Supramolecular aggregates formed by L-glutamic acid-oligomers: SANS and SAXS studies of the hydrogen bonded self-assembly

Abstract

N-Acetyl-L-glutamic acid oligomeric benzyl esters with various residue numbers (N_p = 4, 5, 6, 8, 10, 12 and 14) have been synthesized by a stepwise procedure. The microstructures of these oligopeptide aggregates in dioxane or benzene have been investigated by IR, small angle neutron scattering (SANS), and small angle X-ray scattering (SAXS) spectra. It has been confirmed from the IR spectral data that preferential stabilization of antiparallel-type β-sheet structures occurs above the critical aggregation concentration and that the population of this antiparallel β-sheet increases with an increase in concentration. On the basis of these IR results, the model of the rod-like aggregate, in which the disk-like β-sheet monomers are one-dimensionally stacked antiparallel to each other, has been presented for analysis of the observed SANS and SAXS intensity profiles. The best fit intensity profiles, calculated with variation only of the aggregation number and with fixed molecular parameters based on the assumption of polydispersity, have furnished the monomer–monomer bond energies (ακT), corresponding to the hydrogen bonding energies, the number-average aggregation numbers, and the number-average molecular weights for these oligopeptide aggregates. Thus, the rod-like aggregates, formed by these oligopeptides in dioxane or benzene, can be regarded as supramolecular aggregates.