Chemical modification of cytochrome c by a ruthenium complex containing phenanthroline quinone

The chemical modification of proteins by the quinone moiety of a 1,10-phenanthroline-5,6-dione (pdon) complex was investigated using [Ru(pdon)(bpy)2](ClO4)2 (bpy = 2,2′-bipyridyl) ([1](ClO4)2) and cytochrome c (cyt. c) at various pH (7–9). Mass spectra revealed a peak of cyt. c modified with 1. The reactivity of 1 for cyt. c increased with the pH of the solution. These results suggest that 1 was successfully attached to cyt. c by a reaction between the quinone moiety of 1 and the amino group or guanidino group of cyt. c. In the reaction at pH 9, the ratio of cyt. c to 1 in the product was estimated to be 1:0.8 by UV–vis spectroscopy.