Adhesion of lipid membranes induced by CrCl3

We describe the apparently first reversible unbinding transition of fluid phosphatidylcholine bilayers. It is induced by minute concentrations of CrCl3 in aqueous 0.1 M NaCl solution. Mutual adhesion sets in at a threshold of 1.1 mu M. The adhesion energy increases steeply with CrCl3 concentration up to 20 mu J/m(2). It continues to rise with a much smaller slope until the transition becomes irreversible at ca. 40 mu M.