Zr-Based MOF-Stabilized CO2-Responsive Pickering Emulsions for Efficient Reduction of Nitroarenes.

A Pickering emulsion is a natural microreactor for interfacial catalysis in which an emulsifier is critical. Recently, a metal-organic framework (MOF) has attracted attention to emulsify water-organic mixtures for constructing a Pickering emulsion. However, a few stimuli-responsive Pickering emulsions based on MOFs have been reported, and the MOF emulsifiers cannot be regenerated at room temperature. Herein, the Zr-MOF with a rodlike morphology is synthesized using ionic liquid as a modulator and then modified with n-(trimethoxysilylpropyl)imidazole (C3im) to prepare a series of functionalized Zr-MOFs (MOF-C3im). It is found that MOF-C3im is an excellent emulsifier to construct stable and CO2-responsive Pickering emulsions even at low content (>0.20 wt %). Notably, the emulsification and demulsification of the emulsions can be easily and reversibly switched by bubbling of CO2 and N2 alternatively at room temperature because CO2 and imidazole molecules anchored on the Zr-MOF underwent a reversible acid-base reaction, resulting in an obvious change in the wettability of the emulsifier. As a proof of concept, the reduction reactions of nitrobenzene have been successfully carried out in these Pickering emulsions, demonstrating the efficient integration as a microreactor for chemical reaction, product separation, and emulsifier recycling under ambient conditions. This strategy provides an innovative option to develop stimulus-responsive Pickering emulsions for sustainable chemical processes.

Li-Mn Bimetallic Metal-Organic Framework and Its Derivative as a Cathode for Lithium-Ion Batteries.

The bimetallic organic-inorganic hybrid complex [Li2Mn3(ipa)4(DMF)4]n (ipa = deprotonated 1,3-isophthalic acid, DMF = N,N'-dimethyl formamide) was synthesized via a solvothermal method and then further calcined at high temperature to prepare a spinel-type lithium manganate (LiMn2O4) cathode under different atmospheres with various calcination conditions. The structure of the complex [Li2Mn3(ipa)4(DMF)4]n was represented by single-crystal X-ray diffraction (XRD), powder XRD, and thermogravimetric (TG) analysis. The morphology and elements of LiMn2O4 were analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The electrochemical properties of LiMn2O4 indicated that the direct calcination in an air atmosphere at 850 °C for 12 h was the optimal synthetic condition. The initial discharge specific capacity can reach 95.9 mA h g-1 with an open-circuit voltage of ca. 3.0 V and an upper cutoff voltage of ca. 4.3 V at 0.1 C. The initial discharge-specific capacity of 89.8 mA h g-1 at 1 C had a Coulombic efficiency of 95.3%. This was 73 mA h g-1 at a high rate of 5 C increasing to 91.6 mA h g-1 after returning to 0.1 C. After 500 cycles at 1 C, the system remained at 80.7 mA h g-1 with 89.9% of the initial discharge specific capacity. These features exhibit better stability than that of the reported LiCoO2 and LiNiO2 in battery material for LiMn2O4 enforcement.

Isomerization of DASA Molecules in the Nanopores of Metal-Organic Frameworks: What Determines Its Reversibility?

In recent years, light-responsive molecules have been incorporated in metal-organic frameworks (MOFs) to fabricate light-responsive intelligent devices, where reversible isomerization of the guest molecules in the nanopores is crucial. However, how to design a porous environment of MOFs to achieve a reversible isomerization remains unknown until now. In this work, donor-acceptor Stenhouse adducts (DASAs), a new kind of visible light responsive compound, were confined in the nanopores of different MOFs to study their isomerization upon visible-light irradiation/mild heating. We found that the polarity of the pore environment is the key to control the reversibility of isomerization of such guest molecules. Under the guidance of this principle, MIL-53(Al) was screened to investigate the proton conductivity and switching performance of the DASA-confined MOF. The proton conductance was up to 0.013 S cm-1 at 80 °C and 98 % RH, and at least 30 switching cycles were achieved thanks to the Grotthuss-type mechanism and the low polarity of MIL-53(Al) pore environment.

Two-dimensional coordination polymers with high proton conductivity and ultrafast highly efficient molecular sieving constructed by the structural inductive effect.

