Blending effects on adsorption and micellization of different membrane protein solubilizers: II. A thermodynamic study on a mixed system of CHAPS with a bile salt in pH 7.4 phosphate buffer solution

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• 作者：Se-Woung Oh ; Jin-Su Na ; Jeong-Soo Ko ; Shigemi Nagadome ; Gohsuke Sugihara
• 关键词：Mixed surfactant systems ; CHAPS ; Sodium glycocholate (NaGC) ; Critical micelle concentration (CMC) ; Adsorbed film ; Membrane protein solubilizer ; Surface excess Gibbs energy ; Partial molecular area (PMA) ; Interaction parameters ; Surface tension study
• 刊名：Colloids and Surfaces B: Biointerfaces
• 出版年：2008
• 出版时间：15 March 2008
• 年：2008
• 卷：62
• 期：1
• 页码：112-124
• 全文大小：1048 K

文摘

For a mixed system of a typical membrane protein solubilizer CHAPS (a derivative of a bile acid cholic acid) combined with a bile salt (sodium salt of glycocholic acid, NaGC), which is also a candidate as a membrane protein solubilizer, micellization and adsorbed film formation in a phosphate buffer solution of pH 7.4 at 303 K were studied paying special attention to the synergistic effect upon mixing. The collection of sufficient data based on plots of surface tension (γ) versus logarithmic concentration (C_t or m_t) in total molality at discrete mole fractions (X₂) in the mixture of surfactants 1 and 2 (where 1 and 2 correspond to CHAPS and NaGC, respectively) allowed us to accurately determine critical micelle concentration (CMC), minimum surface tension at CMC (γ_CMC), and the slope (dγ/d ln C_t) from the γ–ln C_t curves in the concentration range just below CMC. These data enabled us to estimate surface excess (Γ_t), and mean molecular area (A_m) in addition to such parameters as the minimum surface Gibbs energy (), pC₂₀ and CMC/C₂₀ related to synergism accompanied by blending. Applying the regular solution theory (RST), the relation of compositions of the singly dispersed phase (X₂) and the micellar phase (Y₂) as well as the interaction parameter (ω_R) (by using the Rubingh's equations) were estimated. The relation between the composition in the adsorbed film (Z₂) and X₂ together with the interaction parameter (ω_A) in the adsorbed film was also estimated. The partial molecular area (PMA), γ_CMC, and were examined as functions of X₂ and/or Z_2. The resultant CMC–X₂ and CMC–Y₂ curves and ω_R and ω_A values have demonstrated that mixed micelles and adsorbed film formation are attained accompanying to some extent enhanced intermolecular interaction (with negative ω_R and ω_A values). Comparing with previous results for mixed systems of CHAPS with n-acyl (octanoly, nonanoyl, and decanoyl)-N-methylglucamides [MEGA-n's (n = 8, 9, and 10)] and of sodium chenodeoxycholate (NaCDC) with sodium ursodeoxycholate (NaUDC), the synergism observed for the mixed system of CHAPS with NaGC lies between both combinations. However the expected properties as a membrane protein solubilizer are judged to be sufficient.