In this work, using the idea of an electrically conducting "functional unit," monomers and polymers with possible electronic and electro-optic applications were synthesized. The synthesis and polymerizations were, in many cases, novel and non-trivial. Dithiafulvene (1,3-dithiole) and variations of this functional unit were synthesized and incorporated into new condensation polymers. Polyesters, polyamides and polyhydrazones were all successfully synthesized and could be cast into films. These new polymers might be applicable as processable conducting materials if compatible dopants are employed or by themselves in the area of third order non-linear optics. Using a (meth)acrylate backbone, a spacer group of six methylene units, and a phenyl-CO₂-phenyl mesogen, linked by an ester group to a strongly polar optically active center containing a methoxy group, three new novel monomers and polymers were designed to exhibit smectic C* liquid-crystal phases. The polymers exhibited liquid crystalline behavior as was shown in differential scanning calorimetry and optical microscopy. Further studies and investigations in the synthesis of pure (meth)acrylate esters and their homopolymers yielded surprising results with regard to the Schotten-Baumann reaction. Interestingly, the use of meth(acryloyl) chloride in this scheme leads to (meth)acrylic anhydride, which is not easily isolable from distillable products. This anhydride is responsible for gelation in the polymerization of glycolate esters, and cannot be removed by work-up with various nucleophiles without disrupting desired ester functions. An S(N)2 method is recommended in this work.

The root epidermis, being the outermost cell layer of the organ, is in contact with the soil environment. The position of the epidermis determines its important roles, such as taking up water and ions from the surrounding soil, and defending against harmful microorganisms. What is the chemical composition of the walls in this layer? The chemical nature of the soybean epidermal wall modifying substance was investigated in this study with the use of histochemical tests coupled with electron microscopy, and chemical depolymerizations in combination with chromatography. Soybean (<em>Glycine max</em>) was used as a test species in the present studay. Results of histochemical and electron microscopical studies indicated that the epidermal walls are modified with suberin. The suberized epidermal walls were permeable to apoplastic tracers, differing from those of cells with suberized Casparian bands, possibly due to the spatial distribution or chemical components of the suberin. Suberin may occur in a diffuse form linked with other wall components in the epidermis. What is the chemical nature of this modification, and does it play a role in pathogen resistance? The root epidermal wall compositions of two soybean cultivars were compared; one (cv. Conrad) is resistant to <em>Phytophthora sojae</em> and the other (cv. OX 760-6) is susceptible to this root-rot oomycete. Their epidermal walls were isolated enzymatically and subjected to two different degradation methods, i. e. BF₃-MeOH transesterification and nitrobenzene oxidation. The compositions of depolymerisates of the cell walls determined by GC-MS indicated four dominant suberin monomers varying in chain length from C16 to C24. In all epidermal cell walls, &omega;-hydroxycarboxylic acids were more abundant than diacids, carboxylic acids and alcohols. Two of the monomers detected (hydroxycarboxylic acid and a,&omega;-dicarboxylic acid) are known to be characteristic suberin markers. The quantitative chemical compositions significantly differed in the epidermal cell walls of the two soybean varieties. Walls of the resistant cultivar (Conrad) had a greater quantity of both the aliphatic and aromatic components of the polymer than the susceptible cultivar (OX760-6), providing evidence to support the hypothesis that preformed suberin plays a role in plant defense.

L'objectif de ce travail est d'étudier la faisabilité d'ajout de sel nylon à un polyamide (PA) par un procédé d’extrusion réactive. Dans ce cadre, l'ajout de sel 6T comprenant des motifs aromatiques à du PA 66 est réalisé dans le but de synthétiser du PA 66/6T. En effet, ce dernier répond à la demande actuelle en polymères à haute résistance thermique. Le taux d'avancement de la réaction et le taux de motifs 6T insérés doivent dès lors être maximisés.Le travail comprend les synthèses et les analyses du sel 6T, du PA 6T et du PA 66/6T. Le sel 6T est produit puisqu'il n'est pas commercialisé. Le PA 6T est synthétisé pour permettre l’identification des hydrogènes aromatiques du PA 66/6T. Le travail sur ce dernier nécessite la mise au point et l'étude du procédé d'extrusion. Pour ce faire, les influences d'un certain nombre de paramètres opératoires sont étudiées comme, par exemple, le niveau de vide sur les évents de l'extrudeuse.Les meilleures conditions opératoires du procédé permettent d’obtenir un taux d'avancement de 93 mol% et un taux d'insertion de motifs 6T de 15,3 mol%. Néanmoins, le PA 66/6T produit présente un fort excès de fonctions terminales acides / The aim of this work