Interplay between interior and boundary geometry in Gromov hyperbolic spaces

We show that two visual and geodesic Gromov hyperbolic metric spaces are roughly isometric if and only if their boundaries at infinity, equipped with suitable quasimetrics, are bilipschitz-quasimoebius equivalent. Similarly, they are quasi-isometric if and only if their boundaries are power quasimoebius equivalent.     

Efficient regioselective synthesis of 6-amino-5-benzoyl-1-substituted 2(1H)-pyridinones

[Reaction: see text]. A regioselective and efficient approach toward 6-amino-5-benzoyl-1-substituted 2(1H)-pyridinones by reaction of acyclic ketene aminals with propiolic acid ester was developed. The effect of the solvent and temperature on the regioselectivity of the reaction and the compatibility of the target compounds to functional group manipulations was examined. Substrates with an ortho substituent build atropisomers due to the restricted rotation around the C-N bond. The enantiomers were separated, and the barrier of rotation was determined experimentally. Quantum chemical calculations allowed a ranking of the barrier heights, and a new mechanism of rotation by deformation of the central pyridinone moiety is proposed.     

Phosphine-substrate recognition through the C-H...O hydrogen bond: application to the asymmetric Pauson-Khand reaction

A unique methine moiety attached to three heteroatoms (O, P, S) and contained in the PuPHOS and CamPHOS ligands serves as a strong hydrogen-bond donor. Nonclassical hydrogen bonding of this methine with an amido-carbonyl acceptor provides a completely diastereoselective ligand exchange process between an alkyne dicobalthexacarbonyl complex and a phosphine ligand. This weak contact has been studied by means of X-ray analysis, 1H NMR, and quantum mechanical calculations and revealed that the present interaction falls in the range of strong C-H...O=C bonds. The hydrogen-bond bias obtained in the ligand exchange process has been exploited in the asymmetric intermolecular Pauson-Khand reaction to yield the corresponding cyclization adducts in up to 94% ee.     

Nitrogen Sorption Studies of Silica Particles Obtained in Emulsion and Microemulsion Media

The internal surface structures of silica aerogel particles synthesized using different catalysts in emulsion and microemulsion media have been investigated by means of N(2) adsorption and desorption isotherms. Surface fractal dimensions have been computed using different methods: Frankel-Halsey-Hill plots of the adsorption isotherms, the thermodynamic fractal isotherm equation, and a modification of the thermodynamic fractal isotherm equation. Silica aerogels synthesized in emulsion media with an acidic catalyst have a high specific surface area without micropores and show two separate ranges of scales where the surface fractal dimensions are different and constant. Silica aerogels synthesized in emulsion media with a basic catalyst have a moderate specific surface area with a high percentage of micropores and show constant surface fractal dimensions over a larger range. Silica aerogels synthesized in microemulsion media with a basic catalyst have a low specific surface area with a moderate percentage of micropores and show a moderate range of scales over which the surface fractal dimension is constant. Analyses by both the thermodynamic and modified thermodynamic methods give similar ranges of the surface fractal dimensions of the silica particles. Copyright 2000 Academic Press.     

Cathodically activated nucleophilic aromatic substitution of hydrogen: a novel electrochemical mechanism

Cathodically activated nucleophilic aromatic substitution of hydrogen (SNArH) is reported for the first time; the 1,3,5-trinitrobenzene radical anion reacts with the nucleophile N-methylformamide leading to high yields of the sigma H-complex radical anion; this intermediate can be easily oxidised electrochemically by means of a three-electron mechanism giving rise to the nucleophilic aromatic substitution product (NASH product) in good yield.     

Intrinsic reaction coordinate of perturbed potential energy surfaces: Construction of perturbed energy profiles

This contribution analyzes the changes in the intrinsic reaction coordinate (IRC ) and in the potential energy profiles (PEP ) caused by application of a uniform electric field evaluated using standard ab initio MO methods. Two typical organic processes have been studied, namely, the Friedel–Crafts and the Walden inversion reactions, which are modeled by suitable simple systems. The results for the Walden inversion reaction show that the IRC for the field-free and that for perturbed processes are almost coincident; in this case, using the field-free IRC to compute the perturbed energy profile is a very good approximation. On the contrary, for the Friedel–Crafts model reaction, the two IRC s differ slightly, so the energy profiles using the perturbed and the unperturbed IRC s are somewhat different. © 1993 John Wiley & Sons, Inc.     

Strategies for internal quality control in antidoping analyses

Internal quality control (IQC) is one of the most important elements contributing to quality assurance in the laboratory. In this study, the strategy for the implementation of an IQC program to monitor performance of the analytical procedures used in an antidoping control laboratory is presented. Different IQC parameters have been defined according to the aim of the method (qualitative or quantitative, screening or confirmation). They are based on the analysis of control and calibration samples in each analytical batch and on the use of an internal standard in chromatographic methods. IQC parameters for chromatographic and immunological methods and the acceptance criteria used to check the quality control data obtained are described and discussed. These IQC procedures have been applied during routine antidoping analyses of more than 5000 samples per year in a laboratory accredited by the International Olympic Committee (IOC) and meeting the requirements of the quality standard ISO 17025.     

On the structure of tetracoordinated organocobalt complexes of the type [CoR2L2]

A series of square-planar organocobalt complexes of the type [CoR₂L₂] (R = 2,3,4,6-C₆,HCl₄ and 2,3,6-C₆H₂Cl₃, L = PEtPh₂, PEt₂Ph, and PEt₃; R = 2,3,5,6-C₆HCl₄, and 2,6-C₆H₃Cl₂, L = PEt₂Ph, PEt₃, and $\text{1}\text{2}$dpe) have been prepared in which the electronegativities of the ligand R vary progressively. The reaction of o-C₆H₄ClMgBr with [CoCl₂L₂] (L = PEtPh₂ PEt₂Ph, γ-pic or $\text{1}\text{2}$bipy) did not give air stable compounds at room temperature, but the solutions obtained at ?78°C appear to contain square-planar species for L = PEtPh₂, PEt₂Ph, and γ-pic, and tetrahedral for L₂ = bipy. The tendency towards square-planar or tetrahedral structures for the compounds [CoR₂L₂] depends on the following factors in order of importance: (i) when the neutral ligand is a phosphine a square-planar structure is adopted; (ii) when L is an aromatic amine, bulky ortho substituents on R favour a square-planar structure; and (iii) a tetrahedral geometry is favoured by bidentate amine ligands. The electronegativity of the organic group R seems to be less important.     

Application of a potentiometric electronic tongue as a classification tool in food analysis

This paper reports on the application of a potentiometric sensor array to the food analysis field, in order to distinguish simple tastes and to classify food samples. This array is formed by a set of non-specific all-solid-state potentiometric sensors and has been used in combination with principal component analysis (PCA) for the classification of food samples in batch and in flow injection mode. First attempt was to classify synthetic samples prepared with controlled variability. Once this ability is proven, satisfactory classification results are presented for commercial waters, orange-based drinks and tea samples. An interesting correlation is achieved between the natural juice content and its first calculated component, which allows for a very simple tool for screening purposes.     

Disordered grown systems: Generation and fractal analysis. Electrodeposition

The basic concepts of fractal geometry are reviewed and applied to quasi-two-dimensional zinc electrodeposits. Among the different structures developed during zinc electrodeposition, we have identified the open texture (obtained at large zinc sulfate concentration and small applied potential values) as a typical fractal self-similar structure. © 1994 John Wiley & Sons, Inc.