The combined effects of nitrates on multibilayer lipid membranes: Thermodynamic effects

Abstract

Model multibilayer membranes based on L-α-dimyristoylphosphatidylcholine containing nitrates of silver, sodium, potassium, and copper as AgNO₃–NaNO₃, AgNO₃–KNO₃, and AgNO₃–Cu(NO₃)₂ pairs were investigated. In each system studied the molar fraction of nitrates relative to the lipid was kept unchanged at 0.35, whereas the molar fraction of silver nitrate (x_Ag) was varied from 0.0 tо 1.0 within the pair. Thermodynamic parameters of the main phase transition and pre-transition of the model membranes were determined using differential scanning calorimetry. Positive deviations from additivity as a function of x_Ag for a number of these parameters were detected, including changes in the main phase transition and the pre-transition temperatures of up to 0.5 and 2.7°C, respectively; the deviation for hysteresis and half-width of the main phase transition reached up to 30%. The physicochemical mechanisms of competitive interactions between cations in membranes composed of L-α-dimyristoylphosphatidylcholine are discussed.