苝醌类光敏剂构象的分子力学研究

用分子力学方法,计算了苝醌类光敏剂竹红菌甲素(HA),乙素(HB)等不同构象的生成热及酚羟基质子解离前后生成热的变化.发现:(1)1(1)HA,HB4种构象导构体的生成热相近,因而室温下即可相互转化;(2)2(2)HA,HB酚羟基质子解离能力有差别,HA强于HB.(3)3(3)HA,HB存在两个分子内氢键,键能均在8kJ/mol左右,而且Ⅰ型构象键能低于Ⅱ型构象,HA低于HB;(4)4(4)当酚羟基键从形成氢键位置扭转180°左右时存在一能量低点,提示这种构象也是可能存在的;(5)5(5)HBMC的酚羟基氢与相邻的氮原子之问也形成分子内氢键,这是HBMC仍有光敏活性的结构基础.     

金属丝桃蒽酮结构变化的理论研究

用MMX和AM1方法对金属桃蒽酮(HYP)结构变化过程的生成热进行了计算.发现:1.HYP1,2位OH可越过20kJ/mol左右的势,绕C--O键旋转而形成分子内氢键,并估算出键能约为10kJ/mol;2.HYP其他四个OH也可进行类似的构象变化,势垒在26kJ/mol左右,相应分子内氢键键能约为20kJmol;3.HYP分子内氢传递产生的异构体在能量上不稳定,进而在基础上探讨了1,2位OH分子内氢键的形成对HYP光敏活性的影响。     

HMB体系分子内质子传递的量子化学计算研究

首次利用量子化学半经验AM1方法和从头算HF/6-31G方法对一种新型的苝醌类光? 艏?PQP)-菌生素(HMB)的结构及其分子内质子传递(IPT)进行了理论计算研究，并? 捎弥鸩皆黾硬嗔吹姆椒ㄉ杓屏艘幌盗心Ｐ突衔镆钥悸歉鞑嗔炊訦MBIPT的影响，? 峁推p醌(PQ)的IPT作了对比。同于HMB只有一个分子内氢键，此项研究对解释PQP的光敏活性有十分重要的意义。本研究主要结论：(1)基态时HMB的IPT势垒只有10.0180kJ/mol(反式)和37.9819kJ/mol(顺式)，分子中存在着快速的IPT。(2)侧链对HMB的IPT势垒影响较小，IPT主要受它的大共轭结构和共振模式的影响。(3)过渡态时质子的电荷增加，质子传递势垒与它的电荷变化成线性关系，此关系可推广到其它质子传递体系。(4)HMB的IPT势垒和IPT过程中羟基氧氢键以及氢键的键长变化均成较好的线性关系。(5)虽然只有一个IPT模式，HMB的IPT以及共振模式仍然和PQ十分相似，这是HMB保持光敏活性的基础。     

基于分子间卤键的超分子平面大环自组装

本工作报道了含卤键供体和受体片段的三种芳酰胺分子(化合物1~3)的设计和合成, 并对固相中卤键的不同作用模式进行了探索和分析. 化合物1的晶体数据显示, 由于没有分子内氢键, 组成分子的三个芳环相互扭转一定角度, 并且在分子间交替排列的N···I和O···I卤键的控制下, 组装成了一条线型的超分子组装体. 由于酰胺羰基和两个紧邻的氟原子之间的排斥作用, 化合物2未能形成分子内三中心氢键. 在此基础上, 将三氟碘代苯作为卤键供体片段引入到化合物3中, 并且在折叠体骨架中嵌入了嘧啶单元. 化合物3的晶体数据显示, 基于多组有效的分子内三中心氢键和分子间较强的卤键作用, 双分子间形成了[1+1]的超分子大环. 另外, 由于嘧啶环的引入, 使得该超分子大环接近共平面.     

