CALORIMETRIC STUDIES OF THE INTERACTION OF 4-BIPHENYLACETIC ACID AND ITS BETA-CYCLODEXTRIN INCLUSION COMPOUND WITH LIPID MODEL MEMBRANE

The thermotropic properties of hydrated dispersions of dipalmitoylphosphatidylcholine (DPPC) containing 4-biphenylacetic acid (BPAA) or β-cyclodextrin-4-biphenylacetic acid (BPAA-β-Cyd) at different molar ratios, have been investigated by differential scanning calorimetry (DSC). Addition of increasing amounts of BPAA or BPAA-β-Cyd to phospholipidic dispersions leads to a main transition peak temperature (Tm) shift towards lower temperatures with a concomitant broadening of the peak. The main transition enthalpy ΔH remains almost constant increasing BPAA concentration. Tm shift in the presence of BPAA, observed for DPPC dispersions, was interpreted in terms of increasing membrane "fluidity". The interaction between BPAA-β-Cyd and DPPC liposomes depends on the fraction of BPAA exchanged from the complex with membranes and it is allowed by the amphiphatic nature of this molecule. Kinetic experiments were carried out and the diffusion rate of BPAA coming from the complex into liposomes was slower than that shown by free BPAA. The results demonstrate a possible interaction of BPAA with phospholipids in cell membranes and the potential effects of such an interaction in regulating adsorption in natural membranes modulating the fluidity