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The cytotoxic activity of a series of dinitrosyl iron complexes (DNICs) with thioureas against cells of different origin has been studied in this work. The cytotoxicity of the studied DNICs proved to be substantially different depending on the structure of the complexes and cell line. Complexes with thiourea and 1,3-dimethylthiourea were found to induce notable cell death in different cell lines of both cancerous and non-cancerous origin, while the N -ethylthiourea-bearing complex induced cell death in cells derived from brain tumors. The studied DNICs effectively release NO while decomposing in solutions, as follows from the electrochemical analysis. It was found that the cytotoxic effects of the studied DNICs did not correlate with their NO-donating ability, hence suggesting that their cytotoxic activity is, in a big part, defined by the long-lived nitrosyl iron-sulfur intermediates formed during the decomposition of the complexes. The structures of the products formed upon hydrolytic decomposition of all studied DNICs have been studied by electrospray ionization mass spectrometry. Stable high-molecular cluster ions containing NO groups namely [Fe 4 S 3 (NO) 7 ] - (Roussin's "black salt" anion), [Fe 4 S 3 (NO) 5 ] - , [Fe 4 S 4 (NO) 4 ] - , [Fe 4 S 3 (NO) 4 ] - and [Fe 4 S 3 (NO) 6 ] - have been detected in the solution of the N -ethylthiourea-bearing complex. The mechanism of Roussin's "black salt" anion formation in a solution of DNIC with N '-ethylthiourea was studied using density functional theory. This moved us near understanding the reasons for the formation of biologically active intermediates upon the decomposition of the complex with N '-ethylthiourea, which are apparently responsible for the unique antiglioma activity of the complex.

High-molecular-weight dinitrosyl iron complexes (DNICs) are formed in living systems and are a stable depot of nitrogen monoxide (NO). In this work, using experimental and theoretical methods, we investigated the interaction of their synthetic analog, a promising cardiotropic complex of the composition [Fe(SC(NH 2 ) 2 ) 2 (NO) 2 ] 2 [Fe 2 (S 2 O 3 ) 2 (NO) 4 ], with bovine serum albumin (BSA) in aqueous aerobic solutions. We suggested that, under these conditions, the decomposition product of the initial complex with oxygen, the [Fe(NO)(NO 2 )] + fragment, can bind in the hydrophobic pocket of the protein. As a result of this interaction, high-molecular-weight Fe(Cys34)(His39)(NO)(NO 2 ) is formed. The binding constant of the complex with protein measured by the quenching of intrinsic fluorescence of BSA is 7.2 × 10 5 M -1 . According to EPR and UV-spectroscopy data, the interaction of the complex with the protein leads to its significant stabilization. In addition to coordination binding, the studied complex can be adsorbed onto the protein surface due to weak intermolecular interactions, resulting in the prolonged generation of NO.

Interaction and transformation of the mononuclear cationic dinitrosyl iron complex [Fe(SC(NH2)2)2(NO)2]+ (complex 1) upon binding with bovine serum albumin (BSA) have been explored using kinetic measurements, UV-Vis and fluorescence spectroscopy, and computational molecular modeling. BSA was found to bind up to five molecules of complex 1 per one protein molecule; as a result, the rate of NO release by complex 1 into solution decreases by a factor of 10. The binding constant of complex 1 with BSA measured by the quenching of intrinsic fluorescence of BSA is 5 × 105 М-1. Molecular docking calculations at pH = 7 have determined five-six low-energy binding sites for complex 1 at subunits I and II of BSA. The most stable protein-ligand complexes are located at the protein pockets near Cys34. The spectroscopic measurements and docking calculations have shown that the decomposition product of complex 1, the Fe(NO)2+ fragment, can form an adduct Fe(Cys34)(His39)(NO)2 (complex 2) with the coordination bonds of Fe with atoms S of Cys34 and ND of His39. The structure of complex 2 was supported by the density functional calculations of the absorption spectrum. Decomposition of complex 2 leads to nitrosylation of BSA at atom S of Cys34. Complexes 1 (bound with BSA), 2 and the nitrosylated BSA can serve as NO depot in plasma.