Gradient-enhanced heteronuclear correlation spectroscopy: theory and experimental aspects. 1992

A detailed theoretical and experimental treatment is given for gradient-enhanced heteronuclear correlation spectroscopy. Both multiple-quantum and single-quantum sequences are described. In addition to a comparison with conventional experiments using phase cycling, the effects of different gradient combinations are examined with respect to artifacts occurring in the heteronuclear dimension. The influence of gradient performance and diffusion on sensitivity is discussed. Approaches to attain phase-sensitive spectra are also analyzed.     

Determination of U and Ra in rock samples by gamma-spectrometric method

A gamma-spectrometric method independent of radon escape for the determination of U and Ra in rock samples based on the 63 keV and 1001 keV as well as 185 keV lines is described and discussed. A simple experimental procedure is given for the determination of the self-absorption factor. The method has been applied for the determination of uranium and radium in rock samples from Morocco containing uranium between 17.5 wt.% and 0.026 wt.%. The limits of determination, at 95% confidence level and 10% standard deviation, for the 63 keV and 1001 keV lines were found to be 0.075 wt.% and 0.62 wt.%, respectively, using samples of 6 g and chosing 1 h measuring time.     

A two-dimensional artifact from asynchronous decoupling

Many heteronuclear NMR experiments employ decoupling to collapse the heteronuclear multiplet, using decoupling schemes with a periodic phase modulation like WALTZ, MLEV, or GARP. Because of the periodic nature of these schemes, cycling sidebands are generated, whose intensity can be strongly reduced by decoupling asynchronously. We show that the most common implementation of asynchronous decoupling on modern spectrometers is such that the cycling sidebands are subjected to a periodic modulation. For multidimensional experiments, this results in ridges that can seriously compromise the quality of the spectrum. Based on our model, the artifact in a 2D [(1)H]-(15)N NOE equilibrium experiment is simulated and it is shown that the artifact can be prevented by using synchronous decoupling.     

CEESY: characterizing the conformation of unobservable protein states

Protein conformations that are only marginally populated often play important roles as intermediate states in many processes such as ligand binding, enzyme catalysis, allostery, and protein folding. An NMR method is presented that can give valuable information about the structure of these "excited states" by measuring the relative position of exchanging excited- and ground-state resonances using a single 2D spectrum. This new approach can be applied to any nucleus, which will facilitate a complete structural characterization of these states.