准确快速计算含多肽酰胺和核酸碱基的氢键复合物的氢键强度和氢键作用势能曲线

N-H···O=C、C-H···O=C、N-H···N和C-H···N等氢键作用是蛋白质a-螺旋结构、b-折叠结构和DNA双螺旋结构形成的主要因素,在生物分子识别、蛋白质复制以及遗传信息传递等过程中起重要作用。准确快速计算生物体系中存在的N-H···O=C、C-H···O=C、N-H···N和C-H···N等氢键作用强度以及氢键强度随分子几何结构(距离和角度)变化的势能曲线对正确模拟(从而正确认识和理解)蛋白质折叠机制和DNA双螺旋结构形成机制等生物过程意义重大,对设计合成具有特殊功能的生物分子材料有重要指导价值。本文主要介绍了近年来建立的偶极-偶极氢键作用模型及其在快速预测多肽-多肽分子间和核酸碱基-多肽分子间氢键作用强度和氢键作用势能曲线方面的应用。     

DFT方法研究基于脲及硫脲衍生物的阴离子受体

采用密度泛函理论(DFT)模拟了两个基于脲和硫脲衍生物的受体分子对卤素阴离子的识别过程.结构优化表明基于脲衍生物的受体分子1最稳定构象为"反反"构象,分子内部形成稳定的C~α-H…O=C分子内氢键;而基于硫脲衍生物的受体分子2,不能形成分子内氢键,最稳定构象为"反顺"构象.受体1、2与卤素阴离子F~-、Cl~-可形成稳定的双氢键复合物,在此过程中,受体2经历了由"反顺"构象到"反反"构象的异构化过程.结构和能量分析表明,1、2受体分子与F~-离子间的氢键强度远大于其与Cl~-离子间的氢键;另一方面,受体2与阴离子间的氢键明显强于受体1,这是由于硫脲基N-H键具有更强的酸性.此外,对受体分子、氢键复合物及去质子化产物的吸收光谱计算结果表明,受体与F~-离子作用可产生明显的吸收光谱红移,而与Cl~-离子的作用对光谱影响较小.     

单嘧磺隆晶体-活性构象转换的分子动力学模拟

应用分子动力学模拟方法对单嘧磺隆在水、正辛醇和正辛烷3种不同溶剂中的构象行为、单嘧磺隆与3种溶剂之间的相互作用能及氢键相互作用进行了计算研究. 计算结果表明, 在3种不同的溶剂中, 单嘧磺隆的优势构象不同; 其构象转换过程, 特别是转换成活性构象的过程主要发生在水溶液中; 与溶剂分子间的相互作用是分子构象行为的决定因素; 单嘧磺隆的脲桥部分可以和含氢键接受体的溶剂形成氢键, 分子间与分子内氢键的竞争可能是从晶体构象转换成活性构象的主要驱动力.     

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.     

α-单取代环十二酮构象转换的溶剂效应和温度效应

利用1H NMR技术研究了α-单取代环十二酮的α-边外取代[3333]-2-酮构象(A)和α-角顺取代[3333]-2-酮构象(B)相互转换的溶剂效应和温度效应.结果显示,一般情况下随着溶剂极性的增加,构象B的含量增加,这可以解释为构象B较构象A有较大的偶极矩.当分子中的取代基能与羰基形成分子内氢键时,情况则相反,随着溶剂极性的增加,构象B的含量降低,这可以解释为构象B的分子内氢键的减弱.结果还显示,温度的升高有利于两个构象的相互转换而达到新的平衡.     

a-单取代环十二酮构象转换的溶剂效应和温度效应

利用^1H NMR技术研究了a-单取代环十二酮的a-边外取代[3333]-2-酮构象(A)和-角顺取代[3333]-2-酮构象(B)相互转换的溶剂效应和温度效应．结果显示，一般情况下随着溶剂极性的增加，构象B的含量增加，这可以解释为构象B较构象A有较大的偶极矩．当分子中的取代基能与羰基形成分子内氢键时，情况则相反，随着溶剂极性的增加，构象B的含量降低，这可以解释为构象B的分子内氢键的减弱．结果还显示，温度的升高有利于两个构象的相互转换而达到新的平衡．     

离子速度成像方法研究溴代环己烷的紫外光解动力学

利用二维离子速度成像方法对C6H11Br分子在234 nm附近的光解动力学行为进行了研究. 通过(2+1)共振增强多光子电离探测了光解产物Br*(2P1/2)和Br(2P3/2), 得到它们的相对量子产率. 从光解产物Br*(2P1/2)和Br(2P3/2)的速度图像得到了能量和角度分布. 结果表明, Br*原子主要来自于S1态的直接解离, 而Br则绝大部分是从S2态向T3态的系间交叉跃迁得到, 并导致了两种解离通道能量分布的差别. 实验发现C6H11Br分子解离过程中大部分能量都转化为内能, 但与其它长链溴代烷烃分子相比, 可资用能更多地被分配到平动能中, 结合软反冲模型分析了这种能量分配跟环烷基的构象和稳定性的关系.     

