Galactose-containing amphiphiles prepared with a lipophilic radical initiator: association processes between liposomes triggered by enzymatic reaction.

A galactose-containing monomer (2-(methacryloyloxy)ethyl beta-D-galactopyranoside, MEGal) was polymerized by using a lipophilic radical initiator. The amphiphile obtained formed a liposome by mixing with bis(trans,trans-2,4-dioctadecadienoyl)phosphatidylcholine (DDPC), and the liposome obtained was physically stabilized by the polymerization of DDPC by UV irradiation. The enzymatic treatment of the galactose-containing liposomes with galactose oxidase resulted in the formation of aldehyde groups on the liposome surface. By the subsequent mixing of the liposome suspension with the amino group-containing liposome suspension, a rapid increase in turbidity was observed due to the formation of Schiff bases between the aldehyde groups and the amino groups at the interface of the liposomes. The rate of turbidity change strongly depended on the degree of polymerization of MEGal, the surface densities of galactose and amino groups on the liposome, the distance from the liposome surface to amino end groups, and the flexibility and deformability of the liposomes.