No description available.

A series of novel triphenylstannyl-C, (triphenylstannyl)methyl- O- and (tributylstannyl)methyl-O- substituted pentofuranose compounds have been synthesised. Two methods were employed: (i) the reaction of triphenyltinlithium with derivatised and protected (or partially protected) carbohydrates, and (ii) the reactions of carbohydrate alkoxides with (iodomethyl)triphenyltin and (iodomethyl)tributylin. The solution structures of the triorganotin-carbohydrate compounds were investigated by 1H, 13C and 119Sn NMR spectroscopy. In solution all of the triorganotin-carbohydrates were shown to contain four-co-ordinate tin atoms. The solid-state structures were investigated by a combination of solid-state NMR spectroscopy and single-crystal X-ray diffraction. There were no major conformational changes between the two phases for any of the compounds. The molecular structures of methyl 5-deoxy-2,3- O-isopropylidine-5-triphenylstannyl-beta-D-ribofuranoside and 5-deoxy-1,1- O-isopropylidine-5-triphenylstannyl-alpha-D-xylofuranose were determined. Two different molecular conformations were identified for the former compound, and hydrogen-bonding between adjacent molecules was shown to be present in the latter case. The reactions of the triorganotin-carbohydrate compounds with iodine and bromine were studied. The results indicated that the rate of cleavage of butyl-tin bonds was much slower than the cleavage of phenyl-tin bonds. The reactivity of the tin-phenyl bond was found to depend greatly on the structure of the carbohydrate ligand. Evidence of increased co-ordination in solution was found for the mono-halo derivatives of methyl 5-deoxy-2,3-O-isopropylidine-5-triphenylstannyl-beta-D-ribofuranoside and 5-deoxy-1,2-O-isopropylidine-5-triphenylstannyl-alpha-D-xylofuranose. The molecular structures of 5-deoxy-5-iododiphenylstannyl-1,2-O-isopropylidine-alpha-D-xylofuranose and 5-deoxy-5-diiododiphenylstannyl-1,2-O-isopropylidene-alpha-D-xylofuranose were determined. In the solid-state the geometry about the tin atoms was found to be distorted trigonal bipyramidal.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 111-113). 1 folded diaghram included. Also available via the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1959. / Typescript. Abstracted in Dissertation abstracts, v. 20 (1960) no. 8, p. 3114-3115. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 255-261).

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The effect of viscoplastic deformation of the energetic material HMX on the mechanical, thermal, and ignition response of a two-phase (HMX and Estane) polymer bonded explosive (PBX) is analyzed. Specific attention is given to the high strain rate response of the material during the first passage of the stress wave when impacted by a constant velocity piston. PBX microstructures are subjected to impact loading from a constant velocity piston traveling at a rate of 50 to 200 m/s using a 2D cohesive finite element (CFEM) framework. The initial focus is to fully quantify the effect that viscoplastic HMX has on the behavior of a PBX composite, a thorough thermo-mechanical analysis is performed. The thermal response of the PBX specimens having viscoplastic HMX is characterized by a significant reduction in average heating, peak temperature rise, and the number or amount of material experiencing localized heating (hotspots). This reduction in heating is found to be accomplished through the mechanism of greatly reducing the density of fracture in the PBX. The second focus of this work is to evaluate the ignition sensitivity of these materials to determine the effect, if any, of the viscoplastic HMX. Viscoplastic HMX is shown to increase the minimum load duration, mean load duration, and range of critical load durations required for ignition. A 3D crystal plasticity framework is employed to quantify the potential heterogeneities in the stress and temperature field resulting from the inherent crystalline anisotropy of the HMX grains. It is found that in a densely packed HMX, the heterogeneities due to material anisotropy can contribute to increased stress gradients and localized temperature rise. Finally, the 2D framework is used to study a hypothetical composite containing HMX grains suspended in an aluminum matrix. This investigation focuses not on the feasibility of producing such a composite, but on determining whether such an arrangement would be advantageous from a mechanical and ignition sensitivity standpoint. Results indicate that this hypothetical composite would be considerably less sensitive than a similar PBX.

