title: Non-kramers ENDOR and ESEEM of the S = 2 ferrous ion of [Fe(II)EDTA](2-).
abstract: We report here the first non-Kramers (NK) ESEEM and ENDOR study of a mononuclear NK center, presenting extensive parallel-mode ESEEM and ENDOR measurements on the S(t) = 2 ferrous center of [Fe(II)ethylenediamine-N,N,N',N'-tetraacetato](2-); [Fe(II)EDTA)](2-). The results disclose an anomalous equivalence of the experimental patterns produced by the two techniques. A simple theoretical treatment of the frequency-domain patterns expected for NK-ESEEM and NK-ENDOR rationalizes this correspondence and further suggests that the very observation of NK-ENDOR is the result of an unprecedentedly large hyperfine enhancement effect. The mixed nitrogen-carboxylato oxygen coordination of [Fe(II)EDTA](2-) models that of the protein-bound diiron centers, although with a higher coordination number. Analysis of the NK-ESEEM measurements yields the quadrupole parameters for the (14)N ligands of [Fe(II)EDTA](2-), K = 1.16(1) MHz, 0 </= eta </= 0.05, and the analysis indicates that the electronic zero-field splitting tetragonal axis lies along the N-N direction.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: R
authors.initials: R
authors.lastname: Song
authors.forename: P E
authors.initials: PE
authors.lastname: Doan
authors.forename: R J
authors.initials: RJ
authors.lastname: Gurbiel
authors.forename: B E
authors.initials: BE
authors.lastname: Sturgeon
authors.forename: B M
authors.initials: BM
authors.lastname: Hoffman
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004492:Edetic Acid / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005296:Ferrous Compounds / Q000737:chemistry*; D008962:Models, Theoretical
chemical_list: D005296:Ferrous Compounds; D004492:Edetic Acid