Unusual Structural Features in the Lysozyme Derivative of the Tetrakis(acetato)chloridodiruthenium(II,III) Complex

The reaction between the paddle-wheel tetrakis(acetato)chloridodiruthenium(II,III) complex, [Ru-2(mu-O2CCH3)(4)Cl] and hen egg-white lysozyme (HEWL) was investigated through ESI-MS and UV/Vis spectroscopy and the formation of a stable metal-protein adduct was unambiguously demonstrated. Remarkably, the diruthenium core is conserved in the adduct while two of the four acetate ligands are released. The crystal structure of this diruthenium-protein derivative was subsequently solved through X-ray diffraction analysis to 2.1 angstrom resolution. The structural data are in agreement with the solution results. It was found that HEWL binds two diruthenium moieties, at Asp101 and Asp119, respectively, with the concomitant release of two acetate ligands from each diruthenium center.