We demonstrate that RuII(CO)2–protein complexes, formed by the reaction of the hydrolytic decomposition products of [fac-RuCl(κ2-H2NCH2CO2)(CO)3] (CORM-3) with histidine residues exposed on the surface of proteins, spontaneously release CO in aqueous solution, cells, and mice. CO release was detected by mass spectrometry (MS) and confocal microscopy using a CO-responsive turn-on fluorescent probe. These findings support our hypothesis that plasma proteins act as CO carriers after in vivo administration of CORM-3. CO released from a synthetic bovine serum albumin (BSA)–RuII(CO)2 complex leads to downregulation of the cytokines interleukin (IL)-6, IL-10, and tumor necrosis factor (TNF)-α in cancer cells. Finally, administration of BSA–RuII(CO)2 in mice bearing a colon carcinoma tumor results in enhanced CO accumulation at the tumor. Our data suggest the use of RuII(CO)2–protein complexes as viable alternatives for the safe and spatially controlled delivery of therapeutic CO in vivo.

A few ruthenium based metal carbonyl complexes, e.g. CORM-2 and CORM-3, have therapeutic activity attributed to their ability to deliver CO to biological targets. In this work, a series of related complexes with the formula [Ru(CO)3Cl2L] (L = DMSO (3), L-H3CSO(CH2)2CH(NH2)CO2H) (6a); D,L-H3CSO(CH2)2CH(NH2)CO2H (6b); 3-NC5H4(CH2)2SO3Na (7); 4-NC5H4(CH2)2SO3Na (8); PTA (9); DAPTA (10); H3CS(CH2)2CH(OH)CO2H (11); CNCMe2CO2Me (12); CNCMeEtCO2Me (13); CN(c-C3H4)CO2Et) (14)) were designed, synthesized and studied. The effects of L on their stability, CO release profile, cytotoxicity and anti-inflammatory properties are described. The stability in aqueous solution depends on the nature of L as shown using HPLC and LC-MS studies. The isocyanide derivatives are the least stable complexes, and the S-bound methionine oxide derivative is the more stable one. The complexes do not release CO gas to the headspace, but release CO2 instead. X-ray diffraction of crystals of the model protein Hen Egg White Lysozyme soaked with 6b (4UWN) and 8 (4UWN) shows the addition of Ru(II)(CO)(H2O)4 at the His15 binding site. Soakings with 7(4UWN) produced the metallacarboxylate [Ru(COOH)(CO)(H2O)3](+) bound to the His15 site. The aqueous chemistry of these complexes is governed by the water-gas shift reaction initiated with the nucleophilic attack of HO(-) on coordinated CO. DFT calculations show this addition to be essentially barrierless. The complexes have low cytotoxicity and low hemolytic indices. Following i.v. administration of CORM-3, the in vivo bio-distribution of CO differs from that obtained with CO inhalation or with heme oxygenase stimulation. A mechanism for CO transport and delivery from these complexes is proposed.

The one-dimensional organic-inorganic hybrid material [MoO 3 (bipy)] (3) (bipy = 2,2 0 -bipyridine) is obtained rapidly and in quantitative yield by the reaction of the complex cis-[Mo(CO) 4 (bipy)] (1) with excess tert-butylhydroperoxide (TBHP) in n-decane/dichloromethane at room temperature. A similar oxidative decarbonylation of the complex cis-[Mo(CO) 4 (di-t-Bu-bipy)] (2) (di-t-Bu-bipy = 4,4 0 -di-tert-butyl-2,2 0 -bipyridine) leads to the isolation of the polynuclear complex [Mo 8 O 24 (di-t-Bubipy) 4 ] (4). The structure of 4, as the CH 2 Cl 2 solvate, was determined by X-ray crystallography. The unit cell contains two crystallographically independent octameric windmill-type complexes, formulated as [Mo 8 O 24 (di-t-Bu-bipy) 4 ], both of which contain a central cubane-type Mo 4 (μ 3 -O) 4 core. Four peripheral [MoO 2 (di-t-Bu-bipy)] 2þ units cap the long edges of the Mo 4 tetrahedron of the central cubane. The close packing of these complexes via weak offset π-π contacts involving the organic ligands leads to a structure having large channels (occupied by solvent molecules) running in various directions of the unit cell. Compounds 3 and 4 can be used as the basis for active catalytic systems for the liquid-phase epoxidation of cis-cyclooctene with TBHP as the oxidant, giving the corresponding epoxide as the only product. Notably higher activities, with no change in selectivity, are possible by using microwave-assisted heating instead of conventional oil bath heating and/or by increasing the reaction temperature from 55 °C to 75 °C. The excellent stability of these Mo VI catalytic systems was confirmed by carrying out six consecutive reaction runs at 75 °C under microwave-assisted heating. The stable parent carbonyls (1 and 2) can be used as catalyst precursors since they are transformed into 3 and 4 under the operating catalytic conditions.