is to study the feasibility of addition of nylon salt to polyamide (PA) by a reactive extrusion process. As example, the addition of 6T salt, which includes aromatic monomers, to PA 66 is performed in order to synthesize PA 66/6T. This latter replies to demand of high resistance temperature polymer. Consequently, the progress rate of the reaction and the rate of 6T motifs insertion have to be maximized.This work includes the synthesis and the analysis of 6T salt, PA 6T and PA 66/6T. 6T salt synthesis is performed since it is not commercialised. PA 6T is synthesized in order to identify aromatic hydrogen in PA 66/6T molecule. About this latter, it is necessary to adjust and to study the extrusion process. So, the influences of few process parameters are studied as, for example, pressure level on vent gas of the extruder.With the best process parameters, the progress rate is 93 mol% and the rate of 6T motifs insertion is 15,3 mol%. Yet, PA 66/6T presents a significant excess of acidic end group

Este estudo teve como objetivo investigar múltiplos aspectos relacionados a polimerização da resina composta como: o grau de conversão monomérica (GC), parâmetros da cinética de polimerização e a determinação de monômeros residuais TEGDMA e BisGMA, além de avaliar o desempenho de aparelhos fotoativadores. As resinas compostas experimentais foram manipuladas variando-se os fotoiniciadores R1-) canforoquinona/amina, R2-) PPD/amina, R3-) PPD + canforoquinona/amina) e foram utilizados dois aparelhos para a fotoativação (I-) lâmpada halógena (Demetron LC/ SDS Kerr-USA) e II-) LED (Poly 600/Kavo-Brasil) ambos com 600 mW cm-2, por 40 s. O GC após 300 s e os parâmetros de cinética como taxa máxima de conversão (Rpmáx), tempo em que ocorreu a taxa máxima de polimerização (tmáx) e a conversão quando ocorreu a Rpmáx, foram determinados por meio de espectroscopia de absorção no infravermelho em tempo real (RT-FTIR), Os espectros foram coletados dos espécimes (n=5) no modo cinética, durante 305 s, entre 1680 e 1550 cm-1. As 5 primeiras varreduras coletadas serviram para fornecer o espectro de absorção da resina não polimerizada (utilizado no cálculo do GC). Na 6&ordm; varredura, o fotoativador foi ligado (por 40 segundos) enquanto o espectro continuava a ser coletado até 300 s após a ativação da luz. A presença de monômeros residuais (TEGDMA e BisGMA) foi avaliada por meio da cromatografia líquida de alta eficiência (HPLC), sendo que os espécimes (n=6) foram imersos em acetonitrila (5 mL-24 h) com agitação mecânica, o método desenvolvido utilizou: HPLC, coluna C18, fase móvel A: água com trietilamina (0,05%) acidificada com ácido acético (pH 4) e B: acetonitrila, modo de eluição com gradiente (40-85%-17 min/ 55&deg;C), fluxo de 1 mL min-1, detector UV em 210 nm, injeção de 20 &micro;L. Em relação aos resultados de GC após 300 s os maiores valores foram para a resina R1 tanto fotoativada com LED (65,90% &plusmn;1,81) quanto com a lâmpada halógena (64,40% &plusmn;0,83), e os menores valores encontrados foram quando a resina R2 foi fotoativada pelo LED (35,64% &plusmn;1,73) e a única resina que apresentou diferenças significantes em relação as fontes de luz foi a R2. Os valores da Rpmáx diminuíram nas resinas que apresentavam o fotoiniciador PPD. O tempo de ocorrência da taxa máxima de conversão (tmáx) aconteceu mais rapidamente para a resina com CQ. Todas as resinas apresentaram valores de grau de conversão similares no tmáx. Em relação aos resultados de HPLC, a quantidade de monômeros extraídos (M/M%) variou de 1,98% &plusmn;0,16 à 3,34% &plusmn;0,07 para os monômeros TEGDMA e de 3,57% &plusmn;0,30 à 7,57% &plusmn;0,40 para os monômeros BisGMA. A resina R2 apresentou a maior quantidade de monômeros residuais quando fotoativada com ambas as fontes, principalmente quando fotoativada com o LED. As resinas R1 e R3 obtiveram comportamento parecidos para ambos fotoativadores. Conclui-se que a resina R3 pode ser uma boa opção, pois quando comparada com a resina R1 apresentou vantagens como: redução na Rpmáx, bem como o momento em que esta ocorreu (tmáx), além de ser adequadamente fotoativada com aparelhos de LED. / This study aimed to investigate multiple aspects of composite resin polymerization as the degree of monomer conversion (DC), the kinetic parameters of polymerization and the determination of residual monomers TEGDMA and BisGMA, and evaluate the performance of light curing units. The experimental composites were manipulated by varying the photoinitiators R1-) camphorquinone/amine, R2-) PPD/amine, R3-) PPD + camphorquinone/ amine) and two devices were used for the polymerization I-) halogen lamp (Demetron LC / SDS Kerr, USA) and II-) LED (Poly 600/Kavo-Brasil) both with 600 mW cm-2 for 40 s. DC after 300 s and the kinetic parameters such as maximum rate of polymerization conversion (Rpmax), time of occurrence of the maximum rate of polymerisation (tmax) and the conversion occurred when Rpmax were determined by infrared absorption spectroscopy in real time (RT-FTIR), the infrared spectrum was collected from the specimen (n=5) in order kinetics for 305 s, between 1680 and 1550 cm-1. The first 5 scans were used to provide the