Adsorption and diffusion of molecular nitrogen in single wall carbon nanotubes

Using molecular simulation, the adsorption and self-diffusion of diatomic nitrogen molecules inside a single wall carbon nanotube have been studied over a range of nanotube diameters (8.61-15.66 A) and loadings at temperatures of 100 and 298 K. Nitrogen adsorption energy is found to increase as the nanotube diameter is reduced toward the molecular diameter of nitrogen. A discrete organization of the nitrogen into adsorbed layers is observed at high loadings that follows a regular progression determined primarily by geometric considerations. The formation of an adsorbate core at the center of the nanotube is found to increase the self-diffusion of nitrogen. A "wormlike" phase is found for the adsorbed nitrogen in the (15, 0) carbon nanotube at high loadings and at 100 K.     

Laser Raman and IR spectra and force fields for 2,6-difluorobenzonitrile

Raman spectrum of 2,6-difluorobenzonitrile in the powder form has been recorded in the region 50–4000 cm⁻¹ on a Jasco K-500 spectrophotometer using the 488.0 nm radiation from an argon laser. IR spectra in the region 200–4000 cm⁻¹ have been recorded in KBr pellet and nujol mull on a Nicolet DX spectrometer and in liquid and vapour phases on a Jasco FTIR/7000 spectrometer. Using these observed frequencies force field calculations for the planar and non-planar modes have been carried out assuming a general valence force field.     

Novel RNA catalysts for the Michael reaction

BACKGROUND: In vitro selected ribozymes with nucleotide synthase, peptide and carbon-carbon bond forming activity provide insight into possible scenarios on how chemical transformations may have been catalyzed before protein enzymes had evolved. Metabolic pathways based on ribozymes may have existed at an early stage of evolution. RESULTS: We have isolated a novel ribozyme that mediates Michael-adduct formation at a Michael-acceptor substrate, similar to the rate-limiting step of the mechanistic sequence of thymidylate synthase. The kinetic characterization of this catalyst revealed a rate enhancement by a factor of approximately 10(5). The ribozyme shows substrate specificity and can act as an intermolecular catalyst which transfers the Michael-donor substrate onto an external 20-mer RNA oligonucleotide containing the Michael-acceptor system. CONCLUSION: The ribozyme described here is the first example of a catalytic RNA with Michael-adduct forming activity which represents a key mechanistic step in metabolic pathways and other biochemical reactions. Therefore, previously unforeseen RNA-evolution pathways can be considered, for example the formation of dTMP from dUMP. The substrate specificity of this ribozyme may also render it useful in organic syntheses.     

Carbazole-substituted dehydroalanine main chain polymers. Synthesis and characterization of poly[methyl 2-(9-carbazolyl) acetylaminopropenoate] and poly[2-(9-carbazolyl) acetylaminopropenoic acid]

The preparation and radical-initiated polymerization of a carbazole-substituted N-acylated dehydroalanine, namely, 2-(9-carbazolyl)acetylaminopropenoic acid ( 7 ) and its methyl ester ( 6 ) is reported. The monomers 6 and 7 were prepared by dehydrochlorination of N-acylated β-chloroalanine derivatives. The monomer model compounds for the two polymers, namely, 2-(9-carbazolyl)acetylamino-2-methylpropanoic acid ( 11 ) and its methyl ester ( 10 ), were also prepared. The polymers and their monomer model compounds were characterized by elemental analysis, IR and ¹H-NMR spectra. The polymers 12 and 13 of different molecular weights could be obtained by changing the monomer-to-initiator ratios used in polymerization experiments.     

Trace analysis of 1,10-phenanthroline based herbicide in water and soil samples

A sensitive analytical procedure for diquat herbicide viz. 5,6-dihydropyrazino[1,2,3,4-lmn]-1,10-phenanthrolinium dichlorides in drinking water and soil samples, using differential pulse adsorptive stripping voltammetry (DPAdSV) has been developed. This involved the adsorptive accumulation of a diquat herbicide onto a hanging mercury drop electrode [accumulation potential -0.8 V vs Ag/AgCl, accumulation time 60 s, pH 7.0, ionic strength 0.1 M] for DPAdSV measurement. The detection limit for diquat herbicide was as low as 0.034 micromol L(-1) level (S/N 2, RSD 2.9%) at an accumulation time of 60 s.     

A highly regio- and chemoselective addition of carbon nucleophiles to pyrimidinones. A new route to C4 elaborated Biginelli compounds

Ethyl 6-methyl-pyrimidine-2-one-5-carboxylates react with C-nucleophiles in a diversity oriented synthetic sequence to afford C4 substituted congeners of medicinally potent Biginelli dihydropyrimidinones, in a highly regioselective manner.     

Amorphous Coatings and Surfaces on Structural Materials

Metallic glasses show a unique combination of high strength, excellent corrosion, and wear resistances because of their amorphous structure having a short-range order. In spite of excellent properties, the application of metallic glasses is restricted because of their inherent limitations in the bulk form, including limited tensile ductility. Using metallic glasses as the coatings for structural applications is an attractive way of taking advantage of their superior properties. Additionally, metallic glass-based composites having crystalline phases embedded in a amorphous matrix have also shown improved properties. Thus, metallic glasses can be synthesized as the coatings or subjected to surface modification to provide functionally superior surfaces. This article is a review of metallic glass-based coatings and surface modification of metallic glasses to achieve functionally superior surfaces for structural applications. Essential theoretical concepts were discussed which influence the processing. Common ways of processing along with the influence of various processing parameters were explored. Some non-conventional techniques which emerged as a result of continued efforts were also taken into account. Corrosion and wear properties of these materials along with the underlying mechanisms were discussed in detail. Focus was given to the recent product level applications explored in the open literature. Current challenges in the field were reviewed and guidelines for the future developments were provided.     

A novel and facile one‐pot synthesis of pyridylselenium compounds through selective bromine–magnesium exchange with isopropylmagnesium halide

One‐pot synthesis of various unsymmetrical 2‐bromo‐5‐pyridylselenium compounds has been carried out under non‐cryogenic conditions by selective single bromine–magnesium exchange of 2,5‐dibromopyridine using isopropylmagnesium chloride. This exchange gives 2‐bromo‐5‐pyridylmagnesium chloride, which upon the insertion of elemental selenium followed by the treatment with alkyl halide gives the title compounds in good yield. This exchange has also been extended towards bromine–magnesium exchange of 2‐bromopyridine for the improved synthesis of 2‐pyridylselenium compounds. The molecular structure of 2‐bromo‐5‐selenopyridyltribromomethane has been examined by single crystal X‐ray diffraction. This compound crystallizes in the monoclinic space group P2₁/n. From the molecular structure it was found that intermolecular BrBr, NSe and SeBr interactions control its crystal packing. Copyright © 2005 John Wiley & Sons, Ltd.