Photoredox-Cobaloxime Catalysis for Selective Oxidative Dehydrogenative [4+2] Annulation of Imidazo-Fused Heterocycles with Alkenes.

A selective oxidative [4+2] annulation of alkenes with imidazo-fused heterocycles has been developed by using the synergistic combination of photoredox and cobaloxime catalysts. It allows facile access to various imidazole-fused polyaromatic scaffolds accompanied by H2 evolution. This protocol features high regioselectivity as well as a broad substrate scope. Detailed mechanistic studies indicate that twice the electron/H transfer processes facilitated by this catalytic system achieve the annulation π-extension of imidazo-fused heterocycles with alkenes.

The essence of the effect of strain rate on the mechanical behavior of the Fe14.6Ni (at%) elastocaloric refrigeration alloy: a molecular dynamics study.

In this research, a molecular dynamics (MD) model was adopted to investigate the essence of the effect of strain rate on the mechanical behavior of the Fe14.6Ni (at%) elastocaloric refrigeration alloy. The study showed that the mechanical behavior of the Fe14.6Ni (at%) alloy was dependent on the strain rate. Besides, the investigation of temperature demonstrated that the strain rate influenced mechanical behavior by changing the transient temperatures. Furthermore, it was found that the adiabatic temperature change (ΔTadi) was high and up to 51 K, which was a 1.57 times improvement. Finally, the conclusion was drawn that the strain rate influenced the mechanical behavior by changing the transient total kinetic energy and the phase content evolution processes, which was the essence of the effect of strain rate on the mechanical behavior. This work has clarified the essence and enriched the theory of the effect of strain rate on the mechanical behavior of elastocaloric refrigeration alloys.

Enhanced cycling stability and rate capability of a graphene-supported commercialized Vat Blue 4 anode for advanced Li-ion batteries.

Commercialized Vat Blue 4 (VB4) has attracted more attention as a promising anode for large-scale applications in Li-ion batteries (LIBs) due to its high electrochemical activity, low price, and large-scale production. However, its moderate solubility results in severe capacity decay and low utilization of active components. Herein, we present a graphene-supported VB4 composite (VB4/rGO) prepared by a facile sonication and hydrothermal process for long cycling stability and high-rate capability. This design can significantly enhance the Li-storage properties, including high capacity (1045 mA h g-1 at 0.1 A g-1), long cycling stability (537 mA h g-1 even over 1000 cycles at 1 A g-1), and rate capability (315 mA h g-1 at 5 A g-1). Strong π-π interaction derived from the aromatic rings within the π-conjugated system (graphene and VB4) and spatial confinement in-between graphene sheets both can suppress the high solubility of VB4 for superior capacity retention. Moreover, conductive graphene and channels in-between nanosheets can simultaneously facilitate the electron and Li+ transfer. This work demonstrates a simple and effective method to improve the electrochemical performance of commercialized Vat dyes and provides a low-cost and large-scale strategy to develop their practical application in the energy storage field.

A Photoluminescent Cd(II) Coordination Polymer with Potential Active Sites Exhibiting Multiresponsive Fluorescence Sensing for Trace Amounts of NACs and Fe3+ and Al3+ Ions.

The elaborately designed π-electron-rich fluorescent ligand 1,4-bis(1-carboxymethylene-4-imidazolyl)benzene (H2L), possessing bifunctional groups including the carboxylate groups (building units) and 4-imidazoyl groups (N-donor potential active sites) has been employed to construct fluorescent coordination polymers. A luminescent sensor, namely [Cd(L)(phen)2]·5H2O (1), was obtained, which has a one-dimensional structure. The fluorescent material shows a blue emission maximum at 457 nm with a luminescence lifetime of 488 ns and a quantum yield (QY) of 4.56%. Significantly, 1 serves as a promising multiresponsive luminescent sensor to detect trace nitroaromatic compounds (NACs) with the limits of detection (LOD) of 7.21 × 10-8, 1.85 × 10-5, and 1.15 × 10-5 mol/L for 2-nitrophenol (2-NP), 3-nitrophenol (3-NP), and 4-nitrophenol (4-NP), respectively. Furthermore, CP 1 exhibits fluorescent turn-off and turn-on sensing behavior for Fe3+ and Al3+ metal ions with trace amounts of 1.05 × 10-7 and 1.13 × 10-7 mol/L, respectively. Experimental methods and theoretical calculations were employed to elucidate the sensing mechanism in detail.

