The role of hydrogen-bonding interaction in poly(vinyl alcohol)/poly(acrylic acid) blending solutions and their films

<正>The aim of this work is to investigate the hydrogen-bonding interaction in poly(vinyl alcohol)(PVA)/poly(acrylic acid)(PAA) blending system and its influence on rheological properties in solution and the physical properties in solid state. Introducing PAA into PVA solutions resulted in a thickening behavior of blend solutions.The viscosity of the solutions increased with PAA content increasing,and a maximum viscosity could be obtained when the ratio of PVA/PAA was 70/30. The intermolecular hydrogen-bonding and miscibility between PVA and PAA in solid state were investigated by differential scanning calorimetry(DSC),Fourier transform infrared spectroscopy(FTIR) and mechanical measurements.The results displayed the great influence of introducing PAA on the properties of blending films.The tensile strength increased from 89.31 MPa to 119.8 MPa and Young's modulus improved by over 300%with increasing PAA concentration compared with those of pure PVA films.By systematically studying the rheological behaviors of solutions and the physical properties of films,the influence of hydrogen-bonding in solutions and solid states were discussed.     

特殊缔合体系TFE水溶液分子动力学模拟

三氟乙醇(TFE)水溶液是一类特殊的缔合体系. 采用分子动力学模拟方法结合核磁共振化学位移研究了TFE水溶液体系全浓度范围的氢键网络, 并对动力学模拟结果和核磁共振化学位移进行了比较. 从径向分布函数(RDF)发现, TFE水溶液中存在着强氢键, 而体系中的C—H…O弱相互作用较为明显, 也不能忽略. 氢键网络分析发现TFE 水溶液体系的氢键大致分为以下三个区域: 在水富集区域, 水分子倾向于自身缔合形成稳定的簇结构, 随着TFE 浓度的增加, 水的有序结构受到破坏, 水分子和TFE分子发生交叉缔合作用形成氢键; 在TFE富集区域, 水分子较少, TFE分子自身通过氢键形成多缔体结构. 此外, 分子动力学统计的平均氢键数的变化和文献报导的核磁共振化学位移变化趋势相同, 实验和理论的结果吻合较好.     

Diastereo- and enantioselective conjugate addition of 3-substituted oxindoles to enones via bifunctional catalysts

This paper presents a synthetically challenging vicinal quaternary-tertiary C–C forming reaction of 3-substituted oxindoles and chalcones by a simple aryl substituted bifunctional thiourea catalyst. The reactions work with a broad range of chalcones, giving chiral 3,3′-substituted oxindoles type compounds with adjacent quaternary-tertiary stereocenters in high yields (up to 99%), very good dr (up to >98:2) and very good ee (up to 96%).     

Theoretical analysis of solvent effects on nitrogen NMR chemical shifts in oxazoles and oxadiazoles

Using quantum chemistry methods we have evaluated the solvent effects on the ¹⁴N NMR chemical shifts in five oxa- and oxadiazoles dissolved in twelve solvents. These solvents differ in their polarity with the dielectric constants varying from 2 to 80. Moreover, three of them have a hydrogen-bond donor character. All possible hydrogen-bonding in the water solution with the oxygen and nitrogen (hydrogen-acceptor) centers in oxazoles (2) and oxadiazoles (3) have been considered in our studies. It has been shown that both the pure solvent and hydrogen-bonding effects are significant and result in ¹⁴N magnetic shielding increase. In water solutions the pure solvent effect is larger than the hydrogen-bonding effect. In addition, the solvent effect has been analyzed in terms of its direct and indirect contributions. It should be emphasized that our theoretical results for ¹⁴N chemical shifts in oxa- and oxadiazoles remain in a very good agreement with the accurate experimental data.     

Fluorophenyl Bilirubins: Synthesis and Stereochemistry

Summary.  Analogs of bilirubin with vinyl groups replaced by symmetrically-disposed o-fluorophenyls (1, bis-exo, and 2, bis-endo) were synthesized and characterized spectroscopically. Their ¹H NMR spectra and NOE data are consistent with an intramolecularly hydrogen-bonded ridge-tile conformation where each propionic acid group embraces an opposing dipyrrinone. Like bilirubin, 1 and 2 exhibit negative chirality induced circular dichroism (ICD) Cotton effects in chloroform containing quinine. Unlike bilirubin, however, in aqueous buffer containing human serum albumin, 2 exhibits a negative exciton chirality ICD, whereas that of 1 is positive. Received May 22, 2001. Accepted May 29, 2001     

Switching on Hydrogen Bonding in Oligopyridine Ligands

We have prepared two new 2,2′-bipyridine ligands bearing 3-aryl substituents at the 5 and 5′-positions using Suzuki methodology. The substituents differ only in the presence of a methoxy group or a phenolic hydroxy group. In the solid state a beautiful self-complementary hydrogen-bonded lattice incorporating one water molecule per ligand is formed with the phenolic compound.     