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,重点介绍了大环化合物、折叠体与含孔螺旋化合物、分子拉链等超分子组装体的合成以及它们在促进有机反应、分子识别、跨膜通道、分子机器、软物质材料等领域的应用.希望为此类超分子组装体的合成及应用提供有益参考.     

端炔基对水溶液中聚(N-异丙基丙烯酰胺)相转变的影响

通过原子转移自由基聚合,制备出低分子量、窄分布、端炔基的线形聚(N-异丙基丙烯酰胺)(alkynylPNIPAM),利用高灵敏示差扫描微量热技术,在升—降温循环过程中确定端炔基对alkynyl-PNIPAM相转变行为的影响.结果显示,随循环次数增加,升温热容曲线明显变宽,降温热容曲线由双峰逐渐变为单峰;升温和降温的相转变温度有逐渐降低的趋势,但焓变的变化很小.聚合物的低的分子量使端基效应不可忽视,alkynylPNIPAM的端炔基可诱导分子链聚集,形成小的端基聚集体,由于这些聚集体中链内和链间氢键作用,链构象调整变得困难,导致PNIPAM链在升温时更易塌缩、降温时更难解离.     

FC(O)SNCO的电子结构和光电离解离过程

由于拥有―C(O)S―和―NCO基团, FC(O)SNCO的分子和电子结构是非常有趣的. 利用FC(O)SCl和AgNCO制备了FC(O)SNCO,并利用HeI光电子能谱(PES)、光电离质谱(PIMS)以及理论计算研究了其分子和电子结构. 通过将实验、理论计算以及自然键轨道(NBO)分析结合起来, 获得了FC(O)SNCO的最稳定分子构型. 利用外壳层格林函数(OVGF)方法以及与相似化合物的比较, 对其光电子能谱进行了指认. 理论计算表明,对于中性分子最稳定的构型为syn-syn非平面构型, 而电离后的离子最稳定构型为syn-syn平面构型. 实验结果表明, 第一电离能来自于S的孤对电子轨道, 为10.33 eV. 第二至第六电离能分别为12.03、13.23、13.77、14.78、15.99 eV, 并对这些电离能进行了指认. 在光电离质谱中产生了六个质谱峰, 分别为SN⁺、FC(O)⁺、SNCO⁺、FC(O)SN⁺、C(O)SNCO⁺、FC(O)SNCO^+·, 其中FC(O)SNCO^+·的峰是最强峰. 结合HeI光电子能谱和理论计算, 对PIMS进行了分析,并研究了可能的电离和解离过程并对其进行了讨论.     

Decavanadates with [Et3NH] and [Me2HN(CH2)2NHMe2]: Variation in protonation state and self-assembly

Synthesis, thermal behaviour and crystal structures of [Et₃NH]₄[V₁₀O₂₆(OH)₂] (1) and [Me₂HN(CH₂)₂NHMe₂]₃[V₁₀O₂₈] · 4H₂O (2) are reported. In the crystal lattice of 1, the anions form discrete dimers via O–H···O hydrogen bonds and the cations are connected to the respective anions through N–H···O hydrogen bonds. On the other hand, 2 forms a complex three-dimensional network due to involvement of the cations, the anions and the lattice water in O–H···O and N–H···O hydrogen bonds.     

Cobalt(III) α-Dimethylglyoximates [Co(DH)2(Py)2]2SiF6 · 10H2O and [Co(DH)2(Thio)2]2SiF6 · 2H2O · C2H5OH: Synthesis and Structure

[Co(DH)₂(Py)₂]₂SiF₆ · 10H₂O and [Co(DH)₂(Thio)₂]₂SiF₆ · 2H₂O · C₂H₅OH complexes are synthesized and characterized by X-ray diffraction analysis. Two radicals of -glyoxime linked by hydrogen O–H···O bonds lie in the equatorial plane of the octahedral Co(III) complexes. Intramolecular (– and N–H···O) and intermolecular (O–H···F, O–H···O, N–H···F, N–H···O, N–H···S) interactions are discovered in the crystal. The influence of nonvalence interactions on the structures is discussed.     