Stacked Cu2-xSe nanoplates with 2D nanochannels as high performance anode for lithium batteries.

Transition metal chalcogenides are considered as promising alternative materials for lithium-ion batteries owing to their relatively high theoretical capacity. However, poor cycle stability combined with low rate capacity still hinders their practical applications. In this work, the Cu-N chemical bonding directed the stacking Cu2-xSe nanoplates (DETA-Cu2-xSe) is developed to solve this issue. Such unique structure with small nanochannels can enhance the reactive site, facilitate the Li-ion transport as well as inhibit the structural collapse. Benefitting of these advantages, the DETA-Cu2-xSe exhibits high specific capacity, better rate capacity and long cyclability with the specific capacities of 565mAhg-1 after 100 cycles at 200 mA g-1 and 368mAhg-1 after 500 cycles at 5000 mA g-1. This novel DETA-Cu2-xSe structure with nanochannels is promising for next generation energy storage and the synthetic process can be extended to fabricate other transition metal chalcogenides with similar structure.

A Fluorescent and Colorimetric Chemosensor for Hg2+ Based on Rhodamine 6G With a Two-Step Reaction Mechanism.

A fluorescent and colorimetric chemosensor L based on rhodamine 6G was designed, synthesized, and characterized. Based on a two-step reaction, the chemosensor L effectively recognized Hg2+. The interaction between the chemosensor and Hg2+ was confirmed by ultraviolet-visible spectrophotometry, fluorescence spectroscopy, electrospray ionization-mass spectrometry, Fourier-transform infrared spectroscopy, and frontier molecular orbital calculations. The chemosensor L was also incorporated into test strips and silica gel plates, which demonstrated good selectivity and high sensitivity for Hg2+.

Using Smartphone APP To Determine the CN- Concentration Quantitatively in Tap Water: Synthesis of the Naked-Eye Colorimetric Chemosensor for CN- and Ni2+ Based on Benzothiazole.

A naked-eye colorimetric chemosensor DK based on benzothiazole could recognize CN- effectively. When DK interacted with CN- in the aqueous solution, the obvious color change of the solution was directly observed by the naked eye. Other anions did not cause any interference. It is interesting that DK could also discriminate Ni2+ from other cations, and the possible interaction mode between them was verified based on the Job's plot, 1H nuclear magnetic resonance titration, infrared , electrospray ionization mass spectrometry, scanning electron microscopy analysis, and density functional theory calculation methods. As a result, it is clear that the mode of action between DK and CN- was different from that between DK and Ni2+. Meanwhile, the limit of detection of DK toward CN- and Ni2+ was calculated to be 1.7 × 10-8 or 7.4 × 10-9 M, respectively. In addition, CN- was recognized qualitatively by a test paper and silica gel plates made from DK. DK was able to detect CN- in tap water quantitatively, rapidly, and on-site by the use of a smartphone APP. All results implied that DK has certain prospects for practical application to identify CN- in water.

Long-Wavelength Fluorescent Chemosensors for Hg2+ based on Pyrene.

A novel long-wavelength turn-on fluorescent chemosensor CS based on pyrene was synthesized to detect Hg2+. In the presence of other metal ions, CS could effectively recognize Hg2+ and produce the turn-on fluorescent emission at 607 nm. Also, the absorption spectrum exhibited red-shift. Meanwhile, the change of the solution color from yellow to orange was directly observed by the naked eye. The interaction between CS and Hg2+ was confirmed by the Job's plot, electrospray ionization mass spectrometry, scanning electron microscopy, and density functional theory calculations. It was found that the fluorescence of CS could be reversible when I- was added into the solution of CS and Hg2+. CS illustrated high selectivity and good sensitivity for Hg2+ with the limit of detection of 36 nm. Moreover, CS could be utilized as test strips and silica gel plates to identify Hg2+.

