Synthesis and structures of a pincer-type rhodium(iii) complex: reactivity toward biomolecules

Abstract

A novel rhodium(III) complex [Rh^III(H₂L^tBu)Cl₃] (1) (H₂L^tBu = 2,6-bis(5-tert-butyl-1H-pyrazol-3-yl)pyridine) containing a pincer type, tridentate nitrogen-donor chelate system was synthesized. Single crystal X-ray structure analysis revealed that 1 crystallizes in the orthorhombic space group Pbcn with a = 20.7982(6), b = 10.8952(4), c = 10.9832(4) Å, V = 2488.80(15) ų, and eight molecules in the unit cell. The rhodium center in the complex [Rh^III(H₂L^tBu)Cl₃] (1) is coordinated in a slightly distorted octahedral geometry by the tridentate N,N,N-donor and three chloro ligands, adopting a mer arrangement with an essentially planar ligand skeleton. Due to the tridentate coordination of the N,N,N-donor, the central nitrogen atom N1 is located closer to the Rh^III center. The reactivity of the synthesized complex toward small biomolecules (L-methionine (L-Met), guanosine-5′-monophosphate (5′-GMP), L-histidine (L-His) and glutathione (GSH)) and to a series of duplex DNAs and RNA was investigated. The order of reactivity of the studied small biomolecules is: 5′-GMP > GSH > L-Met > L-His. Duplex RNA reacts faster with the [Rh^III(H₂L^tBu)Cl₃] complex than duplex DNA, while shorter duplex DNA (15mer GG) reacts faster compared with 22mer GG duplex DNA. In addition, a higher reactivity is achieved with a DNA duplex with a centrally located GG-sequence than with a 22GTG duplex DNA, in which the GG-sequence is separated by a T base. Furthermore, the interaction of this metal complex 1 with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) was examined by absorption (UV-Vis) and emission spectral studies (EthBr displacement studies). Overall, the studied complex exhibited good DNA and BSA interaction ability.