A Ruthenium Nitrosyl That Rapidly Delivers NO to Proteins in Aqueous Solution upon Short Exposure to UV Light

Two Ru(III) complexes, [Ru(PaPy3)(Cl)](BF4) (2) and [Ru(PaPy3)(NO)](BF4)2 (3) (PaPy3H = N,Nʹ-bis(2-pyridylmethyl)amine-N-ethyl-2pyridine-2-carboxamide), have been synthesized and characterized by spectroscopy and X-ray diffraction. Nitrosyl complex 3 has been prepared by passage of purified NO gas to the hot methanolic solution of the chloro derivative 2. Complex 3 exhibits (nu)NOstretching frequency at 1899 cm^-1 indicating a {Ru-NO}6 configuration. Clean 1H NMR spectra of 3 in D2O and CD3CN confirm the S = 0 ground state. When an aqueous solution of [Ru(PaPy3)(NO)](BF4)2 is exposed to low intensity UV light, it rapidly loses NO and forms [Ru(PaPy3)(H2O)]2+. This reaction can be conveniently used to transfer NO to proteins such as myoglobin (Mb) and cytochrome c oxidase. The NO transfer reaction is clean and occurs upon short exposure to light.