A dependência com a temperatura dos tempos de relaxação nuclear e da forma da linha de ressonância dos núcleos F0, nos antiferromagnetos diluidos Fex Zn1-x F2 e Mnx Zn1-x F2, foram estudados na faixa TN&#8804;T&#8804;300K. Os tempos de relaxação spin, rede (1/T1) dos núcleos F0, os quais não estão acoplados aos spins Fe (ou Mn) através da interação hiperfina transferida, foram medidos e calculados teoricamente em função da concentração x. Os resultados teóricos apresentam uma boa concordância com os dados experimentais para concentrações na faixa 0.1&#8804;x&#8804;0.8. A dependência com a temperatura de 1/T1, para TN<T&#8804;300K foi entendido qualitativamente em ambos sistemas. Os resultados obtidos para 1/T1, em temperaturas próximas de TN foram utilizados para estudar os \"Efeitos de Campo Aleatório\" no comportamento crítico do Mn.65Zn.35 F2 com o campo aplicado paralelamente e perperdicularmente ao eixo fácil (C). Encontrou-se neste caso, que a temperatura de transição TN decresce substancialmente com o aumento da intensidade do campo somente quando H0 || C. Os resultados experimentais obtidos estão de acordo com as teorias do Efeito de Campos Aleatórios em antiferromagnetos anisotrópicos diluídos. A divergência crítica do segundo momento da linha de ressonância não homogeneamente alargada do F0 foi estudada acima de TN. Os resultados experimentais concordam com os cálculos de Heller para o alargamento não homogêneo causado por Efeitos de Campos Aleatórios. Observou-se que a forma da linha se altera na região crítica. Longe de TN ela é Gaussiana e para t&#8804;10-2 ela mostra uma tendência a se tornar Lorentziana. Abaixo de TN a sua meia largura aumenta, seguindo qualitativamente o aumento da magnetização das sub-redes. / The temperature dependence of the nuclear relaxation rates and line shapes of the F0 resonance in the diluted antiferromagnet Fex Zn1-x F2 and Mnx Zn1-x F2 are studied over a large temperature range TN&#8804;T&#8804;300K. The high (room) temperature spinlattice relaxation rates (1/ T1) of the F0 nuclei, which are not transfer hiperfine coupled to the Fe (or Mn) spins, have been measured and calculated as a function of the concentration x. Good agreement with experiment is found for the theoretical results, which have been obtained in the range 0.1&#8804;x&#8804;0.8. The temperature dependence of TN<T&#8804;300K was qualitatively understood \"Random Field Effects\" on the critical behavior of Mn.65Zn.35 F2, for fields applied parallel and perpendicular to the easy (C) axis. It was found that the transition temperature TN depressed substantially with field only for H0 || C. The experimental results are in general accord with the theory for Random Field Effects in desordered, anisotropic antiferromagnets. The critical divergence of the in homogeneously broadened F0 NMR was studied in Fe.6Zn.4F2 above TN. The experimental results agree with Heller\'s calculation of the NMR line broadening by Random Field Effects. With H0 || C the line shape changes from Gaussian towards Lorentzian for t&#8804;10-2 and below TN its line width increase qualitatively following increase in the sublattice magnetization.