金属丝桃蒽酮结构变化的理论研究

用MMX和AM1方法对金属桃蒽酮(HYP)结构变化过程的生成热进行了计算.发现:1.HYP1,2位OH可越过20kJ/mol左右的势,绕C--O键旋转而形成分子内氢键,并估算出键能约为10kJ/mol;2.HYP其他四个OH也可进行类似的构象变化,势垒在26kJ/mol左右,相应分子内氢键键能约为20kJmol;3.HYP分子内氢传递产生的异构体在能量上不稳定,进而在基础上探讨了1,2位OH分子内氢键的形成对HYP光敏活性的影响。     

B炸药主要组分TNT和RDX分子间相互作用的理论研究

在B3LYP/6-31G(d)水平上研究了B炸药的主要成分--2,4,6-三硝基甲苯(TNT)与环三亚甲基三硝胺(RDX)分子间的相互作用, 得到了10种TNT＋RDX的全优化构型. 讨论了稳定构型在几何参数、稳定性、红外光谱和电荷分布上的差异. 借助自然键轨道(NBO)理论揭示了TNT与RDX分子间相互作用的本质, 主要由氢键所贡献. 分子间相互作用能在－3.930～－14.652 kJ•mol^－1之间, 经基组叠加误差(BSSE)校正, 相互作用能顺序为VI＞III＞V＞IV＞X＞I＞IX＞II＞VII＞VIII. 对全优化构型进行了热力学性质的分析, 探讨了由单体分子形成混合体系的热力学性质的变化, 结果发现, 形成分子间氢键是个放热过程. 运用Kamlet-Jacobs方程基于理论密度(ρ)估算了混合体系TNT＋RDX的爆轰性质爆速(D)和爆压(p), 与文献值进行比较表明理论计算方法和结果是可靠的.     

分子内氢键——Ⅱ.邻苯基偶氮芳香酚的内氢键和互变异构

本文通过羟基的化学位移(δ_OH),解离常数(pK_α),质谱外光谱的测量以及PM0和HMO计算,较详细地研究了分子内氢键强度和偶氮-醌腙式互变异构与分子结构的关系.结果表明,内氢键强度(以⊿δ_OH和⊿pK_α来衡量)与PMO和HMO计算的内氢键稳定化能(⊿BE_H)和给予氮原子上的电荷密度(q_N)有正比关系.HMO计算还表明,醌腙式异构体的稳定性(⊿BE_A-H)与⊿BE_H有很好的线性关系.当有内氢键存在时,化合物4～7的醌腙式比偶氮式稳定;而在气体离子态时,HMO计算和质谱结果都表明1～7皆以偶氮式更为稳定,且质谱碎片分布和HMO计算的断裂键的键序(P_xy)有近似的直线关系.所有的实验结果和分子轨道计算结果都证实了1～3具有偶氮式,4～7为偶极偶氮式结构.     

硝酸酯分子几何构型的量子化学研究

运用MINDO / 3、MNDO 和AM1 三种半经验分子轨道(MO)方法, 通过SCF计算, 首次系统地获得了32个硝酸酯化合物分子的全优化几何构型。三种方法的计算结果与已报道的四个化合物(硝酸甲酯、吉纳、硝化甘油和太安)的实验结果相比, AM1法较好。所有硝酸酯的酯基(-ONO~2)具有近似不变的几何参数。直链烷基硝酸酯的键长和键角极为相近, 全部重原子均共平面。二元直链和四元硝酸酯具有对称的分子构型。     

9-羟基苯并萘酮分子内氢传递过程的理论计算

借助MNDO、AM 1、HF/ 3 2 1G、HF/ 6 31G 量子化学理论计算方法 ,对 9 羟基苯并萘酮 (9 HPO)的分子内氢传递过程进行了理论探讨 ,并与X射线衍射的结构数据作了比较。发现 :1 .A构型的 9 HPO比B构型的更稳定 ,两个等同的A可以通过分子内氢传递相互转化 ,反应的过渡态就是B .2 .B是一种严格对称的平面构型 ,它的H电荷和偶极矩都较A增大 ,所以分子内氢传递速率在极性溶剂中将加快。3.共轭在 9 HPO分子内氢传递反应中起了重要的作用。 4.对于类似分子IHT的计算 ,先用半经验方法或小基组的从头计算方法优化结构 ,再用大基组的从头计算方法计算单点能可以得到较好的结果。     

