Quantitative small molecule NOESY. A practical guide for derivation of cross‐relaxation rates and internuclear distances

Abstract

Abstract The pure absorption 2D NOE experiment can provide small molecule cross‐relaxation rate data suitable for quantitative conformational analysis even when the data are collected in a time‐saving manner using preparatory delays (PD) far short of the recommended values of 3–5 times T 1 . In our experience, the relative NOE intensities and cross‐relaxation rates are most readily extracted from cross‐relaxation spectra which are sums of adjacent rows (or columns) of the 2D data matrix. Intensity anomalies associated with t 1 streaks can be removed by plotting cross‐relaxation difference spectra. PD truncation produces significant deviations from diagonal symmetry which must be accounted for in the data analysis. The influence of PD truncation on apparent auto‐peak decay rates and cross‐/auto‐peak intensity ratios is examined in both real and simulated spectra in order to develop appropriate quantitation strategies. These strategies, when applied to NOESY data for aqueous prostaglandin (PG) F 2 α and a PG analog in organic media, yield cross‐relaxation rates that are within experimental error of those calculated from structural models or determined by more time‐consuming 1D NOE methods.