Heterogeneous photosynthetic production of amino acids at platinum/titanium dioxide suspensions by near ultraviolet light

Abstract

Studies of the previously reported production of amino acids (glycine, alanine, serine, aspartic acid, glutamic acid) from methane, ammonia, and water in contact with irradiated suspensions of Pt/TiO, were extended. Products were analyzed by LC, HPLC, and coupled GC/mass spectroscopy. Analysis of product mixtures also shows the presence of MeOH, EtOH, and CH3NH2 as products of the photoprocess. Experiments with nitrogen-15 labeled ammonia showed that the nitrogen in the amino acids originated with the N H 3 rather than from contaminants. Amino acids were also produced from the CH4-NH3-H20 mixture during decomposition of hydrogen peroxide at Pt foil. A mechanism for the reaction based on free-radical reactions initiated by hydroxyl radical produced at the irradiated catalyst is proposed. A previous communication from this laboratory' described the production of amino acids by xenon lamp irradiation of platinized TiOz powders (Pt/TiO,) suspended in aqueous ammoniacal solutions saturated with methane. The process apparently occurs by a photosynthetic (energetically uphill) reaction driven by the absorption of the near-ultraviolet (A e405 nm) radiation by the TiO,. These reaction conditions for amino acid formation from a simple reducing mixture are mild compared to previous methods for amino acid production that involved electrical discharge or very short wavelength radiation.2