FLEXIBLE-TO-SEMIFLEXIBLE CHAIN CROSSOVER ON THE PRESSURE-AREA ISOTHERM OF A LIPID BILAYER
Krivonos I.N., Mukhin S.I.

Поступила в редакцию: 11 Июня 2007

PACS: 87.16.Dg, 87.15.Kg, 31.15.Kb

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We find theoretically that competition between and terms in the Fourier-transformed conformational energy of a single lipid chain, in combination with interchain entropic repulsion in the hydrophobic part of the lipid (bi)layer, may cause a crossover on the bilayer pressure-area isotherm . The crossover manifests itself in the transition from α=5/3 to α=3. Our microscopic model represents a single lipid molecule as a worm-like chain with a finite irreducible cross-section area A₀, a flexural rigidity K_f, and a stretching modulus Q in a parabolic potential with the self-consistent curvature B(A) formed by entropic interactions between hydrocarbon chains in the lipid layer. The crossover area A^* obeys the relation . We predict a peculiar possibility of deducing the effective elastic moduli K_f and Q of an individual hydrocarbon chain from the analysis of the isotherm with such a crossover. Also calculated is crossover-related behavior of the area compressibility modulus K_A, the equilibrium area per lipid A_t, and the chain order parameter S(θ).