Distance measurements in the borderline region of applicability of CW EPR and DEER: a model study on a homologous series of spin-labelled peptides.
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.
Banham
J E
JE
Centre for Advanced Electron Spin Resonance, University of Oxford, OX1 3QR, UK.
Baker
C M
CM
Ceola
S
S
Day
I J
IJ
Grant
G H
GH
Groenen
E J J
EJ
Rodgers
C T
CT
Jeschke
G
G
Timmel
C R
CR
D000465:Algorithms; D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D010455:Peptides / Q000737:chemistry*; D013113:Spin Labels
D010455:Peptides; D013113:Spin Labels