O objetivo principal da presente Tese é expor um método de Tomografia de Estado Quântico desenvolvido para ser aplicado em sistemas de núcleos quadrupolares isolados. O espaço de Hilbert de tais sistemas pode ser usado para processar a informação quântica de um sistema equivalente constituído por vários q-bits. O método proposto baseia-se na aplicação de pulsos de radiofrqüência não-seletivos que possuem a propriedade de promover rotações globais do estado quântico do sistema. Utilizando uma descrição analítica dessas rotações foi possível generalizar o método proposto para núcleos quadrupolares com qualquer número quântico de spin. O método também pode ser adaptado para sistemas de núcleos acoplados, embora para esses casos seja necessário utilizar períodos de evolução sob a hamiltoniana de interação livre para determinar alguns dos elementos da correspondente matriz densidade. Como aplicação do método de Tomografia de Estado Quântico, utilizaram-se núcleos de 23Na dissolvidos em um cristal líquido liotrópico para obter os resultados experimentais das implementações do algoritmo de Deutsch e do algoritmo de busca de Grover, além da medida da dinâmica de relaxação de vários estados pseudo-puros. Também foram realizadas simulações do método proposto para o caso de um sistema quadrupolar de spin 7/2 e para três spins 1/2 homonucleares acoplados. / The main purpose of the present thesis is to propose a Quantum State Tomography method developed to be applied in quadrupolar isolated nuclei systems. The Hilbert space of such systems can be used to process the quantum information of an equivalent system formed by many qubits. The proposed method is based on the application of non-selective radiofrequency pulses that produce global rotations of the system quantum state. Using an analytical description of those rotations, it was possible to generalize the proposed method to quadrupolar nuclei with any spin quantum number. The method can also be adapted to coupled nuclear systems, although in such cases it is necessary the use of evolution periods under the free interaction hamiltonian in order to determine some of the density matrix elements. As an application of the method, 23Na nuclei dissolved in a lyotropic liquid crystal were used to obtain the experimental results of the Deutsch and Grover algorithms, together with the measurement of the relaxation dynamics of some pseudo-pure states. Simulations of the proposed method applied to the quadrupolar spin 7/2 nucleus and to three homonuclear coupled spin 1/2 were also obtained.

O silício (Si) é benéfico ao desenvolvimento das plantas por proporcionar aumento na capacidade de defesa contra o ataque de pragas e de doenças, além de garantir porte ereto das plantas, o que aumenta a capacidade fotossintética dos vegetais. Fontes silicatadas, como silicatos de cálcio e de magnésio, fornecem Si ao solo e podem funcionar como corretivos de acidez. O acúmulo de resíduos vegetais e fertilizantes, mesmo no sistema semeadura direta (SSD), acelera o processo de acidificação do solo em curto prazo, principalmente em sua camada mais superficial. Esse processo é contínuo em solos tropicais úmidos e tem por consequência a baixa disponibilidade de nutrientes e elevados teores tóxicos de Al+3. Assim como no sistema convencional de manejo do solo, o SSD também demanda a aplicação de insumos, especialmente materiais corretivos de acidez. A aplicação de silicato pode interferir na disponibilidade de Si às plantas e nas formas desse elemento na solução do solo. O ácido silícico (H4SiO4) é a espécie de Si predominante em solos ácidos; e o aumento do pH pode causar sua desprotonação, gerando o ânion silicato (H3SiO4-). Estudos ligados ao Si em solos sob SSD são escassos, principalmente em experimentos de longa duração conduzidos sob condições de clima tropical úmido. Desde 2002 está sendo conduzido experimento de campo em um Latossolo Vermelho distroférrico sob SSD que recebeu aplicação superficial de calcário e de silicato de cálcio e de magnésio. Foram determinados os teores disponíveis de macronutrientes e silício, pH, soma de bases, saturação por bases, capacidade de troca catiônica, matéria orgânica, H+Al e Al3+, minerais silicatados e óxidos de Fe e Al, 24 meses após a reaplicação superficial dos corretivos. Foi feita especiação iônica de Al, Ca, Mg e Si em extrato aquoso e realizada a quantificação de Al por espectroscopia de ressonância magnética nuclear (27Al-NMR). Os principais óxidos encontrados foram a gibbsita, goethita e hematita. Diferentemente do Ca e do Mg, o Al não estava presente, em sua maioria, na forma livre Al3+, mas formando complexos com o carbono orgânico dissolvido. O silício estava quase que totalmente na forma de H4SiO4, sendo que a atividade dessa espécie foi semelhante à sua concentração em solução. A análise quantitativa de 27Al-NMR forneceu somente picos do complexo de alumínio hexa-hidratado ([Al(H2O)6]3+), não havendo espécies de alumínio complexadas com ácidos orgânicos. Amostras com teores moderados a alto de Al (27Al-NMR) se correlacionaram com as concentrações totais de Al provenientes da análise de espectroscopia de emissão atômica (ICP-AES). / Silicon (Si) is an element which is beneficial to plant development in that it provides a line of defense against attack by pests and disease as well, as ensure a plant posture that is more erect that increases their photosynthetic capacity. Silicon sources such as calciummagnesium silicates provide Si to the soil and act as acidity correctives. The accumulation of plant residues and fertilizers, even under a no-till system (NT), accelerates the process of soil acidification in the short