Showing papers by "Kaixian Chen published in 2001"
TL;DR: With flavone as a structural template, three-dimensional quantitative structure-activity relationship (3D-QSAR) studies and ab initio calculations were performed on a series of flavonoids to build a reasonable pharmacophore model and propose specific S1 and S2 subsites relating to substituent positions.
Abstract: With flavone as a structural template, three-dimensional quantitative structure-activity relationship (3D-QSAR) studies and ab initio calculations were performed on a series of flavonoids. A reasonable pharmacophore model was built through CoMFA, CoMSIA, and HQSAR analyses and electrostatic potential calculations. A plausible binding mode for flavonoids with GABA(A) receptors was rationalized. On the basis of the commonly recognized binding site, the specific S1 and S2 subsites relating to substituent positions were proposed. The different binding affinities could be explained according to the frontier orbitals and electrostatic potential (ESP) maps. The ESP could be used as a novel starting point for designing more selective BZ-binding-site ligands.
83 citations
TL;DR: The consistency between the BD simulation and the experimental data indicates that the three-dimensional model of Lq2-K(+) channel complex is reasonable and can be used in further biological studies such as rational design of blocking agents of K(+ channels and mutagenesis in both toxins and K(+) channels.
34 citations
TL;DR: In this paper, a complex formed by silicane and ammonium was analyzed to investigate the binding characteristics and nature of the dihydrogen bond and the calculated enthalpies of formation of this complex using B3LYP/6-311++G(2df,2pd) and MP2/6311++g(d,p) methods, corrected by basis-set superposition error (BSSE) and thermal energy, are −5.595 and −4.465 kcal/mol, respectively.
Abstract: Quantum chemical calculations are performed on the complex formed by silicane and ammonium in order to investigate the binding characteristics and nature of the dihydrogen bond. The calculation results using B3LYP and MP2 methods with the basis sets from 6-31G* to 6-311++G(2df,2pd) reveal that the dihydrogen-bond angle is ∼180.0° and that the bond length is ∼1.60 A. The calculated enthalpies of formation of this complex using B3LYP/6-311++G(2df,2pd) and MP2/6-311++G(d,p) methods, corrected by basis-set superposition error (BSSE) and thermal energy, are −5.595 and −4.465 kcal/mol, respectively. Taking into account our CCSD(T)/6-311++G(2df,2p) and G2 results, we suggest that the binding strength between SiH4 and NH4+ is ∼5.0 ± 0.5 kcal/mol. The BSSE released from the B3LYP method seems to converge at the basis set 6-311++G(d,p). In addition, charge distribution, electrostatic interaction energy, and the molecular-orbital coefficient analysis on all molecular orbitals of this complex show that s−s orbital in...
16 citations
TL;DR: In this article, the UHF/4-31G results on 19 carefully designed fullerene intermediates reveal that the core of an intermediate, rather than the number of dangling bonds or abutting pentagon rings, has an intrinsic effect on its energy.
Abstract: Quantum chemical ab initio (U)HF/4-31G investigation on buckminsterfullerene and some proposed intermediates in its formation is carried out in this study with a view to better understanding how small carbon species carry out self-assembly to form fullerenes. The calculations on 19 carefully designed fullerene intermediates reveal that the core of an intermediate, rather than the number of its dangling bonds or abutting pentagon rings, has an intrinsic effect on its energy. The computational results show that hexagonal-core structures have lower energies than pentagonal-core structures. In addition, the pentagonal core enclosed completely by hexagonal rings has the highest energy. The UHF/4-31G results also suggest that some intermediates such as C18, C21 and C30 with hexagonal cores have unusually low energies in comparison with their isomers or neighbours. Based on these calculated results, we outline the possible pathways from precursor to intermediates to fullerenes, subject to synthesis conditions and raw materials. These pathways support some existing proposals, such as medium monocyclic ring stacking and small ring polymerization mechanisms. However, our results do not suggest that the numbers of dangling bonds or abutting pentagonal rings have the highest impact on fullerene formation. The calculated thermodynamic parameters of the dimerization and addition reactions between two bowl-shaped intermediates suggest that these reactions are favorable to fullerene formation, and that the concentration of bowl-shaped fullerene intermediates should be very low in all detectable carbon species.
2 citations
TL;DR: In this article, the UHF/4-31G results on 19 carefully designed fullerene intermediates reveal that the core of an intermediate, rather than the number of dangling bonds or abutting pentagon rings, has an intrinsic effect on its energy.
Abstract: Quantum chemical ab initio (U)HF/4-31G investigation on buckminsterfullerene and some proposed intermediates in its formation is carried out in this study with a view to better understanding how small carbon species carry out self-assembly to form fullerenes. The calculations on 19 carefully designed fullerene intermediates reveal that the core of an intermediate, rather than the number of its dangling bonds or abutting pentagon rings, has an intrinsic effect on its energy. The computational results show that hexagonal-core structures have lower energies than pentagonal-core structures. In addition, the pentagonal core enclosed completely by hexagonal rings has the highest energy. The UHF/4-31G results also suggest that some intermediates such as C18, C21 and C30 with hexagonal cores have unusually low energies in comparison with their isomers or neighbours. Based on these calculated results, we outline the possible pathways from precursor to intermediates to fullerenes, subject to synthesis conditions and raw materials. These pathways support some existing proposals, such as medium monocyclic ring stacking and small ring polymerization mechanisms. However, our results do not suggest that the numbers of dangling bonds or abutting pentagonal rings have the highest impact on fullerene formation. The calculated thermodynamic parameters of the dimerization and addition reactions between two bowl-shaped intermediates suggest that these reactions are favorable to fullerene formation, and that the concentration of bowl-shaped fullerene intermediates should be very low in all detectable carbon species.