The two-dimensional Quantitative Structure-Activity Relationship （2D-QSAR） models have been developed to estimate and predict the inhibitory activities of a series of HEPT analogues against HIV-1 by using quantum chemical parameters and physicochemical parameters. The best model of three parameters yields r = 0.908, r^2A = 0.800 and s = 0.467 based on stepwise multiple regression （SMR） method. The stability of the model has been verified by t-test, and the results show that the model has perfect robustness. The predictive power of QSAR models has been tested by Leave-One-Out （LOO） and Leave-Group（regularly random set）-Out（LGO） procedure Cross-Validation methodology. The r^2cv of 0.755 and r^2pred of 0.759 were obtained, respectively.
Two possible reactions of NbS＋ （3∑^-, 1Г） with CO in the gas phase have been studied by using B3LYP and CCSD（T） methods： the O/S exchange reaction （NbS^＋ ＋ CO → NbO^＋ ＋ CS） and the S-transfer reaction （NbS＋ ＋ CO → Nb^＋ ＋ COS）. The two reactions have a one-step mechanism. The barriers of the O/S exchange reaction on the triplet and singlet surfaces are 51.2 and 52.4 kcal/mol, respectively, and the barriers of the S-transfer reaction are 58.3 and 78.0 kcal/mol, respectively. The results indicate that the Stransfer and the O/S exchange reaction of the 3∑^- ground state of NbS＋ are competing, but, for the S-transfer reaction, the 1F exited state is more reactive. The differences between the reactions of NbS＋ （3∑^_, 1Г） and VS＋ （3∑^_, 1Г） are discussed.
Shi Wen YuTaoHong LiXiao Mei YangLi Qing YinLi Feng YaoXiao Guang Xie
The PM3 and B3LYP methods were employed to calculate the properties of 18 7-substituted fluoroquinolones. The correlation between biological activity （against gram-positive organisms or gram-negative organisms） and structural properties was obtained by using multiple linear regression （MLR） methods： The best model generated correlates the antibacterial activity with EHOMO and QF8 for gram-positive organisms, and EHOMO and dipole moment for gram-negative organisms, respectively. It suggests that the interaction mechanisms ,of fluoroquinolons with gram-positive and gram-negative organisms are different.
The reaction of Os^＋ （^6D, ^4F） with N20 has been investigated at B3LYP/TZVP and CCSD（T）/6-311＋G^＊ levels of theory. The mechanisms corresponding to O-atom and N-atom transfer reactions have been revealed. It was found that on the sextet reaction surface both the O-atom and N-atom transfer reactions undergo through direct-abstraction mechanism, leading to the formation of OsO^＋ and OsN^＋, whereas on quartet surface the two reactions undergo through O-N bond or N-N bond insertion mechanism. The calculated energetics shows that the reactions on the sextet surface have notable energy barriers, whereas the reactions on quartet surface are barrierless. ？2009 Xiao Guang Xie. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Tao Hong LiChuan Ming WangShi Wen YuXiang Yi LiuHui FuXiao Guang Xie
The AM1 and B3LYP methods were employed to calculate the structural properties of 20 6-（1-naphthylmethyl） substituted S-DABO derivatives with β-carbonyl group on the C（2） side chain as novel potent non-nucleoside HIV-1 reverse transcriptase inhibitors. The correlation analysis （CA） and stepwise multiple regression analysis （SMR） were performed. The QSAR models indicate that the physicochemical parameters of Qc9, MRR1, ELUMO, ∏R2 and μ have significant influence on the activities of these derivatives. The substitution of hydrophobic R2 and bulky aromatic R1 to form a conjugated system with the frame of those S-DABO series compounds should be considered to design new potent compounds for anti-HIV-1.
The title reaction proceeds via a one- and two-step mechanism along the ^3A＂ and ^3A＇ surfaces, respectively. The ^3A＇ excited state surface has a lower barrier than the ^3A＂ ground state surface （11.6 and 16.0 kca1/mol, respectively）, We suggest that, at low energies, the reaction proceeds along the A＇ surface and then makes an intersystem crossing to the A＂ surface and yields the ground state product VO^＋（^3∑^-）, which may explain the small VO^＋ cross-section at low energies observed in the experiment
Two possible reaction mechanisms of VS^＋（^3∑^-, 1^Г） with CO in the gas phase have been studied by using B3LYP/TZVP and CCSD（T）/6-311＋G （3df, 3pd） methods： the O/S exchange reaction （VS^＋＋CO→VO^＋＋CS） and the S-transfer reaction （VS^＋ ＋ CO → V^＋ ＋ COS）. The two reactions proceed via two-step and one-step mechanism, respectively. The barriers of the triplet and singlet PESs are 30.6 and 50.9 kcal/mol, respectively, for O/S exchange reaction and 7.3 and 50.2 kcal/mol, respectively, for the S-transfer reaction. The results indicate that the triplet ground state reaction is more favorable, and the S-transfer reaction is more favorable than the O/S exchange reaction, which is in good agreement with the experimental observation.
Shi Wen Yu Li Qing Yin Li Feng Yao Ming Li Xiao Guang Xie
The elimination of HBr from CH3Br by ground state of Cu＋ and Au＋ has been investigated by using DFT methods. A mechanism of one-step HBr elimination leading to CuCH2＋ was identified. For the formation of AuCH2＋, besides the one-step mechanism, another two-step HBr elimination pathway through a C-Br bond insertion intermediate was also found, and this pathway is energetically more favorable than the one-step mechanism. The calculated reaction energy barriers show that the formation of AuCH2＋ is energetically much more favorable than the formation of CuCH2＋. The experimental observations are well explained.
Tao Hong LiChuan Ming WangXiang Yi LiuXiao Guang Xie
