Benzotrithiophene-based MOFs: interchromophoric interactions affected Ln(III) crystallization selectivity and optoelectronic properties.

Metal-organic frameworks (MOFs) provide an ideal platform for the assembly of chromophores and thus show wide potential applications in optoelectronic devices. The spatial arrangement and interaction of the incorporated chromophores play a key role in the generation of coherent optical and electronic properties. In this work, two series of benzo-(1,2;3,4;5,6)-tristhiophene (BTT) based Ln-MOFs (Ln-1s and Ln-2s) were synthesized. These two series of MOFs present different assembly states of BTT chromophores, that is, BTT-containing ligands exist as separated monomers in Ln-1s but gather as dimers in Ln-2s. From the comparison between these two series of MOFs and theoretical calculations, we show for the first time that this chromophore assembly state difference could affect the crystallization selectivity of MOFs towards different Ln3+ ions. In addition, the interaction between BTT chromophores in the dimer also leads to the red-shifted photoluminescence and enhanced photocurrent of Ln-2s relative to those of Ln-1s. The results of this work demonstrate the multiple functions of interchromophoric interactions in the structures and optoelectronic properties of MOFs.

Highly improved dechlorination of 2,4-dichlorophenol in aqueous solution by Fe/Ni nanoparticles supported by polystyrene resin.

2,4-dichlorophenol (2,4-DCP) is a typical chlorophenol that has been widely used in industrial production and caused serious pollution to the environment. In this study, the performance of Fe/Ni bimetallic nanoparticles supported on polystyrene cation exchange resin (Fe/Ni-D072) to remove 2,4-DCP was evaluated. The effects including the doping amount of Ni, the dosage of Fe/Ni-DCP, the initial concentration of 2,4-DCP, and pH value of the solution on the removal efficiency were also investigated. The results showed that when the initial concentration of 2,4-DCP was 20 mg/L and pH = 7.3, 90% of 2,4-DCP could be dechlorinated by Fe/Ni-D072 (Ni% = 30 wt%, dosage: 6.7 g/L) after 12 h reaction. The dechlorination process followed a pseudo-first-order model, and the reaction constant was 0.252 h-1. In addition, the effects of humic acid and common coexisting ions on dechlorination were studied. The results showed that humic acid with a low concentration (5 mg/L) and CO32- restrained the degradation of 2,4-DCP. The dechlorination products of 2,4-DCP were identified by HPLC and the result showed phenol was the main product with a slight amount of 2-CP as the dechlorination intermediate, and 4-CP was barely detected. These results suggest that Fe/Ni-D072 was a promising catalytic material for the removal of chlorophenol and has great application prospects in groundwater remediation.

Aftershock: CEO Great Famine Experience and Stock Price Crash Risk.

This study examines the effect of CEOs' early-life traumatic experience on firm-specific stock price crash risk. Drawing on the idea of natural experiments, we take the Great Famine in China as an external traumatic event which cannot be selected or controlled by human. The analysis points out that compensation psychology and irrational defense psychology after the trauma of Great Famine are important factors that cause CEOs to hoard bad news. Based on a large sample of Chinese companies from 2007 to 2017, we find evidence that CEOs who experienced the Great Famine during early-life tend to hoard bad news, which result in higher stock price crash risk. The more severe and prolonged the Great Famine that the CEOs experienced, the greater the effect of this traumatic experience. CEOs decision-making power enhances the adverse effect of CEOs' early-life traumatic experiences on crash risk. Findings of this study contributes to the literature by providing a new explanation for the stock price crash risk, which is of great significance for the sustained and healthy development of capital markets.

Ultrasensitive Assay of Alkaline Phosphatase Based on the Fluorescent Response Difference of the Metal-Organic Framework Sensor.

The assay of alkaline phosphatase (ALP) is important in clinical diagnosis because the abnormal expression of this enzyme is related to many serious diseases. In this work, using a luminescent metal-organic framework (MOF) as the sensor, a fluorescent method was developed for the activity assay of ALP. With nanoscale particle size, the prepared MOF sensor exhibited good dispersability and stable photoluminescence in aqueous suspension. The emission of this MOF is inert to p-nitrophenylphosphate (NPP) but could be efficiently quenched by its dephosphorylated product, p-nitrophenol. Taking advantage of this feature, this MOF was added to the system of ALP-catalyzed NPP dephosphorylation to transduce the proceeding of the reaction real-timely to the fluorescent signal. The enzyme activity could be calculated based on the recorded kinetic trace. This method presented a low detection limit (2 × 10-3 U L-1) and a wide quantification range (0.6-90 U L-1) in our experiments, showing its quantification capability challenges the best of current ALP analytical methods. As a practical application, our method was successfully applied to the ALP analysis in human serum samples.

Metal-organic frameworks based fluorescent sensor array for discrimination of flavonoids.

