Raman spectroscopy in AB2X4 pseudoternary layered compounds

We have synthesized several pseudoternary layered compounds by cation or anion cross substitution in ternary AB₂X₄ compounds. Here we report on the low frequency Raman spectra obtained from Zn_xCd_1-xIn₂S₄, Zn(In_xGa_1-x)₂S₄ and ZnIn₂(S_xSe_1-x)₄ single crystals. Within these systems we have identified five compositionally or dynamically different phases. Each of these phases may be characterized by its peculiar low frequency Raman spectrum which is connected to the dynamics of the layers in the unit cell. Abrupt structural/dynamical changes are observed as a function of composition between different phases. Within each phase compositional changes cause only smooth and small spectral variations.     

Liquid chromatography-tandem mass spectrometry for the identification of impurities in d-allethrin samples

A previous GC/MS study highlighting the impurity profile of the synthetic pesticide d-allethrin is extended here to validate and confirm the impurities identity through the development of soft ionisation HPLC-MS methods. To accomplish this, we developed a reverse phase LC-MS analysis in gradient elution with two distinct soft ionisation techniques, the atmospheric pressure ionisation with electrospray source (API-ESI) and the chemical ionisation (APCI). A single quadrupole and an ion trap, which allowed the simultaneous determination of the molecular masses and structural information of the impurities by acquisition of collisionally induced (CID) product ions spectrum and in-source fragmentation, were employed as analysers. Single quadrupole and ion trap analysers resulted perfectly matching in the d-allethrin impurity fragmentation patterns. All the main impurities over 0.1% identified by GC/MS were confirmed. Results indicate that the proposed HPLC/MS method was found appropriate to confirm the presence of impurities such as chrysolactone, chloro allethrin derivatives, allethrolone and chrysanthemic acid, excluding their formation under GC/MS strong ionisation condition.     

Determination of chloride and bromide in lead telluride and bismuth telluride systems

Summary An indirect analytical method, based on measurement of silver, for determining chloride and bromide in bismuth and lead tellurides was developed. The samples were dissolved in dilute nitric acid and the halides were separated as the silver salts by strong centrifugation. The excess of silver was directly determined in the sample solution by solvent extraction with dithizone in carbon tetrachloride and by spectrophotometric determination. Suitable conditions for masking interfering elements were established so that a very selective procedure for silver determination was achieved. Chloride and bromide down to 0.01 mole % could be determined. A procedure for determining chloride and bromide in the same sample with no interference from iodide, was also developed.

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Zusammenfassung Ein indirektes, auf der Messung von Silber beruhendes Verfahren zur Bestimmung von Chlorid und Bromid in Wismut- und Bleitelluriden wurde entwickelt. Die Proben werden in verd. Salpetersäure gelöst und die Halogenide als Silbersalze scharf abzentrifugiert. Der Silberüberschuß wird unmittelbar aus dem Filtrat mit Dithizonlösung extrahiert und spektro-photometrisch gemessen. Geeignete Maßnahmen zur Maskierung störender Elemente wurden angegeben, so daß ein sehr selektives Verfahren zur Silberbestimmung vorliegt. Bis zu 0,01 Molprozent Chlorid und Bromid sind noch bestimmbar. Außerdem wurde ein Verfahren zur Chlorid- und Bromidbestimmung in Gegenwart von Jodid entwickelt.

     

Green and sustainable chemistry in Latin America: Which type of research is going on? And for what?

Green (and sustainable?) frame around ‘Inverted America’ (adapted from Torres García, 1943, Museo Juan Manuel Blanes, Montevideo, CC BY 4.0).

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Experimental observation of the alpha relaxation in supercooled water

Intermediate scattering functions for density fluctuation in D2O contained in pores of a Vycor glass have been measured using an improved neutron spin-echo spectrometer at two supercooled temperatures. The measurements cover the time range from 1 to 2300 ps with the Q range spanning the first diffraction peak of water. The time correlation functions can be fitted to a stretched exponential relaxation function with a Q-dependent amplitude. Both the stretch exponent and the relaxation time peak approximately at the Q value corresponding to the first diffraction peak, confirming the validity of the mode coupling idea in supercooled water.     

Cosmic-muon results from the NUSEX experiment

Summary Muon underground data collected in the NUSEX experiment at Mont Blanc have been analysed concerning the following topics: I) vertical muon intensity, II) prompt muon flux, III) muons from the direction of Cygnus X-3. Preliminary results from the analysis of more than 20 000 muons are presented and discussed.

