Analysis of constrained concerted motions in hydrocarbon chains with applications to kinks in lipid bilayers

Abstract

Motions in hydrocarbon chains can be severely restricted in high concentration phases e.g. in lipid bilayers. Such a motion can still be accomplished by rotations around several bonds in such a way that the motion is moderately extensive in space and still not require very large dihedral energies. In this paper, the creation of a kink in a lipid tail, restricted to move inside a cylinder, is considered with emphasis on the multidimensional character of the motion. It is not sufficient only to regard the motion across a saddle point in the multidimensional space, but a more extensive ‘density of energy barriers’ must be considered. The main result is that the creation of a kink that involves the rotation of two dihedral angles over the potential maxima does not require twice that energy but only about 1·3 times it.