竹红菌甲素光敏活性的量子化学研究

利用密度泛函B3LYP/6-31G^*方法对茈醌类光敏剂竹红菌甲素hypocrellin A(HA)及其模型化合物的结构性质和分子内氢传递(IHT)过程进行了系统的计算研究,比较了各侧链对分子结构和IHT过程的影响.利用CIS/6-31G^*方法对HA的活性中心苝醌(PQ)及与其结构类似的一系列化合物激发态的IHT过程进行了研究.得到的主要结论包括:(1)常温下,处于基态的HA分子能够进行快速的分子内氢传递.(2)HA的几种模型化合物在基态时的IHT势垒、分子内电荷分布与HA差别很小,这说明侧链对IHT过程的影响不大.(3)HA模型化合物的IHT势垒与氧氢键键长变化和氢键键长变化呈良好的线性关系.(4)IHT反应中伴随着一个电荷分离过程,在氢传递过程中占主导地位的是静电相互作用,这说明此IHT过程本质上是质子转移过程.(5)共轭结构对该类分子的激发态IHT过程具有重要影响,总的趋势是对小共轭体系,单重激发态和三重激发态IHT反应的势能曲线分离,随着分子共轭结构的增大,两个激发态势能曲线逐渐接近,发生交叉的可能性以及交叉的程度也随之增大,即从单重态到三重态发生系间窜越的可能性也随之增大.由于分子内氢传递导致单重激发态和三重激发态势能曲线交叉,致使发生系间窜越,使体系三重态量子效率显著提高,从而提高了茈醌类光敏剂的光敏活性.这说明IHT过程对该类分子保持其光敏活性具有重要的意义.     

Shake-up peak positions and intensities by many-body theory methods

The valence shell X-ray photoelectron spectrum of N₂ is calculated using the equations-of-motion—Green's function method. The inclusion of shake-up basis operator configurations in the primary operator space along with the simple ionization operator configurations allows for the calculation of shake-up peak positions on an equal footing with the simple ionization energies. The important shake-up basis operator configurations are identified using configuration selection techniques similar to those which have been successfully employed in large scale configuration interaction problems, thus minimizing the size of the matrices to be diagonalized. The relative peak intensities are calculated within the plane wave approximation. The intensity equations are analyzed indicating that the relative peak intensities are more sensitive to ground state correlation effects than the peak positions. Modifications of the theory to improve the calculations of shake-up energies are discussed.     

N,N-二(N-亚甲基-2-吡咯烷酮)甘氨酸(C12H19N3O4)的结构及配位性能的研究

用量子化学 Ｐ Ｍ３ 方法优化了 Ｎ, Ｎ二（ Ｎ亚甲基２吡咯烷酮） 甘氨酸（ Ｃ１２ Ｈ１９ Ｎ３ Ｏ４） 分子的顺式和反式两种构型;计算了分子的电离能、电子亲合能、电荷密度和前线轨道,并研究了该分子的配位性能。结果表明标题化合物稳定,顺式构型分子内有氢键,反式则没有。 Ｐ Ｍ３ 计算的标题化合物顺式构型几何参数与实验测定结果一致,顺式构型能与希土金属离子形成稳定的配合物。     

