Complexes of folic acid, lumiflavin and riboflavin with bis(2, 2′-bipyridine)ruthenium(II). Facilitated formation of flavosemiquinone complexes and substantial decrease of p Ka(NH)

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Folic acid, lumiflavin and riboflavin bind one Ru(bpy) 2 2+ complex fragment (bpy=2, 2′-bipyridine). In view of previous results for lumazine and methoxatine complexes, the appearance of characteristically pH-dependent metal-to-ligand charge transfer spectra and a facilitated ligand reduction strongly suggest an α-iminocarbonyl chelate coordination of the metal at positions O(4) and N(5). The p K a values of the heterocyclic N(3)−H protons are lowered from about 9 to about 5 upon metal coordination.