IONIZATION AND PHASE-BEHAVIOR OF FATTY-ACIDS IN WATER - APPLICATION OF THE GIBBS PHASE RULE
IONIZATION AND PHASE-BEHAVIOR OF FATTY-ACIDS IN WATER - APPLICATION OF THE GIBBS PHASE RULE
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DOI：
10.1021/bi00406a013
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发表时间：
1988-03-22
期刊：
影响因子：
2.9
通讯作者：
SMALL, DM
中科院分区：
文献类型：
--
作者：
CISTOLA, DP;HAMILTON, JA;SMALL, DM
研究了几种中链（10-和12-碳）和长链（18-碳）脂肪酸在水中的相行为，作为羧基电离状态的函数。平衡滴定曲线产生以上和以下的脂肪酸和酸-皂链的熔融温度和临界胶束浓度，并形成的相，其特征在于通过X-射线衍射，13 C NMR光谱，相差和偏振光显微镜。将所得滴定曲线分为五个区域：（i）在pH值< 7时，含有油或脂肪酸晶体和水相的两相区域;（ii）在pH值<7时，含有油或脂肪酸晶体和水相的两相区域; 7，含有油相、层状相和水相（或脂肪酸晶体、1：1酸-皂晶体和水相）的三相区域;（iii）在pH 7和9之间，在水相中含有层状脂肪酸/皂（或结晶1：1酸-皂）相的两相区域;（iv）在pH约7和9之间，在水相中含有层状脂肪酸/皂（或结晶1：1酸-皂）相的两相区域; 9，含有层状脂肪酸皂（或结晶1：1酸皂）、胶束和水相的三相区;和（v）在pH值> 9时，含有胶束和水相的两相区。使用吉布斯相规则对结果的解释表明，对于油酸/油酸钾，层状脂肪酸/皂相的组成从1：1至1：3的非离子化与离子化脂肪酸物质。此外，滴定曲线中观察到的恒定pH区域是热力学不变性（零自由度）的结果，而不是缓冲能力。结果提供了深入了解脂肪酸在生物系统中的物理状态。在生理pH和温度下形成的主要相是层状脂肪酸/皂相。此外，水中的脂肪酸在低于pH 9时不会形成胶束相，因此，非酯化脂肪酸的局部积累不太可能对细胞膜产生洗涤剂作用，正如人们广泛认为的那样。
The phase behavior of several medium-chain (10- and 12-carbon) and long-chain (18-carbon) fatty acids in water was examined as a function of the ionization state of the carboxyl group. Equilibrium titration curves were generated above and below fatty acid and acid-soap chain melting temperatures and critical micelle concentrations, and the phases formed were characterized by X-ray diffraction, 13C NMR spectroscopy, and phase-contrast and polarized light microscopy. The resulting titration curves were divided into five regions: (i) at pH values < 7, a two-phase region containing oil or fatty acid crystals and an aqueous phase; (ii) at pH .apprx. 7, a three-phase region containing oil, lamellar, and aqueous (or fatty acid crystals, 1:1 acid-soap crystals, and aqueous) phases; (iii) between pH 7 and 9, a two-phase region containing a lamellar fatty acid/soap (or crystalline 1:1 acid-soap) phase in an aqueous phase; (iv) at pH .apprx. 9, a three-phase region containing lamellar fatty acid-soap (or crystalline 1:1 acid-soap), micellar, and aqueous phases; and (v) at pH values > 9, a two-phase region containing micellar and aqueous phases. Interpretation of the results using the Gibbs phase rule indicated that, for oleic acid/potassium oleate, the composition of the lamellar fatty acid/soap phase varied from .apprx. 1:1 to 1:3 un-ionized to ionized fatty acid species. In addition, constant pH regions observed in titration curves were a result of thermodynamic invariance (zero degrees of freedom) rather than buffering capacity. The results provide insights into the physical states of fatty acids in biological systems. The predominant phase formed at physiologic pH and temperature is the lamellar fatty acid/soap phase. In addition, fatty acids in water do not form a micellar phase below pH 9, and hence, it is unlikely that local accumulations of nonesterified fatty acids cold exert detergent effects on cellular membranes, as has been widely suggested.