Synthesis and Structures of New Enaminones

Two isomeric enaminones were obtained by reaction of ethyl 2-hydroxy-4-(4-hydroxy-6-methyl2H-pyran-2-on-3-yl)-4-oxo-2-butenoate (1) and amines (aniline, benzylamine, butylamine and tyramine) in ethanol. The structures of isomers were studied by ¹³C and ¹H NMR spectra, whereas in the case of isomers 2b, 3a, and 4a (Scheme 1), the crystal structures have been determined by single crystal X-ray diffractometry. The compounds 2b and 3a exist in the solid state as N–C=C–C=O, whereas 4a is in the N–C=C–C–OH tautomeric form (Scheme 2, form A and B, respectively). All three structures exhibit very short intramolecular hydrogen bonds of O–H···O [in the range 2.396(3) – 2.448(3) Å] and N–H···O [in the range 2.580(5) – 2.679(3) Å] type, that are reinforced by delocalization. The crystal structures are in addition stabilized by C–H···O weak hydrogen bonds. In 2b and 3a, the discrete dimers are formed by eight-membered ring containing hydrogen bonds; in 4a, the infinite chains along [1 0 1] direction are formed.     

Synthesis,structure and properties of a series of scorpionate oxovanadium(IV)–carboxylate complexes

A series of oxovanadium(IV) complexes: TpVO(pzH)(2,4-Cl–C₆H₃–OCH₂COO) (1), TpVO(pzH)(C₆H₅–OCH₂COO) (2), TpVO(pzH)(p-Cl–C₆H₄–COO) (3), TpVO(pzH)(3,5-NO₂–C₆H₃–COO) (4), Tp∗VO(pzH∗)(p-Cl–C₆H₄–COO) (5) and Tp∗VO(pzH∗)(p-Cl–C₆H₄–COO) · CH₃OH (6) (Tp = hydrotris(pyrazolyl)borate, pzH = pyrazole, Tp∗ = hydrotris(3,5-dimethylpyrazolyl)borate, pzH∗ = 3,5-dimethylpyrazole) were synthesized and their crystal structures were determined by X-ray diffraction. In all the complexes, the vanadium ions are in a distorted-octahedral environment with a N₄O₂ donor set. Hydrogen bonding interaction exists in each complex. Complexes 1 and 2 are hydrogen-bonded dimers. Dimeric units of 2 are connected to one another via weak inter-molecular C–H···O interactions to form a 2D network on the bc-face. In 3–6 there exist intramolecular N–H···O hydrogen bonds between the neutral pyrazole/3,5-dimethylpyrazole and the uncoordinated carboxyl oxygen atom. In addition, the catalytic activity of complex 2 in a bromination reaction in phosphate buffer with phenol red as a trap was evaluated by UV–Vis spectroscopy. Furthermore, the elemental analyses, IR spectra and thermal stabilities were recorded.     

Crystal and Molecular Structure of 5-Acetylamino-3-nitro-1,2,4-triazole

This paper reports on an X-ray diffraction study of 5-acetylamino-3-nitro-1,2,4-triazole. Monoclinic crystals, space group P2_1/c; a=8.2079(7), b=13.096(1), c=13.650(1) , =100.64(1)°. Two independent molecules are identical in conformation and both have an N–H···sO intramolecular hydrogen bond; the difference lies in their interactions with neighbors. In molecule A, the acetyl oxygen atom and all nitrogen atoms (except those of the amino group) are involved in the intermolecular hydrogen bonds; in molecule B, these hydrogen bonds are formed by only two NH groups in addition to the above oxygen. The crystal structure of the title compound is compared with that of 5-amino-3-nitro-1,2,4-triazole.     

NMR Study of the Steric and Electronic Structure of 2-(2-Acylethenyl)pyrroles

According to the ¹H and ¹³C NMR data, 2-(2-acylethenyl)- and 2-(2-acyl-1-phenylethenyl)pyrroles in chloroform exist exclusively in the keto form. The Z isomers of these compounds are characterized by coplanar arrangement of the olefinic fragment, carbonyl group, and pyrrole ring. The strong intramolecular hydrogen bond NÄH···O is responsible for the presence of only one rotamer. The corresponding E isomers give rise to equilibrium between conformers with syn and anti arrangement of the olefinic fragment with respect to the pyrrole ring. A very strong conjugation between the ketovinyl group and the pyrrole ring is likely to arise from an appreciable contribution of the zwitterionic structure.     