collected absorption spectrum of the uncured resin (calculated DC). In the sixth scan, the curing unit was connected (by 40 seconds) while the spectrum continued to be collected up to 300 s after activation of the light. The presence of residual monomers (TEGDMA and BisGMA) was assessed by high performance liquid chromatography (HPLC), and the specimens (n=6) were immersed in acetonitrile (5 mL-24 h) with mechanical stirring, the method developed used: HPLC, C18 column, mobile phase A: water with triethylamine (0,05%) acidified with acetic acid (pH 4) and phase B: acetonitrile, gradient elution mode (40-85% -17 min/55 &deg;C), flow 1 mL/min, UV detector at 210 nm, injection of 20 &micro;L. Regarding the results of DC after 300s were the highest values for both R1 resin polymerized with LED (65.90% &plusmn;1.81) and with a halogen lamp (64.40% &plusmn;0.83), and lower values when the resin was found that R2 was polymerized by LED (35.64% &plusmn;1.73) and the only resin that showed significant differences in the sources of light was the R2. The values of the resins decreased Rpmax who had PPD photoinitiator. The time of occurrence of the maximum rate of conversion (tmax) occurred more rapidly for the resin with CQ. And all resins showed values similar degree of conversion in tmax. For HPLC results, the amount of monomer extracted (M/M%) ranged from 1.98% &plusmn;0.16 to 3.34% &plusmn;0.07 for the monomers of TEGDMA and 3.57% &plusmn;0.30 to 7.57% &plusmn;0.40 for the monomers BisGMA. Resin R2 showed the highest amount of residual monomers as polymerized with both sources, especially when polymerized with LED. Resins R1 and R3 had similar behavior for both curing units. In conclusion, the resin R3 can be a good choice, as compared with the resin obtained R1 advantages as reduction in Rpmax as well as the time it occurred (tmax), and be suitably photoactivated with LED devices.

Os monômeros ligantes 3amdpy2oxaNBE (1), 3imdpyoxaNBE (2) e ácido âmico (3) foram sintetizados e caracterizado por analise elementar (CHN), infravermelho e RMN 1H e 13C. A partir do monômero 1 sintetizou-se compostos partindo de complexos do tipo [RuCl2(LL)], onde foi LL=bpy 37 (complexo 4), phen (complexo 6) ou 5-Cl-phen (complexo 7), e foram realizados estudos de fotoquímica e fotofísica. Os complexos 6 e 7 apresentaram uma eficiente fotofísica e não apresentaram fotoquímica, enquanto os complexos semelhante [Ru(bpy)2(3amnpy)2](PF6)2 (5) e [Ru(phen)2(3amnpy)2](PF6)2 (8) que possui a aminopiridina no lugar do monômero 1, apresentaram fotoquímica. Observou-se que as diferenças na rigidez dos ligantes phen e bpy podem causar diferentes propriedades fotoquímicas e fotofísicasem sistemas do tipo cis-[RuCl2(?-diimina)]. Todos os complexos exibiram absorções na região de 350 nm e entre 420 a 500 nm. Sendo que 5 e 8 apresentaram fotoquímica e os complexos 6 e 7 apresentaram fotofisica. Estes foram estudados em diferentes solventes (DMF, CH3CN, CH2Cl2, THF) e em diferentes comprimentos de onda de irradiação (340, 440 e 500 nm). A emissão dos complexos 6 (580 nm) e 7 (582 nm) em acetonitrila é atribuída a uma MLCT (Ru_phen). Sendo observada a independência do _irr, mas existe dependência da emissão quando a temperatura é abaixada. Além disso, suas propriedades fotocatalíticas são demonstradas pela supressão oxidativa através de íons receptores do metilviologenio. Ainda deve-se levar em conta que, o anel quelante do monômero ligante 1 contribui ainda mais para a estabilização destes complexos, ao contrario, 5 e 8 possuem uma fotolabilização . / The monomer ligands 3amdpy2oxaNBE (1), 3imdpyoxaNBE (2) and amic acid (3) were synthesized and characterized by elementar analysis (CHN), infrared and 1H e 13C NMR. Since monomer 1, it was synthesized complexes of type [RuCl2(LL)], where LL=bpy 37 (complex 4), phen (complex 6) or 5-Cl-phen (complexo 7), with which photophysics and photochemical studies were performed. The complexes 6 and 7 presented efficient photophysics and they do not presented photochemistry, while the similar complexes [Ru(bpy)2(3amnpy)2](PF6)2 (5) and [Ru(phen)2(3amnpy)2](PF6)2 (8), which possess the aminopyridine in place of monomer 1, presented photochemistry. It was observed that the difference in the rigidity of the ligands phen and bpy may cause different photochemical and photophysical properties in systems of type cis-[RuCl2(?- diimine)]. All complexes exhibited absorptions in region of 350 nm and between 420 and 500 nm, where 5 and 8 presented photochemistry and the complexes 6 and 7 presented photophysics. They were studied in different solvents (DMF, CH3CN, CH2Cl2, THF) and in different irradiation wavelength (340, 440 e 500 nm). The emission of the complexes 6 (580 nm) and 7 (582 nm) in acetonitrile is attributed to an MLCT (Ru_phen). It was observed independence of _irr, however there is dependence of emission when the temperature is lowered. Furthermore, their photocatalytic properties are demonstrated by oxidative quenching using methylviologen ion. One should consider that the chelating ring of monomer ligand 1 contributes even more to the stabilization of these complexes, unlike, 5 and 8 that possess photolabilization.

