A new insight into the understanding of the collapsed form of poly(N-isopropylacrylamide) molecules

Possible collapsed forms of poly(N-isopropylacrylamide) molecules are reviewed on the basis of first principle calculations. Various configurations and associated conformations are detailed. The calculated optimized structures exhibit different possibilities of creating networks of intra-molecular bonds of the hydrogen type. We show that the most remarkable one is able to form a local, self-saturated and well ordered helix. We also indicate in which direction the synthesis of the molecule should be oriented to improve its global behavior in term of hydrophobic/hydrophilic behavior.     

聚电解质与相反电荷表面活性剂的相互作用

通过透光度测定、电导滴定和粘度法考察了阳离子聚电解质聚苯乙烯 4 乙烯基吡啶硫酸甲酯盐与阴离子表面活性剂十二烷基硫酸钠 (SDS)的相互作用。研究表明 ,在表面活性剂未过量时 ,二者之间的静电作用占主导地位 ,并且当二者电荷总量相等时 ,生成的复合物沉淀最多 ;在表面活性剂过量后 ,复合物可部分溶解 ,溶解的原因是疏水相互作用。本文初步阐述了二者的作用机理     

中性盐对谷氨酸脱羧酶活性的影响机制

通过不同阳离子和不同阴离子对唾液链球菌嗜热亚种(Streptococcus salivariussub sp.thermophilus)谷氨酸脱羧酶活性的影响以及NaNO3对不同蛋白质浓度的谷氨酸脱羧酶活性的影响进行考察,结果表明:中性盐对谷氨酸脱羧酶活性的影响不是由于增加蛋白质亚基间的疏水作用引起的,而可能是由中性盐对谷氨酸脱羧酶活性的弱抑制作用与中性盐增加了谷氨酸脱羧酶的胶体体系稳定性共同作用所致,同时还可能与中性盐降低了反应体系CO2的溶解度有关.     

碳氟链与碳氢链表面活性剂在固液界面上的吸附

全氟辛酸及其钠盐和十二烷基硫酸钠在R972上的吸附等温线均为S型或LS型，指示固液界面吸附过程中有表面疏水缔合物生成．碳氟表面活性剂的饱和吸附量显著高于碳氢表面活性剂的饱和吸附量．加电解质于液相使各体系吸附量上升．对于碳氟表面活性剂，甚至引起吸附等温线类型变化．例如，不加电解质时全氟辛酸在R972上的吸附等温线为S型，而加入HCl（c＝0．05mol·dm－3）使吸附等混线变成LS型．全氟辛酸比全氟辛酸钠在R972上的吸附更强．几种表面活性剂在R972上的吸附均随温度升高而减少。应用两阶段吸附模型及通用吸附等温线公式可以很好地解释所得实验结果．     

利用荧光探针研究聚甲基丙烯酰胺溶液中的疏水微区

利用荧光探针研究聚甲基丙烯酰胺溶液中的疏水微区沈燕清，江鹏飞，吴世康（中国科学院感光化学研究所，北京，１００１０１）关键词荧光探针，疏水微区，聚甲基丙烯酰胺微多相体系研究近年来受到广泛的注意，它不仅是由于长期来已经发现：不同结构的微多相体系如胶束，乳...     

使用疏水作用色谱研究蛋白质的构象变化

研究了高效疏水作用液相色谱中(HIC)色谱条件改变对蛋白质构象的影响。发现固定相配体的疏水性、温度及流动相中盐的阴离子、阳离子和pH值都影响蛋白质的构象。     

Zur Chemie der Pyrrolpigmente, 54. Mitt.: Phytochrommodellstudien: Ein 2,3-Dihydrobilatrien-abc-3-Cholesterylderivat

The diastereomeric 2,3-Dihydrobilatrienes-abc derivatives (4Z, 9Z, 15Z)-7 and (4Z, 9Z, 15E)-7 bearing a cholesterylacetate moiety in position 3 of the chromophore are prepared. The reaction sequence contains an isomerisation step providing quantitative enantioselective formation of the chiral center in position 3. Configurations and conformations of the diastereomers are elucidated using¹H- and¹³C-NMR spectra, NOE-difference spectra, 2D-NMR experiments (NOESY) and arguments from UV-VIS and CD data. It is concluded that the hydrophobic interactions between chromophore and cholesteryl-fragment yield a compact conformation where the two substructures are in close contact with each other. On the other hand these interactions seem to be too weak to induce significant changes in the chemistry, absorption spectra and conformational characterics of the bile pigment chromophore. Therefore hydrophobic interactions between chromophor and apolar amino acid residues of the protein in phytochrome should be of minor relevance for determining spectroscopic shifts.

     

Heats of solution of gaseous hydrocarbons in water at 25°C

The heats of solution at 25°C for a number of hydrocarbon gases are reported as measured by a calorimetric method. There is excellent agreement between the standard enthalpy changes of solution measured calorimetrically and those derived from high precision temperature dependent solubility measurements. However the calorimetrically determined standard enthalpies of solution of a number of gases are greatly improved over values obtained from low precision temperature dependent solubility measurements. A method is presented to readily estimate the standard errors in the standard enthalpy change for any process derived from the temperature dependence of the equilibrium constant for the process. Comparison of the standard enthalpies and entropies of solution of hydrocarbon gases in water shows that the standard free energies of solution for all hydrocarbon gases investigated are dominated by unfavorable entropy contributions. A strong linear correlation between the standard entropy of solution and the number of hydrogens in the hydrocarbon molecule is found. This correlation suggests that the hydrocarbon hydrophobic effect is regulated by the number of allowable configurations of a water molecule in contact with each C–H group.     

表面活性剂对纤维素接枝共聚物溶液粘度性质的影响

研究了阴离子十二烷基硫酸钠(SDS)、阳离子十六烷基三甲基溴化铵(CTAB)和非离子聚乙二醇辛基苯基醚(OP)等三种不同类型的表面活性剂对疏水化水溶性两性纤维素接枝共聚物(CGAO)溶液粘度性质的影响.结果表明,在SDS和OP的临界胶束浓度(cmc)附近，CGAO溶液粘度最大，SDS引起CGAO粘度的变化大于OP；即使在CTAB的cmc附近，随着CTAB浓度的增加，CGAO的粘度一直呈下降趋势；非疏水改性的纤维素接枝共聚物的溶液粘度随SDS或CTAB浓度的增加而下降，但几乎不随OP浓度的增大而变化.此外，通过凝胶渗透色谱法测得的保留时间证实了SDS、CTAB和OP与CGAO之间的疏水缔合作用.