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Volume 215, 2022, 115647

Interplay of the intermolecular and intramolecular interactions in stabilizing the thione-based copper(I) complexes and their significance in protecting the biomolecules against metal-mediated oxidative damage

Ashish Chalanab,c,1, Rakesh Kumar Raia,1, Ramesh Karric

Department of Chemistry, Indian Institute of Technology Tirupati (IIT Tirupati), Tirupati, AP 517506, India


The synthesis, characterization, and X-ray structure of a series of mono, tri, and polynuclear copper complexes of benzimidazole-based N-substituted thiones, BzMeSH (10) and BzOHSH (11), and N,N'-disubstituted, BzMeSMe (12) and BzOHSMe (13) are reported here. The X-ray structure analyses of the copper-thione complexes have revealed that the coordination behaviour and the geometry of the central metal ion in these complexes are significantly dependent on the type of the counter anion used in the reaction. For instance, the reactions of benzimidazole-based thiones with CuCl2 afforded mononuclear trigonal planar Cu(I) complexes 141518, and 19. On contrast, upon reaction with CuSO4, 10 afforded the trinuclear copper complex 16, in which thione 10 acts as a bridging as well as terminal ligand, leading to the formation of a six-membered Cu3S3 cluster. The chair-form of six-membered Cu3S3 ring is further stabilized by six intramolecular H-bonding interactions, with overall stabilization energy of 19.28 kcal.mol−1, between the free NH group of 10 and O atom of the counter anion SO42–. Whereas, when thione 10 was reacted with CuI, a 1D-polymeric chain-like copper complex 17 was obtained as a thermodynamically stable product, in which both 10 and iodine act as bridging ligand. The 3D network of complexes has revealed that these copper-thione compounds are stabilized by the presence of various types of intermolecular and intramolecular H-bonding and π − π stacking interactions in the solid state. NBO analysis of the crystal geometries revealed that the strength of these interactions ranging from 0.14 to 5.67 kcal.mol−1. We have also demonstrated that the N-substituted thiones have excellent reactive oxygen species (ROS) scavenging property and, thus, protect biomolecules including DNA and protein against Cu(I)-mediated oxidative damage.

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