Hydrogen adsorption in defected carbon nanotubes

Recently there has been lot of interest in the development of hydrogen storage in various systems for the large-scale application of fuel cells, mobiles and for automotive uses. Hectic materials research is going on throughout the world with various adsorption mechanisms to increase the storage capacity. It was observed that physisorption proves to be an effective way for this purpose. Some of the materials in this race include graphite, zeolite, carbon fibers and nanotubes. Among all these, the versatile material carbon nanotube (CNT) has a number of favorable points like porous nature, high surface area, hollowness, high stability and light weight, which facilitate the hydrogen adsorption in both outer and inner portions. In this work we have considered armchair (5,5), zig zag (10,0) and chiral tubes (8,2) and (6,4) with and without structural defects to study the physisorption of hydrogen on the surface of carbon nanotubes using DFT calculations. For two different H₂ configurations, adsorption binding energies are estimated both for defect free and defected carbon nanotubes. We could observe larger adsorption energies for the configuration in which the hydrogen molecular axis perpendicular to the hexagonal carbon ring than for parallel to C–C bond configuration corresponding to the defect free nanotubes. For defected tubes the adsorption energies are calculated for various configurations such as molecular axis perpendicular to a defect site octagon and parallel to C–C bond of octagon and another case where the axis perpendicular to hexagon in defected tube. The adsorption binding energy values are compared with defect free case. The results are discussed in detail for hydrogen storage applications.     

甲醛与甲酰胺相互作用的从头算研究

The optimizations geometries and vibrational frequencies of H2CO,HCONH2 and acquired 3 complexes between H2CO?HCONH2 have been calculated by using the ab initio method at the MP2/6-31G（ d）and MP2 （FC）/6-311++G（d,p）level. The non-minimum structures with negative vibrational frequencies are excluded. The lowest energy conformer of these complexes is a cyclic structure with N - H?O and C - H?O hydrogen bonds in a common plane. No significant changes are observed in the geometries of the monomers in their complexed state. The most characteristic geometrical properties of the complex are the lengthening of the contacting N-H bonds by 0.4-1.1 pm,and the general shortening of the contacting C-H bonds by 0.3-0.4 pm with respect to the monomers. The interaction energies of complexes have been corrected by the basis set superposition error （BSSE）using the full Boys-Bernardi counterpoise correction scheme. The corrected complex interaction energies of 3 structures at MP2/6-311++G（2df,3p）/ / MP2（FC）/6-311++G（d,p）level are -29.94, -16.10 and -18.45 kJ/mol,respectively. The interaction energies indicate that C - H?O is a weak hydrogen bond. The results of natural bond orbital population analysis reveals that there is only a small charge-transfer in the process of forming the complexes. The results of natural bond orbital analysis and atom in the molecule scheme appear quite significant in view of their importance for understanding the mechanisms of intermolecular interaction leading to hydrogen bonding. The results of molecular interaction energy decomposition analysis show that the electrostatic interaction plays an essential role in stabilizing the H2CO?HCONH2 complexes.     

AM1 semiempirical MO calculation of specific solvation interaction: a scale for hydrogen bond donation ability of solvents

Semiempirical molecular orbital calculations at the AM1 level have been carried out to obtain specific solvation interaction energies involving hydrogen bonding for various solute-protic solvent systems. A scale for hydrogen bond donating ability of the protic solvents is proposed. A comparison of the calculated parameters with solvatochromic parameters is presented.     

Semiempirical computation of homolytic O-H bond dissociation energies of alcohols: comparison of the AM1 and PM3 methods

The heats of formation of various alcohols and alkoxy radicals were calculated using the AM1 and PM3 semiempirical methods, which were then used to calculate the bond dissociation energies of the alcohols. Both restricted Hartree-Fock (RHF) and unrestricted Hartree-Fock (UHF) calculations were performed to determine which technique was most applicable to the computation of bond dissociation energies within the semiempirical frameworks. It was determined that AM1/RHF calculations gave the most accurate results for O-H bond dissociation energies of alcohols. The effect of using configuration interaction calculations to calculate bond dissociation energies within the semiempirical framework was also examined.     

