Publications

Abstract Reported is the first enantioselective oxidative Pummerer‐type transformation using phase‐transfer catalysis to deliver enantioenriched sulfur‐bearing heterocycles. This reaction includes the direct oxidation of sulfides to a thionium intermediate, followed by an asymmetric intramolecular nucleophilic addition to form chiral cyclic N , S ‐acetals with moderate to high enantioselectivites. Deuterium‐labelling experiments were performed to identify the stereodiscrimination step of this process. Further analysis of the reaction transition states, by means of multidimensional correlations and DFT calculations, highlight the existence of a set of weak noncovalent interactions between the catalyst and substrate that govern the enantioselectivity of the reaction.

Filling the pores: A zinc-based metal–organic framework (MOF) can be transformed reversibly from an open (a) to a dense (b) configuration. The microporous solid is the first example of a MOF that is highly selective in the gas-chromatographic separation of alkanes.

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTCu2(ATC)·6H2O: Design of Open Metal Sites in Porous Metal−Organic Crystals (ATC: 1,3,5,7-Adamantane Tetracarboxylate)Banglin Chen, M. Eddaoudi, T. M. Reineke, J. W. Kampf, M. O'Keeffe, and O. M. YaghiView Author Information Materials Design and Discovery Group Department of Chemistry, University of Michigan 930 North University, Ann Arbor, Michigan 48109-1055 Department of Chemistry and Biochemistry Arizona State University, Tempe, Arizona 85287-1604 Cite this: J. Am. Chem. Soc. 2000, 122, 46, 11559–11560Publication Date (Web):November 4, 2000Publication History Received24 August 2000Published online4 November 2000Published inissue 22 November 2000https://pubs.acs.org/doi/10.1021/ja003159khttps://doi.org/10.1021/ja003159krapid-communicationACS PublicationsCopyright © 2000 American Chemical SocietyRequest reuse permissionsArticle Views6661Altmetric-Citations434LEARN 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-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Crystal structure,Ligands,Mathematical methods,Metal organic frameworks,Metals Get e-Alerts

ABSTRACT Radiocarbon dating and 40 Ar/ 39 Ar analysis of overlying tephra indicate that plant fossil assemblages exposed by stream erosion and well construction in and near La Selva Biological Station in eastern lowland Costa Rica are Pleistocene in age. We identified plant taxa based on wood, leaves, fruits, seeds, pollen, and spores examined from three sites at ca 30 m elevation. Extrapolating from modern ranges and surface temperature lapse rates suggests paleotemperatures 2.5–3.1°C cooler than at present

Alloying III–V compounds with small amounts of nitrogen leads to a dramatic reduction of the fundamental band-gap energy in the resulting dilute nitride alloys. The effect originates from an anticrossing interaction between the extended conduction-band states and localized N states. The interaction splits the conduction band into two non-parabolic subbands. The downward shift of the lower conduction subband edge is responsible for the N-induced reduction of the fundamental band-gap energy. The changes in the conduction band structure result in a significant increase in electron effective mass and a decrease in the electron mobility, and lead to a large enhancement of the maximum doping level in GaInNAs doped with group VI donors. In addition, a striking asymmetry in the electrical activation of group IV and group VI donors can be attributed to mutual passivation process through formation of the nearest neighbour group-IV donor nitrogen pairs.

The elastic properties and structural phase transitions of individual VO(2) nanowires were studied using an in situ push-to-pull microelectromechanical device to realize quantitative tensile analysis in a transmission electron microscope and a synchrotron X-ray microdiffraction beamline. A plateau was detected in the stress-strain curve, signifying superelasticity of the nanowire arising from the M1-M2 structural phase transition. The transition was induced and controlled by uniaxial tension. The transition dynamics were characterized by a one-dimensionally aligned domain structure with pinning and depinning of the domain walls along the nanowire. From the stress-strain dependence the Young's moduli of the VO(2) M1 and M2 phases were estimated to be 128 ± 10 and 156 ± 10 GPa, respectively. Single pinning and depinning events of M1-M2 domain wall were observed in the superelastic regime, allowing for evaluation of the domain wall pinning potential energy. This study demonstrates a new way to investigate nanoscale mechanics and dynamics of structural phase transitions in general.

We present an approach for building an active agent that learns to segment its visual observations into individual objects by interacting with its environment in a completely self-supervised manner. The agent uses its current segmentation model to infer pixels that constitute objects and refines the segmentation model by interacting with these pixels. The model learned from over 50K interactions generalizes to novel objects and backgrounds. To deal with noisy training signal for segmenting objects obtained by self-supervised interactions, we propose robust set loss. A dataset of robot's interactions along-with a few human labeled examples is provided as a benchmark for future research. We test the utility of the learned segmentation model by providing results on a downstream vision-based control task of rearranging multiple objects into target configurations from visual inputs alone. Videos, code, and robotic interaction dataset are available at https://pathak22.github.io/seg-by-interaction/

Disordered rocksalt Li-excess (DRX) compounds have emerged as promising new cathode materials for lithium-ion batteries, as they can consist solely of resource-abundant metals and eliminate the need for cobalt or nickel. A deeper understanding of the lithium-ion transport kinetics in DRX compounds is essential for enhancing their rate performance. This study employs first-principles calculations, cluster expansion techniques, and kinetic Monte Carlo simulations to investigate the Li+ transport properties in DRX Li2–xVO3, where 0 ≤ x ≤ 1. Our findings underscore (i) the necessity of accounting for both tetrahedral and octahedral Li occupancy when predicting the transport properties in DRX materials, (ii) the factors influencing the variation in the diffusion coefficients with Li content in Li2–xVO3, and (iii) the impact of Li+ correlated motion on the kinetics of Li+ transport. We reveal that the relative stability of tetrahedral and octahedral Li determines the number of active sites within the percolation network, subsequently affecting the Li+ transport properties. Furthermore, we demonstrate that the wide site energy distribution causes correlated motion in Li2–xVO3, which hinders Li+ transport.