The characterization of the sol-gel encapsulated curcumin as a possible sensor for small biologically important...

Curcumin, a known phytochemical antioxidant was found to be useful as a potential sensor for some small biologically important molecules. Hydrogen peroxide, the sodium salt of nitrite (NO2-), hydroxide (OH-), bromide (Br-) and iodide (I-) were observed to quench the fluorescence of sol-gel encapsulated curcumin, which emits radiation at 530 nm when excited at 420 nm. The observed bimolecular quenching constant which is related to the Stern-Volmer quenching constant, KSV, for the species studied in this work was determined by a modified Stern-Volmer relation for molecular surface accessibility, was observed to be specific for each of these anions and correlates quite well with their half-wave potentials, E1/2. The extent of permeability of these molecules through the pores of the sol-gel matrix was determined and they, also, correlated with these molecules' charge densities and sizes. In all the species, the reaction was quite exergonic and the free energy change, DeltaGoET, obtained in each case, suggest an outer-sphere, long range electron transfer mechanism. These observations open up the possible use of curcumin as a sensor for probing and characterizing some relevant bio-molecules in biological systems.