2D self-assembly of oligo(p-phenylene vinylene) derivatives: from dimers to chiral rosettes

Enantiomerically pure oligo(p-phenylene vinylene) diaminotriazine derivatives and a short structurally related achiral diaminotriazine derivative, all having a rigid backbone in common, are studied to self-assemble at the solution-graphite interface by scanning tunneling microscopy. As a function of the length of the backbone, different two-dimensional motifs are formed (dimers and rosettes) that are rationalized in terms of the balance between different intermolecular interactions, in this case, intermolecular hydrogen bonding and the packing requirements of the alkyl chains on a graphite surface. In addition, the effect of molecular chirality on monolayer chirality is investigated, revealing molecular size-dependent expressions of the monolayer chirality.     

Inter-comparison of laser photoacoustic spectroscopy and gas chromatography techniques for measurements of ethene in the atmosphere

Laser photoacoustic spectroscopy (LPAS) is highly suitable for the detection of ethene in air due to the overlap between its strongest absorption lines and the wavelengths accessible by high-powered CO2 lasers. Here, we test the ability of LPAS to measure ethene in ambient air by comparing the measurements in urban air with those from a gas chromatography flame-ionization detection (GC-FID) instrument. Over the course of several days, we obtained quantitative agreement between the two measurements. Over this period, the LPAS instrument had a positive offset of 330 +/- 140 pptv (parts-per-trillion by volume) relative to the GC-FID instrument, possibly caused by interference from other species. The detection limit of the LPAS instrument is currently estimated around 1 ppbv and is limited by this offset and the statistical noise in the data. We conclude that LPAS has the potential to provide fast-response measurements of ethene in the atmosphere, with significant advantages over existing techniques when measuring from moving platforms and in the vicinity of emission sources.     

Sediment dilution method to determine sorption coefficients of hydrophobic organic chemicals

Sorption coefficients of hydrophobic organic chemicals (HOC) to sediments and soils can easily be underestimated in traditional batch experiments, especially because analysis of the aqueous concentration often includes compounds sorbed to colloidal organic matter. In this work, a "sediment dilution approach" has been combined with measurements of freely dissolved concentrations to determine sorption coefficients of five chlorobenzenes and two chloroanilines in spiked sediment and of two unknown chemicals in field-contaminated sediment. A range of sediment suspensions with different sediment-water ratios was made. Freely dissolved concentrations in these suspensions were measured by negligible depletion solid-phase microextraction (nd-SPME). Sediment-water sorption coefficients (KD) were derived from the decrease of the freely dissolved concentrations as a function of the "dilution factor" (DF = volume water/mass sediment). The determined sorption coefficients were very similar to literature values. The experimental setup provides sorption coefficients without the need for total extractions, and the negligible depletion SPME technique does not require phase separation. The proposed method might be an alternative for batch equilibrium experiments to determine sorption coefficients.     

Community assessment of availability, consumption, and cultural acceptability of food sources of (pro)vitamin A: toward the development of a dietary intervention among preschool children in rural Burkina Faso

BACKGROUND: Vitamin A deficiency remains a public health problem in Burkina Faso and elsewhere in the developing world. Dietary diversification is a promising strategy that needs to be explored to strengthen the country's ongoing supplementation program. OBJECTIVE: The purpose of this study was to identify locally available and acceptable (pro)vitamin A-rich foods to be included in a dietary intervention addressing vitamin A deficiency in children aged six months to three years. METHODS: A food ethnographic study combining recall methods, observation, and focused group discussion was conducted in the dry and rainy seasons. Thirty-five mother-child pairs were randomly selected and included in the study. RESULTS: The dietary pattern of children was characterized by low diversity with extremely low energy and vitamin A intake in both seasons. The study identified the availability of numerous (pro)vitamin A-rich foods, but these foods are either not consumed or consumed by few in low amounts and/or in low frequencies. The main constraining factors identified are related to financial accessibility (for liver), seasonal availability (for egg, milk, mango, papaya, and green leafy vegetables), and beliefs related to consumption and preparation (for green leafy vegetables). However, the study also revealed that the study population associated all identified (pro)vitamin A-rich foods with positive attributes such as health, strength, and vitamin richness, which might offer an entry point for designing and implementing dietary interventions. CONCLUSIONS: Based on the findings of this formative research, intervention strategies with mango and liver are proposed to improve the vitamin A intake and status of children in the rural areas of Burkina Faso.     

