Kinetics of the ClO + CH3O2 reaction over the temperature range T = 250 – 298 K

The kinetics of the potentially atmospherically important ClO + CH3O2 reaction (1) have been studied over the range T = 250–298 K at p = 760 Torr using laser flash photolysis radical generation, coupled with time resolved ultraviolet absorption spectroscopy, employing broad spectral monitoring using a charge coupled device detector array. ClO radicals were monitored unequivocally using this technique, and introduction of CH3O2 precursors ensured known initial methylperoxy radical concentrations. ClO temporal profiles were thereafter analysed to extract kinetic parameters for reaction (1). A detailed sensitivity analysis was also performed to examine any potential systematic variability in k1 as a function of kinetic or physical uncertainties. The kinetic data recorded in this work show good agreement with the most recent previous study of this reaction, reported by Leather et al. The current work reports an Arrhenius parameterisation for k1, given by: k(1)(T) = 2.2+3.4-1.3 x 10^-11 e(-(642+-253)K/T)cm^3 molecule^-1 s^-1. This work therefore concurs with that of Leather et al. implying that the title reaction is potentially less significant in the atmosphere than inferred from preceding studies. However, reaction (1) is evidently a non-terminating radical reaction, whose effects upon atmospheric composition therefore need to be ascertained through atmospheric model studies

Kinetics of the ClO + HOreaction over the temperature range T = 210–298 K

The rate coefficient for the atmospherically important radical reaction: ClO + HO2 → Productswhich leads to ozone depletion, has been studied over the temperature range T = 210–298 K and at ambient pressure p = 760 ± 20 Torr. The reaction was studied using laser flash photolysis radical generation coupled with broadband charge coupled device absorption spectroscopy employing a two-dimensional charge-coupled-device (CCD) detection system. ClO radicals were generated following the photolysis of Cl2 and Cl2O gas mixtures diluted in nitrogen and oxygen. ClO radicals were monitored using broadband fingerprinting of their characteristic vibronic (A2Π ← X2Π) spectral structure, representing a definitive monitoring of this radical. Addition of hydroperoxy radical precursors to the gas mixture (methanol and oxygen) subsequently led to a competition for photolytically generated Cl atoms and a simultaneous prompt formation of both ClO and HO2 radicals. Detailed analysis and modelling of the radical production routes provided a degree of constraint into numerical integration simulations which were then used to interrogate and fit to ClO temporal profiles to extract the rate coefficient k1. The ambient temperature (T = 298 K) rate coefficient reported is k1 = (8.5 ± 1.5) × 10−12 cm3 molecule−1 s−1. The rate coefficient, k1, is described by the Arrhenius expression:where errors are 1σ statistical only. This significant rate coefficient is greater than previously reported, with a stronger negative temperature dependence than previously observed. Consequently this suggests that the contribution of reaction (1) to ozone loss, in particular at mid-latitudes might be currently underestimated in models. This work reports atmospheric pressure kinetic parameters for this reaction which are greater than those reported from low pressure studies, perhaps supporting ClO and HO2 association as predicted by previous theoretical studies of this process and highlighting the need for further pressure dependent experimental studies of the title reaction, which has been demonstrated here to be effective as an ozone loss process over a wide temperature range

