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 d L and the surface area A L in fluid lyotropic lamellar L α phases of dipalmitoylphosphatidylcholine (DPPC) containing amphiphilic monohydrochiorides of [2-(alkyloxy)phenyl]-2-(1-piperidinyl)ethyl esters of carbamic acid (C n A, n =number of alkyloxy chain carbons) at DPPC:C n A=1:1 and H 2 O:DPPC· 20:1 molar ratios have been estimated from small angle synchroton X-ray diffractograms. C n As intercalate between DPPC molecules, resulting in a lateral bilayer expansion and in a decrease of d L . At the reduced temperature T r =( T − T c )/ T c =0.035, where T c is the gel-fluid L β − L α phase transition temperature, the values of d L ( A L ) equal to 3.289±0.012 nm (1.060±0.012 nm 2 ), 3.391±0.011 nm (1.055±0.013 nm 2 ), 3.403±0.013 nm (1.080±0.012 nm 2 ), 3.418±0.012 nm (1.090±0.013 nm 2 ), and 3.730±0.012 nm (1.025±0.012 nm 2 ) were obtained for C5A, C7A, C9A, C10A, and C12A containing L α phases, respectively. The increase of d L with increasing n is caused by the decrease in the difference in DPPC acyl and C n A alkyloxy chains lengths. The values of d L =3.733±0.011 nm and A L =0.902±0.012 nm 2 obtained for C3A indicate that its location in the L α phase is different from that of the other C n As studied. The nonlinear dependencies of d L and A L on n can contribute to C n A's biological (local anesthetic, antimicrobial, antiphotosynthetic) effects that display similar dependencies on n .