of the thesis entitled: Computational studies on supramolecular hydrogen-bonded structures: from nanocapsules to proteins.In this thesis different methods were used to study several systems in which the hydrogen bond has a key role. The validity of the theoretical methods applied was always contrasted with the experimental evidences available from the group of Prof. Javier de Mendoza in the context of an intense collaboration in the Institute of Chemical Research of Catalonia (ICIQ). In certain cases the theoretical results provided an explanation to experimental observations and in other cases they had the prediction as main objective. In Chapter II the general concepts of the Density Functional Theory (DFT) and of the Molecular Mechanics (MM) are described, emphasizing the specific methods used in the thesis.In Chapter III a DFT study is presented on the dimerization of the 2-ureidopyrimidone (UPy), and also on the tautomeric equilibrium established from this molecule. The influence of the substituent in position 6 of the pyrimidinone ring and the solvent effects were explained.Chapter IV deals with systems also based in dimers of ureidopyrimidone, but much larger. A molecule is described, composed of 3 UPy moieties bound to a cyclotriveratrylene unit, which self-assembles leading to the formation of a nanocapsule able to trap fullerenes inside. The nanocapsule shows higher affinity for certain fullerenes. The viability of the complexes (CTV-3UPy)2Cn(n=60,70,76,78,84,90) was studied as well as the preferences of the host. The aim was giving an explanation to experimental results obtained with C60 and C70 and predicting selectivity for higher fullerenes.Chapter V presents a Molecular Dynamics study on the effect of the punctual mutation R337H in the stability of the tetramerization domain of the protein p53 (p53TD). It has been experimentally demonstrated that this mutation prevents the protein from carrying out its normal function as a tumour suppressor. The simulations allowed explaining the disruption process suffered by the mutant protein.Using the same methods as in the previous chapter, chapter VI presents a study on the interaction of several ligands with the surface of the wild type protein (p53TD) and the mutant protein (R337H p53TD). The ligands tested were of the oligoguanidinium type and tetraguanidilated calix[4]arenes. The calixarenes proved to stabilize the structure of the mutant protein, maintaining it in a conformation similar to that of the wild type protein. Chapter VII describes the study, by means of Molecular Dynamics, of the unspecific interaction between a DNA molecule and undecaguanidinium ligands. The simulations proved that the ligands have high affinity for the DNA. In Chapter VIII the conclusions of the overall thesis are summarized.Resumen de la tesis doctoral titulada: Computational studies on supramolecular hydrogen-bonded structures: from nanocapsules to proteins. / En esta Tesis se han utilizado diferentes métodos computacionales para estudiar diversos sistemas en los cuales los enlaces de hidrógeno juegan un papel crucial. La validez de los métodos teóricos aplicados se ha contrastado siempre con las evidencias experimentales disponibles, procuradas por el grupo del Prof. Javier de Mendoza en el contexto de una estrecha colaboración en el Instituto Catalán de Investigación Química (ICIQ). En determinados casos los resultados teóricos han proporcionado una explicación a fenómenos observados experimentalmente y en otros casos han tenido como objetivo la predicción.En el Capítulo II se exponen los conceptos generales de la Teoría del Funcional de la Densidad (DFT) y de la Mecánica Molecular, poniendo mayor énfasis en los métodos concretos que se han utilizado en la Tesis. En el Capítulo III se presenta un estudio mediante métodos DFT sobre la dimerización y el equilibrio tautomérico establecido a partir de la 2-ureidopirimidona (UPy). Se estudió la influencia del sustituyente en posición 6 del anillo de pirimidona y del disolvente CHCl3. En el Capítulo IV se presenta un estudio sobre sistemas también basados en el dímero de UPy, pero mucho más grandes. Se describe una molécula compuesta por 3 UPys unidas a una unidad de ciclotriveratrileno (CTV) que dimeriza por auto-ensamblaje dando lugar a una nanocápsula capaz de atrapar fulerenos, mostrando mayor afinidad por algunos de ellos. Se estudió la viabilidad de los complejos (CTV-3UPy)2Cn(n=60,70,76,78,84,90) y las preferencias de la cápsula con ánimo explicativo y predictivo.En el Capítulo V se presenta un estudio de Dinámica Molecular sobre el efecto de la mutación puntual R337H en la estabilidad del dominio de tetramerización de la proteína p53 (p53TD). Se ha demostrado experimentalmente que tal mutación impide que la proteína lleve a cabo su función como supresor tumoral y por tanto favorece el desarrollo de tumores. Las simulaciones permitieron explicar el proceso de disrupción de la proteína mutada.Usando los mismos métodos que en el capítulo anterior, el Capítulo VI presenta un estudio sobre la interacción de ligandos tipo oligoguanidinas y calix[4]arenos tetraguanidilados con la superficie de la proteína de tipo salvaje p53TD y de la proteína mutada R337H p53TD. Los calixarenos demostraron estabilizar la estructura de la proteína mutada, manteniéndola en una conformación parecida a la de la proteína de tipo salvaje. En el Capítulo VII se describe el estudio, también mediante Dinámica Molecular, de la interacción inespecífica entre una molécula de ADN y ligandos undecaguanidina. Las simulaciones demostraron que los ligandos tienen una alta afinidad por el ADN.En el Capítulo VIII se presenta un resumen de las conclusiones de la Tesis.

Thesis (M. Sc.)--University of Toronto, 1998. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.