痂囊腔菌素A的结构

对实验室生物合成方法制得的痂囊腔菌素A做X射线晶体衍射测定,与文献对照,所属品系及空间群相同,晶胞参数接近,但发现北醌母体外的侧基构型有明显差异,主要表现在两个手性碳原子是R-R型而非S-S型,分别以衍射数据和分子力学优化数据为起始结构,进行STO-3G水平上的结构全优化。计算结果表明所制得的痂囊腔菌素A是一种新的光学活性对映体,由此推测痂囊腔菌素A的高光敏活性可能与手性结构特征有关。     

痂囊腔菌素A与咔唑化合物间的光致电子转移

研究了咔唑、咔唑-9-乙酸、3-溴-咔唑-9-乙酸在缺氧条件下对天然苝醌化合物痂囊腔菌素A(简记为EA)的荧光猝灭行为;由竹红菌甲素(HA)和乙素(HB)的荧光寿命估算了EA在乙腈中的荧光寿命,并进而计算了三个咔唑化合物的双分子猝灭速度常数.结果表明,三个咔唑化合物在EA的可见光吸收区无光吸收,据此推测其对EA的荧光猝灭作用归因于咔唑化合物作为电子给体而EA作为电子受体的光致电子转移作用.三个咔唑化合物的Stern-Volmer猝灭常数分别为698、704和1 063L·mol-1;乙酸基对咔唑环的光致电子转移速率几乎没有影响,而溴原子取代能够增加咔唑化合物对EA的荧光猝灭程度和光致电子转移速率.此外,EA在乙腈中的荧光寿命为1.98ns,而三个咔唑化合物的双分子猝灭速率常数分别为3.52×1011,3.56×1011和5.37×1011 L·mol-1·s-1.     

一个新的七元环吡咯-吡啶氢键分子激发态分子内质子转移的理论研究

运用含时密度泛函理论(TD-DFT)方法和以环己烷为溶剂的可极化连续模型(PCM),研究了2-[2-(1 H-pyrrol-2-yl)-cyclopent-1-enyl]-pyridine(7-HB)发生激发态分子内质子转移(ESIPT)的反应机制.结果表明,7-HB分子被光激发到Franck-Condon区域后,在第一光学亮态(S_1)上会发生一个超快的从Normal(N)式到Tautomer(T)式的质子转移反应,其反应的能垒仅有0.05eV.此外,在相同计算水平下,还研究了7-HB分子的吸收和发射光谱,所得结果与实验数据吻合得很好.     

静电力理论与分子构型

简要介绍了静电力理论的基本概念、方法原理、影响因素等内容，具体说明了该理论在确定分子空间构型时的处理过程，所得结果表明该理论在定性处理分子构型问题上，与ＶＳＥＰＲ模型、Ｗａｌｓｈ规则等理论的处理结果一致。     

取代苯酚中共振增强的分子内氢键

根据晶体结构资料，计算了59个邻位取代苯酚中分子内氢键的几何．在STO－3G水平上计算了一些分子中原子部分电荷．结果表明，酚基氧与苯环上碳之间的键长，酚基上氢原子的部分电荷，酚基所在位置处的苯环环内角与取代苯酚的酸常数pKa均有近似线性关系，当邻位上存在硝基或羰基时，内氢键由于共振而得到显著的增强，据此可说明这一类酚的显著酸性     

氢键诱导侧链液晶高分子的分子理论

将自组装概念引入Flory-Huggins格子理论,导出定向混合的氢键诱导侧链液晶高分子体系在各向同性相的混合自由能和各组分的化学势;由Maier-Saupe平均场理论给出在向列相的混合自由能和各组分的化学势,建立了氢键诱导侧链液晶高分子的分子理论模型.计算结果表明,由于氢键的方向性和饱和性决定自组装体中主客体的容纳能力,在相图上出现一个峰值;提高氢键相互作用参数和增加羧基含量,不仅自组装体的热稳定性增加,而且峰值向小分子含量低的方向移动;聚合物分子量对自组装体的热稳定性影响存在一个临界值,超过临界值后,热稳定性与分子量无关.     

