http://hdl.handle.net/2005/15 2013-06-15T14:22:55Z 2013-06-15T14:22:55Z Hebbar, Sankeerth http://hdl.handle.net/2005/1933 2013-02-20T10:47:50Z 2013-02-19T18:30:00Z

Title: Applications Of Multiple Quantum Methods In NMR For Determination Of Dipolar Couplings And Chiral Discrimination Authors: Hebbar, Sankeerth Abstract: This thesis is about excitation, detection, properties and applications of multiple quantum coherences applied to different dipolar coupled spin systems. Major focus of the work is on spectral simplification, measurement of residual dipolar couplings and discrimination of enantiomers in chiral aligning media. The first chapter gives a brief account on the fundamentals of nuclear magnetic resonance spectroscopy and multiple quantum coherences. This includes a description of product operator and polarization operator formalisms of pulses and evolution of magnetization. Subsequently a detailed account of two dimensional multiple quantum – single quantum (MQ-SQ) correlation experiments is given. Demonstration of the homonuclear MQ-SQ pulse sequence on a weakly coupled spin system and analysis of the spectrum obtained are also discussed. Homo-nuclear multiple quantum studies carried out to obtain relative the signs of the couplings have been reported in the initial part of the second chapter. The technique has been applied on doubly labeled acetonitrile (13CH313C15N) aligned in a liquid crystalline medium. Special situations like ambiguity in the determination of relative signs of the couplings from the appearance of two dimensional MQ-SQ spectra and the explanation for the same are also discussed. Homo-nuclear MQ experiments on indistinguishable spins, like protons in a methyl group of 13CH313C15N oriented in liquid crystal, and distinguishable spins, like the two carbons in the same molecule, have been carried out. Different directions of approach in which these results need to be analyzed have been discussed. Subsequent part of the chapter is about the correlation of connected MQ-SQ coherences. These experiments are significant in reducing the cross-peaks further from the MQ-SQ spectra. This concept is extended for the discrimination of optical enantiomers dissolved in chiral aligning medium made of poly-Γ-benzyl-L-glutamate (PBLG) and CDCl3. In molecules of Chemical and biological interest one encounters several nuclei such as, 1H, 13C, 15N and 19F. It will be of general interest to determine magnitudes and relative signs of the couplings among these coupled nuclei by NMR experiments. Utilization of hetero-nuclear MQ Experiments in solving such problems is discussed in the third Chapter. Hetero-nuclear MQ experiments were carried out on dipolar coupled 13CH313C15N, with the aim of obtaining the values and signs of various hetero-nuclear couplings in the molecule. The splitting of transitions in the spectra of oriented molecules is always influenced by the sum of dipolar and scalar couplings. Hence precise determination of dipolar couplings requires the knowledge of scalar couplings. To determine the J couplings, experiments were carried out on the same molecule in isotropic medium. When many coupled nuclei are involved one has to carry out several experiments to derive all the spectral parameters. In circumventing this problem heteronuclear multiple quantum experiments involving more than two nuclei as active spins are advantageous. This reduces the number of experiments and thereby reducing the total experimental time. Second part of this chapter demonstrates how a triple resonance triple quantum experiment can provide majority of the couplings from a given coupled system. The feasibility of the experiment is demonstrated even for molecules containing natural abundant isotopes. Application of multiple quantum j-resolved technique for chiral discrimination and obtaining complete one dimensional spectrum of each enantiomer from their racemic mixture is discussed in the fourth chapter. The two dimensional experiment consists of a selective double quantum excitation period followed by selective refocusing during indirect time domain, isotropic mixing and nonselective detection of SQ transitions. Hence this pulse sequence is named as DQSERF-COSY (Double Quantum Selective Refocused Correlation Spectroscopy). The experiment exploits the existence of different intra-methyl couplings between the enantiomers dissolved in chiral liquid crystal medium to separate the one dimensional spectra of each enantiomer in different cross sections. This is possible due to the fact that all the nuclei in any one of the enantiomers are coupled among themselves and there is no inter molecular interaction between the two enantiomers. Also one can extract all the couplings between protons in each enantiomer, which can subsequently be utilized for determination of the residual dipolar couplings, structure and orientation parameters.

