Observation of Chiral Channels in Helical Covalent Organic Frameworks.

Unraveling the mechanism of chirality transfer across length scales is crucial to the rational development of functional materials with hierarchical chirality. The key obstacle is the lack of structural information, especially at the mesoscopic level. We report herein the structural identification of helical covalent organic frameworks (heliCOFs) with hierarchical chirality, which integrate molecular chirality, channel chirality, and morphology chirality into one crystalline entity. Specifically, benefiting from the highly ordered structure of heliCOFs, the existence of chiral channels at the mesoscopic level has been confirmed by electron crystallography, and the handedness of these chiral channels has been directly determined through the stereopair imaging technique. Accordingly, the chirality transfer in heliCOFs from microscopic to macroscopic levels could be rationalized with a layer-rotating model that has been supported by both crystal structure analysis and theoretical calculations. Observation of chiral channels in heliCOFs not only provides unprecedented data for the understanding of the chirality transfer process but also sheds new light on the rational construction of highly ordered polymeric materials with hierarchical chirality.

Symmetry-breaking dynamics in a tautomeric 3D covalent organic framework.

The enolimine-ketoenamine tautomerism has been utilised to construct 2D covalent organic frameworks (COFs) with a higher level of chemical robustness and superior photoelectronic activity. However, it remains challenging to fully control the tautomeric states and correlate their tautomeric structure-photoelectronic properties due to the mobile equilibrium of proton transfer between two other atoms. We show that symmetry-asymmetry tautomerisation from diiminol to iminol/cis-ketoenamine can be stabilised and switched in a crystalline, porous, and dynamic 3D COF (dynaCOF-301) through concerted structural transformation and host-guest interactions upon removal and adaptive inclusion of various guest molecules. Specifically, the tautomeric dynaCOF-301 is constructed by linking the hydroquinone with a tetrahedral building block through imine linkages to form 7-fold interwoven diamondoid networks with 1D channels. Reversible framework deformation and ordering-disordering transition are determined from solvated to activated and hydrated phases, accompanied by solvatochromic and hydrochromic effects useful for rapid, steady, and visual naked-eye chemosensing.

Guest-adaptive molecular sensing in a dynamic 3D covalent organic framework.

Molecular recognition is an attractive approach to designing sensitive and selective sensors for volatile organic compounds (VOCs). Although organic macrocycles and cages have been well-developed for recognising organics by their adaptive pockets in liquids, porous solids for gas detection require a deliberate design balancing adaptability and robustness. Here we report a dynamic 3D covalent organic framework (dynaCOF) constructed from an environmentally sensitive fluorophore that can undergo concerted and adaptive structural transitions upon adsorption of gas and vapours. The COF is capable of rapid and reliable detection of various VOCs, even for non-polar hydrocarbon gas under humid conditions. The adaptive guest inclusion amplifies the host-guest interactions and facilitates the differentiation of organic vapours by their polarity and sizes/shapes, and the covalently linked 3D interwoven networks ensure the robustness and coherency of the materials. The present result paves the way for multiplex fluorescence sensing of various VOCs with molecular-specific responses.

Atomic-level structural responsiveness to environmental conditions from 3D electron diffraction.

Electron microscopy has been widely used in the structural analysis of proteins, pharmaceutical products, and various functional materials in the past decades. However, one fact is often overlooked that the crystal structure might be sensitive to external environments and response manners, which will bring uncertainty to the structure determination and structure-property correlation. Here, we report the atomic-level ab initio structure determinations of microcrystals by combining 3D electron diffraction (3D ED) and environmental transmission electron microscope (TEM). Environmental conditions, including cryo, heating, gas and liquid, have been successfully achieved using in situ holders to reveal the simuli-responsive structures of crystals. Remarkable structural changes have been directly resolved by 3D ED in one flexible metal-organic framework, MIL-53, owing to the response of framework to pressures, temperatures, guest molecules, etc.

Femoral artery cannulation as a safe alternative for aortic dissection arch repair in the era of axillary artery cannulation.

