Specificity for Stereoselective Hydrolysis in Membrane Systems

Abstract

The reactive and binding specificities have been obtained for acyl transfer reaction of pnitrophenyl decanoate (S₁₀) with 2-hexyldecanehydroxamic acid (HDHA) in the bilayer system (didodecyldimethylammonium bromide: 2C₁₂N2C₁). They are attributed to the stronger hydrophobic, interaction between the substrate (S₁₀) and the mixed nucleophile (HDHA+2C₁₂N2C₁).
In the stereoselective hydrolysis of p-nitrophenyl N-decanoyl-D(L)-phenylalaninate (D-, L-S₁₀)and p-nitrophenyl N-hexadecanoyl-D(L)-phenylalaninate (D-, L-S₁₆), the liquid crystalline bilayer systems of N-palmitoyl-L-histidine (PalHis) and double-chain surfactants (2C₁₄N2C₁and C₁₄N2C₁, [ditetradecyldimethylammonium bromide]) offered the relatively higher enantiomer rate ratios as compared with those obtained in the crystalline bilayer system of PAU-lis and dioctadecyldimethylammoniunm bromide (2C₁₈N2C₁) and the comicellar system of PalHis and octadecyltrimethylammonium chloride (OTAC). Furthermore, the acyl transfer rate of D(L)-S₁₀ possessing an appropriately long N-acyl chain was found to be largest in both of the bilayer and micellar systems. The notable aspects of the present reaction are also reflected Kb in the kinetic parameters (A+S_n ⇔K_bAS_n→kp;A, AS_n, and P stand for an aggregate composed of nucleophilie and surfactant, an aggregate-substrate cOmplex, and p-nitrophenol, respectively). Although the difference in the microenvironment of the bilayer (PalHis+2C_mN2C₁ [m=12, 18]) and the spherical micellar (PalHis+OTAC) systems offered a different relative order of the binding efficiency (K_b) between the L- and D-enantiorners, the Kb values of the long-chain substrate (D(L)-S₁₀) were fairly large as compared with those of the shortchain substrate (D(L)-S₂ [p-nitrophenyl N-acetyl-D(L)-phenylalaninate]) in all the reaction systems.