From model compounds to protein binding:: syntheses, characterizations and fluorescence studies of [RuII(bipy)(terpy)L]2+ complexes (bipy=2,2′-bipyridine; terpy=2,2′:6,2"-terpyridine; L = imidazole, pyrazole and derivatives, cytochrome c)

Compounds [Ru-II(bipy)(terpy)L](PF6)(2) with bipy = 2,2'-bipyridine, terpy = 2,2':6',2"-terpyridine, L = H2O, imidazole (imi), 4-methylimidazole, 2-methylimidazole, benzimidazole, 4,5-diphenylimidazole, indazole, pyrazole, 3-methylpyrazole have been synthesized and characterized by H-1 NMR, ESI-MS and UV/Vis (in CH3CN and H2O). For L = H2O, imidazole, 4,5-diphenylimidazole and indazole the X-ray structures of the complexes have been determined with the crystal packing featuring only few intermolecular C-H...pi or pi-pi interactions due to the separating action of the PF6-anions. Complexes with L = imidazole and 4-methylimidazole exhibit a fluorescence emission with a maximum at 662 and 667 nm, respectively (lambda(exo) = 475 nm, solvent CH3CN or H2O). The substitution of the aqua ligand in [Ru(bipy)(terpy)(H2O)](2+) in aqueous solution by imidazole to give [Ru(bipy)(terpy)(imi)](2+) is fastest at a pH of 8.5 (as followed by the increase in emission intensity). Coupling of the [Ru(bipy)(terpy)](2+) fragment to cytochrome c (Yeast iso-1) starting from the Ru-aqua complex was successful at 35 degreesC and pH 7.0 after 5 d under argon in the dark. The [Ru(bipy)(terpy)(cyt c)]-product was characterized by UV/Vis, emission and mass spectrometry. The location where the [Ru(bipy)(terpy)] complex was coupled to the protein was identified as His44 (corresponding to His39 in other numbering schemes) using digestion of the Ru-coupled protein by trypsin and analysis of the tryptic peptides by HPLC-high resolution MS.