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Speeding up borylation Catalytic borylation is the rare reaction that can selectively target stronger over weaker saturated carbon–hydrogen (C–H) bonds. However, the trade-off has been that the reaction is slow and requires high excess of the hydrocarbon. Oeschger et al. now report that the right ligand (2-methylphenanthroline) coordinated to iridium can accelerate the reaction by 50- to 80-fold. This rate enhancement enables selective borylation of primary C–H bonds with the hydrocarbon as limiting reagent. The reaction is also unusually selective for β-C–H bonds in saturated heterocycles. Science , this issue p. 736
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFunctionalization of Polystyrene Resins by Chemical Modification: Characterization of Halogenated Polystyrenes by Carbon-13 Nuclear Magnetic Resonance SpectroscopyM. Jean Farrall and Jean M. J. FréchetCite this: Macromolecules 1979, 12, 3, 426–428Publication Date (Print):May 1, 1979Publication History Published online1 May 2002Published inissue 1 May 1979https://pubs.acs.org/doi/10.1021/ma60069a016https://doi.org/10.1021/ma60069a016research-articleACS PublicationsRequest reuse permissionsArticle Views505Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Engineering of the various components of the experiment is discussed, and the first experiments are described. In the last three months engineering has been virtually completed on all aspects of this experiment, and the various components of the apparatus have been successfully integrated and utilized.
ISSN:1029-7006
Results suggest that both presleep cognitive arousal and presleep physiological arousal contribute to distorted perception of sleep.
This paper considers several of the problems caused by the presence of small parasitic capacitances and inductances in nonlinear network models. It first gives the condition for which the behavior of a network model can be approximated by the behavior of a simplified model recently with the parasitics removed. The condition is that the resistive subnetwork viewed from the terminals of the parasitics be strictly locally passive for a certain set of currents and voltages. This condition is independent of the relative magnitudes of the parasitics. The paper then considers networks whose equations cannot be put into normal form without the addition of a parasitic. In the case where two different choices of parasitics enable the network equations to be put into normal form, it gives conditions on the resistive subnetwork which ensure that the behavior of the two resulting networks is the same. It then exhibits a class of networks such that the networks resulting from the addition of any choice of parasitic which enables the network equations to be put into normal form have the same behavior. Finally, the paper shows how the behavior of this class of networks can be determined without the addition of parasitics. It formulates an inertia postulate and an explicit jump postulate to enable the multivalued normal form equations to be solved unambiguously.
The coupled-environment fracture model (CEFM) for inter-granular stress corrosion cracking (IGSCC) of sensitized type 304 (UNS S30400) stainless steel (SS) in light-water reactor (LWR) heat-transport circuits was extended by incorporating steel corrosion, hydrogen (H2) oxidation, and hydrogen peroxide (H2O2) reduction in addition to oxygen (O2) reduction as charge-transfer reactions occurring on the external surfaces. A theoretical fracture mechanics approach was incorporated to estimate the crack-tip strain rate, and a void nucleation model was included to account for ductile failure at very negative potentials. In the CEFM, coupling between the internal and external environments and the need to conserve charge are the key physical and mathematical constraints that determine the rate of crack advance. The model provides rational explanations for the effects of O2, H2O2, H2, conductivity, stress intensity, and flow velocity on the crack growth rate (CGR) in sensitized type 304 SS in simulated LWR in-vessel environments. The CEFM was proposed as the basis of a deterministic method for estimating component lifetimes in LWR heat-transport circuits.
Die hoch regio- und enantioselektive Allylierung von Arylaminen vermittelt ein cyclometallierter Iridium-Phosphoramidit-Komplex (siehe Schema). Der aktive Katalysator wird aus [{Ir(cod)Cl}2] und dem Liganden L in situ erzeugt, entweder durch Reaktion mit einem flüchtigen Alkylamin vor der Zugabe der Reagentien oder durch Zusatz eines tertiären Amins als Additiv.
Machine-learning potentials (MLPs) for atomistic simulations are a promising alternative to conventional classical potentials. Current approaches rely on descriptors of the local atomic environment with dimensions that increase quadratically with the number of chemical species. In this article, we demonstrate that such a scaling can be avoided in practice. We show that a mathematically simple and computationally efficient descriptor with constant complexity is sufficient to represent transition-metal oxide compositions and biomolecules containing 11 chemical species with a precision of around 3 meV/atom. This insight removes a perceived bound on the utility of MLPs and paves the way to investigate the physics of previously inaccessible materials with more than ten chemical species.
This article outlines several aspects of sleep regulation relevant to pediatric pain management. A broad range of connections between sleep and pain are described: (1) pain can interfere with the quality and quantity of children's sleep; (2) insufficient sleep (quality or quantity) can cause daytime sequelae (behavioral and emotional changes) that interfere with the coping skills necessary for effective pain management; (3) fear and anxiety often have a negative impact on both pain and sleep; (4) feelings of safety and control frequently have a positive effect on both sleep and pain symptoms; (5) adequate sleep seems to promote both physiological (tissue repair) and psychological (transient cessation of the perception of pain signals) processes relevant to recovery from pain, injury, and illness; and (6) treatment approaches to pediatric sleep and pain problems show considerable overlap with respect to many pharmacological as well as cognitive-behavioral interventions. Given these multiple links, a better understanding of sleep--and its importance in physical and mental health--is likely to be of value to clinicians and researchers working in areas of pediatric pain management. One specific hypothesis to be addressed is the possible contribution of sleep disruption as a step in the progression to some chronic pain syndromes.
An experimental study has been made to investigate the cyclic crack propagation resistance of ductile-particle toughened brittle materials, specifically, ductile TiNb-reinforced γ-TiAl intermetallic composites, as a function of microstructure. Under cyclic loading, cracks are found to grow subcritically at stress intensities of 4–5 MPa m 1 2 , far below their maximum toughness levels. Such behavior is associated with the susceptibility of the ductile TiNb phase to fatigue failure, and consequently to the diminished role of crack tip shielding from crack bridging by unbroken TiNb ligaments, in contrast to observations under monotonic loading. No evidence for bridging is seen under cyclic loading and bridging zone lengths in the wake of the crack tip are limited to less than 150 μm, compared with 4–5 mm under monotonic loading. Moreover, crack growth rates are very sensitive to applied ΔK level, with measured exponents for the da/dN-ΔK relationship ranging from 10 to 20. The exponent decreases with an increase in volume fraction of the ductile phase, but is independent of particle thickness; fatigue thresholds are, however, less affected.
