Werawatganone Pornpen, Muangsiri Walaisiri, Roopdee Amaraporn
Department of Pharmacy, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Pathumwan, Bangkok 10330, Thailand.
Int J Pharm. 2006 Sep 14;321(1-2):138-42. doi: 10.1016/j.ijpharm.2006.05.003. Epub 2006 May 9.
Micelle formation is an important property of surfactants. Micellar solutions of cetyltrimethylamonium bromide (CTAB) have been found to accelerate the hydrolysis of alpha-naphthyl acetate (alpha-NA) by o-iodosobenzoic acid (IBA), a strong nucleophile. Critical micelle concentration (CMC) of CTAB was determined in the absence and presence of various concentrations and grades of hydroxypropylmethyl cellulose (HPMC) using surface tension measurement. Reaction under pseudo-first-order condition was utilized for rate constant determination. The aggregation of CTAB in the polymer solution started at higher concentration than in the absence of the polymer. The observed rate constants for the degradation of alpha-NA in the presence of various concentrations of CTAB with and without HPMC were calculated. The presence of HPMC retarded the reaction rate. However, there was no obvious difference in the observed rate constant among the different grades of HPMC (Methocel E50, Methocel E4M, Methocel E10M) while the higher the polymer concentration the lower the rate constant.
胶束形成是表面活性剂的一项重要特性。已发现十六烷基三甲基溴化铵（CTAB）的胶束溶液能加速强亲核试剂邻碘苯甲酸（IBA）对α-萘乙酸酯（α-NA）的水解。使用表面张力测量法，在不存在和存在不同浓度及等级的羟丙基甲基纤维素（HPMC）的情况下，测定了CTAB的临界胶束浓度（CMC）。利用伪一级反应条件下的反应来测定速率常数。与不存在聚合物时相比，CTAB在聚合物溶液中的聚集起始浓度更高。计算了在存在不同浓度CTAB且有和没有HPMC的情况下，α-NA降解的观测速率常数。HPMC的存在使反应速率减慢。然而，不同等级的HPMC（美多秀E50、美多秀E4M、美多秀E10M）之间观测到的速率常数没有明显差异，而聚合物浓度越高，速率常数越低。
