Structural and chemical investigation of a tridentate fluorescein hydrazone (LH3), a selective Cu2+ and Hg2+ chelator: detection of CN− and HSO4− by its Cu2+ complexes and effect on HeLa cell division

Abstract

A tridentate ligand (LH₃) has been synthesized via the condensation of azobenzene (AS) with fluorescein hydrazide (FH). This ligand was fully characterized using various spectroscopic techniques, including IR, UV-visible, NMR, and HRMS, and its structure was finally confirmed by X-ray crystallography. Given selective detection of Cu²⁺ ions by LH₃ and a distinctive absorption peak observed at λ_max = 501 nm, three distinct Cu²⁺ complexes, [Cu(LH₂)·2H₂O]NO₃ (1), [Cu(LH₂)·H₂O]ClO₄ (2), and [Cu(LH₂)Cl] (3) were synthesized by altering the counter anions and crystallized in a MeOH:DCM mixture. These complexes were also fully characterized using spectroscopic techniques (IR, UV-visible) and X-ray crystallography. These complexes, in turn, detect CN⁻ and HSO₄⁻ ions individually in an EtOH : H₂O (1 : 1, v/v) mixture. Notably, upon addition of CN⁻ or HSO₄⁻, the peak at 501 nm disappeared, and a new absorption band appeared at λ_max = 360 nm or λ_max = 398 nm, respectively. Complex 1 also shows significant emission spectrum changes with CN⁻ anions and minor changes with HSO₄⁻ anions at λ_em = 530 nm. The free ligand (LH₃) also displayed remarkable selectivity and sensitivity towards Hg²⁺ ions, with an emission peak response at λ_em = 540 nm, due to emission enhancement facilitated by ring-opening of the fluorescein spirocyclic ring. The limits of detection of free LH₃ for Cu²⁺ and Hg²⁺ are mentioned in the article, whereas the limits of detection of its Cu²⁺ complexes are tabulated in the article. The effect of LH₃ on the cell viability and division of HeLa cells has also been investigated, and it was observed that LH₃ induced cell death following metaphase arrest.