Este estudo teve como objetivo investigar múltiplos aspectos relacionados a polimerização da resina composta como: o grau de conversão monomérica (GC), parâmetros da cinética de polimerização e a determinação de monômeros residuais TEGDMA e BisGMA, além de avaliar o desempenho de aparelhos fotoativadores. As resinas compostas experimentais foram manipuladas variando-se os fotoiniciadores R1-) canforoquinona/amina, R2-) PPD/amina, R3-) PPD + canforoquinona/amina) e foram utilizados dois aparelhos para a fotoativação (I-) lâmpada halógena (Demetron LC/ SDS Kerr-USA) e II-) LED (Poly 600/Kavo-Brasil) ambos com 600 mW cm-2, por 40 s. O GC após 300 s e os parâmetros de cinética como taxa máxima de conversão (Rpmáx), tempo em que ocorreu a taxa máxima de polimerização (tmáx) e a conversão quando ocorreu a Rpmáx, foram determinados por meio de espectroscopia de absorção no infravermelho em tempo real (RT-FTIR), Os espectros foram coletados dos espécimes (n=5) no modo cinética, durante 305 s, entre 1680 e 1550 cm-1. As 5 primeiras varreduras coletadas serviram para fornecer o espectro de absorção da resina não polimerizada (utilizado no cálculo do GC). Na 6&ordm; varredura, o fotoativador foi ligado (por 40 segundos) enquanto o espectro continuava a ser coletado até 300 s após a ativação da luz. A presença de monômeros residuais (TEGDMA e BisGMA) foi avaliada por meio da cromatografia líquida de alta eficiência (HPLC), sendo que os espécimes (n=6) foram imersos em acetonitrila (5 mL-24 h) com agitação mecânica, o método desenvolvido utilizou: HPLC, coluna C18, fase móvel A: água com trietilamina (0,05%) acidificada com ácido acético (pH 4) e B: acetonitrila, modo de eluição com gradiente (40-85%-17 min/ 55&deg;C), fluxo de 1 mL min-1, detector UV em 210 nm, injeção de 20 &micro;L. Em relação aos resultados de GC após 300 s os maiores valores foram para a resina R1 tanto fotoativada com LED (65,90% &plusmn;1,81) quanto com a lâmpada halógena (64,40% &plusmn;0,83), e os menores valores encontrados foram quando a resina R2 foi fotoativada pelo LED (35,64% &plusmn;1,73) e a única resina que apresentou diferenças significantes em relação as fontes de luz foi a R2. Os valores da Rpmáx diminuíram nas resinas que apresentavam o fotoiniciador PPD. O tempo de ocorrência da taxa máxima de conversão (tmáx) aconteceu mais rapidamente para a resina com CQ. Todas as resinas apresentaram valores de grau de conversão similares no tmáx. Em relação aos resultados de HPLC, a quantidade de monômeros extraídos (M/M%) variou de 1,98% &plusmn;0,16 à 3,34% &plusmn;0,07 para os monômeros TEGDMA e de 3,57% &plusmn;0,30 à 7,57% &plusmn;0,40 para os monômeros BisGMA. A resina R2 apresentou a maior quantidade de monômeros residuais quando fotoativada com ambas as fontes, principalmente quando fotoativada com o LED. As resinas R1 e R3 obtiveram comportamento parecidos para ambos fotoativadores. Conclui-se que a resina R3 pode ser uma boa opção, pois quando comparada com a resina R1 apresentou vantagens como: redução na Rpmáx, bem como o momento em que esta ocorreu (tmáx), além de ser adequadamente fotoativada com aparelhos de LED. / This study aimed to investigate multiple aspects of composite resin polymerization as the degree of monomer conversion (DC), the kinetic parameters of polymerization and the determination of residual monomers TEGDMA and BisGMA, and evaluate the performance of light curing units. The experimental composites were manipulated by varying the photoinitiators R1-) camphorquinone/amine, R2-) PPD/amine, R3-) PPD + camphorquinone/ amine) and two devices were used for the polymerization I-) halogen lamp (Demetron LC / SDS Kerr, USA) and II-) LED (Poly 600/Kavo-Brasil) both with 600 mW cm-2 for 40 s. DC after 300 s and the kinetic parameters such as maximum rate of polymerization conversion (Rpmax), time of occurrence of the maximum rate of polymerisation (tmax) and the conversion occurred when Rpmax were determined by infrared absorption spectroscopy in real time (RT-FTIR), the infrared spectrum was collected from the specimen (n=5) in order kinetics for 305 s, between 1680 and 1550 cm-1. The first 5 scans were used to provide the collected absorption spectrum of the uncured resin (calculated DC). In the sixth scan, the curing unit was connected (by 40 seconds) while the spectrum continued to be