Tuning sensitivity of a simple hydrazone for selective fluorescent "turn on" chemo-sensing of Al 3+ 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 Al3+ in dimethyl formamide/water (DMF/H2O) (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 Al3+. Similarly a red shift was observed in the emission wavelength of hydrazone/Al3+ mixture from non-substituted (SMPH) to fluoro-substituted (FSMPH) and in turn to methyl-substituted (MSMPH). They also showed high selectivity towards Al3+ 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 Al3+ detection. The binding phenomenon of SMPH was analyzed by 1H NMR and HR-ESI-MS. Mass analysis showed a 1: 1 complex formation of SMPH with Al3+. Job's plot also confirmed their 1: 1 interaction. SMPH showed a good tolerance for Al3+ detection in acidic to neutral pH, ranges 3–8. The limit of detection (LOD) for Al3+ was observed to be 1.5×10−7M. 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 Al3+ in living cells.