Asymmetric aldol reactions catalyzed by the promiscuous aldo–ketoreductase enzyme

The promiscuous aldo–ketoreductase (AKR) enzyme is used as a sustainable biocatalyst for the first time to catalyze asymmetric aldol reactions in aqueous medium. The reactions between aromatic aldehydes and cyclic/acyclic ketones give the corresponding products in moderate yields and enantioselectivities in the presence of water. The influence of solvents, the mole ratio of substrates, and enzyme concentration are investigated. The mechanism of the AKR1A1-catalyzed aldol reaction is also discussed.     

Effect of Oil Palm and Jute Fiber Treatment on Mechanical Performance of Epoxy Hybrid Composites

In this work, oil palm empty fruit bunch (EFB) and jute fibers were treated with 2-hydroxy ethyl acrylate (2-HEA) to improve interfacial bonding of oil palm EFB and jute fibers with epoxy matrix. Hybrid composites were fabricated by incorporation of modified oil palm EFB and jute fibers into an epoxy matrix by the hand lay-up technique. Mechanical (flexural and impact) and morphological properties of modified hybrid composites were measured. Results indicated that flexural and impact properties of modified fiber–reinforced hybrid composites improved as compared to untreated hybrid composites due to better fiber/matrix interfacial bonding, which was confirmed by scanning electron microscopy. We confirmed that treated oil palm/jute hybrid composite may be fabricated by advanced techniques such as resin transfer molding, extrusion, and injection molding for industrial applications in the automotive sector.     

Gel-assisted synthesis of anatase TiO2 nanoparticles and application for electrochemical determination of L-tryptophan

Anatase titanium dioxide nanoparticles (TiO₂-NPs) were synthesized with and without gelatin via the sol-gel method. The TiO₂-NPs were characterized by a number of techniques, such as thermogravimetric analysis (TGA), X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR) and ultraviolet visible spectroscopy (UV-Vis). The particle sizes of the TiO₂-NPs prepared with and without gelatin were ～13 and ～17 nm, respectively. The main advantage of using gelatin as a stabilizing agent is that it provides long-term stability for nanoparticles by preventing particles agglomeration. The results indicated that gelatin was a reliable green stabilizer, which can be used as a polymerization agent in the sol-gel method for synthesis of tiny size TiO₂-NPs. Moreover, the composite film was prepared by synthesized TiO₂-NPs nanoparticles and multi wall carbon nanotube (MWNT) on glassy carbon electrode (TiO₂-MWNT/GCE). The TiO₂-MWNT/GCE responded linearly to L-tryptophan (L-Trp) in the concentration of 1.0 × 10^?6 to 1.5 × 10^?4 M with detection limit of 5.2 × 10^?7 M at 3 using amperometry. The studied sensor exhibited good reproducibility and long-term stability.     

An efficient one-pot synthesis of flavones

Flavones were prepared using a one-pot procedure starting from the corresponding 2′-hydroxyacetophenones. The latter were treated with 3 equiv of aroyl chloride in wet K₂CO₃/acetone (1% w/w water) to afford a good yield of flavone and a smaller amount of 3-aroylflavone. Evidence was obtained that the reaction proceeds via a triketone intermediate. When the reactants were heated in 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and pyridine, the 3-aroylflavone was obtained exclusively. Use of a stoichiometric amount of aroyl chloride afforded only the corresponding flavone.     

The intramolecular Morita-Baylis-Hillman-type alkylation reaction

From the initial development of a homologous Morita-Baylis-Hillman reaction utilizing epoxides as electrophiles, the method was expanded to enable the exclusively organocatalyzed intramolecular allylation of enones and to develop the intramolecular MBH-type alkylation of activated alkenes. We successfully utilized both enones and unsaturated thioesters as the activated alkene component. This work, carried out using stoichiometric amounts of the trialkylphosphine, gave an array of functionalized five- and six-membered carbocycles in high yields. With the cycloalkylation of enones and thioesters, conditions that allowed the use of substoichometric amounts of the phosphine catalyst were developed. As a result both five- and six-membered rings can be formed efficiently with little to no loss in yield upon comparison to yields obtained when stoichiometric amounts of trialkylphosphines were employed. We isolated, for the first time, an MBH-type intermediate exhibiting unprecedented trans geometry of the phosphonium salt and acyl group.     