collected up to 300 s after activation of the light. The presence of residual monomers (TEGDMA and BisGMA) was assessed by high performance liquid chromatography (HPLC), and the specimens (n=6) were immersed in acetonitrile (5 mL-24 h) with mechanical stirring, the method developed used: HPLC, C18 column, mobile phase A: water with triethylamine (0,05%) acidified with acetic acid (pH 4) and phase B: acetonitrile, gradient elution mode (40-85% -17 min/55 &deg;C), flow 1 mL/min, UV detector at 210 nm, injection of 20 &micro;L. Regarding the results of DC after 300s were the highest values for both R1 resin polymerized with LED (65.90% &plusmn;1.81) and with a halogen lamp (64.40% &plusmn;0.83), and lower values when the resin was found that R2 was polymerized by LED (35.64% &plusmn;1.73) and the only resin that showed significant differences in the sources of light was the R2. The values of the resins decreased Rpmax who had PPD photoinitiator. The time of occurrence of the maximum rate of conversion (tmax) occurred more rapidly for the resin with CQ. And all resins showed values similar degree of conversion in tmax. For HPLC results, the amount of monomer extracted (M/M%) ranged from 1.98% &plusmn;0.16 to 3.34% &plusmn;0.07 for the monomers of TEGDMA and 3.57% &plusmn;0.30 to 7.57% &plusmn;0.40 for the monomers BisGMA. Resin R2 showed the highest amount of residual monomers as polymerized with both sources, especially when polymerized with LED. Resins R1 and R3 had similar behavior for both curing units. In conclusion, the resin R3 can be a good choice, as compared with the resin obtained R1 advantages as reduction in Rpmax as well as the time it occurred (tmax), and be suitably photoactivated with LED devices.

Thesis (Ph. D.)--University of Wyoming, 2006. / Title from PDF title page (viewed on Dec. 21, 2007). Includes bibliographical references.

Thesis (Ph. D.)--University of Wyoming, 2006. / Title from PDF title page (viewed on Dec. 21, 2007). Includes bibliographical references.

The root epidermis, being the outermost cell layer of the organ, is in contact with the soil environment. The position of the epidermis determines its important roles, such as taking up water and ions from the surrounding soil, and defending against harmful microorganisms. What is the chemical composition of the walls in this layer? The chemical nature of the soybean epidermal wall modifying substance was investigated in this study with the use of histochemical tests coupled with electron microscopy, and chemical depolymerizations in combination with chromatography. Soybean (<em>Glycine max</em>) was used as a test species in the present studay. Results of histochemical and electron microscopical studies indicated that the epidermal walls are modified with suberin. The suberized epidermal walls were permeable to apoplastic tracers, differing from those of cells with suberized Casparian bands, possibly due to the spatial distribution or chemical components of the suberin. Suberin may occur in a diffuse form linked with other wall components in the epidermis. What is the chemical nature of this modification, and does it play a role in pathogen resistance? The root epidermal wall compositions of two soybean cultivars were compared; one (cv. Conrad) is resistant to <em>Phytophthora sojae</em> and the other (cv. OX 760-6) is susceptible to this root-rot oomycete. Their epidermal walls were isolated enzymatically and subjected to two different degradation methods, i. e. BF₃-MeOH transesterification and nitrobenzene oxidation. The compositions of depolymerisates of the cell walls determined by GC-MS indicated four dominant suberin monomers varying in chain length from C16 to C24. In all epidermal cell walls, &omega;-hydroxycarboxylic acids were more abundant than diacids, carboxylic acids and alcohols. Two of the monomers detected (hydroxycarboxylic acid and a,&omega;-dicarboxylic acid) are known to be characteristic suberin markers. The quantitative chemical compositions significantly differed in the epidermal cell walls of the two soybean varieties. Walls of the resistant cultivar (Conrad) had a greater quantity of both the aliphatic and aromatic components of the polymer than the susceptible cultivar (OX760-6), providing evidence to support the hypothesis that preformed suberin plays a role in plant defense.

