Anharmonic treatment of vibrational resonance polyads—the diborane: a critical case for numerical methods

Based on accurate computational results, the IR spectra of diborane B₂H₆ and its deuterated derivative B₂D₆ were experimentally revisited to reconsider or complete their band assignments. A pure, variational approach, developed in both mechanical and electrical anharmonicities, was applied to study the diborane molecule for which many uncertainties remain in the spectral IR assignment. This work, together with all the experiments on this system over recent decades, shows the difficulty of interpreting the spectral data, making it a “benchmark” ideal for testing the mathematical approaches for the implementation of vibrational codes.     

Crystal structure of the 1 : 1 : 6 complex between 18-crown-6, hydroquinone and water

Hydroquinone forms a 1 : 1 : 6 complex with 18-crown-6 and water. Crystals of this complex are monoclinic, space groupP2₁/a witha = 14.289(1),b = 7.972(1),c = 11.596(1) Å, = 97.72(1)°,Z = 2,D _c = 1.22 g cm^–3. The hydroquinone and crown ether molecules lie on centres of symmetry with the crown in theD _3d conformation. The water molecules act as a bridge between hydroquinone and the crown ether. The structure consists of molecules linked by a 3-dimensional network of hydrogen bonds: the hydroquinone and two water molecules lie roughly in the (001) plane; the crown ether and four water molecules form bipyramidal structures which are stacked in layers alternating with the previous planes.     

Thermochemistry of natural hypersaline water systems using the Dead Sea as a case

In order to study the heat effect of mixing of fresh waters (winter rains in the form of floods) with Dead Sea water, the heats of mixing of Dead Sea water with distilled water at 25°C have been measured. On the basis of these experimental data, the heats of dilution of fresh water in Dead Sea water and Dead Sea water in fresh water have been calculated. By considering the isothermal cycle of the dilution of Dead Sea water, the partial heat of evaporation of water from Dead Sea water was found to be ca. 24585 kJ-(kgH₂O)^–1 at 25°C.     

EPR and UV–visible spectroscopic studies of alumina-supported chromium oxide catalysts

The oxidation state, the mobility and the molecular structure of chromium species present on CrO_x–Al₂O₃ catalysts have been studied by combined diffuse reflectance spectroscopy, EPR and reduction–extraction by ethane 1,2 diol. CrO₄²⁻ species exist on the alumina surface in the form of loosely-interacting species on hydrated surface (species A) and in the form of strongly bonded species on dehydrated Al₂O₃ surface (species B). The CrO₄²⁻ species show high mobility and are probably responsible for the formation of CrO_x clusters.     

N-Heterocyclic tridentate aromatic ligands bound to [Ln(hexafluoroacetylacetonate)3] units: thermodynamic, structural, and luminescent properties

Herein, we discuss how, why, and when cascade complexation reactions produce stable, mononuclear, luminescent ternary complexes, by considering the binding of hexafluoroacetylacetonate anions (hfac(-)) and neutral, semi-rigid, tridentate 2,6-bis(benzimidazol-2-yl)pyridine ligands (Lk) to trivalent lanthanide atoms (Ln(III)). The solid-state structures of [Ln(Lk)(hfac)(3)] (Ln=La, Eu, Lu) showed that [Ln(hfac)(3)] behaved as a neutral six-coordinate lanthanide carrier with remarkable properties: 1) the strong cohesion between the trivalent cation and the didentate hfac anions prevented salt dissociation; 2) the electron-withdrawing trifluoromethyl substituents limited charge-neutralization and favored cascade complexation with Lk; 3) nine-coordination was preserved for [Ln(Lk)(hfac)(3)] for the complete lanthanide series, whilst a counterintuitive trend showed that the complexes formed with the smaller lanthanide elements were destabilized. Thermodynamic and NMR spectroscopic studies in solution confirmed that these characteristics were retained for solvated molecules, but the operation of concerted anion/ligand transfers with the larger cations induced subtle structural variations. Combined with the strong red photoluminescence of [Eu(Lk)(hfac)(3)], the ternary system Ln(III)/hfac(-)/Lk is a promising candidate for the planned metal-loading of preformed multi-tridentate polymers.     

Rapid and convenient semi-automated microwave-assisted solid-phase synthesis of arylopeptoids

A facile and expedient route to the synthesis of arylopeptoid oligomers (N-alkylated aminomethyl benz-amides) using semi-automated microwave-assisted solid-phase synthesis is presented. The synthesis was optimized for the incorporation of side chains derived from sterically hindered or unreactive amines and both ortho- and para-substituted arylo-backbones. By utilizing this optimized protocol a complex nonameric arylopeptoid was synthesized in less than 11 h, featuring a novel alternating ortho-, meta-, and para-substituted backbone pattern and a variety of chemically diverse and challenging side chains.     

