Interference by Nitrous Acid Decomposition in the Kinetic Study of Nitrosation Reactions

Abstract

Under the acidic conditions of the stomach lumen, nitrosation reactions can occur in the human body between nitrite (added to meat because of its antibotulinic properties) and many compounds such as amino acids. From the results obtained, two conclusions can be drawn: (i) In the quantitative study of nitrosation reactions, it is necessary to take into account the competing reaction of HNO 2 decomposition, which in some conditions is the dominant reaction; (ii) two alternative approaches based on the initial rate method are necessary to assess the weight of nitrous acid decomposition using taurine and homotaurine as nitrosatable substrates. In strongly acidic media, the decomposition reaction is dominant: In the case of taurine, the decomposition rate is negligible at pH ≥ 3.2. In the pH 3.2−2.5 range, decomposition is lower than nitrosation but not negligible, and at pH ≤ 2.5 decomposition is faster than nitrosation. With homotaurine, HNO 2 decomposition is negligible at pH higher than 4.1. In the pH 4.1−2.8 range, nitrosation is faster but decomposition should be considered, and at pH ≤ 2.8 decomposition is the dominant reaction. C

Mutagenic products are promoted in the nitrosation of tyramine

“…These results are akin to those observed in the nitrosation of other amines (Arenas-Valgañón, González-Pérez, Gómez Bombarelli, González-Jiménez, Calle, & Casado, 2014;García-Santos, González-Mancebo, Hernández-Benito, Calle, & Casado, 2002), in which the reaction rate was diffusion controlled and the effective nitrosating agent was dinitrogen trioxide, N2O3 (Arenas-Valgañón, Gómez Bombarelli, González-Pérez, González-Jiménez, Calle, & Casado, 2012;Casado, Castro, Leis, López-Quintela, & Mosquera, 1983). Accordingly, an analogous mechanism is proposed here (Scheme 1a), from which the following theoretical rate equation can be deduced:…”

“…The reaction was followed using the initial rate method to avoid the decomposition of nitrous acid (Arenas-Valgañón, González-Pérez, Gómez Bombarelli, González-Jiménez, Calle, & Casado, 2014), measuring the absorbance of the nitrous acid/nitrite system at λ = 371 nm (the absorbance of phenethylamine was very weak). To determine reaction orders and the rate constants, an excess of phenethylamine was used.…”

Nitrosation and analysis of amino acid derivatives by isocratic HPLC

“…34 NO from decomposition of nitrous acid may also contribute to the total gas production, especially at low pH. 35 Still, the gas yields were close to 1 mole of gas per mole amino acid. This indicates that the degree of conversion of most of the amino acids into their corresponding a-hydroxy acids have been high.…”

“…Nitrosation of amino acids have previously been carried out in different acid solutions. The original nitrosation procedure used by van Slyke 7 used acetic acid while other authors used nitrous acid, 34 sulphuric acid, 32 perchloric acid, 26,35 butyric acid, 6 or HCl. 6,36 We used HCl.…”