This thesis presents the crystal structures of 2', 5', cyclic and modified nucleosides / nucleotides. Chapter I gives a brief account of the structural studies on 2', 5' and modified nucleotides. It also presents a short, summary of unusual nucleic acids structures studies on hydration patterns and metal ion interactions Nomenclature and conventions used for describing the conformatioNa1 features are presented. FiNa1ly, the crystallographic suite of programs used for processing the intensity data, structure solution, refinement and generating various diagrams are mentioned. Chapter II describes the crystal structures of anhydrous and hydrated sodium salt of N6-methyl adenosine-S'-monophosphate. N6-AMP-A (anhydrous form) belongs to the trigoNa1 space group P3221 with unit cell dimensions a = b = 10.30 A and c= 25.03 A while N6-AMP-H (hydrated form) belongs to orthorhombic space group C222X with a= 6.910 A, b= 19.318 A, and c= 41.070 A. CuKα intensity data consisting of 1740 and 2740 observed reflections were collected on a CAD4 diffractometer. Both structures were solved using SHELXS97 and refined to R factors of 0.0336 and 0 0381 for anhydrous and hydrated forms respectively. In both structures the adenine bases are in the ant% conformation with respect to the ribose but their torsion angles XCN differ significantly by 78° The ribose moiety shows CS-endo puckering and the conformation about the C4/-C5/ bond is g+ and t in the anhydrous and hydrated structures respectively. The two Na+ ions, present m the hydrated form, coordinate with water oxygen atoms only. A notable feature of the Na+ ion coordination in the anhydrous form is the participation of N3 and N7 of the base besides macrochelation between base-ribose and base-phosphate moieties. Adenine bases in both forms stack at a separation of about 3.4 A between them N6-AMP molecules pack as if one set of bases intercalate between the other set in the hydrated structure while they form helix like pattern m the anhydrous structure Molecular dynamics calculations were carried out for both structures with a view to obtain greater insight into the effect of hydration on the conformation of the molecule. Stereochemically permissible models for poly-A using the N6-AMP-H coordinates were generated using the method developed by Srinivasan and Olson. Its features and possible biological relevance are discussed. Chapter III deals with the structure of sodium adenosine-5'-monosulfate trihydrate (5'-AMS). Intensity data for this modified nucleotide were collected at the Brookhaven NatioNa1 Laboratory, Synchrotron facility, USA. 5'-AMS belonged to the orthorhom bic space group P2!2!2i with unit cell parameters a= 20.698 A, b= 24.621 A and c= 25.925 A and eight molecules, eight Na+ ions and 23 water molecules in the asymmetric unit of the lattice. Never before a nucleotide structure having eight molecules in the asymmetric unit has been reported. Out of 84177 reflections collected using a radiation of A =0.92 A, 9108 independent reflections having Io>2a(Io) were considered observed. The structure was solved using the program Shake and Bake (SnB) and refined by, SHELXL97. The fiNa1 R factor for 1971 parameters was 0.0397. Adenine bases of all the eight 5'-AMS molecules are in anti conformation with respect to the ribose moiety with XCN angles varying from -150 to -177°. But the conformations of the ribose moieties and the sulfate groups about the C4/-C5/ bond are not the same for all the molecules. 5'-AMS molecules A, B and D show C2-exo-C3-endo mixed puckering while C has C£-exo puckering. The remaining four molecules E, F, G and H have C3-endo conformation. The conformation about the C4/-C5/ bond for molecules A, B, C and D is g~ while for E, F and G it is g+. Molecule H shows both g+ and g~ since the 05' atom is disordered. An important feature of the metal ion coordination is the bidentate formation by sodium ions Na3 and Na7 with the sulfate group of molecule C and ribose hydroxyl oxygen atoms of molecule D respectively. Another feature which deserves mention is the participation of Nl and N7 of the adenine base m metal coordination Adenine bases of molecules A, B, C and D form self pairs with those of H, G, F and E respectively through N6...N7 and N6...N1 hydrogen bonds. The 5'-AMS molecules pack as duplexes in the unit cell. A Stereochemically permissible model for poly-A with sugar sulfate backbone using the 5'-AMS coordinates were generated using the method developed by Srinivasan and Olson and its features are discussed. Crystal structures of two polymorphs of mixed sodium and potassium salts of cytidine-5'-monophosphate hexahydrate are discussed in Chapter IV. The two polymorphs of 5'-CMP were grown using methanol and DMF respectively m the crystallization experiments. MoKα intensity data for CMP-I were collected on a Rigaku AFC image plate system while that for CMP-II were collected on a Bruker CCD Smart