水环境对GC和AT碱基对质子转移的影响

采用B3LYP/DZP++的方法研究了第一水化层作用和连续化处理的水溶剂作用对鸟嘌呤-胞嘧啶(GC)碱基对和腺嘌呤-胸腺嘧啶(AT)碱基对质子转移反应的影响. GC和AT碱基对在连续化水溶剂作用下,均发生单质子转移(SPT1)和分步的双质子转移(DPT),而在第一水化层5 个水分子的作用下(GC·5H₂O,AT·5H₂O)或同时考虑第一水化层作用和连续化水溶剂作用(GC·5H₂O+PCM,AT·5H₂O+PCM)时,GC和AT碱基对的质子转移均只得到单质子转移反应(SPT1). 单质子转移过程中的活化能变化情况表明：第一水化层对GC和AT碱基对结构和质子转移影响较大,水环境对碱基对的作用主要发生在第一水化层.     

2-(2′-羟基苯基)间氮杂氧茚的旋转异构和质子转移反应

用INDO系列方法对2-(2′-羟基苯基)间氮杂氧茚的旋转异构和质子转移反应进行研究,求得基态和激发态反应的位能面、势垒、过渡态,对有关化合物的吸收和荧光光谱进行了理论指认。计算与实验结果符合较好,并对光化学反应机理和应用前景进行了讨论。     

Solid-Phase Molecular Recognition of Cytosine Based on Proton-Transfer Reaction

Abstract  The proton-transfer molecular adducts cytosine/isoorotic acid (1:1) dihydrate (CytIsor) and cytosine/maleic hydrazide (2:2) dihydrate (CytMal) have been studied by X-ray diffraction methods. CytIsor crystallizes in the orthorhombic system, space group Pbnb, a = 7.4859 (4), b = 12.7977 (9), c = 26.4573 (16) ?, V = 2534.7 (3) ?³. CytMal crystallizes in the triclinic system, space group P − 1, a = 6.7767 (9), b = 12.063 (2), c = 12.937 (3) ?, α = 78.58 (2), β = 75.87 (2), γ = 75.63 (1)°, V = 982.8 (3) ?³. In both compounds protonation occurs at the N3 atom of the cytosine aminooxo tautomer as a result of the proton-transfer process from the acidic hydroxy groups of the counterions. In the crystal structure, both cocrystals are stabilized by a plethora of N–H···O, N–H···N and O–H···O hydrogen bonds. It is shown the ability of cytosine to form large organic assemblies, with the appropriate guest, due to solid-state recognition involving synthons based on hydrogen bonding between functional groups as sites of proton-transfer reactions. Index Abstract  The proton-transfer molecular adducts of cytosine with isoorotic acid and with maleic hydrazide have been synthesized in the solid state and their hydrogen-bonding patterns have been studied by X-ray diffraction methods.      

Cu2+对腺嘧啶-胸腺嘧啶碱基对阴离子质子转移的影响

采用B3LYP/DZP++方法研究了腺嘌呤-胸腺嘧啶(A-T)碱基对阴离子(AT)-的单质子转移机理以及金属离子Cu2+对(AT)-碱基对质子转移的影响.(AT)-碱基对的单质子转移路径是由胸腺嘧啶N25位上的质子H26沿分子间的氢键N25-H26…N10转移到腺嘌呤的N10位.金属Cu2+可通过络合作用分别吸附在(AT)-碱基对O24、O28、N4、N13上,从而影响(AT)-碱基对中质子转移过程.Cu2+络合作用在胸腺嘧啶(T)的O24、O28上时,发生了从胸腺嘧啶到腺嘌呤方向上的单质子转移反应;而作用在腺嘌呤(A)的N4、N13上时,得到了双质子转移的稳定产物.     

离聚物及其共混体系的研究──2．配位络合和质子转移对共混体系的增容作用

通过将苯乙烯（Ｓ）及甲基丙烯酸正丁酯（ｎＢｍａ）分别与少量的４－乙烯基吡啶（４－Ｖｐ）自由基共聚，在聚苯乙烯（ＰＳ）及聚甲基丙烯酸丁酯（ＰＢｍａ）链上分别引入了功能基团吡啶基制得共聚物ＳＶｐ和ＢｍａＶｐ．然后将共聚物络合上过渡金属离子或结合上来自羧酸的质子，以制得离聚物及其共混物．这里共混物的两组分均具有正电荷．红外光谱（ＩＲ）、差示扫描量热法（ＤＳＣ）及透射电镜（ＴＥＭ）的研究结果表明，通过配位络合和质子转移而引入两聚合物的同种离子对共混体系有显著的增容作用．     

Some fundamental questions in chemical reactivity

This paper provides an overview of recent progress on some fundamental questions in chemical reactivity. The following issues are emphasized: (1) the choice of electronic structure level for dynamics study; (2) Diels-Alder reactions; (3) combined molecular orbital/molecular mechanics methods; (4) solvent effects; (5) S_N2 reactions; (6) dynamics simulations; (7) proton-transfer reactions; and (8) femtochemistry. Received: 25 November 1997 / Accepted: 23 December 1997     

Theoretical Studies of Proton Transfer Reactions—Energy Barriers and the Marcus Equation

The reactants, ion-dipole complexes, transition states, and products for the proton transfer reactions HBCOH⁺ + OCXH → HBCO + ⁺HOCXH optimized at the SCF/4–31G* level of theory for B, X = F, Cl, H, CH₃, CH₂Cl, CHCl₂ and CCl₃ are studied. The intrinsic barrier ΔE*_BX correlates with the degree of the O-O bond contraction in the transition structure. Both intrinsic and overall barriers can be predicted with the aid of Marcus theory. Progressive degrees of chlorination of the alkyl group in B produce decreases in the barrier to proton transfer from HBCOH⁺ to OCXH and increases in the reverse transfer barriers. These changes can be quantitatively reproduced by the Marcus equation for all systems.     

Dioxo- and oxovanadium(V) complexes of biomimetic hydrazone ONO and NNS donor ligands: Synthesis, crystal structure and catalytic reactivity

Oxo- and dioxo-vanadium(V) complexes of hydrazone ONO donor ligands with the formula [V^VO(μ₂-OCH₃)(L¹)]₂ (1) and [V^VO₂(L²)]·H₂O (2) were synthesized by the reaction of [VO(acac)₂] with proton-transfer complexes of benzenetricarboxylic acid/benzoylhydrazide and benzenetricarboxylic acid/isonicotinohydrazide, respectively (H₂L¹ = monocondensation of benzoylhydrazide and acetylacetone, H₂L² = monocondensation of isonicotinohydrazide and acetylacetone). Dioxo complex of V(V), [VO₂(L³)] (3), was synthesized by the reaction of equimolar amounts of VO(acac)₂, 2-acetylpyridine and thiosemicarbazide (H₂L³ = hydrazone Schiff base of acetylpyridine and thiosemicarbazide and Hacac = acetylacetone). They were characterized by FT-IR, UV-Vis and NMR spectroscopic methods. The crystal structures of 1 and 2 were determined by X-ray analyses. The ¹H NMR spectrum of the complex 1 in CDCl₃ solution indicated that this dimeric complex is converted appreciably into its respective monomeric form. The catalytic potential of the complexes has been tested for the oxidation of alkene, alkane and aromatic hydrocarbons using H₂O₂ as the terminal oxidant. Good to excellent conversions have been obtained for the oxidation of most of the hydrocarbons.