A family of unique 2D-layered Cu-based coordination polymers (abbreviated as HNNU-1α, 1ß and 1γ) with different halide anions were successfully constructed using a zwitterion pyridiniumolate as the structural inductive agent (SIA). More importantly, we found that the laminates of HNNU-1α exhibit ultrafast highly-efficient molecular sieving in a water system, and HNNU-1α to 1γ display a good proton conductivity of ca. 2.2 × 10-2, 4.9 × 10-5, and 3.0 × 10-4 S cm-1 at 90 °C and 98% relative humidity (RH), respectively.

Controllable Synthesis of Centrosymmetric/Noncentrosymmetric Phases for the Family of Halogen-Based Photonic Coordination Polymers to Enhance the Phase-Matching Second-Harmonic-Generation Response.

The nonlinear-optical (NLO) materials with second-harmonic-generation (SHG) response need to crystallize in the noncentrosymmetric space group. It is very difficult to control the synthetic conditions to solely form a noncentrosymmetric phase for the materials with noncentrosymmetric and centrosymmetric conformations. Herein, we found that the temperature and halogen anion play an important role during the formation procedure of the pure noncentrosymmetric or centrosymmetric phase for the halogen-based family of coordination polymers to yield hybrid materials with a phase-matching SHG response as well as inherit the primary excellent photonic property of organic linkers. Our results provide a good choice for the design and construction of novel materials with a particular photonic property.

A molecular-logic gate for COX-2 and NAT based on conformational and structural changes: visualizing the progression of liver disease.

Lighting up the relevant lesion boundaries during operations is vital for guiding the effective resection of hepatopathic tissue. We envisioned that molecular-logic gates, which are known for their excellent digital correlation between input and output signals, could be used to facilitate differential visualization of lesion boundaries. Herein, a series of flexible molecules, naphthalene imide-indole derivatives (IAN) were prepared and evaluated as molecular-logic gates. The input and output signals of the IAN derivatives were successfully used to highlight different hepatopathic regions in order to facilitate boundary differentiation. The IAN derivatives produce different signals due to collaborative changes in the conformation and structure. The hepatopathy-related enzymes (COX-2 and NAT) were used to induce conformational and structural changes in IAN derivatives. Based on these enzyme induced synergistic effects, IAN can sensitively emit different coloured signals such as green, cyan and blue (output signals) as a function of the different input signals, i.e. the different activity of COX-2 and NAT in solution and living cells. Significantly, the IAN derivatives were successfully used to distinguish the boundaries of hepatopathic lesions in tissues after spraying with IAN derivatives (mild cirrhosis, severe cirrhosis, in addition to early and late hepatocellular carcinoma) under a hand held lamp at 365 nm by naked eye.

Ultrasensitive Apurinic/Apyrimidinic Site-Specific Ratio Fluorescent Rotor for Real-Time Highly Selective Evaluation of mtDNA Oxidative Damage in Living Cells.

The unrepaired apurinic/apyrimidinic site (AP site) in mitochondrial DNA (mtDNA) promotes misincorporation of nucleotides and further causes serious damage for the living organism. Thus, accurate quantitative detection of AP sites in mtDNA in a rapid, highly sensitive, and highly selective fashion is important for the real-time evaluation of mtDNA oxidative damage. In this study, a targeting mtDNA ultrasensitive AP site-specific fluorescent rotor (BTBM-CN2) was designed by the strategy of molecular conformation torsion adjustment ratio fluorescent signal. The specific recognition reaction is activated when it encountered AP sites in mtDNA within 20 s, and BTBM-CN2 presented a "turn-on" red fluorescence signal at 598 nm. Then, about 100 s later, BTBM-CN2 emitted a new green fluorescence signal at 480 nm, which is mainly due to the activation of the rate-limiting reaction. With increasing numbers of AP sites (1-40 in 1 × 105 bp of mtDNA), the fluorescence emission at 598 nm decreased gradually, and the new emission at 480 nm increased. Intracellular experiments indicated that BTBM-CN2 could detect AP sites in mtDNA in a rapid and quantitative fashion with high selectivity and ultrasensitivity. On the basis of the emergence of the fluorescence signal at 480 nm and its signal strength, the cell whose mtDNA was damaged could be screened by flow cytometry and its degree of damage could be evaluated in real time by comet assay. Hence, the rotor may have potential applications varying from accurate and ultrasensitive detection of AP sites to the real-time evaluation of the oxidative damage in living cells.

