Ultrafast Photochemical Dynamics of Dinitrosyl Iron Complexes Investigated by Femtosecond Time-Resolved Infrared Spectroscopy

Dinitrosyl iron complexes (DNICs) are the most abundant nitric oxide (NO) metabolites in NO-producing cells and can be used as a platform for photochemical vehicles for NO donors. However, not much is known about the photochemical dynamics of DNICs. This study investigates the photoexcitation dynamics of a mononuclear DNIC ligated with 2-mercaptoethanol, [(HOCH2CH2S)2Fe(NO)2]−, in D2O solution through femtosecond infrared spectroscopy. Approximately 70% of the excited [(HOCH2CH2S)2Fe(NO)2]− at 400 nm relaxes back to the ground state with a time constant of 270 ps, and the remaining dissociates NO− with a time constant of 630 ps. The resulting mononitrosyl iron complex, [(HOCH2CH2S)2Fe(NO)(D2O)2], formed by a rapid coordination of D2O molecule to the nascent photoproduct, [(HOCH2CH2S)2Fe(NO)], reacts with the abundant thiolate, HOCH2CH2S−, in solution, producing [(HOCH2CH2S)3Fe(NO)]− with a rate constant of 1.3 × 107 M−1s−1. The detailed photochemical dynamics described herein lays the groundwork for the development of NO− donors using DNICs with controlled and tunable photoreactivity for potential therapeutic applications.