term, especially in the uppermost surface layer. This process is continuous in moist tropical soils and results in a low level of nutrients and a high level of Al3+. As is the case under the conventional system of soil management, NT also requires the application of additives, especially acidity corrective materials. The application of silicate can interfere with the availability of Si to plants and the forms in which this element is found in soil solution. Silicic acid (H4SiO4) is the predominant form of Si found in acidic soils; and increases in the pH can cause deprotonation, which generates silicate anions (H3SiO4-). Studies related to Si in soils under NT are scarce, especially long-term experiments carried out under humid tropical conditions. Since 2002, a field experiment has been conducted on a dystroferric Oxisol under NT, where lime and calcium-magnesium silicate were surface applied. The contents of macronutrients and silicon available, as well as pH, basis total and basis saturation, cationic exchange capacity, organic matter, H+Al and Al3+, silicate minerals and Fe and Al oxides, were all determined 24 months after the correctives were applied. The ionic speciation of Al, Ca, Mg and Si took place in aqueous extract as well as the quantification of Al by nuclear magnetic resonance spectroscopy (27Al-NMR). The main oxides found were gibbsite, goethite and hematite. Unlike Ca and Mg, Al was not, for the most part, present in its free form Al3+ but complexed with dissolved organic carbon. Silicon was almost entirely in the form of H4SiO4, and its activity was similar to the concentration of this specie in solution. Quantitative analysis of 27Al-NMR has provided only peaks of Hexaaquaaluminium complex ([Al(H2O) 6]3+), with no species of organic-aluminum complexes. Samples with moderate to high levels of Al (27Al-NMR) were positively correlated with the total concentration of Al derived from the atomic emission spectroscopy analysis (ICP-AES).

Actuellement, une voie de développement de formulations médicamenteuses novatrices passe par la vectorisation de principes actifs connus dans des nanoparticules. Des matériaux hybrides sont ainsi formés, possédant de nouvelles propriétés liées au nano-confinement. Les travaux ici menés s’appuient sur la sensibilité de la Résonance Magnétique Nucléaire (RMN) du solide aux phénomènes prenant place aux échelles moléculaires, pour effectuer une analyse structurelle et dynamique de deux vecteurs. Le premier, hydrophile, est une matrice nanoporeuse de silice sol-gel, dans laquelle sont confinés des complexes de nitroprussiate de sodium isolés. À partir de mesures de relaxation de spin et d’anisotropie de déplacement chimique, différents régimes de dynamique moléculaire sont mis en évidence. Ils sont modulés par la présence de molécules de solvant résiduelles (H2O). Des gammes de température et d’hydratation sont identifiées, pour lesquelles le complexe reste associé malgré un état ‘‘pseudo-liquide’’. Dans la condition limite d’absence d’eau, la restriction du mouvement des complexes confinés est élucidée en caractérisant les interactions dipolaires hôtes / invités. Le second système allie la double vectorisation de la curcumine hydrophobe dans des nanoparticules de lipides solides encapsulées dans une matrice de silice (SBA-15). Une stratégie d’étude conjointe par RMN du solide et par calorimétrie différentielle à balayage (DSC) est mise en place. Les résultats montrent que d’autres facteurs que la compartimentalisation (polymorphisme, dynamique moléculaire des composés hôtes) doivent également être pris en compte pour la compréhension des propriétés de ces matériaux très hétérogènes. Malgré le recours à une instrumentation RMN de dernière génération (spectromètre 1GHz, sonde MAS 1.3mm), la présence de principe actif est observée uniquement dans les compartiments de tensioactif. Ces résultats permettent d’émettre de nouvelles hypothèses sur la distribution du principe actif, tout en montrant les limites de l’approche RMN basée uniquement sur l’étude des noyaux 1H. / Nowadays, a way of developing novel medicinal compounds focuses on confinement of known active molecules inside nanoparticles. Therefore, hybrid materials emerge, exhibiting new properties related to nano-confinement. This work relies on the sensibility of solid-state Nuclear Magnetic Resonance (SS-NMR) towards molecular scale phenomena in order to perform structural and dynamical analysis of two delivery systems. They are modulated by the influence of residual solvent molecules (H2O). Temperature and hydration ranges are identified, for which the complex stays associated, although it is in a liquid-like state. Toward the limit of water absence, movement restrictions of the confined complexes are elucidated by characterizing dipolar host / guest interactions. The second system combines a double vectorization of hydrophobic curcumin molecules inside solid lipid nanoparticles, encapsulated inside a silica matrix (SBA-15). A joint SS-NMR and Differential Scanning Calorimetry (DSC) characterization strategy is put in place. The results show that other factors than compartmentalization (polymorphism, molecular dynamics of host compounds) should also be taken into account to understand the properties of these very heterogeneous materials. Despite resorting to the latest NMR instrumentation (1GHz spectrometer, 1.3mm MAS probehead), presence of the active ingredient is only detected inside the surfactant compartment. These results allow making new assumptions for the distribution of curcumin inside the material while showing the limits of an NMR approach relying solely on the study of 1H nuclei.

