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81.
Laser-ablated beryllium atoms react with H2 upon co-condensation in excess hydrogen and neon to form BeH2 and (BeH2)2, which are identified through isotopic substitution and DFT calculations. Unreacted Be atoms isolated in solid neon or hydrogen are excited to the 1P0 state and react further with H2 to enhance the BeH2 and (BeH2)2 concentrations and produce (BeH2)n polymers. The series of strong infrared-active parallel Be-H-Be bridge-bond stretching modes observed for (BeH2)n polymers suggests one-dimensional structures, and this conclusion is supported by DFT calculations. The computed polymerization energy per BeH2 unit is about 33 kcal/mol. 相似文献
82.
Laser-ablated Mo atoms react with H2 upon condensation in excess argon, neon, and hydrogen. The molybdenum hydrides MoH, MoH2, MoH4, and MoH6 are identified by isotopic substitution (H2, D2, HD, H2 + D2) and by comparison with vibrational frequencies calculated by density functional theory. The MoH2 molecule is bent, MoH4 is tetrahedral, and MoH6 appears to have the distorted trigonal prism structure. 相似文献
83.
Matrix photoionization of methylene bromide produced absorptions at 1019, 897, and 788 cm?1 identified previously as CBr2+, CHBr2+, and CHBr2. High-resolution FTIR spectra revealed overlapping 1/2/1 triplets for natural bromine isotopes with individual linewidths near 0.2 cm?1. New absorptions at 3121, 2897, and 1345 cm?1 are assigned to the (CH2Br+)Br cation complex which yields CHBr2+ on photolysis. A substantially increased yield of the CHCl2+ species made possible observation of the CH stretching mode at 3033 cm?1 and the symmetric CCl2 stretching mode at 845 cm?1 along with the previously observed stronger 1291- and 1044-cm?1 fundamentals. The high resolution and enhanced signal-to-noise capability of the FTIR are clearly demonstrated in this investigation. 相似文献
84.
85.
Sanae A. Ishijima Lester Clowney Masashi Suzuki 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2004,80(4):183
Microcrystals of the feast/famine regulatory protein (FFRP) pot0434017 (FL11) were prepared by sonicating larger crystals. Using the microcrystals a cryo-electron micrograph was obtained, which showed a hexagonal packing of cylinder-like assemblies of FL11. This micrograph was processed by selecting, in the Fourier space, spots reflecting the crystal lattice, thereby removing the noise. The microcrystal was not totally free from distortion, and cylinders in local clusters adopted slightly different orientations. Thus, 25 hexagonal units closest to the ideal, each containing a cylinder at the center surrounded by six others, were manually selected. The averaged image was further processed to yield a perfect six-fold symmetry. These processed images, and some of the original images too, show bridges connecting cylinders, each corresponding to two pairs of N-domains, protruding from the two cylinders and contacting between them in the X-ray structure. 相似文献
86.
Laursen JB Nielsen J Haack T Pusuluri S David S Balakrishna R Zeng Y Ma Z Doyle TB Mitscher LA 《Combinatorial chemistry & high throughput screening》2006,9(9):663-681
A synthetic reexamination of a series of ketodihydronicotinic acid class antibacterial agents was undertaken in an attempt to improve their therapeutic potential. A convenient new synthesis was developed involving hetero Diels-Alder chemistry producing 74 new analogs in a multiple parallel synthetic manner and these were examined in vitro for their antimicrobial potential. Several compounds demonstrated significant broad-spectrum activity against clinically derived bacterial strains but previously known 1-(2,4-difluorophenyl)-6-(4-dimethylaminophenyl)-4-pyridone-3-carboxylic acid (7) remained the most potent compound in this class. Cross-resistance with ciprofloxacin supported a commonality of mode of action. Permiabilization of Escherichia coli cells by polymyxin B significantly enhanced potency with these agents suggesting that poor cellular uptake was primarily responsible for the disappointing activity against bacteria that some of the analogs exhibited. 相似文献
87.
Methane activation by group 5 transition-metal atoms in excess argon and the matrix infrared spectra of reaction products have been investigated. Vanadium forms only the monohydrido methyl complex (CH3-VH) in reaction with CH4 and upon irradiation. On the other hand, the heavier metals form methyl hydride and methylidene dihydride complexes (CH3-MH and CH2=MH2) along with the methylidyne trihydride anion complexes (CHMH3-). The neutral products, particularly the methylidene complex, increase markedly on irradiation whereas the anionic product depletes upon UV irradiation or addition of a trace of CCl4 or CBr4 to trap electrons. Other absorptions that emerge on irradiation and annealing increase markedly at higher precursor concentration and are attributed to a higher-order product ((CH3)2MH2)). Spectroscopic evidence suggests that the agostic Nb and Ta methylidene dihydride complexes have two identical metal-hydrogen bonds. 相似文献
88.
Non-relativistic configuration interaction (CI) ab initio calculations using large basis sets have been carried out to determine the potential curves of the first electronic states of Ne2 +, Ar2 + and Kr2 +. The spin—orbit interaction was treated assuming that the spin—orbit coupling constant is independent of the internuclear separation (R). For Ar2 +, calculated dissociation energies and equilibrium separations are in good agreement with experimental results. The calculations for Ne2 + suggest that the lowest vibrational level of the I(1/2u) ground state observed by threshold photoelectron spectroscopy by Hall et al. [1995, J. Phys. B: At. molec. opt. Phys., 28, 2435] and assigned to either ν = 0 or ν = 2 actually corresponds to ν = 4. The calculations also predict the I(1/2g) state of Ne2 + and Ar2 + to possess a double-well potential and that of Kr2 + to be repulsive at short range and to only possess a single shallow well at large internuclear separation. The ab initio calculations provide an explanation for the observation made by Yoshii et al. [2002, J. chem. Phys., 117, 1517] that Kr2 + and Xe2 + dissociate after photoemission from the II(1/2u) state to the I(1/2g) state whereas Ar2 + does not. 相似文献
89.
90.