| Autor: |
Jodts RJ; Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States., Wittkop M; Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States., Ho MB; Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States., Broderick WE; Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States., Broderick JB; Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States., Hoffman BM; Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States., Mosquera MA; Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States. |
| Abstrakt: |
The radical S -adenosyl methionine (SAM) enzyme superfamily has widespread roles in hydrogen atom abstraction reactions of crucial biological importance. In these enzymes, reductive cleavage of SAM bound to a [4Fe-4S] 1+ cluster generates the 5'-deoxyadenosyl radical (5'-dAdo•) which ultimately abstracts an H atom from the substrate. However, overwhelming experimental evidence has surprisingly revealed an obligatory organometallic intermediate Ω exhibiting an Fe-C5'-adenosyl bond, whose properties are the target of this theoretical investigation. We report a readily applied, two-configuration version of broken symmetry DFT, denoted 2C-DFT, designed to allow the accurate description of the hyperfine coupling constants and g-tensors of an alkyl group bound to a multimetallic iron-sulfur cluster. This approach has been validated by the excellent agreement of its results both with those of multiconfigurational complete active space self-consistent field computations for a series of model complexes and with the results from electron nuclear double-resonance/electron paramagnetic resonance spectroscopic studies for the crystallographically characterized complex, M-CH 3 , a [4Fe-4S] cluster with a Fe-CH 3 bond. The likewise excellent agreement between spectroscopic results and 2C-DFT computations for Ω confirm its identity as an organometallic complex with a bond between an Fe of the [4Fe-4S] cluster and C5' of the deoxyadenosyl moiety, as first proposed. |
