Singh SK, Nilsson S
Department of Pharmaceutics, Pharmacia & Upjohn AB, Uppsala, S-751 82, Sweden
J Colloid Interface Sci. 1999 May 1;213(1):133-151. doi: 10.1006/jcis.1999.6122.
The interaction between certain nonionic cellulose ethers (ethyl hydroxyethyl cellulose and hydroxypropyl methyl cellulose) and sodium dodecyl sulphate (SDS) has been investigated using isothermal titration microcalorimetry at temperatures between 25-50 degrees C. The observed heat flow curves have been interpreted in terms of a plausible mechanism of the interaction of the substituent groups with SDS monomers and clusters. The data have been related to changes occuring in the system at the macro- and microscopic levels with the addition of surfactants and with temperature. The process consists predominantly of polymer-surfactant interactions initially and surfactant-surfactant interactions at the later stages. A phenomenological model of the cooperative interaction (adsorption) process has been derived, and earlier published equilibrium binding data have been used to recover binding constants and Gibbs energy changes for this process. The adsorption enthalpies and entropies have been recovered along with the heat capacity change. The enthalpic cost of confining the nonpolar regions of the polymers in surfactant clusters is high, but the entropy gain from release of hydration shell water molecules as well as increased freedom of movement of these nonpolar regions in the clusters gives the process a strong entropic driving force. The process is entropy-driven initially and converts to being both enthalpy and entropy-driven at high SDS concentrations. An enthalpy-entropy compensation behavior is seen. Strongly negative heat capacity changes have been obtained resulting from the transfer of nonpolar groups from aqueous into nonpolar environments, as well as a reduction of conformational domains that the chains can populate. Changes in these two components cause the heat capacity change to become less negative at the higher binding levels. The system can be classified as exhibiting nonclassical hydrophobic binding at the later stages of binding. Copyright 1999 Academic Press.
利用等温滴定量热法，在25至50摄氏度的温度范围内，研究了某些非离子型纤维素醚（乙基羟乙基纤维素和羟丙基甲基纤维素）与十二烷基硫酸钠（SDS）之间的相互作用。已根据取代基与SDS单体及聚集体相互作用的合理机制，对观察到的热流曲线进行了解释。这些数据与添加表面活性剂以及温度变化时，体系在宏观和微观层面发生的变化相关。该过程主要由最初的聚合物 - 表面活性剂相互作用以及后期的表面活性剂 - 表面活性剂相互作用组成。推导了协同相互作用（吸附）过程的唯象模型，并使用先前发表的平衡结合数据来获取该过程的结合常数和吉布斯自由能变化。同时还得到了吸附焓、熵以及热容变化。将聚合物的非极性区域限制在表面活性剂聚集体中的焓成本很高，但水合壳层水分子释放带来的熵增以及这些非极性区域在聚集体中运动自由度的增加，赋予了该过程强大的熵驱动力。该过程最初由熵驱动，在高SDS浓度下转变为焓和熵共同驱动。呈现出焓 - 熵补偿行为。由于非极性基团从水相转移到非极性环境中，以及链可占据的构象域减少，导致热容变化呈现强烈的负值。在较高结合水平时，这两个组分的变化使热容变化的负值减小。在结合后期，该体系可归类为表现出非经典疏水结合。版权所有1999年，学术出版社。