A sulfur coordination polymer with wide bandgap semiconductivity formed from zinc(II) and 5-methylsulfanyl-1,3,4-thiadiazole-2-thione.

The sulfur coordination polymer catena-poly[zinc(II)-µ2-bis[5-(methylsulfanyl)-2-sulfanylidene-2,3-dihydro-1,3,4-thiadiazol-3-ido-κ2N3:S]], [Zn(C3H3N2S3)2]n or [Zn2MTT4]n, constructed from Zn2+ ions and 5-methylsulfanyl-1,3,4-thiadiazole-2-thione (HMTT), was synthesized successfully and structurally characterized. [Zn2MTT4]n crystallizes in the tetragonal space group I-4 (No. 82). Each MTT- ligand (systematic name: 5-methylsulfanyl-2-sulfanylidene-2,3-dihydro-1,3,4-thiadiazol-3-ide) coordinates to two different ZnII ions, one via the thione group and the other via a ring N atom, with one ZnII atom being in a tetrahedral ZnS4 and the other in a tetrahedral ZnN4 coordination environment. These tetrahedral ZnS4 and ZnN4 units are alternately linked by the organic ligands, forming a one-dimensional chain structure along the c axis. The one-dimensional chains are further linked via C-H...N and C-H...S hydrogen bonds to form a three-dimensional network adopting an ABAB-style arrangement that lies along both the a and b axes. The three-dimensional Hirshfeld surface analysis and two-dimensional (2D) fingerprint plots confirm the major interactions as C-H...S hydrogen bonds with a total of 35.1%, while 7.4% are C-H...N hydrogen-bond interactions. [Zn2MTT4]n possesses high thermal and chemical stability and a linear temperature dependence of the bandgap from room temperature to 270 °C. Further investigation revealed that the bandgap changes sharply in ammonia, but only fluctuates slightly in other solvents, indicating its promising application as a selective sensor.

Light-activated "cycle-reversible intramolecular charge transfer" fluorescent probe: monitoring of pHi trace change induced by UV light in programmed cell death.

Under the synergistic effects of protonation and deprotonation, a light-activated fluorescent probe (UV-SP) exhibited "cycle-reversible intramolecular charge transfer (ICT)" for different pH after activation by UV light, resulting in emission of multiple ratio fluorescent signals (FI563/FI595 and FI664/FI595). Based on these kinds of response signals, UV-SP can specifically monitor the cycle-reversible trace change of intracellular pH caused by UV radiation. More importantly, according to the stable and invariant multiple ratio fluorescent signals, UV-SP can sort cells entering programmed death.

Structural Transformation Pathways of Alkaline Earth Family Coordination Polymers Containing 3,3',5,5'-Biphenyl Tetracarboxylic Acid.

The understanding of crystal stepwise transformation is very important to enclose the "black box" in the preparation of crystal materials. In this work, different structural intermediates were isolated prior to the formation of the final alkali earth coordination polymers (CPs) during the preparation of three pairs of alkali earth CPs through solvothermal method and convenient oil-bath reactions. Single crystal X-ray diffraction analysis demonstrated the structural transformation from a 0 D to 1 D inorganic connectivity for the Ca-CPs and Sr-CPs, but a 1 D to 0 D inorganic connectivity for Ba-CPs, involving the breakage/formation of chemical bonds in the reaction solutions. Further analyses indicated that these two different structural transformation pathways are determined by the deprotonation of organic acid, competitive balance between the inorganic and organic connectivity, and the twist of the linker. FT-IR spectra, thermogravimetric and luminescence behaviors agree with their structural characteristics.

pH-Dependent reversible crystal transformation of 1-carboxymethyl-1-methyl-pyrrolidinium bromides and their spectroscopic fingerprint.

In this work, two 1-carboxymethyl-1-methyl-pyrrolidinium bromides (N-methylpyrrolidine betaine hydrobromides) with the stoichiometry of betaine:hydrobromic acid as 1:1 and 2:1, denoted as CMPRHBr-I and CMPRHBr-II, respectively, were prepared and crystallographically determined. The large difference in these two structures is the type of hydrogen bonds, resulting in the different thermal stability. A strong OH⋯Br hydrogen bond was observed in CMPRHBr-I, whereas O⋯H⋯O hydrogen bond in CMPRHBr-II. Both these two crystals can mutually transform by changing the pH value of the aqueous solution. Vibrational spectroscopic studies shows that these two structures can be easily distinguished by the characteristic bands such as νCO stretching vibration and the D-type bands. Our studies indicate that it should be cautious of the structural change as this type of organic salts was purified and recrystallized.

