Short communications

Preconcentration of phosphate as molybdoantimonylphosphoric acid on polyurethane foam has been combined with X-ray fluorescence measurement of antimony for the indirect determination of phosphate. The extraction is optimum between pH 1 and 3.6 and no interference is observed from silicate. The precision is 5% RSD at the 0.25-mug ml level and the detection limit is 20 ng ml for 100 ml of sample solution.     

Biologically active metabolites from fungi, 19: new isocoumarins and highly substituted benzoic acids from the endophytic fungus, Scytalidium sp

Six known metabolites, two new isocoumarins 4 and 8, and one new highly substituted benzoic acid derivative 9 were isolated from the ethyl acetate culture extract of a fungal endophyte, Scytalidium sp. In addition, another new benzoic acid 10 with an unusual 1,2-dicarbonyl side chain was indirectly identified from its methylated derivatives 10a-10d.     

Investigation of the addition of dialkyl(aryl)phosphine oxides to alkyl(aryl)vinyldialkoxysilanes

Conclusions Alkyl(aryl){2-[dialkyl(aryl)phosphoryl]ethyl}dialkoxysilanes were obtained as a result of addition of dialkyl(aryl)phosphine oxides to alkyl(aryl)vinyldialkoxysilanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 183–186, January, 1985.     

Studies on the thermal behaviour of detonating fuse and detonators

Investigations of the thermal stability of detonating fuse containing 10 g pentaerythrol tetranitrate (PETN) revealed that the cord burnt under unconfinement at 403 K. Under confinement in a steel pipe or copper tube there was a partial detonation at 403 K. In order to characterize the thermal stability of PETN and pyrotechnic composition used in fuse head of electric detonators differential thermal analysis (DTA) was used.The electric detonators of aluminium cell and copper cell were heated from ambient temperature to 373 K at an average rate of 0.4 deg/min. The rate of heating was increased gradually to 1.5 deg/min till explosion. The detonation temperature varied between 373 K and 375 K.The impact and friction sensitivity of detonating fuse was poor. There was no detonation when a 5 kg hammer was repeatedly hit over the fuse from a height of one metre. There was no detonation when the detonating fuse was rubbed by a blunt edge of steel plate till it was smashed.

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Zusammenfassung Untersuchungen der thermischen Stabilität von Sprengschnuren mit 10 gm^–1 PETN zeigten, daß die Schnur frei bei 403 K verbrennt. Unter Abschluß in einem Stahloder Kupferrohr tritt bei 403 K eine partielle Detonation auf. Zur Charakterisierung der thermischen Stabilität von PETN und von pyrotechnischen Mischungen, die in Zünderköpfen von elektrischen Sprengkapseln verwendet werden, wurde Differentialthermoanalyse (DTA) angewendet. Die elektrischen Sprengkapseln von Aluminium- und Kupferzellen wurden mit einer durchschnittlichen Aufheizgeschwindigkeit von 0.4 Grad/min von Raumtemperatur auf 373 K erhitzt. Die Aufheizgeschwindigkeit wurde bis zur Explosion allmählich auf 1,5 Grad/min erhöht. Die einzelnen Detonationen erfolgten bei einer Temperatur zwischen 373 und 375 K. Die Stoß- und Reibempfindlichkeit der Sprengschnur war gering. Bei einem mehrmaligen Einwirken eines 5 kg-Hammers aus einer Höhe von 1 m erfolgte keine Detonation. Bei Reiben mit der unscharfen Kante einer Stahlplatte bis zur Zerstörung erfolgte keine Detonation.

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, 10 ^–1 PETN, , 403 , 403 . PETN , , . 373 0,4°/. 1,5°/ . 373 375 . . 5 1 . , .

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The authors are indebted to the Director, Central Mining Research Station for giving permission to publish this paper. The views expressed in the paper are those of the authors and not necessarily of the institute which they belong to.     

N-Bromosuccinimide-dibenzoyl peroxide/azabisisobutyronitrile: a reagent for Z- to E-alkene isomerization

N-Bromosuccinimide-dibenzoyl peroxide/azobisisobutyronitrile is used to carry out several types of Z- to E-alkene isomerizations. The NBS-bromination conditions are sufficient for both allylic bromination and alkene isomerization. When the allylic hydrogens are not available in substrates, only the isomerization of the alkene takes place. The present conditions for isomerization of carbon-carbon double bonds are mild and efficient.     

