Photolability of NO in designed metal nitrosyls with carboxamido-N donors: a theoretical attempt to unravel the mechanism

During the past few years, photoactive metal nitrosyls (NO complexes of metals) have drawn attention as potential drugs for delivery of nitric oxide (NO) to biological targets under the control of light. Major success in this area has been achieved with designed metal nitrosyls derived from ligands that contain carboxamide group(s). A number of iron, manganese and ruthenium {MNO}(6) nitrosyls of such kind exhibit excellent NO photolability under low-power visible and near-IR light. The results of theoretical studies on these NO-donors have provided insight into (a) the electronic transitions that lead to photorelease of NO and (b) the structural features of the ligands that dictate the sensitivity of the nitrosyls to light of specific wavelengths. In addition, the results have afforded clear understanding of the electronic configurations of the various nitrosyls. This article highlights these results in a coherent manner. Good matches between the predicted and observed spectral features and NO photolability strongly suggest that theoretical studies should be an integral part of the smart design of such NO-donors in the future research.