Cancer is the second leading cause of death in the United States. Cisplatin is one of the well-known anti-cancer agents used to treat testicular and ovarian cancers. It mainly binds to the DNA bases, which leads to cell death. The cytotoxic activity of the cisplatin analogs is due to the interaction of platinum with nucleotides like adenine at N7 or N1 position and guanine at N7 position. Guanine is the primary target for cisplatin analogs whereas adenine is the secondary target. Cisplatin analogs, [Pt(Me5dien)(D2O)]2+[Me5dien = N,N,N’,N’,N’’-pentamethyl diethylene triamine] and [Pt(dien)(D2O)]2+[dien=diethylene triamine] were synthesized and their effects on AMP and GMP were studied using NMR spectroscopy. The experiments were conducted to examine the effects of bulk on 5’-GMP and 5’-AMP. The results suggest that bulk slows down the reaction with AMP more than with that of GMP. The order of reactivity is Pt(dien)(GMP)> Pt(dien)(AMP) > Pt(Me5dien)(GMP) > Pt(Me5dien)(AMP). The reaction of the [Pt(Me5dien)(D2O)]2+ complex with AMP leads to multiple products, some of which appear to be due to coordination at N1 instead of N7.

This thesis aims at the methodological developments in Nuclear Magnetic Resonance (NMR). The methodological developments in NMR has a long and successful history. The present thesis attempts to contribute some novel methods in this direction. This thesis restricts itself to two methodological developments, namely, (1) effects of cross-correlations between the chemical shift anisotropy (CSA) and dipole-dipole interactions in the relaxation of various nuclei and experiments which utilize spatial encoding. The cross-correlation has been successfully utilized to investigate the anisotropic motions of liquid crystals, and to understand the chemical shift anisotropy of fluorine atoms of Fluorine substituted ring compounds. Spatial encoding schemes have been developed to facilitate single scan measurements of longitudinal spin lattice relaxation times and implementations of parallel search algorithms.

Thesis(MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The SQUID-NMR technique has been increasingly recommended by many researchers as holding a lot of potential, and it is believed it will become an invaluable tool for non-destructive evaluation in the future. Most of its potential is yet to be exploited. Non-destructive quality control of food products is one of the applications where such a system is being tried. Much of the progress that has been made in improving such a system to the present degree of user friendliness and cost effectiveness shows that, with more effort, it would be possible to implement the technology for on-line sorting, and possibly to reduce it down to hand-held devices. The goal was to investigate the feasibility of the internal fruit quality measurements using the NMR technique, and to develop a SQUID system suitable for SQUID-NMR application, intended for a later integration in a full SQUID-NMR system. A working dc SQUID was manufactured on an YBCO (Y Ba2Cu3O7􀀀 ) thin film deposited on a 10 mm x 10 mm MgO substrate. The SQUID was made of microbridge Josephson junctions, patterned by using the double resist laser lithography method, implemented during the course of this manufacturing process. The test of the SQUID showed a non-hysteretic current-voltage characteristic. Under the action of bringing a magnet closer to the SQUID under test, and then retracting it, the modulation of the I-V curve was observed. The critical current of the SQUID was 20 A and the resistance was 5.5 A series of experiments were performed on destructive measurements of the sugar content in table grapes using NMR, in order to evaluate the feasibility of this technique. The