Synthesis, characterization, and DNA-binding studies of nitro(oligopyridine) ruthenium(II) complexes

The complexes of general formulas [Ru-II(terpy)(4-CO2H-4'-Mebpy)(X)](n+) (X = NO (n = 3) and NO2 (n = 1); 1, 2) and [Ru-II(terpy)(4-COGHK-4'-Mebpy)(X)] (X = NO (n = 3) and NO2 (n = 1); 3, 4) were synthesized and characterized. The complex [Ru-II(terpy)(4-CO2-4'-Mebpy)(NO2)](-)7.5H(2)O has also been characterized by X-ray crystallographic studies. It crystallizes in the triclinic system: a = 9.4982(1) angstrom, b = 13.1330(1) angstrom, c = 14.2498(2) angstrom; alpha = 110.5870(6)xbc, beta = 98.4048(5)xbc, gamma = 106.4353(5), P (1) over bar, Z = 2. The crystal structure reveals an extended hydrogen-bonding network. Two water molecules form strong hydrogen bonds with the nitro and the carboxylic oxygen atoms of two separate units of the complex, resulting in a dimeric unit. The dimers are bridged by a (H2O)(15) cluster, consisting of two cyclo-(H2O)(6) species, while an exo-H2O(8) connects them. Two more exo-H2O molecules are joined together and connect the cyclo-(H2O)(6) units with the H2O(1) of the dimeric unit. It was found that complexes 1 and 3 can be transformed into their nitro derivatives in aqueous media at neutral pH. Photorelease of NO in dry MeCN solutions was observed for complexes 1 and 3. Also, complex 2 partially releases (NO2)(-) in MeCN upon visible light irradiation. Complex 2 interacts with short fragments (70-300 bp) of calf thymus DNA shortening slightly the apparent polynucleotide length, while the conjugation of the peptide GHK to it (2) affects its DNA-binding mode. The peptide moiety of complex 4 was found to interact with the DNA helix in a synergistic way with the whole complex. Preliminary results of photocleavage of DNA by complex 2 are also reported. Inorg Chem