2013-02-19T18:30:00Z Manna, Uttam http://hdl.handle.net/2005/2020 2013-06-03T07:54:11Z 2013-06-02T18:30:00Z

Title: Stimuli Responsive Multilayer Thin Films And Microcapsules Of Polymers Via Layer-By-Layer Self-Assembly Authors: Manna, Uttam Abstract: The present thesis focuses on the selection of polymers and methods to fabricate stable and stimuli responsive multilayer self-assembly via layer-by-layer (LbL) approach. The polymers utilized in this study are biodegradable and biocompatible such as hyaluronic acid, chitosan and poly(vinyl alcohol) (PVA). The thesis is comprised of six chapters and a brief discussion on the contents of the individual chapters is given below. Chapter I reviews the LbL self-assembly approach in the context of drug delivery. The various interactions such as electrostatic, hydrogen bonding and covalent bonding involved in preparation of stable multilayer assemblies via LbL approach are discussed. Stimuli responsive behaviour of these multilayer assemblies can be tuned by choosing suitable depositing materials and method. Preparation of hollow microcapsules using LbL approach and its application in drug delivery has also been described in this chapter. Chapter II deals with the LbL assembly of a neutral polymer, poly(vinyl alcholol) (PVA). The negative charge on PVA backbone was induced by physical cross-linking with borax. The PVA-borate can undergo electrostatic interaction with positively charged chitosan in LbL process to form multilayer thin film. The thin film of PVA-borate complex/chitosan was found be responsive towards glucose concentration; disintegration of the multilayer assembly was observed at a high glucose concentration. This finding was rationalized on the basis of strong interaction of glucose with borate ions leading to dissociation of PVA-borate complex and subsequent collapse of the assembly. Thus, this multilayer self-assembly is potent for glucose triggered drug delivery. Chapter III reports the construction of a stable hydrogen bonded multilayer self-assembly based on complementary DNA base pairs (adenine and thymine) interaction. The natural polymer such as chitosan was modified with adenine whereas hyaluronic acid was modified with thymine. These two modified polymers were sequentially deposited on flat substrate and melamine formaldehyde (MF) particles; wherein strong interaction among the DNA base pairs led to the formation of stable assembly without utilizing any external cross-linking agent. The modified polymers are non-cytotoxic as proved from MTT assay. Further the multilayer assembly was used for pH responsive anticancer drug doxorubicin hydrochloride (DOX) release. In Chapter IV, glutaraldehyde mediated LbL self-assembly of single polymer multilayer thin films on flat and colloidal substrate by covalent bonding is described. A comparitive study between the native polymer (chitosan) and adenine modified polymer in the growth of thin film is performed. It is established from the study that the conformation of polymer and the availability of cross-linking points on the polymer play a crucial role in controlling the growth of these multilayer assemblies. Chapter V is divided into two parts (A and B). Part A describes a simple and unique protocol for fabrication of water dispersed chitosan nanoparticles (CH NPs). The method utilized in this work is based on the fast desolvation technique without using any additional stabilizer or any sophisticated instrumental setup. Furthermore, the CH NPs prepared from the mentioned protocol were proved to be cell-viable and are found to be responsive towards pH of the solution. In part B of this chapter, the LbL self-assembly of the responsive CH NPs is fabricated via electrostatic interaction with hyaluronic acid (HA). The growth of the multilayer thin film was found to be linear as function of number of bilayers. The morphology of thin film was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The microscopic images reveal the uniform film morphology devoid of any phase separation of nanoparticles and polymers. Subsequently, the film was loaded with an anticancer therapeutic, doxorubicin hydrochloride (DOX). The release dynamics of encapsulated drug from the self-assembly are tunable and pH responsive. Chapter VI deals with the general and versatile method for the encapsulation of hydrophobic model drugs into polymeric multilayer assembly by using LbL approach. Electrical charge was induced on the surface of pyrene (uncharged organic substance) using an amphiphilic surfactant, sodium dodecyl sulfate (SDS) by micellar solubilization. The SDS micellar solution of pyrene was utilized to grow LbL multilayer thin film on a planar substrate and colloidal particles along with chitosan as a polycation. The LbL self-assembly of pyrene loaded SDS micelles/chitosan is additionally able to encapsulate hydrophobic or hydrophilic model therapeutics, thus providing an opportunity for dual-drug delivery. The desorption kinetics of the two model drugs from the thin film is found to follow a second order rate model.

