Quantum-Mechanical Driven 1H Iterative Full Spin Analysis Addresses Complex Peak Patterns of Choline Sulfate

Choline and choline esters are essential nutrients in biological systems for carrying out normal functions, such as the modulation of neurotransmission and the formation and maintenance of cell membranes. Choline sulfate is reportedly involved in the defense mechanism of accumulating sulfur resources against sulfur deficiency. Contrary to expectations, a full assignment of the 1H NMR spectrum of choline sulfate has not been reported. The present study pioneered a full assignment by quantum-mechanical driven 1H iterative full spin analysis. The complex peak patterns were analyzed in terms of heteronuclear and non-first-order coupling. The 1H–14N coupling constants, including two-bond coupling, which can be neglected, were accurately determined by iterative optimization. Non-first-order splitting has been described to be due to the presence of magnetically non-equivalent geminal protons. Moreover, in the comparison of the methylene proton resonance patterns of choline sulfate with choline and choline phosphate, the differences in the geminal and vicinal coupling constants were further examined through spectral simulation excluding the heteronuclear coupling. The precise spectral interpretation provided in this study is expected to contribute to future 1H NMR-based qualitative or quantitative studies of choline sulfate-containing sources.