Expedious synthesis of polyhydroxylated selena and thia-heterocycles via Se and S-ring closure of α,ω-dibromoalditols

The selena and thiaanhydro alditols (with xylo, ribo, d-arabino, erythro, d,l-threo and d-manno configuration) were easily and expeditiously synthesized in good to excellent yields by reaction of selenure and sulfur ions as binucleophiles with α,ω-dibromoalditols as bis-electrophilic substrates. With the 1,6-dibromo-d-glucitol derivative as substrate, only the corresponding thiepane derivative was obtained while the selenaheterocyclistation attempte led to complex mixture.     

Capillary electrophoresis of methyl-substituted phenols in acetonitrile

The separation of mono- and dimethylphenols by capillary electrophoresis in pure acetonitrile was investigated. In acetonitrile, uncharged phenols interact with background electrolyte anions forming negatively charged complexes, which can be separated from each other by capillary electrophoresis. The background electrolyte anions tested were acetate, bromide and chloride. The calculated formation constants for phenol–anion complexes were highest with acetate and smallest with bromide. Complex formation was found to be sensitive to traces of water in the background electrolyte. The separation of methylphenols was also carried out in acetonitrile at high pH using background electrolytes prepared from diprotic acids and tetrabutylammonium hydroxide. At high pH the phenols were partly dissociated, providing an additional mechanism for the separation. All methylphenols were separated with the use of malonate background electrolyte. However, this approach was prone to interference from methanol resulting from the tetrabutylammonium hydroxide solution.     

Silane adsorption onto cellulose fibers: hydrolysis and condensation reactions

The hydrolysis of three alkoxysilane coupling agents, gamma-methacryloxypropyltrimethoxysilane (MPS), gamma-aminopropyltriethoxysilane (APS), and gamma-diethylenetriaminopropyltrimethoxysilane (TAS), was carried out in an ethanol/water (80/20) solution and followed by 1H, 13C, and 29Si NMR spectroscopy, which showed that its rate increased in the order MPS < APS < TAS. The formation of the silanol groups was followed by their self-condensation to generate oligomeric structure. APS and MPS only gave soluble products, whereas colloidal particles precipitated in the medium when TAS was hydrolyzed. Pristine and hydrolyzed MPS were then adsorbed onto a cellulose substrate and thereafter a thermal treatment at 110-120 degrees C under reduced pressure was applied to the modified fibers to create permanent bonding of the coupling agent at their surface.     

A semi-coherent interface with nanoledges intersecting the free surface of an elastic half-space

Abstract

The elastic field generated by a semi-coherent interface formed by a succession of parallel terraces and nanoledges is investigated when the interface intersects the free surface of an isotropic half-space medium. The method uses the combination of semi-infinite Somigliana dislocations placed on each terrace and semi-infinite translation (or Volterra) dislocations placed at one or two corners of the nanoledges. Numerical examples depict the deformation fields nearby emerging regions of two semi-coherent interfaces; one is flat, while the other includes nanoledges.     

Tosylation and acylation of cellulose in 1-allyl-3-methylimidazolium chloride

Tosylation and acylation of cellulose were performed under mild reaction conditions using imidazolium based ionic liquids (ILs) as solvents. The non-degradative nature, lower viscosity, as well as higher solubility of cellulose in [amim]Cl encouraged us to carry out the reactions in this media. The reactions described here were optimised for this particular solvent in order to obtain different cellulose derivatives with high yields, homogeneity and degree of substitution (DS). Two reagents employed for the in situ activation of carboxylic acids were N,N′-carbonyldiimidazole (CDI) and 1-ethyl-3-(3′-dimethylaminopropyl)carbodiimide hydrochloride (EDCI). Final products were characterised by solution and solid-state NMR techniques. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Strength of a Magnetically Permeable Surface Layer on Transient Electromagnetic Field by Using Natural-frequency Concept

The complete time-domain fields due to a vertical magnetic dipole on the surface of two-layer earth model are reexamined when the usually neglected magnetic permeability contrast is considered using the natural-frequency concept. It is shown that for two-layered earth model, where the upper one is permeable, the electromagnetic induction response is modified with respect to the nonpermeable case. The step responses of the induced voltage in a horizontal receiving loop is found to have definite diagnostic features for the ground beneath. These features have been demonstrated by numerical results and illustrated by figures.     

Marches aléatoires sur certains groupes unimodulaires p-adiques

We give central and off-diagonal estimates for the transition kernels corresponding to simple random walks on certain unimodular solvable p-adic groups. To cite this article: S. Mustapha, C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

The homotopy analysis method for Cauchy reaction-diffusion problems

In this Letter, the homotopy analysis method (HAM) is employed to obtain a family of series solutions of the time-dependent reaction-diffusion problems. HAM provides a convenient way of controlling the convergence region and rate of the series solution.     

A Logarithmic-Quadratic Proximal Method for Variational Inequalities

We present a new method for solving variational inequalities on polyhedra. The method is proximal based, but uses a very special logarithmic-quadratic proximal term which replaces the usual quadratic, and leads to an interior proximal type algorithm. We allow for computing the iterates approximately and prove that the resulting method is globally convergent under the sole assumption that the optimal set of the variational inequality is nonempty.