1,721,119 research outputs found
Solution structure and structural rearrangement in chiral dimeric ytterbium(iii) complexes determined by paramagnetic NMR and NIR-CD
Full text linkChiral lanthanide complexes are attracting interest in enantioselective catalysis and due to their unique optical and magnetic properties. Here, we investigate the chiral ytterbium complex [Yb((S)-THP)] ((S)-THP = ((1S,4S,7S,10S)-1,4,7,10-tetrakis(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane), which has found applications in catalysis and as a CEST agent in MRI, by means of near-IR circular dichroism (NIR CD), NMR, and mass spectrometry, in different solvents. The NMR analysis revealed that this complex, different from the analogues including early lanthanides, is not axially coordinated by the solvent. In non-protic solvents, and in the presence of bases, [Yb((S)-THP)] 3+ dimerizes to [Yb((S)-H 2 THP)] 22+ . The careful analysis of the paramagnetic contributions in the NMR spectra allowed us to determine the structure of the dimeric species in solution, revealing a structural rearrangement of the coordination cage following the dimerization process
Geochemistry of the Albano and Nemi crater lakes in the volcanic district of Alban Hills (Rome, Italy)
No full textLake Albano, located 20 km to the SE of Rome, is hosted within the most recent crater of the quiescent Alban Hills volcanic complex that produced hydromagmatic eruptions in Holocene times. Stratigraphic, archaeological and historical evidence indicates that the lake level underwent important variations in the Bronze Age. Before the IV century B.C. several lahars were generated by water overflows from the lake and in the IV century B.C. Romans excavated a drainage tunnel. The lake is located above a buried carbonate horst that contains a pressurized medium-enthalpy geothermal reservoir from which fluids escape to the surface to produce many important gas manifestations of mostly CO2. Previous studies recognized the presence of gas emissions also from the crater bottom. In 1997 the possibility of a Nyos-type event triggered by a lake rollover was considered very low, because the CO2 water concentration at depth was found to be far from saturation. However, considering the high population density nearby, the Italian Civil Protection Department recommended that periodical monitoring be carried out. To this scope we initiated in 2001 a systematic geochemical study of the lake. Thirteen vertical profiles have been repeatedly carried out in 2001–2006, especially in the deepest part of the lake (167 m in 2006), measuring T, pH, dissolved O2 and electrical conductivity. Water samples were collected from various depths and chemically and isotopically analysed. Two similar profiles have been measured also in the nearby Nemi crater lake. Results indicate that in the 4.5 years of monitoring the pressure of gas dissolved in the Lake Albano deep waters remained much lower than the hydrostatic pressure. A CO2 soil survey carried out on the borders of the two lakes, indicates the presence of some zones of anomalous degassing of likely magmatic origin. A water overturn or a heavy mixing of deep and shallow waters likely occurred in winter 2003–2004, when cold rainfall cooled the surface water below 8.5 °C. Such overturns cause only a limited gas exsolution from the lake when the deep water is brought to a few meters depth but can explain the observed decrease with time of dissolved CO2 at depth and related water pH increase. A gas hazard could occur in the case of a sudden injection through the lake bottom of a huge quantity of CO2-rich fluids, which might be caused by earthquake induced fracturing of the rock pile beneath the lake. A limnic gas eruption might also occur should CO2 concentration build up within the lake for a long time
Solution study of chiral 1,2-diol Yb3+ chelates through near-IR circular dichroism
No full textYtterbium is efficiently chelated by 1,2-diols in a variety of very different solvents. We found a set of solution equilibria among three complexes of minimum formula [Yb center dot(diol)],[Yb center dot(diol)(2)] and [Yb-(diol)(3)]. By extensive near-Infrared circular dichroism (NIR CD) investigation. we determined fingerprint CD spectra of the di- and tri-chelated species and the relative formation constants. Since NIR CD is sensitive only to chiral Yb-species, NIR CD can be very useful for studying complex mixtures, such as those used in enantioselective catalysis an involving a chiral non-racemic diol as an auxiliary and an ytterbium salt. The chiroptical spectra show completely conserved features through very different diol structures, demonstrating the identity of the coordination polyhedron around Yb(III) and giving rise to a new empirical method for assigning 1,2-diols absolute configuration
The impact of battery electric buses in public transport
No full textIn this work we evaluate the changes in energy demand and resulting air pollutant emissions from the introduction of Battery Electric Buses into the public transport fleet operating in Rome. Our approach to evaluation is based on the adoption of geo-referenced open-data set, published in GTFS format by the Rome's public transport agency, that contains detailed information about transit stops, routes and service schedules of the bus lines. We use an electric bus simulation tool to obtain specific energy consumption models based on real driving cycles. The findings of this study indicate noticeable reductions in the primary energy consumption and the emissions of both GHG gases and toxic local air pollutants such as NOx and PM. © 2017 IEEE
Ligand Lability and Chirality Inversion in Yb Heterobimetallic Catalysts
No full textWe have investigated the exchange dynamics between the free and bound ligand in K-3[Yb{(R)-binol}(3)], the most active heterobimetallic lanthanoid catalyst for cyclic imine hydrophosphonylation; we found that the Yb-binol bond is labile. The rate constant for this exchange was determined through NMR saturation transfer experiments. Upon addition of (S)-bi-naphthol, ligand exchange leads to the formation of a small quantity of heterochiral complexes and, in the presence of a molar excess of (S)-binaphthol, to chirality inversion of the whole complex. This demonstrates that, in contrast to other analogous systems, K-3[Yb(binol)(3)] displays a strong chiral discrimination, with the overwhelming preference for ligands of the same configuration. The lability of Yb-binol bond in THF may suggest a ligand-to-substrate exchange as a key step in the catalytic process
TEE: An advanced software tool for the modeling of direct impacts of transportation systems
No full textThe new version of TEE model (Transport Energy Environment) has been developed in the frame of the FP5 ISHTAR and HEARTS Projects with several features for better analyzing transport related direct impacts, taking into account vehicles kinematics, cold start emissions distribution and parking processes. Specific efforts were dedicated to the modeling of the effects of vehicles kinematics on hot emissions, where the software calculates link emissions by adopting average speed based functions, instantaneous emissions, or the innovative kinematics correction functions' model, and the modeling of parking processes which are relevant for cold start and evaporative emissions. Copyright © 2007 SAE International
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
