Photoexcitation dynamics of azide ion bound ferric myoglobin probed by femtosecond infrared spectroscopy

• Published in: Bulletin of the Korean Chemical Society Vol. 45; no. 2; pp. 171 - 177
• Main Authors: Park, Seongchul, Kim, Jooyoung, Lim, Manho
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley‐VCH Verlag GmbH & Co. KGaA 01.02.2024; 대한화학회
• Subjects: anion‐bound heme proteins; ferric heme protein; photodeligation of myoglobin; spin transition; thermal relaxation; 화학
• ISSN: 1229-5949; 0253-2964; 1229-5949
• DOI: 10.1002/bkcs.12803

The photoexcitation dynamics of N3−‐bound ferric myoglobin (MbN3) were investigated after exciting MbN3 in D2O at 283 K with a 575 nm pulse by probing the anti‐symmetric stretching mode of the azide. Global fitting of the overall time‐resolved spectra revealed that thermal relaxation of two stretching bands proceeded with a time constant of 6 ps, and that a new absorption band formed and decayed with time constants of 0.6 and 23 ps, respectively. The new absorption near 2040 cm−1 was attributed to the high‐spin species 2.4 kJ/mol above the low‐spin species, as the excited low‐spin relaxes thermally via the high‐spin species. However, this absorption could also arise from deligated N3̄ remaining within the protein. The decay of this absorption can be interpreted as either spin transition of the high‐spin species into the low‐spin species or geminate recombination of the dissociated N3̄. The implications of both interpretations are discussed.