Electric field effects in the infrared multiphoton dissociation of CF2HCl

The infrared multiphoton dissociation of chlorodifluoromethane is studied in a dc electric field. The reaction yield is measured as a function of the laser energy fluence, the CF2HCl pressure, and the electric field strength in the range 0⩽E⩽5.4 kV cm−1. At low fluence (F<1J cm−2) and intensity, under essentially collision free conditions, the multiphoton dissociation is strongly enhanced by the electric field. This is tentatively explained by a breakdown in the angular momentum selection rules caused by the applied field

Atmospheric pollution measurement by lidar

A review, with 12 refs., on the instrumentation for and principles of the differential absorption lidar technique

Laser-induced temperature jump measurements in the kinetics of association and dissociation of the nitrogen oxide (N2O3) + M = nitrogen dioxide + nitrous oxide + M system

Kinetic measurements have been made on the gas-phase reaction N2O4 + M .dblharw. 2NO2 + M by applying the temp.-jump relaxation method. Equil. mixts. contg. NO2, N2O4, a small quantity of an IR absorber, and an excess of a third-body bath gas, have been subjected to a short CO2 laser pulse. The induced temp. jump, of the order of 1 K, displaces the equil. towards NO2 formation. After the fast heating of the mixt., the time dependence of the NO2 and N2O4 concns. has been monitored at 420 and 250 nm, resp. For small perturbations, the relaxation to the new equil. concns. at the higher temp. follows first-order kinetics, and the thermal rate const. can be deduced from the measured relaxation rate const. Measurements have been made at 255 K at 0.3-200 bars He, which corresponds to the falloff range for this reaction. The high- and low-pressure limiting rate consts., krec,... = (7.0 +- 0.7) * 1011 cm3 mol-1 s-1 and krec,0/[He] = (2.1 +- 0.2) * 1014 cm3 mol-1 s-1, resp., extrapolated from the exptl. data at 255 K, were in agreement with those calcd. with a simplified statistic adiabatic channel model. The temp. dependence of the high- and low-pressure recombination rate const., detd. at 255-273 K, is given by the relations krec,... = (2.2 +- 0.2) * 106 * T(2.3+-0.2) cm3 mol-1 s-1 and krec,0/[He] = (7.5 +- 0.8) * 1035 * T(-9.0+-0.9) cm3 mol-1 s-1. The corresponding high- and low-pressure dissocn. rate consts. are kdiss,... = (2.8 +- 0.3) * 1013 * T(1.3+-0.2) exp{-(6790 +- 700)/T} s-1 and kdiss,0/[He] = (9.6 +- 0.9) * 1042T(-10.0+-1.0) * exp{-(6790 +- 700)/T} s-1, resp.The kinetics of the N2O3 + M = NO + NO2 + M reaction was studied over a wide range of pressure by a laser-induced temp. jump relaxation method. Equil. mixts. at 225 K contg. nitrogen dioxide, dinitrogen trioxide, dinitrogen tetroxide, nitric oxide, a small quantity of SiF4 as an IR absorber, and an excess of Ar as a 3rd-body gas collider are rapidly heated by a short pulse of CO2 laser radiation. The induced temp. jump, at 0.5-3 K, displaces the equil. toward NO2 and NO formation. The rate of recombination reaction to the new equil. concns. at higher temp. is monitored by observing spectroscopically the time dependence of the N2O3 concn. in the UV. For small perturbations, simple mathematics relates the measured chem. relaxation time const. to the thermal rate consts. of the system. Exptl. results (obtained in the 0.5-200 bar pressure range of Ar corresponding to the 3rd-order and falloff region of the reaction) were fitted by falloff curves established accordingly to a method developed by Troe. High- and low-pressure limiting rate consts. for the NO + NO2 recombination at 227 K are extrapolated from the exptl. data. These values lie within a factor of 2 of those that may be predicted using a simplified statistic adiabatic channel (SAC) model. The temp. dependence of the recombination rate const., measured exptl. at 227-260 K is reported as well as the calcd. kinetics of dissocn. for N2O3

Electric and magnetic field effects in the infrared multiphoton dissociation of trifluoromethane-d1