Determination of enzyme kinetic parameters of cyclic CMP-specific phosphodiesterase by quantitative fast atom bombardment tandem mass spectrometry

The determination of cytidine 3′,5′-cyclic monophosphate-specific phosphodiesterase activity by means of fast-atom bombardment (FAB) mass Spectrometry with mass-analysed ion kinetic energy (MIKE) spectrum scanning is described. Initial efforts to determine the activity of the enzyme by this method were unsuccessful owing to the obfuscation of sample-related peaks by peaks emanating from the incubation buffer and cation adducts; dilution of buffer and a desalting procedure overcame these difficulties. In the resulting positive-ion FAB mass spectra, characteristic peaks of the enzyme substrate and product could be readily identified and the protonated molecular ions selected for MIKE scanning. By spiking enzyme incubates with known amounts of substrate and product, and measuring peak heights in the MIKE spectra of both spiked and unspiked samples, the substrate/product ratio at the end of a series of phosphodiesterase incubations was determined. From the data obtained, the K_m and V_max of the phosphodiesterase were calculated as 6.08 mM and 11 μmol min^?1 mg^?1, respectively, showing good agreement with the analogous values of 8.06 mM and 5.8 μmol^?1 min^?1 mg^?1 obtained by radioactive assay.     

Kinetics and electrochemical studies on superoxide

Rate constants for the reaction of superoxide O^- ₂ with various substrates were obtained through stationary electrode polarography theory and technique. In solvent acetonitrile, the substrate and the rate constants of the reaction O^- ₂ + AH^{- k2}Product, are, AH = isopropanol (k₂ < 0.01 M^-1 s^-1); ethanol (k₂ = 1.42 × 10² M^-1 s^-1); methanol (k₂ = 1.1 × 10⁷ M^-1 s^-1), H₂O (k₂ = 1.0 × 10⁵ M^-1 s^-1). In MeCN, O^-2 was found to be rather unreactive towards glucose and acetone but it reacts with fructose and sucrose catalytically. However, in DMF2, O^- ₂reacts with glucose and fructose with k2 order of 105 M-1 s-1. The mechanism of the reaction of O^- ₂ with the substrates (AH) is proposed as O^- ₃ + AH k₂O, AH^k2 _k-1 k [O₂H + AH]^-, _k-2O₂H + A^- with k₁ = 10⁹ M^-1 s^-1 and k^-1 = 10⁸ -10⁹ s^-1. With these values of k_-1 and k₁, k k₂(obs). The reversible E_1/2 for O₂ + e O^- ₂ in various solvents: MeCN, acetone, isopropanol, methanol, H₂O were obtained either directly from the reversible voltammogram or from experimental voltammograms and the rate constants obtained (as above) using stationary electrode polargraphy theory; E_1/2 being -0.82 (MeCN),-0.85 (acetone),-0.72 (isopropanol);-0.66 (MeOH),-0.56 (H2O) vs SCE.     

Hydroarylation of alkynes and alkenes through alumina-sulfuric acid catalyzed regioselective CC bond formation

A highly atom-efficient synthetic protocol for hydroarylation of terminal-aryl alkynes and styrene through the regioselective CC bond formation via the electrophilic addition of naphthols and substituted phenols has been developed using alumina-sulfuric acid as a heterogeneous supported solid acid catalyst. This methodology shows excellent regioselectivity and affords the desired product in good to excellent yield. The heterogeneous catalyst can also be recycled efficiently without much loss of activity.     

Structure and Stereochemistry of New Sesquiterpene Esters from Echinacea purpurea (L.) MOENCH. (Preliminary communication)

The structure elucidation of four new constituents from the roots of Echinacea purpurea is described. They are shown to be cinnamoyl esters of sesquiterpene alcohols with a germacrane or a guaiane skeleton. First pharmacological results indicate immunological activities.     

Aqueous polymerization of acrylonitrile by ascorbic acid–peroxodisulfate redox system

The polymerization of acrylonitrile initiated by an ascorbic acid–peroxodisulfate redox system was studied in an aqueous solution at 35°C in the presence of air. Molecular oxygen was found to have no effect on the polymerization reaction. An increase in ionic strength slightly increased the rate. The overall rate of polymerization, R_p, showed a square dependence on [monomer] and a half-order dependence on [peroxodisulfate]. A first-order dependence on [ascorbic acid] at low concentrations (<3.0 × 10^?3 mol L^?1) followed by a decrease in R_p at higher concentrations of ascorbic acid (>3.0 × 10^?3 mol L^?1) was also noted. R_p remained unchanged up to 40°C and showed a decline thereafter. Addition of catalytic amounts of cupric ions decreased the rate whereas ferric ions were found to increase the rate. Added sulfuric acid in the range (6.0?50.0) × 10^?5 mol L^?1 decreased the R_p.