Synchrotron radiation total reflection X-ray fluorescence (SR-TXRF) for evaluation of food contamination

Summary The objective of this study was to use synchrotron radiation total reflection X-ray fluorescence analysis (SR-TXRF) for the determination of metals and other elements in food available to the population in commercial establishments, in order to evaluate the risks of contamination by these products. The analyzed species were vegetables, leafy vegetables, fruits, cereal and grain. The results indicated that some species were contaminated by Cr, Cu, Zn and Pb with concentrations much higher than the reference values.     

Prevalence of voice disorders in African American and European American preschoolers

Several studies have reported prevalence rates for voice disorders in school-aged children. Less is known, however, about such prevalence in preschoolers, and whether racial, ethnic, or cultural diversity may influence it. The presence of voice disorders in a total of 2445 African-American and European-American preschool children, 1246 males and 1199 females, from 2 to 6 years of age is reported here. Presence of a voice disorder characterized by hoarseness was identified by a three-prong approach including teacher identification, investigator screening, and parent identification. Speech-language pathologists listened individually to each child's speech as they engaged each child in play-conversation activities. A voice disorder was identified on the basis of the judgment of two speech-language pathologists. Voice disorders characterized by hoarseness were identified in 95 children or 3.9% of the total sample by the investigators. Statistical analysis revealed no significant differences for age, gender, or race.     

HPLC-NMR of fatty alcohol ethoxylates

The application of HPLC-NMR for the analysis of a mixture of fatty alcohol ethoxylates (FAEs) is described. The use of the new generation, cryogenically cooled probes is investigated in respect of the sensitivity advantage that they provide. The FAE mixture is separated using liquid chromatography at the critical point of adsorption. The ability of the method to differentiate between the different end groups and the degree of polymerization of the mixture constituents is investigated. Both on-flow and stop-flow HPLC-NMR techniques were used together with two-dimensional NMR spectroscopy. The results are compared with those obtained by using an evaporative light scattering detector for the HPLC.     

Thermally reversible light scattering films based on the melting/crystallization of organic crystals dispersed in an epoxy matrix

Films that can be reversibly switched from opaque to transparent states by varying temperature (TRLS films), have potential applications in thermal sensors, optical devices, recording media, etc. A dispersion of organic crystals in a thermoset may be used for these purposes provided that at temperatures higher than the melting point there is a matching of refractive indices of both phases. A model system consisting on a dispersion of diphenyl (DP) crystals in an epoxy matrix based on diglycidyl ether of bisphenol A and m-xylylenediamine, was analyzed as a possible TRLS film encapsulated between transparent covers to avoid sublimation of DP. To obtain a uniform dispersion of DP-rich domains in the epoxy matrix by polymerization-induced phase separation, it was necessary to add 5 wt% of polystyrene (PS) to the initial formulation. Phase separation induced by polymerization at 80 °C led to a dispersion of PS/DP domains in the epoxy matrix due to the low compatibility of PS with the epoxy and its high compatibility with DP. Crystallization and melting processes were confined to the interior of dispersed domains leading to an excellent reproducibility of the optical properties of TRLS films in the course of successive heating-cooling cycles.     

Invertomers at nitrogen in aziridine carboxylates by mltltinuclear (1H,13C,17O,and15N) NMR study

A confrgurational and conformational study of NH, N-acetyl- and N-sulfonylaziridine carboxylates is performed by¹H ,¹³C,¹⁷O, and¹⁵N NMR spectroscopy. The presence of acetyl and su fonyl groups on the ring nitrogen atom seems to reduce greatly the configurational stability at nitrogen.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1226–1234, September, 1995.     

Reaction between quinone and thiazolidine. A study on the formation mechanism of new antiproliferative quinolindiones

Reaction between quinolinquinone and thiazolidine in basic medium was investigated. 2-Arylthiazolidine-4-carboxylic acid ethyl esters undergo two different cleavages in basic medium, yielding the 1-aryl-2-azadiene and a thiolic species. In the presence of quinolinquinone, the isomeric 1-aryl-3-ethoxycarbonyl-pyridoisoquinolin-5,10-diones and 3-amino-3-ethoxycarbonyl-dihydrothienoquinolin-4,9-diones are formed by a hetero-Diels-Alder reaction and 1,4-Michael addition reaction, respectively. A mechanism for the formation of the reaction products is presented.     

Biosynthesis of aglajnes, polypropionate allomones of the opisthobranch mollusc Bulla striata

The biogenesis of aglajnes, polypropionate allomones of the cephalaspidean mollusc Bulla striata, has been investigated in vivo by feeding experiments. Incorporation of the committed precursor, [1-¹⁴C]-propionate, into aglajne-1 (1) and -3 (3) established the de novo origin of these compounds in B. striata. In the letter we also discuss briefly the ecological meaning of the origin of polypropionates in B. striata and in other cephalaspidean molluscs.     

The role of molecular shape in bilayer elasticity and phase behavior

A previously developed molecular level model for lipid bilayers [G. Brannigan and F. L. H. Brown, J. Chem. Phys. 120, 1059 (2004)] is extended to allow for variations in lipid length and simulations under constant surface tension conditions. The dependence of membrane elasticity on bilayer thickness is obtained by adjusting lipid length at constant temperature and surface tension. Additionally, bilayer fluidity at various lipid lengths is quantified by analysis of a length versus temperature phase diagram at vanishing tension. Regions of solid, gel-like (hexatic) and fluid bilayer behavior are established by identification of phase boundaries. The main melting transition is found to be density driven; the melting temperature scales inversely with lipid length since thermal expansion increases with lipid aspect ratio.     

Dinitrogen reduction by TmII,DyII, and NdII with simple amide and aryloxide ligands

Dinitrogen can be reduced to the planar M2(mu-eta2:eta2-N2) structure without employing cyclopentadienyl or complicated polydentate ligands using the recently discovered divalent oxidation states of Tm(II), Dy(II), and Nd(II). Complexes of these ions with common monodentate amide and aryloxide ligands can effect N2 reduction. THF solutions of LnI2 (Ln = Tm, Dy) in the presence of 2 equiv of NaN(SiMe3)2 reduce dinitrogen to form {[(Me3Si)2N]2(THF)Ln}2(mu-eta2:eta2-N2) complexes that have planar Ln2N2 units and 1.264(7) and 1.305(6) A NN bonds consistent with (N2)2- moieties. With the stronger reductant Nd(II), aryloxides are sufficient ancillary ligands: the NdI2/2KOC6H3tBu2-2,6 (KOAr) system forms [(ArO)2(THF)2Nd]2(mu-eta2:eta2-N2), which has a 1.242(7) A NN bond.