Trapping and Electron Paramagnetic Resonance Characterization of the 5′dAdo • Radical in a Radical S -Adenosyl Methionine Enzyme Reaction with a Non-Native Substrate
- Award ID(s):
- 1905336
- Publication Date:
- NSF-PAR ID:
- 10174639
- Journal Name:
- ACS Central Science
- Volume:
- 5
- Issue:
- 11
- Page Range or eLocation-ID:
- 1777 to 1785
- ISSN:
- 2374-7943
- Sponsoring Org:
- National Science Foundation
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The millimeter/submillimeter-wave spectrum of the SiP radical (X 2 Π i ) has been recorded using direct absorption spectroscopy in the frequency range of 151–532 GHz. SiP was synthesized in an AC discharge from the reaction of SiH 4 and gas-phase phosphorus, in argon carrier gas. Both spin–orbit ladders were observed. Fifteen rotational transitions were measured originating in the Ω = 3/2 ladder, and twelve in the Ω = 1/2 substate, each exhibiting lambda doubling and, at lower frequencies, hyperfine interactions from the phosphorus nuclear spin of I = 1/2. The lambda-doublets in the Ω = 1/2 levels appeared to be perturbed at higher J, with the f component deviating from the predicted pattern, likely due to interactions with the nearby excited A 2 Σ + electronic state, where ΔE Π-Σ ∼ 430 cm −1 . The data were analyzed using a Hund’s case a β Hamiltonian and rotational, spin–orbit, lambda-doubling, and hyperfine parameters were determined. A 2 Π/ 2 Σ deperturbation analysis was also performed, considering spin–orbit, spin-electronic, and L-uncoupling interactions. Although SiP is clearly not a hydride, the deperturbed parameters derived suggest that the pure precession hypothesis may be useful in assessing the 2 Π/ 2 Σ interaction. Interpretation ofmore »