A dynamic invertible intramolecular charge-transfer fluorescence probe: real-time monitoring of mitochondrial ATPase activity.

A dynamic invertible intramolecular charge-transfer (ICT) process could provide abundant response signals for real-time monitoring in living organisms. Herein, based on dynamic invertible ICT, we have reported a cancer cell-targeted fluorescence probe (OPM) for mitochondrial ATPase activity. Due to its abundant response signals, OPM could real-time monitor mitochondrial ATPase activity during the cancer apoptosis process, successfully.

Ultrasensitive fluorescent ratio imaging probe for the detection of glutathione ultratrace change in mitochondria of cancer cells.

Glutathione (GSH) ultratrace change in mitochondria of cancer cells can mildly and effectively induce cancer cells apoptosis in early stage. Thus, if GSH ultratrace change in mitochondria of cancer cells could be recognized and imaged, it will be beneficial for fundamental research of cancer therapy. There have reported a lot of fluorescent probes for GSH, but the fluorescent probe with ultrasensitivity and high selectivity for the ratio imaging of GSH ultratrace changes in mitochondria of cancer cells is scarce. Herein, based on different reaction mechanism of sulfonamide under different pH, a sulfonamide-based reactive ratiometric fluorescent probe (IQDC-M) was reported for the recognizing and imaging of GSH ultratrace change in mitochondria of cancer cells. The detection limit of IQDC-M for GSH ultratrace change is low to 2.02nM, which is far less than 1.0‰ of endogenic GSH in living cells. And during the recognition process, IQDC-M can emit different fluorescent signals at 520nm and 592nm, which results in it recognizing GSH ultratrace change on ratio mode. More importantly, IQDC-M recognizing GSH ultratrace change specifically occurs in mitochondria of cancer cells because of appropriate water/oil amphipathy (log P) of IQDC-M. So, these make IQDC-M possible to image and monitor GSH ultratrace change in mitochondria during cancer cells apoptosis for the first time.

Nucleoside-Based Ultrasensitive Fluorescent Probe for the Dual-Mode Imaging of Microviscosity in Living Cells.

Microviscosity changes of living cells have a far-reaching influence on diffusion and movement capacity of RNA and, more seriously, could modify RNA functions in living cells. Fluorescent rotor, whose fluorescence responds to different environmental viscosities, holds great potential for the imaging of viscosity in biosystem. Although many fluorescent rotors have been reported for viscosity, the fluorogenic rotor with ultrasensitivity for the determination of microviscosity (<10 cP) was rarely reported. Herein, we report a nucleoside-based two-photon fluorescent rotor (dABp-3) that can selectively and ultrasensitively image microviscosity in RNA region of living cells for the first time. 2'-Deoxyadenosine is selected as an electron donor to permit energy transfer via the acetylenic bond to acceptor, a typical boron dipyrromethene moiety. Another highlight, dABp-3 is based on 2'-deoxyadenosine, which result in its recognition capacity for RNA. dABp-3 with ultrasensitivity provides a varied linear response to the microrange viscosity (1.8-6.0 cP) in RNA region of living cells on dual-mode-two-photon ratio mode and fluorescence lifetime mode. After screening and optimization, advantageously, dABp-3 can be used to screen reticulocytes from mature blood cells of thrombosis models in vitro and in vivo because of targeting RNA, while simultaneously image microviscosity changes in these cells. So, dABp-3 as an analytical tool holds considerable promise for bioimaging and monitoring of microviscosity changes in complex biological systems.

Cancer cell-targeted two-photon fluorescence probe for the real-time ratiometric imaging of DNA damage.

Real-time imaging of DNA damage in cancer cells could provide valuable information on the formation and development of cancer. Herein, a two-photon fluorescence probe was discovered. Through sequential ICT processes, it allows successful in vivo visualization of DNA damage in cancer cells by one/two-photon microscopic imaging or by the unaided eye and a hand-held ultraviolet lamp.

A four-unit [c2]daisy chain connected by hydrogen bonds.

A mono-adenine-functionalized pillar[5]arene and a guest including uracil were prepared. They formed a novel four-unit [c2]daisy chain both in the solid state and in a chloroform solution. As far as we know, this [c2]daisy chain is the first one without a covalently bound linear thread. This unique assembly behavior is mainly induced by hydrogen-bond interactions between A and U in the A-U base pairs.

