Photolysis (193 nm) of aliphatic amino acids in aqueous solution

Abstract

An investigation of the photochemical properties of glycine, aspartic acid, valine, leucine and methionine was carried out using nanosecond 193 nm laser irradiation and high performance liquid chromatography analysis. The quantum yields of formation of hydrated electrons ( Φ e−) and decomposition of the substrate ( Φ d) were determined for the five aliphatic amino acids in neutral aqueous solution at room temperature. From the dependences of Φ e− on the laser intensity it follows that the mechanism of photo-ionization is monophotonic (single step). The Φ d values under Ar and in the presence of oxygen or N 2O are interpreted on the basis of photo-ionization as the dominant process for decomposition of methionine and a significant contribution from photo-ionization in the other cases. A comparison was made between the Φ d values (in the presence of oxygen) using irradiation at 193 nm and those from previous measurements at 213 nm.