Interpretation of vicinal proton–proton coupling constants of heteroaromatic molecules in terms of topological electron density descriptors

The indirect vicinal proton–proton coupling constants for pyrrole, furan, thiophene and 15 related heteroaromatic compounds were calculated using the Khon–Sham approximation. An analysis of the four Ramsey contributions to the coupling constants was carried out showing that the Fermi contact term is always positive and dominant, although the remaining contributions have a nonnegligible net negative contribution. The trends observed for the proton–proton coupling constants were rationalized in terms of the properties of the electron density. It was found that electron delocalization between the corresponding hydrogen atoms plays a major role on the observed behavior with the charges of the carbon atoms bonded to them and the accompanying geometric variations being also of importance in the coupling mechanism. Copyright © 2010 John Wiley & Sons, Ltd.     

Chromium(VI) oxide oxidation of non‐ethoxylated and ethoxylated alcohols for determination by electrospray ionization mass spectrometry

A new derivatization procedure to increase the sensitivity of electrospray ionization mass spectrometry (ESI‐MS) to non‐ethoxylated and ethoxylated alcohols was investigated. The analytes were oxidized with chromium(VI) oxide and the resulting carboxylic and ethoxy‐carboxylic acids were isolated by extraction with ethyl acetate; the extracts were alkalinized and infused into the ESI‐MS system working in the negative‐ion mode. The yields of the combined oxidation‐extraction were ca. 100% for non‐ethoxylated fatty alcohols dissolved in acetone and they decreased moderately in samples containing increasing amounts of water (e.g., a 75% yield was obtained with 50% water). Ethoxylated alcohols with more than two ethylene oxide units resulted in yields of ca. 60%. Low limits of detection (LODs) were obtained when the procedure was applied to the analysis of body‐care products and cosmetics containing fatty alcohols, e.g., in a varicose‐vein cream, the LODs were 25 µg cetyl alcohol and 7.5 µg stearyl alcohol (detected as palmitic acid and stearic acid, respectively) per gram of sample. High molecular mass alcohols were also detected in seawater after pre‐concentration by solid‐phase extraction. Thus, the proposed method is particularly valuable for use in industrial samples having complex matrices and in environmental samples and it is competitive with other methods for the analysis of trace amounts of fatty alcohols. Copyright © 2010 John Wiley & Sons, Ltd.     

Reactions of naphthalene in N2O5?NO3?NO2? air mixtures

The reactions of naphthalene in N₂O₅? NO₃? NO₂? N₂? O₂ reactant mixtures have been investigated over the temperature range 272–297 K at ca. 745 torr total pressure and at 272 K and ca. 65 torr total pressure using long pathlength Fourier transform infrared absorption spectroscopy. 2,3-Dimethyl-2-butene was added to the reactant mixtures at 272 K to rapidly scavenge the NO₃ radicals both initially present in the added N₂O₅ and formed from the thermal decomposition of N₂O₅ during the reactions. The data obtained in the presence and absence of added 2,3-dimethyl-2-butene showed that napthalene undergoes initial reaction with the NO₃ radical to form an NO₃-naphthalene adduct, which either rapidly decomposes back to the reactants (at a rate of ca. 5 × 10⁵ s^?1 at 298 K) or reacts exclusively with NO₂ to form products. When NO₃ radicals, N₂O₅ and NO₂ are in equilibrium, this overall process is kinetically equivalent to reaction of naphthalene with N₂O₅, and previous kinetic and product studies have indeed assumed the reactions of naphthalene and alkyl-substituted naphthalenes in N₂O₅? NO₃? NO₂? air mixtures to be with N₂O₅, and not with NO₃ radicals.     

Extraction and analysis of ellagic acid from novel complex sources

Ellagic acid (EA) was quantified by reversed-phase high-performance liquid chromatography (RPHPLC) coupled with photodiode array detection (DAD) in five fine-powdered plants collected from the semiarid region of Mexico. Samples analysed included Jatropha dioica branches (Dragon’s blood), Euphorbia antisyphyllitica branches (Candelilla), Turnera diffusa Willd leaves (Damiana), Flourensia cernua leaves (hojasén) and Punica granatum husk (pomegranate) at two maturity stages (“turning” or intermediate and maturated fruit, considered as positive controls). The results demonstrated high EA concentrations in all tested samples which are novel sources of this natural antioxidant. The method developed for the EA analysis is fast and it showed an excellent linearity range, repeatability, intra-and inter-day precision and accuracy with respect to the methods reported for the EA analysis.