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

A novel rhodium( iii ) complex [Rh III (H 2 L t Bu )Cl 3 ] ( 1 ) (H 2 L t Bu = 2,6-bis(5- tert -butyl-1 H -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) Å 3 , and eight molecules in the unit cell. The rhodium center in the complex [Rh III (H 2 L t Bu )Cl 3 ] ( 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 (H 2 L t Bu )Cl 3 ] 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. A novel Rh III complex containing a pincer type nitrogen-donor ligand was synthesized; its interaction toward small biomolecules, duplex DNAs and RNA as well as CT-DNA and BSA was investigated.