CTABr 미셀 용액속에서 2-Alkylbenzimidazole 음이온에 의해 추진되는 Isopropyl phenyl-4-nitrophenyl phosphinate(IPNPIN)의 탈인산화반응

Abstract

This study is mainly focused on micellar effect of cetyltrimethyl ammonium bromide(CTABr) solution including alkylbenzimidazole(R-BI) on dephosphorylation of isopropyl-4-nitrophenylphosphinate(IPNPIN) in carbonate buffer(pH 10.7). The reactions of IPNPIN with R-<TEX>$BI^{\ominus}$</TEX> are strongly catalyzed by the micelles of CTABr. Dephosphorylation of IPNPIN is accelerated by <TEX>$BI^{\ominus}$</TEX> ion in <TEX>$10^{-2}$</TEX> M carbonate buffer(pH 10.7) of <TEX>$4{\times}10^{-3}$</TEX> M CTABr solution up to 89 times as compared with the reaction in carbonate buffer by no benzimidazole(BI) solution of <TEX>$4{\times}10^{-3}$</TEX> M CTABr. The value of pseudo first order rate constant(<TEX>$k_{\Psi}$</TEX>) of the reaction in CTABr solution reached a maximum rate constant increasing micelle concentration. Such rate maxima are typical of micellar catalyzed bimolecular reactions. The reaction mediated by R-<TEX>$BI^{\ominus}$</TEX> in micellar solutions are obviously slower than those by <TEX>$BI^{\ominus}$</TEX>, and the reaction rate were decreased with increase of lengths of alkyl groups. It seems due to steric effect of alkyl groups of R-<TEX>$BI^{\ominus}$</TEX> in Stern layer of micellar solution. The surfactant reagent, CTABr, strongly catalyzes the reaction of IPNPIN with R-BI and its anion(R-<TEX>$BI^{\ominus}$</TEX>) in carbonate buffer(pH 10.7). For example, <TEX>$4{\times}10^{-3}$</TEX> M CTABr in <TEX>$1{\times}10^{-4}$</TEX> M BI solution increase the rate constant(<TEX>$k_{\Psi}=98.5{\times}10^{-3}\;sec^{-1}$</TEX>) of the dephosphorylation by a factor ca.25, when compared with reaction(<TEX>$k_{\Psi}=3.9{\times}10^{-4}\;sec^{-1}$</TEX>) in <TEX>$1{\times}10^{-4}$</TEX> M BI solution(without CTABr). And no CTABr solution, in <TEX>$1{\times}10^{-4}$</TEX> M BI solution increase the rate constant(<TEX>$k_{\Psi}=3.9{\times}10^{-4}\;sec^{-1}$</TEX>) of the dephosphorylation by a factor ca.39, when compared with reaction (<TEX>$k_{\Psi}=1.0{\times}10^{-5}\;sec^{-1}$</TEX>) in water solution(without BI). This predicts that the reactivities of R-<TEX>$BI^{\ominus}$</TEX> in the micellar pseudophase are much smaller than that of <TEX>$BI^{\ominus}$</TEX>. Due to the hydrophobicity and steric effect of alkyl group substituents, these groups would penetrate into the core of the micelle for stabilization by van der Waals interaction with long alkyl groups of CTABr.