This study is mainly focused on micellar effect of tetradecyltrimethyl ammonium bromide(TTABr) solution including alkylbenzimidazole(R-BI) on dephosphorylation of diphenyl-4-nitrophenylphosphinate(DPNPIN) in carbonate buffer(pH 10.7). Dephosphorylation of DPNPIN is accelerated by BI⊖ ion in 10-2 M Carbonate buffer(pH 10.7) of 4×10-4 M TTABr solution up to 80 times as compared with the reaction in Carbonate buffer by no benzimidazole(BI) solution of TTABr. The value of pseudo first order rate constant(kψ) of the reaction in TTABr solution reached a maximum rate constant increasing micelle concentration. The reaction mediated by R-BI⊖ in micellar solutions are obviously slower than those by BI⊖, and the reaction rate were decreased with increase of lengths of alkyl groups. It seems due to steric effect of alkyl groups of R-BI⊖ in Stern layer of micellar solution. The surfactant reagent, TTABr, strongly catalyzes the reaction of DPNPIN with R-BI and its anion(R-BI⊖) in Carbonate buffer(pH 10.7). For example, 4×10-4 M TTABr in 1×10-4 M BI solution increase the rate constant(kψ=99.7×10-4 1/sec) of the dephosphorylation by a factor ca. 28, when compared with reaction(kψ=3.5×10-4 1/sec) in BI solution(without TTABr). And no TTABr solution, in BI solution increase the rate constant(kψ=3.5×10-4 1/sec) of the dephosphorylation by a factor ca. 39, when compared with reaction (kψ=1.0×10-5 1/sec) in water solution(without BI).

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-BI⊖ are strongly catalyzed by the micelles of CTABr. Dephosphorylation of IPNPIN is accelerated by BI⊖ ion in 10-2 M carbonate buffer(pH 10.7) of 4×10-3 M CTABr solution up to 89 times as compared with the reaction in carbonate buffer by no benzimidazole(BI) solution of 4×10-3 M CTABr. The value of pseudo first order rate constant(kψ) 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-BI⊖ in micellar solutions are obviously slower than those by BI⊖, and the reaction rate were decreased with increase of lengths of alkyl groups. It seems due to steric effect of alkyl groups of R-BI⊖ in Stern layer of micellar solution. The surfactant reagent, CTABr, strongly catalyzes the reaction of IPNPIN with R-BI and its anion(R-BI⊖) in carbonate buffer(pH 10.7). For example, 4×10-3 M CTABr in 1×10-4 M BI solution increase the rate constant(kψ=98.5×10-3 sec-1) of the dephosphorylation by a factor ca.25, when compared with reaction(kψ=3.9×10-4 sec-1) in 1×10-4 M BI solution(without CTABr). And no CTABr solution, in 1×10-4 M BI solution increase the rate constant(kψ=3.9×10-4 sec-1) of the dephosphorylation by a factor ca.39, when compared with reaction (kψ=1.0×10-5 sec-1) in water solution(without BI). This predicts that the reactivities of R-BI⊖ in the micellar pseudophase are much smaller than that of BI⊖. 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.

