No abstract

A family of Re(I) carbonyl complexes of general formula [ReX(CO)3(phen)]0/1+ (where X = Cl−, CF3SO3−, MeCN, PPh3, and methylimidazole) derived from 1,10-phenanthroline (phen) exhibits variable emission characteristics depending on the presence of the sixth ancillary ligand/group (X). All complexes but with X = MeCN exhibit moderate CO release upon irradiation with low-power UV light and are indefinitely stable in anaerobic/aerobic environment in solution as well as in solid state when kept under dark condition. These CO donors liberate three, one, or no CO depending on the nature of sixth ligand upon illumination as studied with the aid of time-dependent IR spectroscopy. Results of excited-state density functional theory (DFT) and time-dependent DFT calculations provided insight into the origin of the emission characteristics of these complexes. The luminescent rheinum(I) photoCORMs uniformly displayed efficient cellular internalization by the human breast adenocarcinoma cells, MDA-MB-231, while the complex with PPh3 as ancillary ligand showed moderate nuclear localization in addition to the cytosolic distribution. These species hold significant promise as theranostic photoCORMs (photoinduced CO releasing molecules), where the entry of the pro-drug can be tracked within the cellular matrices.

A photoactive manganese carbonyl complex derived from dansylimidazole (Imdansyl), namely, [Mn(Imdansyl)(CO)(phen)](CFSO) (1), has been synthesized and structurally characterized. This is the first luminescent manganese carbonyl-based photoCORM reported in the literature. This complex exhibits CO release under the exclusive control of low-power broadband visible light. The corresponding rhenium carbonyl complex, namely, [Re(Imdansyl)(CO)(phen)](CFSO) (2), has also been reported, which is luminescent but sensitive only to UV-B (λ<315 nm) light. The entry of the manganese photoCORM into the human colorectal adenocarcinoma cells (HT-29) has been demonstrated with the aid of fluorescence microscopy. Irradiation of the photoCORM-loaded cancer cells to visible light leads to a dose-dependent apoptotic cell death.

A photo-active luminescent rhenium carbonyl complex namely, [Re(CO)3(phen)(pyAl)](CF3SO3) was grafted on a biocompatible carboxymethyl chitosan (CMC) matrix through Schiff base condensation reaction. The light-induced CO delivery from ReCMC has been shown to eradicate human colorectal adenocarcinoma cells (HT-29) very efficiently in a dose-dependent fashion. The onset of CO-induced apoptosis was realized by caspase-3,-7 detection aided by fluorescence confocal microscopy. ReCMC represents a unique example of a biocompatible and biodegradable antineoplastic agent that could find its use in cancer photopharmacology.