Lipid Bilayer Thickness and Surface Area in Lamellar Phases of Hydrated Mixtures of Dipalmitoylphosphatidylcholine and Homologs of Local Anesthetic Heptacaine

Abstract

The lipid bilayer thickness and the surface area in fluid lyotropic lamellar phases of dipalmitoylphosphatidylcholine (DPPC) containing amphiphilic monohydrochlorides of [2-(alkyloxy)phenyl]-2-(1-piperidinyl)ethyl esters of carbamic acid (CnA, n=number of alkyloxy chain carbons) at DPPC:CnA=1:1 and HO:DPPC≈20:1 molar ratios have been estimated from small angle synchrotron X-ray diffractograms. CnAs intercalate between DPPC molecules resulting in a lateral bilayer expansion and in a decrease of . At the reduced temperature =(-)/=0.035 where is the gel-fluid phase transition temperature, the values of () equal to 3.289±0.012 nm (1.060±0.012 nm), 3.391±0.011 nm (1.055±0.013 nm), 3.403±0.013 nm (1.080±0.012 nm), 3.418±0.012 nm (1.090±0.013 nm) and 3.730±0.012 nm (1.025±0.012 nm) were obtained for C5A, C7A, C9A, C10A and C12A containing phases, respectively. The increase of with increasing n is caused by the decrease in the difference in DPPC acyl and CnA alkyloxy chains lengths. The values of =3.733±0.011 nm and =0.902±0.012 nm obtained for C3A indicate that its location in the phase is different from that of the other CnAs studied. The non-linear dependencies of and on n can contribute to CnAs biological (local anesthetic, antimicrobial, antiphotosynthetic) effects that display similar dependencies on n.