The structural uniqueness of covalent organic frameworks (COFs) has brought these new materials great potential for advanced applications. One of the key aspects yet to be developed is how to improve ...the robustness of covalently linked reticular frameworks. In order to make the best use of π-conjugated structures, we develop herein a “killing two birds with one stone” strategy and construct a series of ultrastable benzoxazole-based COFs (denoted as LZU-190, LZU-191, and LZU-192) as metal-free photocatalysts. Benefiting from the formation of benzoxazole rings through reversible/irreversible cascade reactions, the synthesized COFs exhibit permanent stability in the presence of strong acid (9 M HCl), strong base (9 M NaOH), and sunlight. Meanwhile, reticulation of the benzoxazole moiety into the π-conjugated COF frameworks decreases the optical band gap and therefore increases the capability for visible-light absorption. As a result, the excellent photoactivity and unprecedented recyclability of LZU-190 (for at least 20 catalytic runs, each with a product yield of 99%) have been illustrated in the visible-light-driven oxidative hydroxylation of arylboronic acids to phenols. This contribution represents the first report on the photocatalytic application of benzoxazole-based structures, which not only sheds new light on the exploration of robust organophotocatalysts from small molecules to extended frameworks but also offers in-depth understanding of the structure–activity relationship toward practical applications of COF materials.
Density, dynamic viscosity, and electrical conductivity of binary mixtures of ethaline (choline chloride+ethylene glycol at molar ratio 1:2) as a deep eutectic solvent (DES) with dimethyl sulfoxide ...were measured under atmospheric pressure at temperatures, T, from (308.15 to 363.15)K covering the entire mixture range. The mixtures exhibited negative excess molar volumes, VE, with a minimum at ethaline mole fractions of ×1≈0.4…0.5 that became more pronounced with increasing temperature. A similar minimum was found for the excess viscosity, Δη, of the mixtures. However, in contrast to VE the minimum of Δη became more shallow with increasing T. As expected, the electrical conductivity of the mixtures increased monotonically with increasing ×1 and T. The temperature dependence of viscosity and conductivity is well described by the Vogel−Fulcher−Tamman (VFT) equation.
Display omitted
•Density, viscosity, and conductivity of ethaline-DMSO mixtures were measured at 308.15–363.15K.•The volumetric properties of mixtures showed negative deviation from ideality.•Non-specific interactions and packing efficiency caused the shrinking of mixtures.•Viscosity and conductivity were well-described by Vogel−Fulcher−Tamman equation.•The transport behavior results confirmed the inference from excess molar volumes.
Gold nanoclusters have attracted extensive interest for catalysis applications in recent years due to their ultrasmall sizes and well-defined compositions and structures. However, at least two ...challenges exist in this emerging field. First, the steric hindrance of the ligands inhibits the catalysis activity, and second, the mechanism underlying water-phase catalysis using gold nanoclusters is often ambiguous. Herein, we introduce a “kill two birds with one stone” strategy to address these two challenges via the use of host–guest chemistry. As an illustration, a novel adamantanethiolate-protected Au40(S-Adm)22 nanocluster was synthesized, bound with γ-CD-MOF, and then transferred to the HRP-mimicking reaction system. The as-obtained catalyst exhibits excellent water solubility and catalytical activity, totally different from the virgin Au40(S-Adm)22 nanoclusters. Further, the detailed HRP-mimicking catalysis mechanism was proposed and supported by DFT calculation. Another interesting finding is the unique structure of Au40(S-Adm)22, which can be regarded as an Au13 icosahedron unit derived structure but different from the widely reported icosahedron contained nanocluster where the Au13 icosahedrons are often centered. These novel, intriguing results have important implication for the property tuning and practical application of metal nanoclusters in the future.
Feathers are widely used to represent mercury contamination in birds. Yet, few recommendations exist that provide guidance for using bird feathers in mercury monitoring programs. We conducted a ...literature review and 5 experiments to show that mercury concentrations vary substantially within (vane >100% higher than calamus) and among (>1000%) individual feathers from the same bird. We developed a research tool and guidelines for using bird feathers for mercury studies based on 3 components: 1) variability of feather mercury concentrations within an individual bird (coefficient of variation), 2) desired accuracy of the measured mercury concentration, and 3) feather and bird mass. Our results suggest a general rule that if the goal is to limit analytical and processing costs by using whole feathers in only one sample boat, then to achieve an accuracy within 10% of a bird's overall average feather mercury concentration a bird with a coefficient of variation ≤10% must be <190 g (size of a large shorebird). To achieve an accuracy within 20%, a bird with a coefficient of variation ≤10% must be <920 g (a large duck). When more than one sample boat is needed to fit the required number of feathers to achieve the desired accuracy, the results suggest homogenizing feathers and analyzing an aliquot of ≥20 mg for mercury. The present study suggests increasing the number of feathers typically used per bird to assess mercury concentrations. Environ Toxicol Chem 2019;38:1164–1187. Published 2019 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.