2013-06-02T18:30:00Z Sahoo, Prangya Parimita http://hdl.handle.net/2005/1911 2013-02-07T06:41:32Z 2013-02-06T18:30:00Z

Title: Variants Of Complex Bismuth And Zirconium Oxides : Structure-Property Correlation Studies Authors: Sahoo, Prangya Parimita Abstract: The thesis entitled “Variants of Complex Bismuth and Zirconium Oxides: Structure-Property Correlation Studies” consists of five chapters. A short introductory note outlines the synthetic procedures, characterization techniques and evaluated properties such as photocatalysis, second harmonic generation, ionic conductivity and thermal expansion in these materials. Chapter 1 deals with a new solid solution Pb3-xBi2x/3V2O8 (0.20 ≤ x ≤ 0.50), stabilizing the high temperature γ form of Pb3V2O8 in the system Pb3V2O8−BiVO4. Single-crystals of the composition x = 0.50 were grown and the structure is a new variant in palmierite structural type as determined by both single crystal X-ray and powder neutron diffraction. Several refinement strategies backed up by difference Fourier methods were used to arrive at the final crystal structure. ac impedance studies indicate conductivity of the order of 10-4 Ω-1 cm-1 for Pb2.5Bi1/3V2O8. Chapter 2 has two sections and describes the structure property correlation in bismuth based vanadate and phosphate eulytites. Section 2.1 discusses the crystal structure of Pb3Bi(VO4)3, the first eulytite compound containing [VO4]3- moieties. The compound displays incongruent melting behavior. Single-crystals were grown by melt-cool technique adding excess amount of BiVO4. The crystal structure has been characterized by both X-ray and neutron diffraction studies. Section 2.2 describes the crystal structures of four phosphate eulytites A3Bi(PO4)3 ( A = Ca, Cd, Sr, Pb). The crystals were grown from melt-cool technique with considerable difficulty as the compounds melt incongruently. While Pb3Bi(VO4)3 and Pb3Bi(PO4)3 have an unique position for one of the oxygen atoms, Sr3Bi(PO4)3, Ca3Bi(PO4)3, Cd3Bi(PO4)3 display split oxygen atomic sites. The SHG efficiencies measured on polycrystalline samples were 5.3, 3.8, 2.85, 1.21 and 0.64 times that of KDP (KH2PO4) for Pb3Bi(VO4)3, Cd3Bi(PO4)3, Sr3Bi(PO4)3, Pb3Bi(PO4)3 and Ca3Bi(PO4)3 respectively. Chapter 3 describes the isolation of the compound Sr2Bi2/3V2O8, a variant palmierite, in the phase diagram of SrO-Bi2O3-V2O5. The compound was synthesized by ceramic method and it is of interest to note that the Sr(1) site also accommodates Bi as found by single crystal X-ray studies unlike that found in the case described in chapter 1. Chapter 4 has two sections, dealing with synthesis, characterization and photocatalytic properties of trigonal and monoclinic polymorphs of ZrMo2O8, a negative thermal expansion material in its cubic form. Section 4.1 describes the synthesis of trigonal polymorph of ZrMo2O8 by both ceramic and combustion synthesis methods. SEM images show a particle size of 40-50 nm for combustion synthesized samples and 8-10 μm for solid state synthesized ZrMo2O8. The band gap obtained by UV-visible diffuse reflectance spectra for the combustion synthesized and solid state synthesized samples were 2.70 and 2.74 eV and the BET surface area were 1.0 m2/g and 10.0 m2/g. DFT electronic structure calculations reveal the indirect band gap nature of this polymorph. Photo-degradation studies performed on pollutant water show specific affinity to degrade dyes which do not possess anthraquinonic moieties. Section 4.2 describes the single-crystal structure determination and catalytic properties of monoclinic polymorph of ZrMo2O8. The band gap measured for the monoclinic form by UV-visible diffuse reflectance spectra was 2.57 eV. This polymorph was found to be specific towards the degradation of cationic dyes. Chapter 5 discusses a new solid solution ZrV2-xMo5x/6O7 (0 ≤ x ≤ 0.8) identified in the phase diagram of ZrO2−V2O5−MoO3. These compounds were synthesized via the solution combustion method. The resulting products were characterized by powder X-ray diffraction, solid-state UV-visible diffuse reflectance spectra, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photo-catalytic activity shows specificity towards the degradation of non-azo dyes. Single-crystals were grown by melt-cool technique from the starting materials with twice the MoO3 quantity. Since, these crystals belong to a cubic system, space group Pa 3, they were tested for negative thermal expansion using variable temperature single-crystal XRD and indeed they exhibit this property above 370 K.

