Studies on Thermodynamics for the Hydrolysis. II. The Temperature Effect on the Stereoselective Deacylation of Amino Acid Esters in Bilayer and Micellar Systems

Stereoselective deacylations of p-nitrophenyl N-acyl-d(or l)-phenylalaninates(d(or l)-Sn; n=2, 12, and 16) and N-benzyloxycarbonyl-d(l)-phenylalaninates(d(l)-ZS) by the bilayer and micellar catalytic systems of l-histidine derivatives (LauHis, MyrHis, PalHis, LauHisLeu, and MyrHisLeu) and surfactants (2CmN2C1Br with m=12, 14, and 16, CTAB, OTAC, and (R)-(+)-SUR16) were performed. It is noteworthy that the temperature dependence of enantioselectivity for the deacylation of S12 having a long acyl chain is bell-shaped with maxima at 25 °C and 15–25 °C in the bilayer systems of MyrHis+2C12N2C1Br and MyrHisLeu+2C12N2C1Br, respectively. On the other hand, the enantioselectivity for the S12 deacylation catalyzed by LauHisLeu in the presence of the CTAB micelles increases as temperature is lowered (the highest enantiomer rate ratio (kLa,obsd⁄kDa,obsd=12) is attained at 20 °C). The enantioselectivity for the deacylation of S2 having a short acyl chain, however, is almost constant and considerably lowered in comparison with that for the deacylation of S12 in both the bilayer and micellar systems. According to the isokinetic temperature (β), the deacylation of Sn (n=2 and 12) and ZS in the bilayer systems might be entropy-driven, whereas that in the micellar systems might be enthalpy-driven. The stronger hydrophobic microenvironment of the bilayer systems in the ester-deacylation would probably be connected with the entropy-driven nature.