A simple double quantum coherence ESR sequence that minimizes nuclear modulations in Cu2+-ion based distance measurements
 

A simple double quantum coherence ESR sequence that minimizes nuclear modulations in Cu2+-ion based distance measurements

Publication date: Available online 29 May 2015
Source:Journal of Magnetic Resonance</br>
Author(s): Sharon Ruthstein , Ming Ji , Byong-kyu Shin , Sunil Saxena</br>
Double quantum coherence (DQC) ESR is a sensitive method to measure magnetic dipolar interactions between spin labels. However, the DQC experiment on Cu2+ centers presents a challenge at X-band. The Cu2+ centers are usually coordinated to histidine residues in proteins. The electron–nuclear interaction between the Cu2+ 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 Cu2+–NO system in a polyalanine-based peptide and on a coupled Cu2+ system in a polyproline-based peptide. The modified DQC data were compared with the DEER data and good agreement was found.
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