Reactivity of Radicals Generated on Irradiation of trans-[Ru(NH₃)₄(NO₂)P(OEt)₃](PF₆)

Abstract

The electronic absorption spectrum of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in aqueous solution is characterized by a strong absorption band at 334 nm (lambda(max) = 1800 mol(-1) L cm(-1)). On the basis of quantum mechanics calculations, this band has been assigned to a MLCT transition from the metal to the nitro ligand. Molecular orbital calculations also predict an LF transition at 406 nm, which is obscured by the intense MLCT transition. When trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in acetonitrile is irradiated with a 355 nm pulsed laser light, the absorption features are gradually shifted to represent those of the solventocomplex trans-[Ru(NH(3))(4)(solv)(P(OEt)(3)](2+) (lambda(max) = 316 nm, epsilon = 650 mol(-1) L cm(-1)), which was also detected by (31)P NMR spectroscopy. The net photoreaction under these conditions is a photoaquation of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+), although, after photolysis, the presence of the nitric oxide was detected by differential pulse polarography. In phosphate buffer pH 9.0, after 15 min of photolysis, a thermal reaction resulted in the formation of a hydroxyl radical and a small amount of a paramagnetic species as detected by EPR spectroscopy. In the presence of trans-[Ru(NH(3))(4)(solv)P(OEt)(3)](2+), the hydroxyl radical initiated a chain reaction. On the basis of spectroscopic and electrochemical data, the role of the radicals produced is analyzed and a reaction sequence consistent with the experimental results is proposed. The 355 nm laser photolysis of trans-[Ru(NH(3))(4)(NO(2))(P(OEt)(3)](+) in phosphate buffer pH 7.4 also gives nitric oxide, which is readily trapped by ferrihemeproteins (myoglobin, hemoglobin, and cytochrome C), giving rise to the formation of their nitrosylhemeproteins(II), (NO)Fe(II)hem.

Photoactive ruthenium nitrosyls: Effects of light and potential application as NO donors

“…Quantum yield (φ) measurements on this series of nitrosyls have afforded values ranging from φ = 0.04 ( 6 , Im) to 0.23 ( 7 , 4-acpy) [115,116]. Significant NO photolability (φ = 0.30) has been observed when X = phosphite ligand such as P(OEt) 3 ( 8 ) [121,122]. The d π (Ru) → π * (NO) metal-to-ligand charge transfer (MLCT) transition around 330–450 nm is believed to be responsible for the NO photolability of these nitrosyls.…”

Pharmacological Characterization of the Vasodilating Effect Induced by the Ruthenium Complex cis-[Ru(NO)(NO2)(bpy)2].(PF6)2

“…15 In physiological conditions, the NO coordinated to ruthenium (Ru-NO + ) can undergo electrophilic attack by hydroxide or water, to form an analogous Ru-NO 2 2 species 16 (equation 1) ½RuðNOÞðbpyÞ 2 ðLÞ nþ þ2OH 2 % K ½RuðNO 2 ÞðbpyÞ 2 ðLÞ ðn 2 2Þ þH 2 O: (1) Then, the Ru-NO 2 2 species can generate NO through NO 2 2 conversion to NO. 12,17,18 The scientific literature has reported on a number of mechanisms for in vivo NO 2 2 conversion to NO-indeed, nitrite metabolism takes place in tissues and blood, to form NO. 19 Here, we synthesized the complex cis-[Ru(NO)(NO 2 )(bpy) 2 ].…”

The inducing NO-vasodilation by chemical reduction of coordinated nitrite ion in cis-[Ru(NO2)L(bpy)2]+ complex

“…1 In addition, certain disease states are associated with nitric oxide deficiencies, and this has raised interest in exogenous donors that can deliver NO to specific targets under external stimulation. 5 Although the nitrite ruthenium species might still serve as photochemical NO delivery agents, 13 [2][3][4][5][6][7][8][9][10][11][12] Perhaps the most studied NO donors among metal nitrosyls are those based on ruthenium.…”