Dissociative excitation of water by metastable argon

On the Liquid Chemistry of the Reactive Nitrogen Species Peroxynitrite and Nitrogen Dioxide Generated by Physical Plasmas

Cold physical plasmas modulate cellular redox signaling processes, leading to the evolution of a number of clinical applications in recent years. They are a source of small reactive species, including reactive nitrogen species (RNS). Wound healing is a major application and, as its physiology involves RNS signaling, a correlation between clinical effectiveness and the activity of plasma-derived RNS seems evident. To investigate the type and reactivity of plasma-derived RNS in aqueous systems, a model with tyrosine as a tracer was utilized. By high-resolution mass spectrometry, 26 different tyrosine derivatives including the physiologic nitrotyrosine were identified. The product pattern was distinctive in terms of plasma parameters, especially gas phase composition. By scavenger experiments and isotopic labelling, gaseous nitric dioxide radicals and liquid phase peroxynitrite ions were determined as dominant RNS. The presence of water molecules in the active plasma favored the generation of peroxynitrite. A pilot study, identifying RNS driven post-translational modifications of proteins in healing human wounds after the treatment with cold plasma (kINPen), demonstrated the presence of in vitro determined chemical pathways. The plasma-driven nitration and nitrosylation of tyrosine allows the conclusion that covalent modification of biomolecules by RNS contributes to the clinically observed impact of cold plasmas.

Hydrogen-atom attack on phenol and toluene is ortho-directed

The reaction of H + phenol and H/D + toluene has been studied in a supersonic expansion after electric discharge. The (1 + 1') resonance-enhanced multiphoton ionization (REMPI) spectra of the reaction products, at m/z = parent + 1, or parent + 2 amu, were measured by scanning the first (resonance) laser. The resulting spectra are highly structured. Ionization energies were measured by scanning the second (ionization) laser, while the first laser was tuned to a specific transition. Theoretical calculations, benchmarked to the well-studied H + benzene → cyclohexadienyl radical reaction, were performed. The spectrum arising from the reaction of H + phenol is attributed solely to the ortho-hydroxy-cyclohexadienyl radical, which was found in two conformers (syn and anti). Similarly, the reaction of H/D + toluene formed solely the ortho isomer. The preference for the ortho isomer at 100-200 K in the molecular beam is attributed to kinetic, not thermodynamic effects, caused by an entrance channel barrier that is ∼5 kJ mol(-1) lower for ortho than for other isomers. Based on these results, we predict that the reaction of H + phenol and H + toluene should still favour the ortho isomer under elevated temperature conditions in the early stages of combustion (200-400 °C).

Significant change of alignment effect by dimer formation in the dissociative energy transfer reaction of Ar(3P2)+(N2O)n and (H2O)n

An alignment effect in the dissociative energy transfer reaction of Ar((3)P(2))+(X(2)O)(n)(X=N,H) was directly measured using an oriented Ar((3)P(2),M(J)=2) beam. The chemiluminescence intensity of N(2)(B,(3)Pi(g)) for (N(2)O)(n) and OH(A,(2)Sigma(+)) for (H(2)O)(n) was measured as a function of the magnetic orientation field direction in the collision frame. The relative reaction cross section for each magnetic substate in the collision frame, sigma(M(J) (') ), was determined. In both the reaction systems, it is observed that the dimer formation significantly enhances the alignment effect and decreases the reactivity, especially for sigma|1| and sigma|2|. A significant contribution of rank 4 moment is recognized in the dimer reaction.