title: Coherence transfer and electron T1-, T2-relaxation in nitroxide spin labels.
abstract: Abragam's double-commutator spin operator method is used to analyse: 1) electron coherence transfer by intermolecular dipolar interaction between spin-label radicals, and 2) longitudinal and transverse electron spin relaxation by rotational modulation of the Zeeman and nitrogen-hyperfine anisotropies of isolated nitroxide spin labels. Results compatible with earlier treatments by Redfield theory are obtained without specifically evaluating matrix elements. Extension to single-transition operators for isolated nitroxides predicts electron coherence transfer by pseudosecular electron-nuclear dipolar interaction, in the absence of intermolecular dipolar coupling. This explains earlier experimental findings that coherence transfer (specifically dispersion-like distortion of the EPR absorption line shape) does not extrapolate to zero at low concentrations of nitroxide spin labels.
authors.affiliation: Max-Planck-Institut für biophysikalische Chemie, 37070 Göttingen, Germany; University of Southern Denmark, MEMPHYS-Centre for Biomembrane Physics, Campusvej 55, 5230 Odense M, Denmark. Electronic address: dmarsh@gwdg.de.
authors.forename: Derek
authors.initials: D
authors.lastname: Marsh
keywords: Dipole-dipole interaction; Dispersion admixture; Double commutator; EPR; Longitudinal and transverse relaxation; Spin operator; Transverse magnetisation transfer