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

N-Acetyl-l-glutamic acid oligomeric benzyl esters with various residue numb ers (N-p=4, 5, 6, 8, 10, 12 and 14) have been synthesized by a stepwise pro cedure. 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 fr om the IR spectral data that preferential stabilization of antiparallel-typ e beta -sheet structures occurs above the critical aggregation concentratio n and that the population of this antiparallel beta -sheet increases with a n increase in concentration. On the basis of these IR results, the model of the rod-like aggregate, in which the disk-like beta -sheet monomers are on e-dimensionally stacked antiparallel to each other, has been presented for analysis of the observed SANS and SAXS intensity profiles. The best fit int ensity profiles, calculated with variation only of the aggregation number a nd with fixed molecular parameters based on the assumption of polydispersit y, have furnished the monomer-monomer bond energies (alpha kappaT), corresp onding to the hydrogen bonding energies, the number-average aggregation num bers, and the number-average molecular weights for these oligopeptide aggre gates. Thus, the rod-like aggregates, formed by these oligopeptides in diox ane or benzene, can be regarded as supramolecular aggregates.