BACKGROUND: To evaluate the safety and efficacy of femoral artery cannulation as an alternative to axillary artery cannulation, we retrospectively compared outcomes between patients with axillary or femoral artery cannulation during open aortic arch repair for type A aortic dissection (TAAD). METHODS: Between January 2014 and January 2019, 646 patients underwent open aortic arch repair with circulatory arrest for TAAD using antegrade selective cerebral perfusion (SACP) and were divided into two groups according to the site of arterial cannulation: an axillary artery group (axillary group, n=558) or a femoral artery group (femoral group, n=88). The axillary artery was considered as the primary cannulation site, and the femoral artery was used as an alternative when axillary artery cannulation was deemed unsuitable or had failed. Propensity score matching was performed to correct baseline differences. RESULTS: After propensity score matching, the patients' characteristics were comparable between groups (n=85 in each). The incidence of in-hospital mortality (10.6% vs. 14.1%; P=0.642) and stroke (3.5% vs. 5.9%; P=0.720) were comparable between the axillary and femoral groups. The incidence of newly required dialysis was lower in the femoral group, but the difference was not statistically significant (34.1% vs. 20.0%; P=0.050). Other outcomes and major adverse events were comparable. CONCLUSIONS: Femoral artery cannulation produced similar perioperative outcomes to axillary cannulation after open arch repair for TAAD. The femoral artery can be used as a safe and effective alternative to the axillary artery for arterial cannulation in TAAD patients undergoing open arch repair.

Docking of CuI and AgI in Metal-Organic Frameworks for Adsorption and Separation of Xenon.

We present a metal docking strategy utilizing the precise spatial arrangement of organic struts as metal chelating sites in a MOF. Pairs of uncoordinated N atoms on adjacent pyrazole dicarboxylate linkers distributed along the rod-shaped Al-O secondary building units in MOF-303 [Al(OH)(C5 H2 O4 N2 )] were used to chelate CuI and AgI with atomic precision and yield the metalated Cu- and Ag-MOF-303 compounds [(CuCl)0.50 Al(OH)(C5 H2 O4 N2 ) and (AgNO3 )0.49 Al(OH)(C5 H2 O4 N2 )]. The coordination geometries of CuI and AgI were examined using 3D electron diffraction and extended X-ray absorption fine structure spectroscopy techniques. The resulting metalated MOFs showed pore sizes matching the size of Xe, thus allowing for binding of Xe from Xe/Kr mixtures with high capacity and selectivity. In particular, Ag-MOF-303 exhibited Xe uptake of 59 cm3 cm-3 at 298 K and 0.2 bar with a selectivity of 10.4, placing it among the highest performing MOFs.

Direct-Space Structure Determination of Covalent Organic Frameworks from 3D Electron Diffraction Data.

Structure determination of covalent organic frameworks (COFs) with atomic precision is a bottleneck that hinders the development of COF chemistry. Although three-dimensional electron diffraction (3D-ED) data has been used to solve structures of sub-micrometer-sized COFs, successful structure solution is not guaranteed as the data resolution is usually low. We demonstrate that the direct-space strategy for structure solution, implemented using a genetic algorithm (GA), is a successful approach for structure determination of COF-300 from 3D-ED data. Structural models with different geometric constraints were considered in the GA calculations, with successful structure solution achieved from room-temperature 3D-ED data with a resolution as low as ca. 3.78 Å. The generality of this strategy was further verified for different phases of COF-300. This study demonstrates a viable strategy for structure solution of COF materials from 3D-ED data of limited resolution, which may facilitate the discovery of new COF materials in the future.

Probing Interactions between Metal-Organic Frameworks and Freestanding Enzymes in a Hollow Structure.

It has been reported that the biological functions of enzymes could be altered when they are encapsulated in metal-organic frameworks (MOFs) due to the interactions between them. Herein, we probed the interactions of catalase in solid and hollow ZIF-8 microcrystals. The solid sample with confined catalase is prepared through a reported method, and the hollow sample is generated by hollowing the MOF crystals, sealing freestanding enzymes in the central cavities of hollow ZIF-8. During the hollowing process, the samples were monitored by small-angle X-ray scattering (SAXS) spectroscopy, electron microscopy, powder X-ray diffraction (PXRD), and nitrogen sorption. The interfacial interactions of the two samples were studied by infrared (IR) and fluorescence spectroscopy. IR study shows that freestanding catalase has less chemical interaction with ZIF-8 than confined catalase, and a fluorescence study indicates that the freestanding catalase has lower structural confinement. We have then carried out the hydrogen peroxide degradation activities of catalase at different stages and revealed that the freestanding catalase in hollow ZIF-8 has higher activity.

Atomically deviated Pd-Te nanoplates boost methanol-tolerant fuel cells.

