Toward selective reactions with C-H bonds: a rationale for the regio- and stereochemistry of dichlorocarbene insertions into cyclic hydrocarbons

DFT calculations have been performed to study the course of dichlorocarbene insertion reactions into alkanes and to better understand the regio- and stereoselectivities observed. At the B3LYP/6-31G(d) level of theory, the selectivity of dichlorocarbene insertions into a number of hydrocarbons agrees well with the obtained experimental results. The reactivity of a specific C-H bond is determined by the capacity of the remaining alkyl fragment to effectively delocalize the partial positive charge buildup during the reaction. This activity can readily be estimated by calculation of the hydride transfer potential (HTP). A comparison with the structure and the stability of the corresponding cation is useful to emphasize the origins of the selectivity. Dichlorocarbene is also predicted to react efficiently with acidic C-H bonds through a nucleophilic-electrophilic mechanism. In principle, an attack of a carbene on an appropriately substituted three-membered ring may lead to fragmentation of the molecule.     

Charge transport parameters of the pentathienoacene crystal

Pentathienoacene, the thiophene equivalent of pentacene, is one of the latest additions to the family of organic crystal semiconductors with a great potential for use in thin film transistors. By using density functional theory and gas-phase ultraviolet photoelectron spectroscopy, we investigate the microscopic charge transport parameters of the pentathienoacene crystal. We find that the valence band exhibits a stronger dispersion than those in the pentacene and rubrene single crystals with marked uniaxial characteristics within the molecular layer due to the presence of one-dimensional pi-stacks; a small hole effective mass is also found along the direction perpendicular to the molecular layers. In the conduction band, strong intermolecular sulfur-sulfur interactions give rise to a significant interstack electronic coupling whereas the intrastack dispersion is greatly reduced. The intramolecular vibronic coupling (reorganization energy) is stronger than that in pentacene but comparable to that in sexithiophene; it is larger for holes than for electrons, as a result of low-frequency modes induced by the sulfur atoms. The polarization energy is large, but its effect on the vibronic coupling remains small. Charge transport is discussed in the framework of both band and hopping models.     

Nonaqueous capillary electrophoresis in pharmaceutical analysis

This review presents different solvents and electrolytes commonly used as BGEs in NACE for the analysis of pharmaceutical compounds. Most NACE applications carried out since 1998 for the analysis of compounds of pharmaceutical interest are presented in four tables: (i) analysis of drugs and related substances, (ii) analysis of chiral substances, (iii) analysis of phytochemical extracts and (iv) analysis of drugs in biological fluids. These selected examples are used to illustrate the interest in NACE versus conventional aqueous CE.     

The mixing efficiency of open flows

Mixing in open incompressible flows is studied in a model problem with inhomogeneous passive scalar injection on an inlet boundary. As a measure of the efficiency of stirring, the bulk scalar concentration variance is bounded, and the bound is shown to be sharp at low Péclet number. Although no specific flow saturating the bound at high Péclet number is produced here, the estimate is conjectured to be approached for flows possessing sufficiently sustained chaotic regions.     

Axiomatizations of quasi-Lovász extensions of pseudo-Boolean functions

We introduce the concept of quasi-Lovász extension as being a mapping \({f\colon I^n\to\mathbb{R}}\) defined on a nonempty real interval I containing the origin and which can be factorized as f(x ₁, . . . , x _n ) =  L(φ(x ₁), . . . , φ(x _n )), where L is the Lovász extension of a pseudo-Boolean function \({\psi\colon \{0, 1\}^n \to \mathbb{R}}\) (i.e., the function \({L\colon \mathbb{R}^n \to \mathbb{R}}\) whose restriction to each simplex of the standard triangulation of [0, 1] ⁿ is the unique affine function which agrees with ψ at the vertices of this simplex) and \({\varphi\colon I \to \mathbb{R}}\) is a nondecreasing function vanishing at the origin. These functions appear naturally within the scope of decision making under uncertainty since they subsume overall preference functionals associated with discrete Choquet integrals whose variables are transformed by a given utility function. To axiomatize the class of quasi-Lovász extensions, we propose generalizations of properties used to characterize Lovász extensions, including a comonotonic version of modularity and a natural relaxation of homogeneity. A variant of the latter property enables us to axiomatize also the class of symmetric quasi-Lovász extensions, which are compositions of symmetric Lovász extensions with 1-place nondecreasing odd functions.     

On signature-based expressions of system reliability

The concept of signature was introduced by Samaniego for systems whose components have i.i.d. lifetimes. This concept proved to be useful in the analysis of theoretical behaviors of systems. In particular, it provides an interesting signature-based representation of the system reliability in terms of reliabilities of k-out-of-n systems. In the non-i.i.d. case, we show that, at any time, this representation still holds true for every coherent system if and only if the component states are exchangeable. We also discuss conditions for obtaining an alternative representation of the system reliability in which the signature is replaced by its non-i.i.d. extension. Finally, we discuss conditions for the system reliability to have both representations.     

Cleaning validation using thermogravimetry

The health authorities require that equipment used in the pharmaceutical industry is clean prior to use. The main raison is to prevent any contamination of the drug products. This article demonstrates that thermogravimetry (TG) can be used for the determination of the residual impurities during the cleaning validation of the equipment of pharmaceutical production plants. The accuracy and the recovery rate of this method are comparable with those of the classical analysis method (determination of the distillation residue using a rotary evaporator). The fully automation of the testing equipment even allows its utilization around the clock by plants operators, leading to a significant reduction of the time necessary for the cleaning validation and to an increase of the plant capacity.     

About Polynomials Whose Divided Differences are Integer-Valued on Prime Numbers

We first globalize some recent results about polynomials whose divided differences are integer-valued on subsets of discrete valuation domains. This allows us to describe explicit computations, in particular for polynomials which are integer-valued on the prime numbers. Then, we specialize other recent results about integer-valued polynomials on triangular matrices to matrices whose coefficients are in some subsets, and in particular, when the coefficients are primes.     

Characterization of Interfacially Active Fractions and Their Relations to Water-in-Oil Emulsion Stability.

Natural surfactants from four crude oils have been extracted by adsorption on silica after precipitation of the asphaltenes by means of centrifugation or decantation. The extracted fractions have been characterized, analytically by FT-IR spectroscopy (chemical functions) and chromatography (molecular weight and polarity) and by their interfacial properties with emulsification and interfacial tension measurements on the model system water/decane with interfacially active fractions in different concentrations. The importance of these fractions (precipitated and adsorbed) on the stability of w/o emulsions is investigated. The influence of some extraction parameters (centrifugation or decantation, different adsorbents) on the nature and the emulsion behaviour of the fractions is studied and shows that the classification of the surfactants (asphaltenes, resins) is diffuse. It also shows that all the interfacially active constituents of the crude are interacting and are involved in the interfacial processes.