Fracture Behavior of Covalently Re-Modified MWNT/Epoxy Nanocomposites

Summary: In this work, a surface re-modified multi-walled carbon nanotube (MWNT) was prepared by the chemical attachment of oligomeric unsaturated polyester on the MWNT surface. The re-modified MWNT was incorporated in two concentrations of 0.35 and 0.70 Wt.% into epoxy resin in order to investigate its effect on morphology and mechanical behavior of the MWNT/epoxy nanocomposite. The transmission electron microscopy showed that the re-modification of MWNT surface improves its dispersion state in the epoxy matrix. The tensile measurements for the nanocomposite having different amounts of surface re-modified/not-modified MWNT showed that the fracture mechanism changed from brittle to tough beyond a certain amount of surface re-modified MWNT. The scanning electron microscopy findings on the fracture surface morphology of the resulted nanocomposite substantiated the observed phenomena.     

Kinetics of malachite green fading in alcohol–water binary mixtures

The rate constant of alkaline fading of malachite green (MG⁺) was studied in alcohol–water binary mixtures. This reaction was studied under pseudo‐first‐order conditions at 283–303 K. It was observed that the reaction rate constants were increased in the presence of different weight percentages of methanol, ethanol, 1‐propanol, 2‐propanol, ethylene glycol, 1,2‐propanediol, and glycerol (up to 19.3%). In aqueous glycerol solutions higher than 19.3%, the rate constant of reaction slightly decreases, which is due to high viscosity values of solvent mixtures. The fundamental rate constants of MG⁺ fading in these solutions were obtained by using the SESMORTAC model. Owing to the charged character of activated complex, with an increase in the weight percentage of the used cosolvents or temperature, k₂ values change according to the trend of hydroxide ion nucleophilic parameter values. Also, using MG⁺ solvatochromism, a simple test, called MAGUS, is introduced for measuring the glycerol concentration in its aqueous solutions. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 508–518, 2010     

β-Cyclodextrin as an efficient catalyst for the one-pot synthesis of 1-aminophosphonic esters in water

A simple, efficient, and general method has been developed for the one-pot synthesis of α-aminophosphonic esters in water using β-cyclodextrin as an efficient catalyst. α-Aminophosphonic esters were obtained in good yields (45-82%) and purity under mild conditions by the reaction of diethyl phosphite with a mixture of aldehyde and amine in water at reflux.     

2, 4, 6-Trichloro-1, 3, 5-triazine/dimethylformamide as an efficient reagent for one-pot conversion of alcohols into N-alkylphthalimides

<正>An efficient and mild method for the direct conversion of alcohols into N-alkylphthalimides using 2,4,6-trichloro-1,3,5-triazine and dimethylformamide was described.The reaction was preceded via(alcoxymethylene) dimethylammonium chloride intermediate and produced corresponding N-alkylphthalimides in good-to-excellent yields.     

Development and validation of a capillary electrophoresis-indirect photometric detection method for the determination of the non-UV-absorbing 1,4-dideoxy-1,4-imino-D-arabinitol in active pharmaceutical ingredients,solutions and tablets using an internal standard

A high speed, selective, and robust capillary electrophoresis (CE) method with high capacity was developed and validated for determination of assay of 1,4-dideoxy-1,4-imino-D-arabinitol in active pharmaceutical ingredients, solutions, and tablets during the development work at preclinical and Phase I and II clinical studies. 1,4-Dideoxy-1,4-imino-D-arabinitol, tartrate has (almost) no UV absorption. Therefore, the developed CE method for quantification was based on indirect UV detection. A cation CE principle was chosen using an electrolyte at pH 4.0 containing dimethyldiphenylphosphonium hydroxide, which has a strong UV absorbance. The quantification was performed using internal standard technique, by which piperidine was used as internal standard. The method was validated. The validation results showed that the CE method was suitable for the assay (and dissolution) analysis.     

Novel method for efficient aerobic oxidation of silyl ethers to carbonyl compounds catalyzed with N-hydroxyphthalimide (NHPI) and lipophilic Co(II) complexes

In this work, a new method for highly efficient and selective oxidative deprotection of a variety of structurally diverse trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBS) ethers using molecular oxygen in the presence of N-hydroxyphthalimide (NHPI) and various types of Co(II) complexes is reported. As a result of the relatively neutral reaction medium, acid-sensitive functional groups such as phenolic TBS ethers survived intact under the presented reaction conditions.     

A chiroptical approach for the absolute stereochemical determination of P-stereogenic centers

A simple chiroptical solution for the absolute stereochemical determination for asymmetric phosphorus V stereocenters is presented. Strong coordination of the phosphorus oxide with the Zn-metallo center of the racemic host Zn-MAPOL 2 leads to an induced axial chirality of the host, yielding a strong ECCD signal. A mnemonic is proposed to correlate the asymmetry of the guest molecule with the observed ECCD signal.

A simple chiroptical solution for the absolute stereochemical determination for asymmetric phosphorus V stereocenters is presented.     

Kinetics of the Initial Stage of Gelation in Chitosan Solutions Containing Glutaric Aldehyde: Viscometric Study

The effects of glutaric aldehyde concentration C _GA(in the range from 0.07 to 0.2 wt %) and temperature T(from 20 to 65°C) on the kinetics of an increase in the effective viscosity _effof aqueous solutions of chitosans (C _CH= 2.4 wt %, pH 3.6, and ionic strength I= 0.05) with molecular masses equal to 33 × 10⁴and 55 × 10⁴and the degrees of substitution at N-acetyl and amino groups of 0.08 and 0.90, respectively were studied. The kinetic curves _eff(t) exhibited the induction periods of a relatively slight increase in the viscosity of chitosan–glutaric aldehyde mixed solutions with time followed by the periods of a drastic increase in the viscosity. The former periods correspond to the formation of gel clusters; the latter periods, to the gelation over the whole volume of a solution. Optimal ranges of the parameters C _GAand Twere determined for the preparation of spherical gel particles of slightly cross-linked chitosan, which are used for the sorption of heavy metals from low-concentrated solutions.     

Efficient synthesis of imidazo[1,2-a]pyridin-3(2H)-ones

2-Aminopyridines react with diaroylacetylenes to produce imidazo[1,2-a]pyridin-3(2H)-ones in good to excellent yields.