Photosensitive iron(II)-based CO-releasing molecules (CORMs) with vicinal amino and diphenylphosphino substituted chelating ligands

Diiron Hexacarbonyl Complex Induces Site-Specific Release of Carbon Monoxide in Cancer Cells Triggered by Endogenous Glutathione

In this study, we have evaluated a water-soluble, nontarget reagent and a carrier-free diiron hexacarbonyl complex, [Fe₂{μ-SCH₂CH(OH)CH₂(OH)}₂(CO)₆] (TG-FeCORM), that can induce the site-specific release of carbon monoxide (CO) in cancer cells triggered by endogenous glutathione (GSH). The releasing rate of CO was dependent on the amount of endogenous GSH. Being the amount of endogenous GSH higher in cancer cells than in normal cells, the CO-releasing rate resulted faster in cancer cells. Moreover, the anti-inflammatory properties related to the intracellular CO release of TG-FeCORM were also confirmed in the living HeLa cells.

Diiron Dithiolate Hydrides Complemented with Proton-Responsive Phosphine-Amine Ligands

The reaction of Fe₂(pdt)(CO)₆ with two equivalents of Ph₂PC₆H₄NH₂ (PNH₂) affords the amido hydride HFe₂(pdt)(CO)₂(PNH₂)(PNH) {[H1H]⁰, pdt^2- = CH₂(CH₂S^-)₂}. Isolated intermediates in this conversion include Fe₂(pdt)(CO)₅-(κ¹-PNH₂) and Fe₂(pdt)(CO)₄(κ²-PNH₂). X-ray crystallographic analysis of [H1H]⁰ shows that the chelating amino/amido-phosphine ligands occupy trans-dibasal positions. The ³¹P NMR spectrum indicates that [H1H]⁰ undergoes rapid proton exchange between the amido and amine centers. No exchange was observed for the hydride. Protonation of [H1H]⁰ gives [HFe₂(pdt)(CO)₂(PNH₂)₂]⁺ ([H₂1H]⁺), which contains two equivalent amino-phosphine ligands. Single-crystal X-ray crystallographic analysis of [H₂1H]⁺ also reveals hydrogen bonds between the exo amine protons with a THF molecule and BF₄. Deprotonation of [H1H]⁰ with potassium tert-butoxide gave [HFe₂(pdt)(CO)₂(PNH)₂]^- ([1H]^-), which was characterized spectroscopically. The complex has time-averaged C₂ symmetry with two amido-phosphine ligands. FTIR spectroscopic measurements show that υ_CO shifts by approximately 20 cm^-1 in the series [1H]^-, [H1H]⁰, and [H₂1H]⁺. These shifts are comparable to those seen for the S-protonation of the (NC)₂(CO)Fe-(μ-Scys)₂Ni(Scys)₂ site in the [NiFe]-hydrogenases.^[1].

CORM-EDE1: A Highly Water-Soluble and Nontoxic Manganese-Based photoCORM with a Biogenic Ligand Sphere

[Mn(CO)5Br] reacts with cysteamine and 4-amino-thiophenyl with a ratio of 2:3 in refluxing tetrahydrofuran to the complexes of the type [{(OC)3Mn}2(μ-SCH2CH2NH3)3]Br2 (1, CORM-EDE1) and [{(OC)3Mn}2(μ-SC6H4-4-NH3)3]Br2 (2, CORM-EDE2). Compound 2 precipitates during refluxing of the tetrahydrofuran solution as a yellow solid whereas 1 forms a red oil that slowly solidifies. Recrystallization of 2 from water yields the HBr-free complex [{(OC)3Mn}2(μ-S-C6H4-4-NH2)2(μ-SC6H4-4-NH3)] (3). The n-propylthiolate ligand (which is isoelectronic to the bridging thiolate of 1) leads to the formation of the di- and tetranuclear complexes [(OC)4Mn(μ-S-nPr)2]2 and [(OC)3Mn(μ-S-nPr)]4. CORM-EDE1 possesses ideal properties to administer carbon monoxide to biological and medicinal tissues upon irradiation (photoCORM). Isolated crystalline CORM-EDE1 can be handled at ambient and aerobic conditions. This complex is nontoxic, highly soluble in water, and indefinitely stable therein in the absence of air and phosphate buffer. CORM-EDE1 is stable as frozen stock in aqueous solution without any limitations, and these stock solutions maintain their CO release properties. The reducing dithionite does not interact with CORM-EDE1, and therefore, the myoglobin assay represents a valuable tool to study the release kinetics of this photoCORM. After CO liberation, the formation of MnHPO4 in aqueous buffer solution can be verified.

Carbon monoxide release properties and molecular structures of phenylthiolatomanganese(i) carbonyl complexes of the type [(OC)4Mn(μ-S-aryl)]2

Arylthiolatomanganese(i) tetracarbonyls form dimers or trimers and show a two-step CO release, triggered by ligand exchange and irradiation.

Carbon monoxide--physiology, detection and controlled release

Carbon monoxide (CO) is increasingly recognized as a cell-signalling molecule akin to nitric oxide (NO). CO has attracted particular attention as a potential therapeutic agent because of its reported anti-hypertensive, anti-inflammatory and cell-protective effects. We discuss recent progress in identifying new effector systems and elucidating the mechanisms of action of CO on, e.g., ion channels, as well as the design of novel methods to monitor CO in cellular environments. We also report on recent developments in the area of CO-releasing molecules (CORMs) and materials for controlled CO application. Novel triggers for CO release, metal carbonyls and degradation mechanisms of CORMs are highlighted. In addition, potential formulations of CORMs for targeted CO release are discussed.

Diiron hexacarbonyl complexes as potential CO-RMs: CO-releasing initiated by a substitution reaction with cysteamine and structural correlation to the bridging linkage

Substitution-initiated CO-releasing rate of diiron hexacarbonyl complexes are highly dependent on their bridging linkages and the complexes of the “open” form release CO much faster than those of the “close” form.