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 low-power broad-band visible-light illumination. CO photorelease from [Mn(CO)3(pbt)(PTA)]CF3SO3 (1, where PTA = 1,3,5-triaza-7-phosphaadamantane) is accompanied by an emergence of a strong fluorescence around 400 nm from almost nonfluorescent preirradiated 1. However, [Mn(CO)3(phen)(PTA)]CF3SO3 (2) showed no such phenomenon upon prolonged illumination under similar experimental conditions. The two analogous rhenium(I) complexes, namely, [Re(CO)3(pbt)(PTA)]CF3SO3 (3) and [Re(CO)3(phen)(PTA)]CF3SO3 (4), have also been synthesized and characterized to compare their photo properties with the manganese congeners. Complexes 3 and 4 exhibit moderate CO release upon irradiation with low-power UV light. 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 3 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 (1 and 2) have been applied to assess the cell viability of these malignant cells upon CO delivery.