Series of Cadmium(II) Coordination Polymers Based on a Versatile Multi-N-Donor Tecton or Mixed Carboxylate Ligands: Synthesis, Structure, and Selectively Sensing Property.

Five Cd(II) metal-organic frameworks (MOFs), [Cd(HL)2] (1), [Cd(HL)2(H2O)2] (2), [Cd3(HL)2(obda)2] (3), [Cd2(HL)2(ohmbda)(DMA)(H2O)] (4), and [Cd2(HL)(btc)(H2O)2]·3H2O (5), were prepared by reactions of Cd(NO3)2·4H2O with 1-(1H-imidazol-4-yl)-4-(4H-tetrazol-5-yl)benzene (H2L) or mixed carboxylate ancillary ligands of 1,2-benzenedicarboxylic acid (H2obda), 5-hydroxy-1,3-benzenedicarboxylic acid (H2ohmbda), and 1,3,5-benzenetricarboxylic acid (H3btc), respectively. Their structures have been characterized by single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy (IR), thermogravimetric analysis, and powder X-ray diffraction. Compounds 1 and 2 are supramolecular isomeric frameworks without consideration of the solvent molecules. Complex 1 exhibits a binodal (3, 5)-connected two-dimensional (2D) layer structure with the point (Schläfli) symbol of (52·6)(55·64·7), while complex 2 shows a 2D + 2D → 3D (three-dimensional) framework. Complex 3 is a (3, 5, 6)-connected tetranodal 3D net with the point (Schläfli) symbol of (4·82)2(45·6·84)2(45·65)2(48·66·8). Compound 4 is a (3, 3, 8)-connected trinodal 3D net with the point (Schläfli) symbol based on a binuclear [Cd2N2O] subunit, while 5 is a 2-nodal (3, 4)-connected 2D V2O5-type network based on [Cd2N2(COO)2] SBU. The studies of molecular sensing properties show that the luminescent MOFs can be employed as fluorescent sensors for the detection of Fe3+ and nitro compounds. Compound 1 and 3 exhibit quenching responses for Fe3+ in dimethylformamide solution with detection limits of 2.3 × 10-6 and 8.6 × 10-7 M, respectively. Meanwhile, compound 5 can sense 4-nitrophenol with a detection limit as low as 5.75 × 10-7 M.

Synthesis of methionine methyl ester-modified coumarin as the fluorescent-colorimetric chemosensor for selective detection Cu2+ with application in molecular logic gate.

A methionine methyl ester-modified coumarin derivative was designed and synthesized, which could discriminate Cu2+ from other metal ions in HEPES buffer (10 mM, pH 7.4)/CH3CN (40:60, V/V). The detection limit of WM toward Cu2+ was 1.84 × 10-7 M, which was lower than the concentration of Cu2+ in drinking water suggested by WHO and EPA. And the proposed coordination mode exhibiting the interaction between WM and Cu2+ was studied by UV-Vis, fluorescence spectrum, ESI-MS and FT-IR. Based on the fluorescent reversibility of WM, WM was considered as a molecular logic gate and molecular keypad lock. In addition, the test strips and the silica gel plates prepared from the solution of WM also demonstrate the favorable selectivity toward Cu2+.

A highly selective and reversible fluorescence "OFF-ON-OFF" chemosensor for Hg2+ based on rhodamine-6G dyes derivative and its application as a molecular logic gate.

