Effect of phospholipids on the kinetics of dioxygen transfer across a 1,2-dichloroethane/water interface

The effect of a series of 1,2-diacyl-sn-glycero-3-phosphocholines (C14:0, C16:0, C18:0) adsorbed at the interface between a buffered aqueous phase and 1,2-dichloroethane on the transfer of molecular oxygen between the two phases has been investigated by scanning electrochemical microscopy (SECM) in the induced transfer mode. A monolayer of C18:0 forms a barrier for dioxygen transfer from the organic to the aqueous phase. An increase in surface concentration of C18:0 results in a decrease in the interfacial rate constant characterising the transfer. This behaviour is analysed in terms of a simple energy barrier model. In contrast, C14:0 and C16:0 have only a small effect on dioxygen transfer on the SECM timescale, although surface tension measurements show similar adsorption behaviour and excess surface concentrations for all three phospholipids. Reasons for these observations are discussed.