One great challenge in understanding the history of life is resolving the influence of environmental change on biodiversity. Simulated annealing and genetic algorithms were used to synthesize data from 11,000 marine fossil species, collected from more than 3000 stratigraphic sections, to generate a new Cambrian to Triassic biodiversity curve with an imputed temporal resolution of 26 ± 14.9 thousand years. This increased resolution clarifies the timing of known diversification and extinction events. Comparative analysis suggests that partial pressure of carbon dioxide (Pco2) is the only environmental factor that seems to display a secular pattern similar to that of biodiversity, but this similarity was not confirmed when autocorrelation within that time series was analyzed by detrending. These results demonstrate that fossil data can provide the temporal and taxonomic resolutions necessary to test (paleo)biological hypotheses at a level of detail approaching those of long-term ecological analyses.
We reported an example of metal-organic framework (MOF)-based porous liquid by dispersing ZIF-8 ({Zn(mim)}, mim = 2-methylimidazole) nanocrystallites in ionic liquid (IL) of [Bpy][NTf] ( N-butyl pyridinium bis(trifluoromethyl sulfonyl)imide). Two essential challenges, stable colloid formation and porosity retention, have been overcome to prepare MOF-based porous liquid. Preventing ZIF-8 nanocrystals from aggregation before dispersing is vital to form a stable ZIF-8 colloid in IL via enhancing the interaction between ZIF-8 and IL. The resultant ZIF-8-[Bpy][NTf] colloid is able to be stable over months without precipitating. [Bpy][NTf] with larger ion sizes cannot occupy pores in ZIF-8, leaving the ZIF-8 cage empty for enabling access by guest molecules. The porosity of this porous liquid system was verified by positron (e) annihilation lifetime spectroscopy and I adsorption in ZIF-8 in the colloid. MOF-based porous liquids could provide a new material platform for liquid-bed-based gas separations.
The synthesis of kekulene and its
higher homologues is a challenging
task in organic chemistry. The first successful synthesis and characterization
of the parent kekulene were reported by Diederich and Staab in 1978.
Herein, we report the facile preparation of a series of edge-extended
kekulenes by bismuth(III) triflate-catalyzed cyclization of vinyl
ethers from the properly designed macrocyclic precursors. Their molecular
structures were confirmed by X-ray crystallographic analysis and NMR
spectroscopy. Their size- and symmetry-dependent electronic structures
(frontier molecular orbitals, aromaticity) and physical properties
(optical and electrochemical) were investigated by various spectroscopic
measurements, assisted by theoretical calculations. Particularly,
the acene-like units along each zigzag edge demonstrate a dominant
local aromatic character. Our studies provide an easy synthetic strategy
toward various fully fused carbon nanostructures and give some insights
into the electronic properties of cycloarenes.
A porphyrinic metal-organic framework (MOF), PCN-222(Fe), was found to exhibit sound activity and selectivity to cyclohexanone and cyclohexanol (known as KA oil) toward cyclohexane oxidation. Remarkably, hydrophobicity engineering of the MOF pore walls led to significantly enhanced activity and selectivity to KA oil, far superior to that of the homogeneous porphyrin catalyst.
Despite rapid progress over the past decade, most polycondensation systems even upon a small structural variation of the building units eventually result in amorphous polymers other than the desired crystalline covalent organic frameworks. This synthetic dilemma is a central and challenging issue of the field. Here we report a novel approach based on module‐patterned polymerization to enable efficient and designed synthesis of crystalline porous polymeric frameworks. This strategy features a wide applicability to allow the use of various knots of different structures, enables polycondensation with diverse linkers, and develops a diversity of novel crystalline 2D polymers and frameworks, as demonstrated by using the C=C bond‐formation polycondensation reaction. The new sp2‐carbon frameworks are highly emissive and enable up‐conversion luminescence, offer low band gap semiconductors with tunable band structures, and achieve ultrahigh charge mobilities close to theoretically predicted maxima.
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