Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh 160 014, India.
J Colloid Interface Sci. 2010 Apr 1;344(1):105-11. doi: 10.1016/j.jcis.2009.12.036. Epub 2009 Dec 24.
The mixed micellar behavior of anionic surfactant, sodium dodecylsulfate (SDS) and cationic surfactant, dodecylethyldimethylammonium bromide (DDAB) at varying mole fractions of DDAB, i.e. alpha(DDAB) in aqueous solution of papain has been investigated with the aid of spectroscopy and physiochemical measurements. Thermodynamic parameters have been computed over the entire mole fraction range of DDAB. The Clint equation and the regular approximation method have been used to investigate the interactions between mixed surfactants in the presence of protein. The two surfactants have similar tails, however, the charges on respective polar head groups are expected to have significant effect on their colloidal behavior. The cmc values of mixed surfactants have been estimated from fluorescence, conductivity, surface tension, ultrasonic speed and density measurements. The results show that lower and higher mole fractions of DDAB give negative departure from ideality whereas intermediate mole fractions have positive deviation. The aggregation number, N(agg) of mixed micelles has also been calculated. The turbidity or cloudiness at intermediate mole fractions demonstrates a reduction in the background free monomer concentration due to neutralization of the monomers of opposite charge. The effect of concentration of papain on mixed micellar behavior indicates that with increase in the concentration of protein, the cac and cmc values increase. The unfolding of polypeptide chain in the presence of mixed surfactant has been observed.
在木瓜蛋白酶水溶液中，研究了离子型表面活性剂十二烷基硫酸钠（SDS）和阳离子表面活性剂十二烷基二甲基溴化铵（DDAB）在不同 DDAB 摩尔分数，即α（DDAB）下的混合胶束行为，借助光谱学和物理化学测量。在整个 DDAB 摩尔分数范围内计算了热力学参数。克林特方程和正则逼近法被用于研究存在蛋白质时混合表面活性剂之间的相互作用。两种表面活性剂具有相似的尾部，然而，各自极性头基团上的电荷预计会对它们的胶体行为产生重大影响。通过荧光、电导率、表面张力、超声速度和密度测量来估算混合表面活性剂的 cmc 值。结果表明，较低和较高的 DDAB 摩尔分数会产生负偏离理想状态，而中间摩尔分数会产生正偏离。还计算了混合胶束的聚集数 N（agg）。在中间摩尔分数下的浊度或混浊度表明，由于相反电荷的单体被中和，背景游离单体浓度降低。木瓜蛋白酶浓度对混合胶束行为的影响表明，随着蛋白质浓度的增加，cmc 和 cac 值增加。在混合表面活性剂存在下观察到多肽链的展开。
