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921.
A room temperature cured polysiloxane rubber (Rhodorsil RTV5370) has been irradiated using an accelerated beam of He2+ ions. Such an irradiation simulates the effects of large alpha radiation doses. A mass spectrometer linked directly to the sample chamber allowed the analysis of volatile species evolved as a result of exposure. The polydimethylsiloxane rubber showed high resistance to radiation damage when exposed to He2+ ions at doses up to 3.5 MGy. At higher doses, the cyclic hexamethylcyclotrisiloxane was evolved and is indicative of damage to the main chain. The cyclic octamethylcyclotetrasiloxane was only observed at very high doses (10 MGy and above) and is indicative of significant head-to-tail unzipping reactions. Methane, benzene and carbon dioxide were the three main gases evolved. The ratio of phenyl (2%) to methyl groups (93%) within RTV5370 rubber is very small but the amount of benzene evolved was found to be significant. The results suggest that the aromatic groups within the rubber appear to have a much greater susceptibility to radiation induced volatile evolution than other groups making up the polymer structure. In addition, the depletion of phenyl groups (from the reduction in evolution of benzene) from the irradiated zone corresponds to an increase in damage of the siloxane linkages (from the increased evolution of octamethylcyclotetrasiloxane) suggesting the aromatic groups offer a protective action from the incident radiation. 相似文献
922.
Richard J. Tucker Ian A. Fallis Robert D. Farley Damien M. Murphy David J. Willock 《Chemical physics letters》2003,380(5-6):758-766
The ‘solvatochromic’ effects of a vanadyl salen complex [VOIV(salen)] in frozen solution was studied by ENDOR and DFT calculations. In a non-coordinating solvent (dichloromethane), both ENDOR and DFT were in excellent agreement on the expected square pyramidal structure, where VIV=O is positioned out of the equatorial ligand xy-plane (as determined from calculated VH distances). In a coordinating solvent (dimethylformamide), a subtle perturbation from the square pyramidal structure was observed, suggesting that DMF coordinates trans to the vanadyl oxo-ligand, pulling VIV=O back into the ligand plane. The axial coordination of DMF was confirmed by ENDOR and in the DFT optimised [VOIV(salen)]–DMF complex. 相似文献
923.
Murphy DL Malachowski MR Campana CF Cohen SM 《Chemical communications (Cambridge, England)》2005,(44):5506-5508
A novel tris(chelate) metalloligand has been used to synthesize a chiral, heterometallic metal-organic framework that is robust to solvent removal and shows selective uptake of nitroaromatic compounds. 相似文献
924.
McDonnell C López O Murphy P Fernández Bolaños JG Hazell R Bols M 《Journal of the American Chemical Society》2004,126(39):12374-12385
The effect of conformation on glycoside reactivity was investigated by studying the hydrolysis of a selection of 3,6-anhydroglucosides as models for glucose in the highly reactive (1)C(4) conformation. Methyl 3,6-anhydro-beta-D-glucopyranoside was found to hydrolyze 200-400 times faster than methyl glucosides in the (4)C(1) conformation, while methyl 3,6-anhydro-beta-D-galactopyranoside, which is in the B(1,4) conformation, was less reactive than methyl beta-D-galactopyranoside. Methyl (3,6-anhydro-beta-D-glucopyranosyl)-(1 --> 6)-alpha-D-glucopyranoside, methyl (3,6-anhydro-alpha-D-glucopyranosyl)-(1 --> 6)-alpha-D-glucopyranosyl-(1 --> 6)-alpha-D-glucopyranoside, and methyl (3,6-anhydro-beta-D-glucopyranosyl)-(1 --> 6)-alpha-D-glucopyranosyl-(1 --> 6)-alpha-D-glucopyranoside were prepared and found to react selectively at the anhydro residue. The finding that (1)C(4) conformers of glucosides are highly reactive species is in accordance with and supports previous results showing that axial OH groups are less electron withdrawing than equatorial OH groups. 相似文献
925.
Roberts-Bleming SJ Davies GL Kalaji M Murphy PJ Celli AM Donati D Ponticelli F 《The Journal of organic chemistry》2003,68(18):7115-7118
Whereas irradiation of 4,5-dithiophen-2-yl[1,3]dithiol-2-one leads to the expected 2,3,5,6-tetrathiophen-2-yl-1,4-dithiine product, similar reaction of thiophen-3-yl-substituted [1,3]dithiol-2-ones leads to thieno[3,4-c]dithiines via a unique ring cleavage reaction. 相似文献
926.
