Structure-Photoreactivity Relationship of 3-Hydroxyflavone-BasedCO-Releasing Molecules

Carbon monoxide (CO) is an endogenous signalingmolecule that regulates diverse physiological processes. The therapeuticpotential of CO is hampered by its intrinsic toxicity, and its administrationposes a significant challenge. Photoactivatable CO-releasing molecules(photoCORMs) are an excellent tool to overcome the side effects ofuntargeted CO administration and provide precise spatial and temporalcontrol over its release. Here, we studied the CO release mechanism of asmall library of derivatives based on 3-hydroxy-2-phenyl-4H-benzo[g]-chromen-4-one (flavonol), previously developed as an efficient photo-CORM, by steady-state and femto/nanosecond transient absorptionspectroscopies. The main objectives of the work were to explore in detailhow to enhance the efficiency of CO photorelease fromflavonols,bathochromically shift their absorption bands, control their acid-baseproperties and solubilities in aqueous solutions, and minimize primary orsecondary photochemical side-reactions, such as self-photooxygenation. The best photoCORM performance was achieved bycombining substituents, which simultaneously bathochromically shift the chromophore absorption spectrum, enhance the formationof the productive triplet state, and suppress the singlet oxygen production by shorteningflavonol triplet-state lifetimes. In addition,the cell toxicity of selectedflavonol compounds was analyzed using in vitro hepatic HepG2 cells.