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The exchangeable counterions in ionic metal–organic frameworks (IMOFs) provide facile and versatile handles to manipulate functions associated with the ionic guests themselves and host–guest interactions. However, anion-exchangeable stable IMOFs combining multiple anion-related functions are still undeveloped. In this work, a novel porous IMOF featuring unique self-penetration was constructed from an electron-deficient tris(pyridinium)-tricarboxylate zwitterionic ligand. The water-stable IMOF undergoes reversible and single-crystal-to-single-crystal anion exchange and shows selective and discriminative ionochromic behaviors toward electron-rich anions owing to donor–acceptor interactions. The IMOFs with different anions are good ionic conductors with low activation energy, the highest conductivity being observed with chloride. Furthermore, integrating Lewis acidic sites and nucleophilic guest anions in solid state, the IMOFs act as heterogeneous and recyclable catalysts to efficiently catalyze the cycloaddition of CO2to epoxides without needing the use of halide cocatalysts. The catalytic activity is strongly dependent upon the guest anions, and the iodide shows the highest activity. The results demonstrate the great potential of developing IMOFs with various functions related to the guest ions included in the porous matrices.

Positive cooperative binding, a phenomenon prevalent in biological processes, holds great appeal for the design of highly sensitive responsive molecules and materials. It has been demonstrated that metal–organic frameworks (MOFs) can show positive cooperative adsorption to the benefit of gas separation, but potential binding cooperativity is largely ignored in the study of sensory MOFs. Here, we report the first demonstration of positive cooperative protonation of a MOF and the relevant pH response in fluorescence and proton conduction. The MOF is built of Zr–O clusters and bipyridyl-based tetracarboxylate linkers and has excellent hydrolytic stability. It shows a unique pH response that features two synchronous abrupt turn-off and turn-on fluorescent transitions. The abrupt transitions, which afford high sensitivity to small pH fluctuations, are due to cooperative protonation of the pyridyl sites with a Hill coefficient of 1.6. The synchronous dual-emission response, which leads to visual color change, is ascribable to proton-triggered switching between (n, π*) and (π, π*) emissions. The latter emission can be quenched by electron donating anion-dependent through photoinduced electron transfer and ground-state charge transfer. Associated with cooperative protonation, the proton conductivity of the MOF is abruptly enhanced at low pH by two orders, but overhigh acid concentration is adverse because excessive anions can interrupt the conducting networks. Our work shows new perspectives of binding cooperativity in MOFs and should shed new light on the development of responsive fluorescent MOFs and proton conductive materials.

The recently emerging vinylene-linked covalent organic frameworks (VCOFs) stand out from other COFs with exceptional chemical stability and favorable light-emitting properties, promising sensing applications for acids/bases or in strong acidic/basic conditions. Here we systematically investigated the reversible color and fluorescent response of a VCOF functionalized with pyridyl groups to acids/pH. The COF was synthesized with a record surface area for VCOFs and shows reversible hydrochromic and acidochromic behaviors and concomitant fluorescence quenching. The mechanisms were probed with systematical experimental comparison with relevant COFs and model molecules in combination with orbital analysis. The response is related to significant electronic changes in the ground and photoexcited states as a result of protonation or hydrogen bonding at pyridyl sites. The COF in aqueous dispersion displays a reversible fluorescence transition with pH change, which follows the Hill equation for multisite protonation. The COF-modified test paper shows immediate and remarkable color change and fluorescence turn-off/on when alternately exposed to HCl and NH3gases. The work illustrates the great potential of developing highly robust sensory COFs through the vinylene approach.