Theoretical study on the molecular structures of toluene,para‐fluorotoluene,para‐chlorotoluene,and 4‐methylpyridine and their sixfold internal rotational barriers

Two kinds of sixfold internal rotational configurations of toluene, para‐fluorotoluene, para‐chlorotoluene, and 4‐methylpyridine were calculated using Hartree–Fock (HF), second‐order Møller–Plesset (MP2), and Beck's three parameter hybrid functional using the LYP correlation functional (B3LYP) theory methods with various high‐level basis sets. Structures and energies were compared for different configurations. Calculations indicate that the orthogonal configuration has a local minimum while the planar configuration is a transition structure. Furthermore, geometries of the orthogonal and the planar configurations are quite similar, except for a methyl CH bond. Sixfold internal rotational barriers were calculated from the energy difference of two different configurations. For the calculated results, HF methods underestimated the rotational barriers, but MP2 calculations overestimated them. However, the density functional theory (DFT) method is a reliable method since the calculated internal rotational barriers are similar to the experimental ones. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 772–778, 2000     

Studies on solid-state proton transfer along hydrogen bond of pyrazolone-ring

Evidence from the time-dependent UV-vis reflection spectra studies indicates the compound 1-phenyl-3-methyl-4-(4-methylbenzal)-5-pyrazolone 4-ethylthiosemicarbazone (PM4MBP-ETSC) undergoes a solid-state photochromism. The reaction rate constant was studied by the first-order kinetics curves. X-ray single crystal structural analysis shows that the pyrazolone-ring stabilizes in the keto form. The conclusion can be made that its photochromism in crystalline is associated with a photoinduced proton transfer reaction (inter- and intra-molecular hydrogen transfer) along hydrogen bond leading to a colored tautomer as the compound crystallizes in H-bonded supramolecular configuration.     

SiH_4与Na、Mg和Be等金属氢化物分子间反向氢键相互作用

在B3LYP/6-311++g**、MP2/6-311++g(3df,3pd)及MP2/aug-cc-pvtz水平上分别求得H3SiH…MeHn(Me=Na,Mg,Be;n=1或2)复合物势能面上的3个稳定构型,探讨了以Si-H为电子供体的红移反向氢键相互作用(IHB).经MP2/6-311++g(3df,3pd)水平的计算,在3个复合物中,含基组重叠误差(BSSE)校正的单体间相互作用能分别为-5.98、-8.65和-3.96kJ.mol-1,与MP2/aug-cc-pvtz水平下计算得到的-6.18、-9.12和-4.28kJ·mol-1接近,可见3个反向氢键复合物的相对稳定性顺序为:SiH4...MgH2SiH4...NaHSiH4...BeH2.NBO分析及对相关原子化学位移的计算表明,在复合物中,电子流向总体表现为SiH4→MeHn(n=1或2),且直接参与反向氢键形成的H3的化学位移向低场移动.与传统氢键相比,这里Si1-H3既是氢键供体,又是电子供体,从而形成反向氢键相互作用.另外,采用分子中原子理论(AIM)分别对各复合物中相关键鞍点处的电子密度拓扑性质进行了分析,结果表明3个复合物中均存在以静电性质为主的分子间反向氢键弱相互作用.     

单电子卤键复合体系H3C···Br-Y(Y=H, CN, NC, CCH, C2H3)的作用机制

对单电子溴键复合物H₃C···Br—Y(Y=H, CCH, CN, NC, C2H3)的结构与性质进行了理论研究. 在B3LYP/6-311++G**水平上计算了稳定构型并做了频率分析. BSSE矫正的相互作用能(E^BSSE)和NBO及AIM分析输入的波函数在MP2/6-311++G**水平下完成. 复合物H₃C···Br—Y中, CH₃(供电子体)自由基均提供一未成对电子与Br—Y中Br(受电子体)形成了单电子溴键, 此单电子溴键也具有“三电子”键的特征. 单电子溴键的形成导致甲基H的背向Y弯曲和Br—Y键的拉长及红移单电子溴键复合物的产生. 考察了电子受体中不同取代基, C(spⁿ)-Br杂化及溶剂的存在对复合物作用的影响, 将单电子氢键, 单电子卤键和单电子锂键的作用强度做了对比, 进一步对Popelier提出的氢键体系中的前三个重要拓扑指标在单电子溴键体系中的重现性进行了探讨.