Abstract
Summary: 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 ^1^H 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 °C. The copolymers adsorption capacities were in the range of 15–30 mg · ml^−1^ gel (14–36 µmol 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 µmol · 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 (15 mg · 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.
Frontal chromatogram of the AA‐NAAPBA copolymer (○) and polyacrylamide (•).
magnified imageFrontal chromatogram of the AA‐NAAPBA copolymer (○) and polyacrylamide (•).