Sensory materials that show color and/or fluorescence changes in response to specific gases or vapors have important applications in many fields. Here, we report the postsynthetic preparation of novel sensory metal–organic frameworks (MOFs) and their multiple responsive properties. Through postsynthetic N-amination, the 2,2′-bipyridyl spacers in a Zr(IV) MOF are partially transformed into N-aminobipyridinium. The new MOF (Zr-bpy-A) shows chromic behavior toward ammonia and amines because the electron-deficient pyridinium groups form charge-transfer complexes with amino moieties. It also shows a unique chromic response to formaldehyde owing to the Schiff-base condensation with the N-amino groups. Furthermore, the N-amino group can be used to graft different polycyclic aromatic hydrocarbons, which endow the MOF with strong fluorescence of variable colors and afford a high-contrast fluorescence response to ammonia/amines and formaldehyde associated with the chromic response. The presence of the unquaternized bipyridyl group also leads to a fluorescence response to HCl. The multiple responsive behaviors hold appeal for applications in sensing, switching, and antifake marking, which are illustrated with a test paper and writing ink.

Due to its great relevance to environmental, biological, and chemical processes, the precise detection of pH or acidic/basic species is an ongoing and imperative need. In this context, pH-sensitive luminescent systems are highly desired. We reported a three-dimensional Zn(II) MOF synthesized from a bipyridyl-tetracarboxylic ligand and composed of 4-fold interpenetrated diamond frameworks. Because the steric hindrance in the ligand prevents metal coordination with the pyridyl group, the MOF features free basic N sites accessible to the small H+ions, which renders pH responsivity. The aqueous dispersion exhibits an abrupt, high-contrast, and reversible on–off fluorescence transition in the narrow pH range of 5.4–6.2. The sensitive bistable system can be used for the precise monitoring of pH within the range and for use as a pH-triggered optical switch. The responsive mechanism through pyridyl protonation is collaboratively supported by data fitting, absorption spectra, and molecular orbital calculations. In particular, spectral and theoretical analyses reveal the destruction of n → π* transitions and the appearance of intramolecular charge-transfer transitions upon pyridyl protonation. Moreover, by virtue of the pH-responsive fluorescence, the MOF shows appealing sensing performance for the detection of 3-nitropropionic acid, a major mycotoxin in moldy sugar cane.

Smart materials that respond to chemical stimuli with color or luminescence changes are highly desirable for daily-life and high-tech applications. Here, we report a novel porous metal–organic framework (MOF) that shows multiple, selective, and discriminative responsive properties owing to the combination of different functional ingredients [tripyridinium chromogen, Eu(III) luminophore, cationic framework, and special porous structure]. The MOF contains two interpenetrated three-dimensional cationic coordination networks built of a tetrahedral [Eu4(μ3-OH)4] cluster and a tripyridinium-tricarboxylate zwitterionic linker. It shows reversible and discriminative chromic response to aliphatic amines and aniline through different host–guest interactions between electron-deficient pyridinium and electron-rich amines. The size- and shape-selective response to aliphatic amines is ascribed to the radical formation through host–guest electron transfer, whereas the response to aniline is ascribed to the formation of sandwich-type acceptor–donor–acceptor complexes. The MOF is capable of reversible anion exchange with various anions and shows selective and discriminative ionochromic response to iodide, bromide, and thiocyanate, which is attributed to charge-transfer complexation. The above chromic behaviors are accompanied by efficient quenching of Eu(III) photoluminescence. The MOF represents a multi-stimuli dual-output responsive system. It can be used for discrimination and identification of anions and amines. The potential use in invisible printing, reusable sensory films, and optical switches was demonstrated by the ink and the membrane made of the MOF and organic polymers.

