Kinetics and mechanism of the oxidation of L-ascorbic acid by 2,6-dichlorophenol-indophenol in aqueous solution

The kinetics of oxidation of L-ascorbic acid by 2,6-dichlorophenolindophenol in aqueous solution has been studied. The rate of the reaction decreases with increasing pH since the hydrogen ascorbate ion is less reactive than the unionized L-ascorbic acid. The rate constants for the oxidation of the two species have been evaluated and a plausible mechanism of the reaction is suggested.

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L- 2,6-- . pH, , L- . .

     

Design and Synthesis of Aminoglycoside Antibiotics to Selectively Target 16S Ribosomal RNA Position 1408

The glucopyranosyl moiety (ring I) of paromomycin was modified in a search for novel aminoglycoside antibiotics. The key intermediates were the 4′,6′‐O‐benzylidenated N‐Boc derivative 3 and the azido analogue 18 . The bromobenzoates 4 and 19 were prepared by treating the benzylidene acetals 3 and 18 , respectively, with N‐bromosuccinimide (NBS), and the diol 8 was obtained by hydrogenolysis of 3. The C(6′)‐deoxy derivative 5 was obtained from 4 by treatment with Bu₃SnH. Selective fluorodehydroxylation of 8 gave the fluoro derivative 9. The pseudotrisaccharide 13 was obtained by reductive fragmentaion of the iodo compound 12 obtained from the bromobenzoate 4 . The 3′,6′‐anhydro derivative 20 was obtained upon deacetylation of 19. Standard deprotection gave the C(6′)‐deoxy compound 7 , the fluoro compound 11 , the pseudotrisaccharide 15 , and the 3′,6′‐anhydro‐paromomycin 22 . As compared to paromomycin, the C(6′)‐deoxy and fluorodeoxy derivatives 7 and 11 showed a lower activity against both wild type 1408A and 1408G mutant ribosomes. A lower activity was also found for the 3′,6′‐anhydro derivative 22 and for the pseudotrisaccharide 15 .     

Extraction and characterization of cellulose single fiber from native Ethiopian Serte (Dracaena steudneri Egler) plant leaf

Biomaterials are renewable sources which are widely distributed, locally accessible, high possibility of recycling and biodegradation behavior. This investigation deals with the extraction and characterizing of new fiber obtained from Serte plant leaf that is found in Ethiopia. The physical, chemical and mechanical characters of the fiber had been tested and comparison with other plant fibers was done for the first time. Optimization of fiber extraction process has been done by varying the extraction variables like NaOH concentration, temperature and extraction time. Fibers possessing 56% cellulose content along with significant amount of hemicellulose, lignin and ash with tensile strength of 330?MPa were obtained. FTIR as well as X-ray diffraction analysis were also done to further analyze the fiber. This new plant leaf fiber can be another alternative resource in place of synthetic fibers depending on their application such as reinforcing polymer matrices.     

Self-organisation properties of homomeric dipeptides derived from valine

Three optically active liquid crystal (LC) homomeric dipeptides, in particular, a pair of enantiomers and a diastereomer formed by joining two half-disc-like entities through a dipeptide spacer comprising L-L, D-D and L-D valine residues, have been synthesised and characterised. Hydrogen-bond-directed self-assembly of these non-discoid supramolecules results in the formation columnar (Col) LC phase. They form a stable organo gel in polar organic solvents through intermolecular hydrogen bond, and their scanning electronic microscopy (SEM) images reveal the presence of entangled network. The interaction of these homomeric dipeptides with nanaoparticles (silica species) has also been investigated by SEM images and UV-visible experiments.     

A simple and efficient levitation technique for noncontact coating of inertial confinement fusion targets

A simple and very efficient gas jet levitation technique for levitating inertial confinement fusion (ICF) targets has been developed. A low velocity gas jet through diverging nozzle generates precisely controlled low Reynolds number flow pattern, capable of levitating polymer microballoons up to 2500 μm diameter. Different shaped diverging nozzle are investigated, satisfactory levitation is achieved with simple conical shapes. With this setup microballoon can be levitated for hours with excellent stability, continuous rotation and at the desired height (reproducible with in less than 100 μm). The height of stabilization depends upon cone angle of diverging nozzle and velocity of levitating gas. This technique is very robust and highly insensitive to external disturbances like nonuniform temperature fields and vibrations. This setup is very economical to fabricate, easy to operate and can be used efficiently in various spray coating application involving plastic and metallic layers on microballoons.     

Reconfigurable Multiplier Blocks: Structures,Algorithm and Applications

This paper presents the efficient design methodology and applications of reconfigurable multiplier blocks (ReMB). ReMB offers significant area, delay and possibly power reduction in time-multiplexed implementation of multiple constant multiplications in many application areas from fixed digital filters, adaptive filters, and filter banks to DFT, FFT and DCT. The reader will be exposed to the fundamental principles of ReMB structures coupled with a novel algorithm for their design as well as illustrative examples where appropriate that help the reader understand the technique in action. The paper also looks into the pros and cons of deploying the technique on standard FPGA platforms as well as discussing the effectiveness of the ReMB approach in custom silicon realization by means of application examples. Area, delay and power (where possible) of the ReMB designs are compared to standard implementations. S.S. Demirsoy now with Altera European Technology Centre, High Wycombe, UK. A. Dempster now with the School of Surveying and Spatial Information Systems, University of New South Wales, Sydney, Australia.     

Organocatalyzed Kabbe condensation reaction for mild and expeditious synthesis of 2,2-dialkyl and 2-spiro-4-chromanones

An expeditious Kabbe condensation reaction for the synthesis of 2,2-dialkyl and 2-spiro-chroman-4(1H)-ones has been developed using pyrrolidine-butanoic acid in DMSO as bifunctional organocatalyst. Unlike existing methods, this reaction proceeds at room temperature with high yields, rendering it an attractive method to synthesize a vast variety of privileged 4-chromones.     

Effect of temperature on structural and optical properties of solvothermal assisted CdS nanowires with enhanced photocatalytic degradation under natural sunlight irradiation

Research on Chemical Intermediates - Photocatalytic degradation of toxic dyes is an important topic across the globe. This paper reports the photocatalytic degradation of methylene blue (MB) dye...     

Glycerol acetylation considering competing dimerization

Glycerol acetylation is a very interesting reaction for studies of consecutive kinetics. In this short communication, we present a pseudo-homogeneous model for the synthesis of triacetyl glycerol from the reaction of glycerol and acetic acid over strongly acidic Amberlyst-15 and Amberlyst-70 catalysts, considering a dimerization of diacetyl glycerol (DAG) into diglycerol tetraacetate as a parallel reaction and compare the results with a model without side reactions. The best fits were obtained for apparent zeroth-order dimerization and first-order consecutive reactions in the presence of acetic acid in excess and with removal of water. An adaptation was made for DAG. The proposed model shows that the formation of DAG is faster than the consumption of glycerol, which could be an explanation for the occurrence of DAG dimerization instead of other parallel reactions in acetylation.