Synthesis,structure and spectroelectrochemical property of (2,2′-bipyridine)–metal (M = Pt,Pd) dichloride with 4,4′-bis(fluorous-ponytail) on bipyridine

The 4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy ligands [R_f = n-C₃F₇ (1a), HCF₂(CF₂)₃ (1b)] were prepared and then treated with [MCl₂(CH₃CN)₂] (M = Pt or Pd) to result in the corresponding metal complexes, [MCl₂(4,4′-bis(R_fCH₂OCH₂)-2,2′-bpy)] (M = Pt 2a–b; Pd 3a–b). Both ligands and metal complexes were fully characterized by multi-nuclei NMR (¹H, ¹⁹F and ¹³C), FTIR, and mass (GC/MS or HR-FAB) methods. The X-ray structures of 2a–b and 3a–b were studied. With terminal CF₃, the structures of 2a and 3a exhibit disordered polyfluorinated regions in solid state. With terminal HCF₂, the structures of 2b and 3b show a π–π stacking of the bpy planes, five-membered C–H···O hydrogen bond and an unusual intramolecular blue-shifting C–H···F–C hydrogen bond system, whereas without terminal HCF₂, the structures of 2a and 3a show the similar π–π stacking, five-membered C–H···O hydrogen bond and typical orientation of polyfluorinated ponytails, but not the C–H···F–C hydrogen bond system. The CV and UV/Vis studies were also carried out.     

Piperazinediium,Zr(IV) and Ce(IV) pyridine-2,6-dicarboxylates: Syntheses,characterizations, crystal structures, ab initio HF,DFT calculations and solution studies

The novel title compounds, (pipzH₂)_1.5(pydcH)₃·3.7H₂O, 1, (pipzH₂)[Zr(pydc)₃]·8H₂O, 2 and (pipzH₂)[Ce(pydc)₃]·8H₂O, 3 in which pydcH₂ is pyridine-2,6-dicarboxylic acid and pipz is piperazine were obtained in aqueous solution. The compounds were characterized by IR, ¹H NMR and ¹³C NMR spectroscopy, elemental analyses, and X-ray crystallography. Compound 1 is resulted from proton transfer between pydcH₂ and pipz. However, compounds 2 and 3 are resulted from complexation of 1 and corresponding metallic salts. Both compounds 2 and 3 contain three pyridine-2,6-dicarboxylate species as tridentate ligands, one piperazinediium as counter ion, and eight-uncoordinated water molecules in the asymmetric unit. In both structures each M(IV) is coordinated in a distorted tricapped trigonal prism geometry by three nitrogen and six oxygen atoms of carboxylate groups of three (pydc)²⁻ fragments. In the crystal structures of 1, 2 and 3, extensive O–H···O, N–H···O and C–H···O hydrogen bonds as well as electrostatic forces, C–H···π, C–O···π and π–π stacking play important roles in stabilizing structures. The geometrical parameters of the [M(pydc)₃]²⁻ anionic complexes, where M = Ce(IV), Zr(IV) have been optimized with the B3LYP method of density functional theory (DFT) and ab initio Hartree–Fock (HF) methods for comparison. In addition, we have studied the structures of (pydc)²⁻ anion and its mono and doubly protonated forms, (pydcH)⁻ and pydcH₂. The electronic properties of the anionic complexes and ligands have been investigated based on the natural bond orbital (NBO) analysis at the B3LYP method which verifies that the synergistic effect has been occurred in the title complexes. In solution study of 2, the stoichiometry and stability constant of complexation of pipz, pydc, pydc–pipz proton transfer system and Zr(IV) ion in aqueous solution were investigated by potentiometric method.     

Spatial and Electronic Structure of 2-(2-Furyl)- and 2-(2-Thienyl)pyrroles According to 1H and 13C NMR Data

In 2-(2-furyl)- and 2-(2-thienyl)pyrroles the heterocycles are in efficient ,-conjugation. The presumably possible for this compounds intramolecular hydrogen bond N-H···O or N-H···S is lacking. The COCF₃ group in position 2 of the pyrrole ring is syn-oriented with respect to pyrrole fragment, and the orientation is fixed by an intramolecular hydrogen bond N-H···O. However no bifurcating hydrogen bonds arise in the molecules containing COCF₃ group.