Sometimes pulses just have to be perfect – An example based on the measurement of amide proton transverse relaxation rates in proteins

• Published in: Journal of magnetic resonance (1997) Vol. 349; p. 107412
• Main Authors: Rangadurai, Atul Kaushik, Toyama, Yuki, Kay, Lewis E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.04.2023
• Subjects: 1HN transverse relaxation; Amides; Cross-correlated relaxation; Multiple quantum coherences; Nuclear Magnetic Resonance, Biomolecular; Proteins; Protons; Pulse imperfections; Multiple quantum coherences; 1HN transverse relaxation; Pulse imperfections; Cross-correlated relaxation; H(N) transverse relaxation
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1016/j.jmr.2023.107412

[Display omitted] •Suppression of cross-correlation via pulses can lead to aberrant (oscillatory) relaxation curves.•Oscillations can be eliminated by using broadband inversion pulses for suppression.•Inversion profiles for these pulses must be close to perfect to avoid oscillations.•An explanation of the effect is provided. The measurement of spin relaxation rates provides a unique avenue for quantifying dynamic processes in biomolecules. In order to simplify analysis of the measurements so that a few key intuitive parameters can be extracted, it is often the case that experiments are designed to eliminate interference effects between different classes of spin relaxation. One example emerges in the measurement of amide proton (1HN) transverse relaxation rates in 15N labeled proteins, where 15N inversion pulses are applied during a relaxation element to eliminate cross-correlated spin relaxation between 1HN-15N dipole-1HN CSA interactions. We show that unless these pulses are essentially perfect, significant oscillations in magnetization decay profiles can be obtained, due to the excitation of multiple-quantum coherences, leading potentially to errors in measured R2 rates. With the recent development of experiments for quantifying electrostatic potentials via amide proton relaxation rates, the need for highly accurate measurement schemes becomes critical. Straightforward modifications to existing pulse sequences are suggested to achieve this goal.