INTERACTION OF SURFACTANTS WITH MODEL AND BIOLOGICAL-MEMBRANES INTERACTION OF [2-(ALKYLOXY)-PHENYL]-2-(1-PIPERIDINYL)ETHYL ESTERS OF CARBAMIC ACID WITH DIPALMITOYLPHOSPHATIDYLGLYCEROL MODEL MEMBRANES - A CALORIMETRIC STUDY

As detected by adiabatic differential scanning microcalorimetry, [2-(a lkyloxy)-phenyl]-2-(1-piperidinyl)ethyl esters of carbamic acid (C(n)P PEECA, n is the number of carbon atoms in the alkyloxy substituent) wi th local anesthetic and antiarrhytmic activities interact with ipalmit oyl-sn-glycero-3-[phospho-rac-(1-glycerol)] model membranes (DPPG). C( n)PPEECAs form solid-like solutions with DPPG at low C(n)PPEECA concen trations and with short alkyloxy chain lengths (n < 4), while at highe r concentrations and with longer alkyloxy chains (10 greater-than-or-e qual-to n greater-than-or-equal-to 5) demixing and separation Of C(n)P PEECA+DPPG clusters of unknown stoichiometry occurs in the gel phase. The temperature of the gel - liquid crystal phase transition T(m) is d epressed in the presence of C(n)PPEECA; the depression of T(m) scaled for unity C(n)PPEECA concentration in the lipid phase indicates higher intrinsic perturbation activity of the charged form of C(n)PPEECA tha n that of the basic form of C(n)PPEECA. It is suggested that this migh t be caused by a deeper location of the basic form of C(n)PPEECA in th e lipid bilayer.