title: A simple double quantum coherence ESR sequence that minimizes nuclear modulations in Cu(2+)-ion based distance measurements.
abstract: Double quantum coherence (DQC) ESR is a sensitive method to measure magnetic dipolar interactions between spin labels. However, the DQC experiment on Cu(2+) centers presents a challenge at X-band. The Cu(2+) centers are usually coordinated to histidine residues in proteins. The electron-nuclear interaction between the Cu(2+) ion and the remote nitrogen in the imidazole ring can interfere with the electron-electron dipolar interaction. Herein, we report on a modified DQC experiment that has the advantage of reduced contributions from electron-nuclear interactions, which enhances the resolution of the DQC signal to the electron-electron dipolar modulations. The modified pulse-sequence is verified on Cu(2+)-NO system in a polyalanine-based peptide and on a coupled Cu(2+) system in a polyproline-based peptide. The modified DQC data were compared with the DEER data and good agreement was found.
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, United States.
authors.forename: Sharon
authors.initials: S
authors.lastname: Ruthstein
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, United States.
authors.forename: Ming
authors.initials: M
authors.lastname: Ji
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, United States.
authors.forename: Byong-Kyu
authors.initials: BK
authors.lastname: Shin
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, United States. Electronic address: sksaxena@pitt.edu.
authors.forename: Sunil
authors.initials: S
authors.lastname: Saxena
mesh_terms: D000465:Algorithms; D000595:Amino Acid Sequence; D003300:Copper / Q000737:chemistry*; D003627:Data Interpretation, Statistical; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D005583:Fourier Analysis; D006639:Histidine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009569:Nitric Oxide / Q000737:chemistry; D011487:Protein Conformation; D011506:Proteins / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D011506:Proteins; D009569:Nitric Oxide; D006639:Histidine; D003300:Copper
keywords: DQC; Distance measurement; ESR spectroscopy; Electron–electron dipolar interaction; Electron–nuclear interaction