant development of versatile computational methods for analysis of chemical and physical properties of molecules and crystals. A huge progress has been made in the fifield of density functional theory, since nowadays this theory offers the best compromise between precision of results and efficiency fiof computation. The chemical bonding analysis can be easily performed with real space methods based on chemical concepts introduced via partitioning of real space into chemically meaningful domains, since the orbital based approach is not well applicable due to the delocalized nature of plane waves. However the practical usage of those methods often requires a signifificant amount of computational resources. Some methods require the evaluation of so called domain overlap matrices, that is a formidable task for complex and low-symmetry systems. In the present research the author enables the investigation of complex solid compounds with real space chemical bonding indicators by introducing the derivation of the expression for the evaluation of the domain overlap matrix elements from the projected-augmented wave method. The corresponding program module was developed, which is capable to perform the real space chemical bonding analysis with a number of methods, like electron localizability indicators, electron localization function, localization/delocalization indices and domain averaged Fermi hole orbitals. The efficiency and the accuracy of the developed implementation is demonstrated by the comparison with the domain overlap matrix elements evaluation from the full-potential linearized augmented plane wave method on a set of simple compounds with three atoms per primitive cell at most. A set of complex periodic structures is analyzed and the capability of the present implementation to unravel intricate chemical bonding patterns is demonstrated.

<p>  </p> <p>Magnetism plays a vital role in the technologies of today, and materials used for magnetic applications largely consist of solid state phases. Intermetallic chalcogenides are one such material which have exhibited a full range of properties useful for a variety of applications requiring soft magnets, superconductors, magnetocalorics, and even rarer magnetic phenomenon such as 1D Heisenburg magnetic chains. Solid state chemists continue to develop new synthesis methods for chalcogenides as they produce both new phases and modifications of existing phases, usually with the express intent of improving their physical and chemical properties. Low dimensional chalcogenides often have predictable structure-property relationships which when understood aids in these efforts of optimizing existing materials.</p> <p>In this work, we have synthesized novel, low-dimensional Tl1-xAxFe3Te3 (A = K, Na)-based magnetocalorics for magnetic refrigeration technologies utilizing a variety of synthetic methods. Doping of alkali metals into the thallium site simultaneously reduces the toxicity and cost of the material, and also modifies their crystal structures leading to changes in their magnetic properties including ordering temperature, magnetic anisotropy, magnetic hysteresis, coercivity, and magnetic entropies. Most notably, the magnetic ordering temperature has been boosted from 220 K of the prior known TlFe3Te3 phase up to 233 K in the new Tl0.68Na0.32Fe2.76Te3.32 phase, further towards room temperature which is required for the commercialization of magnetic refrigerants for home appliances. There exist strong magnetostructural correlations for most of the alterations in the magnetic properties, and relationships have been modelled where trends exist to match the magnetism to the changes in the unit cell of the structure.</p> <p>New synthetic methods were also developed for the ternary TBi4S7 (T = transition metal) phase which exhibits a pseudo-1D structure of Heisenberg antiferromagnetic chains. These synthetic techniques resulted in more consistent high purity of phases than methods reported previously in literature. Attempts at synthesizing new phases were made, and crystallographic and composition analysis methods suggested the synthesis of a new Mn1-xCoxBi4S7 phase, though magnetic impurities prevented characterization of this new material’s magnetic properties. </p>

<p dir="ltr">Directed hydrogenation, in which product geometric selectivity is dictated by the binding of an ancillary directing group on the substrate to the catalyst, is typically achieved by homogeneous Rh and Ir complexes. No heterogeneous catalyst has been able to achieve equivalently high directivity due to a lack of control over substrate binding orientation at the catalyst surface. In this work, we demonstrate through structure-activity studies that careful control of surface ensemble geometry in bimetallic nanoparticle catalysts can confer hydroxyl-directed selectivity in heterogeneous double bond hydrogenation. We postulate that the oxophilic alloy component binds hydroxyl groups to pre-orient the molecule on the surface, while proximal noble metal atoms impart facially selective addition of hydride to the olefin. We found that controlling the degree of surface alloying between oxophilic and noble metal component as well as alloy component identity is critical to maximizing reaction selectivity and starting material conversion. Our optimized catalysts exhibit good functional group tolerance on a variety of cyclohexenol and cyclopentenol scaffolds, with Pd-Cu and Pt-Ni systems being developed for the diastereoselective hydrogenation of tri- and more challenging tetra-substituted olefins, respectively. The applicability of this method is then demonstrated in a four-step synthesis of a fine fragrance compound, (1<i>R</i>,2<i>S</i>)-(+)-<i>cis</i>-methyldihydrojasmonate (Paradisone®), with high yield and enantiopurity.</p>