Mono- and di-phenylboronic acid receptors with fluorescence sensitivity to D-fructose

Three monoboronic acids, namely, [3-(benzoylamindo) phenyl] boronic acid (1), [3-(nicotinamido) phenyl] boronic acid (2), and [3-(isonicotinamido)phenyl]boronic acid (3), as well as four dibornomic acids. [3.3 '-[N,N'-(2,6-pyridinedicarboxamido)[biphenyl]-diboronic acid (6), and [3.3 '-[N,N'-(2,5-pyridinedicarboxamido)[biphenyl] diboronic acid. All compounds are fully characterised. The crystal structure of compound 3 is determined using single-crystal X-ray diffraction analysis. Fluorescence tests are performed using a general fluroscence assay method called indicator displacement assay, which uses alizarin red S as the optical reagent to monitor the binding of the unmodified boronic acid compound with the carbohydrate. The monoboronic acids show fluorescence quenching for D-fructose in aqueous solution, whereas the diboronic acids show fluorescence enhancement in DMF solutions. The Stern-Volmer plot within the total concentration range of the compounds is linear, indicating significant sphere quenching caused by the interaction between D-fructose and boronic acid receptors. (C) 2014 Elsevier B.V.All rights reserved.