Introducing [Mn(CO)3(tpa-κ3N)]+ as a novel photoactivatable CO-releasing molecule with well-defined iCORM intermediates – synthesis, spectroscopy, and antibacterial activity

Abstract

[Mn(CO)3(tpa-κ(3)N)]Br was prepared as a novel photoactivatable CO-releasing molecule (PhotoCORM) from [MnBr(CO)5] and tris(2-pyridylmethyl)amine (tpa) for the delivery of carbon monoxide to biological systems, with the κ(3)N binding mode of the tetradentate tpa ligand demonstrated by X-ray crystallography. The title compound is a CORM prodrug stable in solution in the dark for up to 16 h. However, photoactivation at 365 nm leads to CO release from the metal coordination sphere and transfer to haem proteins, as demonstrated by the standard myoglobin assay. Different iCORM intermediates could be detected with solution IR spectroscopy and assigned using DFT vibrational calculations. The antibacterial activity of the complex was studied on Escherichia coli. No effects were observed when the cultures were either kept in the dark in the presence of PhotoCORM or illuminated in the absence of metal complex. However, photoactivation of [Mn(CO)3(tpa-κ(3)N)]Br at 365 nm led to the appearance of the spectral signatures of CO-coordinated haems in the terminal oxidases of the bacterial electron transport chain in whole-cell UV/Vis absorption spectra. Significant internalization of the PhotoCORM was demonstrated by ICP-MS measurement of the intracellular manganese concentration. In particular when using medium with succinate as the sole carbon source, a very pronounced and concentration-dependent decrease in the E. coli growth rate could be observed upon illumination in the presence of metal complex, which is attributed to the constrained energy metabolism under these conditions and a strong indicator of terminal oxidase inhibition by carbon monoxide delivered from the PhotoCORM.

Targeting heme oxygenase-1 and carbon monoxide for therapeutic modulation of inflammation

“…Among these, Mn(CO)3(tpa-κ(3)N)](+) is stable in the dark, releases CO in solution upon photoactivation at 365 nm, and has demonstrated anti-bacterial activity. 301–303 Recent innovation in this area also includes the development of nanoparticle delivery systems for CORMs, 303–304 as well as bifunctional hybrid molecules with both Nrf2-activating and CORM functions. 305 …”

“…319 Recent advances using PhotoCORMs demonstrate photoactivatable toxicity of these compounds toward E. coli bacteria. 301 CORMs may also find application in reducing gastrointestinal inflammation in various models including post-operative ileus and necrotizing enterocolitis. 312 Finally, applications for CORMs in transplantation models have also been described.…”

Organic CO Prodrugs: Structure–CO‐Release Rate Relationship Studies

“…[1] Now, CO is recognized as an important gasotransmitter with importance on par with that of hydrogen sulfide (H 2 S) and nitric oxide (NO). [2] Moreover, past decades have witnessed the demonstration of a myriad of therapeutic indications for CO, including cytoprotective, [3] anti-inflammatory, [4] anti-bacterial [5] and anti-cancer effects, [6] among many others. However, work in taking CO into clinical applications is still in its infancy.…”

Selective cytotoxicity of arene tricarbonylchromium towards tumour cell lines

“…This type of compounds is known as CO-releasing molecules (CORMs) [32,33]. However, their use as antitumour agents has not been well developed.…”