Non-Kramers ENDOR and ESEEM of the S = 2 Ferrous Ion of [Fe(II)EDTA]2-

Ruitian Song*, Peter E. Doan, Ryszard J. Gurbiel, Bradley E. Sturgeon, Brian M. Hoffman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


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 St = 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 14N ligands of [Fe(II)EDTA]2-, K = 1.16(1) MHz, 0 ≤ η ≤ 0.05, and the analysis indicates that the electronic zero-field splitting tetragonal axis lies along the N-N direction.

Original languageEnglish (US)
Pages (from-to)291-300
Number of pages10
JournalJournal of Magnetic Resonance
Issue number2
StatePublished - Dec 1999


  • Electron spin-echo envelope modulation
  • Electron-nuclear double resonance
  • Non-Kramers
  • [Fe(II)EDTA]

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Nuclear and High Energy Physics
  • Biophysics
  • Biochemistry


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