Stimuli-responsive properties of aminophenylboronic acid-carrying thermosensitive copolymers

Thermosensitive copolymers of N-isopropylacrylamide (NIPA) and N-acryloxysuccinimide (NASI) were obtained by solution polymerization using azobisisobutyronitrile as the initiator in a tetrahydrofuran-toluene mixture at 65 °C. A boronic acid-carrying ligand, m-aminophenylboronic acid (APBA) was covalently attached to the thermosensitive copolymer via the reaction between amino and succinimide groups. APBA-coupled thermosensitive copolymer exhibited both temperature and pH sensitivity. Thermally reversible phase transitions were observed both in the acidic and alkaline pH region for the APBA-modified copolymers obtained with different NASI feed concentrations. In our study, ribonucleic acid (RNA) was selected as a biomolecule having reactive groups which could potentially interact with the boronic acid functionality. The response of boronic acid-carrying thermosensitive copolymer against RNA was investigated in aqueous media in the pH range 4-9. In the acidic pH region, an increase was observed in the lower critical solution temperature (LCST) of the APBA-coupled thermosensitive copolymer with increasing RNA concentration. However, LCST decreased with increasing RNA concentration at both neutral and alkaline pH values. The LCST of the APBA-attached copolymer varied linearly with the RNA concentration at pH of 3, 4 and 7. © 2003 Society of Chemical Industry