An efficient transition metal-free aziridination of alkenes with Chloramine-T using aqueous H2O2/HBr

The combination of aqueous H₂O₂ and HBr was found to be an efficient transition metal-free green catalytic system for the aziridination of a variety of alkenes under very mild reaction conditions.     

Synthesis of licoflavone-a and 6',6'-dimethylpyrano(2',3':7,8)flavone

Licoflavone-A assigned structure of 6-C-prenyl-7,4'-dihydroxyflavone 5 has been synthesized by condensing 5-C-prenyl-2-hydroxy-4-prenyloxyacetophenone 2 with p-prenyloxybenzaldehyde in the presence of alkali. The resulting chalcone 3 on cyclodehydrogenation with DDQ gave 6-C-prenyl-7,4'-diprenyloxyflavone 4 which on boiling with aqueous morpholine afforded the natural product. This synthesis uses, for the first time, protection of phenolic hydroxyls by O-prenylation and DDQ for conversion of chalcone to flavone. 6',6'-Dimethylpyrano (2',3':7,8)navone 8 has been synthesized by the Hlubucek reaction of 7-hydroxyflavone 6 with 2-chloro-2-methyl-3-butyne.     

Thermomechanical investigation of a thick film of aniline-formaldehyde copolymer and poly(methyl methacrylate)

A thick film of aniline-formaldehyde copolymer and PMMA is synthesized via dispersion of aniline-formaldehyde copolymer powder as filler particles in PMMA with two different concentrations. Variation of the complex elastic modulus and mechanical loss factor (tanδ) with temperature is studied. It is observed that the complex elastic modulus decreases with temperature owing to thermal expansion of films. On the other hand, tanδ increases up to a characteristic temperature beyond which it shows a decreasing trend toward melting. Transition temperature T _g of sample S₁ (pure PMMA) is found to be 80°C. In sample S₂ (1 wt % aniline formaldehyde copolymer), the peak of tanδ at a lower temperature (66°C) corresponds to glass transition temperature T _g of the PMMA matrix, while the peak of tanδ at a higher temperature (107.8°C) corresponds to T _g of a polymer chain restricted by filler particles of aniline-formaldehyde copolymer. A further increase (10 wt % aniline-formaldehyde copolymer) in the concentration of filler particles of aniline-formaldehyde copolymer results in a more compact structure and a shift of T _g to a higher temperature, 122.2°C. This shift in the glass transition temperature of thick films of aniline-formaldehyde copolymer and PMMA is dependent upon the concentration of filler particles in the sample.     

AOT water-in-oil microemulsions as a penetration enhancer in transdermal drug delivery of 5-fluorouracil

In vitro transdermal permeation of 5-fluorouracil (antineoplastic), a hydrophilic drug encapsulated in AOT/water/isopropylmyristate water-in-oil microemulsions (MEs), were studied using a modified Keshary and Chien diffusion cell. AOT (aerosol-OT or sodium bis(2-ethylhexyl) sulfosuccinate) is an anionic surfactant, which forms 'water-in-oil' ME in non-aqueous medium. The effect of water and AOT concentrations in MEs to the transdermal permeation of 5-fluorouracil through hairless mouse skin was investigated. MEs with 5:95 weight ratio of AOT:isopropylmyristate, containing 0.9, 1.8, 2.7 and 3.6% w/w of water have showed 1.68-, 2.36-, 3.58- and 3.77-fold increases in the skin flux of 5-fluorouracil (5-FU) respectively, compared to the aqueous solution of drug. The MEs with 5:95, 9:91 and 13:87 weight ratio of AOT:isopropyl myristate at fixed water content W0=15 (W0=[H2O]/AOT]) gave 3.58-, 5.04- and 6.3-fold enhancement of drug. In addition, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy was used to examine the effect of ME on lipid alkyl chain, hydration level, and corneocyte cells of the stratum corneum (SC). Results reveal that the ME interacts with a component of the SC and perturbs its architectural structure. The extent of perturbation in the SC depends on the concentration of water and AOT in the ME. Preliminary dermal toxicity studies indicate that the AOT/water/isopropylmyristate ME be safe for the transdermal permeation of 5-FU.     

