Electron spin relaxation measurements on the blue-copper protein plastocyanin: Deviations from a power law
A R Drews1, B D Thayer, H J Stapleton
1Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.
Abstract:
Electron spin relaxation rates over the temperatue range 1.41-15.6 K are presented for the copper-containing protein plastocyanin. Measurements are described for two samples, each derived from a different preparation of equivalent purity, for which the ionic, redox, and protein compositions varied slightly. X-band data are analyzed in terms of a phonon-limited direct process and a Raman relaxation process, where the index of the Raman transport integral is treated as a fitting parameter. Both samples yield rate data at the highest temperatures that are characterized by small deviations from a simple T(n) power law dependence, with n in the range 4.8-5.2. These deviations are most easily quantified when the T(n) power law fits are compared with similar functions that allow for a finite cutoff in the phonon density of states corresponding to Debye temperatures between 90 and 100 K with n in the range 5.0-5.5.
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