From a binary salt to salt co-crystals of antibacterial agent lomefloxacin with improved solubility and bioavailability.

The cocrystallization of lomefloxacin (Lf) with barbituric acid (HBA) and/or isophthalic acid (H2ip) leads to novel binary and ternary salts via hydrogen-bonding recognition. X-ray single-crystal diffraction analyses show that zwitterionic lomefloxacin can adjust itself to fulfill a different supramolecular array in either binary salts or ternary salt co-crystals, formulated as [HLf]·[Hip]·H2O (1), [HLf]·[BA]·[HBA]·H2O (2) and [HLf]·[BA]·[H2ip]·CH3OH·H2O (3). These pharmaceutical agents present uniform charge-assisted hydrogen-bonding networks between HLf cations and acidic coformers with the lattice capturing water molecules. Structural comparison of (2) and (3) indicated that a delicate balance of geometries and hydrogen-bonding partners is required for stacking to favor the formation of ternary salt co-crystals. Cocrystallization was able to overcome the water insolubility of lomefloxacin. Both the salt co-crystals display enhanced solubility and better pharmaceutical applicability.

How the cation-cation π-π stacking occurs: A theoretical investigation into ionic clusters of imidazolium.

The cation-cation π-π stacking is uncommon but it is essential for the understanding of some supramolecular structures. We explore theoretically the nature of non-covalent interaction occurring in the stacked structure within modeled clusters of 1,3-dimethylimidazolium and halide. The evidences of the energy decomposition analysis (EDA) and reduced density gradient (RDG) approach are different from those of common π-π interaction. Isosurfaces with RDG also illustrate the strength of the titled π-π interaction and their region. Additionally, we find that the occurrence of this interaction is attributed to a few C-H···X interactions, as depicted using atom in molecule (AIM) method. This work presents a clear picture of the typical cation-cation π-π interaction and can serve to advance the understanding of this uncommon interaction.

Ionothermal synthesis, properties and vibrational spectra of zinc (II) complex with nicotinamide.

The zinc (II) complex with nicotinamide, (C6H11N2)[ZnBr3(C6H6N2O)], was prepared under ionothermal condition by using the ionic liquid 1-ethyl-3-methylimidazolium bromide ([EMIM]Br) as a solvent. At the same time, [EMIM]Br also functions as a structure-directing agent, leading to a framework structure different from those obtained by the conventional methods. Single-crystal X-ray analysis revealed that the coordinated compound crystallizes in monoclinic space group P2(1)/c, and the Zn (II) ion is four-coordinated by one pyridine ring N atom and three bromide anions in a slightly distorted tetrahedron arrangement. The [EMIM](+) cations acting as the extra framework charge balancing species occupy the channels of this asymmetric unit. In the crystal structure, intermolecular NH⋯Br and NH⋯O hydrogen bonds link the molecules to form a supramolecular structure. In addition, this compound was further characterized by FT-IR and Raman spectroscopic techniques, and the observed important bands were assigned. Thermogravimetric analysis (TG), Differential Scanning Calorimetry (DSC) and fluorescent properties of solid samples were also studied at room temperature.

1-Carboxymethyl-3-methyl-1H-imidazol-3-ium chloride 2-(3-methyl-1H-imidazol-3-ium-1-yl)acetate monohydrate: a crystal stabilized by imidazolium zwitterions.

The title compound, C6H9N2O2(+)·Cl(-)·C6H8N2O2·H2O, contains one 2-(3-methyl-1H-imidazol-3-ium-1-yl)acetate inner salt molecule, one 1-carboxymethyl-3-methyl-1H-imidazol-3-ium cation, one chloride ion and one water molecule. In the extended structure, chloride anions and water molecules are linked via O-H···Cl hydrogen bonds, forming an infinite one-dimensional chain. The chloride anions are also linked by two weak C-H···Cl interactions to neighbouring methylene groups and imidazole rings. Two imidazolium moieties form a homoconjugated cation through a strong and asymmetric O-H···O hydrogen bond of 2.472 (2) Å. The IR spectrum shows a continuous D-type absorption in the region below 1300 cm(-1) and is different to that of 1-carboxymethyl-3-methylimidazolium chloride [Xuan, Wang & Xue (2012). Spectrochim. Acta Part A, 96, 436-443].