共查询到17条相似文献,搜索用时 844 毫秒
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河豚毒素(TTX)及其衍生物的电子结构和构效关系及与石房蛤毒素(STX)的比较研究 总被引:1,自引:0,他引:1
对河豚毒素(TTX)及其五个衍生物进行了量子化学计算, 根据对其电子结构及相关分析研究结果, 结合其空间结构特点, 讨论了它们的活性部位、作用方式及构效关系, 发现胍基是最重要的正电中心,在与受体作用时发挥接受电子的重要作用; O(17), O(18), O(15),O(21), O(19)等氧原子是供电子的主要负电部位。对TTX与石房蛤毒素(STX)进行了电子结构和空间结构比较, 发现它们具有相似的电子结构特征, 而且主要活性部位在空间位置上基本相互对应。这表明钠离子通道阻断剂在与受体相互作用时具有共同的结构特征和作用方式, 同时也为探讨受体结构提供了有价值的信息。 相似文献
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4H-甲基咪唑苯二氮(艹卓)酮类抗HIV-1药物的量子化学研究 总被引:3,自引:0,他引:3
用分子力学MM3方法、量子化学MNDO法和从头算STO-3G基组计算了20个4H-甲基咪唑苯二氮(廿卓)酮HIV-1逆转录酶抑制剂的优势构型和电子结构,用逐步回归方法和BP神经网络方法得到其抗HIV-1活性与电子结构的定量构效关系.结果表明:(1)TIBO类衍生物的体积越大,极性越小,即流水性越大对抑制HIV-1活性越有利.(2)C环N上H原子可能是化合物的正电活性部位.(3)R′原子与受体作用时可能作为电子给予体,前线轨道中S的贡献比O大得多,故含S的TIBO化合物比含O化合物的活性高.(4)苯环上连接吸电子基团对活性有利,由于分子的正负电荷中心距离较近,极性较小,疏水性较大,故3位取代比2位取代活性更高. 相似文献
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Komaba S Yabuuchi N Nakayama T Ogata A Ishikawa T Nakai I 《Inorganic chemistry》2012,51(11):6211-6220
Layered NaNi(0.5)Mn(0.5)O(2) (space group: R ?3m), having an O3-type (α-NaFeO(2) type) structure according to the Delmas' notation, is prepared by a solid-state method. The electrochemical reactivity of NaNi(0.5)Mn(0.5)O(2) is examined in an aprotic sodium cell at room temperature. The NaNi(0.5)Mn(0.5)O(2) electrodes can deliver ca. 105-125 mAh g(-1) at rates of 240-4.8 mA g(-1) in the voltage range of 2.2-3.8 V and show 75% of the initial reversible capacity after 50 charge/discharge cycling tests. In the voltage range of 2.2-4.5 V, a higher reversible capacity of 185 mAh g(-1) is achieved; however, its reversibility is insufficient because of the significant expansion of interslab space by charging to 4.5 V versus sodium. The reversbility is improved by adding fluoroethylene carbonate into the electrolyte solution. The structural transition mechanism of Na(1-x)Ni(0.5)Mn(0.5)O(2) is also examined by an ex situ X-ray diffraction method combined with X-ray absorption spectroscopy (XAS). The staking sequence of the [Ni(0.5)Mn(0.5)]O(2) slabs changes progressively as sodium ions are extracted from the crystal lattice. It is observed that the original O3 phase transforms into the O'3, P3, P'3, and P3" phases during sodium extraction. XAS measurement proves that NaNi(0.5)Mn(0.5)O(2) consists of divalent nickel and tetravalent manganese ions. As sodium ions are extracted from the oxide to form Na(1-x)Ni(0.5)Mn(0.5)O(2), nickel ions are oxidized to the trivalent state, while the manganese ions are electrochemically inactive as the tetravalent state. 相似文献
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Shinohara R Akimoto T Iwamoto O Hirokawa T Yotsu-Yamashita M Yamaoka K Nagasawa K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(43):12144-12152
Skeletal analogues of saxitoxin (STX) that possess a fused-type tricyclic ring system, designated FD-STX, were synthesized as candidate sodium ion channel modulators. Three kinds of FD-STX derivatives 4a-c with different substitution at C13 were synthesized, and their inhibitory activity on sodium ion channels was examined by means of cell-based assay. (-)-FD-STX (4a) and (-)-FD-dcSTX (4b), which showed moderate inhibitory activity, were further evaluated by the use of the patch-clamp method in cells that expressed Na(V)1.4 (a tetrodotoxin-sensitive sodium channel subtype) and Na(V)1.5 (a tetrodotoxin-resistant sodium channel subtype). These compounds showed moderate inhibitory activity towards Na(V)1.4, and weaker inhibitory activity towards Na(V)1.5. Uniquely, however, the inhibition of Na(V)1.5 by (-)-FD-dcSTX (4b) was "irreversible". 相似文献
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We used a hybrid quantum-mechanics/molecular-mechanics (QM/MM) approach to simulate the adsorption of Au(n)() (n = 1-5), AuPd, and Au(2)Pd(2) clusters inside the TS-1 and S-1 pores. We studied nondefect and metal-vacancy defect sites in TS-1 and S-1 for a total of four different environments around the T6 crystallographic site. We predict stronger binding of all clusters near Ti sites in Ti-substituted framework compared to adsorption near Si sites-consistent with the experimental finding of a direct correlation between the Ti-loading and the Au-loading on the Au/TS-1 catalysts with high Si/Ti ratio. The cluster binding is also stronger near lattice-metal vacancies compared to fully coordinated, nondefect sites. In all the cases, a trend of binding energy (BE) versus Au cluster size (n) shows a peak at around n = 3-4. Our results show that there is enough room for the attack of H(2)O(2) on the Ti-defect site even with Au(1-4) adsorbed-a result that supports the possibility of H(2)O(2) spillover from the Au clusters to the adjacent Ti-defect sites. Mulliken charge analysis indicates that in all the cases there is electron density transfer to adsorbed clusters from the zeolite lattice. In the case of both gas-phase and adsorbed Au-Pd clusters, all the Pd atoms were positively