total sugars(TSS) measurements of the same samples were carried out by refractometry, chosen as a conventional method for validation. The NMR measurements were evaluated to be 5.4% precise and have an accuracy of 9.3% relative to the refractometry measurements. A further series of experiments were carried out on a high-Tc SQUID-NMR system. A high correlation coefficient (0.85) of the increasing values of the T1 and T2 relaxation times to the decreasing concentration of sugar (sucrose) in water was obtained. Non-destructive measurements T1 and T2 in table grapes suggested a possible prediction of sugar content in table grapes from the values of T1 or T2. This technique also presented many advantages compared to the conventional high field NMR technique, such as the fast measurements that do not require spectral processing, the ease of sample preparation, and its non-destructive nature. / AFRIKAANSE OPSOMMING: Die SQUID-NMR tegniek word al hoe meer aanbeveel deur navorsers oor die groot potensiaal, en dit beloof om in die toekoms van onskatbare waarde te wees in nie vernietigende evaluering. Die potensiaal moet grotendeels nog ontgin word, en die nie vernietigende kwaliteitsbeheer van voedselprodukte is een van die toepassings wat hier getoets word. Die vooruitgang tot dusver om die stelsel te verbeter wat die gebruikersvriendelikheid en koste-effektiwiteit betref, toon dat met effens meer moeite dit moontlik sal wees om die tegnologie aan te pas vir lynsortering van vrugte, en om dit dalk ook as handtoestel beskikbaar te stel. Die vooruitgang tot dusver om die stelsel te verbeter wat die gebruikersvriendelikheid en koste-effektiwiteit betref, toon dat met effens meer moeite dit moontlik sal wees om die tegnologie aan te pas vir lynsortering van vrugte, en om dit dalk ook as handtoestel beskikbaar te stel. Die doel is om die uitvoerbaarheid van interne vrugtekwaliteit metings deur hierdie tegniek te ondersoek en om ’n SQUID stelsel te ontwikkel wat gepas is vir SQUIDNMR toepassing, met die doel om dit later in ’n volledige SQUID-NMR stelsel te kan integreer. ’n Werkende GS-SQUID is vervaardig op ’n YBCO dunfilm wat op ’n 10 mm x 10 mm MgO substraat gedeponeer is. Die SQUID is van mikro-brug Josephson aansluitings/ voegvlakke, waarop in die loop van die vervaardigingsproses ’n patroon m et dubbelweerstand laser litografie neergelê is. Toets van die SQUID het ’n niehisterese stroom-spanning as kenmerkend getoon. Die nader bring en terugtrekking van ’n magneet het gelei tot waarneming van die modulasie van die I-V kurwe. Die kritieke stroom van die SQUID was 20 A en die weerstand was 5.5 ohm. ’n Reeks eksperimente is uitgevoer oor vernietigende metings van die suikerinhoud van tafeldruiwe met gebruik van NMR, om die gangbaarheid van hierdie tegniek te evalueer. Totale suikers (TSS) metings van dieselfde monsters is uitgevoer deur refraktometrie, wat gekies is as gebruiklike metode vir geldigheidsbepaling. Die NMR metings is as 5.4% presies/noukeurig evalueer, en met ’n akkuraatheid van 9.3% teenoor die refraktometrie metingsyfers. ’n Verdere reeks eksperimente is uitgevoer op ’n hoë-Tc SQID-NMR stelsel. ’n Hoë korrelasiekoëffisiënt van 0.85 van die toenemende waardes van T1 en T2 ontspantye teenoor die afname in konsentrasie van sukrose in water is waargeneem. Nie-vernietigende metings van T1 eb T2 in tafeldruiwe het gelei tot die moontlikheid van gebruik van hierdie tegniek om suikerinhoud van tafeldruiwe te voorspel. Die tegniek het ook baie voordele getoon in teenstelling met die gebruiklike hoëveld NMR tegniek, onder andere dat hierdie metings vinniger is, nie verdere verwerking van die spektrum benodig nie, die maklike voorbereiding van die monsters en die nie-vernietigende aard van die proses.

