http://hdl.handle.net/2005/15 Tue, 30 Apr 2013 09:32:13 GMT 2013-04-30T09:32:13Z http://hdl.handle.net/2005/1933 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. Tue, 19 Feb 2013 18:30:00 GMT http://hdl.handle.net/2005/1933 2013-02-19T18:30:00Z http://hdl.handle.net/2005/1911 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. Wed, 06 Feb 2013 18:30:00 GMT http://hdl.handle.net/2005/1911 2013-02-06T18:30:00Z http://hdl.handle.net/2005/1890 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. Mon, 21 Jan 2013 18:30:00 GMT http://hdl.handle.net/2005/1890 2013-01-21T18:30:00Z http://hdl.handle.net/2005/1920 Title: Influence Of Nanostructuring On Electrochemical Performance Of Titania-Based Electrodes And Liquid Electrolytes For Rechargeable Lithium-Ion Batteries Authors: Das, Shyamal Kumar Abstract: The present thesis deals with the beneficial influence of nanostructuring on electrochemical performance of certain promising electrode and electrolyte materials for lithium-ion batteries (LIBs). Electrochemical performances of chosen electrodes and electrolytes have been presented in a systematic and detailed manner via studies related to both transport and lithium storage. Titanium dioxide (TiO2) or titania, a promising non-carbonaceous anode material for LIBs was chosen for the study. As part of the study, variety of nanostructured titania were synthesized. In general, all materials exhibited high lithium storage ( theoretical value for lithium storage in titania) and some of them showed exemplary rate capability, typically desired for modern lithium-ion batteries. Studies related to performance of these materials and mechanistics of lithium storage and kinetics are presented in Chapters 2-5. “Soggy sand” electrolyte, a promising soft matter electrolyte for LIBs was studied on the electrolyte side. Ion transport, mechanical strength and electrochemical properties of “soggy sand” electrolytes synthesized via dispersion of various surface chemically functionalized silica particles dispersed in model as well as LIB relevant electrolytes were studied in this thesis. Extensive physico-chemical and battery performance studies of “soggy sand” electrolytes are discussed in Chapters 6-8. A brief discussion of the contents and highlights of the individual chapters are described below: Chapter 1 briefly discusses the importance of electrochemical power sources as a viable green alternative to the combustion engine. Various facets of rechargeable LIBs, one of the most important electrochemical storage devices, are presented following the general discussion on electrochemical power devices. The importance of nanostructuring of electrodes with special emphasis on anodes for high lithium storage capacities and rate capabilities are also discussed in the opening chapter. The various advantages and disadvantages of the most commonly used electrolytes in LIB i.e. the liquid electrolytes are also discussed in Chapter 1. Suggestions for improvement of the physico-chemical properties of liquid electrolytes especially via nanostructuring (demonstrated via dispersions of fine oxide particles in liquid electrolytes in Chapters 6-8) using the concept of Heterogeneous doping are discussed in detail. A brief description on the importance of rheology for comprehension of soft matter microstructure is also provided in this chapter. Chapter 2 discusses composite of anatase titania (TiO2) nanospheres and carbon grown and self-assembled into micron-sized mesoporous spheres via a solvothermal synthesis route as prospective anode for rechargeable lithium-ion battery. The morphology and carbon content and hence the electrochemical performance are observed to be significantly influenced by the synthesis parameters. Synthesis conditions resulting in a mesoporous arrangement of an optimized amount of carbon and TiO2 exhibited the best lithium battery performance. The first discharge cycle capacity of carbon-titania mesoporous spheres (solvothermal reaction at 150 oC at 6 h, calcination at 500 oC under air, BET surface area 80 m2g-1) was 334 mAhg-1 (approximately 1 Li) at current rate of 66 mAg-1. High storage capacity and good cyclability is attributed to the nanostructuring (i.e. mesoporosity) of TiO2 as well as due to formation of a percolation network of carbon around the TiO2 nanoparticles. The micron-sized mesoporous spheres of carbon-titania composite nanoparticles also show good rate cyclability in the range (0.066-6.67) Ag-1. The electrochemical performance of the mesoporous carbon-TiO2 spheres has been compared with nonporous