Monohydroxamic acids and bridging dihydroxamic acids as chelators to ruthenium(III) and as nitric oxide donors: syntheses, speciation studies and nitric oxide releasing investigation

The synthesis and spectroscopic characterisation of novel mononuclear Ru-III(edta)(hydroxamato) complexes of general formula [Ru(H(2)edta)(monoha)] (where monoha = 3- or 4-NH2, 2-, 3- or 4-Cl and 3-Me-phenylhydroxamato), as well as the. rst example of a Ru-III-N-aryl aromatic hydroxamate, [Ru(H(2)edta)(N-Me-bha)]center dot H2O (N-Me-bha = N-methylbenzohydroxamato) are reported. Three dinuclear Ru-III complexes with bridging dihydroxamato ligands of general formula [{Ru(H(2)edta)}(2)(mu-diha)] where diha = 2,6-pyridinedihydroxamato and 1,3- or 1,4-benzodihydroxamato, the first of their kind with Ru-III, are also described. The speciation of all of these systems (with the exception of the Ru -1,4-benzodihydroxamic acid and Ru-N-methylbenzohydroxamic systems) in aqueous solution was investigated. We previously proposed that nitrosyl abstraction from hydroxamic acids by Ru-III involves initial formation of Ru-III-hydroxamates. Yet, until now, no data on the rate of nitric oxide (NO) release from hydroxamic acids has been published. We now describe a UV-VIS spectroscopic study, where we monitored the decrease in the ligand-to-metal charge-transfer band of a series of Ru-III-monohydroxamates with time, with a view to gaining an insight into the NO-releasing properties of hydroxamic acids.