Interactions of Alkali Ions and Phospholipid Monolayers at Organic-Water Interfaces

Abstract

The self-assembled phospholipids monolayers at interfaces between two immiscible electrolyte solutions (ITIES) are commonly used to study the interactions between cell membranes and species passing in and out through membrains such as ions, drugs, and other nutrients. In this study, we utilized electrochemical techniques such as open circuit potential (OCP), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) to study the pure phospholipd monolayer formed by 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) and its mixture with 1,2-dioleoyl-sn-glycero-3-phospho-(1'-racglycerol) (sodium salt) (DOPG) at 1,2-dichloroethane-water interfaces. Our study has shown that at higher applied electric potentials, there seems to be no change in the facilitation of cation transfers by DOPC/DOPG monolayer compared to DOPC monolayer. However, at lower applied potentials, the DOPGs in the mixed monolayer seemed to leave the interface under the influence of the applied electric field, indicated by both the higher capacitance obtained throught the EIS measurements and the higher currents from the CV measurements compared to results obtained from the sample consisted of the pure DOPC monolayer. Furthermore, our study also showed a general rise in capacitance when incorporating heavier alkali ions in the aqueous phase for the sample with the mixture of DOPC/DOPG at higher applied electric potentials.