Dy(OTf)3 as a versatile catalyst for the synthesis of 3-pyrrolyl-indolinones and pyrrolyl-indeno[1,2-b]quinoxalines

Dysprosium(III) triflate is found to catalyze efficiently the coupling of 4-hydroxyproline with indeno[1,2-b]quinoxalin-11-one and isatin derivatives under mild conditions to produce 11-(1H-pyrrol-1-yl)-11H-indeno[1,2-b]quinoxalin-11-one and 3-(1H-pyrrol-1-yl)indolin-2-one derivatives, respectively, in excellent yields in short reaction times. A comparative study with both InCl₃ and Dy(OTf)₃ is described.     

Determination of K-factors for isotope abundance measurements of uranium and plutonium by thermal ionisation mass spectrometry

K-factors (= certified isotope ratio/observed isotope ratio) are determined for the isotope abundance measurements of uranium and plutonium by thermal ionisation mass spectrometry. An mdf of 0.07% and 0.18% per mass unit differing by a factor of about 3, is obtained for uranium and plutonium, respectively, employing double rhenium filament assembly in the ion source and Faraday cup as the detector using the presently available isotopic reference materials of uranium and plutonium.     

Asymmetric synthesis of (+)-negamycin

An asymmetric synthesis of the antibiotic (+)-negamycin (1) has been achieved, starting from commercially available (5R,6S)-4-(benzyloxycarbonyl)-5,6-diphenyl-2,3,5,6-tetrahydro-4H-1,4-oxazin-2-one (2). The synthesis involved the stabilized Wittig olefination of the lactone carbonyl group of 2 and subsequent asymmetric hydrogenation to generate the corresponding all-syn oxazine 4 with excellent diastereoselectivity. Conversion of 4 into beta-alkoxy imine 7 and subsequent CeCl3-promoted chelation-controlled allylation of 7 generated the corresponding homoallylamine 8 with good diatereoselectivity, which was readily converted into (+)-negamycin (1) in 25% overall yield over 11 steps.     

Extraction of lanthanoids and some associated elements by mono-(2-ethylhexyl)phosphoric acid and their separations

Mono-(2-ethylhexyl)phosphoric acid (H₂MEHP) has been used to study the extraction of some lanthanoids and other associated elements from nitric acid medium. Effect of various variables like kind of diluent, concentration of metal ion, nitric acid and extractant has been investigated. Based on distribution data, it was possible to achieve some separations of lighter lanthanoids from metals like titanium, zirconium, thorium and uranium with high separation factors.     

Prediction of aqueous solubility of organic compounds by the general solubility equation (GSE)

The revised general solubility equation (GSE) is used along with four different methods including Huuskonen's artificial neural network (ANN) and three multiple linear regression (MLR) methods to estimate the aqueous solubility of a test set of the 21 pharmaceutically and environmentally interesting compounds. For the selected test sets, it is clear that the GSE and ANN predictions are more accurate than MLR methods. The GSE has the advantages of being simple and thermodynamically sound. The only two inputs used in the GSE are the Celsius melting point (MP) and the octanol water partition coefficient (K(ow)). No fitted parameters and no training data are used in the GSE, whereas other methods utilize a large number of parameters and require a training set. The GSE is also applied to a test set of 413 organic nonelectrolytes that were studied by Huuskonen. Although the GSE uses only two parameters and no training set, its average absolute errors is only 0.1 log units larger than that of the ANN, which requires many parameters and a large training set. The average absolute error AAE is 0.54 log units using the GSE and 0.43 log units using Huuskonen's ANN modeling. This study provides evidence for the GSE being a convenient and reliable method to predict aqueous solubilities of organic compounds.     

Effect of structure on thermal behaviour of epoxy resins

The paper deals with the curing behaviour of diglycidyl ether of bisphenol-A (DGEBA) using three novel multifunctional aromatic amines having phosphine oxide and amide-acid linkages. The amines were prepared by reacting tris(3-aminophenyl)phosphine oxide (TAP) with 1,2,4,5-benzenetetracarboxylic acid anhydride (P)/4,4^′-(hexafluoroisopropylidene)diphthalic acid anhydride (F)/3,3^′,4,4^′-benzophenonetetracarboxylic acid dianhydride (B). Amide-acid linkage in these amines is converted to thermally stable imide linkage during curing reaction. Curing temperatures of DGEBA were higher with phosphorylated amines than the conventional amine 4,4^′-diamino diphenyl sulphone (D). A decrease in initial decomposition temperature and higher char yields were observed when phosphorus containing amide-acid amines were used as curing agents for DGEBA.