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Articles you may be interested inA multifrequency high-field pulsed electron paramagnetic resonance/electron-nuclear double resonance spectrometer Rev. Sci. Instrum. 79, 064703 (2008); 10.1063/1.2937630 17O hyperfine and quadrupole interactions for water ligands in frozen solutions of high spin Mn2+

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Cytochrome P450cam (CP450cam) was studied by pulsed ENDOR and two-and four-pulse ESEEM spectroscopies. Spectra were recorded and simulated at the three principal g-values of the rhombic EPR spectrum. The four-pulse ESEEM experiment gave a direct measure of the anisotropic hyperfine interaction for the protons. Using the point dipole approximation this gives a Fe-H distance of 2.6 Å. The measured anisotropic hyperfine interaction reduced the number of hyperfine interaction parameters required to simulate the ENDOR line shapes. Both the four-pulse ESEEM frequencies and the ENDOR spectra at all three principal g-values could be satisfactorily simulated using two magnetically equivalent protons and a water orientation similar to that obtained in our previous 17 O ESEEM study. Thus, the pulsed ENDOR and four-pulse ESEEM results are self-consistent with the 17 O ESEEM data and indicate that the axial ligand is a water molecule rather than an OH -ligand. The isotropic hyperfine value derived from the numerical simulations is in agreement with previous values derived from proton NMR relaxation studies.