Improving neutron activation analysis accuracy for the measurement of gold in the characterization of heterogeneous catalysts using a TRIGA reactor

To measure the gold content of a catalyst accurately, neutron activation analysis (NAA) is one of the methods of choice. NAA is preferred for such heterogeneous catalysts because: (1) it requires minimal sample preparation; (2) NAA provides consistent and accurate results; and (3) in most cases results are obtained much quicker than competing methods. NAA is also used as a referee for the other elemental techniques when results do not fall within expected statistical uncertainties. However, at very high gold concentrations, applying NAA to determine the gold in a heterogeneous catalyst is more challenging than a routine NAA procedure. On the one hand, the neutron absorption cross section for gold is very high, resulting in significant self-shielding related errors. On the other hand, gold exhibits low energy resonance neutron absorptions. In this application the self-shielding minimization effort was handled more rigorously than the classic suppression of neutron flux within a specimen. This non-routine approach was used because: (1) for most applications, high accuracy, <3 % relative, is desired, (2) the low energy resonances of gold make its neutron reaction rate complex and (3) the TRIGA reactor flux profile used in this study contains both thermal and significant epithermal neutron fluxes. Accuracy and precision, using this new approach, are expected to improve from 15 % to better than 3 % relative uncertainty. This has been accomplished through a rigorous assessment of the observed effects of low energy resonance on the neutron flux spectral shape within the sample and designing an experiment to minimize the effects.     

Physical-chemistry of silica/alkaline silicate interactions during consolidation. Part 1: Effect of cation size

The purpose of this work is to identify the effect of the cation nature on mechanisms of the sand consolidation with alkaline silicate solution at low temperature (70 °C). Three diluted lithium, sodium and potassium silicate solutions with [Si] = 2.8 mol/l were used to agglomerate sand composed of grains which mean diameter is 340 μm. According to the cation, different behaviors were observed in terms of the drying time and the material cohesion. Essentially, the drying time increases with decreasing cation size. In contrast, the compressive strength raises when the cation size increases inducing intra-granular rupture highlighted by SEM observations. This could find an explanation in the cation hydration sphere of cations. The strength of the cation–water electrostatic interaction becomes less important as the size of the cations increase leading to more ionic bonds. Despite their strong consolidation, potassium-based materials have a high solubility in water. This result is consistent with the ionic nature of bonds.     

Intramolecular Cyclization of 1-(ω-Phenylalkyl)-2-(nitromethylene)pyrrolidines in Triflic Acid

1-(ω-Phenylalkyl)-2-(nitromethylene)pyrrolidines in triflic acid undergo a C,O-diprotonation, followed by loss of water, to form conjugated iminium–hydroxynitrilium dications, which react with the tethered phenyl ring by electrophilic aromatic substitution to afford tricyclic iminium compounds as triflate salts. The scope and mechanism of this reaction are discussed.     

New antitumour active platinum compounds containing carboxylate ligands in trans geometry: synthesis, crystal structure and biological activity

New asymmetric trans-platinum(II) complexes, composed of an isopropylamine, an azole and two carboxylate leaving groups, are presented. The crystal and molecular structures of one of the complexes has been determined and the cytotoxicity and reactivity with 5'-guanosine monophosphate is reported. The complexes show a reduced reactivity, but no decrease in cytotoxic activity compared to their chloro-counterparts. Furthermore the complexes largely overcome cisplatin resistance, they therefore present an interesting class of antitumour active trans-platinum complexes.     

Synthesis of 6- to 10-membered ring (E)-hydroxyiminohydroazaazoniabenzocycloalkenes derivative from cyclization of 2-nitromethylene-1-(ω-phenylalkyl)imidazolidine or 2-nitromethylene-1-(ω-phenylalkyl)hexahydropyrimidine in trifluoromethanesulfonic acid

In trifluoromethanesulfonic acid, 2-nitromethylene-1-(ω-phenylalkyl)imidazolidine or 2-nitromethylene-1-(ω-phenylalkyl)hexahydropyrimidine derivatives undergo an intramolecular cyclization to afford (E)-hydroxyiminohydroazaazoniabenzocycloalkenes, in their trifluoromethanesulfonate salt form. The reaction probably occurres via the formation of an electrophilic transient hydroxynitrilium ion (or O-protonated nitrile oxide). The yields are generally good, except for the higher-membered ring derivatives.     

