Nitric Oxide and Nitroxyl Products from the Reaction of L-Cysteine with trans-[RuNO(NH3)4P(OEt)3](PF6)3

The reaction between the trans-[RuNO(NH3)(4)P(OEt)(3)](PF6)(3) and L-cysteine (RS-) was studied over a pH range of 2.0-7.4. In this reaction, the concentrations of NO and HNO produced varied as a function of the pH of the solution. The first step of this reaction proceeded quickly [k(1) = (3.5 +/- 0.3)x10(3) M-1 s(-1), pH = 3.5, 25 degrees C] and resulted in the formation of trans-[Ru(NH3)(4)P(OEt)(3)N(O)SR](2+), which dissociated to yield trans-[Ru(NH3)(4)P(OEt)(3)NO](2+) and RS. However, trans-[Ru(NH3)(4)P(OEt)(3)N(O)SR](n-1) can react with a second L-cysteine, yielding trans-[Ru(NH3)(4)P(OEt)(3)N(O)(SR)(2)](+) [k(2) = (3.6 +/- 0.1) M(-1)s(-1), pH = 3.5, 25 degrees C]. Therefore, the trans-[Ru(NH3)(4)P(OEt)(3)NO](2+) species released NO and the trans-[Ru(NH3)(4)P(OEt)(3)N(O)(SR)(2)](n-2) species released HNO.