Phase diagrams and phase structure of theN-octanoyl-L-glutamic acid oligomer benzyl esters-CHCl₃ systems

Abstract

N-Octanoyl-L-glutamic acid oligomer benzyl esters (residue number,N=1–4, 6, 8, and 12) have been synthesized. For the solid samples ofN=3–12, x-ray powder diffraction pattern and vibrational spectroscopic measurements have led to the assumption of a β-sheet structure. For the CHCl₃-solutions of theN-octanoyl tetramers, hexamers, and octamers, the phase diagram consists of three regions (I, II, and III). Region I is an isotropic phase, in which the aggregate structure strongly depends upon concentration, and region II is a lyotropic liquid crystal area. Region III is a two-phase area in which regions I and II coexist. In the case of the trimer solutions, it consists of two regions (I and II). For the oligomers withN=3–12 in region I, it was assumed that micellization induces preferential stabilization of the β-sheet structure depending on the concentration. Further stabilization of the β-sheet structure, was found to occur in region II. For the hexamer, octamer, and dodecamer in CHCl₃, results from light-scattering measurements have led to an estimate of the apparent weight-average molecular weights and aggregation numbers of the micelle in region I.