The effect of static elec. and magnetic fields on the IR multiphoton dissocn. (IRMPD) yield of CF3D was investigated in the range 0-4.3 kV cm-1 and 0-17.3 kG. The applied static fields induced increases in the reaction yield of up to a factor of 5 at moderate energy fluences in the essentially collision free dissocn. For all cases considered, the field effects were independent of the orientation of the laser beam polarization relative to the direction of the applied elec. and magnetic fields. At higher pressures, where collisions enhanced the reaction yield, lower yields were obsd. in the 17.3 kG magnetic field than in the magnet's residual field of .apprx.100 G. The measurements on the magnetic field effect were completed with new results on the IRMPD of CF2HCl. Possible IR spectral changes induced by a 5 kV cm-1 field in CF3D, CF3H, and CF2HCl were investigated at a resoln. of 0.06 cm-1

Temperature jump measurements in gas kinetics

The temp. jump relaxation method was used for kinetic measurements in the gas phase. The system N2O4 .dblarw. 2NO2 was studied. Fast temp. jumps were induced by IR absorption from a CO2 laser. Temp. jumps of <1 K led to readily detectable concn. changes which were monitored by UV absorption in a simple single shot expt. krec(Ar) is 1.05 * 1010 cm3-mol-1-s-1 at PAr = 1 bar and T = 258 K, in agreement with recent exptl. data

Radioactivity levels in mussels and sediments of the Golden Horn by the Bosphorus Strait, Marmara Sea

The Golden Horn is an estuary located in the center of Istanbul receiving freshwater discharges from two creeks and connecting to the Bosphorus Strait. Activity concentrations of natural and artificial radionuclides were determined in mussels (Mytilus galloprovincialis) and sediments from the Golden Horn sampled in February 2012. Mean activity concentrations of Cs-137, K-40, Ra-226, Ra-228, Po-210 and Pb-210 in the mussels were determined at 1.03 +/- 0.23, 389 +/- 41.6, 2.61 +/- 1.23, not detected (ND), 91.96 +/- 37.88 and 11.48 +/- 4.85 Bq kg, respectively. In sediments, it was observed that Cs-137, K-40, Ra-226, Ra-228, Po-210 and Pb-210 activity concentrations in <63 mu m particle fraction of sediment were generally higher than those determined in mussels. Po-210 and Po-210/Pb-210 ratios in mussels from the Golden Horn were much lower than in mussels from other coastal regions and this was related to low plankton productivity and eutrophication of the Golden Horn. (C) 2014 Elsevier Ltd. All rights reserved

Insights in the molecular mechanisms of an azole stress adapted laboratory-generated Aspergillus fumigatus strain

Aspergillus fumigatus is the main cause of invasive aspergillosis, for which azole drugs are the first-line therapy. Emergence of pan-azole resistance among A. fumigatus is concerning and has been mainly attributed to mutations in the target gene (cyp51A). However, azole resistance may also result from other mutations (hmg1, hapE) or other adaptive mechanisms. We performed microevolution experiment exposing an A. fumigatus azole-susceptible strain (Ku80) to sub-minimal inhibitory concentration of voriconazole to analyze emergence of azole resistance. We obtained a strain with pan-azole resistance (Ku80R), which was partially reversible after drug relief, and without mutations in cyp51A, hmg1, and hapE. Transcriptomic analyses revealed overexpression of the transcription factor asg1, several ATP-binding cassette (ABC) and major facilitator superfamily transporters and genes of the ergosterol biosynthesis pathway in Ku80R. Sterol analysis showed a significant decrease of the ergosterol mass under voriconazole exposure in Ku80, but not in Ku80R. However, the proportion of the sterol compounds was similar between both strains. To further assess the role of transporters, we used the ABC transporter inhibitor milbemycine oxime (MLB). MLB inhibited transporter activity in both Ku80 and Ku80R and demonstrated some potentiating effect on azole activity. Criteria for synergism were reached for MLB and posaconazole against Ku80. Finally, deletion of asg1 revealed some role of this transcription factor in controlling drug transporter expression, but had no impact on azole susceptibility.This work provides further insight in mechanisms of azole stress adaptation and suggests that drug transporters inhibition may represent a novel therapeutic target. A pan-azole-resistant strain was generated in vitro, in which drug transporter overexpression was a major trait. Analyses suggested a role of the transporter inhibitor milbemycin oxime in inhibiting drug transporters and potentiating azole activity