Rosette nanotubes (RNTs) are a class of materials formed by molecular self-assembly of a fused guanine–cytosine base (G∧C base). An important feature of these self-assembled nanotubes is their precise atomic structure, intriguing for rational design and optimization as synthetic transmembrane porins. Here, we present experimental observations of ion transport across 1.1 nm inner diameter RNT porins (RNTPs) of various lengths in the range 5–200 nm. In a typical experiment, custom lipophilic RNTPs were first inserted into lipid vesicles; the vesicles then spontaneously fused with a planar lipid bilayer, which produced stepwise increases of ion current across the bilayer. Our measurements in 1 M KCl solution indicate ion transport rates of ∼50 ions s–1V–1m, which for short channels amounts to conductance values of ∼1 nS, commensurate with naturally occurring toxin channels such as α-hemolysin. Measurements of interaction times of α-cyclodextrin with RNTPs reveal two distinct unbinding time scales, which suggest that interactions of either face of α-cyclodextrin with the RNTP face are differentiable, backed with all-atom molecular dynamics simulations. Our results highlight the potential of RNTPs as self-assembled nonproteinaceous single-molecule sensors and selective nanofilters with tunable functionality through chemistry.

A novel metal–organic framework (MOF), formulated as [Cd2(TTVTC)Cl2(H2O)3]·2H2O (1), was synthesized from a tetracarboxylate ligand ([TTVTC]2–) functionalized with the thiazolothiazole extended viologen (TTV2+) fluorophore. The MOF features three-dimensional (10,3)-dframeworks with 6-fold interpenetration. The MOF exhibits reversible photochromism, due to photoinduced electron transfer from carboxylate to TTV2+. The photoactivity benefits from the electron donor–acceptor contacts enabled by mutual interpenetration of the frameworks. This is the first demonstration of photochromism in TTV2+derivatives. In addition, the fluorescence arising from the TTV2+fluorophore can be reversibly modulated during the photochromic process. The work demonstrates the great potential of extended viologen based ligands in the construction of MOFs with dual photomodulable optical properties, which could find future applications in photoelectronics.

Background: Phospholipase D (PLD)is closely related to browning and senescence of postharvest longan fruit. Objective: This study investigated the effects of 2-butanol (a PLD inhibitor) on the expression and regulation of PLD during storage of longan fruit at a low temperature. Methods: Senescence-related quality indices showed that the 2-butanol-treated fruit presented lower pericarp browning index, pulp breakdown index and total soluble solid value than the untreated fruit. Results: The fruit treated by 60 μL/L 2-butanol exhibited the strongest inhibition on senescence, which significantly delayed changes in weight, titratable acidity content, total soluble solid content and ascorbic acid content. This treatment maintained a high level of total phenolic content and caused significant inhibition on pericarp browning and pulp breakdown. Through ELISA method, 60 μL/L 2-butanol treatment also reduced PLD activity. Real-time RT-PCR (RT-qPCR) results showed that PLD mRNA expression level was inhibited by 60 μL/L 2-butanol within 15 days. Western-blotting results further confirmed the differential expression of PLD during storage, and a relatively higher expression for PLD protein was found in control compared to the 2-butanoltreated fruit during 15-d storage. Conclusion: These results provided a scientific basis and reference to further investigating postharvest longan quality maintenance by regulating the PLD gene expression.

Soluble acid invertases (SAIs) cleave sucrose into hexose in vacuoles and play important roles in influencing fruit quality. However, their potential roles in regulating sugar composition and the “sugar receding” process of longan fruits lacked systematic investigations. Our results showed that sucrose/hexose ratios and sugar receding rates of longan pulp varied among cultivars. Analysis of enzymes for sucrose synthesis and cleavage indicated that DlSAI showed the highest negative correlation with sucrose/hexose ratio at both of activity and expression level. Moreover, high SAI activity and DlSAIexpression resulted in extremely low sucrose/hexose ratio in ‘Luosanmu’ longan from development to mature stages and a remarkable loss of sugar in ‘Shixia’ longan fruits during on-tree preservation. In conclusion, DlSAIs act as key factors influencing sucrose/hexose ratio and sugar receding through transcriptional and enzymatic regulations. These results might help improve the quality of on-tree preserved longan.

•Electron beam radiation inhibits the growth and reproduction of R. oryzae.•Electron beam irradiation can damage the cell wall structure of R. oryzae.•Electron beam irradiation can destroy the cell membrane integrity of R. oryzae.•Electron beam irradiation can cause oxidative stress in R. oryzae.

