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showing 10 items of 16992 documents
The effect of cavity tuning on oxygen beam currents of an A-ECR type 14 GHz electron cyclotron resonance ion source.
2016
The efficiency of the microwave-plasma coupling plays a significant role in the production of highly charged ion beams with electron cyclotron resonance ion sources (ECRISs). The coupling properties are affected by the mechanical design of the ion source plasma chamber and microwave launching system, as well as damping of the microwave electric field by the plasma. Several experiments attempting to optimize the microwave-plasma coupling characteristics by fine-tuning the frequency of the injected microwaves have been conducted with varying degrees of success. The inherent difficulty in interpretation of the frequency tuning results is that the effects of microwave coupling system and the ca…
Theoretical investigation of the potential energy surface of the van der Waals complex CH4-N-2
2009
International audience; The interaction potential energy surface of the van der Waals CH4-N-2 complex has been calculated for a broad range of intermolecular separations and configurations in the approximation of rigid interacting molecules at the CCSD(T) and MP2 levels of theory using the correlation consistent aug-cc-pVTZ basis set. The BSSE correction was taken into account for all the calculations. The most stable configurations of the complex were found. Binding energies were calculated in the CBS limit with accounting for the molecular deformations. The harmonic and anharmonic fundamental vibrational frequencies and rotational constants for the ground and first excited vibrational sta…
An aryl-fused redox-active tetrathiafulvalene with enhanced mixed-valence and radical-cation dimer stabilities.
2018
Molecular recognition of stable organic radicals is a relatively novel, but important structural binding motif in supramolecular chemistry. Here, we report on a redox-switchable veratrole-fused tetrathiafulvalene derivative VTTF which is ideally suited for this purpose and for the incorporation into stimuli-responsive systems. As revealed by electrochemistry, UV/Vis measurements, X-ray analysis, and electrocrystallisation, VTTF can be reversibly oxidised to the corresponding radical-cation or dication which shows optoelectronic and structural propterties similar to tetrathiafulvalene and tetrakis(methylthio)tetrathiafulvalene. However, theoretical calculations, variable temperature EPR, and…
Protonation of a Spherical Macrotricyclic Tetramine: Water Inclusion, Allosteric Effect, and Cooperativity
2017
The spherical macrotricyclic cryptand tetramine "C24" (1) displays remarkable protonation behaviour. It undergoes protonation in four successive steps for which pKa values of 11.17±0.05, 10.28±0.04, 6.00±0.06 and 3.08±0.08 have been determined at 298 K. The unusually close values for the first two protonations provide evidence for the encapsulation of a water molecule serving as effector for the second protonation, which is consistent with earlier observations that the exchange of protons bound in the diprotonated species with solvent protons is unusually slow and that 17 O NMR spectra show the presence of an oxygen centre in the same species quite distinct from that of solvent water. Encap…
Synthesis of 1,3-bis(trimethylcyclam) and 1,3-bis(trimethylcyclen) substituted benzenes
2009
Pd-catalyzed amination of 1,3-dibromobenzene with N,N',N''-trimethylcyclam and N,N',N''-trimethylcyclen provided corresponding 1,3-bis(tetraazamacrocyclic) derivatives of benzene in 25-32% yields. The dependence of the products yields on the phosphine ligand applied (BINAP, DavePHOS) as well as on the stoichiometry of starting compounds was established. Scope and limitations for the synthesis of N-phenyl and N-(3-bromophenyl) derivatives of trimethylcyclam and trimethylcyclen were demonstrated.
Substitution of the laser borane anti-B18H22 with pyridine: a structural and photophysical study of some unusually structured macropolyhedral boron h…
2018
Reaction of anti-B18H221 with pyridine in neutral solvents gives sparingly soluble B16H18-3',8'-Py23a as the major product (ca. 53%) and B18H20-6',9'-Py22 (ca. 15%) as the minor product, with small quantities of B18H20-8'-Py 4 (ca. 1%) also being formed. The three new compounds 2, 3a and 4 are characterized by single-crystal X-ray diffraction analyses and by multinuclear multiple-resonance NMR spectroscopy. Compound 2 is of ten-vertex nido:ten-vertex arachno two-atoms-in-common architecture, long postulated for a species with borons-only cluster constitution, but previously elusive. Compound 3a is of unprecedented ten-vertex nido:eight-vertex arachno two-atoms-in-common architecture. The si…
Enantiomeric Resolution of Asymmetric-Carbon-Free Binuclear Double-Stranded Cobalt(III) Helicates and Their Application as Catalysts in Asymmetric Re…
2018
A series of double-stranded binuclear helicates [Co2(H1)2]4+, [Co2(H2)2]4+, and [Co2(H3)2]4+, derived from monodeprotonated bis-pyridyl hydrazine-based ligands of H21, H22, and H23 with one, two, and three -CH2 spacers, were obtained. These asymmetric-carbon-free racemic helicates were separated into their ΔΔ and ΛΛ enantiomers. The resolved helicates were examined for the first time as enantioselective catalysts in asymmetric benzoylation and nitroaldol reactions.
Diabetes and renin-angiotensin-aldosterone system: Implications for covid-19 patients with diabetes treatment management
2020
In the context of the COVID-19 continuous spreading, this paper focuses on the increased risk of diabetic patients regarding the metabolic control and the uncertainties related to SARS-CoV-2 infection. Chronic hyperglycaemia negatively affects the immune system, which triggers an increase of morbidity and mortality for viral infections. A key aspect of COVID-19 resides in the involvement of renin-angiotensin-aldosterone (RAAS) system that causes a cascade of reactions mediated by vasoactive peptides with implications in vasoconstriction, vascular permeability, oxidative stress remodelling and tissue injuries. Activation of RAAS at pulmonary level, is responsible for the local damage. Many q…
The global forest above-ground biomass pool for 2010 estimated from high-resolution satellite observations
2021
Funding Information: We are thankful to the GlobBiomass project team and Frank Martin Seifert (ESA) for valuable suggestions and stimulating scientific discussions. We are thankful to Takeo Tadono (JAXA EORC), Masato Hayashi, (JAXA EORC), Kazufumi Kobayashi (RESTEC), Åke Rosenqvist (soloEO), and Josef Kellndorfer (EBD) for support with the use and interpretation of the ALOS PALSAR mosaics. Support by the CCI Land Cover project team, in particular Sophie Bontemps (UCL), is greatly acknowledged. The help from Martin Jung (MPI-BGC) in feature selection and Ulrich Weber (MPI-BGC) for data processing for the GSV-to-AGB conversions is greatly acknowledged. Forest inventory data for the validation…
Environmental and biological factors are joint drivers of mercury biomagnification in subarctic lake food webs along a climate and productivity gradi…
2021
Subarctic lakes are getting warmer and more productive due to the joint effects of climate change and intensive land-use practices (e.g. forest clear-cutting and peatland ditching), processes that potentially increase leaching of peat- and soil-stored mercury into lake ecosystems. We sampled biotic communities from primary producers (algae) to top consumers (piscivorous fish), in 19 subarctic lakes situated on a latitudinal (69.0-66.5 degrees N), climatic (+3.2 degrees C temperature and +30% precipitation from north to south) and catchment land-use (pristine to intensive forestry areas) gradient. We first tested how the joint effects of climate and productivity influence mercury biomagnific…