Nakamura Shohei, Kobayashi Lisa, Tanaka Ryo, Isoda-Yamashita Teruyo, Lee Jungno, Moroi Yoshikiyo
Daiichi College of Pharmaceutical Sciences, 22-1 Tamagawamachi, Minami-ku, Fukuoka 815-8511, Japan.
Colloids Surf B Biointerfaces. 2009 Feb 15;69(1):135-40. doi: 10.1016/j.colsurfb.2008.12.011. Epub 2008 Dec 11.
Solubilization of benzene, toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, n-pentylbenzene, and n-hexylbenzene into micelles of decanoyl-N-methylglucamide (Mega-10) was studied at 303.2, 308.2, 313.2, and 318.2K, where equilibrium concentrations of the above solubilizates were determined spectrophotometrically. The concentration of the above solubilizates remained constant below the critical micelle concentration (cmc) and increased linearly with an increase in Mega-10 concentration above the cmc at each temperature above. The Gibbs free energy change of the solubilizates from aqueous bulk to their liquid solubilizate phase was evaluated from dependence of their aqueous solubility on alkyl chain length of the solubilizates, which leads to the DeltaG(CH0)(2) values (-3.60 to -3.38 kJ mol(-1)), the energy change per CH2 group of the alkyl chain with no strong temperature dependence. The first stepwise solubilization constant (K1) was evaluated from the slope for the change of solubilizate concentration vs. Mega-10 concentration. The Gibbs free energy change (DeltaG(0,s)) for the solubilization decreased linearly with the carbon number of alkyl chain of the solubilizates, and the DeltaG(CH0)(2)(s) values (-2.71 to -2.54 kJ mol(-1)) obtained from the linearity showed a slight increase with temperature. The DeltaG(CH0)(2) values are less than the DeltaG(CH0)(2)(s) values, where the latter values clearly indicate that the location of alkyl chain is a hydrophobic micellar core. The fact is also supported by the absorption spectrum of the solubilized molecules. Temperature dependence of DeltaG(0,s) indicated that the solubilization is entropy-driven for the solubilizates with shorter alkyl chains, while it becomes enthalpy-driven for those with longer alkyl chains.
在303.2K、308.2K、313.2K和318.2K温度下，研究了苯、甲苯、乙苯、正丙苯、正丁苯、正戊苯和正己苯在癸酰基-N-甲基葡糖酰胺（Mega-10）胶束中的增溶情况，通过分光光度法测定了上述增溶物的平衡浓度。在上述每个温度下，当低于临界胶束浓度（cmc）时，上述增溶物的浓度保持恒定，而在高于cmc时，增溶物浓度随Mega-10浓度的增加呈线性增加。根据增溶物在水中的溶解度对增溶物烷基链长度的依赖性，评估了增溶物从水相主体到其液态增溶物相的吉布斯自由能变化，这得出了ΔG(CH0)(2)值（-3.60至-3.38 kJ mol(-1)），即烷基链每个-CH2-基团的能量变化，且温度依赖性不强。根据增溶物浓度相对于Mega-10浓度变化的斜率评估了第一步增溶常数（K1）。增溶的吉布斯自由能变化（ΔG(0,s)）随增溶物烷基链的碳原子数呈线性下降，从线性关系得出的ΔG(CH0)(2)(s)值（-2.71至-2.54 kJ mol(-1)）随温度略有增加。ΔG(CH0)(2)值小于ΔG(CH0)(2)(s)值，后者清楚地表明烷基链位于疏水胶束核心。这一事实也得到了增溶分子吸收光谱的支持。ΔG(0,s)的温度依赖性表明，对于烷基链较短的增溶物，增溶是由熵驱动的，而对于烷基链较长的增溶物，增溶则变为由焓驱动。