Synthesis of novel symmetrical and nonsymmetrical 6-membered heterocycles with pendant electron-rich organoiron substituents

The functionalized complexes [(dppe)Cp^*Fe(CC)]₂-(Py) (Py=2,6-C₅H₃N and 3,5-C₅H₃N (dppe=1,2-bis(diphenylphosphino)ethane) were isolated in good yields from reaction of the chloro complex (dppe)Cp^*FeCl with the protected bis-acetylenic heterocyclic precursor. These electron-rich pyridyl ligands constitute interesting examples of organometallic heterocycles bearing redox-active substituents. Attempts to find an alternative route starting from the alkynyl complex [(dppe)Cp^*Fe(CCH)] and the corresponding dibromopyridines using a Sonogashira cross-coupling reaction are also described. By this route, the monofunctionalized products [(dppe)Cp^*Fe(CC)]-2,6-Py-Br and [(dppe)Cp^*Fe(CC)]-3,5-Py-Br could be cleanly isolated. These compounds open the way to the generation of heteroaromatics featuring nonequivalent alkyne substituents such as [(dppe)Cp^*Fe(CC)]-2,6-Py-[(CC)SiMe₃] or [(dppe)Cp^*Fe(CC)]-3,5-Py-[(CC)SiMe₃] by further coupling.In commemoriation of the centenary of Academician A. N. Nesmeyanov.UMR CNRS 6509 Organométalliques et catalyse: Chimie et Electrochimie Moléculaires, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1207–1218, September, 1999.     

Molecular dynamics simulation in aqueous solution of N-methylazetidinone as a model of β-lactam antibiotics

In this article, we analyze the results of a molecular dynamics simulation in aqueous solution of the N-methylazetidinone molecule, often used to model β-lactam antibiotics. The radial distribution functions (RDFs) corresponding to the most interesting atoms, in terms of reactivity, are presented. We focus our study on the effect of a polar environment on the molecule. The solvent structure around the system is compared to the structure of β-lactam-water complexes, as obtained in a previous study of reaction mechanisms for the neutral and alkaline hydrolyses of N-methylazetidinone. Two types of complexes have been considered which are related to different hydrolysis mechanisms having similar energy barriers at the rate-limiting step of the reaction path. In the first type, the β-lactam-water interaction takes place through the oxygen carbonyl atom and there is agreement between the maxima of the RDFs obtained here and the ab initio structure of the complexes previously reported. In the second type, the interaction takes place through the nitrogen atom and we do not predict a coordination layer around the β-lactam nitrogen atom. The results suggest that in aqueous solution hydrolysis of the carbonyl group is the most probable starting point for the overall hydrolysis reaction. Some discussion on the use of cluster models to represent the solvent effect is included. Received: 29 July 1998 / Accepted: 13 October 1998 / Published online: 1 February 1999     

Blood banking quality: minimum requirements for TQM

In 1995, the Council of Europe published a guide with recommendations providing transfusion services with a set of guidelines and principles relating to the preparation, use and quality assurance of blood components. As a blood transfusion service is at the same time a supplier of blood products and a test laboratory the quality management system must include good medical practice, good manufacturing practice and good laboratory service, all of which are closely linked. We made a critical evaluation of the content of the guide and analysed requirements and recommendations in comparison with quality management systems applied by the concerned partners. As a major critic we observed that the guide does not take into account any quality system of the in vitro diagnostic (IVD) supplier and/or distributor. With the addition of some items outlined in ISO 25 and ISO 9000, the Council of Europe document can be improved so that it complies with internationally accepted quality management standard recommendations.     

Étude de la distribution des ions sur colonnes échangeuses

Résumé L'auteur étudie la distribution de divers ions seuls ou mélangés sur une résine cationique, par voie semimicro-analytique.

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Summary A column constructed from eight sacks filled with ion exchangers was used to study the distribution of metal ions of various valency from pure solutions or mixtures. If the chlorides of the metals are used in all cases, sodium and ammonium are retained in the first two sacks; magnesium and zinc in all sacks, especially in the first and sixth; iron and aluminium in all, particularly the first and sixth; nickel and cadmium in the first two, particularly the first; thorium in the first sack. These findings, which are independent of the atomic weight and valency, are possibly related to the formation of solvates and their various stabilities.

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Zusammenfassung Mit Hilfe einer Säule, die aus acht mit einem Ionenaustauscher gefüllten Säckchen bestand, wurde die Verteilung von Metallionen verschiedener Wertigkeit aus reinen Lösungen oder Gemischen untersucht. Verwendet man stets Chloride der betreffenden Metalle, so werden Natrium und Ammonium in den beiden ersten Säckchen, Magnesium und Zink in allen Säckchen, insbesondere im ersten und sechsten, Nickel und Cadmium in den beiden ersten, insbesondere im ersten, Eisen und Aluminium in allen, insbesondere im ersten und sechsten, Thorium im ersten Säckchen zurückgehalten. Diese von Atomgewicht und Wertigkeit unabhängigen Ergebnisse stehen möglicherweise mit der Bildung von Solvaten und deren verschiedener Stabilität im Zusammenhang.