Kinetics of the BrO + HO2 reaction over the temperature range T = 246–314 K

The kinetics of the reaction between gas phase BrO and HO2 radicals (1) have been studied over the atmospherically relevant temperature range T = 246 – 314 K and at ambient pressure, p = 760 ± 20 Torr, using laser flash photolysis coupled with ultraviolet absorption spectroscopy. BrO + HO2 → HOBr + O2 (1) The reaction was initiated by the generation of bromine monoxide radicals following laser photolytic generation of Br atoms from Br2/Cl2 containing mixtures and their reaction with ozone. Subsequently, the addition of methanol vapour to the reaction mixture, in the presence of excess oxygen, afforded the efficient simultaneous post-photolysis formation of HO2 radicals using well-defined chemistry. The decay of BrO radicals, in the presence and absence of HO2, was interrogated to determine the rate coefficients for the BrO + BrO and the BrO + HO2 reactions. A detailed sensitivity analysis was performed to ensure that the BrO + HO2 reaction was unequivocally monitored. The rate coefficient for reaction (1) is described by the Arrhenius expression: "k1 (T / K) = (" 〖"9.28 " 〗_"‒ 4.04" ^"+ 7.17" ")× " 〖"10" 〗^"‒12" "e" ^(((("316 ± 157" ))/"T" ) ) 〖"cm" 〗^"3" 〖" molecule" 〗^"‒1" "s" ^"‒1" where errors are 1σ. The negative temperature dependence of this reaction is in general accord with those reported by previous studies of this reaction. However, the present work reports greater absolute values for k1 than those of several previous studies. An assessment of previous laboratory studies of k1 is presented. This work confirms that reaction (1) plays a significant role in HOBr formation throughout the atmosphere following both anthropogenic, biogenic and volcanic emissions of brominated species. Reaction (1) therefore contributes to an efficient ozone depleting process in the atmosphere, and further confirms the significance of interactions between two different families of reactive atmospheric trace species

Kinetic studies of the BrO plus ClO cross-reaction over the range T=246-314 K

The kinetics of the atmospherically important gas phase radical reaction between BrO and ClO have been studied over the temperature range T = 246–314 K by means of laser flash photolysis coupled with UV absorption spectroscopy. Charge-coupled-device (CCD) detection allowed simultaneous monitoring of both free radicals and the OClO product using ‘differential’ spectroscopy, which minimised interference from underlying UV absorbing species. In this way, the total rate coefficient for BrO + ClO → products (1) was measured, along with that for the OClO producing channel of this process BrO + ClO → OClO + Br (1c). These reaction rate coefficients are described by the Arrhenius expressions: k1/cm3 molecule−1 s−1 = (2.5 ± 2.2) × 10−12 exp[(630 ± 240)/T] and k1c/cm3 molecule−1 s−1 = (4.6 ± 3.0) × 10−12 exp[(280 ± 180)/T], where errors are 2σ, statistical only. An extensive sensitivity analysis was performed to quantify the potential additional systematic uncertainties in this work arising from uncertainties in secondary chemistry, absorption cross-sections and precursor concentrations. This analysis identified the reactions of initial and secondarily generated bromine atoms (specifically Br + O3 and Br + Cl2O) as particularly important, along with the reversible combination of ClO with OClO forming Cl2O3. Potential uncertainty in this latter process was used to define the lowest temperature of the present study. Results from this work indicate larger absolute values for k1 and k1c than those reported in previous studies, but a weaker negative temperature dependence for k1c than previously observed, resulting in a branching ratio for channel (1c) with a positive temperature dependence, in disagreement with previous studies. Reaction (1c) is the principal source of OClO in the polar stratosphere and is commonly used in atmospheric models as an indicator of stratospheric bromine chemistry. Thus these measurements might lead to a reinterpretation of modelled stratospheric OClO, which has also been suggested by previous comparisons of observations with atmospheric model studies

Is TrpM5 a reliable marker for chemosensory cells? Multiple types of microvillous cells in the main olfactory epithelium of mice

<p>Abstract</p> <p>Background</p> <p>In the past, ciliated receptor neurons, basal cells, and supporting cells were considered the principal components of the main olfactory epithelium. Several studies reported the presence of microvillous cells but their function is unknown. A recent report showed cells in the main olfactory epithelium that express the transient receptor potential channel TrpM5 claiming that these cells are chemosensory and that TrpM5 is an intrinsic signaling component of mammalian chemosensory organs. We asked whether the TrpM5-positive cells in the olfactory epithelium are microvillous and whether they belong to a chemosensory system, i.e. are olfactory neurons or trigeminally-innervated solitary chemosensory cells.</p> <p>Results</p> <p>We investigated the main olfactory epithelium of mice at the light and electron microscopic level and describe several subpopulations of microvillous cells. The ultrastructure of the microvillous cells reveals at least three morphologically different types two of which express the TrpM5 channel. None of these cells have an axon that projects to the olfactory bulb. Tests with a large panel of cell markers indicate that the TrpM5-positive cells are not sensory since they express neither neuronal markers nor are contacted by trigeminal nerve fibers.</p> <p>Conclusion</p> <p>We conclude that TrpM5 is not a reliable marker for chemosensory cells. The TrpM5-positive cells of the olfactory epithelium are microvillous and may be chemoresponsive albeit not part of the sensory apparatus. Activity of these microvillous cells may however influence functionality of local elements of the olfactory system.</p

