Journal of Physical Chemistry A, Vol.103, No.20, 3890-3903, 1999
Distance measurements in multiply labeled crystalline cytidines by dipolar recoupling solid state NMR
To systematically explore the effects of spin system size and geometry on the precision and accuracy of two-dimensional solid state NMR distance measurements, we have applied two homonuclear dipolar recoupling experiments, 2D DRAWS and 2D RFDR, to five polycrystalline samples of uniformly or selectively C-13-labeled cytidine. Distance information has been obtained from the intensities and time behavior of cross-peaks observed in the resulting two-dimensional spectra. The experimental cross-peak buildup curves obtained from these crystalline cytidine samples have been analyzed by comparison with simulations. In uniformly C-13-labeled cytidine, indirect coherence transfer mechanisms lead to low-precision distance measurements not unlike those measured in solution state NOESY experiments. In the selectively labeled cytidines, the distance measurements are considerably more precise, allowing the possibility of very accurate structure determinations from selectively or randomly labeled spin systems. Of the two techniques, the 2D DRAWS method allows identification of indirect coherence transfer mechanisms that hinder accurate distance measurement.
Keywords:NUCLEAR-MAGNETIC-RESONANCE;ANGLE SPINNING NMR;ROTATIONALRESONANCE;MAGIC-ANGLE;COUPLING-CONSTANTS;SPECTROSCOPY;C-13;C-13-C-13;SPECTRA