Aerosols affect climate change, the energy balance of the atmosphere, and public health due to their variable chemical composition, size, and shape. Aerosols from natural and anthropogenic sources can be primary organic aerosols (POA), which are directly emitted to the atmosphere, or secondary organic aerosols (SOA) that are formed from chemical reactions of gas-phase precursors. At variance with the well investigated formation of SOA from gas phase precursors, the chemistry of aqueous SOAs that contribute to the total SOA budget remains unknown. Field measurements have revealed that carboxylic, dicarboxylic and oxocarboxylic acids are abundant species present in SOAs. This thesis explores the fate of two such acids, pyruvic (PA) and glyoxylic (GA) acids surrogates of the oxocarboxylic acids in the atmosphere, in their cross reaction under solar irradiation and dark thermal aging. Mixtures of complex photoproducts are identified by ion chromatography (IC) with conductivity and electrospray (ESI) mass spectrometry (MS) detection, direct ESI-MS analysis in the negative ion mode, and nuclear magnetic resonance spectroscopy (NMR) analysis including one-dimensional (1H- and 13C-NMR) and two-dimensional techniques such as gradient correlation spectroscopy (gCOSY) and heteronuclear single quantum correlation (HSQC). A reaction mechanism for the cross reaction is provided based on all experimental observations.

Using ����C cross polarization magic angle spinning nuclear magnetic resonance techniques on 5 species of dead trees from the northwest (western hemlock, Douglas fir, Sitka spruce, lodgepole pine and ponderosa pine) I tracked the lignin and cellulose content over a 22 to 36 year period in order to determine the effects of decay fungi, if any, that is attacking certain species of tree. I had samples from the wood of the roots, the bark on the roots and, in some cases, the resin core of the roots. The Department of Forest Science at Oregon State University has studied this problem by using wet chemical analysis, and direct visual observation. Mark Harmon and Hua Chen of the Department of Forest Science believe that white rot occurred most frequently in the lodgepole pine and ponderosa pine and brown rot was more frequent in the Douglas-fir and Sitka spruce. Western hemlock seemed to have both brown and white rots active. The Douglas fir bark sample showed definite decomposition consistent with white rot during the first 10 years. The ponderosa pine sap showed decomposition consistent with white rot in the 10 to 22 year period. Sitka Spruce showed some decomposition consistent with white rot in the bark from 7 to 33 years, and the western hemlock showed some decomposition consistent with white rot in the sap in the first 10 years. The decompositions consistent with brown rot were much easier to see in this study. Virtually all the sap and bark samples showed decomposition consistent with brown rot at some point. The Douglas fir was the only species, other than lodgepole pine, not to show any decomposition consistent with brown rot in the bark of the tree, only decomposition consistent with white rot. The Douglas fir did show a decay consistent with brown rot in the sap for the first ten years. Ponderosa pine showed evidence of decay that brown rot would cause for the first 10 years in the sap and the bark. The Sitka spruce species analysis showed brown rot type decay in the bark for the first 7 years and in the sap for the entire time studied of 33 years. The lodgepole pine was the only species to not show any brown rot type decay in the sap or bark for the entire 22 year period studied. The western hemlock was distinct by not showing any definitive brown rot type decay for the first 10 years, but showed massive decay consistent with brown rot in both sap and bark during the following 26 years studied. I used an 8 Tesla magnet and the MAS frequency was at 5 kHz. The recycle time was 1.5 seconds and the contact time was 1 ms. I generally took about 10,000 acquisitions per sample, which added up to about 4 hours total acquisition time per sample. Presence of these rots shows that certain species are more susceptible than others, and also shows that local environmental conditions can contribute to rot susceptibility. / Graduation date: 2003

<p>In this study two medicinal plant species, namely Galenia africana and Elytropapus rhinocerotis, the former belonging to the family Aizoceae and the latter belonging to the family Asteraceae, have been investigated and different compounds isolated and characterized. Both species are important plants used in traditional medicine in Africa and particularly in South Africa. Flavanoids are secondary metabolites found in plants. They have a protective function against UV radiation and have a defence against invading illnesses due to their important antioxidant activity. Much of the food we eat and some beverages we drink contain flavonoids. The aim of this study was to investigate the electrochemistry of flavanoids isolated from these species.</p>

