Synthesis, Structures, and CO Release Capacity of a Family of Water-Soluble PhotoCORMs: Assessment of the Biocompatibility and Their Phototoxicity toward Human Breast Cancer Cells

Two manganese­(I) carbonyl complexes derived from 2-(pyridyl)­benzothiazole (pbt) and 1,10-phenanthroline (phen) release carbon monoxide (CO) under <i>low-power</i> broad-band <i>visible-light</i> illumination. CO photorelease from [Mn­(CO)₃(pbt)­(PTA)]­CF₃SO₃ (<b>1</b>, where PTA = 1,3,5-triaza-7-phosphaadamantane) is accompanied by an emergence of a strong fluorescence around 400 nm from almost nonfluorescent preirradiated <b>1</b>. However, [Mn­(CO)₃(phen)­(PTA)]­CF₃SO₃ (<b>2</b>) showed no such phenomenon upon prolonged illumination under similar experimental conditions. The two analogous rhenium­(I) complexes, namely, [Re­(CO)₃(pbt)­(PTA)]­CF₃SO₃ (<b>3</b>) and [Re­(CO)₃(phen)­(PTA)]­CF₃SO₃ (<b>4</b>), have also been synthesized and characterized to compare their photo properties with the manganese congeners. Complexes <b>3</b> and <b>4</b> exhibit moderate CO release upon irradiation with low-power <i>UV light</i>. All four complexes are highly soluble in anaerobic/aerobic aqueous media and are also considerably more stable when kept under dark conditions. The inherently luminescent rhenium complex <b>3</b> was utilized to demonstrate cellular internalization of these types of compounds by MDA-MB-231 (human breast cancer) cells, while the two biocompatible manganese­(I) complexes (<b>1</b> and <b>2</b>) have been applied to assess the cell viability of these malignant cells upon CO delivery