system. Both belong to the monoclinic space group P2X with a= 8.869 A, b= 20 580 A, c= 23.179 A, β= 105.79° and a= 8.929 A, b= 22.257 A and c= 20.545 A, β= 90.02° for CMP-I and II respectively. The the unit cell volume of the two polymorphs differ by just 12 A3 as the unit cell parameters are same, although the b and c axes are interchanged m CMP-II and their β value differs by 16°. Both polymorphs of CMP have four nucleotide molecules in the asymmetric unit of their orthorhombic lattices. But the number of metal ions and solvents are not the same in the two structures. CMP-I has five sodium ions, three potassium ions, 23 water and two methanol molecules while CMP-II has two sodium ions, four potassium ions, 22 water and an unknown solvent molecule (assigned as dimethyl ether) in the asymmetric unit. This is the first nucleotide structure having two different alkali metal ions (Na+ and K4") in the crystal structure. Out of 36946 and 31293 reflections collected 12247 and 15476 independent reflections having IO>2<J(I0) were considered observed for CMP-I and II respectively. Both structures were solved by combination of heavy-atom and direct methods using DIRDIF96 and refined using SHELXL97 to R factors of 0.0819 and 0 0867 for CMP-I and II respectively In both forms all the four molecules have anti conformation about the glycosidic bond, CS-endo conformation for the ribose moiety and g+ conformation about the C4'-C5' bond but their metal coordination patterns are significantly different. K1 ion in CMP-I forms an intra molecular macrochelate between the ribose and adenine base while K2 and K3 ions form bidentates with the cytosine and phosphate group of molecules A and D respectively. Na1, Na3 and Na5 are all involved in bidentate interactions with the ribose of molecule C, ribose of molecule A and phosphate of molecule D respectively. In contrast, Na2 and Na4 coordinates with solvent atoms only and do not interact with the nucleotide atoms at all. K1 and K2 ions of CMP-II form bidentates with the cytosines of molecules C and D respectively while K2 and K4 form intra molecular macrochela-tion between the base and ribose of molecules C and B respectively. Na1 and Na2 form bidentates with the ribose of molecules C and D respectively Comparison of the two polymorphs of CMP reveals that despite several striking conformatioNa1 similarities there are also significant differences between them. It was noticed that molecules A, B, C and D of CMP-I corresponds to C, B, D and A of CMP-II. Out of eight metal ions (five Na+ and three K+ ions) present in CMP-I four of them (Kl, K2, K3 and Na3) are found to have partners (K4, Kl, K3 and Na1) in CMP-II within a distance of 0.75 A. One of the water molecules OW8 of CMP-I is replaced by a potassium ion K2 in CMP-II within a distance of 0.92 A. Out of 23 water molecules present in the structure 14 are common to both of them and only 8 are different while one is replaced by an ion. The four crystallographically independent 5'-CMP molecules are linked by metal ions Kl, K3, Na1, Na3, Na5 and Kl, K2, K4, Na1 ions forming a tetramers in CMP-I and CMP-II respectively. An interesting feature of CMP-I and CMP-II is the simultaneous display of base-base and base-ribose stacking patterns. The four nucleotide molecules in the asymmetric unit are related by several pseudo two-fold axis and the r.m.s. Deviations between them after applying the pseudo symmetry are 0.21 and 0.17 A for CMP-I and II respectively. The nucleotide molecules in CMP-I and II pack as infinite linear chains parallel to the b and c axis respectively which repeat along the c and b axis respectively. In between these nucleotide columns metal ions and water molecules are located forming channels between them. Chapter V deals with anhydrous cytidine-2/-phosphate and potassium uridine-5'-phosphate hexahydrate structures. 2'-CMP crystallizes m the orthorhombic space group P212121 with a= 6.698 A, b= 7.436 A and c= 25.291 A with one molecule in the asymmetric unit. MoKα intensity data were collected on a CCD SMART system consisting of 7647 reflection of which 1456 independent reflections having lo>2a(lo) were considered observed. The structure was solved and refined to an R factor of 0.0385 for 186 parameters using SHELXL97. The cytosine base is in the anti conformation with respect to the ribose with XCN = -141.1° similar to that in the hydrated structure. But it differs significantly from the syn conformation observed in several 2'-purine and 2'-5' dinucleotide structures containing purine-pyrimidine sequences. The ribose moiety shows Ctf-endo and the conformation about the C4/-C5/ bond is t with (f)α = 169.3° and <pO( = -72 7° The t conformation in the anhydrous form is different from the g+ conformation m the hydrated form of 2'-CMP 5'-UMP.K crystallizes in the monoclinic space group P2;i with a= 13 034 A, b= 8 916 A, c= 16 205 A and β=98 64° with two nucleotides, four