Confinement of discrete coordination cages within nanoporous lattices is an intriguing strategy to gain unusual properties and functions. We demonstrate here that the confinement of coordination cages within metal–organic frameworks (MOFs) allows the spin state of the cages to be regulated through multilevel host–guest interactions. In particular, the confined in situ self-assembly of an anionic FeII4L6nanocage within the mesoporous cationic framework of MIL-101 leads to the ionic MOF with an unusual hierarchical host–guest structure. While the nanocage in solution and in the solid state has been known to be invariantly diamagnetic with low-spin FeII, FeII4L6@MIL-101 exhibits spin-crossover (SCO) behavior in response to temperature and release/uptake of water guest within the MOF. The distinct color change concomitant with water-induced SCO enables the use of the material for highly selective colorimetric sensing of humidity. Moreover, the spin state and the SCO behavior can be modulated also by inclusion of a guest into the hydrophobic cavity of the confined cage. This is an essential demonstration of the phenomenon that the confinement within porous solids enables an SCO-inactive cage to show modulable SCO behaviors, opening perspectives for developing functional supramolecular materials through hierarchical host–guest structures.

•The aroma compounds of CWC were analyzed for the first time.•A total of 146 aroma compounds were characterized and annotated in processed CWC.•The flavor compounds of the FF are different from the other samples.•GC–MS and GC-IMS exhibited the difference results between the five samples.

Abstract: This paper introduces a parameterization-based approach for anisotropic surface meshing. Given an input surface equipped with an arbitrary Riemannian metric, this method generates a metric-adapted mesh with user-specified number of vertices. In the proposed method, the edge length of the input surface is directly adjusted according to the given Riemannian metric at first. Then the adjusted surface is conformally embedded into a parametric 2D domain and a weighted Centroidal Voronoi Tessellation and its dual Delaunay triangulation are computed on the parametric domain. Finally the generated Delaunay triangulation can be mapped from the parametric domain to the original space, and the triangulation exhibits the desired anisotropic property. We compute the high-quality remeshing results for surfaces with different types of topologies and compare our method with several state-of-the-art approaches in anisotropic surface meshing by using the standard measurement criteria. [Copyright &y& Elsevier]

Cooperative binding plays essential roles in many biochemical processes and has important implications for the development of sensory materials. Metal–organic frameworks (MOFs) can be designed to possess multiple binding sites on pore surfaces, but binding cooperativity within the confined space is rarely recognized. Here, we present a systematic study on cooperative protonation in MOFs in order to gain structural insights into the phenomenon. Three microporous Zr(IV) MOFs were studied for comparison, two furnished with sterically hindered but proton-accessible sites (Zr-PTB and Zr-PPTB) and one free of pyridyl sites (Zr-BTB, isostructural to Zr-PTB). Zr-PTB and Zr-PPTB show two opposite and simultaneous fluorescence transitions in narrow pH changes, which has the appeal for ultrasensitive pH probing. The dual-emission response is ascribable to pyridyl protonation, which turns off the (n, π*) emission and, meanwhile, turns on the (π, π*) emission. The abrupt fluorescence transitions arise from positive cooperativity of multisite protonation. Zr-PPTB shows stronger cooperativity (Hill coefficient h= 1.6) than Zr-PTB (h= 1.2). Structural inspection suggests that the arrangement of the pyridyl sites in Zr-PPTB is conducive to the interplay between pyridyl sites. Moreover, we demonstrate abrupt enhancement (up to 500 times) in proton conduction for Zr-PTB below the pH of cooperative protonation, with a maximum conductivity of 1.2 × 10–2S cm–1at 347 K and 98% RH. Zr-PPTB also shows abrupt conductivity enhancement upon cooperative protonation, but the enhancement is smaller. We ascribe the difference to the biased allocation of pyridyl sites between different channels of Zr-PPTB.