Water soluble sulfaguanidine based Schiff base as a “Turn-on” fluorescent probe for intracellular recognition of Zn2+ in living cells and exploration for biological activities

Abstract

(E)-N-(diaminomethylene)-4-(3,5-dichloro-2-hydroxybenzylideneamino)benzene (HL), a sulfaguanidine (SGN) appended Schiff base, acts as fluorescent ‘turn-on’ Zn2+ sensor in aqueous medium and limit of detection (LOD) is 37.13 nM which is much lower than the WHO recommended value (76 µM) in the drinking water. The composition of the complex has been supported by Job’s plot and mass spectral analysis. HL is weakly emissive which may be due to excited state induced proton transfer; however, binding with Zn2+ may stop this quenching and induce the chelation enhancement of fluorescence (CHEF) at 514 nm in presence of large number of biologically important cations. The complex shows much higher antibacterial efficiency than HL and sulfaguanidine (SGN) (MIC of SGN, >1000 μg/ml; HL, >1000 μg/ml and that of [ZnL2(H2O)] is 64 μg/ml for Escherichia coli). In living cells (African Monkey Vero Cells) the trace quantity of Zn2+ has been detected using the probe (HL). MTT assay confirms that the probe is non-toxic upto 200 μg/ml (774 µM). Both Density Functional Theory and molecular docking (PDB id, 5EVA) computation have been used to explain the electronic properties and to forecast the interaction of metal–ligand complex with target protein β-lactamase in bacterial cells.