Targeted F 19 - tags to detect amino acids in complex mixtures using NMR spectroscopy

Nuclear magnetic resonance spectroscopy of fluorine-19 nucleus ( ${}^{19}F$ -NMR) emerges as a powerful tool because of the high sensitivity due to its high natural abundance, broad spectral range, and the simplicity of a spin-half system. However, it is still seldom utilized in the chemistry classroom or research. This article thus aims to demonstrate the power of NMR by investigating the kinetics when a ${}^{19}F-\text{tag}$ reacts with individual amino acids (AA) and eventually utilizing the approach to identify and quantify various AAs from a complex mixture such as a metabolomics sample. The ${}^{19}F-\text{tag}$ named 2,5-dioxopyrrolidin-1-yl-2-(trifluoromethyl)benzoate was synthesized following a previously established method. The reaction kinetics of the tag was then continuously measured using ${}^{19}F$ NMR in the presence of selected AAs. The estimated reaction rate constants to form the ${}^{19}F-\text{tags}$ with each AA differ, which could be used as an identification tool. The tag formations were typically completed in 24-48 h in water for all the samples. These demonstrations suggest that ${}^{19}F-\text{tags}$ could form the basis for chemical kinetics and AA detection using ${}^{19}F$ -NMR.