The program package MAGRES (MAcnetic msonance) is able to calculate e.s.r., ENDOR (without relaxation) and ESEEM spectra for, in principle, any spin system in single crystals as well as in powders. The spin Hamiltonian may be constructed from electron and/or nuclear Zeeman interactions, exchange and hyperfine couplings, zero-field splittings and nuclear quadrupole interactions. For the calculation of eigenvalues and eigenvectors the program uses exact diagonalization, hence no assumptions have to be made about the relative magnitude of the various interactions. Comparison of the calculated with the experimental frequencies of singlecrystal spectra permits the optimization of the interaction tensors. The computed tensors may be checked by comparison of the experimental and the calculated intensities of single-crystal and powder spectra. Simulation of ESEEM spectra is possible for the two-and three-pulse sequence, and the effect of the dead-time may be included. The program can also be used for the calculation of C.W. n.m.r. spectra. * pulse profile WIDTH 100.0 * pulse width TAU 0.200 * time between pulses 1 and 2 (3-pulse DEADTIME 0.800 TIME SAVE MAGNITUDE SAVE POWDER 30 * 2250 integration points in powder calculation SHAPE GAUSSIAN DERIVATIVE CHANNELS 0.01953125 WRITE * plotting info OUTPUT LAST PLOTTING SWEEP FREQUENCY SPECTRUM 3123.0 2.5 2.5 8409.0 I S 0 -0.38 xz -0.015 * electron S = 1/2; tensor 1 * copper I = 3/2; tensor 2 * sequence) * save time-domain spectrum on file * save magnitude spectrum on file 0.075* lineshape and linewidth * specification of output options : plotting * frequency swept ESEEM spectrum from 0 to * 5 M H z * magnetic field : 3 123.0 G * excitation frequency : 8409.0 MHz START

Vanadium bromoperoxidase from the brown seaweed Ascophyllum nodosum was studied with electron spin echo envelope modulation (ESEEM) spectroscopy. After comparing the Fourier transformed (FT) ESEEM spectra with those of a number of vanadyl model compounds, it could be concluded that nitrogen is present in the equatorial plane of the vanadyl cation of reduced bromoperoxidase (14N frequencies occurred at 3.1, 4.2, 5.3 and 8.1 MHz). Furthermore, the FT‐ESEEM spectra of reduced bromoperoxidase exhibited an intense 1H modulation (13.8 MHz), which was completely replaced by a deuterium modulation at ∼2 MHz when bromoperoxidase was dissolved in D2O, instead of H2O. These latter data confirm earlier EPR experiments on reduced bromoperoxidase [(1988) Biochemistry 27, 1629–1635], showing that the oxo‐vanadium (IV) ion is coupled to exchangeable protons.

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The crystal structure of the complex [Cun(mnt)2]1 2'[MB+]2-(acetone) [CuC4oN10S6H36'C3H60] is reported, where mnt = maleonitriledithiolato (C4N2S2)2" and MB+ = the methylene blue cation = 3,9-bis(dimethylamino)phenazothionium.The space group is PI, with a = 10.346 (3) A, b = 14.522 (3) A, c = 15.524 (5) A, a = 93.69 (3)°, ß = 90.69 (2)°, y = 105.87 (3)°, and with Z = 2. The residuals are R = 4.4% and Pw = 4.4% for 4235 independent reflections collected with a diffractometer using Mo Ka radiation. The MB+ cations are stacked along the c axis. The [Cu(mnt)2]2" anions are paired, these pairs being stacked along the c axis as well. The anions have approximately D2 symmetry with a dihedral angle of 47.4°between the planes of the ligands. The copper-sulfur distances range from 2.240 (2) to 2.261 (2) A. Susceptibility measurements reveal an antiferromagnetic exchange coupling. An exchange J of -2.6 cm"1 was derived from a fit of a singlet-triplet model to the experimental data. Single-crystal EPR spectra are in accord with a triplet state of two coupled Cu(II) ions. The experimental g, copper hyperfine, and zero-field splitting tensors are compared with tensors which are calculated from semiemperical molecular orbital data.

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