Major constituents of the venom of various animals are peptidogenic in nature. Marine snails belonging to the species Conus are venomous predators that use small, structurally constrained peptides present in their venom for prey capture and defense. It is known that ~500 Conus species are present in nature and the venom of each of these Conus species is a complex mixture of nearly 100 peptides accounting for > 50,000 peptides with little overlap among the different species. The peptides isolated from the venom of Conus species are commonly known as conotoxins or conopeptides. Some of the common targets of these peptides include the different ion channels like Na+, K+, and Ca2+, and receptor subtypes such as nicotinic acetylcholine and NMDA receptors. The ion channels and receptor subtypes were targeted by conopeptides with high degree of specificity and selectivity. The structural information on the peptides from cone snails can prove to be a valuable starting tool for the understanding of the function of different ion channels and hence in the design of neuropharmacologically active drugs. Conotoxins are disulfide-rich peptides and the number of disulfide generally ranges from two to five. Based on the arrangement of cysteines in their primary sequence, they are classified into different superfamilies. The signal sequences of the precursors belonging to a particular superfamily are highly conserved and hence the members within the same family have, in common, the unique disulfide arrangement and pharmacological activity. Conotoxins are classified into eleven superfamilies till date. In order to understand the underlying the principles involved in the action of these peptides on different ion channels, one needs to know the three-dimensional structures which, in potential, will help in the identification of the pharmacophores responsible for the observed pharmacological activity. With the aim of studying the structure-activity relationships found among the conotoxins, we have initiated a study on the peptides isolated from the marine snails found in the Indian coastal waters. This thesis is focused in the structural studies of the peptide toxins from marine cone snails and a terrestrial scorpion. The tool used for the structural studies of these peptide toxins is Nuclear Magnetic Resonance Spectroscopy. Chapter 1 provides an overview of the peptide toxins found among various animal species with more emphasis on conotoxins and scorpion toxins. In addition, the rationale behind the present study has also been explained. Chapter 2 describes the structure determination of two conopeptides isolated from Conus amadis, δ-Am2766 and Am2735, which are active on mammalian sodium channels. The structural aspects and comparison with other known conopeptides belonging to the same superfamily as that of these two peptides have also been described. Solution NMR studies of Ar1446 and Ar1248, two conopeptides isolated from the species Conus araneosus have also been studied using Homonuclear NMR methods. Ar1446 is a three disulfide-bonded peptide. Our studies have revealed that this peptide has a novel disulfide connectivity not previously observed in the M superfamily or any other superfamily of conotoxins. The structural features of Ar1446 will be described along with the NMR studies on two-disulfide bonded peptide, Ar1248, belonging to the A-superfamily of conotoxins. The main problem faced in the kind of study of peptides isolated from natural sources is the amount that can be isolated and purified to homogeneity. In order to obtain large quantities of peptides, we have successfully used Cytochrome b5 as fusion host to clone, over express and purify these peptides using recombinant methods. The use of recombinant methods has aided in the preparation of isotopically enriched peptides. The use of cyt b5 as fusion host for the large scale production of some of the peptides from Indian marine snails is described in Chapter 4. A novel pharmacologically active linear peptide, Mo1659 isolated from Conus monile, have been studied using Heteronuclear NMR methods. This peptide was cloned, over expressed and purified using Cytochrome b5 as a fusion host. Another linear peptide, Mo1692 (also from Conus monile), has been prepared using the same method and was studied using Homonuclear NMR methods. Both these peptides were liberated from the fusion host using cyanogen bromide cleavage and were subsequently purified using RP-HPLC. The results of the biosynthetic preparation and NMR studies of these two peptides have been described in Chapter 5. Chapter 6 describes the solution structure determination of a novel scorpion toxin characterized in the venom of the Indian red scorpion Buthus tamulus. The cloning, over expression, folding and purification of BTK-2 is described here. The structure and the function of this recombinantly produced BTK-2 will also be described.

