Abstract
Abstract The initial-slope and full-relaxation-matrix methods of extracting internuclear distances from NOE data are examined with special emphasis on the effect of the geometrical arrangement of the spins on the accuracy of the ratios of distances determined. The source of geometric error may be understood in terms of the relationship of molecular conformation to the relative sizes of the eigenvalues of the NOE relaxation matrix. If these eigenvalues differ greatly in magnitude, large distance errors may result. It is shown tha for certain molecular geometries the distance between spins may be accurately measured by either method, while some geometries require the full-matrix analysis for accuracy. There are a few structures which cannot be resolved by either procedure. These distinctions are revealed by an analytical solution for the homonuclear NOE in an isotropically tumbling three-spin system in the limit of long correlation time. This solution was utilized to obtain computer simulation of the NOE for a variety of geometrical arrangements. Contour maps are presented to depict the errors in the distances determined from NOE and to indicate exactly which structures are resistant to NOE analysis.
Published Version
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