Structural Analyses on Aggregates of Graft Copolypeptides Containing Tryptophan in Aqueous Media and Efficiency of Drug Release

Abstract

The amphiphilic graft copolypeptide, consisting of poly (N-hydroxyethyl L-glutamine) (PHEG) and poly (L-tryptophan (L-Trp)) PTrp (denoted as PHEG-g-PTrp), was synthesized. At the L-Trp composition of 10-25mol%, L-Trp residues aggregated to form the hydrophobic cores in the aqueous solution. The hydrophobic substance could be incorporated in this L-Trp core. This function had not been seen for the random copolypeptide consisting of the same constituent molecules. The aggregation of PHEG-g-PTrp was observed by dynamic light scattering, transmission electron microscopy and small-angle X-ray scattering. The film specimen was prepared from PHEG-g-PTrp by modifying L-Trp residues in trifluoroacetic acid. The hydrophobic substances were incorporated in the high pH region, and the control of the release was achieved by changing pH through the dissociation of the indole rings in the L-Trp residues.