Chemosenors based on quinone and boronic acid and their complexation properties

Abstract

Six A-D-A sensors containing naphthoquinone imidazole boronic acid were synthesized including protonated derivatives, o-HNQB, m-HNQB and p-HNQB and methylated derivatives, o-MNQB, m-MNQB and p-MNQB. Complexation properties of all sensors were studied by fluorescence spectrophotometry. All protonated sensors showed quenching of fluorescence intensity at λ[subscript emiss] = 554 nm due to an inverse PET character upon the deprotonation by basic anions such as F⁻, OAC⁻ and CN⁻. Anion binding properties of methylated sensors were carried out in four solvent systems: DMSO, DMSO:H₂O (1:1), DMSO:HEPES pH 7.4 (1:1) and CTAB micelles. The appearance of a new emission band at 460 nm was observed in the presence of F⁻, CN⁻ and OH⁻ corresponding to the disturbance of an ICT efficiency of the sensor upon changes in hybridization changes at the boron center from sp² to sp³. In the DMSO system, p-MNQB preferred binding F⁻ whereas in aqueous solution m-MNQB and p-MNQB showed the selectivity toward CN⁻. In the CTAB micellar system, m-MNQB and p-MNQB showed promising characteristics of fluorescence probes in term of selectivity and limit of detection for micromolar cyanide detection in water. Two anthraquinone imidazole boronic based sensors, HAQB and MAQB were synthesized. The saccharide binding properties were studied using fluorescence spectrophotometry. At pH 8.5, affinity trends of both sensors were D-fructose > D-galactose > D-mannose > D-glucose