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Carr–Purcell–Meiboom–Gill (CPMG) relaxation dispersion is a powerful NMR method to study protein dynamics on the microsecond–millisecond time scale. J -coupling, resonance offset, radio frequency field inhomogeneity, and pulse imperfection often introduce systematic errors into the measured transverse relaxation rates. Here we proposed a modified continuous wave decoupling CPMG experiment, which is more unaffected by resonance offset and pulse imperfection. We found that it is unnecessary to match the decoupling field strength with the delay between CPMG refocusing pulses, provided that decoupling field is strong enough. The performance of the scheme proposed here was shown by simulations and further demonstrated experimentally on a fatty acid binding protein. [ABSTRACT FROM AUTHOR]

Abstract: Choline nitrogen (14N) has a long relaxation time (seconds) which is due to the highly symmetric chemical environments. 14N in choline also has coupling constants with protons (0.6Hz to methyl protons, 2.7Hz to CH2O protons and 0.2Hz to NCH2 protons). Based on these properties, we introduce a two-dimensional NMR method to detect choline and its derivatives in solutions. This method is the 1H–14N hetero-nuclear single-quantum correlation (HSQC) experiment which has been developed in solid-state NMR in recent years. Experiments have demonstrated that the 1H–14N HSQC technique is a sensitive method for detection of choline-containing compounds in solutions. From 1mM choline solution in 16min on a 500MHz NMR spectrometer, a 1H–14N HSQC spectrum has been recorded with a signal-to-noise ratio of 1700. Free choline, phosphocholine and glycerophosphocholine in milk can be well separated in 1H–14N HSQC spectra. This technique would become a promising analytical approach to mixture analyses where choline-containing compounds are of interest, such as tissue extracts, body fluids and food solutions. [ABSTRACT FROM AUTHOR]