This thesis presents results of novel methodologies applied to oriented systems. Both pure liquid crystalline materials as well as molecules oriented in liquid crystalline matrices have been studied. In particular this thesis presents investigations related to various aspects of NMR in liquid crystalline media, such as, assignment of resonances and the study of director dynamics of spinning liquid crystals in different phases and with different symmetry. Simplified methods for structure determination of solutes dissolved in liquid crystal solvents have been proposed. Diffusion ordered spectroscopy has been used to study a mixture of liquid crystals of opposite diamagnetic susceptibility at its coexistent phase. The methods presented represent novel techniques to characterize the liquid crystalline phase. NMR spectroscopy which has become a method of choice for understanding ordering mechanisms of mesogens requires a robust method for obtaining assignments of the NMR spectra of various nuclei that are found in the mesogens [1, 2]. It turns out that the spectra in the isotropic phase and in the nematic phase of a liquid crystal molecule are very different due to the presence of chemical shift anisotropy in the mesophase spectrum. There are a host of methodologies available for assigning spectra in the isotropic phase [3]. These methods however fail, when applied to the spectrum of the molecules in the mesophase due to the dominating role of strong anisotropic interactions, such as homonuclear couplings among protons. Problems arising while assigning spectral lines of liquid crystals in their nematic phase have been dealt with in chapter 2. To circumvent these problems, a property of the liquid crystal molecules under off-magic angle sample spinning can be utilized. It has been shown by Courtieu et al. [4] that the director/symmetry axis of a Δχ + ve liquid crystal aligns along the spinning axis for θ between 0 ° and θm, where θ is the angle between the spinning axis and the magnetic field and θm = 54.7° is the magic angle. It may be noted that the spectrum of θ = 0° spinning angle corresponds to the normal static spectrum, while the spectrum of θ = θm corresponds to the isotropic spectrum. In an earlier study, Teearr et al. [5] had recorded the 13C liquid crystal spectra as a function of very closely spaced θ values from 90° all the way up to 0°. From these plots of chemical shift versus the angle of spinning, it is possible to follow the trajectory of each 13C line from its position from θ = θm to θ = 0° and then match the spectrum in the isotropic phase (equivalently the magic angle sample spinning spectrum of the nematic phase) to the spectrum of the static sample in the nematic phase. However this method requires recording spectra at closely spaced angle intervals, so that one can unambiguously follow the trajectory of each of the lines without missing out any crossover of trajectories. However, this operation is time consuming. In this thesis we propose an alternate method, where we utilize the fact that the above trajectory has a very distinct relationship to the isotropic and anisotropic chemical shift and the problem of assignment does not require a continuous variation of angles, but just a few selected experiments should enable the assignment of the spectrum in the anisotropic phase. Thus the method of assignment has been made simpler and faster. It is shown that in addition to the assigned isotropic spectrum, only one other Off-magic angle spinning spectrum whose spinning angle θ is accurately known is necessary to obtain the complete assignment of the static spectrum. This procedure is non-trivial due to possibilities of errors in assignments arising out of inaccuracies in the knowledge of chemical shifts and the spinning angle. A computational procedure is proposed to take into account deviations arising out of non-ideal experimental conditions. A discussion regarding the details of the procedure and also situations where there can be ambiguities and how they can be resolved has been elaborated. The developed method has been demonstrated on a well known thermotropic liquid crystalline system, N-(4-ethoxybenzylidene)-4-n-butlyaniline [EBBA]. Since assignment of resonances in the nematic phase is a primary requirement for any further analysis regarding the ordering and deeper understanding of the role of various substituents in the mesogens we believe our novel prescription will be of immense use and utility. The third chapter presents the study of director dynamics in a lyotropic liquid crystal composed of Potassium laurate, 1-Decanol and D2O [6] under variable angle sample spinning using 2H NMR spectrum of D2O. A very interesting interplay of the magnetic orienting torque due to interaction of the liquid crystal director with the magnetic field and viscous torque arising from the viscosity of the sample on the director comes to fore. The relative magnitude of these torques has a direct bearing on the spectral pattern and line shapes observed, providing valuable insights into magnetohydrodynamics of the spinning liquid crystals. This study