Deamination of β-alanine induced by hydroxyl radicals and monovalent copper ions. A pulse radiolysis study

Hydroxyl radicals abstract hydrogen atoms from β-alanine (3-aminopropanoate) at the α position to the carboxylate group with specifc rate constants of (4.5±0.8)×10⁷ and (1.1±0.2)×10⁸ M^-1 s^-1 at pH 3 and 6.5, respectively. The carbon-centered free radical (3-amino-2-yl-propanoate) reacts with Cu⁺_aq to form an organometallic intermediate with a rate constant of (3.4±0.7×10⁹ M^-1 s^-1. This intermediate decomposes via a first order reaction with a rate constant of (1.1±0.2)×10⁴ s^-1 at pH>3.5 and (2.7±0.3)×10⁴ s^-1 at pH≤3. A detailed product analysis shows that the yield of carbon dioxide is insignificant and the final stable product is acrylic acid. It is concluded that the complex with the copper-carbon σ-bond decomposes via a β-elimination of ammonia causing degradation of the amino acid. The spectrum of the organometallic intermediate and the factors affecting the mechanism of its decomposition are discussed.