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QCMP136. EPR for Biological Samples (Version 1.0)
by Frank Neese, Department of Biology, University of Konstanz, 78434 Konstanz, Germany The program EPR is a flexible and easy-to-use tool for simulating complicated EPR spectra which are often met in practice, especially in the work on biological samples. Its operation is optimized for speed and data handling but not for absolute accuracy. Since it is my belief that a large percentage of the information contained in biological EPR spectra can be extracted by means of the first-order solution to the spin- Hamiltonian, EPR represents a first-order solution to the spin-Hamiltonian. As there are no first-order effects from the nuclear Zeeman and the nuclear quadrupole interaction, these terms are omitted. A crucial feature of the program is its ability to simulate the overlapping contributions from several distinct paramagnets which are non-interacting. This complication is very often met in practice, and it seems that there is very little optimized software for this purpose. A multi-component approach is also sometimes useful in dealing with systems with zero- field splittings which are larger than the microwave energy, because the subspectra from the Kramers doublets behave approximately like distinct paramagnets. Another feature of the program is its graphical user interface which allows the user to exchange data very quickly and comfortably with the program. This helps to remove one of the more boring aspects of simulating EPR spectra. Another advantage is that simulated and experimental spectra can be directly compared and the "objective" goodness of the fit can be judged by reading the mean-square deviation between experimental and simulated spectra from the screen. Since one of the most important questions in simulating EPR spectra is how to arrive at suitable spin- Hamiltonian parameters, one should worry about a good optimization routine. Experience shows that there is no "golden method" for automatically fitting spin- Hamiltonian parameters, although the SIMPLEX method is probably most convincing in view of its stability. Therefore I have built 5 different fitting routines into the program, and users should judge for themselves the most appropriate one for the particular problem. Of course there will be situations in which none of the fitting procedures will lead to any meaningful result. Lines of Code: 47,506 Turbo PASCAL |