An efficient homogeneous catalytic system for the visible-light-induced production of hydrogen from water utilizing cyclometalated iridium(III) and tris-2,2′-bipyridyl rhodium(III) complexes is ...described. Synthetic modification of the photosensitizer Ir(C∧N)2(N∧N)+ and water reduction catalyst Rh(N∧N)3 3+ creates a family of catalysts with diverse photophysical and electrochemical properties. Parallel screening of the various catalyst combinations and photoreaction conditions allows the rapid development of an optimized photocatalytic system that achieves over 5000 turnovers with quantum yields (1/2 H2 per photon absorbed) greater than 34%. Photophysical and electrochemical characterization of the optimized system reveals that the reductive quenching pathway provides the necessary driving force for the formation of Rh(N∧N)20, the active catalytic species for the reduction of water to produce hydrogen. Tests for system poisoning with mercury or CS2 provide strong evidence that the system is a true homogeneous system for photocatalytic hydrogen production.
A photocatalytic water-reducing system utilizing a bis-cyclometalated bipyridyl iridium(III) photosensitizer (PS) and a platinum or palladium heterogeneous catalyst was used to identify systematic ...property−activity correlations among a library of structural derivatives of Ir(ppy)2(bpy)+. A heterogeneous Pd catalyst proved to be more durable than its previously reported Pt-based counterpart, allowing for more reliable photosensitizer study. The deliberate steric and electronic variations of the ppy and bpy moieties resulted in a dramatic decrease of the degradation rates observed with selected photosensitizers when compared to the more substitution-labile Ir(ppy)2(bpy)+ parent compound. An improved photosensitizer structure with a Pd catalyst in a nonligating solvent exhibited a 150-fold increase in catalyst turnover numbers compared to the system using Ir(ppy)2(bpy)+ and a Pt catalyst. Furthermore, photocatalytic and photophysical studies at varied temperatures provided information on the rate-limiting step of the photocatalytic process, which is shown to be dependent on both the PS and the Pt or Pd catalytic species.
There is strong circumstantial evidence that certain heavy, unstable atomic nuclei are 'octupole deformed', that is, distorted into a pear shape. This contrasts with the more prevalent rugby-ball ...shape of nuclei with reflection-symmetric, quadrupole deformations. The elusive octupole deformed nuclei are of importance for nuclear structure theory, and also in searches for physics beyond the standard model; any measurable electric-dipole moment (a signature of the latter) is expected to be amplified in such nuclei. Here we determine electric octupole transition strengths (a direct measure of octupole correlations) for short-lived isotopes of radon and radium. Coulomb excitation experiments were performed using accelerated beams of heavy, radioactive ions. Our data on (220)Rn and (224)Ra show clear evidence for stronger octupole deformation in the latter. The results enable discrimination between differing theoretical approaches to octupole correlations, and help to constrain suitable candidates for experimental studies of atomic electric-dipole moments that might reveal extensions to the standard model.
How mitochondria process DNA damage and whether a change in the steady-state level of mitochondrial DNA damage (mtDNA) contributes to mitochondrial dysfunction are questions that fuel burgeoning ...areas of research into aging and disease pathogenesis. Over the past decade, researchers have identified and measured various forms of endogenous and environmental mtDNA damage and have elucidated mtDNA repair pathways. Interestingly, mitochondria do not appear to contain the full range of DNA repair mechanisms that operate in the nucleus, although mtDNA contains types of damage that are targets of each nuclear DNA repair pathway. The reduced repair capacity may, in part, explain the high mutation frequency of the mitochondrial chromosome. Since mtDNA replication is dependent on transcription, mtDNA damage may alter mitochondrial gene expression at three levels: by causing DNA polymerase γ nucleotide incorporation errors leading to mutations, by interfering with the priming of mtDNA replication by the mitochondrial RNA polymerase, or by inducing transcriptional mutagenesis or premature transcript termination. This review summarizes our current knowledge of mtDNA damage, its repair, and its effects on mtDNA integrity and gene expression. This article is part of a special issue entitled: Mitochondrial Gene Expression.
► Mitochondrial DNA is susceptible to endogenous and environmental damage. ► Mitochondria lack the full cohort of nuclear DNA repair mechanisms. ► Persistent mtDNA damage poses a threat to mitochondrial gene expression. ► Mitochondrial polymerase disruption by mtDNA damage may underlie human disease and environmental toxicity.
Macrophages are essential for protection against influenza A virus infection, but are also implicated in the morbidity and mortality associated with severe influenza disease, particularly during ...infection with highly pathogenic avian influenza (HPAI) H5N1 virus. While influenza virus infection of macrophages was once thought to be abortive, it is now clear that certain virus strains can replicate productively in macrophages. This may have important consequences for the antiviral functions of macrophages, the course of disease and the outcome of infection for the host. In this article, we review findings related to influenza virus replication in macrophages and the impact of productive replication on macrophage antiviral functions. A clear understanding of the interactions between influenza viruses and macrophages may lead to new antiviral therapies to relieve the burden of severe disease associated with influenza viruses.
The XENON100 dark matter experiment Aprile, E.; Arisaka, K.; Arneodo, F. ...
Astroparticle physics,
April 2012, 2012-4-00, 20120401, Letnik:
35, Številka:
9
Journal Article
Recenzirano
Odprti dostop
► XENON100 is currently one of the most sensitive experiments to detect WIMP dark matter. ► Detector design and active/passive shielding reduce the radioactive background level. ► The event vertex of ...an interaction is reconstructed with a few mm precision. ► All position dependent signal corrections are presented in the paper. ► An energy scale exploiting the light-charge anti-correlation leads to an energy resolution competitive with NaI(Tl) crystals.
The XENON100 dark matter experiment uses liquid xenon (LXe) in a time projection chamber (TPC) to search for xenon nuclear recoils resulting from the scattering of dark matter Weakly Interacting Massive Particles (WIMPs). In this paper we present a detailed description of the detector design and present performance results, as established during the commissioning phase and during the first science runs.
The active target of XENON100 contains 62kg of LXe, surrounded by an LXe veto of 99kg, both instrumented with photomultiplier tubes (PMTs) operating inside the liquid or in xenon gas. The LXe target and veto are contained in a low-radioactivity stainless steel vessel, embedded in a passive radiation shield and is installed underground at the Laboratori Nazionali del Gran Sasso (LNGS), Italy. The experiment has recently published results from a 100 live-days dark matter search. The ultimate design goal of XENON100 is to achieve a spin-independent WIMP-nucleon scattering cross section sensitivity of σ=2×10−45cm2 for a 100GeV/c2 WIMP.
Abstract
Avian influenza viruses can pose serious risks to agricultural production, human health, and wildlife. An understanding of viruses in wild reservoir species across time and space is ...important to informing surveillance programs, risk models, and potential population impacts for vulnerable species. Although it is recognized that influenza A virus prevalence peaks in reservoir waterfowl in late summer through autumn, temporal and spatial variation across species has not been fully characterized. We combined two large influenza databases for North America and applied spatiotemporal models to explore patterns in prevalence throughout the annual cycle and across the continental United States for 30 waterfowl species. Peaks in prevalence in late summer through autumn were pronounced for dabbling ducks in the genera
Anas
and
Spatula
, but not
Mareca
. Spatially, areas of high prevalence appeared to be related to regional duck density, with highest predicted prevalence found across the upper Midwest during early fall, though further study is needed. We documented elevated prevalence in late winter and early spring, particularly in the Mississippi Alluvial Valley. Our results suggest that spatiotemporal variation in prevalence outside autumn staging areas may also represent a dynamic parameter to be considered in IAV ecology and associated risks.
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