TiO2 spheres, normal mesoporous TiO2 and bulk TiO2. Implications of nanostructuring and conductive carbon interface on lithium insertion/removal capacity and insertion kinetics in nanoparticles of anatase polymorph of titania is discussed in Chapter 3. Sol-gel synthesized nanoparticles of titania (particle size ~ 6 nm) were hydrothermally coated ex situ with a thin layer of amorphous carbon (layer thickness: 2-5 nm) and calcined at a temperature much higher than the sol-gel synthesis temperature. The carbon-titania composite particles (resulting size  10 nm) displayed immensely superior cyclability and rate capability (higher current rates  4 Ag-1) compared to unmodified calcined anatase titania. The conductive carbon interface around titania nanocrystals enhances the electronic conductivity and inhibits crystallite growth during electrochemical insertion/removal thus preventing detrimental kinetic effects observed in case of un-modified anatase titania. The carbon coating of the nanoparticles also stabilized the titania crystallographic structure via reduction in the accessibility of lithium ions to the trapping sites. This resulted in decrease in the irreversible capacity observed in case of nanoparticles without any carbon coating. Chapter 4 discusses the morphology and electrochemical performance of mixed crystallographic phase titania nanotubes and nanosheets for prospective application as anode in rechargeable lithium-ion batteries. Hydrothermally grown nanotubes/nanosheets of titania (TiO2) and carbon/silver-titania (C/Ag-TiO2) comprise a mixture of both anatase and TiO2(B) crystallographic phases. The first cycle capacity (at current rate = 10 mAg-1) for bare TiO2 nanotubes was 355 mAhg-1 (approximately 1.06 Li), which is higher than both the theoretical capacity (335 mAhg-1) as well as reported values for pure anatase and TiO2(B) nanotubes. Higher capacity is attributed to a combination of presence of mixed crystallographic phases of titania as well as trivial size effects. The surface area of bare TiO2 nanotubes was very high being equal to 340 m2g-1. Surface modification of the TiO2 nanotubes via amorphous carbon and Ag nanoparticles resulted in significant improvement in battery performance. The first cycle irreversible capacity loss can be minimized via effective coating of the surface. Carbon coated TiO2 nanotubes showed superior performance than Ag nanoparticle coated TiO2 nanotubes in terms of long term cyclability. Unlike Ag nanoparticles which are randomly distributed over the TiO2 nanotubes, the effective homogeneous carbon coating forms an efficient percolation network for the conducting species thus exhibiting better battery performance. The C-TiO2 and Ag-TiO2 nanotubes showed a better rate capability i.e. higher capacities compared to bare TiO2 nanotubes in the current range 0.055-2 Ag-1. Although titania nanosheets retains mixed crystallographic phases, the lithium battery performance (first cycle capacity = 225 mAhg-1) is poor compared to TiO2 nanotubes. It is attributed to lower surface area (22 m2g-1) which resulted in lesser electrode/electrolyte contact area and inefficient transport pathways for Li+ and e-. Implications of iron on electrochemical lithium insertion/removal capacity of iron (Fe3+) doped anatase TiO2 is discussed in Chapter 5. Iron doped anatase TiO2 nanoparticles with different doping concentrations were synthesized by simple sol-gel method. The electrochemistry of anatase TiO2 is observed to be a strong function of concentration of iron (Fe3+). A high 1st cycle discharge capacity of 704 mAhg−1 (2.1 mol of Li) and 272 mAhg−1 (0.81 mol of Li) at the 30th discharge cycle with Coulombic efficiency greater than 96% has been observed for 5% iron (Fe3+) doped TiO2 at a current density of 75 mAg−1. Additional increase in the iron (Fe3+) concentrations deteriorates the lithium storage of TiO2. An improvement in lithium storage of more than 50% is noticed for 5% iron (Fe3+) doped TiO2 compared to pure anatase TiO2 which shows an initial discharge capacity of 279 mAhg−1. The anomalous lithium storage behavior in all the iron (Fe3+) doped TiO2 has been accounted, in addition to homogeneous Li insertion in the octahedral sites, on the basis of formation of metallic Fe and Li2O during initial lithiation process and subsequent heterogeneous interfacial storage between Fe and Li2O interface. Chapter 6 discusses in a systematic manner the crucial role of oxide surface chemical composition on ion transport in “soggy sand” electrolytes. A “soggy sand” electrolytic system comprising