title: A simple method for determination of rotational correlation times and separation of rotational and polarity effects from EPR spectra of spin-labeled biomolecules in a wide correlation time range.
abstract: A method using nitroxide radical spin labels for determining both the isotropic rotational correlation time tau R and the environmental polarity of the label is described. By means of a least square fitting method, the values of an effective hyperfine tensor A' and of an effective g value tensor g' of randomly oriented spin labels are determined from X-band EPR spectra on the basis of an effective time-independent Hamiltonian. The traces of the tensors deliver the information about the environmental polarity of the label and are not dependent on the rotational correlation time tau R. A new averaging parameter S (tau R), calculated on the basis of the principal values of the tensor A', permits the evaluation of the rotational correlation time tau R in a very wide time range between 10(-10) and 10(-6) s. An application of this method to spin-labeled methemoglobin over a large temperature range and in environments of different polarity is discussed.
authors.affiliation: Institut für Biophysik, Ruhr-Universität Bochum, F.R.G.
authors.forename: H J
authors.initials: HJ
authors.lastname: Steinhoff
mesh_terms: D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D008433:Mathematics; D008962:Models, Theoretical; D008968:Molecular Conformation; D013113:Spin Labels
chemical_list: D013113:Spin Labels