leads to even more interesting behavior for liquid crystals which deviate from uniaxial symmetry. This competition between magnetic and viscous torques has been quantitatively visualized by simulation of the 2H spectrum. It has been possible to visualize the observed spread in the director distribution arising out of viscous torque in terms of the energetics of the system under fast spinning. If the magnetic torque dominates over the viscous torque, then the equilibrium corresponds to the director orientation of δ = 0° where the energy is at its minimum. However the viscous and magnetic torques can become comparable as it may happen if the spinning angle is close to the magic angle or when the Δχ of the system is small. In those circumstances additional energy from the viscous torque causes the distribution of the director orientation to spread further away from δ = 0° for a positive Δχ liquid crystal. The trigonometric factor [P2(cosθ)∗P2(cosδ)] being proportional to the total energy of the system has been plotted against the spinning angle. The spectrum of the biaxial phase [7] as a function of the spinning angle shows more interesting director distribution. Here the patterns of the director distribution are observed on either side of the magic angle due to the presence of more than one director. The patterns observed also have information about the symmetry of the phase. This work provides insights into magnetohydrodynamics of spinning liquid crystals and can also be of relevance to samples of biological interest such as bicelles with protein oriented in them [8]. The fourth chapter deals with a novel characterization method relevant for the biaxial phase [9]. As an off shoot of the previous chapter, it effectively overcomes the disadvantages of the previous experimental methods which require simulation and line shape fitting to extract useful parameters. The chapter also presents the measurement of geometrical parameters of oriented solutes in phases exhibiting biaxial symmetry. The measured parameters show the effect of the onset of biaxiality as significant deviation in the value of the measured parameter. The utility of liquid crystalline media as solvents in high resolution NMR spectroscopy has been very rewarding since the pioneering work of Saupe and Englert [6]. The intramolecular interactions within solutes are only partially averaged. As a result one obtains a liquid like spectrum while at the same time very useful anisotropic interactions such as dipolar couplings, chemical shift anisotropies, quadrupolar couplings and anisotropic part spin-spin J couplings are extracted [10]. NMR spectra of molecules dissolved in thermotropic liquid crystals have long been used to obtain structural and orientational information. As the same time the complexity of the spectrum increases with the increase in the number of spins and the reduction in symmetry of the molecule, which can make the spectral analysis forbidding. Generally proton spectra have been used to obtain the geometry of the proton skeleton of the molecule and the information that includes dilute X nuclei such as 13C and 15N are available only from satellites which are buried in the intense proton spectrum. Different inequivalent dilute spins coupled to protons form different coupled spin systems in their natural abundance and appear as satellites in the proton spectra. Identification of transitions belonging to each of the spin system is essential to determine heteronuclear dipolar couplings, which is a formidable task. The fifth chapter deals with development of the techniques to obtain the complete structure of the dissolved molecules including nuclei other than protons in their natural abundance. The use of inverse experiments has been elaborated to overcome the problems of sensitivity and complexity for solute molecules having larger number of spins. In the present study using HSQC and HMQC experiments, we have selectively detected spectra of each inequivalent rare spin coupled to protons in pyrazine, pyrimidine and pyridazine dissolved in thermotropic Phase 4 and Phase 5 liquid crystal solvents. This way we could obtain enhancement in the intensity of satellites signals without the interference from the signals connected to the major isotopomers. Besides, we could resolve a complex spectrum into its sub-spectra corresponding to individual 13C and 15N isotopomers. This separation of the spectra corresponding to individual sub-spin systems makes analysis easy and helps analyze larger systems with higher number of spins and lower symmetry. Besides 1H-1H dipolar couplings, 13C-1H and 15N-1H dipolar couplings have been determined in natural abundance, thereby giving the complete dipolar coupling network between all the spins in the molecule. In this treatment pyrazine, pyrimidine and pyridazine have been used as examples of methodology developed. It is expected that the method will be of wider use for several other similar systems. Chapter six describes the diffusion ordered spectroscopic investigation [11] of a phase arising out of mixing together two liquid crystals having opposite signs