The methanol crossover effect in direct methanol fuel cells (DMFCs) can severely reduce cathodic oxygen reduction reaction (ORR) performance and fuel efficiency. As a result, developing efficient catalysts with simultaneously high ORR activity and excellent antipoisoning methanol capability remains challenging. Here, we report a class of Pd-Te hexagonal nanoplates (HPs) with a Pd20Te7 phase that simultaneously overcome the activity and methanol-tolerant issues in alkaline DMFC. Because of the specific arrangement of Pd atoms deviated from typical hexagonal close-packing, Pd-Te HPs/C displays extraordinary methanol tolerance with high ORR performance compared with commercial Pt/C. DFT calculations reveal that the high performance of Pd-Te HPs can be attributed to the breakthrough of the linear relationship between OOH* and OH* adsorption, which leaves sufficient room to improve the ORR activity but suppresses the methanol oxidation reaction. The concurrent high ORR activity and excellent methanol tolerance endow Pd-Te HPs as practical electrocatalysts for DMFC and beyond.

Atomic-Level Characterization of Dynamics of a 3D Covalent Organic Framework by Cryo-Electron Diffraction Tomography.

Understanding the dynamics of covalent organic frameworks (COFs) is desirable for developing smart materials with coherent responses to external stimulus. Here we illustrate the structural determination of dynamics at atomic level by cryo-electron diffraction tomography (EDT) with single crystals of COF-300 having only submicrometer sizes. We observe and elucidate the crystal contraction upon H2O adsorption by ab initio structural solution of all non-hydrogen atoms of framework and unambiguous location of guest molecules in the pores. We also observe the crystal expansion of COF-300 upon inclusion of ionic liquid or polymer synthesized in the channels, whose conformational aspects of frameworks can be confirmed.

A Crystalline Polyimide Porous Organic Framework for Selective Adsorption of Acetylene over Ethylene.

The separation of acetylene from ethylene is a crucial process in the petrochemical industry, as even small acetylene impurities can lead to premature termination of ethylene polymerization. Herein, we present the synthesis of a robust, crystalline naphthalene diimide porous aromatic framework via imidization of linear naphthalene-1,4,5,8-tetracarboxylic dianhydride and triangular tris(4-aminophenyl)amine. The resulting material, PAF-110, exhibits impressive thermal and long-term structural stability, as indicated by thermogravimetric analysis and powder X-ray diffraction characterization. Gas adsorption characterization reveals that PAF-110 has a capacity for acetylene that is more than twice its ethylene capacity at 273 K and 1 bar, and it exhibits a moderate acetylene selectivity of 3.9 at 298 K and 1 bar. Complementary computational investigation of each guest binding in PAF-110 suggests that this affinity and selectivity for acetylene arises from its stronger electrostatic interaction with the carbonyl oxygen atoms of the framework. To the best of our knowledge, PAF-110 is the first crystalline porous organic material to exhibit selective adsorption of acetylene over ethylene, and its properties may provide insight into the further optimized design of porous organic materials for this key gas separation.

Balsam-pear-like rutile/anatase core/shell titania nanorod arrays for photoelectrochemical water splitting.

In this work, a solution combustion followed by dissolution in hydrogen peroxide is adopted to achieve a precursor for decorating anatase TiO2 nanosheets along single-crystalline rutile TiO2 nanorods, which achieves balsam-pear-like core/shell nanorod arrays with enhanced photoelectrochemical water splitting. The enhanced photoelectrochemical performance is attributed to the novel nanoarchitecture, which can simultaneously offer a high surface area, enhanced light-harvesting, a rutile/anatase junction for charge carrier separation and a conductive pathway for charge carrier collection. The photoanode design can also give hints to other functional materials.

Bowel ischemia caused by a giant thrombus in the ascending aorta. A case report.

Although an ascending aortic thrombus is a rare condition, it can cause serious complications of thromboembolism. Here we present a rare case of a patient who was hospitalized due to ileal arteries embolization caused by emboli from a giant thrombus in the ascending aorta. After 10 days anti-coagulation therapy, we performed a surgery to replace the ascending aorta containing the strip organized thrombus with a synthetic graft. During two years of postoperative follow-up, no recurrence of aortic thrombosis was found. Although the exact cause of this thrombus remains unclear, we believe that it is important to perform a surgery as soon as the presence of an ascending aortic thrombus is confirmed, which could help preventing the major recurrent embolic events.