Kinetic Aspects of Polyelectrolyte Adsorption: Adsorption of Chitin Derivatives onto Liposomes as a Model System

Abstract

Carboxymethylchitin (CMC) and Carboxymethyl/Glycolchitin (CO) have been adsorbed onto liposomes at physiological ionic strength (I) and pH using phosphate buffer saline (PBS, I= 154 mM, pH =7.4). Adsorption isotherms at different polymer weight average molecular weights (M_w), for Positive ([+]) or high surface affinity liposomes (DSPC:CHOL:DMTAP, 5:4:1), and Neutral ([N]) or low surface affinity liposomes (DSPC:CHOL, 1:1), have been obtained at T=25°C. For all CMCs, the adsorbed amount increases with polymer concentration ([P]_o) and no true plateau is observed. The CMC M_w = 4.19 × 10⁵ adsorbed on a positive surface fits Langmuir kinetics with maximal coverage γGM_max =325.4μg/mg (polymer/lipid), and inverse of equilibrium constant K* = 4.743 × 10⁻⁴ mg/ml. For all isotherms the predicted amount of polymer needed to coat the entire surface based on the Radius of Gyration (R_g) is inferior to the amount adsorbed. This fact in conjunction with the dependence of γ_max on the number of adsorption shots, suggests that the adsorption is not thermodynamically but kinetically controlled.