278 research outputs found
Molecular and electronic structure of the dithiooxalato radical ligand stabilised by rare earth coordination
Heterometallic rare earth transition metal compounds of dithioxalate (dto)2–, [NiII{(dto)LnIIITp2}2] (Ln = Y (1), Gd (2); Tp = hydrotris(pyrazol-1-yl)borate) were synthesised. The Lewis acidic rare earth ions are bound to the dioxolene and chemical reduction of 1 and 2 with cobaltocene yielded [CoCp2]+[NiII{(dto)LnIIITp2}2]˙− Ln = Y (3), Gd (4). The reduction is ligand-based and 3 and 4 are the first examples of both molecular and electronic structural characterisation of the dithiooxalato radical (dto)3˙−
Tuning and mechanistic insights of metal chalcogenide molecular catalysts for the hydrogen-evolution reaction
The production of hydrogen through water splitting using earth-abundant metal catalysts is a promising pathway for converting solar energy into chemical fuels. However, existing approaches for fine stoichiometric control, structural and catalytic modification of materials by appropriate choice of earth abundant elements are either limited or challenging. Here we explore the tuning of redox active immobilised molecular metal-chalcoxide electrocatalysts by controlling the chalcogen or metal stoichiometry and explore critical aspects of the hydrogen evolution reaction (HER). Linear sweep voltammetry (LSV) shows that stoichiometric and structural control leads to the evolution of hydrogen at low overpotential with no catalyst degradation over 1000 cycles. Density functional calculations reveal the effect of the electronic and structural features and confer plausibility to the existence of a unimolecular mechanism in the HER process based on the tested hypotheses. We anticipate these findings to be a starting point for further exploration of molecular catalytic systems
Electrocatalytic hydrogen production by dinuclear cobalt(ii) compounds containing redox-active diamidate ligands: a combined experimental and theoretical study
The chiral dicobalt(II) complex [CoII2(μ2-L)2] (1) (H2L = N2,N6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide) and its tert-butyl analogue [CoII2(μ2-LBu)2] (2) were synthesized and structurally characterized. Addition of one equivalent of AgSbF6 to the dichloromethane solution of 1 and 2 resulted in the isolation of the mixed-valent dicobalt(III,II) species [CoIIICoII(μ2-L)2]SbF6 (3) and [CoIIICoII(μ2-LBu)2]SbF6 (4). Homovalent 1 and 2 exhibited catalytic activity towards proton reduction in the presence of acetic acid (AcOH) as the substrate. The complexes are stable in solution while their catalytic turnover frequency is estimated at 10 and 34.6 h−1 molcat−1 for 1 and 2, respectively. Calculations reveal one-electron reduction of 1 is ligand-based, preserving the dicobalt(II) core and activating the ligand toward protonation at the quinoline group. This creates a vacant coordination site that is subsequently protonated to generate the catalytically ubiquitous Co(III) hydride. The dinuclear structure persists throughout where the distal Co(II) ion modulates the reactivity of the adjacent metal site by promoting ligand redox activity through spin state switching
Dynamical Fine Tuning in Brane Inflation
We investigate a novel mechanism of dynamical tuning of a flat potential in
the open string landscape within the context of warped brane-antibrane
inflation in type IIB string theory. Because of competing effects between
interactions with the moduli stabilizing D7-branes in the warped throat and
anti-D3-branes at the tip, a stack of branes gives rise to a local minimum of
the potential, holding the branes high up in the throat. As branes successively
tunnel out of the local minimum to the bottom of the throat the potential
barrier becomes lower and is eventually replaced by a flat inflection point,
around which the remaining branes easily inflate. This dynamical flattening of
the inflaton potential reduces the need to fine tune the potential by hand, and
also leads to successful inflation for a larger range of inflaton initial
conditions, due to trapping in the local minimum.Comment: 23 pages, 9 figures. v2: Updated D3-dependence in potential, small
changes to numerical result
Book Reviews
Book reviews of:
Hattiesburg: An American City in Black and White By William Sturkey. (Cambridge: Harvard University Press, 2019. Acknowledgements, illustrations, map, notes, index. Pp. 442. 64.95 cloth. ISBN: 978-1-62190-454-0.)
Mothers of Massive Resistance: White Women and the Politics of White Supremacy. By Elizabeth Gillespie McRae. (New York: Oxford University Press, 2018. Acknowledgements, Abbreviations, illustrations, notes, index. Pp. xiv, 343. 90 cloth, 55 cloth, 47.50 cloth. ISBN: 978-0-8071-6933-9.)
Desegregating Dixie: The Catholic Church in the South and Desegregation, 1945-1992. By Mark Newman. (Jackson: University Press of Mississippi, 2018. Acknowledgements, appendices, notes, bibliography, index. Pp. xvii, 455. 30 paper. ISBN: 978-1-4968-1886-7.)
The Loyal Republic: Traitors, Slaves, and the Remaking of Citizenship in Civil War America. By Erik Mathisen. (Chapel Hill: The University of North Carolina Press, 2018. Acknowledgments, illustrations, map, notes, index. Pp. xi, 219. 105 cloth, 26.95 hardcover. ISBN: 978-0-674-98797-5.)
Lines Were Drawn: Remembering Court-Ordered Integration at a Mississippi High School. Edited By Teena F. Horn, Alan Huffman, and John G. Jones. (Jackson: University Press of Mississippi, 2016. Acknowledgments, illustrations, map, notes, index. Pp. xi, 266. 45.00, ISBN 978-0-8071-7068-7.)
Integration Now: Alexander v. Holmes and the End of Jim Crow Education. By William P. Hustwit. (Chapel Hill: University of North Carolina Press, 2019. 8 halftones, 1 map, notes, bibl., index. 288 pp. $39.95, hardcover. ISBN: 978-1-4696-4855-2.
