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71.
72.
Bendazzoli Gianni L. Raimondi Mario Garetz Bruce A. George Thomas F. Morokuma Keiji 《Theoretical chemistry accounts》1977,44(4):341-350
Semiclassical calculations are carried out by two methods for the problem of collision-induced predissociation of electronically excited I2. The first method is that of surface-hopping with the Landau-Zener model. The second method is similar to surface-hopping, except that analytic continuation of the adiabatic potential energy surfaces replaces the Landau-Zener model. Results of the calculations by the two methods compare favorably with each other and with experiment. The possible advantages of the second method are discussed.Camille and Henry Dreyfus Teacher-Scholar, Alfred P. Sloan Research Fellow. 相似文献
73.
74.
A facile process to prepare uniform dumbbell-shaped ZnO crystallites was presented. The evidence in this Article discovered a unique morphological effect on the UV-blocking property. The as-prepared ZnO crystallites were characterized by XRD, HRTEM, FESEM, UV-blocking, and Raman scattering spectra. Our tentative investigation created a breakthrough to both the ultrahigh "Ultraviolet protection factor" (UPF) and the overall-range of complete UV-radiation blocking. Therefore, the as-prepared structural material demonstrated a significant advance in protective functional treatment and provided a potential commercialization. 相似文献
75.
Herein, we report a stereospecific E-olefin dipeptide isostere synthesis that can be used to make gram quantities of the Phe-Phe isostere desired for eliminating a specific backbone H-bond donor and acceptor in the Alzheimer's disease related Abeta peptide. The Phe19-Phe20 E-olefin analogue of Abeta(1-40) was prepared by solid-phase peptide synthesis and was subjected to amyloidogenesis conditions. This analogue can aggregate into spherical morphologies but does not progress on to form protofibrils or fibrils as is the case for the all-amide sequence, providing insight into the structural requirements for amyloidogenesis. 相似文献
76.
Dehydrocyclization of 4-amino-5-arylamidopyrimidines in polyphosphoric acid to 8-arylpurines was further investigated. Various other 8-arylpurines were synthesized by this new procedure in high purity and yield. The ultraviolet absorption spectra of the arylpurines and the corresponding acylamidopyrimidines were measured at pH 1, 7, and 13 at 0.1 molar ionic strength. The spectra of the purines resemble those of the corresponding acylamidopyrimidines and, to a lesser extent, the corresponding 4,5-diaminopyrimidines. The bathochromic shifts caused by different substituting groups in monosubstituted purines, in general, parallel the inductive effect of the substituting groups. The hyperchromicity and the inductive constant of the substituting groups assume a linear relationship, for substitution at either the 2 or 6 position. These changes in the wave length of maximum absorption and in the molar extinction coefficient caused by 2, 6 and 8 substitutions of the purines reported here are in agreement with previous studies by Mason. 相似文献
77.
Three new linear compounds of the type Co(3)(dpa)(4)X(2), where dpa is the anion of di(2-pyridyl)amine and X is NCS(-) (5), CN(-) (6), and N(CN)(2)(-) (7), have been prepared, and their structures and magnetic behavior have been studied. In all of them, including three different solvates of 5, the Co(3) chains are symmetrical with Co-Co distances of ca. 2.31-2.32 A. The appearance of four lines in the (1)H NMR spectra of the three compounds is also consistent with a symmetrical structure in solution. For all compounds, the magnetic behavior is quite similar with mu(eff) of ca. 1.9-2.0 micro(B) at temperatures between 1.8 and 200 K. As the temperature increases, the effective moments increase gradually, but since saturation is not reached, even at 400 K, the high-spin state cannot be assigned. 相似文献
78.
79.
An engineered form of iso-1-cytochrome c with lysine 73 mutated to histidine is shown to increase by nearly 500-fold the rate of a conformational gate that modulates the rate of electron transfer into this protein. This result demonstrates the potential of protein engineering to provide electron transfer gates with tailored properties. The pH dependence of the rate of the conformational electron transfer gate correlates well with the pH dependence of the conformational change from a His 73-ligated heme to a Met 80-ligated heme, determined independently by pH jump methods, allowing unambiguous assignment of the conformational electron transfer gating step. The rate of the electron transfer gate is also modulated by a cis to trans proline isomerization, indicating that both amino acid sequence and the nature of the heme ligand provide avenues for rational design of electron transfer gates which open at different rates. 相似文献
80.
Spontaneous vesicle formation was observed in aqueous mixtures of partially hydrolyzed polyacrylamide and single-tailed cationic surfactants. The influences of pH, addition of long-chain alcohols, variation of hydrocarbon chain length, and head group size of the cationic surfactants were investigated systematically. It was found that 30-50% hydrolyzed degree of polyacrylamide and cationic surfactants with 10 or 12 methylene groups are suitable for vesicle formation in the mixed aqueous systems at pH 9.2. Addition of long-chain alcohols was found to be helpful for vesicle formation in some cases. The vesicle stability was also investigated at various temperatures and amounts of ethanol addition. Copyright 2001 Academic Press. 相似文献