Functional Molecular Assemblies Coupled to Steric Control with High Enantioselectivity

点击翻译按钮获取中文摘要

Enantioselective hydrolysis of amino acid esters by L-histidine derivatives in the molecular assemblies composed of single-and double-chain surfactants was investigated. The noteworthy aspects are as follows :1) The remarkably high enantioselectivity (kappa^L_<a, obsd>/kappa^D_<a, obsd>=1000) was sttained for the hydrolysis of longchained substrate (N-dodecanoyl-D (L) -phenylalanine p-nitrophenylester ; C_<12>-D (L) -Phe-PNP) catalyzed by the active tripeptide (N-(benzyloxycarbonyl) -L-phenylalanyl-L-histidyl-L-leucine ; Z-PheHisLeu) in the coaggregate systems composed of 41mol% single-chained hexadecyltrimethylammonium bromide (CTAB) and 59mol% double-chained ditetradecyldimethylammonium bromide (2C_<14>Br) at the specific ionic strength (mu=0.02).Furthermore, the computer modeling (MOPAC calculation) study suggests that a favorable molecular recognition between the substrate and the catalyst through the effective hydrophobic interactions and hydrogen bonds should be very important for the enhancement of enantioselectivity.2) With respect to the hydrolysis of C_<12>-D (L) -Phe-PNP by the tripeptide catalyst Z-PheHisLeu in the coaggregate systems composed of native lipid and nonionic micellar surfactant, a remarkably high enantioselectivity (kappa^L_<a, obsd>/kappa^D_<a, obsd>=28) along with marked rate-enhancement of the hydrolytic cleavage of C_<12>-D (L) -Phe-PNP was obtained with specific coaggregates of 32mol% L-alpha-dipalmitoylphosphatidyl-choline (DPPC) and 68mol% alpha-[4-(1,1,3,3-tetramethylbutyl) phenyl]-omega-hydroxypoly (exy-1,2-ethanediyl) (Triton X-100). The enantioselectivity was maximized at the phase transition temperature (Te) in the 65mol% DPPC/35mol% Triton X-100 and 32mol% DPPC/68mol% Triton X-100 coaggregate systems. The hydrophobicity and fluidity of the coaggregates can apparently be changed around Te on the basis of isokinetic temperature and fluorescence parameter studies.