Interfacial recognition of sugars by novel boronic acid-carrying amphiphiles prepared with a lipophilic radical initiator

Novel amphiphiles which carry several boronic acid groups in their polar head regions were prepared by copolymerization of 3-(acrylamido)phenylboronic acid (APBA) and ((N,N-dimethylamino)propyl)methacrylamide (DMAPMA) using a lipophilic radical initiator. The amphiphiles obtained (Lipid AD) formed a stable monolayer, and the surface pressure-molecular area (pi-A) profile of the monolayer was changed by the addition of sugars in the subphase. The effect was dependent on the structure of the sugars added, which is consistent with the effect of the sugars on the viscosity of aqueous solution of the copolymer of APBA and DMAPMA. The presence of DMAPMA residues together with the APBA residues in the head group of the amphiphile was more effective on the recognition of sugars than that of acrylamide or (3-(methacryloylamino)propyl)trimethylammonium chloride residues, which confirmed the supporting effect of tertiary amines on the recognition of sugars by phenylboronic acid groups previously reported. The monolayer of Lipid AD was expanded by a sugar-carrying protein, ovalbumin, and the expansion was inhibited by the addition of low-molecular weight sugars. Similarly, monomeric sugars inhibited the ovalbumin-mediated aggregation of liposomes composed of Lipid AD and dioctadecyldimethylammonium bromide. These results could be attributed to the selective binding of hydroxyl groups of sugars or sugar groups in the protein to boronic acid groups in the amphiphiles.