Liu Yan, Guo Rong
College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, People's Republic of China.
Biomacromolecules. 2007 Sep;8(9):2902-8. doi: 10.1021/bm7006136. Epub 2007 Aug 14.
The interactions between the classical cationic surfactant dodecyltrimethylammonium bromide (DTAB) and 2.0 mg/mL casein were investigated using isothermal titration calorimetry (ITC), turbidity, dynamic light scattering (DLS), and fluorescence spectra measurements. The results suggest that the cationic headgroup of the surfactant individually binds to the negatively charged amino acid sites on the casein chains because of the electrostatic attraction upon the addition of DTAB. When the surfactant concentration reaches a critical value c1, DTAB forms micelle-like aggregates on the casein chain, resulting in the formation of insoluble casein/DTAB complexes. Further addition of DTAB leads to the redissolution of casein/DTAB complexes because of the net positive charge on casein/DTAB complexes and the formation of DTAB free micelles. The addition of salt screens the repulsion between the surfactant headgroups and the attraction between casein and surfactant molecules, which weakens the binding of surfactant onto the casein chain, favoring the formation of free surfactant micelles.
使用等温滴定量热法（ITC）、浊度法、动态光散射（DLS）和荧光光谱测量法，研究了经典阳离子表面活性剂十二烷基三甲基溴化铵（DTAB）与2.0 mg/mL酪蛋白之间的相互作用。结果表明，由于添加DTAB后产生的静电吸引作用，表面活性剂的阳离子头基分别与酪蛋白链上带负电荷的氨基酸位点结合。当表面活性剂浓度达到临界值c1时，DTAB在酪蛋白链上形成类似胶束的聚集体，导致形成不溶性酪蛋白/DTAB复合物。进一步添加DTAB会导致酪蛋白/DTAB复合物重新溶解，这是因为酪蛋白/DTAB复合物上的净正电荷以及游离DTAB胶束的形成。添加盐会屏蔽表面活性剂头基之间的排斥力以及酪蛋白与表面活性剂分子之间的吸引力，从而削弱表面活性剂与酪蛋白链的结合，有利于游离表面活性剂胶束的形成。
