Pulse Programme Considerations for Quantitative NOE Analysis

Accurate NOE/ROE-based distance determination is a crucial tool in stereochemistry and conformational analysis of both protein and small molecule structure elucidation. Despite being widely used in countless fields of chemistry and biology, the factors determining the accuracy of the obtained distances are sometimes neglected. Herein, we present the systematic analysis of the performance of six commonly used NOESY and ROESY pulse programmes for quantitative NOE/ROE analysis, evaluating the quality of the data based on the number of quantifiable correlations and the accuracy of the corresponding NOE-derived interproton distances. The effect of two solvent suppression schemes on the NOE/ROE quantitativity is assessed. We found that the total number of quantifiable correlations and the errors of the derived distances depend on the pulse programme used, and the error increases drastically when two or more spectra are removed from the build-up curves for the generation of NOE/ROE build-up rates, using the initial-rate approximation. Solvent suppression using excitation sculpting results in the underestimation of the NOE-derived distances. EASY ROESY run without solvent suppression shows a bias towards overestimated NOE-derived distances. The obtained data suggest that the determination of quantitative interproton distances necessitates the careful selection of pulse programme.