Intercomparison of techniques for estimation of sedimentation rate in the Sabah and Sarawak coastal waters

A total of eight sediment cores with 50 cm length were taken in the Sabah and Sarawak coastal waters using a gravity corer in 2004 to estimate sedimentation rates using four mathematical models of CIC, Shukla-CIC, CRS and ADE. The average of sedimentation rate ranged from 0.24 to 0.48 cm year^?1, which is calculated based on the vertical profile of ²¹⁰Pb_ex in sediment core. The finding also showed that the sedimentation rates derived from four models were generally shown in good agreement with similar or comparable value at some stations. However, based on statistical analysis of paired sample t-test indicated that CIC model was the most accurate, reliable and suitable technique to determine the sedimentation rate in the coastal area.     

Green synthesis of bio-ethyl acetate over Egyptian natural red clay as a highly active,selective, and eco-friendly catalyst

The present work focused on the utilization of Egyptian red clay (ERC) without any treatment as a highly efficient, selective, and eco-friendly catalyst for synthesis of bio-ethyl acetate in the gas phase. The best conditions used in conventional fixed bed reactor were 130 cm³/min total flow rate of air with 1.6 and 2.1 vol% bio-ethanol and bio-acetic acid, respectively, 1 g clay catalyst calcined at 300 and 225°C reaction temperature. Under these conditions, the conversions to ester achieved were about 80 and 98% after 5 and 30 min, respectively, from the initial admission of the reactants into the reactor. The amount and type of surface acidity were identified by isopropanol reaction and chemisorption of basic probes. The results demonstrated that the majority of intermediate strength of BrØnsted acid sites are the key role for the dehydration reaction toward ester formation. The virgin and annealed clay solids were characterized using X-ray fluorescence (XRF), thermogravimetry (TG) and differential thermal analysis (DTA), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and N₂ sorption.     

Synthesis and antidiabetic activity of novel triazole derivatives containing amino acids

New series of triazole derivatives coupled with amino acids 1a-h were obtained via multicomponent reaction of 2-hydroxy benzaldehyde or 2-hydroxy acetophenone with thiosemicarbazide and different amino acids. The obtained compounds were reacted with p-toluinesulfonyl chloride 2 to give the corresponding sulfonamides 3a-h . Compound 1b was allowed to react with different aromatic aldehydes or cyclic ketone under alkaline conditions to afford the expected imino compounds 4a-d and 6a-c , respectively. These compounds were allowed to react with ethyl glycolate to yield the expected thiazolidinone derivatives 5a-d or 7a-c , respectively. Structures of the newly synthesized compounds were found to be in accordance with their elemental analyses and spectral data. The obtained compounds exhibited very prominent in vitro and in vivo antihyperglycemic effect at a dose of 40 mg/kg body weight compared to the standard drug gliclazide and control. The antidiabetic effect was investigated using oral glucose tolerance test in normal and non-insulin-dependent diabetes mellitus (NIDDM) in STZ-rat model. Compounds 3a - h , 5b , 5c , 5d , 7a , 7b , and 7c showed significant activity in lowering blood glucose (more than 80%) compared to the NIDDM control.     

Modélisation de fissures elliptiques internes par hybridation de fonctions de poidsEmbedded elliptical cracks modeling with hybridization of weight functions

A method improving the evaluation of the stress intensity factor by hybridization of two weight functions is presented and applied to embedded elliptical cracks under various loadings. The hybridization consists in using one or the other function in the zone of the crack where it is the most efficient. The delimitation of the two zones is achieved after optimizing the axes ratio and the curvature radius of the crack. During this optimization we seek to reduce the effects of the singularities present in the weight functions as well as to take better into account the influence of the ellipse curvature. To cite this article: B. El Khalil Hachi et al., C. R. Mecanique 334 (2006).     

On the Reaction of 3-Acetyl Coumarin with Alkyl Phosphites. Structural Confirmations Based on X-Ray Crystallography

3-Acetyl coumarin ( 1 ) reacts with dialkyl phosphites at 100°;C for 8 h to give the phosphonates 2 . Under the same experimental conditions, 1 reacts with trialkyl phosphites to form a mixture of the phosphonates 2 and 3 . The molecular structures of these products were elucidated by x-ray crystallography.