Light Response of Three Water-Soluble MnI PhotoCORMs: Spectroscopic Features and CO Release Investigation

Abstract

Currently, there is great interest in the study of water-soluble metal compounds capable of releasing carbon monoxide, due to their potential therapeutic use. This paper reports the synthesis, spectroscopic characteristics and CO release properties of three water-soluble manganese(I) carbonyl compounds [Mn(aaz)(CO) 3 ]Br (1; where aaz = 6-amino-6-methylperhydro-1,4-diazepine), [Mn(Me 2 aaz)(CO) 3 ]Br (2; where Me 2 aaz = 6-amino-1,4,6-trimethyl-1,4-diazacycloheptane) and [Mn(tacn)(CO) 3 ]Br (3; where tacn = 1,4,7-triazacyclononane), that can act as photoCORMs (where CORM is carbon monoxide-releasing molecule). The main aim was to propose a mechanism for the CO release. Compounds 1-3 are capable of releasing carbon monoxide when exposed to light (λ 385 and λ 410) and thus, act as photoCORMs. The formation of a biscarbonyl intermediate was identified during the photo-release process at λ 385 and the quantum yields and rates of CO release were determined. The proposed CO release mechanisms involve two steps, where photo and redox processes take place, and compounds 1 and 2 exhibit a slightly different mechanism from compound 3. A good understanding of the CO photo-release mechanism is very important with regard to the development of more efficient compounds, particularly those intended for medical applications.

Luminescent PhotoCORMs: Enabling/Disabling CO Delivery upon Blue Light Irradiation

“…After 560 s of light exposure at 453 nm, a new resonance line for both compounds is detected in the 185 ppm region and is assigned to the free carbonyl in solution. This feature is consistent with the results obtained using other techniques, such as electrochemical and infrared spectroscopy, and was also observed by our group in a previously reported work about CO release from other manganese tricarbonyl compounds . In addition, the 13 C NMR spectra of 1 and 2 also had the appearance of lower intensity signals, initially nonexistent.…”

“…This feature is consistent with the results obtained using other techniques, such as electrochemical and infrared spectroscopy, and was also observed by our group in a previously reported work about CO release from other manganese tricarbonyl compounds. 60 In addition, the 13 C NMR spectra of 1 and 2 also had the appearance of lower intensity signals, initially nonexistent. As one can see in Figure 8 for 2 and Figure S16 for 1, the new resonance lines are located at the same chemical shift as the free ligands in the spectra of both compounds after irradiation.…”

“…In fact, the calculation of a pseudo-first-order release rate was already questioned by Ford's group, which considered use of the decay of the absorbance to be a better tool for correlating the CO release process with the changes in the MLCT. 25 Furthermore, the approximations that we considered in a previous report 60 that considered only the time interval in which the biscarbonyl intermediate concentration is minimal, cannot be used due to the initial consumption of a photon to form the trigonal bipyramidal intermediate.…”

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

“…Peralta and co-workers recently synthesized three analogous water-soluble complexes 268 and 269 (R = H, CH 3 ) that sequentially release three equivalents of CO upon irradiation with blue light. 1190 The thiolato-bridged Mn Idimer 270 (Table 17) prepared from cysteamine by Westerhausen and co-workers was shown to photochemically release all 6 of its bound CO ligands. 1191 Schiller and co-workers demonstrated the photochemically controlled release of CO from non-woven polylactide fibers containing the Mn 0 decacarbonyl complex (Mn 2 (CO) 10 , CORM-1).…”

“…Accumulation of these complexes inside cells was observed by FT-IR imaging. Peralta and co-workers recently synthesized three analogous water-soluble complexes 268 and 269 (R = H, CH 3 ) that sequentially release three equivalents of CO upon irradiation with blue light . The thiolato-bridged Mn I -dimer 270 (Table ) prepared from cysteamine by Westerhausen and co-workers was shown to photochemically release all 6 of its bound CO ligands …”