K ions and ten water molecules in the asymmetric unit MoKα intensity data of 19261 were measured on a Bruker CCD system of which 6891 independent reflections having lo>2a(lo) were accepted as observed. The structure was solved and refined by full matrix least square methods to an R factor of 0.0324 for 609 parameters. Uracil bases of both nucleotide molecules are in the anti conformation with respect to the ribose with XCN= -129.4° and -132 7°. Uracil bases of both nucleotide molecules are protonated at N3 Both ribose moieties show C2’-endo puckering with C2' atom displaced by 0.57 and 0.59 A from the best plane constituted by the remaining atoms The phosphate group is in a staggered orientation and the conformation about the C4/-C5/ bond is g* with <j>00 = -67.1 and -62.7 and Øoc = 54.6 and 59.5 for molecules A and B respectively. Potassium ion K2 forms a bidentate by coordinating with ribose 02' and 03' atoms of molecule B and a macrochelate between the uracil base and ribose of molecule A by coordinating with 02 and 02' atoms. K4 also forms a bidentate by coordinating with ribose O2' and 03' atoms of molecule A. The two 5'-UMP molecules form a dimer by coordinating with K2 and K3 ions. They are related by a pseudo two-fold axis and the r.m.s. deviation between the coordinates is 0 12 A. Crystal structures of 8-Benzylamino cychc-3'-5'-monophosphate (8-Benz-cAMP) and 8-mercaptoguanosine (8-MERG) are presented in Chapter VI. 8-Benz-cAMP crystallizes in the monoclinic space group P2x with unit cell dimensions a= 7.989 A, b= 12 589 A, c= 11.773 A and β= 93.82°. MoKα data were collected on a CCD system yielded 4331 independent observed reflection with Io2cr(Io) out of 9733 reflections collected. The structure was solved and refined to a R factor of 0 0451 with 367 parameters. The adenine base is in the syn conformation with XCN= 84.7° as in few other 8-substituted cyclic purine nucleotides but different from the simple cyclic purine nucleotides. The phenyl moiety is in the trans conformation with respect to the base. The ribose moiety shows rare C4’-exo puckering with a deviation of 0.70 A from the best plane constituted by the remaining four atoms. The 05' atom is m the t conformation with respect to the ribose with cpα = -174.8° and <pα = -59.6° since only in this conformation 3' and 5' cyclization is possible. Hydrogen bonds Nl. .O1P and N6...O5' link two nucleotide molecules. Adenine bases stack on the phenyl ring from above and below. The only water molecule present in the structure form hydrogen bonds with the nucleotide atoms. 8-mercaptoguanosine crystallizes in the monoclinic space group C2 with unit cell dimensions a= 23.246 A, b=9.751 A, c= 6.406 A and b= 90.91°. MoKα intensity data collected on CAD diffractometer yielded 2683 independent observed reflections having I0>2<r(I0). The structure was solved using SHBLXS 97 and refined using SHELXL97 to a R factor of 0.0565. The guanine base is in the syn conformation with XCN= 64.1°. The ribose ring shows C2-endo puckering with C2' atom deviating by 0.62 A from the best plane. An interesting feature of this structure is the intra-molecular hydrogen bond between the base N3 and the ribose 05' atoms. The last chapter (VII) describes the crystal structures of three modified adenine nucleosides N6-benzyl adenosine (N6-BA), N6-cyclohexyl adenosine (N6-CA) and 5'-trityl adenosine (5'-TA). N6-BA belongs to the triclinic space group PI with a= 5.008 A, b= 8.921 A, c= 9.762 A and a = 111.73°, β= 90.37°, 7 = 91.42° while N6-CA and 5'-TA belong to the monoclinic space group P2i with a= 12.205 A, b=15.265 A, c= 15.095 A, P = 110.64° and a= 8.823 A, b= 15.613 A, c= 10.078 A and β = 115.01° with three and one molecules in their asymmetric units respectively. The three structures of N6-BA, N6-CA and 5'-TA were solved and refined to R factors of 0.0355, 0.0655 and 0.0262 using 1656, 7549, 2473 independent reflections and 244, 677, 360 parameters respectively using SHELX97. The adenine base of N6-BA is in the anti conformation with XCN= 168.9°. The benzyl moiety is in the distal geometry with respect to the imidazole ring. The furanose ring shows CSI-exo-CS'-endo mixed puckering. There are several 7r-7r interactions observed in this structure. In contrast to N6-BA all three molecules of N6-CA show syn conformation about the glycosidic bond with XCN= 47.0°, 54 8°, 49 V for molecules A, B and C respectively. The cyclohexyl moiety of all three molecules are in the chair conformation. The ribose moieties of all three molecules show C2-endo puckering with C2' atom deviating by 0 59, 0 54, 0.57 A for molecules A, B and C respectively. The adenine base of the 5'-TA is in the anti conformation with \Cs= 168.4° and the ribose moiety shows C2-endo puckering The three phenyl rings of the trityl group are in staggered orientation. Interesting tape formation via N6…02' and N7...O3' hydrogen bonds is observed in all three nuclosides.