1H-14N HSQC detection of choline-containing compounds in solutions

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 (0.6 Hz to methyl protons, 2.7 Hz to CH2O protons and 0.2 Hz 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 1 mM choline solution in 16 min on a 500 MHz 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.