The isoconversional method for determination of energy of activation at constant heating rates

The isoconversional method for the determination of energies of activation from the reciprocal temperature at which a fraction of conversion was reached in experiments at differing constant heating rates is reviewed and amplified. The error introduced into the calculation of activation energy by the use of a linear approximation of the logarithm of the temperature integral is discussed. Methods for the correction of this error are developed and a table of correction factors are given.

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Zusammenfassung Es wird eine Literaturübersicht über die und eine ausführliche Darstellung der Isokonversionsmethode zur Bestimmung von Aktivierungsenergien aus den Reziprokwerten derjenigen Temperaturen gegeben, bei denen ein bestimmter Konversionsgrad in Experimenten mit verschiedener Aufheizgeschwindigkeit erreicht wird. Der in die Berechnung der Aktivierungsenergie durch lineare NÄherung des Logarithmus des Temperaturintegrals eingehende Fehler wird diskutiert. Es werden Methoden zur Korrektur dieses Fehlers entwickelt und Korrekturfaktoren in Tabellenform angegeben.

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Gas-liquid chromatography of fecal neutral steriods.

A method is described for the analysis of fecal neutral steriods with a dual-column gas-liquid chromatography (GLC) system. After saponification of the fecal slurry, the neutral steroids were extracted with hexane. The GLC separation of the compounds and quantitation were achieved by simultaneous injection of the derivatized and derivatized aliquots of the extract onto dual colmuns under identical conditions. The neutral steroids of interest were than identified by matching the retention times with those of known standards, and identification was confirmed by use of an interfaced GLC high-resolution mass spectrometry system. The detection limit was 0.003 mg of steroid/g of fecal slurry. The pricision of the method is illustrated by a relative standard diviation of 2-10% and a recovery of neutral steroids from 73-96%. The method was applied to the determination of fecal neutral steroids in a "High protein diet in colon cancer study". A considerably larger level of coprostanone than of coprostanol was observed. Data on neutral steroids in fecal samples from subjects on different diets are the subject of a separate publication.     

Regiospecific synthesis of 11-desoxyanthracycline antibiotics starting with aloe-emodin

The regiospecific synthesis of an established 11-desoxyanthracycline synthon ($\text{8b}$) from aloe-emodin ($\text{3a}$) is described.     

Sequences of rational torsions on abelian varieties

Summary We address the question of how fast the available rational torsion on abelian varieties over increases with dimension. The emphasis will be on the derivation of sequences of torsion divisors on hyperelliptic curves. Work of Hellegouarch and Lozach (and Klein) may be made explicit to provide sequences of curves with rational torsion divisors of orders increasing linearly with respect to genus. The main results in §2) are applications of a new technique which provide sequences of hyperelliptic curves for all torsions in an interval [a _g ,a _g +b _g ]] wherea _g is quadratic ing andb _g is linear ing. As well as providing an improvement from linear to quadratic, these results provide a wide selection of torsion orders for potential use by those involved in computer integration. We conclude by considering possible techniques for divisors of non-hyperelliptic curves, and for general abelian varieties.     

Deactivation of vibrationally excited ozone by O(3P) atoms

Using laser-induced fluorescence of ozone (to measure the rate of disappearance of O₃²) and NO₂ titration (to determine O atom concentrations), we have determined bimolecular rate constants for the deactivation by O(³P atoms) of ozone in excited stretching and bending modes. These experiments do not distinguish between deactivation by (a) the exchange of vibrational and translational energy or (b) the chemical reaction O₃ + O → 2O₂. If the non-reactive pathway (a) is assumed to dominate, then O(³P) is 150 times more effective than O₂ in deactivating O²₃. If chemical reaction (b) is dominant, the bimolecular rate constant for O²₃ + O(³P) is larger by a factor of 150–1500 than that for ground-state ozone.     

Novel Copolymers of 4-Fluorostyrene. 9. Some Ring-Disubstituted 2-Phenyl-1,1-dicyanoethylenes

Novel copolymers of trisubstituted ethylene monomers, ring-disubstituted 2-phenyl-1,1-dicyanoethylenes, RC₆H₃CH=C(CN)₂ (where R = 3-Br-4-CH₃O, 5-Br-2-CH₃O, 2-F-5-CH₃, 2-F-6-CH₃, 3-F-2-CH₃, 3-F-4-CH₃, 4-F-2-CH₃, 4-F-3-CH₃) and 4-fluorostyrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, ¹H and ¹³C-NMR. The order of relative reactivity (1/r ₁) for the monomers is 3-F-4-CH₃(1.64) > 5-Br-2-CH₃O (1.62) > 3-Br-4-CH₃O (1.36) > 4-F-2-CH₃(1.3) > 4-F-3-CH₃(1.26) > 3-F-2-CH₃(1.11) > 2-F-5-CH₃ (0.98) > 2-F-6-CH₃ (0.97). High T_g of the copolymers, in comparison with that of poly(4-fluorostyrene) indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 290–400°C range with residue, which then decomposed in 400–800°C range.