6α-formylpenicillins and derivatives

Moffatt type oxidation of 6α-(hydroxymethyl)penicillins has produced a series of 6α-formylpenicillins, which were further used in chain extension reactions with Wittig reagents and diazoalkanes.     

Near- and mid-infrared spectroscopy of sol–gel derived ormosils: vinyl and phenyl silicates

The suitability of ormosils as photonic materials was investigated. Vinyl and phenyl silicates were synthesised below 100°C. A detailed assignment of mid-infrared vibrational absorption bands is given. This allowed assignment of overtone and combination bands in the near-infrared region and an assessment of residual water contamination, which is low and can be expelled by evacuation. These ormosils have low intrinsic and extrinsic optical absorption in the visible spectral region and at useful wavelengths in the near-infrared.     

Steric factors in the gas-phase elimination of esters: The pyrolysis of 2,3-dimethyl-3-pentyl acetate

The kinetics of the thermal decomposition of 2,3-dimethyl-3-pentyl acetate have been studied at a temperature range of 212–260°C and a pressure range of 30–300 mm Hg. The olefins produced are 2-ethyl-3-methyl-1-butene, 3,4-dimethyl-trans-2-pentene, 3,4-dimethyl-cis-2-pentene, and 2,3-dimethyl-2-pentene. The reaction is homogeneous, obeys first-order law, and the value of the rate constant is given by the Arrhenius equation The directions of elimination and their corresponding partial rates are best explained in terms of purely steric factors.     

Oxidation process induced by 2-mercaptopyrimidine at a mercury electrode

The oxidation process induced by 2-mercaptopyrimidine (RSH) at a hanging mercury drop electrode was studied in aqueous media by normal and cyclic voltammetry. The results indicate the formation of a weakly adsorbed HgSR complex according to the reaction Hg+RSH-->HgSR+e(-)+H+. When the surface excess of HgSR is high, a two-dimensional condensation takes place if the potential is positive enough, as proved by phase-sensitive ac and cyclic voltammetry.     

Identification and composition of cuticular hydrocarbons of the major Afrotropical malaria vector Anopheles gambiae s.s. (Diptera: Culicidae): analysis of sexual dimorphism and age-related changes

Forty-eight cuticular hydrocarbons (CHCs) were characterized by gas chromatography-mass spectrometry from the epicuticular surface of the major Afrotropical malaria vector Anopheles gambiae. The hydrocarbons identified were 14 n-alkanes, 16 monomethyl alkanes, 13 dimethyl alkanes, 5 alkenes, with main-chain lengths ranging from C(17) to C(47), and the results are consistent with those from other Culicidae species. Qualitative differences were not observed between laboratory pools of three females and males, between different age-groups (0-16 days) and between single field specimens, whereas quantitative differences in CHC profiles were observed. Differences between sexes were more marked in individuals aged 0-2 days than in older ones. Both sexes undergo strong CHC profile changes with age, and individuals aged 0-2 days differ remarkably from the older ones. The possibility of exploiting these changes for estimating the age of mosquito was explored through multivariate analyses of the relative abundance of the compounds, using either the whole CHC profile or a subset of CHCs. Such a method allows us to assign more than 85% of females and 75% of males to the correct age-group. Although preliminary, these results show that the method is promising, as it has already been shown in Aedes aegypti and An. stephensi. The correct determination of the vector age (particularly in the case of the An. gambiae complex of sibling species) provides valuable information in malaria epidemiology and in evaluation of the effectiveness of vector control strategies. Further efforts will be made to validate this method on single specimens reared in seminatural conditions before being proposed to medical entomologists working in the Afrotropical region.     

Kinetics and mechanistic studies of the atmospheric oxidation of alkynes

Kinetics studies of the OH-initiated oxidation of 2-butyne, propyne, and acetylene were conducted at 100 Torr and 298 K using turbulent flow chemical ionization mass spectrometry. The major oxidation products were identified, and with the aid of supporting electronic structure thermodynamics calculations, a general OH-initiated oxidation mechanism for the alkynes is proposed. The major product branching ratio and the product-forming rate constants for the 2-butyne-OH adduct + O(2) reaction were experimentally determined as well. The atmospheric implications of the chemical oxidation mechanism and kinetics results are discussed.     

Pd-Dissolution through a mild and effective one-step reaction and its application for Pd-recovery from spent catalytic converters

We describe here an innovative method for Pd-dissolution using the reagent N,N'-dimethylperhydrodiazepine-2,3-dithione diiodine adduct which, being safe and powerful, is appealing for practical applications: remarkably almost quantitative Pd-recovery from model spent three-way catalysts has been obtained, showing that the effectiveness of the method is maintained when palladium is contained in a complex system such as a car catalyst, a ceramic material which has undergone severe thermal stress.