Polymerized-Depolymerized Vesicles: Reversible Thiol-Disulfide-Based Phosphatidylcholine Membranes

The synthesis and characterization of 1,2-di(11-mercaptoundecanoyl)-sn-glycero-3-phosphocholine 1a, 1,2-di(16-mercaptoundecanoyl)-sn-glycero-3-phosphocholine 1b, and 1,2-di(2-mercaptohexadecanoyl)-sn-glycero-phosphocholine 3 is reported. Each of these phospholipids has been used to construct vesicles that can be oxidatively polymerized using hydrogen peroxide as well as reductively depolymerized, via dithiothreitol or 1-octane thiol. Based on residual thiol content and the measured vesicle diameters, well sonicated and polymerized vesicles of 1a, 1b and 2 are estimated to contain an average of 80, 350 and 100 polymer chains respectively; the number average degree of polymerization is estimated to be 25, 17 and 20 respectively. Oxidation and reduction efficiency, entrapment and permeability properties, phase transition behavior, osmotic behavior and stability features for each vesicle network are reported. Evidence has been provided for the thermodynamic stability of the vesicle membrane in the polymerized state. The possible relevance of such polymerizable-depolymerizable vesicles to membrane modelling and drug delivery is briefly discussed