Oral dosing of rodents using a palatable tablet

Rationale: Delivering orally bioavailable drugs to rodents is an important component to investigating that route of administration in novel treatments for humans. However, the traditional method of oral gavage requires training, is stressful, and can induce oesophageal damage in rodents. Objectives: To demonstrate a novel administrative technique – palatable gelatine tablets – as a stress-free route of oral delivery. Methods: 24 male Lister hooded rats were sacrificed for brain tissue analysis at varying time-points after jelly administration of 30 mg/kg of the wake-promoting drug modafinil. A second group of 22 female rats were tested on locomotor activity after 30 mg/kg modafinil, or after vehicle jellies, with the locomotor data compared to the brain tissue concentrations at the corresponding times. Results: Modafinil was present in the brain tissue at all time-points, reducing in concentration over time. The pattern of brain tissue modafinil concentration is comparable to previously reported results following oral gavage. Modafinil-treated rats were more active than control rats, with greater activity during the later time-periods – similar to that previously reported following intraperitoneal injection of 40 mg/kg modafinil. Conclusions: Palatable jelly tablets are an effective route of administration of thermally-stable orally-bioavailable compounds, eliminating the stress/discomfort and health risk of oral gavage and presenting as an alternative to previously reported palatable routes of administration where high protein and fat levels may adversely affect appetite for food reward, and uptake rate in the gastrointestinal tract.Publisher PDFPeer reviewe

Three Linked Vasculopathic Processes Characterize Kawasaki Disease: A Light and Transmission Electron Microscopic Study

Kawasaki disease is recognized as the most common cause of acquired heart disease in children in the developed world. Clinical, epidemiologic, and pathologic evidence supports an infectious agent, likely entering through the lung. Pathologic studies proposing an acute coronary arteritis followed by healing fail to account for the complex vasculopathy and clinical course.Specimens from 32 autopsies, 8 cardiac transplants, and an excised coronary aneurysm were studied by light (n=41) and transmission electron microscopy (n=7). Three characteristic vasculopathic processes were identified in coronary (CA) and non-coronary arteries: acute self-limited necrotizing arteritis (NA), subacute/chronic (SA/C) vasculitis, and luminal myofibroblastic proliferation (LMP). NA is a synchronous neutrophilic process of the endothelium, beginning and ending within the first two weeks of fever onset, and progressively destroying the wall into the adventitia causing saccular aneurysms, which can thrombose or rupture. SA/C vasculitis is an asynchronous process that can commence within the first two weeks onward, starting in the adventitia/perivascular tissue and variably inflaming/damaging the wall during progression to the lumen. Besides fusiform and saccular aneurysms that can thrombose, SA/C vasculitis likely causes the transition of medial and adventitial smooth muscle cells (SMC) into classic myofibroblasts, which combined with their matrix products and inflammation create progressive stenosing luminal lesions (SA/C-LMP). Remote LMP apparently results from circulating factors. Veins, pulmonary arteries, and aorta can develop subclinical SA/C vasculitis and SA/C-LMP, but not NA. The earliest death (day 10) had both CA SA/C vasculitis and SA/C-LMP, and an "eosinophilic-type" myocarditis.NA is the only self-limiting process of the three, is responsible for the earliest morbidity/mortality, and is consistent with acute viral infection. SA/C vasculitis can begin as early as NA, but can occur/persist for months to years; LMP causes progressive arterial stenosis and thrombosis and is composed of unique SMC-derived pathologic myofibroblasts