Feather mercury variability within a bird.
Land use change-for example, the conversion of natural habitats to agricultural or urban ecosystems-is widely recognized to influence the risk and emergence of zoonotic disease in humans
. However, ...whether such changes in risk are underpinned by predictable ecological changes remains unclear. It has been suggested that habitat disturbance might cause predictable changes in the local diversity and taxonomic composition of potential reservoir hosts, owing to systematic, trait-mediated differences in species resilience to human pressures
. Here we analyse 6,801 ecological assemblages and 376 host species worldwide, controlling for research effort, and show that land use has global and systematic effects on local zoonotic host communities. Known wildlife hosts of human-shared pathogens and parasites overall comprise a greater proportion of local species richness (18-72% higher) and total abundance (21-144% higher) in sites under substantial human use (secondary, agricultural and urban ecosystems) compared with nearby undisturbed habitats. The magnitude of this effect varies taxonomically and is strongest for rodent, bat and passerine bird zoonotic host species, which may be one factor that underpins the global importance of these taxa as zoonotic reservoirs. We further show that mammal species that harbour more pathogens overall (either human-shared or non-human-shared) are more likely to occur in human-managed ecosystems, suggesting that these trends may be mediated by ecological or life-history traits that influence both host status and tolerance to human disturbance
. Our results suggest that global changes in the mode and the intensity of land use are creating expanding hazardous interfaces between people, livestock and wildlife reservoirs of zoonotic disease.
•Data irregularities can significantly degrade the performance of classifiers.•We present a comprehensive taxonomy and survey of various data irregularities.•We discuss prominent methods to handle ...distribution and feature-based irregularities.•We highlight the co-occurrences and interrelations among different irregularities.•We unearth a number of promising future research avenues.
Most of the traditional pattern classifiers assume their input data to be well-behaved in terms of similar underlying class distributions, balanced size of classes, the presence of a full set of observed features in all data instances, etc. Practical datasets, however, show up with various forms of irregularities that are, very often, sufficient to confuse a classifier, thus degrading its ability to learn from the data. In this article, we provide a bird’s eye view of such data irregularities, beginning with a taxonomy and characterization of various distribution-based and feature-based irregularities. Subsequently, we discuss the notable and recent approaches that have been taken to make the existing stand-alone as well as ensemble classifiers robust against such irregularities. We also discuss the interrelation and co-occurrences of the data irregularities including class imbalance, small disjuncts, class skew, missing features, and absent (non-existing or undefined) features. Finally, we uncover a number of interesting future research avenues that are equally contextual with respect to the regular as well as deep machine learning paradigms.
The tropics contain the overwhelming majority of Earth's biodiversity: their terrestrial, freshwater and marine ecosystems hold more than three-quarters of all species, including almost all ...shallow-water corals and over 90% of terrestrial birds. However, tropical ecosystems are also subject to pervasive and interacting stressors, such as deforestation, overfishing and climate change, and they are set within a socio-economic context that includes growing pressure from an increasingly globalized world, larger and more affluent tropical populations, and weak governance and response capacities. Concerted local, national and international actions are urgently required to prevent a collapse of tropical biodiversity.
Dynamic viscosities of several members of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, CnmimNTf2, ionic liquids family, with the cation alkyl side-chain length varying from 2 to ...14 carbon atoms, have been measured in the 278.15K to 393.15K temperature range using two different apparatuses. To the best of our knowledge, it is the first time that such an extensive assessment of viscosity – in terms of the number of compounds of a single ionic liquid homologous series, of the broad range of temperature covered, and the use of two different experimental techniques – is reported. The use of two different instruments, using different methodologies, provides information about the uncertainties in the measurement of viscosity of ionic liquids, including its dependence on the presence of traces of water and other impurities. An extensive critical analysis of the deviations between the data measured in this work and those reported in literature has been carried out.
PDF