Complementary Supramolecular Aggregation via O–H···O Hydrogen-bonding and Hg···S Interactions in Bis[N,N′-di(2-hydroxyethyl)-dithiocarbamato-S,S′]mercury(II): Hg[S2CN(CH2CH2OH)2]2

Abstract  The central mercury atom in Hg[S₂CN(CH₂CH₂OH)₂]₂ is asymmetrically chelated by two dithiocarbamate ligands leading to a distorted square planar geometry. Molecules aggregate into supramolecular chains via Hg···S interactions that are connected into a three dimensional array by extensive hydrogen bonding interactions. The compound crystallizes in the orthorhombic space group Pna2₁ with a = 13.8173(7) ?, b = 4.5307(1) ?, c = 26.0261(12) ?, and Z = 4. Index Abstract  Molecules associate into supramolecular chains via Hg···S interactions and these are connected into a three dimensional architecture by O–H···O hydrogen-bonding interactions.      

Comparative studies on biophysical interactions between 4-dicyanomethylene-2,6-dimethyl-4H-pyran (DDP) with bovine serum albumin (BSA) and human serum albumin (HSA) via photophysical approaches and molecular docking techniques

Photophysical studies of 4-Dicyanomethylene-2,6-Dimethyl-4H-Pyran (DDP) dye with globular proteins, Human Serum Albumin (HSA) and Bovine Serum Albumin (BSA) were carried out in aqueous solution. An isosbestic point resulted on the addition of serum albumins, which signifies a complex or an equilibrium state of DDP dye with albumin. Addition of BSA to DDP dye results in a fluorescence enhancement accompanied with a significant hypsochromic shift, whereas with that of HSA, a fluorescence quenching with a considerable blue shift resulted. Excited state studies of DDP dye with serum albumins portray that the role of binding sites of dye with albumins vary considerably and the nature of interaction is presumably attributed to combined hydrogen-bonding and hydrophobic interactions. Molecular docking studies of DDP dye with albumins and two other derivatives 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) dye and 4-(Dicyanomethylene)-2-methyl-6-(4-t-buyl)-4H-pyran (DCT) dyes with BSA and HSA elucidates that the hydrogen-bonding interaction accompanied with several hydrophobic, pi–pi an pi–alkyl interactions coexist between dye and albumins. The binding energy, intermolecular energy and stability of the DDP, DCM and DCT dyes through docking techniques with albumins authenticate that the dye predominantly acts as hydrogen-bonding acceptor site and the protein molecule as the donor. DDP dye prefers to exist in four different binding sites of HSA, whereas, in the case of BSA, the most preferred site is found to be hydrophobic domain (site I). Interestingly, the most preferred site of DCT dye is III A subdomain of HSA, whereas DCM dye is oriented towards I B subdomain. DDP and DCT are smaller in size and reside in the domain preferred for smaller ligands (II A and IIIA) as resulted in several drugs-HSA interaction whereas DCM dye which is categorized as medium to larger ligand based on the extended structure resides in the most favoured site IB. Fluorescence techniques in combination with molecular docking methods elucidate binding characteristics and the domain in which the dye resides in a micro heterogeneous environment is established in this study.     

凝胶型交联聚苯乙烯—异氰尿酸树酯对酚类物质的吸附机理研究

由氯甲基化低交联聚苯乙烯和异氰尿酸在三乙胺作用下反应,制得了凝胶型交联聚苯乙烯－异氰尿酸树脂,测定了该树脂对苯酚和间苯二酚在不同温度下的吸附等温线,依据Clapeyron0Clausius方程从吸附等温线计算出了吸附热,从热力学的角度论证了树脂是基于氢键键合的疏水作用而吸附苯酚和间苯二酚的。     

Intermolecular Hydrogen Bonds and the Supramolecular Structure of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-Bis(<Emphasis Type="Italic">p</Emphasis>-tolylsulfonyl)diethylenetriamine

Abstract  The title compound N,N′-bis(p-tolylsulfonyl)diethylenetriamine (1) was synthesized and its crystal structure determined by X-ray diffraction. Adjacent molecules of 1, symmetrically related through a c-glide, are linked by alternating hydrogen bonds that form molecular chains along [0 0 1]. Two molecular chains occur in each unit cell and pack to form alternating layers in a three-dimensional supramolecular structure. The compound crystallizes in the Pca2₁ space group stabilized by the inclusion of solvent dichloromethane molecules in structural voids between molecules of 1. The dichloromethane molecules are related through a twofold screw rotation axis and are not disordered. Index Abstract  Intermolecular hydrogen bonds involving sulfonamide moieties of title compound afford a supramoleular structure that accommodates the inclusion of dichloromethane in alternating layers.