Peter S. Dragovich Thomas M. Bertolini Benjamin K. Ayida Lian-Sheng Li Douglas E. Murphy Frank Ruebsam Zhongxiang Sun Yuefen Zhou 《Tetrahedron》2007,63(5):1154-1166
A general procedure is described for the regiospecific preparation of 1-substituted-5-hydroxy-1H-pyrazoles containing differentiated ester moieties at the 3- and 4-positions. This process involves the coupling of monosubstituted benzyl carbazates with various malonyl chlorides or acids, deprotection of the coupling products via catalytic hydrogenation, and subsequent derivatization of the resulting hydrazides with monoalkyl oxalyl chlorides. The 5-hydroxy-1H-pyrazoles are readily transformed to the corresponding trifluoromethane sulfonates, which undergo palladium-mediated Suzuki coupling with a variety of boronic acids (aryl, heteroaryl, and alkenyl) in moderate to excellent yields (24-92%). The ester groups present in one of the resulting 1,5-disubstituted-1H-pyrazoles are further modified by selective hydrolysis or conversion to the corresponding dicarboxylic acid derivative followed by selective mono-esterification. 相似文献
927.
Titanium-based electrodes have been demonstrated to be useful for measuring free HF concentration in the range 0.01-0.07M at temperatures between 19 and 61 degrees C in acidic, complexed HF solutions, by measurement of the current density resulting when the electrode potential is approximately +0.6 V with respect to an inert electrode. The current density, i, is linearly related to the HF concentration when the solution is adequately stirred to remove diffusion effects at the electrode, and is independent of HNO(3) concentration up to 1.75M. The dependence on the absolute temperature is ln i = - A/T + B + C ln T, and the activation energy at an absolute temperature T(r) is R(A + T(r)C), where A,B and C are constants and R is the gas constant. For a Ti-2% Pd electrode, the activation energy for anodic dissolution is found to be 43.7 +/- 0.2 kJ/mole at 312 K. The equations relating the current density to HF concentration at different temperatures can be combined to give a single equation for [HF] as a function of both i and T. 相似文献
928.
Murphy AR Fréchet JM Chang P Lee J Subramanian V 《Journal of the American Chemical Society》2004,126(6):1596-1597
A symmetrical alpha,omega-substituted sexithiophene derivative containing thermally removable branched ester solubilizing groups has been prepared. These oligomers can be solution cast into thin films and then thermolyzed to remove the solubilizing group, leaving short pendant alkene groups on the oligomer. Device testing of thin film transistors shows an increase in hole mobility from 1 x 10-5 cm2/(V s) with on/off ratios of approximately 100 before thermolysis to 5 x 10-2 cm2/(V s) with on/off ratios >105 after thermolysis. This method offers an attractive route to easily processed and highly performing thiophene oligomers. 相似文献
929.
Kaminski GA Stern HA Berne BJ Friesner RA Cao YX Murphy RB Zhou R Halgren TA 《Journal of computational chemistry》2002,23(16):1515-1531
We present results of developing a methodology suitable for producing molecular mechanics force fields with explicit treatment of electrostatic polarization for proteins and other molecular system of biological interest. The technique allows simulation of realistic-size systems. Employing high-level ab initio data as a target for fitting allows us to avoid the problem of the lack of detailed experimental data. Using the fast and reliable quantum mechanical methods supplies robust fitting data for the resulting parameter sets. As a result, gas-phase many-body effects for dipeptides are captured within the average RMSD of 0.22 kcal/mol from their ab initio values, and conformational energies for the di- and tetrapeptides are reproduced within the average RMSD of 0.43 kcal/mol from their quantum mechanical counterparts. The latter is achieved in part because of application of a novel torsional fitting technique recently developed in our group, which has already been used to greatly improve accuracy of the peptide conformational equilibrium prediction with the OPLS-AA force field.1 Finally, we have employed the newly developed first-generation model in computing gas-phase conformations of real proteins, as well as in molecular dynamics studies of the systems. The results show that, although the overall accuracy is no better than what can be achieved with a fixed-charges model, the methodology produces robust results, permits reasonably low computational cost, and avoids other computational problems typical for polarizable force fields. It can be considered as a solid basis for building a more accurate and complete second-generation model. 相似文献
930.
Berry V Gole A Kundu S Murphy CJ Saraf RF 《Journal of the American Chemical Society》2005,127(50):17600-17601
Gold nanorods and nanospheres capped with positively charged CTAB are deposited on the surface of gram-positive bacterium having negatively charged teichoic acid brushes. The deposition rate is more than an order of magnitude faster than that for peptide and nucleic acid capped nanoparticles. For the nanorods, never been reported before, the strong electrostatic attraction causes the rods to bend conformally over the curved bacterium surface in random orientations. This leads to formation of an efficient percolating cluster (i.e., low contact resistance and high radius of gyration) with 104-fold higher current at 3-fold lower coverage compared to a monolayer from nanospheres. The high monolayer conductivity at only approximately 10% coverage for nanorods has potential for fabricating a novel class of bioelectronic devices by coupling electronic "nanocircuitry" at the surface to the biological function of microorganisms. 相似文献