Low levels of amyloid-beta and its transporters in neonatal rats with and without hydrocephalus
<p>Abstract</p> <p>Background</p> <p>Previous studies in aging animals have shown that amyloid-beta protein (Aβ) accumulates and its transporters, low-density lipoprotein receptor-related protein-1 (LRP-1) and the receptor for advanced glycation end products (RAGE) are impaired during hydrocephalus. Furthermore, correlations between astrocytes and Aβ have been found in human cases of normal pressure hydrocephalus (NPH) and Alzheimer's disease (AD). Because hydrocephalus occurs frequently in children, we evaluated the expression of Aβ and its transporters and reactive astrocytosis in animals with neonatal hydrocephalus.</p> <p>Methods</p> <p>Hydrocephalus was induced in neonatal rats by intracisternal kaolin injections on post-natal day one, and severe ventriculomegaly developed over a three week period. MRI was performed on post-kaolin days 10 and 21 to document ventriculomegaly. Animals were sacrificed on post-kaolin day 21. For an age-related comparison, tissue was used from previous studies when hydrocephalus was induced in a group of adult animals at either 6 months or 12 months of age. Tissue was processed for immunohistochemistry to visualize LRP-1, RAGE, Aβ, and glial fibrillary acidic protein (GFAP) and with quantitative real time reverse transcriptase polymerase chain reaction (qRT-PCR) to quantify expression of LRP-1, RAGE, and GFAP.</p> <p>Results</p> <p>When 21-day post-kaolin neonatal hydrocephalic animals were compared to adult (6–12 month old) hydrocephalic animals, immunohistochemistry demonstrated levels of Aβ, RAGE, and LRP-1 that were substantially lower in the younger animals; in contrast, GFAP levels were elevated in both young and old hydrocephalic animals. When the neonatal hydrocephalic animals were compared to age-matched controls, qRT-PCR demonstrated no significant changes in Aβ, LRP-1 and RAGE. However, immunohistochemistry showed very small increases or decreases in individual proteins. Furthermore, qRT-PCR indicated statistically significant increases in GFAP.</p> <p>Conclusion</p> <p>Neonatal rats with and without hydrocephalus had low expression of Aβ and its transporters when compared to adult rats with hydrocephalus. No statistical differences were observed in Aβ and its transporters between the control and hydrocephalic neonatal animals.</p
Warped Radion Inflation
We show that the radion in a warped geometry bounded by two branes can have a
potential suitable for inflation. Our construction is based upon a solution
known in string theory as the linear dilaton, in which the back-reaction from a
bulk scalar \Phi is exactly accounted for. The radion, stabilized by \Phi, is
much heavier than the TeV scale and its couplings to the standard model are
much more suppressed than in the usual Randall-Sundrum solution. We present a
new formalism for obtaining approximate time-dependent solutions, based on
perturbing the exact solution to the coupled Einstein and scalar field
equations in the bulk. It allows the radion potential to be computed directly
in terms of the brane potentials for \Phi. We show that simple exponential
potentials on the branes can lead to a 4D radion potential with a flattened
hilltop form, yielding inflation with a spectral index of typically n_s=0.96
and no higher than 0.99. With more complicated brane potentials, the descent
from the hilltop can be a linear potential, giving a tensor-to-scalar ratio as
large as r=0.07 with n_s=0.974. The couplings of the radion to the standard
model particles are dictated by general covariance, so the details of reheating
are explicitly calculable, leading to a reheat temperature of at least 10^7
GeV. The quantum corrections to the inflaton potential from its couplings to
matter are also calculable and are shown to be small, so that the prediction
for the shape of the potential is under theoretical control, even with
superPlanckian field excursions.Comment: 32 pages, 15 figure
Honesty above all else? Expectations and perceptions of political conduct in three established democracies
The authors gratefully acknowledge financial support from the ESRC (grant number RES-000-22-3459) and British Academy (grant numbers SG-101785 and SG-52322). They would also like to thank two anonymous reviewers for their helpful comments and suggestions
A Comparative Study of the Short Term Cold Resistance Response in Distantly Related Drosophila Species: The Role of regucalcin and Frost
The molecular basis of short term cold resistance (indexed as chill-coma recovery time) has been mostly addressed in D. melanogaster, where candidate genes (Dca (also known as smp-30) and Frost (Fst)) have been identified. Nevertheless, in Drosophila, the ability to tolerate short term exposure to low temperatures evolved several times independently. Therefore, it is unclear whether variation in the same candidate genes is also responsible for short term cold resistance in distantly related Drosophila species. It should be noted that Dca is a candidate gene for cold resistance in the Sophophora subgenus only, since there is no orthologous gene copy in the Drosophila subgenus. Here we show that, in D. americana (Drosophila subgenus), there is a north-south gradient for a variant at the 5′ non-coding region of regucalcin (a Dca-like gene; in D. melanogaster the proteins encoded by the two genes share 71.9% amino acid identities) but in our D. americana F2 association experiment there is no association between this polymorphism and chill-coma recovery times. Moreover, we found no convincing evidence that this gene is up-regulated after cold shock in both D. americana and D. melanogaster. Size variation in the Fst PEST domain (putatively involved in rapid protein degradation) is observed when comparing distantly related Drosophila species, and is associated with short term cold resistance differences in D. americana. Nevertheless, this effect is likely through body size variation. Moreover, we show that, even at two hours after cold shock, when up-regulation of this gene is maximal in D. melanogaster (about 48 fold expression change), in D. americana this gene is only moderately up-regulated (about 3 fold expression change). Our work thus shows that there are important differences regarding the molecular basis of cold resistance in distantly related Drosophila species
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