Photochemical Decarboxylation of Amino Acids in the Presence of Metal Ions

An electron‐spin‐resonance study of the radicals produced by ultraviolet irradiation of amino acids in the presence of transition metal ions at low temperature has been carried out. For the monocarboxylic acids, the photosensitized irradiation resulted in loss of carbon dioxide, which led to the formation of free radicals of the type H3ŃR1R2. When the amino acid contained two carboxylic groups, e.g. aspartic acid, decarboxylation took place at the position remote from the amino group. When the odd electron is localized at the carbon atom β to the amino group, e.g. β‐alanine and aspartic acid, it was stable enough to be detected at room temperature.