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- Title
Examples of high-frequency EPR studies in bioinorganic chemistry.
- Authors
Andersson, K. Kristoffer; Schmidt, Peter P.; Katterle, Bettina; Strand, Kari R.; Palmer, Amy E.; Sang-Kyu Lee; Solomon, Edward I.; Gräslund, Astrid; Barra, Anne-Laure
- Abstract
Low-temperature EPR spectroscopy with frequencies between 95 and 345 GHz and magnetic fields up to 12 T has been used to study metal sites in proteins or inorganic complexes and free radicals. The high-field EPR method was used to resolve g-value anisotropy by separating it from overlapping hyperfine couplings. The presence of hydrogen bonding interactions to the tyrosyl radical oxygens in ribonucleotide reductases were detected. At 285 GHz the g-value anisotropy from the rhombic type 2 Cu(II) signal in the enzyme laccase has its g-value anisotropy clearly resolved from slightly different overlapping axial species. Simple metal site systems with S>½ undergo a zero-field splitting, which can be described by the spin Hamiltonian Hs = βSgB+D[Sz2 - S(S +1)/3+(E/D)(Sx2-Sy2]. From high-frequency EPR, the D values that are small compared to the frequency (high-field limit) can be determined directly by measuring the distance of the outermost signal to the center of the spectrum, which corresponds to (2S-)∗ |D|. For example, D values of 0.8 and 0.3 cm-1 are observed for S=5/2 Fe(III)-EDTA and transferrin, respectively. When D values are larger compared to the frequency and in the case of half-integer spin systems, they can be obtained from the frequency dependence of the shifts of geff, as observed for myoglobin in the presence (D=5 cm-1) or absence (D=9.5 cm-1) of fluoride. The 285 and 345 GHz spectra of the Fe(II)-NO-EDTA complex show that it is best described as a S=3/2 system with D=11.5 cm)1, E=0.1 cm-1, and gx=gy=gz=2.0. Finally, the effects of HF-EPR on X-band EPR silent states and weak magnetic interactions are demonstrated.
- Subjects
ELECTRON paramagnetic resonance; SPECTRUM analysis; CRYOBIOCHEMISTRY; FREE radicals; HYDROGEN bonding; CARRIER proteins
- Publication
Journal of Biological Inorganic Chemistry (JBIC), 2003, Vol 8, Issue 3, p235
- ISSN
0949-8257
- Publication type
Article
- DOI
10.1007/s00775-002-0429-0