Dye Binding to Polytryptophan and Lysine-Tryptophan Copolymer: Electron Transfer Quenching by Biopolymer Pendant Groups

Abstract

Long range photoinduced electron transfer between potential electron donors and acceptors is of considerable current interest in terms of strategies for artificial photosynthesis and studies regarding the redox properties of proteins. Electron transfer over organized arrays of significant dimension (e.g., 10 nm) may also be important for molecule-based bistable switches or rectifiers. As part of a program of study of long range electron transfer involving biopolymers, we report the results of a study of interaction of the xanthene dye, eosin, (EY), with synthetic peptides constructed of the amino acid residues, lysine (Lys), tryptophan (Trp), and tyrosine (Tyr). The principal interest in these systems has to do with the well ordered secondary structures (e.g., α-helices) adopted by peptide polymers and the capabilities for synthetic modification of peptide side chains and end groups with chromophores or electroactive substituents. In addition to providing mechanisms of charge transport, helical biopolymer backbones may find use in the regular assembly of dipoles or charges necessary for nonlinear optical phenomena.