Interaction of polysaccharides with lipid monolayers

The interactions of model neutral lipids such as lecithin and dipalmitoyl p hosphatidylcholine (DPPC), and of the positively charged lipid dioctadecyl dimethyl ammonium bromide (DOMA) with neutral (dextrans) and acidic polysac charides (carrageenans and xanthan), representing the hydrophilic solutes o ccurring in natural aquatic systems, have been monitored electrochemically and by monolayer techniques. Surface pressure-area (pi-A) and surface poten tial-area (Delta V-A) isotherms have been measured. The values for compress ibility of mixed films and the dipol moments (effective dipole moment mu(T) and polar head group dipole moment mu(alpha)) have been calculated from pi -A and Delta V-A isotherms, respectively. In electrochemical experiments li pid-coated mercury electrodes have been used. The influence of polysacchari des on the monolayers structure has been studied by capacitance measurement s and by using an electrochemical probe (redox processes of cadmium) with p hase-sensitive ac voltammetry. The results presented here are part of more general studies of the interaction of organic solutes naturally occurring i n the aquatic systems with hydrophobic lipids at different phase boundaries . These investigations are of great importance for the interfacial properti es of mixed monolayers and for understanding the influence of hydrophilic a nd hydrophobic substances on the physicochemical properties of natural surf ace films. (C) 2000 Academic Press.