INFLUENCE OF FATTY-ACID COMPOSITION ON THE STRUCTURE AND STABILITY OF FATTY-ACID COMPLEXES WITH VITAMIN-E

The Monte Carlo technique with gradual "cooling" of configurational ensemble was used to establish the potential energy global minima and the corresponding three-dimensional structures of complexes of vitamin E (alpha-tocopherol) with various fatty acids. Empirical potential energy functions were used. Vitamin E and fatty acid molecules were assumed to form a hydrogen bond. The mutual conformational influences of the complex components were investigated. The tocopherol phytyl chain conformation is determined by the fatty acid structure, but in all cases the conformation corresponds to one of the degenerate global energy minima of the isolated molecule. The stability of the complexes increases as the number of fatty acid double bonds increases. Alpha-Tocopherol consists of two parts: a "constant" part including the chromanol moiety and the part of the tail up to the C4' atom, which has the same geometry in all the complexes, and a "changeable" part including the remaining part of the tail. The existence of the "changeable" part is due to the presence of branching 4'-CH3 and 8'-CH3 groups. The mean plane of the tocopherol chromanol moiety is roughly perpendicular to a membrane surface, the 5-CH3 tocopherol group being the nearest to it. The unsaturated fragment of a polyunsaturated fatty acid adopts a beta-spiral structure in the complex.