On the Origin of the Enhanced Acidity of Chalcocyclopentadienes (Cyclopentadiene Chalcogenols) in the Gas Phase

The intrinsic acidity of chalcocyclopentadienes (CpXH; X=O, S, Se, Te) is investigated by high‐level G3B3 and G2 ab initio as well as B3LYP DFT calculations, which show that, independent of the nature of the heteroatom, all chalcocyclopentadienes are stronger acids in the gas phase than cyclopentadiene. However the acidity does not increase regularly down the group, and the acidity enhancement for Te derivatives is five times larger than for O derivatives, but only twice that of S‐containing compounds. The most favorable deprotonation process corresponds to loss of the proton attached to the heteroatom, with the sole exception of the 5‐substituted 1,3‐cyclopentadienes, for which the O and S derivatives are predicted to behave as carbon acids. No matter the nature of the heteroatom, the 1‐substituted 1,3‐cyclopentadienes are the strongest acids. The intrinsic acidity of all isomers, namely, 1‐substituted, 2‐substituted, and 5‐substituted 1,3‐cyclopentadienes, increases with increasing aromaticity of the anion formed on deprotonation, and therefore the Te compound is the strongest acid for the three series. However, the intrinsic acidity of chalcocyclopentadienes is not dictated by aromaticity, so that, in general, the most stable deprotonated species do not coincide with the most aromatic ones.     

Critical aspects of urine profiling for the selection of potential biomarkers using UPLC-TOF-MS

Biomarker selection through the metabolomics approach involves the acquisition of nontargeted metabolic profiles. In this study, some critical factors that may affect this process were investigated using urine test samples and a UPLC‐TOF system. Repeated injections of a single sample demonstrated that the percentage of undetected and poorly repeatable measurements (intensity RSD > 15%) decreased from 22.5 to 5.8% and from 32.9 to 14.7%, respectively, as the scan time was increased up to 0.6 s (approximately 11 data points per peak). An additional critical factor was identified in the presence of broad concentration differences between the samples; the application of a dilution scheme that minimized these differences reduced the number of missing values in the final datasets by 36%. The impact of missing values was further investigated in the study of two groups of samples produced by using a spike as artificial marker. Missing values weakened the models used for the interpretation of the metabolic profiles, and greatly hindered the identification of possible markers. Finally, a simple strategy for an effective analysis of urine samples was outlined; it proved to limit the need for the post‐acquisition elaboration of the data. The same strategy can easily be adapted to other matrices. Copyright © 2011 John Wiley & Sons, Ltd.     

A Convenient Approach to Simultaneous Analysis of a Pharmaceutical Drug and Its Counter-Ion by CE Using Dual-Opposite End Injection and Contactless Conductivity Detection

Capillary electrophoresis (CE) coupled to a capacitively coupled contactless conductivity detector (C⁴D) was used for the determination in a single analysis of a pharmaceutical drug and its counter-ion. Dual-opposite end injection (DOI) was used to introduce hydrodynamically the analytes at each end of the capillary. No modification of the commercial apparatus is required. After applying the voltage, the cations and anions migrate from each end of the capillary in opposite directions toward the detector placed near the cathode outlet. The electrophoretic conditions were initially developed with three test drugs (chlorpheniramine maleate, metoprolol tartrate, clomiphene citrate) and then applied to two Vinca alkaloids (catharanthine sulfate, vinorelbine ditartrate). The 10 mM histidine–50 mM acetic acid buffer (pH 4.1)–methanol 90:10 (v/v) electrolyte was suitable for the analysis of these high or medium mobile anions by CE–C⁴D due to its low conductivity background and high buffer capacity. Finally, the CE procedure developed was successfully validated for catharanthine sulfate. The method developed herein is fast (<10 min) and accurate (repeatability on migration time < 0.6% and peak areas < 1.3%, n = 6).

