Studies on the catalytic hydrogenation of biomembranes. Hydrogenation of phosphatidylcholine liposomes by two water-soluble rhodium-phosphine catalysts.

The reactions of two water-soluble amphiphiolic rhodium-phosphine hydrogenation catalysts, chlorotris(sodium diphenylphosphinobenzene-m-sulfonate)rhodium(I) and chlorotris(bissodium diphenylphosphinoundecylphosphate)rhodium(I), with aqueous dispersions of unsaturated phosphatidylcholines have been studied. Under mild reaction conditions (pH2 = 1.2 atm, 37 degrees C, pH 6.9) hydrogenation of aqueous dioleoylphosphatidylcholine dispersions, prepared by sonication, was achieved. This reaction was not affected by the presence of high salt concentrations. The rate of hydrogenation was independent of catalyst concentration. The reaction with dioleoylphosphatidylcholine dispersions, prepared by the ethanolic injection method, was preceded by a lag period of about 5 h. The reaction with dioleoylphosphatidylcholine dispersions, obtained by vigorous shaking, was rather slow, suggesting the presence of a penetration barrier. The reaction with dioleoylphosphatidylcholine proceeds via the isomerisation of the oleoyl to the elaidoyl moiety, followed by hydrogenation of the elaidoyl moiety. The possible interactions of the catalysts with the bilayer are considered and the implications of these findings are discussed.