of aerosil silica functionalized with various hydrophilic and hydrophobic moeities dispersed in lithium perchlorate ethylene glycol solution ( = 37.7) was used for the study. Detailed rheology studies show that the attractive particle network in case of the composite with unmodified aerosil silica (with surface silanol groups) is most favorable for percolation in ionic conductivity as well as rendering the composite with beneficial elastic mechanical properties. Though weaker in strength compared to the composite with unmodified aerosil particles, attractive particle networks are also observed in composites of aerosil particles with surfaces partially substituted with hydrophobic groups. However, ionic conductivity is observed to be dependent on the size of the hydrophobic moiety. No spanning attractive particle network was formed for aerosil particles with surfaces modified with stronger hydrophilic groups (than silanol) and as a result no percolation in ionic conductivity was observed. The composite with hydrophilic particles was a sol contrary to gels obtained in case of unmodified aerosil and partially substituted with hydrophobic groups. Chapter 7 also discusses the influence of oxide surface chemical composition but additionally the role of solvent on ion solvation and ion transport of “soggy sand” electrolytes. Compared to the liquid electrolyte in Chapter 6, a lower dielectric constant liquid electrolyte was employed for the study in this chapter. A “soggy sand” electrolyte system comprising of dispersions of hydrophilic/hydrophobic functionalized aerosil silica in lithium perchlorate-methoxy polyethylene glycol solution ( = 10.9) was employed for the study. Static and dynamic rheology measurements again showed formation of an attractive particle network in case of the composite with unmodified aerosil silica (i.e. with surface silanol groups) as well as composites with hydrophobic alkane groups. While particle network in the composite with hydrophilic aerosil silica (unmodified) were due to hydrogen bonding, hydrophobic aerosil silica particles were held together via van der Waals forces. The network strength in the latter case (i.e. for hydrophobic composites) were weaker compared with the composite with unmodified aerosil silica. Both unmodified silica as well as hydrophobic silica composites displayed solid-like mechanical strength. However, this time around no enhancement in ionic conductivity compared to the liquid electrolyte was observed in case of the unmodified silica. This is attributed to the existence of a very strong particle network which leads to the “expulsion” of all conducting entities from the interfacial region between adjacent particles. The ionic conductivity for composites with hydrophobic aerosil particles displayed ionic conductivity as a function of the size of the hydrophobic chemical moiety. No spanning attractive particle network was observed for aerosil particles with surfaces modified with stronger hydrophilic groups (than silanol). The composite resembled a sol and no percolation in ionic conductivity was observed. Chapter 8 describes the influence of dispersion of uniformly sized mono-functional or bi-functional (“Janus”) particles on ionic conductivity in lithium battery solutions and it’s implications on battery performance. Mono-functionalized (hydrophilic or hydrophobic) and bi-functionalized Janus (hydrophilic and hydrophobic) particles form physical gels of varying strength over a wide range of concentration (0.1    0.4; , oxide volume fraction). While the composites with mono-functionalized particles display shear thinning typical of gels (due to gradual breaking up spanning particle network held together by hydrogen/van der Walls force), the bi-functionalized “Janus” particles exhibit both complementary properties of gel and sol. The latter observation is interpreted in terms of existence of both hydrogen and van der Waals force arising out of the particle arrangement which get perturbed under the influence of external shear. Composites with homogeneous hydrophilic surface group show the highest ionic conductivity whereas the homogeneous hydrophobic surfaces exhibit superior electrode/electrolyte interface stability and battery cyclability. The Janus particles did not show any enhancement in ionic conductivity however, battery performance is highly satisfactory taking intermediate values between the homogeneously functionalized hydrophilic and hydrophobic particle composites. Mon, 11 Feb 2013 18:30:00 GMT http://hdl.handle.net/2005/1920 2013-02-11T18:30:00Z