     

A comparative study of the topology of the experimental electron density within 2 and 4e- donor alkyne complexes

A comparison of the topology of the experimental electron density, as revealed by high resolution X-ray diffraction, is provided for two prototypal transition metal alkyne complexes where the alkyne formally behaves as a 2 or 4e(-) donor. A higher value of the electron density ρ(r)(bcp) at the M(T)···C bond critical point (bcp), a lower value of ρ(r)(bcp) at the coordinated C≡C bcp, outwardly bent MC bond paths and a close to zero ellipticity for the C[triple bond, length as m-dash]C bond constitute the topological signature of a 4e(-) donor alkyne ligand.     

Nucleation and stability of defect clusters: New energetic model in the case of substituted wustites

Abstract

For wüstite Fe_1?z O (z < 0.08) an energetic model accounts for the stability of cubic defect clusters (m/n) which are partly ordered in the crystal. The Gibbs energy G_T (N) associated with clusters, including their distorted envelope, is expressed as a sum of a volume term in N ³ and of surface terms in N ⁴; N is the number of bonds characteristic of the cluster size. In the case of a (10/4) type cluster, this energy is negative and minimum for N_m ranging between 4 and 5, when the volume and surface energies range between specific values. Using simple assumptions, a volume energy ?0.80 eV per vacancy is found in accordance with the value of stabilization energy calculated by theorists for the (10/4) cluster. The substitution of Fe²⁺ by Ca²⁺ should lead to a decrease of cluster size; this has been recently suggested by neutron diffraction studies.     

Diffraction study of actinides under pressure

Abstract

Uranium and thorium have sufficiently low radioactive dose rates to allow their study at synchrotrons and neutron facilities. Correspondingly, numerous compounds of these two actinides have been studied under pressure by synchrotron x-ray diffraction. The maximum pressures reached were on the order of 60-80 GPa, and 300 GPa in one case.

The situation is much more difficult for all other actinides. Their high level of radioactivity has up to now prevented their study at synchrotrons, except in a few special cases. In contrast, all actinide metals available in sufficient quantities, and a large number of compounds of highly radioactive actinides, have been studied in highpressure laboratory facilities.

Recent examples of in situ high pressure x-ray diffraction work will be described.     

Existence locale de solutions c∞ pour des equations de monge-ampere changeant de type

We prove the C∞ local solvability of the n-dimensional Monge-A mpé:ere equation det (u_ij + a_ij(x,u,▽u))= K(x) f(x, u, ▽u), f> 0, in a neighborhood of any point x₀ where K(x₀)= 0 but dK(x_o) ¦0.     

Un Algorithme pour le Calcul des Syzygies sur V[X] dans le cas où V est un Domaine de Valuation

Soit V un domaine de valuation. Nous donnons un algorithme pour calculer une base du V-saturé d'un sous-module de type fini d'un V-module libre (avec une base éventuellement infinie). Nous l'appliquons pour calculer le V-saturé d'un sous-V[X]-module de type fini de V[X] ⁿ (n ∈ ?*). Ceci permet enfin de calculer un système générateur fini pour les syzygies sur V[X] d'une famille finie de vecteurs de V[X] ^k .

We give an algorithm for computing the V-saturation of any finitely generated submodule of V[X] ⁿ (n ∈ ?*), where V is a valuation domain. This allows us to compute a finite system of generators for the syzygy module of any finitely generated submodule of V[X] ^k .     

Individual decision‐making in dynamic collective systems

One of the most popular individual choice models is the multinomial logit model (MLM). The basic hypothesis of the MLM is that an individual chooses an alternative among a set of alternatives available to him by comparing the utilities of all the choices. The MLM is, however, limited in its usefulness because it doesn't account for the effects of the time factor and the social interactions between individuals. This work describes a dynamic extension of the MLM that allows for such interactions. The new model is formulated as an interactive continuous‐time Markov process, and is approximated, for a large population, by a deterministic system. Some possible consequences of the interaction phenomena are discussed with a special binary choice model.