of diamagnetic susceptibility anisotropy [12]. Towards this end we have used CH3CN as a probe molecule. The spectrum of CH3CN has with it the information about the parallel or perpendicular orientation of the phase. Such a mixture of liquid crystals have shown interesting behavior at the critical temperature where the two phases seem to coexist. It has been an interesting question to understand what exactly happens for the molecular orientation when the macroscopic anisotropy Δχ vanishes. Earlier Jokisaari et al. [13] have varied the temperature very finely taking due precautions to maintain homogeneity and stability of temperature to the tune of ±0.05K across the sample volume. Their observation of a powder pattern exactly in the critical temperature was interpreted as arising out of a distribution of directors equally oriented in all directions. In our experiments we have measured the diffusion coefficient of the probe molecule i.e. acetonitrile as we change the temperature of the system through the critical temperature. At the critical temperature we have a situation of being able to measure the parallel and perpendicular orientational diffusion coefficients simultaneously. The measurements show that the parallel component of the diffusion coefficient has reduced and the perpendicular component has increased in comparison to the trend in the immediate neighboring temperatures, thereby indicating that at the exact critical condition the liquid crystal mixture consists of an isotropic distribution of molecules. As a check to rule out any exchange of molecules in different domains of parallel and perpendicular orientations an EXSY experiment was conducted with a mixing time which was same as that of the diffusion delay in the DOSY experiment. The EXSY spectrum showed no exchange cross peaks between the two orientations, this confirms that the anisotropy of the diffusion vanishes at the critical temperature. Nematic liquid crystals exhibit a rich variety of phases and properties. NMR is a very powerful tool to study the various phases at the microscopic and molecular level. It has also turned out that some of these properties can be usefully utilized for investigation of both small and large molecules by NMR. Thus this thesis has attempted to expand several of the techniques already available for various applications and extend the utility of NMR for the study of partially ordered systems.

Radionuclides, 129I and 239,240Pu, are major products or by-products of nuclear fission and among the top risk drivers for waste disposal at the Savannah River Sites (SRS) and Rocky Flats Environmental Technology Sites (RFETS), respectively, due to their perceived mobility in the environment, excessive inventory, toxicity, and long half-life. The objective of this study is to investigate the role of natural organic matter in retarding or facilitating the migration of 129I and 239,240Pu in the Department of Energy (DOE) sites. Measurements of 127I and 129I in humic acids (HAs) and fulvic acids (FAs) obtained by five successive alkaline, two glycerol and one citric acid-alkaline extractions, demonstrated that these extractable humic substances (HS) together account for 54-56 percent and 46 percent of the total 127I and 129I in the soil, respectively. The variations among 127I and 129I concentrations, isotopic ratios (129I/127I), chemical properties of all these humic substances indicated iodine was bound to a small-size aromatic subunit (~10 kDa), while the large-size subunit (~90 kDa), which likely linked the small-size unit through some weak chemical forces, determined the relative mobility of iodine bound to organic matter. Soil resuspension experiments simulating surface runoff or stormflow and erosion events were conducted with soils collected from SRS. Results showed that 72-77 percent of the newly-introduced I- or IO3- were irreversibly sequestered into the organic-rich soil, while the rest was transformed into colloidal and dissolved organo-iodine by the soil. The resulting iodine remobilization contradicts the conventional view that considers only I- or IO3- as the mobile forms. Quantitative structure analysis by 13C DPMAS NMR and solution state 1H NMR on these humic substances indicate that iodine is closely related to the aromatic regions containing esterified products of phenolic and fomic acid or other aliphatic carboxylic acids, amide functionalities, quinone-like structure activated by electron-donating groups (e.g., NH2) or hemicelluloses-lignin-like complex with phenyl-glycosidic linkage. The micro-molecular environment, such as the hydrophobic aliphatic periphery hindering the active aromatic cores and the hydrophilic polysaccharides favoring its accessibility towards hydrophilic iodine species, play another key role in the interactions between iodine and SOM. NMR spectra of the colloidal organic Pu carrier which can potentially be released from the soil during the surface runoff or stormflow showed Pu was transported, at sub-pM concentrations, by a cutin-derived soil degradation products containing siderophore-like moieties and virtually all mobile Pu.