Medoš Žiga, Plechkova Natalia V, Friesen Sergej, Buchner Richard, Bešter-Rogač Marija
Faculty of Chemistry and Chemical Technology , University of Ljubljana , Večna pot 113 , 1000 Ljubljana , Slovenia.
QUILL, The Queen's University of Belfast , Stranmillis Road , Belfast , Northern Ireland BT9 5AG , U.K.
Langmuir. 2019 Mar 12;35(10):3759-3772. doi: 10.1021/acs.langmuir.8b03993. Epub 2019 Feb 28.
Hydrophobic interactions are one of the main thermodynamic driving forces in self-assembly, folding, and association processes. To understand the dehydration-driven solvent exposure of hydrophobic surfaces, the micellization of functionalized decyldimethylammonium chlorides, XCMeNCl, with a polar functional group, X = COH, COMe, COCOMe, COOEt, together with the "reference" compound decyltrimethylammonium chloride, CMeNCl, was investigated in aqueous solution by density measurements, isothermal titration calorimetry (ITC), and dielectric relaxation spectroscopy (DRS). From the density data, the apparent molar volumes of monomers and micelles were estimated, whereas the ITC data were analyzed with the help of a model equation, yielding the thermodynamic parameters and aggregation number. From the DRS spectra, effective hydration numbers of the free monomers and micelles were deduced. The comprehensive analysis of the obtained results shows that the thermodynamics of micellization are strongly affected by the nature of the functional group. Surprisingly, the hydration of micelles formed by surfactant cations with a single alkyl chain on quaternary ammonium is approximately the same, regardless of the alkyl chain length or functionalization of the headgroup. However, notable differences were found for the free monomers where increasing polarity lowers the effective hydration number.
疏水相互作用是自组装、折叠和缔合过程中的主要热力学驱动力之一。为了理解疏水表面脱水驱动的溶剂暴露，通过密度测量、等温滴定量热法（ITC）和介电弛豫光谱法（DRS），在水溶液中研究了具有极性官能团（X = COH、COMe、COCOMe、COOEt）的功能化癸基二甲基氯化铵XCMeNCl与“参考”化合物癸基三甲基氯化铵CMeNCl的胶束化。根据密度数据估算了单体和胶束的表观摩尔体积，而ITC数据借助模型方程进行分析，得出热力学参数和聚集数。从DRS光谱中推导了游离单体和胶束的有效水合数。对所得结果的综合分析表明，胶束化的热力学受到官能团性质的强烈影响。令人惊讶的是，季铵盐上具有单烷基链的表面活性剂阳离子形成的胶束的水合作用大致相同，而与烷基链长度或头基的官能化无关。然而，对于游离单体发现了显著差异，其中极性增加会降低有效水合数。
