Amphiphiles with Polypeptide-Head Groups III. Regulation of Enantioseiectivity in Micellar Hydrolysis

Abstract

ABSTRACT:Chiral ester cleavage by achiral hydroxamic acids was investigated in the presence of chiral matrix micelles formed from amphiphiles with poly-L-lysine-head groups. The results are summarized as follows. (I) The enantioselectivity was not observed in the alkaline hydrolysis in chiral micelles only. This matrix possesses no selectivity. When an achiral hydroxamic acid was added to the system, selectivity was induced. (2) The direction of selectivity is reversed by the conformational change of the secondary structure formed by the peptide moiety of matrix micelles. L-Selectivity in the random coil and D-selectivity in the cc-helix condition were observed. (3) The degree of selectivity is dependent on the chemical structure of hydroxamic acid; for example, an N-H type hydroxamic acid gives higher selectivity than an N-methyl type one. Thus, it is supposed that enantioselectivity is introduced by the chiral interaction between chiral micelles and achiral nucleophiles, in which the conformation of polypeptide moiety plays an important role.KEY WORDS Amphiphile I Surfactant I Micelle I Enzyme Model I Hydroxamate I Enantioselectivity I Polypeptide I Poly-L-lysine I cc-Helix I Random Coil I Many hydrolysis reactions of chiral esters catalyzed by amino acid-derivatives have been studied in micellar systems in order to mimic the enantioselectivity of enzyme reactions. 1 -3 These studies have proposed or proved that the structural fitting between a catalyst and a substrate is a significant factor to give high enantioselectivity. However, in spite of the recognition that the secondary structure of an enzyme plays a part in the specificity, the relation between the secondary structures and enantioselectivity is not yet clear. On the other hand, we investigated the property of chiral assemblies formed from amphiphiles with polypeptide-head groups. It was previously reported that compounds la-ld can form micelles with structural asymmetries such as ahelical4 and {3-sheet peptide-head groups, 5 and 2 can form helical superstructures composed of single-walled bilayer membranes. (m= I, n= 10) lc: =CH 2 C 6 H 5 (m= I, n= 12) ld: =CH 2 CH(CH 3 ) 2 (m=9, n=9)

Lipid Tubules: A Paradigm for Molecularly Engineered Structures

“…1, A to C) (3)(4)(5)(6) shows the same pattern in relation to soil fertility that is found among trees in tropical forests (Fig. 1, D to F) (4,(7)(8)(9).…”

“…Previous studies bv Kunitake et al (7) on some ~, amino acid-derived amphiphiles gave an indication of self-assembled microstructures with remarkably high circular dichroism. Nakashima et al (8) and Ihara et al (9) have also reported observing helical microstructures as well as tubular structures in single-chain amphiphiles. Similar microstructures have been formed from amphiphiles with different head groups (10) such as poly(~-aspartic acid) derivatives (1 1 ) , monosaccharides (1 2), and diacetylenic phosphocholines (4,13,14).…”

Chiral Molecular Self‐Assembly

“…Helical morphologies were observed in amphiphiles with oligo-L-aspartic acid 75 and oligo-L-proline head groups. 76 Lee et al reported similar results on several glutamic acid dialkyl amides with short peptides in their head group.…”

Self‐Assembled Nanofibrillar Aggregates with Amphiphilic and Lipophilic Molecules

“…Spectroscopic observations provide information on molecular orientations, packing states and lateral diffusion behavior. UV-visible, [19,27,[31][32][33][34] Fourier transform infrared (FT-IR), circular dichroism (CD), [8,9,19,31,[34][35][36] fluorescence [37,38] and nuclear magnetic resonance (NMR) [39] spectrometers have been widely used for investigation and analysis on the molecular orientation. Typical investigations are found in chromophore-containing lipid systems.…”

“…[9,11,18] The detailed study on morphogenesis from lowmolecular compounds to nano-size aggregates was done by them using the corresponding oligo(L-aspartic acid) derivatives. Amphiphilic compound 6 also formed fibrillar and twisted ribbon-like aggregates in aqueous systems and then the process of morphogenesis was moniterd by TEM observation and light scattering measurement [9] : (1) 6 formed globular aggregates with the largest curvature at the initial step; (2) these globules grew to fibrillar aggregates; (3) double-or multiple-strands were produced and then fused themselves to make ribbon-like aggregates. These findings indicate that even a very small difference between L-glutamic and Laspartic acid in the head group strongly influences the morphology of the aggregates.…”