La capacité du virus de la grippe aviaire à traverser la barrière des espèces et à devenir fortement pathogène chez les mammifères est un problème majeur de santé publique. Chez les oiseaux, la réplication a lieu dans l'intestin, à 4C, tandis que chez les humains elle a lieu dans l'appareil respiratoire, plus froid, à 33C. Il a été montré que l'adaptation à la température du virus de la grippe a lieu par de nombreuses mutations de la polymérase virale, notamment dans le domaine 627-NLS situé en C-terminal de la protéine PB2. Ce domaine est impliqué dans l'adaptation à l'hôte et interagit avec la protéine de l'hôte, importine alpha, étant donc indispensable pour l'entrée de la polymérase virale dans le noyau de la cellule [Tarendeau et al., 2008]. Les structures cristallographiques du 627-NLS et du complexe importine alpha/NLS existent. Cependant, lors de la superposition de ces structures via leur domaine NLS commun, un important choc stérique entre le domaine 627 et l'importine alpha devient évident. Ceci indique qu'une autre conformation du 627-NLS est requise pour l'interaction avec l'importine alpha [Boivin and Hart, 2011]. Dans cette étude, nous avons examiné les bases moléculaires de l'adaptation inter-espèces du virus à travers l'étude de la structure et de la dynamique du 627-NLS aviaire et humain. Nous avons identifié deux conformations du 627-NLS en échange lent (10-100 s-1), correspondant apparemment à une conformation ouverte et une conformation fermée des deux domaines. Nous proposons que la conformation ouverte du 627-NLS est la seule conformation compatible avec l'interaction avec l'importine alpha, et que l'équilibre entre conformation ouverte et fermée pourrait jouer le rôle de thermostat moléculaire, contrôlant l'efficacité de la réplication virale chez différents hôtes. La cinétique et la dynamique de ce comportement conformationnel important ainsi que de l'interaction entre le 627-NLS et l'importine alpha ont été caractérisées par résonance magnétique nucléaire (déplacements chimique, augmentation paramagnétique de la relaxation, relaxation de spin, transfert de saturation par l'échange chimique), combinée à la diffusion des rayons X et des neutrons aux petits angles ainsi qu'au transfert d'énergie par résonance de type Förster. Aussi, nous avons déterminé les affinités d'une série de mutants évolutifs du 627-NLS pour l'importine alpha et du 627-NLS aviaire ou humain pour différents isoformes de l'importine alpha, montrant que les affinités observées sont cohérentes avec les préférences d'interactions vues in vivo. / The ability of avian influenza viruses to cross the species barrier and become dangerously pathogenic to mammalian hosts represents a major threat for human health. In birds the viral replication is carried out in the intestine at 40°C, while in humans it occurs in the cooler respiratory tract at 33°C. It has been shown that temperature adaption of the influenza virus occurs through numerous mutations in the viral polymerase, in particular in the C-terminal domain 627-NLS of the PB2 protein. This domain has already been shown to participate in host adaptation and is involved in importin alpha binding and therefore is required for entry of the viral polymerase into the nucleus [Tarendeau et al., 2008]. Crystallographic structures are available for 627-NLS and the complex importin alpha/NLS, however, a steric clash between importin alpha and the 627 domain becomes apparent when superimposing the NLS domain of the two structures, indicating that another conformation of 627-NLS is required for binding to importin alpha [Boivin and Hart, 2011]. Here we investigate the molecular basis of inter-species adaptation by studying the structure and dynamics of human and avian 627-NLS. We have identified two conformations of 627-NLS in slow exchange (10-100 s-1), corresponding to an apparently open and closed conformation of the two domains. We show that the equilibrium between closed and open conformations is strongly temperature dependent. We propose that the open conformation of 627-NLS is the only conformation compatible with binding to importin alpha and that the equilibrium between closed and open conformations may play a role as a molecular thermostat, controlling the efficiency of viral replication in the different species. The kinetics and domain dynamics of this important conformational behaviour and of the interaction between 627-NLS and importin alpha have been characterized using nuclear magnetic resonance chemical shifts, paramagnetic relaxation enhancement, spin relaxation and chemical exchange saturation transfer, in combination with X-ray and neutron small angle scattering and Förster resonance energy transfer. Also, we have determined the affinities of various evolutionnary mutants of 627-NLS to importin alpha and of avian and human 627-NLS to different isoforms of importin alpha, showing that the observed affinities are coherent with the preferred interactions seen in vivo.

