In this work, the high-spin ferric form of the E7Q mutant of human neuroglobin (E7Q-NGB) is studied by X-band continuous-wave electron paramagnetic resonance (CW EPR) and hyperŸ237 sublevel correlation (HYSCORE) spectroscopy. It is shown that the use of matched pulses in the HYSCORE experiment is essential to observe the nitrogen speetral contributions. The validity of approximating the high-spin Fe(IID system (S = 5/2) as an effective S = 1/2 system is tested and the consequences for the HYSCORE simulations are highlighted. Comparative HYSCORE experiments combined with deuterium exchange experiments for aquometmyoglobin and fer¡ E7Q-NGB clearly show that the heme iron of the latter protein is pentacoordinated, tacking the distal water. Furthermore, CW EPR experiments show that, at high pH, the E10K residue is coordinating to the heme iron in this globin. These observations ate corroborated by resonance Raman experiments and could also be reproduced for other E7 mutants of human and mouse neuroglobin. Finally, the proton and nitrogen hyperfine and nuclear quadrupole parameters obtained for ferric E7Q-NGB are discussed in detail.

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Single-crystal W-band (95 GHz) electron paramagnetic resonance (EPR) studies have been performed at 20 K and at room temperature on a tetragonal Mn(III) compound with potential application as a building block for high-spin clusters. The observed EPR spectra correspond to an anisotropic high-spin S = 2 ground state and have been attributed to equivalent centers related by fourfold symmetry. Accurate values for the spin Hamiltonian parameters were obtained from the analysis of the data at both temperatures. At 20 K the contribution of fourth-order zero-field splitting terms was shown to be significant, with parameter values Bá = 0.0009(3) cm -', B = 0.0006(2) cm-' and B = 0.0017(3) cm -', to be considered together with the second-order parameters D = -1.1677(7) cm -' and E = -0.0135(6) cm -'.