Synthesis and characterization of a vitamin B6-tetrazole hydrazone as a fluorescence probe for selective detection of Cd2+ and Ga3+ ions

A simple selective fluorescence probe for cadmium(II) and gallium(III) ions was designed and prepared by a reaction of hydrazone formation between pyridoxal-5′-phosphate and 5-hydrazinyl-1H-tetrazole. The probe shows an enhanced blue fluorescence in the presence of Cd²⁺ ions and a yellow-green fluorescence in the presence of Ga³⁺ ions in aqueous DMSO. The conditional stability constants and stoichiometry of the Cd²⁺ and Ga³⁺ complexes were determined using the maximum likelihood method. Gallium(III) ions form two complexes of different structures with probe in solution. The DFT quantum chemical calculations were performed for obtaining molecular structures of probe 1 and its complexes with Ga³⁺ and Cd²⁺. Simulation of electronic absorption spectra and NMR spectra by TDDFT and GIAO methods allowed to determine the structures, which was obtained. The probe demonstrated a low detection limit of 0.19 μM for Cd²⁺ and 0.97 μM for Ga³⁺, making it suitable for water analysis. This research offers important insights into the design and enhancement of fluorescence probes for the selective detection of metal ions.