Unprecedented lability of the 5'-O-tert-butyldimethylsilyl group from 3'-spiro-5'-(4'-acylamino-1',2'-oxathiole-2',2'-dioxide) nucleoside derivatives via neighboring group participation of the 4'-acylamino residue

Scarce examples of exceptionally mild desilylation of tert-butyldimethylsilyl (TBDMS) ether groups by neighboring group participation have been previously described. Here, we investigate, in detail, the discovery of the unusual lability of the 5'-TBDMS group on 4' '-acylamino TSAO derivatives in DMSO solution. The synthesis and comparative chemical stability studies in different solvents of a variety of 4' '-substituted TSAO derivatives bearing different carbonyl functionalities are reported. Modifications have also been performed at the 5'-position of the TSAO molecule to gain insight into the structural requirements for the desilylation to occur. The role of the solvent has also been studied. Additionally, NMR and theoretical investigations have been carried out to get further insight into the conformational, geometric, and/or electronic parameters that may play a role in the "spontaneous" release of the 5'-TBDMS group. A silyl hydrolysis mechanism involving neighboring group participation of the 4' '-acylamino group is proposed.     

Optimization of the design of air quality monitoring networks and its application to NO2 and O3 in Jaen,Spain

The assessment of air quality is necessary in order to control and reduce pollution to levels which minimise harmful effects on human health and the environment. This paper describes a method to design air quality monitoring networks for nitrogen dioxide and ozone and its application in Jaen (southern Spain). A fibre-glass filter impregnated with triethanolamine was used in diffusive sampling badges for NO₂ determination. For O₃ analysis, sodium nitrite was selected and nitrate, a product of the reaction of ozone and nitrite, was used to assess the ozone concentrations. Sampling campaigns with passive diffusion samplers at 62 sites were then carried out to obtain information on the pollution emissions in Jaen. The sampling campaigns in 2001–2002 revealed an average concentration of 10.4 μg/m³ NO₂ with maximum values up to 22.5 μg/m³ in Jaen City centre. The average ozone concentrations were recorded downwind from the emission source, reaching 96.2 μg/m³; the average ozone value in Jaen was 72.0 μg/m³. After spatial interpolation of the obtained values with Geographical Information Systems, a selection of the best locations for the monitoring stations was made, in line with the macro- and microscale siting requirements of the European Directive 2008/50/EC on ambient air quality and cleaner air for Europe. A second sampling campaign with diffusive samplers was carried out in 2005–2006 to control if the locations of the air quality assessment stations were still representative for their zone.     

Large-scale pesticide testing in olives by liquid chromatography–electrospray tandem mass spectrometry using two sample preparation methods based on matrix solid-phase dispersion and QuEChERS

In this work we have evaluated the performance of two sample preparation methodologies for the large-scale multiresidue analysis of pesticides in olives using liquid chromatography–electrospray tandem mass spectrometry (LC–MS/MS). The tested sample treatment methodologies were: (1) liquid–liquid partitioning with acetonitrile followed by dispersive solid-phase extraction clean-up using GCB, PSA and C₁₈ sorbents (QuEChERS method – modified for fatty vegetables) and (2) matrix solid-phase dispersion (MSPD) using aminopropyl as sorbent material and a final clean-up performed in the elution step using Florisil. An LC–MS/MS method covering 104 multiclass pesticides was developed to examine the performance of these two protocols. The separation of the compounds from the olive extracts was achieved using a short C₁₈ column (50 mm × 4.6 mm i.d.) with 1.8 μm particle size. The identification and confirmation of the compounds was based on retention time matching along with the presence (and ratio) of two typical MRM transitions. Limits of detection obtained were lower than 10 μg kg⁻¹ for 89% analytes using both sample treatment protocols. Recoveries studies performed on olives samples spiked at two concentration levels (10 and 100 μg kg⁻¹) yielded average recoveries in the range 70–120% for most analytes when QuEChERS procedure is employed. When MSPD was the choice for sample extraction, recoveries obtained were in the range 50–70% for most of target compounds. The proposed methods were successfully applied to the analysis of real olives samples, revealing the presence of some of the target species in the μg kg⁻¹ range. Besides the evaluation of the sample preparation approaches, we also discuss the use of advanced software features associated to MRM method development that overcome several limitations and drawbacks associated to MS/MS methods (time segments boundaries, tedious method development/manual scheduling and acquisition limitations). This software feature recently offered by different vendors is based on an algorithm that associates retention time data for each individual MS/MS transition, so that the number of simultaneously traced transitions throughout the entire chromatographic run (dwell times and sensitivity) is maximized.     

