长脂链巴比妥酸和四氨基嘧啶的分子组装体的研究

长脂链巴比妥酸和四氨基嘧啶的分子组装体的研究王志强，王力彦，张希，沈家骢（吉林大学分子光谱与分子结构开放实验室，长春，１３００２３）关键词分子识别，分子组装体，长脂链巴比妥酸，四氨基嘧啶靠氢键、静电、疏水等弱相互作用及其协同作用，在气／液、液／液及液...     

巴比妥酸-NO_2~--铁(Ⅱ)-CPB显色体系光度测定巴比妥酸的研究

本文对巴比妥酸－ＮＯ－２－铁（Ⅱ）－ＣＰＢ显色体系进行了研究,建立了一种测定巴比妥酸的分光光度法,该法巴比妥酸含量在１．０×１０－６～２．０×１０－５ｇ／ｍＬ范围内符合比尔定律。方法简便、快速且具有良好的选择性及重现性,用于巴比妥类药物合成样中巴比妥酸的测定,回收率在９０．２％～１０２．１％     

巴比妥酸—NO2^—2铁（Ⅱ）—CPB显色体系光度测定巴比妥酸的研究

本文对巴比妥酸－ＮＯ＾－２－铁（Ⅱ）－ＣＰＢ显色体系进行了研究,建立了一种测定巴比妥酸的分光光度法,该法巴比妥酸含量在１．０＊１０＾－６－２．０＊１０＾－５ｇ／ｍＬ范围内符合比尔定律。     

巴比妥酸楔形棒状液晶分子的合成、性质及与三嗪衍生物的氢键识别组装体

合成了一端含巴比妥酸, 另一端含带三条烷基链苯甲酸酯楔形单元, 中间为苯乙烯共轭单元的棒状分子5-{4-[3,4,5-三(十二烷氧基)苯甲酸酯]苯乙烯}-(1H,3H)-2,4,6嘧啶三酮(BA³/12); 采用偏光显微镜(POM)、 示差扫描量热法(DSC)、 X射线衍射(XRD)、 扫描电子显微镜(SEM)、 红外光谱(IR)、 核磁共振波谱(NMR)和荧光光谱等对其进行了表征. 结果表明, BA³/12能自组装形成晶格结构为c2mm的长方柱相液晶; 红外光谱及核磁共振氢谱表征数据初步证实了BA³/12与三嗪化合物6-(5-{4-[3,4-双(十二烷氧基)]苄氧基}苯基)噻吩-2,4-二氨基-1,3,5三嗪(1T²/12)形成的等摩尔氢键复合物BA/T的结构; BA/T不仅具有液晶性质且能形成具有三维网络状结构的超分子凝胶.     

硫代巴比妥酸分光光度法测定消毒液中戊二醛

在醋酸介质中，硫代巴比妥酸与戊二醛生成缩合产物，此产物在可见光区有最大吸收，籍此可测定微量戊二醛。线性范围为０．５－１０．０ｍｇ／Ｌ，检出限为０．０１９ｍｇ／Ｌ。方法灵敏度高，体系简单，操作简便，用本方法测定了消毒液中戊二醛的含量，结果满意。     

硫代巴比妥酸光度法测定香草醛

香草醛在强酸性介质中与硫代巴比妥酸（ＴＢＡ） 反应生成黄绿色的化合物,建立了可见光分光光度法测定香草醛方法。线性范围１×１０－ ６～１５×１０－ ４ｍ ｏｌ／Ｌ,检出限为４４７×１０－ ８ｍ ｏｌ／Ｌ。对冰淇淋、麦片等进行了其中香草醛含量测定,结果满意     

CN-与异烟酸-硫代巴比妥酸显色反应的研究及应用

在弱酸性介质中,于氯胺T存在条件下,CN-可与异烟酸-硫代巴比妥酸形成一蓝色染料,该染料最大吸收波长位于642 nm,且其吸光度A与氰化物含量在一定的范围内呈良好的线性关系,据此建立了测定生活饮用水中微量氰化物的异烟酸-硫代巴比妥酸分光光度法。本法氰化物含量在0~4.0μg/10 mL范围内符合比耳定律。方法用于生活饮用水中微量氰化物的测定,结果令人满意。     

CN--异烟酸-硫代巴比妥酸-CTMAB显色体系的研究及应用

在弱酸性介质中,有溴化十六烷基三甲铵(CTMAB)存在条件下,CN-与异烟酸-硫代巴比妥酸形成一蓝色化合物,其最大吸收波长(λmax)位于646 nm,表观摩尔吸光系数6ε46=4.67×104L.mol-1.cm-1,且其吸光度A与氰化物含量在一定的范围内呈良好的线性关系。据此,建立了测定生活饮用水中微量氰化物的CTMAB-异烟酸-硫代巴比妥酸显色光度法。本法氰化物含量在0~4.0μg/10.0 mL范围内符合比耳定律,用于生活饮用水中微量氰化物的测定,结果令人满意。     

铁(Ⅱ)和钴(Ⅱ)与巴比妥酸-NO2-显色反应的研究及应用

在碱性介质中,铁(Ⅱ)和钴(Ⅱ)可与巴比妥酸(BA)-NO2-体系反应,分别形成一种稳定的兰色和黄色配合物,铁(Ⅱ)配合物分别在波长630 nm和350 nm具有吸收峰,钴(Ⅱ)配合物只有一个吸收峰位于365 nm波长处,体系的吸光度AFe630、AFe365和ACo365与铁、钴含量在一定的范围内呈良好的线性关系,且...     

