Multiparameter-controlled laser ionization within a plasma wave for wakefield acceleration

We present an optical setup for well-defined ionization inside a plasma such that precisely controlled spots of high electron density can be generated. We propose to use the setup for Trojan Horse Injection (or Plasma Photocathode Emission) where a collinear laser beam is needed to release electrons inside a plasma wakefield. The reflection-based setup allows a suitable manipulation of the laser near field without disturbing the spectral phase of the laser pulses. A required ionization state and volume can be reached by tuning the beam size, pulse duration and pulse energy. The ionization simulations enable a prediction of the ionization spot and are in good agreement with dedicated experiments which measured the number of electrons created during the laser-gas interaction.

Photocatalytic degradation of ibuprofen using titanium oxide: insights into the mechanism and preferential attack of radicals

The degradation of ibuprofen undergoes a series of elementary reactions, generating different radicals which attack preferentially in the region of the ibuprofen with high electron density.

Acidity and nucleophilic reactivity of glutathione persulfide

Persulfides (RSSH/RSS−) participate in sulfur trafficking and metabolic processes, and are proposed to mediate the signaling effects of hydrogen sulfide (H2S). Despite their growing relevance, their chemical properties are poorly understood. Herein, we studied experimentally and computationally the formation, acidity, and nucleophilicity of glutathione persulfide (GSSH/GSS−), the derivative of the abundant cellular thiol glutathione (GSH). We characterized the kinetics and equilibrium of GSSH formation from glutathione disulfide and H2S. A pKa of 5.45 for GSSH was determined, which is 3.49 units below that of GSH. The reactions of GSSH with the physiologically relevant electrophiles peroxynitrite and hydrogen peroxide, and with the probe monobromobimane, were studied and compared with those of thiols. These reactions occurred through SN2 mechanisms. At neutral pH, GSSH reacted faster than GSH because of increased availability of the anion and, depending on the electrophile, increased reactivity. In addition, GSS− presented higher nucleophilicity with respect to a thiolate with similar basicity. This can be interpreted in terms of the so-called α effect, i.e. the increased reactivity of a nucleophile when the atom adjacent to the nucleophilic atom has high electron density. The magnitude of the α effect correlated with the Brønsted nucleophilic factor, βnuc, for the reactions with thiolates and with the ability of the leaving group. Our study constitutes the first determination of the pKa of a biological persulfide and the first examination of the α effect in sulfur nucleophiles, and sheds light on the chemical basis of the biological properties of persulfides.

Abnormal scattering event in the direction to the pulsar B0834+06

ABSTRACT Analysis of Space-VLBI observations of the pulsar B0834+06 conducted with RadioAstron at 324 MHz shows that in some cases one of the scattering screens could be located very close to the pulsar (about 10 pc from the pulsar), and it has a strong influence on the secondary spectra. For this case, the vertices of inverted arcs are aligned along the main parabolic arc and their width is inversely proportional to the scattering time. The shape of the main arc is determined by another scattering screen that is located at a distance of about 210 pc from the pulsar. The position of this screen is observed to be stable during 19 yr and its spatial scale is larger than 5.6 × 1015 cm. We found that the scattering disc may be approximated by an ellipse with a 2.5 axial ratio and with the position angle of the major axis of about −8○. A small-scale structure with a size of 0.1 au located at the close to observer screen and very high electron density of tens to a few thousand cm−3 for different models can be responsible for arclets in a secondary spectra. Additionally, angular refraction exists in the direction towards the pulsar. That suggests the presence of the cosmic prism. We have estimated the angle of refraction to be θref > 2 mas and the distance from prism to the observer D < 160 pc.