Boronate-containing copolymers: Polyelectrolyte properties and sugar-specific interaction with agarose gel

Copolymers of N-acryloyl-m-aminophenylboronic acid (NAAPBA) with acryamide (AA), N,N-dimethylacrylamide (DMAA), and N-isopropylacrylamide (NIPAM) were found to adsorb on cross-linked agarose gel (Sepharose CL-6B) in the pH range from 7.5-9.2, due to specific boronate-sugar interactions. The molar percentages of phenylboronic acid (PBA) groups in the boronate-containing copolymers (BCCs), as estimated by H-1 NMR spectroscopy, were 13, 10, and 16%, respectively, whereas the apparent ionization constants, the pK(a) values, of the copolymers were similar and equal to 9.0 +/- 0.2 at 20 degrees C. The copolymers adsorption capacities were in the range of 15-30 mg center dot ml(-1) gel (14-36 mu mol pendant PBA ml(-1) gel) at pH 9.2 and decreased with decreasing pH value. The interaction of monomeric NAAPBA with Sepharose CL-6B was characterized by an equilibrium association constant of 53 +/- 17 m(-1), the chromatographic capacity factor k ' = 1.8, and a total content of binding sites of 27 +/- 10 mu mol center dot ml(-1) gel at pH 9.2. The weak reversible binding of monomeric NAAPBA and almost irreversible binding of NAAPBA copolymers to the gel at pH 9.2 suggested a multivalent character of the copolymer adsorption. At pH 7.5, the maximal adsorption capacity was displayed by the AA-NAAPBA copolymer (45 mg center dot ml(-1) gel). All the BCCs could be completely desorbed from the gel by 0.1 m fructose in aqueous buffered media with pH values from 7.5-9.2. The strong adsorption of AA-NAAPBA on agarose gel probably relates to the conformation of the copolymer in aqueous solution and provides opportunities for biomedical applications of the copolymer under physiological conditions. Multivalent, weak-affinity adsorption of BCCs to the agarose gel seems to be a tentative model for the copolymers' binding to oligo- and polysaccharides of cell membranes and mucosal surfaces.