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

Dansyl-derivatized, triazole-linked, glucopyranosyl conjugates, L-5F(OH), (FLOH)-F-2, (FLOH)-F-1, and (FLOH)-F-0 were synthesized and characterized. While the 5FL(OH) acts as a molecular probe for CN-, 2FL(OH), (FLOH)-F-1, and (FLOH)-F-0 acts as control molecules. The reactivity of CN- toward (FLOH)-F-5 has been elicited through the changes observed in NMR, ESI MS, emission, and absorption spectroscopy. The conjugate (FLOH)-F-5 releases a fluorescent product upon reaction by CN- in aqueous acetonitrile medium by exhibiting an similar to 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 (FLOH)-F-5. A minimum detection limit of (2.3 +/- 0.3) x 10(-7) M (6 +/- 1 ppb) was shown by (FLOH)-F-5 for CN- in solution. All the other anions studied showed no change in the fluorescence emission. The utility of (FLOH)-F-5 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 (FLOH)-F-5 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 (FLOH)-F-5 were supported by DFT computational study.