THERMODYNAMIC ASPECTS OF SELF-ASSOCIATION AND HYDROPHOBIC BONDING OF METHYLENE BLUE - A MODEL SYSTEM FOR STACKING INTERACTIONS
THERMODYNAMIC ASPECTS OF SELF-ASSOCIATION AND HYDROPHOBIC BONDING OF METHYLENE BLUE - A MODEL SYSTEM FOR STACKING INTERACTIONS
复制标题
DOI：
10.1021/ja00725a006
复制
发表时间：
1970-01-01
影响因子：
15
通讯作者：
GHOSH, AK
中科院分区：
文献类型：
--
作者：
MUKERJEE, P;GHOSH, AK
平坦的芳香族或杂芳族染料离子在水溶液中的自缔合作用为“堆积”相互作用提供了良好的模型体系。用等萃取法研究了阳离子染料亚甲基蓝在34.9℃和10℃时的自缔合行为。结果在定性上与25.1的结果非常相似。根据三个温度下的二聚常数K2的值，求出了二聚反应的熵和热焓。二聚化的“么正”熵是正的，这表明水结构对二聚体的稳定性有显著贡献。二聚反应的热值是负的，而且是次要的。讨论了可能的影响因素。尽管存在较强的电荷斥力，但阶跃三聚反应常数K‘在所有温度下都大于K2。因此，在堆积过程中存在明显的次近邻吸引相互作用，有助于其协作性。三聚体的“额外”稳定性反映在比值Ks/K2中，似乎是由于有利的正熵变化克服了正焓变化。这表明了水结构效应在促进水溶液中有机分子缔合方面的长期贡献。
The self-association of flat aromatic or heteroaromatic dye ions in aqueous solutions provides a good model system for “stacking” interactions. The self-association behavior of the cationic dye methylene blue has been studiedby the “isoextraction” method at 34.9 and10. 0; the results are qualitatively very similar to those at 25.1. From the values of the dimerization constant K2 at three temperatures, the entropy and enthalpy of dimerization have been derived. The “unitary" entropy of dimerization is positive, suggesting that water-structure contributions are appreciable in the stability of the dimers. The enthalpyof dimerization is negative and sub-stantial in magnitude. Possible contributory factors are discussed. The stepwise trimerization constant K¡ is found to be greater than K2 at all temperatures, in spite of stronger charge repulsion. There is thus an appreciable second-nearest neighbor attractive interaction in the stacking process, contributing to its cooperativity. The “extra” stability of the trimer reflected in the ratio Ks/K2 appears to be due to a favorable positive entropy change overcoming a positive enthalpy change. This is indicative of a long-rang econtribution of water-structure effects in promoting association of organic molecules in aqueous solutions.