2013-02-06T18:30:00Z Prabhu, Uday Ramesh http://hdl.handle.net/2005/1890 2013-01-22T05:43:15Z 2013-01-21T18:30:00Z

Title: Development Of Two Dimensional Correlation And Resolved Methodologies For NMR Spectroscopic Discrimination Of Enantiomers Authors: Prabhu, Uday Ramesh Abstract: The research work reported in this thesis deals with the development of novel NMR experimental techniques for the spectroscopic discrimination of enantiomers dissolved in a chiral liquid crystalline medium. The information on the chemical shifts and coupling constants pertaining to each enantiomer has been derived on the investigated chiral molecules. The enantiomeric excess (ee), a parameter which is of profound importance in pharmaceutical industry and in asymmetric synthesis, has also been measured. A special attention is paid to the use of high sensitivity of H NMR for chiral discrimination. Typical analyses of H NMR spectra are severely hindered due to enormous spectral inhomogeneous broadening arising from too many unresolved transitions, in addition to superposition of spectra from both the enantiomers. Therefore, the major part of the work is focused on the design and application of pulse sequences to overcome many of these drawbacks. This helps to achieve very high resolution, discerning of overlapped transitions, identification of resonances pertaining to each enantiomer and simplification of the spectrum for easy extraction of spectral parameters, in addition to the accurate measurement of ee. Initially a brief discussion is provided on enantiomers, diastereomers, basic principles of NMR spectroscopy, the several interaction Hamiltonians responsible for yielding the NMR spectra, introduction to product and polarization operator formalisms that gives insight into the spin dynamics for designing appropriate two-dimensional (2D) NMR experiments. This sets the foundation to understand the complex multiplet structures of the diagonal peaks and cross peaks in the resulting 2D spectrum. Subsequently, a brief introduction is given for the available techniques for NMR spectroscopic discrimination of enantiomers in isotropic medium, where only chemical shifts are employed as a measurable parameter. The limitations of these techniques are circumvented by the introduction of other anisotropic NMR parameters, such as homo-and hetero-nuclear dipolar couplings, quadrupolar couplings and chemical shift anisotropies. To achieve this goal the enantiomers are dissolved in weakly aligning chiral liquid crystalline (CLC) medium. To understand this, a general introduction to liquid crystals and their utility as an alignment medium in NMR spectroscopy and the anisotropic interactions affecting the NMR spectrum has also been provided. The preparation of the CLC phase of Poly-γ-Benzyl-L-Glutamate (PBLG) employed in the present study and its orientational behaviour has been discussed. The detection of NMR spectra of various nuclei and the interaction parameters utilized for chiral discrimination will be enumerated. A brief summary of the experiments employed for the spectral analyses of the enantiomers dissolved in PBLG will also be presented.

2013-01-21T18:30:00Z