Structural and solution equilibrium studies of trimethylammonium thiosemicarbazones and their interaction with gold nanoclusters

Gátszegi, Gerda T. and Milunovic, Miljan N.M. and Dömötör, Orsolya and May, Nóra V. and Nové, Márta and Spengler, Gabriella and Csapó, Edit and Arion, Vladimir B. and Enyedy, Éva Anna (2026) Structural and solution equilibrium studies of trimethylammonium thiosemicarbazones and their interaction with gold nanoclusters. JOURNAL OF INORGANIC BIOCHEMISTRY, 285. No.-113442. ISSN 0162-0134

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Abstract

A series of three water-soluble methylenetrimethylammonium α-N-heterocyclic thiosemicarbazones (TSCs) was synthesized and characterized, and their proton dissociation and complex formation equilibria with Cu(II), Fe(II), and Fe(III) were studied using UV–visible, NMR, and electron paramagnetic resonance spectroscopic methods. In addition, the structures of one ligand and one Cu(II) complex were determined by single-crystal X-ray diffraction, revealing that the Cu(II) complex adopts coordination of the Schiff base through an (N,N,S) donor set. The interaction of the most active Cu(II) complex with human serum albumin-stabilized gold nanoclusters was also investigated to explore the association of the two systems and the impact of this protein-based matrix on the stability of the complex. The effect of the -CH2-N(CH3)3+substituent in position 6 of the pyridine ring on the solution chemical properties and cytotoxicity was examined. At physiological pH, the positively charged species dominate for all compounds studied, providing excellent aqueous solubility. The -CH2-N(CH3)3+moiety resulted in lower stability of the metal complexes compared to their corresponding non-substituted TSC analogues. Complexation with Cu(II) enhanced the activity against human colon adenocarcinoma (Colo205) and lung adenocarcinoma (A549) cell lines, although only moderate cytotoxicity was observed. Association with the protein-stabilized gold nanoclusters induced partial dissociation of the selected Cu(II) complex. Overall, while the methylenetrimethylammonium group in position 6 of the pyridine ring improves aqueous solubility, it adversely affects both metal ion binding capacity and in vitro cytotoxicity against cancer cell lines.

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