Inhomogenity of the 172 nm VUV light irradiated aqueous solutions

Vacuum ultraviolet (VUV) photolysis is one of the Advanced Oxidation Processes (AOPs) for the elimination of trace pollutants from water and air. The ultraviolet (UV) radiation below 200 nm is named VUV, because it is strongly absorbed by air. Using VUV photolysis reactive species (H and OH) can be generated directly from water without addition of any chemicals. Consequently VUV radiation is used for producing ultrapure water and often investigated as a possible method for elimination of organic pollutants from water. In the case of VUV photolysis low pressure mercury vapor lamp (emits both 254 nm UV and 185 nm VUV photons) or Xe excimer lamp (emits both 172 nm VUV photons) can be applied as light source. In latter case the absorption coefficient of water at 172 nm is 550 cm–1 . Consequently, the penetration depth of VUV radiation is very small, only 0.04 mm. In this work we have investigated the effect of inhomogenity caused within this very thin VUV irradiated layer on the concentration of the primary formed reactive species, such as H and OH, using model calculation

Exploring the boundaries of direct detection and characterization of labile isomers - a case study of copper(II)-dipeptide systems

The investigation of the linkage isomers of biologically essential and kinetically labile metal complexes in aqueous solutions poses a challenge, as these microspecies cannot be separately studied. Therefore, derivatives are commonly used to initially determine the stability or spectral characteristics of at least one of the isomers. Here we directly detect the isomers, describe the metal ion coordination sphere, speciation and thermodynamic parameters by a synergistic application of temperature dependent EPR and CD spectroscopic measurements in copper(II)-dipeptide systems including His-Gly and His-Ala ligands. The Delta H = (-23 +/- 4) kJ mol(-1) value of the standard enthalpy change corresponding to the peptide-type to histamine-type isomerisation equilibrium of the [CuL](+) complex was corroborated by several techniques. The preferential coordination of the side-chains was observed at lower temperatures, whereas, metal-binding of the backbone atoms became favourable upon increasing temperature. This study exemplifies the necessity of using temperature dependent multiple methodologies for a reliable description of similar systems for upstream applications