I Wish The Band Would Play

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Exploring excited states of Pt(ii) diimine catecholates for photoinduced charge separation

The intense absorption in the red part of the visible range, and the presence of a lowest charge-transfer excited state, render Platinum(II) diimine catecholates potentially promising candidates for light-driven applications. Here, we test their potential as sensitisers in dye-sensitised solar cells and apply, for the first time, the sensitive method of photoacoustic calorimetry (PAC) to determine the efficiency of electron injection in the semiconductor from a photoexcited Pt(II) complex. Pt(II) catecholates containing 2,2′-bipyridine-4,4′-di-carboxylic acid (dcbpy) have been prepared from their parent iso-propyl ester derivatives, complexes of 2,2′-bipyridine-4,4′-di-C(O)OiPr, (COOiPr)2bpy, and their photophysical and electrochemical properties studied. Modifying diimine Pt(II) catecholates with carboxylic acid functionality has allowed for the anchoring of these complexes to thin film TiO2, where steric bulk of the complexes (3,5-ditBu-catechol vs. catechol) has been found to significantly influence the extent of monolayer surface coverage. Dye-sensitised solar cells using Pt(dcbpy)(tBu2Cat), 1a, and Pt(dcbpy)(pCat), 2a, as sensitisers, have been assembled, and photovoltaic measurements performed. The observed low, 0.02–0.07%, device efficiency of such DSSCs is attributed at least in part to the short excited state lifetime of the sensitisers, inherent to this class of complexes. The lifetime of the charge-transfer ML/LLCT excited state in Pt((COOiPr)2bpy)(3,5-di-tBu-catechol) was determined as 250 ps by picosecond time-resolved infrared spectroscopy, TRIR. The measured increase in device efficiency for 2a over 1a is consistent with a similar increase in the quantum yield of charge separation (where the complex acts as a donor and the semiconductor as an acceptor) determined by PAC, and is also proportional to the increased surface loading achieved with 2a. It is concluded that the relative efficiency of devices sensitised with these particular Pt(II) species is governed by the degree of surface coverage. Overall, this work demonstrates the use of Pt(diimine)(catecholate) complexes as potential photosensitizers in solar cells, and the first application of photoacoustic calorimetry to Pt(II) complexes in general

Ternary mixtures of sulfolanes and ionic liquids for use in high-temperature supercapacitors

Ionic liquids are a natural choice for supercapacitor electrolytes. However, their cost is currently high. In the present work, we report the use of ternary mixtures of sulfolane, 3-methyl sulfolane, and quaternary ammonium salts (quats) as low-cost alternatives. Sulfolane was chosen because it has a high Hildebrand solubility parameter (δ H = 27.2 MPa 1/2 ) and an exceptionally high dipole moment (μ = 4.7 D), which means that it mixes readily with ionic liquids. It also has a high flash point (165 °C), a high boiling point (285 °C), and a wide two-electrode (full-cell) voltage stability window ( > 7 V). The only problem is its high freezing point (27 °C). However, by using a eutectic mixture of sulfolane with 3-methyl sulfolane, we could depress the freezing point to -17 °C. A second goal of the present work was to increase the electrical conductivity of the electrolyte beyond its present-day value of 2.1 mS cm -1 at 25 °C, currently provided by butyltrimethylammonium bis(trifluoromethylsulfonyl)imide (BTM-TFSI). We explored two methods of doing this: (1) mixing the ionic liquid with the sulfolane eutectic and (2) replacing the low-mobility TFSI anion with the high-mobility MTC anion (methanetricarbonitrile). At the optimum composition, the conductivity reached 12.2 mS cm -1 at 25 °C

LSST Science Book, Version 2.0

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at http://www.lsst.org/lsst/sciboo

Instability of aquaglyceroporin (Aqp) 2 contributes to drug resistance in trypanosoma brucei

Defining mode of action is vital for both developing new drugs and predicting potential resistance mechanisms. Sensitivity of African trypanosomes to pentamidine and melarsoprol is predominantly mediated by aquaglyceroporin 2 (TbAQP2), a channel associated with water/glycerol transport. TbAQP2 is expressed at the flagellar pocket membrane and chimerisation with TbAQP3 renders parasites resistant to both drugs. Two models for how TbAQP2 mediates pentamidine sensitivity have emerged; that TbAQP2 mediates pentamidine translocation across the plasma membrane or via binding to TbAQP2, with subsequent endocytosis and presumably transport across the endosomal/lysosomal membrane, but as trafficking and regulation of TbAQPs is uncharacterised this remains unresolved. We demonstrate that TbAQP2 is organised as a high order complex, is ubiquitylated and is transported to the lysosome. Unexpectedly, mutation of potential ubiquitin conjugation sites, i.e. cytoplasmic-oriented lysine residues, reduced folding and tetramerization efficiency and triggered ER retention. Moreover, TbAQP2/TbAQP3 chimerisation, as observed in pentamidine-resistant parasites, also leads to impaired oligomerisation, mislocalisation and increased turnover. These data suggest that TbAQP2 stability is highly sensitive to mutation and that instability contributes towards the emergence of drug resistance

Optimization of Electrode and Cell Design for Ultrafast-Charging Lithium-Ion Batteries Based on Molybdenum Niobium Oxide Anodes

[Image: see text] Niobium oxides are an emerging class of anode materials for use in high-power lithium-ion batteries. Galvanostatic cycling and electrochemical impedance spectroscopy (EIS) were used in this study to investigate the influence of electrode porosity, electrode mass ratio, and cycling rate on the capacity, cycle life, and ionic conductivity of Li-ion battery cells based on a modified micron-sized MoNb(12)O(33) (MNO) anode powder. Both electrode and cell designs were found to have a significant impact on the rate performance and cycle life of Li-ion half- and full cells. A higher specific capacity, improved rate performance, and a longer cycle life were obtained in both anode and cathode half-cells by lowering the electrode porosity through calendaring. MNO/Li half-coin cells displayed excellent cyclability, reaching 80% state of health (SOH) after 600 cycles at C/2 charge and 1C discharge. MNO/NMC622 full-coin cells displayed a high capacity of 179 mAh g(–1) at 100 mA g(–1) (0.5 mA cm(–2)) and excellent cyclability at 25 °C, reaching 70% SOH after over 1000 cycles at 1 mA cm(–2) after optimizing their N/P ratio. Excellent cyclability was obtained at both 1C/1C and fast 2C/2C cycling, reaching 80% SOH after 700 and 470 cycles, respectively. Full-coin and small pouch cells had outstanding rate performance as they could be charged from 0 to 84% capacity in less than 5 min at 10 mA cm(–2) and to 70% SOC in 120 s at 20 mA cm(–2)

The value of lead time reduction and stabilization: A comparison between traditional and collaborative supply chains

This work quantifies the financial impact of the mean and the variability of production and shipping lead times on multi-echelon supply chains. We combine agent-based modelling and Taguchi methods, through which we develop a framework for supporting entrepreneurial investment decisions. A throughput-based analysis reveals that decreasing mean lead times improves the internal operation of production and distribution systems, while reducing lead time variability enhances the satisfaction of consumers. In this regard, we contrast traditional and collaborative supply chains. We find that the latter are not only more profitable than the former, but also more robust to variations in lead times