Dinuclear PhotoCORMs: Dioxygen-Assisted Carbon Monoxide Uncaging from Long-Wavelength-Absorbing Metal-Metal-Bonded Carbonyl Complexes.

We describe a new strategy for triggering the photochemical release of caged carbon monoxide (CO) in aerobic media using long-wavelength visible and near-infrared (NIR) light. The dinuclear rhenium-manganese carbonyl complexes (CO)5ReMn(CO)3(L), where L = phenanthroline (1), bipyridine (2), biquinoline (3), or phenanthrolinecarboxaldehyde (4), each show a strong metal-metal-bond-to-ligand (σMM → πL*) charge-transfer absorption band at longer wavelengths. Photolysis with deep-red (1 and 2) or NIR (3 and 4) light leads to homolytic cleavage of the Re-Mn bonds to give mononuclear metal radicals. In the absence of trapping agents, these radicals primarily recombine to reform dinuclear complexes. In oxygenated media, however, the radicals react with dioxygen to form species much more labile toward CO release via secondary thermal and/or photochemical reactions. Conjugation of 4, with an amine-terminated poly(ethylene glycol) oligomer, gives a water-soluble derivative with similar photochemistry. In this context, we discuss the potential applications of these dinuclear complexes as visible/NIR-light-photoactivated CO-releasing moieties (photoCORMs).

Photocatalytic carbon disulfide production via charge transfer quenching of quantum dots.

Carbon disulfide, a potentially therapeutic small molecule, is generated via oxidative cleavage of 1,1-dithiooxalate (DTO) photosensitized by CdSe quantum dots (QDs). Irradiation of DTO-QD conjugates leads to λ(irr) independent photooxidation with a quantum yield of ~4% in aerated pH 9 buffer solution that drops sharply in deaerated solution. Excess DTO is similarly decomposed, indicating labile exchange at the QD surfaces and a photocatalytic cycle. Analogous photoreaction occurs with the O-tert-butyl ester (t)BuDTO in nonaqueous media. We propose that oxidation is initiated by hole transfer from photoexcited QD to surface DTO and that these substrates are a promising class of photocleavable ligands for modifying QD surface coordination.

A luminescent and biocompatible photoCORM.

The water-soluble rhenium(I) complex fac-[Re(bpy)(CO)(3)(thp)](+) (1) [CF(3)SO(3)(-) salt; bpy = 2,2'-bipyridine, thp = tris(hydroxymethyl)phosphine] is both strongly luminescent and photoactive toward carbon monoxide release. It is stable in aerated aqueous media, is incorporated into cells from the human prostatic carcinoma cell line PPC-1, and shows no apparent cytotoxicity. Furthermore, the solvated Re(I) photoproduct of CO release (2) is also luminescent, a feature that allows one to track the transformation of 1 to 2 inside such cells using confocal fluorescence microscopy. In this context, 1 is a very promising candidate as a photoactivated CO releasing moiety (photoCORM) with potential therapeutic applications.

Flash and continuous photolysis kinetic studies of the iron-iron hydrogenase model (µ-pdt)[Fe(CO)3]2 in different solvents.

Flash and continuous photolysis studies of (µ-pdt)[Fe(CO)(3)](2) under excess CO were conducted in coordinating and noncoordinating solvents. The back-reaction of CO with the photoproduct showed second-order kinetics with k(CO) values of 1.0 × 10(8), 3.4 × 10(6), 1.2 × 10(6), and 0.90 M(-1) s(-1) in hexanes, benzene, toluene, and THF, respectively. These data indicate a solvent-coordinated intermediate as one photoproduct, but other long-lived species were also apparent.

A photoCORM nanocarrier for CO release using NIR light.

A water-soluble nanocarrier for a photo-activated CO releasing moiety (photoCORM) that can be triggered with NIR excitation is described. This has an upconversion nanoparticle core encapsulated by an amphiphilic polymer imparting both water solubility and a hydrophobic interior containing the photoCORM trans-Mn(bpy)(PPh3)2(CO)2. Such an ensemble offers a unique strategy for CO delivery to biological targets.