This study is mainly focused on micellar effect of cetylpyridinium chloride(CPyCl) solution including alkylbenzimidazole( R-BI) on dephosphorylation of diphenyl-4-nitrophenylphosphinate(DPNPIN) in carbonate buffer(pH 10.7). The reactions of DPNPIN with R-BI⊖ are strongly catalyzed by the micelles of CPyCl. Dephosphorylation of DPNPIN is accelerated by BI⊖ ion in 10 -2 M carbonate buffer(pH 10.7) of 4×10 -3 M CPyCl solution up to 100 times as compared with the reaction in carbonate buffer by no BI solution of 4×10 -3 M CPyCl. The value of pseudo first order rate constant(k m BI) of the reaction in CPyCl solution reached a maximum rate constant increasing micelle concentration. Such rate maxima are typical of micellar catalyzed bimolecular reactions. The reaction mediated by R-BI⊖ in micellar solutions are obviously slower than those by BI⊖, and the reaction rate were decreased with increase of lengths of alkyl groups. It seems due to steric effect of alkyl groups of R-BI⊖ in Stern layer of micellar solution. The surfactant reagent, cetylpyridinium chloride(CPyCl) , strongly catalyzes the reaction of diphenyl-4-nitrophenylphosphinate(DPNPIN) with alkylbenzimidazole (R-BI) and its anion(R-BI⊖) in carbonate buffer(pH 10.7). For example, 4×10 -3 M CPyCl in 1×10 -4 M BI solution increase the rate constant (kψ=1.0×10 -2 sec -1 ) of the dephosphorylation by a factor ca.14, when compared with reaction (kψ=7.3×10 -4 sec -1 ) in 1×10 -4 M BI solution(without CPyCl). And no CPyCl solution, in 1×10 -4 M BI solution increase the rate constant (kψ=7.3×10 -4 sec -1 ) of the dephosphorylation by a factor ca.36, when compared with reaction (kψ=2.0×10 -5 sec -1 ) in water solution(without BI). This predicts that the reactivities of R-BI⊖ in the micellar pseudophase are much smaller than that of BI⊖ . 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 CPyCl.

In the aqueous solutions the dephosphorylations of isopropyl phenyl-4-nitrophenyl phosphinate(IPNPIN) mediated by hydroxide(OH⊖) and o-iodosobenzoate(IB⊖) ions are relatively slow, because of hydrophobicity of the substrate, and however it appears that OH⊖ is inherently better nucleophile than IB⊖, which is more soft ion. On the other hand, in cetyltrimetylammonium bromide(CTABr) solutions which contain cationic micelles, the dephosphorylations of IPNPIN mediated by OH⊖ or IB⊖ are very accelerated to 120 or 100,000 times as compared with those in the aqueous solutions. The values of pseudo first order rate constants reach a maximum with increasing. Such rate maxima are typical of micellar catalysed bimolecular reactions and the rise in rate constant followed by a gradual decrese is characteristic of reactions of hydrophobic substrates. In the cationic micellar solutions of CTABr, IB⊖ accelerates the reactions much more than that OH⊖ does. The reason seems that IB⊖ which is more hydrophobic and soft ion than OH⊖ is more easily moved into the Stern layer of the CTABr micelles than OH⊖. In the anionic micellar solutions of sodium dodecyl sulfate(SDS), the dephosphorylations of IPNPIN are slower than those in aqeous solutions. It means that OH⊖ or IB⊖ cannot easily move and approach to the Stern layer of the micelle in which almost all the hydrophobic substrate are located and which has a negative circumstance.

This study deals with micellar effects on dephosphorylation of diphenyl-4- nitrophenylphosphate (DPNPPH), diphenyl-4-nitrophenylphosphinate (DPNPIN) and isopropylphenyl-4-nitrophenyl phosphinate (IPNPIN) mediated by OH⊖ or o-iodosobenzoate ion (IB⊖) in aqueous and CTAX solutions. Dephosphorylation of DPNPPH, DPNPIN and IPNPIN mediated by OH⊖ or o-iodosobenzoate ion (IB⊖) is relatively slow in aqueous solution. The reactions in CTAX micellar solutions are, however, much accelerated because CTAX micelles can accommodate both reactants in their Stern layer in which they can easily react, while hydrophilic OH⊖ (or IB⊖) and hydrophobic substrates are not mixed in water. Even though the concentrations (>10-3 M) of OH⊖ (or IB⊖) in CTAX solutions are much larger amounts than those (6×10-6 M) of substrates, the rate constants of the dephosphorylations are largely influenced by the change of concentration of the ions, which means that the reactions are not followed by the pseudo first order kinetics. In comparison to effect of the counter ions of CTAX in the reactions, CTACl is more effective on the dephosphorylation of substrates than CTABr due to easier expelling of Cl⊖ ion by OH⊖ (or IB⊖) ion from the micelle, because of easier solvation of Cl⊖ ion by water molecules. The reactivity of IPNPIN with OH⊖ (or IB⊖) is lower than that of DPNPIN. The reason seems that the 'bulky' isopropyl group of IPNPIN hinders the attack of the nucleophiles.