New Chlorido(dimethyl sulfoxide)iridium(III) complexes with N(6)-substituted adenines - Kinetic versus thermodynamic N(9) coordinated adenine isomers

Abstract

[eng] New chlorido(dimethyl sulfoxide)iridium(III) complexes with N6‐substituted adenine derivatives: [IrIIICl4(DMSO‐κS){H‐AdeCx-κN(7)}]·nH2O [x = 3, n = 3 for 1; x = 4, n = 0.5 and 3 for 2a and 2b, respectively; x = 5, n = 0 for 3; x = 10, n = 0.33 for 4] and [IrIIICl4(DMSO‐κS){H‐AdeCx-κN(9)}] [x = 3 for 5; x = 4 for 6, x = 5 for 7; x = 10 for 8] have been synthesized and characterized by spectroscopic techniques and by single‐crystal X‐ray diffraction studies (1, 2b and 5). In all cases, iridium shows octahedral geometry and is coordinated to four chlorido ligands and one S atom from dimethyl sulfoxide (DMSO‐κS). The coordination sphere of the metal is completed by the N6‐substituted adenine molecule. Two different coordination modes are observed: (i) the ligand is protonated at N(1) and coordinated through N(7) (complexes 1-4); (ii) the adenine is protonated at N(3) and coordinated through N(9) (complexes 5-8). The kinetic/thermodynamic mechanisms that yield the different coordination products have been studied by using DFT calculations. Electrophoretic mobility studies and atomic force microscopy (AFM) investigation of the interaction between complexes 1, 5, 8 and plasmid pBR322 DNA have been performed.