Self-Assembly of Pheophorbide-a on Poly-L-Lysine

TL;DR

This study investigates how Pheophorbide-a binds to poly-L-lysine in aqueous solutions, revealing highly cooperative binding, dye aggregation, and significant fluorescence changes, which enhance understanding of dye-polypeptide interactions.

Contribution

It provides detailed spectroscopic analysis of Pheophorbide-a binding to poly-L-lysine, highlighting cooperative binding and aggregate formation under physiological conditions.

Findings

40-fold fluorescence quenching observed

Formation of Pi-stacked dye aggregates on PLL

Highly cooperative binding with q=1000

Abstract

Binding of Pheophorbide-a of to poly-L-lysine (PLL) have been studied in neutral aqueous buffered solutions of low and near-physiological ionic strengths with low ethanol content (2.4-5.9 %) a wide range of molar polymer-to-dye ratios (P/D) using absorption and polarized fluorescence spectroscopy, fluorimetric titration, fluorescence melting. The binding has highly cooperative character (cooperativity parameter q = 1,000) and results in 40-fold quenching of the dye fluorescence as well as in increase in the fluorescence polarization degree up to 0.16, that evidences formation of Pi-stacked dye aggregates on the polypeptide exterior. The spectroscopic properties of these aggregates were established. The cooperative biding constants were estimated by Schwarz's method.