En dépit de l’importance considérable des matériaux alumino- et borosilicates pour la catalyse, l’origine moléculaire de leur activité demeure mal comprise. Ceci tient à la difficulté de caractériser le désordre structural local généré au sein du réseau silicaté par l’incorporation d’hétéroatomes. Le caractère local de la résonance magnétique nucléaire (RMN) à l’état solide en fait une technique adaptée pour résoudre cette question majeure. Les silicates en feuillés auto-assemblés en présence de surfactants sont d’excellents systèmes modèles pour l’étude de la structure locale autour d’hétéroatomes de B ou d’Al car la synthèse, la structure moléculaire et la signature RMN 29Si simple de leurs formes siliceuses sont parfaitement maîtrisées. L’incorporation dans leurs réseaux silicatés de différentes quantités d’Al ou de B et leurs conséquences ont été étudiées par des méthodologies avancées de RMN permettant de sonder les interactions à travers l’espace ou les liaisons chimiques entre noyaux de 29Si, 27Al, 11B et/ou 1H, une approche qui peut être étendue à la substitution atomique dans une argile aluminosilicate et un nouveau borosilicate de calcium. Ces résultats ont été combinés à la modélisation moléculaire pour construire et valider des modèles structuraux capables de décrire les distorsions et les réarrangements parfois profonds du réseau résultant de la substitution. Cela a révélé des différences frappantes entre les conséquences de l’incorporation d’Al ou de B dans deux matériaux de morphologie semblables mais de structures moléculaires différentes, et offre une occasion unique de comprendre les propriétés régissant l’incorporation d’hétéroatomes dans les silicates. / While alumino- and borosilicate materials have paramount importance in catalysis, the molecular origin of their activity is not completely understood. This is mainly because the incorporation of heteroatoms into the silicate framework deteriorates the molecular order by generating local disorder that is particularly difficult to establish. Because of its local vision of ordered and disordered environments, solid-state nuclear magnetic resonance (NMR) can play a key role to solve this long-standing issue. Surfactant-directed layered silicate materials with short-range molecular order are particularly interesting model systems to study the local structures around Al or B heteroatoms because the synthesis, molecular structures, and simple 29Si NMR signatures of their pure-silicate forms are well understood. Various amounts of Al and B atoms were incorporated into their frameworks, and their consequences on the local structure were investigated by state-of-the-art multidimensional NMR measurements probing spatial proximities or bonding interactions between 29Si, 11B, 27Al, and 1H nuclei, an approach that could be extended to atomic substitution in an aluminosilicate clay and a new calcium borosilicate. These results were combined with molecular modeling to build and evaluate structural models that capture the local framework distortions and sometimes profound rearrangements resulting from the atomic substitutions. This reveals remarkable differences between the consequences of the incorporation Al or B in two distinct frameworks of otherwise strongly-related materials, and offers a unique opportunity to understand the properties that drive heteroatom incorporation.

Determinar la configuración absoluta de las moléculas quirales representa un gran reto para los químicos orgánicos. Para conseguir este objetivo existen diversas técnicas, las cuales se describen en el presente trabajo, así como ejemplos de cómo han sido utilizadas para la determinación de la configuración absoluta de productos naturales. / Methods for the assignment of the absolute configuration of an organic molecule: The assignment of the absolute configuration of chiral molecules represents a great challenge for organic chemists. There are several techniques in order to establish it, and they are described in this work, as well as examples of how they can be applied in the assignment of the absolute configuration of natural products.

