Conjugation between catechol derivatives and boronic acid is regarded as one of the strongest single pair interaction in aqueous media for wide applications in sensing, separation and other bio-fields. Compared to catechol, nitrocatechol has a higher binding affinity to boronic acid due to its stronger acidity. However, the detailed comparison of binding affinity between catecholic and nitrocatecholic polymers is still elusive. Here, we established a method to compare the binding constants of catechol-4-fluorophenylboronic acid (catechol-FPBA), nitrocatechol-FPBA, poly(dopamine-co-N-isopropylacrylamide)-FPBA (P(DMA-co-NIPAM)-FPBA) and poly(nitrodopamine-co-N-isopropylacrylamide)-FPBA (P(NDMA-co-NIPAM)-FPBA). P(DMA-co-NIPAM) and P(NDMA-co-NIPAM) were prepared from the same polymer poly(tert-butyldimethylsilyldopamine-co-N-isopropylacrylamide) containing 5 mole % of dopamine moieties. The reactions between diols and FPBA were monitored using 1H NMR. Before performance of conjugation between polymers and FPBA, the binding ability to FPBA between catechol and nitrocatechol were compared in 0.1 M of PBS solution at pH 6.5, 7.4 and 8.5. For both of catechol and nitrocatechol, binding constants increase as pH rises from 6.5 to 8.5. Nitrocatechol shows a stronger binding affinity towards FPBA than that of catechol at pH 6.5 and 7.4, though the gap was closed gradually as the rise of pH to 8.5. These observations exhibit that the stronger binding affinity of nitrocatechol to FPBA relying on its stronger acidity. Based on the conjugation of FPBA with catechol and nitrocatechol, the binding ability of polymers was evaluated. The binding constants obtained after equilibrium are 498 M-1 and 2568 M-1 for P(DMA-co-NIPAM)-FPBA and P(NDMA-co-NIPAM)-FPBA respectively at pH 7.4, demonstrating that the binding ability of P(NDMA-co-NIPAM) to FPBA is about 5 times stronger than that of P(DMA-co-NIPAM).

Enhancement of binding affinity of catechol and catecholic polymer to 4-fluorophenylboronic acid through nitration of aromatic ring

253rd National Meeting (2017)

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