Genotoxic effects of cadmium chloride on human amniotic fluid cells cultured in vitro

In this study we report the results of cytogenetic tests, namely a search for chromosome aberrations (CA) and sister chromatid exchanges (SCEs), performed on human amniotic fluid cells cultured and treated with Cadmium chloride. The cells from primary cultures were exposed to CdCl2 at 1 microM and 10 microM for 24 h. At the higher dose, no metaphases were scored and at the lower dose (1 microM) no effects were evident on cell proliferation, and no chromosome aberrations were found. In the subsequent experiments we used cells from subcultures exposed to 1 microM and 5 microM CdCl2. At the 5 microM dose was evident the induction of chromatid breaks, while the frequency of sister chromatid exchanges shows a small increase, not statistically significant at the dose of 1 microM. In this study we positively demonstrated that amniotic fluid cells grown in vitro are reliable for testing various mutagenic or teratogenic substances. With regard to cadmium treatment results, it is evident a clastogenic effect of cadmium chloride but not a significant induction of SCEs.     

One-step synthesis of diazadihydroacenaphthylene derivatives with an isoxazoline ring, starting from 1-benzylamino-1-methylsulfanyl-2-nitroethenes

At low temperature in trifluoromethanesulfonic acid, 1-benzylamino-1-methylthio-2-nitroethene derivatives form hydroxynitrilium ions (or O-protonated nitrile oxides) observed by NMR. Quenching with water leads to the formation of a reactive nitrile oxide, dipole which undergoes an unexpected INOC reaction leading to new 3-methylsulfanyl-8a,8b-dihydro-5H-1-oxa-2,4-diazaacenaphthylenes.     

What News in the Surface Chemistry of Bulk and Supported Vanadia Based SCR‐Catalysts: Improvements in their Resistance to Poisoning and Thermal Sintering

This paper reports a short review on the impact of poisoning effects and thermal aging on the reactivity of surface vanadate species on benchmark V₂O₅?WO₃/TiO₂ Selective‐Catalytic‐Reduction catalysts. A renewed interest of this SCR technology is related to its diversification notably as after‐treatment systems to treat the exhaust from Diesel engines with higher running temperature especially when SCR catalysts are coated on Diesel Particulates Filters. Particular attention is also paid to poisoning effects in conjunction with the progressive replacement of fossil fuels by bio‐fuels containing alkaline contaminants which drastically deactivate the catalyst through neutralization of strong acid sites. Most of the investigations show that better insight into the mechanisms of poisoning and aging processes is needed especially to understand the relative sensibility of various vanadate species. This could provide original guidelines to catalyst preparation and or the developments of more stable bulk systems as exemplified.     

Bis(benzo)triazinethionoaza-14-crown-4 ether and its complex with CoBr<Subscript>2</Subscript>: Synthesis and crystal structures

8,11,14-Trioxa-22,24,25-triazatetracyclo[19.3.1.0^2,7.0^15,20]pentacosa-2,4,6,15(20),16,18-hexaene-23-thione (L) containing a symmetric triazinethione subunit in its macrocycle and its complex with cobalt(II) bromide of the formula [CoL₂Br₂] · 0.5CHCl₃ (I) were obtained and examined by X-ray diffraction, IR and NMR spectroscopy, and mass spectrometry. It was found that the thiourea fragment in compound L is attached to the nitrogen macrocycle through the C(2) and C(19) atoms, thus forming a substantially nonplanar six-membered triazine ring in a slightly distorted sofa conformation. Its mean-square plane is nearly perpendicular to the mean-square plane of the macrocycle (the dihedral angle between them is 83.3°). Structure L is stabilized by two bifurcate endocyclic hydrogen bonds between the N(1) atom of the triazine ring and the O(1) and O(3) atoms. The size of the macrocyclic cavity is 4.07 Å. The coordination polyhedron of the Co atom is a distorted tetrahedron made up of the sulfur atoms of two monodentate terminal molecules L and two bromine atoms.     

The easy hydrolysis of hexacyanocyclopropane, ethyl 1,2,2,3,3-pentacyanocyclopropane-1-carboxylate, 1,2,2,3,3-pentacyanocyclopropane-1-carboxamide, andN,N-dimethyl-1,2,2,3,3-pentacyanocyclopropane-1-carboxamide tor-1,c-2,c-3-tricyanocyclopropane-t-carboxamide

Hydrolysis of hexacyanocyclopropane (1a), ethyl 1,2,2,3,3-pentacyanocyclopropane-1-carboxylate (1b), 1,2,2,3,3-pentacyanocylopropane-1-carboxamide (1c), andN,N-dimethyl-1,2,2,3,3-pentacyanocylopropane-1-carboxamide (1d) in 95% acetic acid yieldsr-1,c-2,c-3-tricyanocyclopropane-t-1-carboxamide (3). The structure of3 was proved by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 454–456, March, 1998.