Predicting arene rate coe ffi cients with respect to hydroxyl and other free radicals in the gas-phase : a simple and e ff ective method using a single
Predicting arene rate coefficients with respect to hydroxyl and other free radicals in the gas-phase: a simple and effective method using a single topological descriptor M. R. McGillen, C. J. Percival, G. Pieterse, L. A. Watson, and D. E. Shallcross School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, The Sackville Building, Sackville Street, P.O. Box 88, Manchester M60 1QD, UK Department of Air Quality and Climate Change, Energy Research Centre for the Netherlands, P.O. Box 1, 1755 ZG Petten, The Netherlands Biogeochemistry Research Centre, School of Chemistry, The University of Bristol, Cantock’s Close BS8 1TS, UK Received: 13 November 2006 – Accepted: 2 February 2007 – Published: 26 February 2007 Correspondence to: C. J. Percival (c.percival@manchster.ac.uk)
Kinetics and mechanism of reactions between aromatic olefins and hydroxyl radicals
The rates of the reactions of hydroxyl radicals (OH) with styrene, α-methylstyrene, and β-methylstyrene have been measured by irradiating mixtures of these aromatic olefins and NO in an environmental chamber at 298 K. Experimental conditions were used whereby the competition of ozone with OH in oxidizing the hydrocarbons could be considered negligible. The rate constant values, obtained by a relative method using isooctane as reference hydrocarbon, are: styrene (5.3 ± 0.5) × 10−11 cm3/molec·s, α-methylstyrene (5.3 ± 0.6) × 10−11 cm3/molec·s, and β-methylstyrene (6.0 ± 0.6) × 10−11 cm3/molec·s. A simplified kinetic treatment of the experimental data shows that styrene and β-methylstyrene are stoichiometrically converted to benzaldehyde, suggesting that OH attack occurs only on the aliphatic moiety of the aromatic olefins. Benzaldehyde was observed to undergo consecutive oxidation by OH, and its maximum formation yield was about 60%. A reaction mechanism is proposed where the primary rate-determining OH attack leads to the formation of 1-hydroxy-2-phenyl-2-ethenyl radicals, from which benzaldehyde is formed through fast intermediate reactions.
Effect of pretreatment with antibiotics on the hydrolysis of salicyluric acid in rabbit intestinal microorganisms.
The effect of pretreatment with antibiotics on the hydrolysis of salicyluric acid in rabbit intestinal microorganisms was investigated. Latamoxef sodium (LMOX, 25 mg/kg/d, intravenously) and cephalexin (CEX, 16.7 mg/kg/d, orally) were administered for 1 or 3 d. The blood concentration of salicyluric acid and salicylic acid following oral, intracecal and rectal administration of salicyluric acid was determined. By the pretreatment with LMOX for 1 or 3 d, the blood concentration of salicylic acid following oral administration of salicyluric acid was slightly decreased. In rabbits pretreated with CEX for 3 d, the blood concentration of salicylic acid was detected at low concentration. By the pretreatment with LMOX and CEX, however, the decrease in the blood concentration of salicylic acid following rectal administration of salicyluric acid was not observed. Although the examination of population of intestinal microorganisms induced by the pretreatment with antibiotics was not performed, the metabolic activity of intestinal microorganisms may be changed.