A new rhodamine-6G-based chemosensor X was designed and synthesized for the colorimetric and fluorometric detection of Hg2+. The chemosensor X responsed to Hg2+ had good sensitivity, high selectivity and excellent reversibility in HEPES buffer (10 mM, pH 7.4)/CH3CN (40:60, V/V). The recognition mechanism of X toward Hg2+ was evaluated by Job's plot, IR and MS. Meanwhile, X-Hg2+ fluorescence lifetime was also measured. It was interesting that X displayed favorable reversibility to form an "off-on-off" type signaling behavior with the Hg2+-induced emission spectra being quenched by I-. Furthermore, it could be applied as a molecular logic gate and test strips based on X exhibited a good reversibility selectivity to Hg2+.

Metal(II) Coordination Polymers Derived from Mixed 4-Imidazole Ligands and Carboxylates: Syntheses, Topological Structures, and Properties.

Four new metal⁻organic coordination polymers [Cu(L)(mpa)]·3H2O (1), [Co(L)(mpa)]·H2O (2), [Zn(L)(mpa)]·H2O (3), and [Cd(L)(mpa)(H2O)]·H2O (4) were synthesized by reactions of the corresponding metal(II) salts based on mixed ligands of 1,4-di(1H-imidazol-4-yl)benzene (L) and 4-methylphthalic acid (H2mpa), respectively. The structures of the complexes were characterized by elemental analysis, FT-IR spectroscopy, and single-crystal X-ray diffraction. Compound 1 exhibits a binodal 4-connected three dimensional (3D) architecture with (65·8)-CdSO4 topology, while complexes 2 and 3 are isostructural and have two-dimensional (2D) layer structure with (4, 4) sql topology based on the binuclear metal subunits. Complex 4 has the same 2D layer structure with (4, 4) sql topology as complexes 2 and 3, but the inclined interpenetration of parallel sets of layers result in the formation with 2D + 2D → 3D framework. The activated sample 1 shows selective CO2 uptake over N2. The photoluminiscent properties together with quantum yield (QY) and luminescence lifetime are also investigated for complexes 3 and 4 in the solid state at room temperature.

A highly selective colorimetric and fluorescent chemosensor for Al(III) based-on simple naphthol in aqueous solution.

A colorimetric and fluorescent chemosensor (L) for Al(III) was synthesized and fully characterized. L could be both used as a colorimetric and fluorescent chemosensor for the detection of Al(3+) ions with low detection limit (8.87×10(-7) M) in CH3CN-H2O (1:1, v/v) solution. The binding ratio of L-Al(3+) was determined from the Job plot (absorption and fluorescence spectra) and MALDI-TOF MS data to be 1:1. The binding constant (Ka) of Al(3+) binding to L was calculated to be 4.8×10(5) M(-1) from a Benesi-Hildebrand plot. Moreover, the binding site of L with Al(3+) was determined by (1)H NMR titration experiment.

Solvent-dependent "turn-on" fluorescence chemosensor for Mg(2+) based on combination of C=N isomerization and inhibition of ESIPT mechanisms.

A fluorescent chemosensor (L) for Mg(2+) has been synthesized and characterized, which exhibits turn-on fluorescence response for Mg(2+) only in alcohol solvent (methanol or ethanol) with high sensitivity and selectivity. But in both nonpolar and polar solvents (cyclohexane, DCM, DMSO or MeCN), L showed negligible fluorescent response for Mg(2+). In order to discover the unique phenomenon, optical measurements, liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and a high performance liquid chromatography with a fluorescence detector (HPLC-FLD) of L and L with Mg(2+) ions in solvents were studied. In alcohol solvent, [L+alcohol molecule] was formed and the mechanism aspect of L concerning the remarkable fluorescence response for Mg(2+) has been discussed.

Zinc(II) and cadmium(II) metal-organic frameworks with 4-imidazole containing tripodal ligand: sorption and anion exchange properties.

