Optimizing the electron-withdrawing character on benzenesulfonyl moiety attached to a glyco-conjugate to impart sensitive and selective sensing of cyanide in HEPES buffer and on cellulose paper and silica gel strips

Abstract

Dansyl-derivatized, triazole-linked, glucopyranosyl conjugates, ^5FL_OH, ^2FL_OH, ^1FL_OH, and ^0FL_OH were synthesized and characterized. While the ^5FL_OH acts as a molecular probe for CN^–, ^2FL_OH, ^1FL_OH, and ^0FL_OH acts as control molecules. The reactivity of CN^– toward ^5FL_OH has been elicited through the changes observed in NMR, ESI MS, emission, and absorption spectroscopy. The conjugate ^5FL_OH releases a fluorescent product upon reaction by CN^– in aqueous acetonitrile medium by exhibiting an ∼125-fold fluorescence enhancement even in the presence of other anions. Fluorescence switch-on behavior has been clearly demonstrated on the basis of the nucleophilic substitution reaction of CN^– on ^5FL_OH. A minimum detection limit of (2.3 ± 0.3) × 10^–7 M (6 ± 1 ppb) was shown by ^5FL_OH for CN^– in solution. All the other anions studied showed no change in the fluorescence emission. The utility of ^5FL_OH has been demonstrated by showing its reactivity toward CN^– on a thin layer of silica gel as well as on Whatman No. 1 cellulose filter paper strips. The role of glucose moiety and the penta-fluorobenzenesulfonyl reactive center present in ^5FL_OH in the selectivity of CN^– over other anions has been demonstrated by fluorescence, absorption and thermodynamics study. Similar studies carried out with the control molecules showed no selectivity for CN^–. The mechanistic aspects of the reactivity of CN^– toward ^5FL_OH were supported by DFT computational study.