Chemical decarboxylation kinetics and identification of amino acid standards by benchtop NMR spectroscopy

Abstract

In this paper, we examined the competence of amino acids as standards for instrumental biochemical analysis. The chosen amino acids were first dissolved in various aquatic solutions and then measured in a benchtop NMR spectrometer, which is not a common choice in such analytical investigations. Analysis by mass spectrometry was used in addition. As part of these investigations, we examined and determined the stability of the amino acids ornithine, glutamic acid, alanine, glycine, proline, pyroglutamic acid, phenylalanine and trans-4-hydroxy-D-proline under critical basic and acidic pH conditions and under various other conditions. We observed that not all solutions of the amino acid standards remain stable under the given conditions and a chemical transformation takes place. Given our findings by mass spectroscopy, additional kinetic measurements were carried out with the benchtop NMR spectrometer. We discovered that pyroglutamic acid becomes unstable under basic conditions and decarboxylates to pyrrolidone.

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“…The water peak is wide and can cover the characteristic peaks of amino acids. In glutamic acid spectra, there are four characteristic peaks: (b) 2.1 ppm for CH 2 (multiplet), (c) 2.47 ppm for CH 2 (triplet), (a) 3.75 ppm for CH (triplet), and a broad NH 2 proton peak at 4.70 ppm. , In tartaric acid spectra, there are two peaks at 4.39 ppm for CH (singlet) and the other for D 2 O at 4.75 ppm. In G 2 T spectrum, the presence of pyroglutamic acid is evidenced by the presence of a new multiplet peaks at 2.46 and 4.3 ppm that are characteristic for CH 2 (b́) and CH (á), respectively, in the lactam ring of pyroglutamic acid .…”