Lead and zinc contents of food and diets in the Netherlands

Summary The lead and zinc contents of foodstuffs sampled in Dutch retail shops were determined by means of atomic absorption spectrophotometry. Extremely high contents of these metals were not found. The daily intakes through food and beverages calculated on the basis ofper caput consumption data for the Netherlands were 105 microgrammes of lead and 16.8 milligrammes of zinc. Calculations based on diet studies of selected population groups (farmers, inhabitants of a city, families in a northern province and students) provided intakes of lead and zinc of the same order, namely 63 to 161 microgrammes of lead and 15.4 to 24.6 milligrammes of zinc per person per day. The intakes by toddlers were assessed at 42 g and 8.0 mg respectively. These results are compared with those calculated for three other countries. A toxicological evaluation of these levels is given.

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Blei- und Zinkgehalt der Lebensmittel und der Kost in den Niederlanden

Zusammenfassung Die Blei- und Zinkgehalte von Lebensmitteln aus niederländischen Läden wurden durch Atomabsorptionsspektrophotometrie ermittelt. Außerordentlich hohe Gehalte wurden nicht gefunden. Berechnungen auf Grund der täglichen Aufnahme durch Nahrung und Getränke (aus Produktions-, Import- und Exportwerten ermittelt) ergaben pro Kopf der Bevölkerung 105 g Blei und 16,8 mg Zink. Weitere Berechnungen stützten sich auf den täglichen Lebensmittelverbrauch von Sondergruppen (Bauern, Stadtbewohnern, Familien in einer nördlichen Provinz und Studenten); sie ergaben Blei- und Zinkaufnahmen in ähnlichen Mengen, nämlich 63 bis 161 g Blei und 15,4 bis 24,6 mg Zink pro Tag. Für die Aufnahme durch Kleinkinder wurden 42 g Blei und 8,0 mg Zink pro Tag berechnet. Die Ergebnisse wurden mit Daten aus drei anderen Ländern verglichen. Eine toxikologische Beurteilung der Befunde wurde versucht.

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Authors wish to thank Mr. P. W. J. de Graaf and Mr. W. van der Schee for their zinc and lead determinations.     

Absorption der Reaktionspartner am Katalysator bei der Fetthydrierung

Absorption of Reactants on Catalyst in the Hydrogenation of Fats The study involves selective hydrogenation of fatty oils containing polyenoic fatty acids. In the initial stage of hydrogenation the catalyst surface is probably predominently occupied by the polyenoic acids. At that stage the monoenoic acids are hardly hydrogenated and also the isomerisation of the monoenoic acids is largely suppressed. Analysis of the monoenoic acid formed from linoleic acid shows that the reaction product is so composed as if an equimolecular mixture of 9-cis,11-trans- and 10-trans, 12-cis-conjugated isolinoleic acids were taken as starting material. Obviously, the catalyst surface is occupied by the conjugated polyenoic acids.     

Leucine Side‐Chain Conformation and Dynamics in Proteins from 13C NMR Chemical Shifts

Look to the left : The carbon nucleus of a substituent in the gauche position about a subtending dihedral angle experiences an NMR chemical shift of about 5 ppm relative to the same chemical group present in the trans position. We demonstrate that this “γ‐gauche effect” can be utilized to determine the conformation and extent of rotameric averaging for leucine amino acid side chains in the protein calbindin D_9k. The success of this approach suggests that rules can be established to define the orientation of other side chains in proteins as well, offering an easy gauge of protein side‐chain flexibility, as well as avenues to advance protein structure determination by using side‐chain chemical shifts.