核酸中碱基的氢键作用机理及电子特征理论研究

采用耦合簇量子化学方法 CCSD/aug-cc-pVDZ研究了嘧啶与嘌呤之间的相互作用,利用基函数叠加误差法(BSSE)消除相互作用能误差,并进行了几何结构优化;采用Gaussian 03程序包中的NBO程序分析了二阶稳定化能及自然键轨道.与此同时,应用约化密度函数(RDG)填色等值面图对体系进行了图形化分析,分析了氢键相互作用所在的空间位置和相对强度,以及氢键相互作用的性质,以进一步了解二者的相互作用.结果表明,嘧啶-嘌呤体系的相互作用属于闭合壳层静电相互作用.电子密度跃迁矩阵分析结果表明,激发区域主要集中在N原子和O原子处,涉及的空间广度很大,第一激发态主要涉及前线分子轨道,属于σ→π*或n→π*类型跃迁.     

Helical supramolecular aggregates based on ureidopyrimidinone quadruple hydrogen bonding

A series of mono- and bifunctional compounds 2-7, based on the ureido pyrimidinone quadruple hydrogen bonding unit, was prepared to study the mode of aggregation of these compounds in the bulk and in solution. Compounds 2-7 exhibit thermotropic liquid crystalline properties, as evidenced by differential scanning calorimetry and optical polarization microscopy. The presence of an ordered hexagonal discotic (D(ho)) phase of 2 a was confirmed by X-ray diffraction on an aligned sample. In chloroform, the bifunctional compounds form cyclic dimers at millimolar concentrations, and these dimers exist in equilibrium with linear species above a critical concentration, which may be from 6 mM to greater than 260 mM, depending on the structure of the spacer. Circular dichroism measurements in chloroform did not show a Cotton effect. Dodecane solutions of compounds 3, 4 b, and 7 b display a Cotton effect at the absorption band of the phenyl-pyrimidinone unit. Amplification of chirality was observed in mixtures of 7 a and 7 b, but not in mixtures of 4 a and 4 b, indicating that 7 a and 7 b form mixed polymeric aggregates with a helical architecture in dodecane solution, whereas 4 a and 4 b do not. The Cotton effect is lost upon increasing the temperature. Half of the helicity is lost at 25 degrees C for 3 and at 60 degrees C for 4 b, suggesting that 3, bearing the shorter spacer, forms less stable columns than 4 b. Compound 7 b loses half of its helicity at 45 degrees C. Compounds 2 b, 5, and 6 do not exhibit helical organization, as evidenced by the absence of Cotton effects.     

Molecular assemblies from imidazolyl-containing haloalkenes and haloalkynes: competition between halogen and hydrogen bonding

The structural characterization of molecular assemblies constructed from imidazolyl-containing haloalkenes and haloalkynes is reported. 1-(3-Iodopropargyl)imidazole (2) and 1-(2,3,3-triiodoallyl)imidazole (5) were synthesized from 1-propargylimidazole (1). In the solid state, these wholly organic modules self-assemble through N...I halogen-bonding interactions, thus giving rise to polymeric chains. The N...I interaction observed in 2 (d(N...I)=2.717 A, angle-spherical C(sp)-I...N=175.8 degrees) is quite strong relative to previously reported data. The N...I interaction in 5 (d(N...I)=2.901 A, angle-spherical C(sp2)-I...N=173.6 degrees) is weaker, in accordance with the order C(sp)-X<--base>C(sp2)-X<--base. Compound 5 was found to give a 1:1 cocrystal 4 with morpholinium iodide (6). In the X-ray crystal studies of 4, N...I halogen-bonding interactions similar to those observed in 5 were shown not to be present, as the arrangement of the molecules is governed by two interwoven hydrogen-bonding networks. The first network involves N-H...O interactions between nearby morpholinium cations, and the second network is based on N-H...N hydrogen bonding between morpholinium cations and imidazolyl groups. Both hydrogen-bonding schemes are charge-assisted. Halogen bonding is not completely wiped out, however, as the triiodoalkene fragment forms a halogen bond with an iodide anion in its vicinity (d(I...I)=3.470 A, angle-spherical C(sp2)-I...I=170.7 degrees). X-ray crystal studies of 6 show a completely different arrangement from that observed in 4, namely, N-H...O interactions are not present. In crystalline 6, morpholinium cations are interconnected through C-H...O bridges (d(H...O)=2.521 and 2.676 A), and the NH2+ groups interact with nearby iodide anions (d(H...I)=2.633 and 2.698 A).     