分子内氢键对化合物性质的影响

本文从几个方面介绍了分子内氢键对有机化合物性质的影响。     

毛冬青皂苷甲的18,19-脱水皂苷元二甲酯的红外光谱分子内氢键效应的研究

有机化合物稀溶液的红外光谱用来研究分子内氢键是否存在,存在的形式等,以确定分子的构型和构象。毛冬青皂甙甲 IlexsaponinA 是从民间治疗冠心病有效药物毛冬青Ilex     

酰基硫脲分子内氢键与取代基效应的定量关系

对２３个Ｎ－二茂铁甲酰基－Ｎ’－芳基硫脲和４个Ｎ－苯甲酰基－Ｎ’－芳基硫脲的δβ－ＮＨ与各种取代胺的碱性强度ｐＫｂ及苯环下取代基常数σ进行了系统的定量关系研究。结果提示了此类化合物的分子内氢键与取代基效应之间的定量关系。     

基于分子内三中心氢键的超分子组装体系及其应用

分子内三中心氢键被视为是一种高效且可靠地控制分子构象的手段,可以诱导线性分子形成特定构象(折叠、螺旋、扩展及"之"字形等).根据氢键结合原子的种类,系统地综述了基于O…H…O型、S…H…X(X=N,O)型、N…H…X(X=N,O)型、F…H…X(X=F,O,N)型分子内三中心氢键的超分子组装体系的研究进展,重点介绍了大...     

Two-dimensional model of intramolecular hydrogen bond

One- and two-dimensional vibrational problems were solved to determine the states of H and D in the intramolecular hydrogen bond of malonic dialdehyde. Within the one-dimensional approach the model potential (barrier height 51 kJ/mol) satisfied with the IR and microwave spectroscopy data. For the two-dimensional problem an approach to evaluation of eigenvalues with high accuracy based on the Ritz method was developed. Within the two-dimensional approximation the barrier height was taken to be 57 kJ/mol. An introduction of the second dimension was found to give rise to the vibrational non-adiabatic effects.     

氢键对分子器件电学特性的影响

利用密度泛函理论和弹性散射格林函数方法,研究了被不同官能团取代后的联苯分子的电输运特性.计算结果表明,由于氢键的影响,使得分子的电子结构发生了变化,特别是对电子在分子结内的跃迁几率影响较大,从而直接影响了分子器件的伏安特性.     

Influence of intramolecular hydrogen bond of templates on molecular recognition of molecularly imprinted polymers

Three molecularly imprinted polymers (MIPs) were prepared corresponding to three structurally related template compounds 4-hydroxybenzoic acid (4-HBA), gentisic acid (GA) and salicylic acid (SA) that differ in intramolecular hydrogen bonding ability using acrylamide (AA) as a functional monomer. HPLC method was used to evaluate the binding performances of the MIPs to the templates and several analogues. The results showed that the difference in their molecular recognition ability was pronounced. The highest molecular recognition ability was observed for 4-HBA-imprinted polymer. It was proved that the hydrogen bond interaction between the functional monomer and the template (4-HBA) played a major role in the recognition process and Scatchard analysis showed that two classes of binding sites were formed in 4-HBA-imprinted polymer. Their dissociation constants were estimated to be 1.76×10⁻⁴ and 1.40×10⁻³ mol l⁻¹, respectively. But for GA- or SA-imprinted polymer the molecular recognition ability was not improved compared to the blank polymer (BP). By comparison of the structures of the three templates, it was concluded that the molecular recognition ability will decrease when the template itself is able to form intramolecular hydrogen bond in the molecular imprinting process. This study will be helpful for us to understand the molecular recognition mechanism of MIPs and of instructive significance for the prediction of the selectivity of MIPs.     

