title: On Cu(II)-Cu(II) distance measurements using pulsed electron electron double resonance.
abstract: The effects of orientational selectivity on the 4-pulse electron electron double resonance (PELDOR) ESR spectra of coupled Cu(II)-Cu(II) spins are presented. The data were collected at four magnetic fields on a poly-proline peptide containing two Cu(II) centers. The Cu(II)-PELDOR spectra of this peptide do not change appreciably with magnetic field at X-band. The data were analyzed by adapting the theory of Maryasov, Tsvetkov, and Raap [A.G. Maryasov, Y.D. Tsvetkov, J. Raap, Weakly coupled radical pairs in solids:ELDOR in ESE structure studies, Appl. Magn. Reson. 14 (1998) 101-113]. Simulations indicate that orientational effects are important for Cu(II)-PELDOR. Based on simulations, the field-independence of the PELDOR data for this peptide is likely due to two effects. First, for this peptide, the Cu(II) g-tensor(s) are in a very specific orientation with respect to the interspin vector. Second, the flexibility of the peptide washes out the orientation effects. These effects reduce the suitability of the poly-proline based peptide as a good model system to experimentally probe orientational effects in such experiments. An average Cu(II)-Cu(II) distance of 2.1-2.2 nm was determined, which is consistent with earlier double quantum coherence ESR results.
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA.
authors.forename: Zhongyu
authors.initials: Z
authors.lastname: Yang
authors.forename: James
authors.initials: J
authors.lastname: Becker
authors.forename: Sunil
authors.initials: S
authors.lastname: Saxena
mesh_terms: D003300:Copper / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D010455:Peptides / Q000737:chemistry*; D011392:Proline / Q000737:chemistry*; D012815:Signal Processing, Computer-Assisted