Hierarchical self-assembly of a bow-shaped molecule bearing self-complementary hydrogen bonding sites into extended supramolecular assemblies

The bow-shaped molecule 1 bearing a self-complementary DAAD-ADDA (D=donor A=acceptor) hydrogen-bonding array generates, in hydrocarbon solvents, highly ordered supramolecular sheet aggregates that subsequently give rise to gels by formation of an entangled network. The process of hierarchical self-assembly of compound 1 was investigated by the concentration and temperature dependence of UV-visible and (1)H NMR spectra, fluorescence spectra, and electron microscopy data. The temperature dependence of the UV-visible spectra indicates a highly cooperative process for the self-assembly of compound 1 in decaline. The electron micrograph of the decaline solution of compound 1 (1.0 mM) revealed supramolecular sheet aggregates forming an entangled network. The selected area electronic diffraction patterns of the supramolecular sheet aggregates were typical for single crystals, indicative of a highly ordered assembly. The results exemplify the generation, by hierarchical self-assembly, of highly organized supramolecular materials presenting novel collective properties at each level of organization.     

Conformers and intramolecular hydrogen bonding of the oxalic acid monomer and its anions

Density functional theory, B3LYP/6‐31G** and B3LYP/6‐311+G(2d,p), and ab initio MP2/6‐31G** calculations have been carried out to investigate the conformers, transition states, and energy barriers of the conformational processes of oxalic acid and its anions. QCISD/6‐31G** geometrical optimization is also performed in the stable forms. Its calculated energy differences between the two most stable conformers are very near to the related observed value at 7.0 kJ/mol. It is found that the structures and relative energies of oxalic acid conformers predicted by these methods show similar results, and that the conformer L1 (C_2h) with the double‐interfunctional‐groups hydrogen bonds is the most stable conformer. The magnitude of hydrogen bond energies depends on the energy differences of various optimized structures. The hydrogen bond energies will be about 32 kJ/mol for interfunctional groups, 17 kJ/mol for weak interfunctional groups, 24 kJ/mol for intra‐COOH in (COOH)₂, and 60 kJ/mol for interfunctional groups in (COOH)COO⁻¹ ion if calculated using the B3LYP/6‐311+G(2d,p) method. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 541–551, 2000     

Intra and intermolecular hydrogen bonding in formohydroxamic acid

The presence of hydrogen bonding interactions in several tautomeric forms of formohydroxamic acid (FHA) and 1:1 association among the tautomeric forms and water‐coordinated tautomeric forms of FHA is explored theoretically. Out of the seven equilibrium structures, four tautomeric forms have been selected for aggregation with single water molecule and dimer formation. Fifteen aggregates of FHA with H₂O have been optimized at MP2/AUG‐cc‐PVDZ level and analyzed for intramolecular and intermolecular H‐bond interactions. Twenty‐seven dimers of the four tautomeric forms have been obtained at MP2/6‐31+G* level. The stabilization energies associated with dimerization and adduct formation with water are the result of H‐bond interactions and range from very weak to medium. The atomic charges and NBO analysis indicate that the electrostatic and the charge transfer are the important components favoring H‐bond formation. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

On differences between hydrogen bonding and improper blue-shifting hydrogen bonding.

Twenty two hydrogen-bonded and improper blue-shifting hydrogen-bonded complexes were studied by means of the HF, MP2 and B3LYP methods using the 6-31G(d,p) and 6--311 ++G(d,p) basis sets. In contrast to the standard H bonding, the origin of the improper blue-shifting H bonding is still not fully understood. Contrary to a frequently presented idea, the electric field of the proton acceptor cannot solely explain the different behavior of the H-bonded and improper blue-shifting H-bonded complexes. Compression of the hydrogen bond due to different attractive forces-dispersion or electrostatics--makes an important contribution as well. The symmetry-adapted perturbation theory (SAPT) has been utilized to decompose the total interaction energy into physically meaningful contributions. In the red-shifting complexes, the induction energy is mostly larger than the dispersion energy while, in the case of blue-shifting complexes, the situation is opposite. Dispersion as an attractive force increases the blue shift in the blue-shifting complexes as it compresses the H bond and, therefore, it increases the Pauli repulsion. On the other hand, dispersion in the red-shifting complexes increases their red shift.     

Structural rationalisation of co-crystals formed between trithiocyanuric acid and molecules containing hydrogen bonding functionality

Crystallisation of trithiocyanuric acid (TTCA) from various organic solvents that have hydrogen bonding capability (acetone, 2-butanone, dimethylformamide, dimethyl sulfoxide, methanol and acetonitrile) leads to the formation of co-crystals in which the solvent molecules are incorporated together with TTCA in the crystal structure. Structure determination by single-crystal X-ray diffraction reveals that these co-crystals can be classified into different groups depending upon the topological arrangement of the TTCA molecules in the crystal structure. Thus, three different types of single-tape arrangements of TTCA molecules and one type of double-tape arrangement of TTCA molecules are identified. In all co-crystals, hydrogen-bonding interactions are formed through the involvement of N-H bonds of TTCA molecules in these tapes and the other molecule in the co-crystal. Detailed rationalisation of the structural properties of these co-crystals is presented.