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Measuring 1 H chemical shift anisotropy (CSA) is useful for probing proton environments and dynamics but remains a challenge due to strong homonuclear interaction and relatively small shift anisotropy, especially in proteins with multiple proton sites. Here the extended chemical shift anisotropy amplification (xCSA) method is applied for amide proton CSA measurement in uniformly 2 H enriched proteins under fast magic angle spinning. The xCSA method is capable of distinguishing the sign of the CSA asymmetry parameter, complimenting other multiple-pulse recoupling methods. A three-dimensional xCSA experiment is demonstrated for measuring the proton CSA of amide sites in a GB1 protein sample and the possible correlation of amide proton CSA with protein secondary structure is discussed. [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]