Tuning sensitivity of a simple hydrazone for selective fluorescent "turn on" chemo-sensing of Al and its application in living cells imaging.

Salicylaldehyde based hydrazones 2-((2-methyl-2-(pyridin-2-yl)hydrazono)methyl)phenol (SMPH), 4-methyl-2-((2-methyl-2-(pyridin-2-yl)hydrazono)methyl)phenol (MSMPH) and 4-fluoro-2-((2-methyl-2-(pyridin-2-yl)hydrazono)methyl)phenol (FSMPH) were prepared and structurally characterized. These hydrazones exhibited fluorescence "turn on" response toward Al in dimethyl formamide/water (DMF/HO) (1: 1) mixture. SMPH showed enhanced emission (70 folds) as compared to MSMPH (46 folds) and FSMPH (28 folds) upon the addition of 3 equivalents of Al. Similarly a red shift was observed in the emission wavelength of hydrazone/Al mixture from non-substituted (SMPH) to fluoro-substituted (FSMPH) and in turn to methyl-substituted (MSMPH). They also showed high selectivity towards Al over the other common metal ions. Among the tested metal ions only copper interfered and quenched the fluorescence completely. Further SMPH was investigated spectroscopically in details for Al detection. The binding phenomenon of SMPH was analyzed by H NMR and HR-ESI-MS. Mass analysis showed a 1: 1 complex formation of SMPH with Al. Job's plot also confirmed their 1: 1 interaction. SMPH showed a good tolerance for Al detection in acidic to neutral pH, ranges 3-8. The limit of detection (LOD) for Al was observed to be 1.5×10M. Moreover SMPH and MSMPH were studied for living cells imaging in MCF-7 (Michigan Cancer Foundation-7) cells. These analyses also revealed the importance of these hydrazones in monitoring Al in living cells.