title: Distance measurements in the borderline region of applicability of CW EPR and DEER: a model study on a homologous series of spin-labelled peptides.
abstract: Inter-spin distances between 1 nm and 4.5 nm are measured by continuous wave (CW) and pulsed electron paramagnetic resonance (EPR) methods for a series of nitroxide-spin-labelled peptides. The upper distance limit for measuring dipolar coupling by the broadening of the CW spectrum and the lower distance limit for the present optimally-adjusted double electron electron resonance (DEER) set-up are determined and found to be both around 1.6-1.9 nm. The methods for determining distances and corresponding distributions from CW spectral line broadening are reviewed and further developed. Also, the work shows that a correction factor is required for the analysis of inter-spin distances below approximately 2 nm for DEER measurements and this is calculated using the density matrix formalism.
authors.affiliation: Centre for Advanced Electron Spin Resonance, University of Oxford, OX1 3QR, UK.
authors.forename: J E
authors.initials: JE
authors.lastname: Banham
authors.forename: C M
authors.initials: CM
authors.lastname: Baker
authors.forename: S
authors.initials: S
authors.lastname: Ceola
authors.forename: I J
authors.initials: IJ
authors.lastname: Day
authors.forename: G H
authors.initials: GH
authors.lastname: Grant
authors.forename: E J J
authors.initials: EJ
authors.lastname: Groenen
authors.forename: C T
authors.initials: CT
authors.lastname: Rodgers
authors.forename: G
authors.initials: G
authors.lastname: Jeschke
authors.forename: C R
authors.initials: CR
authors.lastname: Timmel
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry*; D013113:Spin Labels
chemical_list: D010455:Peptides; D013113:Spin Labels