It is salutary to look back for a moment to some of the earliest publications that brought together biological EPR data some 40 years ago, and I have in mind particularly the conference volume, Magnetic Resonance in Biological Systems, edited by Ehrenberg, Malmström, and Vanngård . In those days the reports were all based on continuous-wave (CW) EPR, computer simulations were in their infancy, ENDOR (Electron Nuclear Double Resonance) was dominantly still, but not exclusively, found in condensed matter physics and to some extent in chemistry. Pulsed EPR methods had not been applied at that time to biological systems. In those early days dominated by CW EPR it was tempting to think there was a universal EPR experiment — about 4 mW microwave power with a Varian rectangular cavity, 4 gauss modulation, and a relatively slow field sweep. One was aware of the role played by power saturation and sometimes passage effects, especially at lower temperatures, but on the whole these were avoided rather than exploited.
KeywordsMagnetic Resonance Image Contrast Agent ENDOR Spectrum Electron Spin Echo Envelope Modulation Spin Hamiltonian Parameter Biological Magnetic Resonance
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