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排序方式: 共有306条查询结果,搜索用时 31 毫秒
31.
Nicolae Voiculescu 《应用有机金属化学》2002,16(10):569-574
The alumino‐organic combinations of the dioximes (DOxH2) examined in this paper result from the substitution of the hydrogen bonds of oximes by alumino‐organic groups. Relative to the same alumino‐organic derivatives, diphenylglyoxime (DPGH2) behaves similarly to dimethylglyoxime (DMGH2). The chemical reactivity of DPGH2 towards these alumino‐organic compounds is, however, less than in the case of DMGH2. An exception is the monomer state of (DPG)[Al(i‐C4H9)2]2 in benzene solution. The behavior relative to amines of alkyl derivatives is similar to that found in coordinated oximes. In contrast, phenylaluminum derivatives of DMGH2 and DPGH2 are not soluble in amines. All compounds reported in this paper were separated from the reaction mixture as colored powders and were characterized by chemical analyses, IR spectroscopy, X‐ray diffraction spectra and 1H NMR. Finally, a comparison between the reactivity of free and coordinated dioximes is briefly considered. It is hoped that such comparisons will throw light on the problems associated with the reactivity of free and coordinated oxides versus alumino‐organic compounds. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
32.
In this paper, a model equation is presented for the study of rain-wind-induced vibrations of a simple oscillator. As will be shown the presence of raindrops in the wind-field may have an essential influence on the dynamic stability of the oscillator. In this model equation the influence of the variation of the mass of the oscillator due to an incoming flow of raindrops hitting the oscillator and a mass flow which is blown and shaken off is investigated. The time-varying mass is modeled by a time harmonic function whereas simultaneously also time-varying lift and drag forces are considered. 相似文献
33.
The purpose of the study was to examine the energy additivity of the hydrogen bridges in formamide polymers. Consideration was given to both the linear polymers observed in polypeptides, and to the cyclic polymers observed in the crystal structure. Additivity was found in several geometries. The linear polymers were considered as far as the tetramer, and the cyclic as far as the heptamer.Work supported in part by the Instituto Fisica, Universidad Nacional Autónoma de Mexico and Conacyt, México. 相似文献
34.
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
35.
Qianqian Liu Xiaoyu Yang Meng Wang Die Liu Mingzhao Chen Tun Wu Zhiyuan Jiang Pingshan Wang 《Tetrahedron》2019,75(16):2400-2405
A novel family of metallocycles was constructed by a one-pot self-assembly of three analogous bis(terpyridine) ligand monomers L1-L3, having different bent angles, with metal ions (Zn2+ or Cd2+). The dibenzo[b,d]thiophene-containing ligand L3 assembled with the metal ions to form a single trimer, whereas the dibenzo[b,d]furan-containing ligand L2 and dibenzo[b,d]carbazole-containing ligand L1 formed a mixture of trimers and tetramers. Heteroatoms (N, O, S) significantly contributed to the molecular size of the assemblies, owing to the bent angle of the bis-terpyridines ligands. 相似文献
36.
The standard oxidation states of central metal atoms in C
4v
nitrido ([M(N)(L)5]
z
) complexes are four units higher than those in corresponding nitrosyls ([M(NO)(L)5]
z
) (L=CN: z = 3−, M = Mn, Tc, Re; z = 2−, M = Fe, Ru, Os; L = NH3: z = 2+, M = Mn, Tc, Re; z = 3+, M = Fe, Ru, Os). Recent work has suggested that [Mn(NO)(CN)5]3− behaves electronically much closer to Mn(V)[b
2(xy)]2, the ground state of [Mn(N)(CN)5]3−, than to Mn(I)[b
2(xy)]2[e(xz,yz)]4. We have employed density functional theory and time-dependent density functional theory to calculate the properties of the
ground states and lowest-lying excitations of [M(N)(L)5]
z
and [M(NO)(L)5]
z
. Our results show that [M(N)(L)5]
z
and [M(NO)(L)5]
z
complexes with the same z value have strikingly similar electronic structures. 相似文献
37.
