Single and Double Photoionization and Photodissociation of Toluene by Soft X-rays in Circumstellar Environment

The formation of polycyclic aromatic hydrocarbons (PAHs) and their methyl derivatives occurs mainly in the dust shells of asymptotic giant branch (AGB) stars. The bands at 3.3 and 3.4 $\mu$m, observed in infrared emission spectra of several objects, are attributed C-H vibrational modes in aromatic and aliphatic structures, respectively. In general, the feature at 3.3 $\mu$m is more intense than the 3.4 $\mu$m. Photoionization and photodissociation processes of toluene, the precursor of methylated PAHs, were studied using synchrotron radiation at soft X-ray energies around the carbon K edge with time-of-flight mass spectrometry. Partial ion yields of a large number of ionic fragments were extracted from single and 2D-spectra, where electron-ion coincidences have revealed the doubly charged parent-molecule and several doubly charged fragments containing seven carbon atoms with considerable abundance. \textit{Ab initio} calculations based on density functional theory were performed to elucidate the chemical structure of these stable dicationic species. The survival of the dications subjected to hard inner shell ionization suggests that they could be observed in the interstellar medium, especially in regions where PAHs are detected. The ionization and destruction of toluene induced by X-rays were examined in the T Dra conditions, a carbon-rich AGB star. In this context, a minimum photodissociation radius and the half-life of toluene subjected to the incidence of the soft X-ray flux emitted from a companion white dwarf star were determined.Comment: 11 pages, 4 figures, accept for publication in Ap

A simple copper(II) dppy-based receptor for sensing of L-cysteine and L-histidine in aqueous acetonitrile medium

The development of simple yet efficient receptors that rapidly detect and monitor amino acids with high sensitivity and reliability is crucial for the early-stage identification of various diseases. In this work, we report the synthesis and characterisation of a copper(II) complex, CuCl2L, by employing a 2,6-dipyrazinylpyridine (dppy)-based ligand (L = 2,2′-(4-(3,4,5-trimethoxyphenyl)pyridine-2,6-diyl)dipyrazine). The in situ prepared CuCl2L receptor exhibits an instantaneous response to the presence of L-cysteine (Cys) and L-histidine (His) in aqueous acetonitrile (4[thin space (1/6-em)]:[thin space (1/6-em)]1 v/v, 10 mM HEPES buffer, pH 7.4). Furthermore, competitive experiments demonstrate the selectivity of CuCl2L towards Cys (1 equiv.) in the vicinity of other L-amino acids in the aforementioned solvent conditions. The detection limits for Cys and His are calculated as 0.33 μM and 1.40 μM, respectively. DFT calculations offer a plausible explanation for the observed selectivity of the CuCl2L receptor towards Cys and His. They reveal that the most stable conformer of Cu[thin space (1/6-em)]:[thin space (1/6-em)]Cys complex (1[thin space (1/6-em)]:[thin space (1/6-em)]1) is a five-membered ring formed through N,S-coordination mode (ΔG = −26.7 kcal mol−1) over various other possible coordination modes, while comparable ΔG values are only obtained for Cu[thin space (1/6-em)]:[thin space (1/6-em)]His complexes featuring two His moieties

Recuento de Staphylococcus aureus y de coliformes, con previa recuperación de celulas injuriadas

p.291-295En el presente trabajo se analizaron 20 muestras de leche en polvo con el objeto de determinar el porcentaje de células injuriadas de Staphylococcus aureus y de coliformes durante los procesos de elaboración de dicho producto (calor y desecación). Estas muestras fueron seleccionadas de un total de 80 por haber sido detectada en ellas presencia de Staphylococcus aureus. Se siguió una metodología de aceptación general (Speck, 1976) y las determinaciones fueron efectuadas con y sin recuperación previa de células injuriadas. Se encontró que el porcentaje de células injuriadas osciló entre el 18,5 y el 77,7 por ciento en el caso de Staphylococcus aureus y entre el 25 y el 62,5 por ciento, en el caso de los coliformes. Cuando no se observó aumento en el recuento, con previa recuperación de células injuriadas, debe asumirse que la contaminación es posterior a la elaboración. En el caso de las bacterias coliformes, esta contaminación posterior parece más factible y los numerosos recuentos negativos se explican por el muy bajo porcentaje de supervivencia a los procesos de elaboración de la leche en polvo: 0,002 por ciento (Chopin, Mocquot y Le Graet, 1977)