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Riassunto Gli eventi di muoni rivelati sottoterra nell'esperimento NUSEX al Monte Bianco sono stati analizzati per studiare I) l'intensità verticale dei muoni, II) il flusso di muoni pronti, III) l'eccesso di muoni dalla direzione di Cygnus X-3. In questo lavoro sono presentati c discussi i risultati preliminari ottenuti dal'lanalisi di piú di 20.000 eventi.

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Резюме Был проведен анализ данных, собранных в экспеимемнте NUSEX на Мон Блане. Анализировались следующие вопросы: 1) интенсивность вертикальных мюонов, 2) поток мгновенных (быстрых) мюонов, 3) мюоны, движущиеся в направлении от Лебедь X-3. Приводятся и обсуждаются предварительные результаты анализа для более, чем 20 000 муонов.

     

Limit on monopole flux in the Mont Blanc NUSEX experiment

Summary A trigger dedicated to the search of superheavy monopoles operates since about two years in the NUSEX apparatus, installed in the Mont Blanc tunnel. Monopoles are identified by time of flight and visualization of the pulses involved in a trigger. The present upper limit on monopole flux is 2.3·10⁻¹³ cm⁻² s⁻¹ sr⁻¹ (90% c.l.).

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Riassunto Da circa due anni è operativo sull'apparato NUSEX, installato nel tunnel del Monte Bianco, un trigger dedicato alla ricerca dei monopoli previsti dalle teorie di grande unificazione. L'identificazione dei monopoli è basata sul tempo di volo e sulla localizzazione nello spazio degli impulsi coinvolti nel trigger. Il limite superiore fino ad oggi raggiunto per il flusso di monopoli è 2.3·10⁻¹³ cm⁻²s⁻¹ sr⁻¹ (90% c.l.).

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Резюме Триггерная схема, предназначенная для поиска сверхтяжелых монополей, действует в течение почти двух лет в установке NUSEX, расположенной в туннеле под Мон Бланом. Идентификация монополей основана на времени пролета, а локализация в пространстве осуществляется с помощью импульсов в триггерной схеме. Настоящий верхний предел на поток монополей составляет 2.3· ·10⁻¹³ см⁻² с⁻¹ ср⁻¹ (к 90% вероятностью).

     

Transverse spin structure of the nucleon from lattice-QCD simulations

We present the first calculation in lattice QCD of the lowest two moments of transverse spin densities of quarks in the nucleon. They encode correlations between quark spin and orbital angular momentum. Our dynamical simulations are based on two flavors of clover-improved Wilson fermions and Wilson gluons. We find significant contributions from certain quark helicity flip generalized parton distributions, leading to strongly distorted densities of transversely polarized quarks in the nucleon. In particular, based on our results and recent arguments by Burkardt [Phys. Rev. D 72, 094020 (2005)], we predict that the Boer-Mulders function h(1/1), describing correlations of transverse quark spin and intrinsic transverse momentum of quarks, is large and negative for both up and down quarks.     

Blue fluorescent dye-protein complexes based on fluorogenic cyanine dyes and single chain antibody fragments

Fluoromodules are complexes formed upon the noncovalent binding of a fluorogenic dye to its cognate biomolecular partner, which significantly enhances the fluorescence quantum yield of the dye. Previously, several single-chain, variable fragment (scFv) antibodies were selected from a yeast cell surface-displayed library that activated fluorescence from a family of unsymmetrical cyanine dyes covering much of the visible and near-IR spectrum. The current work expands our repertoire of genetically encodable scFv-dye pairs by selecting and characterizing a group of scFvs that activate fluorogenic violet-absorbing, blue-fluorescing cyanine dyes, based on oxazole and thiazole heterocycles. The dye binds to both yeast cell surface-displayed and soluble scFvs with low nanomolar K(d) values. These dye-protein fluoromodules exhibit high quantum yields, approaching unity for the brightest system. The promiscuity of these scFvs with other fluorogenic cyanine dyes was also examined. Fluorescence microscopy demonstrates that the yeast cell surface-displayed scFvs can be used for multicolor imaging. The prevalence of 405 nm lasers on confocal imaging and flow cytometry systems make these new reagents potentially valuable for cell biological studies.     

Kinetic discrimination in recognition of DNA quadruplex targets by guanine-rich heteroquadruplex-forming PNA probes

Guanine-rich peptide nucleic acid probes hybridize to DNA G quadruplex targets with high affinity, forming PNA-DNA heteroquadruplexes. We report a surprising degree of kinetic discrimination for PNA heteroquadruplex formation with a series of DNA targets. The fastest hybridization is observed for targets folded into parallel morphologies.