Spectrophotometric determination of nickel (II) in waters and soils: Novel chelating agents and their biological applications supported by DFT method

A simple and rapid method using two imine ligands,(E)-N1-(2-hydroxy-5-nitrobenzylidene) isonicotinoylhydrazone and 2-(4-fluoro benzylideneamino) benzenethiol for the analysis of nickel(II) is proposed. The ligands react with nickel(II) at pH 4.0 and 4.7 to form red and pale purple complexes respectively with a stoichiometric ratio's of 1:1. The complexes obeyed Beer's law in the range of 0.8-20.0 μg L−1 with an excellent linearity depicted by correlation coefficient value of 0.9996. The molar absorptivity and Sandell's sensitivity were found to be 5.1 × 104, 6.3 × 104 L mol−1 cm−1 and 0.98, 0.91 ng cm−2 for the red or pale purple complex systems. The limit of detection for nickel(II) was noted as 0.89 and 0.82 ng L−1. The method was successfully applied for the determination of nickel (II) in various waters and soils. Additionally, in vitro antibacterial activities of the complexes have been evaluated against gram positive (Bacillus subtillis and Staphylococcus aureus) and gram negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. Density functional theory calculations were performed to compute HOMO-LUMO band gaps for the prediction of the binding affinities of the complexes.