The use of a 4-imidazole containing tripodal ligand 1,3,5-tri(1H-imidazol-4-yl)benzene (H3L) enabled isolation of two three-dimensional (3D) porous metal-organic frameworks (MOFs) [Zn(HL)] · solvent (1) and [Cd(H3L)2](ClO4)2 · 10.5H2O (2) featuring 4,4- and 3,6-connected nets related to the structures of ecl and pyrite, respectively. Framework 1 has 3D channels based on Zn-Im(-) (Im(-) = imidazolate) moieties due to partial deprotonation of the 1H-imidazol-4-yl groups of H3L while porous framework 2 is constructed by the coordination of neutral H3L ligands with Cd(II). Desolvated solid 1' showed remarkable uptake for CO2, N2, H2, CH4 gases as well as the volatile organic vapor of MeOH, EtOH, i-PrOH and C6H6, significantly, exhibiting temperature dependent selective gas sorption for CO2 over N2. Grand Canonical Monte Carlo (GCMC) simulations were performed to elucidate the mechanism of the selective gas adsorption. Cage-like motifs are found in pyrite-net 2, in which ClO4(-) anions are hosted, and the results of IR, elemental analysis and PXRD measurements confirm that 2 has a reversible anion exchange property among perchlorate, nitrate and nitrite anions.

Determination of nitrofuran metabolites in shrimp by high performance liquid chromatography with fluorescence detection and liquid chromatography-tandem mass spectrometry using a new derivatization reagent.

A high performance liquid chromatography with fluorescence detection (HPLC-FLD) method for the simultaneous determination of total nitrofuran metabolite residues (furazolidone, furaltadone, nitrofurantoin, and nitrofurazone) in shrimp was developed. The method involves the acid hydrolysis of protein-bound metabolites, followed by the derivatization of the freed metabolites with the new fluorescent derivatization reagent 2-hydroxy-1-naphthaldehyde (HN) and subsequent liquid-liquid extraction (LLE). Separation is achieved on a YMC-Pack Polymer C18 column under alkaline conditions, and the high fluorescence intensity of the derivatives at an emission wavelength Em=463nm (Ex=395nm) enables, for the first time, their simultaneous determination in shrimp at concentrations as low as 1µg/kg by HPLC-FLD. The method was validated using blank shrimp fortified with all four metabolites at 0.5, 1.0 and 2.0µg/kg. Recoveries were >87% with relative standard deviations of <8.1% for all four metabolites. Furthermore, the results obtained by HPLC-FLD were in very good agreement with those obtained by LC-MS/MS analysis.

High-performance liquid chromatography with fluorescence detection for the determination of nitrofuran metabolites in pork muscle.

A simple and sensitive HPLC method with fluorescence detection (HPLC-FLD) is reported for the simultaneous determination of metabolites of four nitrofuran drugs (furazolidone, furaltadone, nitrofurantoin and nitrofurazone) in pork muscle. The method involves acid hydrolysis of the protein-bound drug metabolites and the conjugation of the released side-chains with a novel fluorescence agent 2-hydroxy-1-naphthaldehyde. After liquid-liquid extraction and effective separation of the derivatives on a YMC-Pack Polymer C18 column at 40°C under alkaline conditions, the high fluorescence intensity of these derivatives at emission wavelength λem = 463 nm enables their simultaneous determination in pork muscle at concentrations as low as 1 µg kg⁻¹. The method was validated using blank pork muscle fortified with all four metabolites at 0.5, 1.0 and 2.0 µg kg⁻¹. Recoveries were > 92.3% with RSDs < 8.5% for all four metabolites. The results obtained with HPLC-FLD and LC-MS/MS methods showed very good agreement for pork muscle samples.

The binding characteristics of isoniazid with copper-zinc superoxide dismutase and its effect on enzymatic activity.