The growing world demand for renewable energy production in substitution of fossil fuels has given great prominence in the culture of sugarcane (Saccharum sp.). This has been considered the most efficient crop for energy production, as Brazil being the world's largest producer, with a production of 655.6 million tons in 2015/2016 harvest in an area of 8.5 million hectares. One of the major obstacles to the production of sugarcane is still the attack by pest and estimates that about 10% of the crop losses are caused by insects, being a sugarcane borer (Diatraea Saccharalis) the most importante pest. The plants, during its evolution, to reduce the damages caused by the attack of pests, they have developed a series of defense mechanisms, among them, physical barriers, proteins and toxic metabolites and volatile metabolic flags. Many works have been developed to decipher the mechanisms of defense of sugarcane to the attack of herbivorous insects, an attempt of genetic breeding programs and information biotechnology for the development of more resistant plants, however, many of the mechanisms still remain to be clarified. These works are mostly restricted to the study of genes and proteins and global studies of transcript and proteome analyzes of the plant. The current work proposes to perform an analysis of the metabolism of two varieties of sugarcane (RB92579 and SP791011) through direct and indirect extraction methods in response to herbivory by Diatraea saccharalis using NMR spectroscopy and multivariate statistical analysis from data by principal component analysis (PCA) and least squares analysis of discrimination (OPLS-DA). In the metabolomic analysis of sugarcane of the variety RB92579 was studied using the direct extraction method (leaves) in the 4 herbivory times (24, 48, 72 and 96 hours), only after 48, 72 and 96 hours of stress by herbivory, it was possible to get differences between the control groups and herbivore groups, which the greater timing of response was obtained in 72 hours, that indicated the increase of the primary metabolites asparagine, aspartic acid, dimethylamine, glutamic acid , isoleucine, leucine, malic acid, tyrosine and phenylalanine. The variety of sugarcane SP791011, the method of indirect extraction of the leaves of the plant was applied in times 24, 48 and 72 hours by stress induced by caterpillars of Diatraea saccharalis and, coincidentally, showed in the time 72 hours a greater number of herbivory response metabolites, which caused a depletion of aconitic acid, formic acid, asparagine, alanine and elevation of acetic acid and chlorogenic acid. Despite their different metabolic profiles in response to herbivory, the elucidated metabolites suggest the metabolic pathway of shikimic acid to produce phenylpropanoids due to the increase of tyrosine, phenylalanine in the leaves of the sugarcane variety RB92579, and increase of chlorogenic acid in the leaves of the cane. In addition to the herbivory test, it was carried out a biological assay with chlorogenic acid inserted in the artificial diet of Diatraea saccharalis caterpillars, which demonstrated a decrease in the development time of the pupae comparing with pupae of Caterpillars Control, which caused an outbreak of moths with deformations at all concentrations of chlorogenic acid used in the bioassay. These results may help in the development of sugarcane varieties more resistant to the attack by Diatraea Saccharalis. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A crescente demanda mundial para a produção de energias renováveis em substituição aos combustíveis fósseis tem dado grande destaque à cultura da cana-de-açúcar (Saccharum sp.). Esta tem sido considerada a cultura mais eficiente para a produção de energia, tendo o Brasil como o maior produtor mundial, com uma produção de 655,6 milhões de toneladas na safra 2015/2016 em uma área de 8,5 milhões de hectares. Um dos grandes entraves à produção de cana-de-açúcar ainda é o ataque de pragas e doenças e estima-se que cerca de 10% das perdas para esta cultura sejam ocasionadas por insetos, sendo a broca da cana-de-açúcar (Diatraea saccharalis) a praga mais importante. As plantas, durante a evolução, para reduzir os danos causados pelo ataque de pragas, têm desenvolvido uma série de mecanismos de defesa, dentre eles, barreiras físicas, proteínas, metabólitos tóxicos e metabólitos voláteis sinalizadores. Muitos trabalhos têm sido desenvolvidos para decifrar os mecanismos de defesa da cana-de-açúcar ao ataque de insetos herbívoros, na tentativa de subsidiar programas de melhoramento genético e a biotecnologia de informação para o desenvolvimento de plantas mais resistentes, porém, muitos destes mecanismos ainda permanecem a ser esclarecidos. Estes trabalhos, em sua maioria, estão restritos ao estudo de genes e proteínas e a estudos globais de análises dos transcritos e do proteoma da planta. O presente trabalho propõe realizar a análise do metaboloma de duas variedades de cana-de-açúcar (RB92579 e SP791011) através dos métodos de extração direto e indireto na resposta a herbivoria por Diatraea saccharalis, utilizando espectroscopia de