PhotoCORMs: Light-triggered release of carbon monoxide from the coordination sphere of transition metal complexes for biological applications

Carbon monoxide is now well-established as a small-molecule biological effector in the human body. Metal-carbonyl complexes are a promising way to achieve safe and controlled delivery of CO for therapeutic applications and thus, such CO releasing molecules (CORMs) have achieved significant attention in the last 10 years. In most CORMs, the liberation of carbon monoxide is triggered by hydrolytic processes in aqueous medium and thus their half-life under physiological conditions determines their potential therapeutic utility. To overcome such limitations, photo-induced CO release from dark-stable metal-carbonyl complex prodrugs is an interesting alternative. Thus, in this review, the current knowledge on PhotoCORMs is summarized and their properties critically evaluated. The main challenge for the future will be to achieve photolytic liberation of carbon monoxide by near-IR excitation in the phototherapeutic window of the cell. Different ways how this goal might be achieved are discussed.