Interaction of Polysaccharides with Lipid Monolayers

Abstract

The interactions of model neutral lipids such as lecithin and dipalmitoyl phosphatidylcholine (DPPC), and of the positively charged lipid dioctadecyl dimethyl ammonium bromide (DOMA) with neutral (dextrans) and acidic polysaccharides (carrageenans and xanthan), representing the hydrophilic solutes occurring in natural aquatic systems, have been monitored electrochemically and by monolayer techniques. Surface pressure-area (π-A) and surface potential-area (ΔV-A) isotherms have been measured. The values for compressibility of mixed films and the dipol moments (effective dipole moment μT and polar head group dipole moment μα) have been calculated from π-A and Δ V-A isotherms, respectively. In electrochemical experiments lipid-coated mercury electrodes have been used. The influence of polysaccharides on the monolayers structure has been studied by capacitance measurements and by using an electrochemical probe (redox processes of cadmium) with phase-sensitive ac voltammetry. The results presented here are part of more general studies of the interaction of organic solutes naturally occurring in the aquatic systems with hydrophobic lipids at different phase boundaries. These investigations are of great importance for the interfacial properties of mixed monolayers and for understanding the influence of hydrophilic and hydrophobic substances on the physicochemical properties of natural surface films.