RMN, e processamento e estatística dos dados pelos métodos de análise de componentes principais (PCA) e análise dos mínimos quadrados parciais-análise discriminante (OPLS-DA). A análise metabolômica da cana-de-açúcar da variedade RB92579 foi realizada pelo método de extração direta (folhas) nos 4 tempos de herbivoria (24, 48, 72 e 96 horas), sendo que, apenas após 48, 72 e 96 horas sob herbivoria, foi possível haver diferenças entre os grupos controle e grupo herbivoria, no qual o tempo em que se obteve maior resposta da planta foi no tempo 72 horas, que indicou o aumento dos metabólitos primários asparagina, ácido aspártico, dimetilamina, ácido glutâmico, isoleucina, leucina, ácido málico, tirosina e fenilalanina. Já com relação a variedade de cana-de-açúcar SP 1011, aplicou-se o método de extração indireto das folhas da planta nos tempos 24, 48 e 72 horas sob estresse induzido pelas lagartas de Diatraea saccharalis e, coincidentemente, apresentou no tempo 72 horas o maior número de metabólitos de resposta a herbivoria, o que causou numa redução dos níveis de ácido cis e trans aconítico, ácido fórmico, asparagina, alanina e no aumento dos níveis de ácido acético e ácido clorogênico. Apesar de fornecerem perfis metabólicos diferentes em resposta a herbivoria, os metabólitos elucidados sugerem a via metabólica do ácido chiquímico devido ao aumento de tirosina, fenilalanina nas folhas da cana-de-açúcar da variedade RB92579, e aumento do ácido clorogênico nas folhas da cana-de-açúcar da variedade SP791011. Além do ensaio de herbivoria, foi realizado um ensaio biológico com o ácido clorogênico inserido na dieta artificial das lagartas de Diatraea saccharalis, que demonstrou uma diminuição do tempo de desenvolvimento das pupas em comparação com as pupas de lagartas controle, que provocou a eclosão das mariposas com deformações em todas as concentrações de ácido clorogênico usadas no bioensaio. Esses resultados podem ajudar no desenvolvimento de variedades de cana-de-açúcar mais resistentes ao ataque da Diatraea Saccharalis.

A Morte Súbita dos Cítros (MSC) é uma doença que afeta plantas de laranjeira-doce enxertadas em limão Cravo ou Volkameriano e ainda não tem o agente causal determinado. Para entender quais são as principais mudanças fisiológicas causadas pela MSC, analisou-se as alterações nos metabolitos primários, tanto da casca da copa quanto do cavalo. Fez-se análises dos extratos hexânico e alcoólico com RMN em alta resolução e do extrato hexânico com cromatografia gasosa. Também analisou-se os metabolitos diretamente nas cascas com técnicas de RMN em alta e baixa resolução. Com essas análises foi possível observar que a MSC altera a deposição de triacilglicerídeos e sacarose nas cascas. A MSC também modifica o perfil de ácidos graxos, com o decréscimo dos teores de ácido oléico e linolênico e aumento dos ácidos cáprico, láurico, mirístico, plamítico, esteárico e linoléico, com a evolução da doença. Com esses resultados foi possível entender as principais alterações bioquímicas causadas pela MSC, como também demonstrar que elas podem ser usadas de forma complementar no diagnóstico da doença. Dentre todos os métodos avaliados, as análises das cascas com RMN em baixa resolução, com as técnicas CPMG e de precessão livre em onda contínua (CWFP), foram as mais rápidas (em alguns segundos) e eficientes para discriminar as plantas assintomáticas das sintomáticas. A discriminação das plantas pelos dados de RMN foi realizada com métodos quimiométricos como análise de componentes principais (PCA), análises de agrupamentos hierárquicos (HCA) e regressão por mínimos quadrados parciais (PLS). / Citrus Sudden Death (CSD) is a new graft-transmissible disease of sweet orange grafted on Rangpur lime and Citrus volkameriana rootstocks. The causal agent is unknown. To understand the main physiological changes caused by the CSD, we analyzed the variations in the primary metabolites content in the bark of scion and rootstock. The hexanic and hydroalcoholic extracts were analyzed by high resolution NMR. The hexanic extracts were also analyzed by gas chromatography. The metabolites were also analyzed directly in the barks with high and low resolution NMR techniques. With these analyses it was possible to observe that CSD modifies the content of triglycerides and sucrose in the barks. The disease also changes the fatty acids profile, with a decrease in the oleic and linolenic and an increase in the capric, lauric, miristic, palmitic, stearic and linoleic content. With these results it was possible to understand the main biochemical disorders caused for the CSD, as well as to demonstrate that they can be used as complementary information in the disease diagnosis. The analysis of the barks with low resolution NMR techniques CPMG and continuous wave free precession (CWFP), had been the fastest (few seconds) and the most efficient one to discriminate between the symptomless and symptomatic plants. The discrimination of the plants by NMR data had been carried with chemometric methods such as principal component analysis (PCA), hierarchic cluster analysis (HCA) and partial least square regression (PLS).