Application of column buckling theory to steel aluminium foam sandwich panels

In steel structures, a lot of attention is paid to lightweight structures, i.e. reduction of dead load without compromising structural safety, integrity and performance. Thanks to modern steel aluminium foam sandwich panel manufacturing technology a new possibility became available for lightweight structural design. Assessment and understanding of the behaviour of this sandwich panel under in-plane compression or flexure is crucial before its application in steel structures. Column buckling theory is considered and applied to the steel aluminium foam sandwich panel to evaluate its behaviour under in-plane compressive load. In this work, various assumptions are made to generalise Euler’s buckling formula. The generalisation requires modification of the buckling stiffness expression to account for sandwich panel composite properties. The modified analytical expression is verified with finite element simulation employing various material models specific to steel faceplates and aluminium foam as well as various geometric imperfections. Based on this study, it can be concluded that Euler’s buckling formula can be successfully modified and used in the prediction of the load-carrying capacity of a sandwich panel

Efectos de una competición de mountain bike sobre el estado de hidratación en ciclistas amateurs

The purpose of this study was to assess the changes in the state of hydration in amateur cyclists of the discipline mountain biking (Rally) during a race of one day. Method: PRE and POST urine samples were obtained, in 13 amateur cyclists of this discipline, and urine specific gravity (USG) was analyzed by refractometer. Change in body mass was also registered and the volume of liquid ingested ad libitum during the competition was controlled. Results: The average pre-competition USG was 1034,33 ±6,8 and post-competition 1034 ± 6,6. The loss of body mass was 2.6 ± 0.7% and the average sweating rate was 707,5 ml/h ± 277,9. Conclusions: The results obtained indicate that the cyclists evaluated began and ended the competition in a severe dehydration state (i.e., USG> 1.020). However, despite starting in state of dehydration and having liquid and solid supplies ad libitum, the cyclists experienced a body mass loss higher than 2% during the competitive event.El propósito del presente trabajo fue valorar los cambios en el estado de hidratación en ciclistas amateurs de la disciplina mountain bike (Rally) durante una prueba de un día. Método: Se obtuvieron dos muestras de orina, una PRE y otra POST competición en 13 varones de nivel amateur en esta disciplina, en las que se analizó la gravedad específica de la orina (USG) mediante refractómetro. Se registró igualmente el cambio en la masa corporal PRE-POST y se controló el volumen de líquido ingerido durante la competición ad libitum. Resultados: Se observó una USG media PRE competición de 1034,33 ±6,8 y POST de 1034 ± 6,6. Una pérdida de masa corporal relativa del 2,6 ± 0,7 % y una tasa de sudoración media de 707,5 ml/h ± 277,9. Conclusiones: Los resultados obtenidos indican que los ciclistas evaluados comenzaron y terminaron la competición en estado de deshidratación severa (i.e., USG> 1.020). No obstante, a pesar de comenzar en este estado de deshidratación y disponer de avituallamiento líquido y sólido ad libitum, los ciclistas experimentaron una pérdida de masa corporal superior a un 2% durante el evento competitivo.

Photocurrents from photosystem II in a metal oxide hybrid system: electron transfer pathways

We have investigated the nature of the photocurrent generated by Photosystem II (PSII), the water oxidizing enzyme, isolated from Thermosynechococcus elongatus, when immobilized on nanostructured titanium dioxide on an indium tin oxide electrode (TiO2/ITO). We investigated the properties of the photocurrent from PSII when immobilized as a monolayer versus multilayers, in the presence and absence of an inhibitor that binds to the site of the exchangeable quinone (QB) and in the presence and absence of exogenous mobile electron carriers (mediators). The findings indicate that electron transfer occurs from the first quinone (QA) directly to the electrode surface but that the electron transfer through the nanostructured metal oxide is the rate-limiting step. Redox mediators enhance the photocurrent by taking electrons from the nanostructured semiconductor surface to the ITO electrode surface not from PSII. This is demonstrated by photocurrent enhancement using a mediator incapable of accepting electrons from PSII. This model for electron transfer also explains anomalies reported in the literature using similar and related systems. The slow rate of the electron transfer step in the TiO2 is due to the energy level of electron injection into the semiconducting material being below the conduction band. This limits the usefulness of the present hybrid electrode. Strategies to overcome this kinetic limitation are discussed

Bicarbonate-controlled reduction of oxygen by the QA semiquinone in Photosystem II in membranes