BACKGROUND: Isoniazid (INH) is front-line anti-tuberculosis (TB) drugs, which are usually prescribed to TB patients for a total period of 6 months. Antituberculosis drug-induced hepatotoxicity (ATDH) is a serious adverse reaction of TB treatment. It is reported that INH-induced hepatotoxicity is associated with oxidative stress. Superoxide dismutase (SOD, EC 1.15.1.1) is the key enzyme for the protection of oxidative stress, which catalyzes the removal of superoxide radical anion, thereby raising the need to better understand the interaction between INH and SOD. RESULTS: The experimental results showed that the fluorescence intensity of Cu/Zn-SOD regularly decreased owing to form a 1:1 INH-SOD complex. According to the corresponding association constants (K SV) between INH and SOD obtained from Stern-Volmer plot, it is shown that values of K A are 1.01 × 10(4), 5.31 × 10(3), 3.33 × 10(3), 2.20 × 10(3) L · mol(-1) at four different temperatures, respectively. The binding constants, binding sites and the corresponding thermodynamic parameters ((Δ) H, (Δ) G and (Δ) S) were calculated. A value of 3.93 nm for the average distance between INH and chromophore of Cu/Zn-SOD was derived from Förster theory of non-radiation energy transfer. The conformational investigation showed that the presence of INH resulted in the microenvironment and conformational changes of Cu/Zn-SOD. In addition, Effects of INH on superoxide dismutase activity was examined. CONCLUSIONS: The results show that the hydrogen bonding and van der Waals forces play major roles in stabilizing the 1:1 INH-SOD complex. After addition of INH during the range of the experiment, the conformation and microenvironment of Cu/Zn-SOD are changed, but the activity of Cu/Zn-SOD is not changed.

Kinetics and mechanism of jack bean urease inhibition by Hg2+.

BACKGROUND: Jack bean urease (EC 3.5.1.5) is a metalloenzyme, which catalyzes the hydrolysis of urea to produce ammonia and carbon dioxide. The heavy metal ions are common inhibitors to control the rate of the enzymatic urea hydrolysis, which take the Hg2+ as the representative. Hg2+ affects the enzyme activity causing loss of the biological function of the enzyme, which threatens the survival of many microorganism and plants. However, inhibitory kinetics of urease by the low concentration Hg2+ has not been explored fully. In this study, the inhibitory effect of the low concentration Hg2+ on jack bean urease was investigated in order to elucidate the mechanism of Hg2+ inhibition. RESULTS: According to the kinetic parameters for the enzyme obtained from Lineweaver-Burk plot, it is shown that the Km is equal to 4.6±0.3 mM and Vm is equal to 29.8±1.7 µmol NH3/min mg. The results show that the inhibition of jack bean urease by Hg2+ at low concentration is a reversible reaction. Equilibrium constants have been determined for Hg2+ binding with the enzyme or the enzyme-substrate complexes (Ki =0.012 µM). The results show that the Hg2+ is a noncompetitive inhibitor. In addition, the kinetics of enzyme inhibition by the low concentration Hg2+ has been studied using the kinetic method of the substrate reaction. The results suggest that the enzyme first reversibly and quickly binds Hg2+ and then undergoes a slow reversible course to inactivation. Furthermore, the rate constant of the forward reactions (k+0) is much larger than the rate constant of the reverse reactions (k-0). By combining with the fact that the enzyme activity is almost completely lost at high concentration, the enzyme is completely inactivated when the Hg2+ concentration is high enough. CONCLUSIONS: These results suggest that Hg2+ has great impacts on the urease activity and the established inhibition kinetics model is suitable.

Poly[[µ-1,4-bis-(1H-imidazol-4-yl)benzene-κN:N](µ-5-methyl-isophthalato-κO:O)cobalt(II)].

In the title coordination polymer, [Co(C(9)H(6)O(4))(C(12)H(10)N(4))](n), the Co(II) atom is four-coordinated by two O atoms from two different 5-methyl-isophthalate bivalent anions and two N atoms from two different 1,4-bis-(1H-imidazol-4-yl)benzene ligands, forming a four-coordinated tetra-hedral coordination geometry. Each 5-methyl-isophthalate ligand acts as a µ(2)-bridge, linking two Co(II) atoms and forming chains which are further linked by 1,4-bis-(1H-imidazol-4-yl)benzene ligands into a two-dimensional network parallel to ([Formula: see text]01). These planes are, in turn, linked by two inter-molecular N-H⋯O inter-actions, forming a three-dimensional structure. Weak C-H⋯O hydrogen bonds are also present in the structure.