[Ph3Sn(O2AsMe2)] ( 1 ) and [PhClSn(O2AsMe2)(μ‐OMe)]2 ( 3 ) have been synthesized by treatment of Ph3SnCl and Ph2SnCl2 with Na(O2AsMe2) in methanol, respectively. [Bu2ClSn(O2AsMe2)] ( 2 ) has been prepared by the reaction of Bu2SnCl2 with HO2AsMe2 in methanol. X‐ray diffraction studies show 1 to crystallize in the monoclinic space group P21/n with a = 699.8(1), b = 1961.4(2), c = 1433.6(2) pm, β = 95.17(1)°, and Z = 4. 2 also crystallizes monoclinic in the space group P21/m, the cell parameters being a = 480.6(1), b = 1992.7(2), c = 808.8(1) pm, β = 103.726(5)°, and Z = 2. Both compounds form infinite chains with alternating (Me2AsO2)? and (R3Sn)+ or (R2ClSn)+ units. The dimer 3 consists of 8‐membered (OSnOAs)2 rings in which the tin atoms are bridged by methanolate bridges. It crystallizes triclinic in the space group with a = 822.8(2), b = 910.4(2), c = 929.2(2) pm, α = 77.04(3)°, β = 82.35(3)°, γ = 68.69(3)°, and Z = 1 for the dimer. The vibrational and mass spectra of 1 , 2 and 3 are given and discussed. 相似文献
38.
Otsuki J Kanazawa Y Kaito A Shafiqul Islam DM Araki Y Ito O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(12):3776-3784
Excited energy-transfer processes were investigated for a supramolecular Zn-porphyrin free-base porphyrin dyad, ZnPA-2 x FbPC-2, in which beta-octaalkylated meso-diarylporphyrins are connected through an amidinium-carboxylate salt bridge. The rate of energy transfer in the dyad (1.3 x 10(9) s(-1)) is substantially slower than that in the previously reported dyad, ZnPA-1FbPC-1 (4.0 x 10(9) s(-1)), in which meso-tetraarylporphyrins are connected through the same amidinium-carboxylate salt bridge. The F?rster-type mechanism can explain only minor parts of these rates (3.3 x 10(8) and 5.1 x 10(8) s(-1), respectively). Thus, Dexter-type through-bond energy transfer may be invoked. Indeed, bridge-mediated electronic processes would be favored in ZnPA-1 x FbPC-1 over ZnPA-2 x FbPC-2 on the basis of steric and electronic factors. Sterically, the phenyl groups in ZnPA-2 and FbPC-2 are more closely perpendicular to the porphyrin planes than those in ZnPA-1 and FbPC-1. Electronically, the energy and symmetry of the occupied frontier orbitals should favor ZnPA-1 x FbPC-1 over ZnPA-2 x FbPC-2 in terms of electronic interactions through the bridge. Therefore, the observed trend (ZnPA-1 x FbPC-1>ZnPA-2 x FbPC-2), consistent with these considerations, lends further support to the through-bond mechanism. Thus, the amidinium-carboxylate salt bridge is effective in mediating through-bond energy transfer even though the bond is noncovalent. 相似文献
39.
40.
Synthesis of Phosphido Chalcogenido Bridged Dirhenium Complexes of the Type Re2(μ‐PCy2)(μ‐ER)(CO)8 (E = S, Se, Te; R = org. Residue) The reaction of Re2(μ‐Br)(μ‐PCy2)(CO)8 with nucleophiles MER (M = Na, Li; E = S, Se, Te; R = org. residue) gives via substitution of the bromido bridge phosphido chalcogenido bridged dirhenium complexes of the general formula Re2(μ‐PCy2)(μ‐ER)(CO)8. The new compounds were characterized by IR, 1H and 13C NMR spectroscopic data and by elemental analyses. In addition the molecular structures for E = S, Se, Te and R = Ph as well as for E = S and R = H, n‐Bu, 2‐pyridyl have been established by single crystal X‐ray analysis. 13C NMR spectra of Re2(μ‐PCy2)(μ‐EPh)(CO)8 (E = S, Se, Te) prove that the sulfur and selenium compounds are at room temperature dynamic molecules due to inversion of the pyramidal chalcogenido bridge. The tellurium compound, however, is rigid on the time scale of 13C NMR spectroscopy. Eventually the reactivity of the SH function of the novel complex Re2(μ‐PCy2)(μ‐SH)(CO)8 was investigated by reaction with Re2(CO)8(MeCN)2. In toluene at 90 °C the novel spirocyclic complex Re2(μ‐PCy2)(CO)8(μ4‐S)Re2(μ‐H)(CO)8 was formed by SH oxidative addition. 相似文献