Local rings of exchange rings

We characterize the exchange property for non-unital rings in terms of their local rings at elements,and we use this characterization to show that the exchange property is Morita invariant for idempotent rings.We also prove that every ring contains a greatest exchange idela(with respect to the inclusion).     

Second-derivative constant-wavelength synchronous scan spectrofluorimetry for determination of benzo[b]fluoranthene, benzo[a]pyrene and indeno[1,2,3-cd]pyrene in drinking water

The use of derivative constant-wavelength synchronous scan fluorimetry is reported for the determination of three polycyclic aromatic hydrocarbon pollutants in drinking water (linearity range 0.4-4 mug 1(-1)). The limits of detection (LD) and quantification (LQ) (mug 1(-1)) are 0.01 and 0.07 for benzo[b]fluoranthene, 0.03 and 0.12 for benzo[a]pyrene and 0.19 and 0.57 for indeno[1,2,3-cd]pyrene in the presence of three other pollutants, benzo[k]fluoranthene, benzo[ghi]perylene and fluoranthene. The precision (RSD /= 85%) were satisfactory.     

Infrared‐to‐Visible Light Conversion in Er3+–Yb3+:Lu3Ga5O12 Nanogarnets

Er³⁺–Yb³⁺ co‐doped Lu₃Ga₅O₁₂ nanogarnets were prepared and characterized; their structural and luminescence properties were determined as a function of the Yb³⁺ concentration. The morphology of the nanogarnets was studied by HRTEM. Under 488 nm excitation, the nanogarnets emit green, red, and near‐infrared light. The decay curves for the (⁴S_3/2, ²H_11/2) and ⁴F_9/2 levels of the Er³⁺ions exhibit a non‐exponential nature under resonant laser excitation and their effective lifetimes are found to decrease with an increase in the Yb³⁺ concentration from 1.0 to 10.0 mol %. The non‐exponential decay curves are well fitted to the Inokuti–Hirayama model for S=8, indicating that the mechanism of interaction for energy transfer between the optically active ions is of dipole–quadrupole type. Upon 976 nm laser excitation, an intense green upconverted emission is clearly observed by the naked eyes. A significant enhancement of the red‐to‐green intensity ratio of Er³⁺ ions was observed with an increase in Yb³⁺ concentration. The power dependence and the dynamics of the upconverted emission confirm the existence of two‐photon upconversion processes for the green and red emissions.     

φ meson production in NA60

NA60 is a fixed-target experiment at the CERN SPS which measured dimuon production in nucleus–nucleus and proton–nucleus collisions. The experiment collected muon pair samples of unprecedented quality in heavy-ion experiments. This paper presents a high quality measurement of the p_T distribution of the φ meson, covering a broad p_T window. The data were collected in 2003 in In-In collisions at 158 GeV per nucleon. The results, presented as a function of centrality, were studied against several possible sources of systematic effects and proved to be fairly stable. We show that the inverse m_T slope measured in In-In collisions, in the φ→μμ decay channel, depends significantly on the range used to perform the fit. When the fit is performed at low transverse momentum, the effective inverse slope increases from peripheral to central collisions, as measured by other experiments. We finally show that our measurement for In-In is compatible with the overall systematics of T slope versus mass, measured in different collision systems by the NA49 experiment PACS 25.75.Nq; 25.75.-q; 25.75.Dw; 14.40.Cs; 12.38.Mh