A. Derzhanski

Saddle splay instability in lipid bilayers

Abstract The arising of saddle splay instability is considered. A necessary condition for this is that the saddle splay elastic modulus K exceeds a given critical positive value. Molecular considerations demonstrate that the signs of K and the molecular asymmetry are opposite. The comparison of the formula for the period of saddle splay deformation with experiment gives K ≈ 10 −12 erg.

Flexoelectricity and Surface Polarization

Abstract The comparison between experimental condition in two experiments measuring MBBA bend flexo-coefficient and an analogy with lyotropic liquid crystals lead to the concept that the reason for the big difference obtained is the opposite direction of the surface polarization due to the hydro-phobic or hydrophilic surfaces used and weak amphiphilic character of MBBA molecule,

Generalized Asymmetry of Thermotropic and Lyotropic Mesogens

Abstract The multipole model of molecular asymmetry of rod-like and disc-like mesogens was developed by us earlier (1981). It included the electrical, sterical and biphilic asymmetry. That model was generalized later on (1985) by including the flexibility asymmetry as well. Accordingly, mesogens were classified as generalized multipoles: monopoles, dipoles, quadrupoles etc. Furthermore, the generalized dipoles were considered as functions of the generalized fields by introducing generalized polarizabilities. These new lines of development of the model are reviewed here. They are especially important for lyotropics and membranes. Since 1981 a number of new mesogens corresponding to the theoretical predictions of the model were synthesized. We are applying our general classification to the following substances: cone-shaped discotics, flexible core discotics, discoidal amphiphilics, phasmids, biforked mesogens etc. Peculiarities in the structural organization of the tilted compounds are qualitatively discuss...

Edge energy and pore stability in bilayer lipid membranes

The problem of pore formation in two-dimensional liquid crystal systems like lipid bilayers, biomembranes and black foam films is considered in terms of a unified molecular structure of the pore, using as a basic parameter the edge energy γ per unit length of the pore perimeter.

Multipole Model of the Molecular Asymmetry in Thermotropic and Lyotropic Liquid Crystals. Volume and Surface Effects

Abstract The molecular asymmetry of mesogenic molecules is defined as a deviation of the corresponding molecular property from spherical and axial symmetry. Three types of asymmetry-electrical, steric and biphilic, are considered using a multipole representation. Two basic molecular shapes are included-rod-like and plate-like. The first three multipoles-monopole, dipole, and quadrupole, are involved. In the steric case a monopole does not exist. The effective shape of a molecule includes not only steric, but also electrical intermolecular repulsive interactions. The biphilic asymmetry is determined by the distribution of the hydrophilic and hydrophobic groups along the molecule. Three types of generalized fields—electrical, deformational, and biphilic, are also defined and their volume and surface sources are discussed. The effects of the molecular asymmetry on the intermolecular interactions in thermotropic (rod-like and disc-like) and lyotropic liquid crystals are qualitatively discussed in an analogy t...

Influence of the Electric Double Layers of the Membrane on the Value of its Flexoelectric Coefficient

Abstract The potential jump due to the electric double layers across a spherically deformed charged membrane is calculated. The equations of Langmuir adsorption are used to estimate the change in the surface density of the membrane. The flexoelectric coefficient due to the electric double layers of the membrane is obtained for the cases of blocked and free flip-flop.

Influence of the lengths and conformation states of hydrocarbon chains on the stability of lyotropic phases

Abstract The changes in the lyotropic phases after mixing amphiphilics with different chain lengths or after changing the environmental temperature are investigated theoretically. Three cases are considered: (a) chains with the same number of carbon atoms deformed because of the thermal motion; (b) a mixture of amphiphilics with hard hydrocarbon chains of different lengths; (c) in a more general phenomenological approach, an expression is proposed for the elastic energy, needed for the packing of the hydrocarbon chain in the building block of every lyotropic phase.

Curvature-induced polarization of bilayer lipid membranes

Abstract The flexoelectric coefficient of a spherically deformed bilayer lipid membrane is considered as the ratio between the deformation-induced transmembrane potential and the curvature. The calculations are carried out on the basis of general electrodynamic considerations without using the analogy with thermotropic liquid crystals.

Latest Theoretical and Experimental Investigations of the Flexoeffect in Membranes

Abstract A new definition is given of the flexocoefficient of a symmetrical membrane. This quantity is expressed through the distribution of the charges along the thickness of the membrane. A relation is found between the value of the flexocoefficient and the difference between the curvature elasticity moduli at forbidden and permitted exchange of charges on both sides of the membrane. Results of experiments are presented for the influence of adsorbed ions on the value and the sign of the flexocoefficient.

Statistical Mechanical Theory for Hydrophobic Core of Lipid Bilayer

Abstract A partition function is proposed for the molten hydrocarbon chains in the hydrophobic region of a lipid bilayer. In the construction, constancy of the volume of the bilayer is accepted as well as constancy of the density within the hydrophobic range when increasing the arqa of the bilayer. MarEeljas method1 for determining the inter- and intramolecular interactions was used. The distribution of the lateral pressure along the thickness of the bilayer and the elasticity modulusof the bilayer (without taking into account the electrostatic interactions between the heads) were determined. Explicite calculations were made for lipids with one and two saturatedalkyl chains with 12 carbon atoms per chain.