Straightforward route for anchoring a glucosyl moiety onto nucleophilic species: reaction of amines and alcohols with carboxymethyl 3,4,6-tri-O-acetyl-alpha-D-glucopyranoside 2-O-lactone

The base-catalyzed reaction of carboxymethyl 3,4,6-tri-O-acetyl-alpha-D-glucopyranoside 2-O-lactone (prepared from isomaltulose) with amino acids and fatty amines under basic catalysis gave a series of new pseudoglucopeptides, nonionic amphiphiles, and polymerizable derivatives. The same reaction applied to alcohols provided the corresponding 2-(alpha-D-glucopyranosyloxy)acetyl esters with either basic or acidic catalysts.     

Electron-transfer-catalyzed ligand substitution of carboxylato niobocene complex induced by electrochemical oxidation

Electrochemical reduction of niobocene dichloride (η⁵-C₅H₄SiMe₃)₂NbCl₂1 formulated as in the presence of 3,4-diaminobenzoic acid yields to the complex [Nb(η⁵-C₅H₄SiMe₃)₂(κ²-O,O-OOC(C₆H₃)(NH₂)₂)] 3. When CN(2,6-Me₂C₆H₃) formulated as xylylisonitrile (CNXylyl) is added to a complex 3 solution, a substitution reaction takes place to lead to the complex [Nb(η⁵-C₅H₄SiMe₃)₂(κ¹-O-OOC(C₆H₃)(NH₂)₂)(CN(2,6-Me₂C₆H₃)) 4 after 3 h. An alternative way to yield quantitatively and nearly instantaneously 4 consists in a previous oxidation of 3 in the presence of CNXylyl. Hence, we present here a new example of electron-transfer-catalyzed (ETC) ligand substitution of carboxylato niobocene complex induced by electrochemical oxidation. The structure of the complexes, the formation mechanism are described using electrochemical and spectroscopic data. Electrochemical simulation have been done to verify experimental results and to complete them with a kinetic study.     

High-Pressure 17O-NMR. Study of Vanadium (II) in Water: A Second Example of an Associative Interchange Mechanism (Ia) for Solvent Exchange on an Octahedral Divalent Transition-Metal Ion

The water exchange of [V(H₂O)₆]Cl₂ in aqueous solution has been studied as a function of temperature and pressure (up to 250 MPa), by measuring the ¹⁷O-FT-NMR. line-widths of the free water resonance at 8.13 MHz. The kinetic parameters obtained are K = 87±4 s^?1, ΔH^* = +61.8 ± 0.7 kJ mo1^?1 and ΔS^* = ?0.4±1.9 J mol^?1 K^?1. A pressure-independent volume of activation ΔV^* = ?4.1±0.1 cm³ mol^?1 is obtained, suggesting an associative interchange (I^a) mechanism for this early divalent metal ion.     

Amas de lacets markoviens

We study the clusters defined by Poisson processes of Markov loops.     

A brand new cheating attempt: a case of usurped identity

We recall some cases of ethical misconduct that occurred in the recent years, and we report a new trick that was recently attempted to cheat the journal in order to obtain the publication of an article through usurped identity.     

The Lyapunov Exponent of Products of Random 2×2 Matrices Close to the Identity

We study products of arbitrary random real 2×2 matrices that are close to the identity matrix. Using the Iwasawa decomposition of SL(2,?), we identify a continuum regime where the mean values and the covariances of the three Iwasawa parameters are simultaneously small. In this regime, the Lyapunov exponent of the product is shown to assume a scaling form. In the general case, the corresponding scaling function is expressed in terms of Gauss’ hypergeometric function. A number of particular cases are also considered, where the scaling function of the Lyapunov exponent involves other special functions (Airy, Bessel, Whittaker, elliptic). The general solution thus obtained allows us, among other things, to recover in a unified framework many results known previously from exactly solvable models of one-dimensional disordered systems.