Non-kramers ENDOR and ESEEM of the S = 2 ferrous ion of [Fe(II)EDTA](2-) |
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Authors: | Song R Doan P E Gurbiel R J Sturgeon B E Hoffman B M |
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Institution: | Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA. |
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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. |
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