Certain types of porphyrins can be used as achiral agent for determination of enantiomeric excess (ee) of chiral molecules. Particular organic chiral molecule (guest) and porphyrin (host) form host-guest complex while inducing nonequiv- alency of particular proton resonances in symmetrical host. It causes splitting of NMR signals linearly dependent on ee of guest. In this work we investigated com- plexation of di-brombenzylated oxoporphyrin with chiral camphorsulfonic acid. NMR titration revealed that they form complex with 1:1 stoichiometry with as- sociation constant K ≈ 5 × 104 l/mol. We confirmed linear dependence of split- ting of host β-protons on ee of guest. Low temperature measurements revealed two conformations of host-guest complex with population around 0.7:0.3 (at −60 ◦ C). DFT quantum mechanical computations at BLYP/3-21G* level revealed also two conformations with population 0.79:0.21. NMR shifts were computed on this geometries with method GIAO/PBE1PBE/6-31G(2df,2pd) and compared to experimental values. 1

Half-metallic ferromagnets (HMFs), with fully spin-polarized conduction electrons, are prime candidates for optimizing spintronic devices. Many Heusler compounds (a class of ternary and quaternary intermetallics) are predicted to be HMFs, in particular Co$_{2}YZ$ (where $Y$ is usually another transition metal, and $Z$ is an s-p element). Crystal structure is controlled by thermodynamics to a large extent. Ideally, one should be able to control and optimize properties which are of interest by appropriately "tuning" the structure (e.g. annealing), but first one must understand the structure and its relation to observed physical properties. A local structural probe technique such as nuclear magnetic resonance (NMR) is an essential tool for identifying and quantifying the various atomic-scale orderings. Different Heusler structure types and antisite disorders affect the material's physical properties. In this thesis, order-disorder phenomena in both bulk and thin film samples of Co$_2$Mn$_{1-x}$Si$_x$ and Co$_2$Mn$_{1-x}$Fe$_x$Si have been systematically studied using NMR. Though it is the films which are directly implemented in actual devices, studying bulk samples as model systems provides invaluable information regarding the material properties. The evolution of local atomic structure in numerous thin films has been shown to depend greatly on preparation parameters, including post-deposition annealing temperature, and specific stoichiometry. For Co$_2$MnSi films, the ideal post-annealing temperature for promoting the $L2_1$ atomic structure was found; the threshold temperature above which structure continues to become higher-ordered in the bulk, but where too much interdiffusion at the buffer interface occurs, degrading the smooth interfaces necessary for high magnetoresistance ratios. NMR also adds evidence that Co$_2$Mn$_x$Si$_{0.88}$ ($x>$1) electrodes in magnetic tunnel junctions have highest tunneling magneto-resistance because the excess Mn suppresses the formation of detrimental Co$_{Mn}$ antisites. A systematic investigation of several thermal and magnetic properties, including Sommerfeld coefficients, Debye temperatures, saturation magnetic moments, spin-wave stiffness, and magnon specific heat coefficient, were measured for selected Co$_2$-based ternary and quaternary Heusler compounds. Obtained values were compared with theoretical ones calculated using electronic band structure methods. It has been systematically shown that adding a magnon term to the specific heat has a negligible effect on the electronic contribution in all cases.