charged, and all the Au atoms were negatively charged due to the higher electron-affinity of Au. We also found a correlation between the BE and the charge transfer to the clusters (the higher the charge transfer to the clusters, the higher the BE), and a universal correlation was found for Au(2-5) when BE and charge transfer were plotted on a per atom basis. A relatively larger charge transfer to the adsorbed clusters was found for the Ti sites versus the Si sites, and for the defect sites versus the nondefect sites. The trends in the BE were corroborated using Gibbs free energy of adsorption (DeltaG(ads)), and the implications of DeltaG(ads) in sintering of Au clusters are also discussed. Our results confirm that electronic factors such as cluster-charging are potentially important support effects for the Au/TS-1 catalyst. 相似文献
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Kang C Troyer JL Robertson EM Rothgeb DW Hossain E Wyrwas RB Parmenter CS Jarrold CC 《The Journal of chemical physics》2008,128(10):104309
Anion photoelectron spectra of the O(2)(-) . arene and O(4)(-) . arene complexes with p-xylene and p-difluorobenzene are presented and analyzed with the aid of calculations on the anions and corresponding neutrals. Relative to the adiabatic electron affinity of O(2), the O(2)(-) . arene spectra are blueshifted by 0.75-1 eV. Solvation energy alone does not account for this shift, and it is proposed that a repulsive portion of the neutral potential energy surface is accessed in the detachment, resulting in dissociative photodetachment. O(2)(-) is found to interact more strongly with the p-difluorobenzene than the p-xylene. The binding motif involves the O(2)(-) in plane with the arene, interacting via electron donation along nearby C-H bonds. A peak found at 4.36(2) eV in the photoelectron spectrum of O(2)(-) . p-difluorobenzene (p-DFB) is tentatively attributed to the charge transfer state, O(2)(-) . p-DFB(+). Spectra of O(4)(-) . arene complexes show less blueshift in electron binding energy relative to the spectrum of bare O(4)(-), which itself undergoes dissociative photodetachment. The striking similarity between the profiles of the O(4)(-) . arene complexes with the O(4)(-) spectrum suggests that the O(4)(-) molecule remains intact upon complex formation, and delocalization of the charge across the O(4)(-) molecule results in similar structures for the anion and neutral complexes. 相似文献
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The origin of O-H vibrational red-shifts observed experimentally in (H2O)n(-) clusters is analyzed using electronic structure calculations, including natural bond orbital analysis. The red-shifts are shown to arise from significant charge transfer and strong donor-acceptor stabilization between the unpaired electron and O-H sigma* orbitals on a nearby water molecule in a double hydrogen-bond-acceptor ("AA") configuration. The extent of e(-) --> sigma* charge transfer is comparable to the n --> sigma* charge transfer in the most strongly hydrogen-bonded X(-)(H2O) complexes (e.g., X = F, O, OH), even though the latter systems exhibit much larger vibrational red-shifts. In X(-)(H2O), the proton affinity of X(-) induces a low-energy XH...(-)OH diabatic state that becomes accessible in v = 1 of the shared-proton stretch, leading to substantial anharmonicity in this mode. In contrast, the H + (-)OH(H2O)(n-1) diabat of (H2O)n(-) is not energetically accessible; thus, the O-H stretching modes of the AA water are reasonably harmonic, and their red-shifts are less dramatic. Only a small amount of charge penetrates beyond the AA water molecule, even upon vibrational excitation of these AA modes. Implications for modeling of the aqueous electron are discussed. 相似文献
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The compound (H3IDC)(Prz)0.5(H2O) (H3IDC = imidazole-4,5-dicarboxylate, Prz = piperazine) has been prepared from a hydrothermal approach and was characterized by IR analysis and X-ray diffraction. Its crystal structure consists of discrete 4,5-imidazole-dicarboxylate, H2O and piperazine molecules. The whole structural motif was assembled by three different non-covalent interactions of O-H…O, N-H…O and π-π stacking, which play an important role in packing the molecules. Interestingly, the connections between imidazole-4,5-dicarboxylate molecule and water molecule result in a helical polymeric chain. Crystal data for compound 1: monoclinic system, space group P21/c, a = 6.4600(13), b = 19.910(4), c = 6.9123(14) A^°, β = 94.26(3)°, V= 886.6(3) A^°^3, Z= 4, C7H10O5N3, Mr = 216.18. 相似文献
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离子对水的17O-NMR化学位移和水结构的影响 总被引:3,自引:0,他引:3
在小于1 mol•L-1的浓度范围内,测试了碱金属、碱土金属氯化物、卤化钠及其它常见含氧酸盐溶液的17O-NMR化学位移(δ(H217O)).发现离子对δ(H217O)的影响与离子的半径、电荷、离子外层电子结构及离子结构有关.其它离子参数相同时,离子半径越大,离子的摩尔δ(H217O)越大;在电子结构相同的情况下,离子电荷越大,离子的摩尔δ(H217O)越大;多原子离子的摩尔δ(H217O)更多地是与其离子结构相关.离子的摩尔δ(H217O)的大小反映了该离子对水的结构的影响情况,离子的摩尔δ(H217O)越大,对水的结构促进作用越强. 相似文献