EFFECT OF CHOLECALCIPHEROL ON THERMOTROPIC BEHAVIOR OF PHOSPHATIDYLETHANOLAMINE AND ITS N-METHYL DERIVATIVES

The thermotropic properties of hydrated dispersions of 1,2-dipalmitoylphosphatidylethanolamine (DPPE) and its N-mono-methyl (N(CH3)DPPE), N,N-dimethyl (NN(CH3)DPPE) derivatives containing cholecalcipherol (vitamin DJ) at different molar ratios, have been investigated by differential scanning calorimetry (DSC). The main transition peak temperature (Tm) for the pure aqueous phospholipidic dispersions decreases in approximately linear fashion with the methylation degree of their polar heads. Addition of vitamin D3 to phospholipidic dispersions leads to a continuous Tm decrease with a concomitant broadening of the peak. The main transition enthalpy ΔH decreases almost linearly with increasing vitamin D3 concentration. Tm and ΔH decreases in presence of vitamin D3 observed for DPPE and its N-methyl derivatives dispersions were interpreted in terms of increasing membrane "f1uidity". The interaction between sterol and phospholipids strongly depends on the degree of rnethylation of the PE group and is explained in terms of steric hindrance of the phospholipidic polar head group. The trend of ΔH values gives an idea of the possible phospholipid/vitamin D3 ratio which are 3: l, 2: l, 1: l, 1: 2, for DPPE, N(CH3)DPPE, NN(CH3),DPPE and DPPC, respectively. These results could be useful in understanding the role played by vitamin D on the structures and functions of membranes