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Di-Palladium Complexes are Active Catalysts for Mono-N-Protected Amino Acid-Accelerated Enantioselective C-H Functionalization
No full textThe role of mono-protected amino acid (MPAA) ligands in accelerating enantioselective cyclopalladation and palladium-catalyzed C–H functionalization was investigated using kinetic, spectroscopic, and computational methods. The catalytic relevance of characterized di-palladium species was evaluated by kinetic analysis. The kinetic method of continuous variation (MCV) demonstrated that a complex containing a single MPAA-bridged di-palladium core (Pd2(MPAA)1) is an active catalyst for the reactions studied. The experimental findings are consistent with density functional theory calculations that indicate that enantioinduction can be achieved by a single MPAA ligand bridging a di-palladium catalyst through secondary sphere hydrogen-bonding interactions that lower the barrier to C–H activation of the major enantiomer
Synthesis, Characterization, and Theoretical Investigation of a Transition State Analogue for Proton Transfer during C-H Activation by a Rhodium-Pincer Complex
No full textA heterobimetallic rhodium-pincer complex bearing a phenylzinc ligand was synthesized and characterized by multinuclear NMR, COSY, NOESY, and X-ray crystallography. The crystalstructure of this complex shows that it possesses a bridging Rh-Zn-C fragment with a geometry similar to the Rh-H-C fragment in a proposed transition state for metal-to-ligand proton transfer during redox-neutral C-H activation with dearomatized rhodium pincer complexes. Bonding analysis indicates that these fragments are isolobal, suggesting that the transition state analogue models not only the structure but also the bonding interactions that underlie metal-ligand cooperativity in the C-H activation transition state. The similarity of the transition state and its analogue prompted re-evaluation of the relevant rate equations to determine relative contributions of viable proton transfer pathways. Parallel analysis of the transition state and its isolobal analogue thus serves as a bridge between theory and experiment that is rarely available in studies of bonding in transition states
Exploring Models for Shared Identity Management at a Global Scale: The Work of the PCC Task Group on Identity Management in NACO
Full text linkThe paper discusses the efforts of the PCC Task Group on Identity Management in NACO to explore and advance identity management activities. The Task Group’s work serves as a recent example of how the Program for Cooperative Cataloging has engaged the metadata community to incubate practical solutions to the perennial capacity issues that libraries face in creating and maintaining authority and bibliographic data. The Task Group's multi-pronged charge compelled several outputs including research, collaboration, education, and publication. This paper outlines the Task Group's labors within the context of the decades of innovations carried out under the banner of the PCC
When Transparency Fails: Bias and Financial Incentives in Ridesharing Platforms
Full text linkProviding transparency into operational processes can change consumer and worker behavior. However, it is unclear whether operational transparency is beneficial with potentially biased service providers. We explore this in the context of ridesharing platforms where early evidence documents bias similar to what has been observed in traditional transportation systems. Platforms responded by reducing operational transparency through removing information about riders’ gender and race from the ride request presented to drivers. However, following this change, bias may still manifest through driver cancelation after a request is accepted, at which point the rider’s picture is displayed. Our primary research question is to what extent a rider’s gender, race, and perception of support for lesbian, gay, bisexual, and transgender (LGBT) rights impact cancelation rates. We investigate this through a large field experiment on a major ridesharing platform in Washington, DC. By manipulating rider names and profile pictures, we observe drivers’ behavior patterns in accepting and canceling rides. Our results confirm that bias at the ride request stage has been eliminated. However, after acceptance, racial and LGBT biases are persistent, while we find no evidence of gender biases. We also explore whether peak times moderate (through increased pay to drivers) or exacerbate (by signaling that there are many riders, allowing drivers to be more selective) these biases. We find a moderating effect of peak timing, with lower cancelation rates for non-Caucasian riders. We do not find a similar moderating effect for riders that signal support for the LGBT community
Electrode-adsorption activates trans-[Cr(cyclam)Cl2]+ for electrocatalytic nitrate reduction
No full textCyclic voltammetry reveals that aqueous trans-[Cr(cyclam)Cl] is reversibly reduced at a mercury electrode, with a small prewave suggesting an adsorptive interaction between the complex and electrode surface. A catalytic current is observed in the presence of excess nitrate, with the onset potential for catalysis at the prewave. Nitrate is electrocatalytically reduced to nitrite, with preliminary mechanistic investigations implicating a chromium oxo intermediate
Two-sided competition with vertical differentiation in both acquisition and sales in remanufacturing