The intramolecular hydrogen bond in 2-hydroxy-benzamides

The two crystal structures of 5-chloro-2-hydroxy-benzamide and 2-hydroxy-N,N-diethyl-benzamide were determined by X-ray diffraction at 100 K. The intramolecular and intermolecular hydrogen bonds were found in these structurally similar 2-hydroxy-benzamides. Analysis of the hydrogen bonding was carried out on the basis of X-ray data, infrared spectra, and DFT calculations. Disruption of the intramolecular hydrogen bonding in the solid state by a steric effect is shown. Conformational analysis and potential energy calculations as functions of the turning angle around the C_aryl–C_alkyl bond were conducted. The values obtained for the HOMA index indicate mutual compensation of the amide and hydroxyl groups (due to the high degree aromaticity of the phenyl ring).     

A study of the hydrogen bond by means of comparative calculations

The nature of the hydrogen bond is investigated by means of a comparative analysis of some hydrogen bonded and hydrogen-like bonded systems. It is concluded that the hydrogen bond is determined by electrostatic interaction between the proton and the region of high electron density in the neighbour molecule.     

Theoretical study on ionic liquids based on DBUH+: Molecular engineering and hydrogen bond evaluation

The new generation of the ionic liquids (ILs) based on 1,8-diazobicylo [5,4,0] undec-7-ene (DBU) are applied as the solvent in organic reactions. In this work, by using a theoretical procedure, the most probable interactions between the ion pairs of DBUH⁺ based ILs, including 10 functionalized imidazole anions were investigated. For this purpose, the electrostatic potential surfaces were analyzed to detect the most probable interaction sites of DBUH⁺. On the basis of the obtained results, hydrogen bond formation between the anions and DBUH⁺ is influenced by the electronic effect of the substituted functional groups. This means that electron donating groups, such as phenyl has a stabilizing effect on the ion pairs, while electron-withdrawing groups, such as nitro, induces a destabilizing effect. These behaviors are described based on the interaction energy values (ΔE_int). To investigate the dispersion interaction effects in ILs formation, M06-2X-D3 functional was applied in energy analysis. The solvent reaction field was investigated by the polarizable continuum model in ethanol and chloroform as the solvent. The results showed that ethanol has a greater effect on the interaction energy of the ILs. Finally, to have a comprehensive understanding of the charge transfer effect on the stability of the studied ILs and to characterize the most probable interactions, natural bond orbital and quantum theory of atoms in molecules analyses were applied and the obtained results were analyzed.     

The intramolecular hydrogen bond in ortho-hydroxy acetophenones

The crystal structures of two ortho-hydroxy ketones (5-chloro-2-hydroxyacetophenone (I K) and 3,5-dichloro-2-hydroxyacetophenone (II K)) have been determined with X-ray diffraction at 100 K. A comparison of steric effects on properties of pseudoaromatic hydrogen bonds in ortho-hydroxy acetophenone and ortho-hydroxy ketimines have been carried out with the application of crystallographic data.

Nuclear quadrupole resonance (NQR) spectra have been measured and interpreted.     

Solvent effect on the intramolecular hydrogen bond in 8-quinolinol N-oxide

Solvent effect on intramolecular hydrogen bond in 8-quinolinol N-oxide has been studied by IR, UV,¹H NMR and¹³C NMR spectroscopy, dipole moment measurements and quantum-mechanical calculations. The solute-solvent interactions are of local character and they vary considerably over the range of solvent under study. The results suggest that formation complexes with solvent molecules weaken the intramolecular hydrogen bond in 8-quinolinol N-oxide.     

Theoretical study of the intermolecular hydrogen bond interaction for furan-HCl and furan-CHCl_3 complexes

The importance of intermolecular interactions in biology and material science has prompted chemists to explore the nature of the variety of such interactions. The strongest of these interac-tions are the hydrogen bonds, which play an important role in determining the molecular confor-mation, crystal packing, and the structure of biological systems such as nucleic acids. Extensive experimental and theoretical efforts[1—5] have been devoted to the studies of this type of interac-tions, such as …