Resveratrol derivatives from Upuna borneensis

Four new resveratrol derivatives, upunaphenols B (1), C (4), D (5) (resveratrol tetramer) and E (6, resveratrol dimer with a C6-C1 unit), together with nine known resveratrol oligomers and resveratrol were isolated from an acetone soluble part of stem of Upuna borneensis (Dipterocarpaceae). The structures of new compounds were determined by spectral analysis including 1D and 2D NMR experiments.     

Optimized water‐based ATRP of an anionic monomer: Comprehension and properties characterization

The effect of pH and the ligand nature over the atom transfer radical polymerization (ATRP) of the anionic monomer sodium 2‐acrylamido‐2‐methylpropanesulfonate (AMPSNa) was investigated in aqueous medium by using ω‐halogenated poly(ethylene oxide) and CuBr, as macroinitiator and catalyst, respectively. The stability of both catalytic complexes and macroinitiator was investigated in function of pH, that is, fixed between 7.5 and 12. UV‐VIS spectroscopy confirmed a good catalytic complex stability in the studied conditions. Hydrolysis of the macroinitiator ester group at pH higher than 7.5 was detected by ¹H NMR and GPC, yielding ill‐defined polymer samples when ATRP is performed in alkaline conditions. 2,2′‐Bipyridyl (Bpy), 1,1,4,7,10,10‐hexamethyltriethylenetetramine (HMTETA), and tris(2‐methylaminoethyl)amine (Me₆‐TREN)‐based complexes were compared at the optimal pH (pH 7.5). When polymerization was carried out in the presence of CuBr · 2Me₆‐TREN complex block copolymers with narrow molecular weight distribution (1.1 ≤ M _W/M _n ≤ 1.3), and good agreement between theoretical and experimental molar masses was obtained. Moreover, increasing the PAMPSNa polymerization degrees (n) did not affect the control over the polymerization. Preliminary characterization of the diblock copolymers behavior in aqueous medium revealed a strong polyelectrolyte effect independently of n. Interestingly, occurrence of interactions between the PEO and PAMPSNa‐blocks was also evidenced by differential scanning calorimetry and thermogravimetric analyses. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1108–1119, 2009     

Method of invariant grid for model reduction of hydrogen combustion

The Method of Invariant Grid (MIG) is a model reduction technique based on the concept of slow invariant manifold (SIM). The MIG approximates the SIM by a set of nodes in the concentration space (invariant grid). In the present work, the MIG is applied to a realistic combustion system: an adiabatic constant volume reactor with H₂-air at stoichiometric proportions. By considering the thermodynamic Lyapunov function of the detailed kinetic system, the notion of the quasi-equilibrium manifold (QEM) is adopted as an initial approximation to the SIM. One- and two-dimensional discrete approximations of the QEM (quasi-equilibrium grids) are constructed and refined via MIG to obtain the corresponding invariant grids. The invariant grids are tabulated and used to integrate the reduced system. Excellent agreement between the reduced and detailed kinetics is demonstrated.     

On the binary projective codes with dimension 6

All binary projective codes of dimension up to 6 are classified. Information about the number of the codes with different minimum distances and automorphism group orders is given.     

Thermodynamic parameterization

A new method of succesive construction of a solution is developed for problems of strongly nonequilibrium Boltzmann kinetics beyond normal solutions. Firstly, the method provides dynamic equations for any manifold of distributions where one looks for an approximate solution. Secondly, it gives a successive procedure of obtaining corrections to these approximations. The method requires meither small parameters, nor strong restrictions upon the initial approximation; it involves solutions of linear problems. It is concordant with the H-theorem at every step. In particular, for the Tamm-Mott-Smith approximation, dynamic equations are obtained, an expansion for the strong shock is introduced, and a linear equation for the first correction is found.     

Anionic polymerization of lactones initiated by alkali graphitides. I. Polymerization of ϵ-caprolactone initiated by KC24

The influence of the reaction conditions (time, temperature, concentrations of the monomer, and the initiator) on the amount and composition of the oligomers and high molecular products formed during the heterogeneous anionic polymerization of ?-caprolactone was investigated. The polymerization was initiated by KC₂₄ in xylene or tetrahydrofuran. Conditions were found under which intra- and intermolecular transesterification was strongly suppressed, thus providing the opportunity for the formation of polyesters with viscometric molecular masses of more than 300,000 and good yields (80% and higher). The total quantity of products with a viscometric molecular mass below 2500 did not exceed 15%; that of the cyclic dimer was not in excess of 5%. Peculiar features of the KC₂₄ initiated polymerization are the insignificant rise in the number of oligomers and the formation of high polymers even in strongly diluted solutions of ?-caprolactone (0.2 mol/L and lower). The quantity and molecular mass of the polymers obtained decreased as the temperature increased. It was also established that the polymerization of the cyclic dimer of ?-caprolactone is not initiated by KC₂₄.     

Polymerization of ε-caprolactone initiated by stable salts. Initiation mechanism

The mechanism of initiation of ε-caprolactone polymerization by stable salts has been investigated. Gel permeation chromatography and ¹H-NMR spectroscopy were used for determining the compositions of the reaction mixtures and of the polymers. It was established that the initiation proceeds by addition of the initiator to the monomer.     

Electrospun Hybrid Nanofibers Based on Chitosan or N‐Carboxyethylchitosan and Silver Nanoparticles

Hybrid nanofibers from chitosan or N‐carboxyethylchitosan (CECh) and silver nanoparticles (AgNPs) were prepared by electrospinning using HCOOH as a solvent. AgNPs were synthesized in situ in the spinning solution. HCOOH slowed down the cross‐linking of the polysaccharides with GA enabling the reactive electrospinning in the presence of poly(ethylene oxide) (PEO). EDX analyses showed that AgNPs are uniformly dispersed in the nanofibers. Since AgNPs hampered the cross‐linking of chitosan and CECh with GA in the hybrid fibers, the imparting of water insolubility to the fibers was achieved at a second stage using GA vapors. The surface of chitosan/PEO/AgNPs nanofibers was enriched in chitosan and 15 wt.‐% of the incorporated AgNPs were on the fiber surface as evidenced by XPS.

     

Three new trimeric stilbenes from Gnetum gnemon

Three stilbene trimers (gnemonols D, E, F) were isolated from the root of Gnetum gnemon. The structures were determined by spectroscopic analysis. In addition, the antioxidant activity of the compounds on lipid peroxide inhibition and super oxide scavenging activity were also investigated.