Photosystem II (PSII), the water/plastoquinone photo-oxidoreductase, plays a key energy input role in the biosphere. Q∙−A, the reduced semiquinone form of the nonexchangeable quinone, is often considered capable of a side reaction with O2, forming superoxide, but this reaction has not yet been demonstrated experimentally. Here, using chlorophyll fluorescence in plant PSII membranes, we show that O2 does oxidize Q∙−A at physiological O2 concentrations with a t1/2 of 10 s. Superoxide is formed stoichiometrically, and the reaction kinetics are controlled by the accessibility of O2 to a binding site near Q∙−A, with an apparent dissociation constant of 70 ± 20 µM. Unexpectedly, Q∙−A could only reduce O2 when bicarbonate was absent from its binding site on the nonheme iron (Fe2+) and the addition of bicarbonate or formate blocked the O2-dependant decay of Q∙−A. These results, together with molecular dynamics simulations and hybrid quantum mechanics/molecular mechanics calculations, indicate that electron transfer from Q∙−A to O2 occurs when the O2 is bound to the empty bicarbonate site on Fe2+. A protective role for bicarbonate in PSII was recently reported, involving long-lived Q∙−A triggering bicarbonate dissociation from Fe2+ [Brinkert et al., Proc. Natl. Acad. Sci. U.S.A. 113, 12144–12149 (2016)]. The present findings extend this mechanism by showing that bicarbonate release allows O2 to bind to Fe2+ and to oxidize Q∙−A. This could be beneficial by oxidizing Q∙−A and by producing superoxide, a chemical signal for the overreduced state of the electron transfer chain

EURADOS IC2012N: EURADOS 2012 intercomparison for whole-body neutron dosimetry

The European Radiation Dosimetry Group (EURADOS) IC2012n intercomparison for neutron dosemeters intended to measure personal dose equivalent, Hp(10), was performed in 2012. A total of 31 participants (27 individual monitoring services from Europe, 2 from Japan, 1 from Israel and 1 from USA) registered with 34 dosimetry systems. Participation was restricted to passive or active neutron dosemeters routinely used in individual monitoring of radiation workers. The dosimetry systems were based on thermoluminescence, polyallyldiglycol carbonate, optically stimulated luminescence, fission track detection and silicon diodes (electronic devices). The irradiation tests were chosen to provide the participants with useful information on their dosimetry systems, i.e. linearity, reproducibility, responses for different energies and angles and to simulated workplace fields. The paper will report and discuss the first analysis of the results of the EURADOS IC2012n intercompariso

Sodium-glucose cotransporter 2 inhibitors antagonize lipotoxicity in human myeloid angiogenic cells and ADP-dependent activation in human platelets: Potential relevance to prevention of cardiovascular events

Background: The clear evidence of cardiovascular benefits in cardiovascular outcome trials of sodium-glucose cotransporter 2 inhibitors (SGLT2i) in type 2 diabetes might suggest an effect on atherosclerotic plaque vulnerability and/or thrombosis, in which myeloid angiogenic cells (MAC) and platelets (PLT) are implicated. We tested the effects of SGLT2i on inflammation and oxidant stress in a model of stearic acid (SA)-induced lipotoxicity in MAC and on PLT activation. The possible involvement of the Na+/H+ exchanger (NHE) was also explored. Method: MAC and PLT were isolated from peripheral blood of healthy subjects and incubated with/without SGLT2i [empagliflozin (EMPA) and dapagliflozin (DAPA) 1-100 μM] to assess their effects on SA (100 μM)-induced readouts of inflammation, oxidant stress and apoptosis in MAC and on expression of PLT activation markers by flow-cytometry after ADP-stimulation. Potential NHE involvement was tested with amiloride (aspecific NHE inhibitor) or cariporide (NHE1 inhibitor). Differences among culture conditions were identified using one-way ANOVA or Friedman test. Results: NHE isoforms (1,5-9), but not SGLT2 expression, were expressed in MAC and PLT. EMPA and DAPA (100 μM) significantly reduced SA-induced inflammation (IL1β, TNFα, MCP1), oxidant stress (SOD2, TXN, HO1), but not apoptosis in MAC. EMPA and DAPA (both 1 μM) reduced PLT activation (CD62p and PAC1 expression). SGLT2i effects were mimicked by amiloride, and only partially by cariporide, in MAC, and by both inhibitors in PLT. Conclusions: EMPA and DAPA ameliorated lipotoxic damage in stearate-treated MAC, and reduced ADP-stimulated PLT activation, potentially via NHE-inhibition, thereby pointing to plaque stabilization and/or thrombosis inhibition as potential mechanism(s) involved in SGLT2i-mediated cardiovascular protection