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.