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Mario Bossa Elena Cervone Carmine Garzillo Andrea Peluso 《Journal of Molecular Structure》1997,390(1-3):101-107
The electronic absorption spectra of Ni, Zn and Mg hemiporphyrazine derivatives are presented and discussed together with theoretical results obtained by INDO/S computations. The absorption spectra of all the metal derivatives show marked red shifts of the lowest energy absorption bands with respect to those of the metal free hemiporphyrazine. The possible explanation that in metal derivatives low lying excited states with a fully conjugated π electron system are present is supported by theoretical computations. 相似文献
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Roccatano D Sbardella G Aschi M Amicosante G Bossa C Di Nola A Mazza F 《Journal of computer-aided molecular design》2005,19(5):329-340
The dynamical aspects of the fully hydrated TEM-1 β-lactamase have been determined by a 5 ns Molecular Dynamics simulation.
Starting from the crystallographic coordinates, the protein shows a relaxation in water with an overall root mean square deviation
from the crystal structure increasing up to 0.17 nm, within the first nanosecond. Then a plateau is reached and the molecule
fluctuates around an equilibrium conformation. The results obtained in the first nanosecond are in agreement with those of
a previous simulation (Diaz et al., J. Am. Chem. Soc., (2003) 125, 672–684). The successive equilibrium conformation in solution
shows an increased mobility characterized by the following aspects. A flap-like translational motion anchores the Ω-loop to
the body of the enzyme. A relevant part of the backbone dynamics implies a rotational motion of one domain relative to the
other. The water molecules in the active site can exchange with different residence times. The H-bonding networks formed by
the catalytic residues are frequently interrupted by water molecules that could favour proton transfer reactions. An additional
simulation, where the aspartyl dyad D214–D233 was considered fully deprotonated, shows that the active site is destabilized. 相似文献
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Mario Bossa Giorgio O. Morpurgo Laura Morpurgo 《Journal of Molecular Structure》1995,330(1-3):395-401
Semiempirical AM1 calculations were used to optimize the geometry of the adducts formed by 2,5-dihydroxy-p quinone (DHpQ) with substituted pyridines or imidazole. Hydrogen bond formation was seen to be responsible for the stability of the adducts. From the study of the total energy function, obtained by imposing fixed positions to the proton, two structures were found to be possible for each adduct, one schematically indicated as -OH … N-base and the proton transfer one, indicated as -O− … HN+base. The proton transfer energy was found to vary linearly with the base pKa value. A study was also carried out on the system formed by DHpQ and a cluster of three water molecules acting as proton acceptors. The implications were discussed relating to possible hydrogen bond formation between trihydroxyphenylalanine quinone, the coenzyme of bovine serum amine oxidase, and some basic residue or water molecule, lying close to the protein active site. 相似文献
5.
C. Battistoni M. Bossa C. Furlani G. Mattogno 《Journal of Electron Spectroscopy and Related Phenomena》1973,2(3):355-361
N 1s, S 2p and Ni 2p3/2 binding energies for the Ni(II) dithiocarbazates and N 1s and S 2p binding energies for the methyl esters of dithiocarbazic acids were measured. It was found that the band width of N 1s narrows on going from the esters to the complexes, thus suggesting a closer similarity between the two nitrogen atoms as a consequence of coordination. S 2p binding energies were found to be similar in the above complexes independent of the chromophore present in them. A possible explanation is suggested for this unusual result. 相似文献
6.
The conformation of 2,2-bipyridyl and 5,5-bis-isoxazole is studied by the CNDO/2 method. Calculations suggest that the trans configuration is more stable than the cis for both systems. For 2,2-bipyridyl a minimum for a non planar form is inferred. 相似文献
7.
The highly localized, atom-like nature of inner molecular electrons is discussed in some simple molecules to obtain computed estimates of the energy corrections accounting for the polarization rearrangements following K-shell ionizations. The “equivalent core” (EC) model already discussed in the literature is invoked to perform true variational computations for the hole-state wavefunctions of the outer electrons and for their potentials at the ionized nucleus. The “chemical shifts” associated with carbon K-shells in fluoromethanes and within all the possible ions for the adenine molecule are also computed and discussed. 相似文献
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Simple Zeros of the Riemann Zeta-Function 总被引:1,自引:0,他引:1
Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26. 相似文献