No full textWe study the competition between two remanufacturers in the acquisition of used products and the sales of remanufactured products. One firm has a market advantage; we consider two separate cases where either rm could have an acquisition advantage. The problem is formulated as a simultaneous game on a market that is vertically dierentiated in both acquisition and sales, where both rms decide on their respective acquisition prices for used products, and selling prices for remanufactured products. A key finding is that a market advantage is significantly more powerful than an acquisition advantage. The rm with a market advantage can preempt the entry of the other rm, even if that rm has a signicant acquisition advantage, but not the other way around. This is accomplished through an aggressive acquisition strategy, where the rm with a market advantage sets signicantly higher acquisition prices
Computational studies of shape control of charged deformable nanocontainers
Full text linkBiological matter is often compartmentalized by soft membranes that dynamically change their shape in response to chemical and mechanical cues. Deformable soft-matter-based nanoscale membranes or nanocontainers that mimic this behavior can be used as drug-delivery carriers that can adapt to evolving physiological conditions, or as dynamic building blocks for the design of novel hierarchical materials via assembly engineering. Here, we connect the intrinsic features of charged deformable nanocontainers such as their size, charge, surface tension, and elasticity with their equilibrium shapes for a wide range of solution conditions using molecular dynamics simulations. These links identify the fundamental mechanisms that establish the chemical and materials design control strategies for modulating the equilibrium shape of these nanocontainers. We show that flexible nanocontainers of radii ranging from 10–20 nm exhibit sphere-to-rod-to-disc shape transitions yielding rods and discs over a wide range of aspect ratio λ (0.3 < λ < 5). The shape transitions can be controlled by tuning salt and/or surfactant concentration as well as material elastic parameters. The shape changes are driven by reduction in the global electrostatic energy and are associated with dramatic changes in local surface elastic energy distributions. To illustrate the shape transition mechanisms, exact analytical calculations for idealized spheroidal nanocontainers in salt-free conditions are performed. Explicit counterion simulations near nanocontainers and associated Manning model calculations provide an assessment of the stability of observed shape deformations in the event of ion condensation
The European Approach to Propaganda confronted with the Realities of Colonial Africa
No full textThrough the comparison of the choices and the difficulties encountered by the British, Belgian and French colonizers when setting up propaganda systems, this article aims to define a transnational conception of the cinematographic medium. Indeed, the syntheses of the propaganda systems set up in Europe and the reports on the experiments carried out in the colonies reveal a number of recurring preconceptions: cinema as a vector of universally decipherable messages; cinema as a form of direct access to the viewer’s subconscious; cinema as a form of expression of a “European technological superiority”
Initiating DNA replication: a matter of prime importance
No full textIt has been known for decades that the principal replicative DNA polymerases that effect genome replication are incapable of starting DNA synthesis de novo. Rather, they require a 3′-OH group from which to extend a DNA chain. Cellular DNA replication systems exploit a dedicated, limited processivity RNA polymerase, termed primase, that synthesizes a short oligoribonucleotide primer which is then extended by a DNA polymerase. Thus, primases can initiate synthesis, proceed with primer elongation for a short distance then transfer the primer to a DNA polymerase. Despite these well-established properties, the mechanistic basis of these dynamic behaviours has only recently been established. In the following, the author will describe recent insights from studies of the related eukaryotic and archaeal DNA primases. Significantly, the general conclusions from these studies likely extend to a broad class of extrachromosomal element-associated primases as well as the human primase-related DNA repair enzyme, PrimPol
Co-existence of Network Architectures Supporting the Human Gut Microbiome
No full textMicrobial organisms of the human gut microbiome do not exist in isolation but form complex and diverse interactions to maintain health and reduce risk of disease development. The organization of the gut microbiome is assumed to be a singular assortative network, where interactions between operational taxonomic units (OTUs) can readily be clustered into segregated and distinct communities. Here, we leverage recent methodological advances in network modeling to assess whether communities in the human microbiome exhibit a single network structure or whether co-existing mesoscale network architectures are present. We found evidence for core-periphery structures in the microbiome, supported by strong, assortative community interactions. This complex architecture, coupled with previously reported functional roles of OTUs, provides a nuanced understanding of how the microbiome simultaneously promotes high microbial diversity and maintains functional redundancy