Metal-organic frameworks (MOFs) are hotly investigated as a novel kind of fluorescent sensing materials in recent years. However, the application of MOF sensing to drug analysis is still very difficult yet, because the structural similarity among drug homolog-ues exceeds the discrimination ability of MOFs. Array sensing technique, which relies on the combined responses of a group of sensing materials, is a viable way to solve this problem. In this work, we chose five luminescent MOFs with different fluorophores to construct a fluorescent sensor array for the analysis of flavonoids. With the response pattern of these MOFs and the statistical methods of linear discriminant analysis and hierarchical cluster analysis, nine flavonoids with similar structures were correctly discriminated. By the combination with UV spectrum, our method could even realize the qualification and quantification of the flavonoid samples with unknown concentrations. This work is the first time of using MOFs to successfully distinguish multiple drug homolog-ues.

Pyrene-based MOFs as fluorescent sensors for PAHs: an energetic pathway of the backbone structure effect on response.

The sensing performance of metal-organic frameworks (MOFs), a novel kind of crystalline fluorescent sensing materials, would be profoundly affected by their backbone structures. The current understanding about the backbone effect is limited to the modulation of analyte accommodation through pore structures. Herein, three topologically different pyrene-based MOFs, including NU-1000, NU-901 and ROD-7, were investigated as potential fluorescent sensors for polycyclic aromatic hydrocarbons (PAHs). Although these MOFs are constructed by the same photoactive component, they exhibited distinct sensing behaviors. NU-1000 gave different forms of fluorescent response to acenaphthylene, pyrene and fluoranthene with detection limits at the ng L-1 level. In contrast, NU-901 and ROD-7 were unresponsive to all tested PAHs. Experimental and computational investigations illustrate that this distinction is due to the variance in the excited state energy. The strong inter-ligand interaction in NU-901 and ROD-7 lowers their excited state energy and thus thermodynamically inhibits the photo-induced electron transfer and excimer/exciplex formation, which works in the NU-1000 system. This work proves for the first time that the topological structure of MOFs could affect their sensing performance in an energetic way.

Metal-organic framework-based fluorescent sensing of tetracycline-type antibiotics applicable to environmental and food analysis.

Antibiotics have been noted as an important class of emerging contaminants in the environment. Metal-organic frameworks (MOFs), which have been intensely investigated as a novel kind of sensing material, have been tentatively applied to the detection of antibiotics in recent years. In this work, a nanoscale MOF (In-sbdc) with a strong (quantum yield = 13%) and stable emission in water was synthesized. With its effective spectral overlap with tetracyclines, adsorption preconcentration and the usage of a masking agent, In-sbdc gave sensitive responses to a series of tetracycline antibiotics (tetracycline, chlorotetracycline and oxytetracycline) with detection limits of 0.28-0.30 µM, but another eight tested kinds of antibiotics did not cause a remarkable change in its emission (<10% of the response caused by an equal amount of tetracyclines). This MOF-based sensing system was successfully applied to tetracyclines detection in a series of actual water and food samples.

MOF based fluorescent assay of xanthine oxidase for rapid inhibitor screening with real-time kinetics monitoring.

The activity assay of xanthine oxidase (XO) is of great application value in clinical diagnosis because the abnormal level of this enzyme is related to a series of pathological states. In this work, a Zr based metal-organic framework (BTB-MOF) with stable photoluminescence in pure water and buffer solution was synthesized. The examination about the fluorescent responses of this material to xanthine and its oxidation product, uric acid, showed that, although both of them affected the emission of BTB-MOF in quenching form, the efficiencies presented much difference. Taking advantage of this feature, a fluorescent method was developed for the activity assay of XO, that is, BTB-MOF was added to the enzymatic oxidation system as a sensor to transduce the proceeding of the reaction real-timely to the signal of fluorescent intensity change. Our method can work under the interference of normal biologically related species, and precisely reflect XO activity in the range of 0.2-40 U L-1 (detection limit = 0.004 U L-1). With consecutive fluorescence intensity scan, this assay could be applied as a high speed screening method of XO inhibitors with the testing time of 1 min. This work shows the wide potential application of MOFs in enzyme analysis.

Enzyme-Assisted Metal-Organic Framework Sensing System for Diethylstilbestrol Detection.

As novel fluorescent-sensing materials, metal-organic frameworks (MOFs) have shown great potential in environmental monitoring. However, most of the researches are limited to traditional pollutants, whereas the application of MOFs to the detection of the pollutants with more complicated structures, such as endocrine disrupting chemicals (EDCs), has rarely been explored. The difficulties faced in the sensing of EDCs include their electronic stability and the structural similarity among homologues, which could be overcome by the incorporation of enzymatic reaction. In this work, the first example of enzyme-assisted MOF-fluorescent-sensing was developed for the analysis of diethylstilbestrol (DES, a synthetic estrogen). In this system, DES is first oxidized by HRP/H2 O2 quantitatively to its quinone form, and then the quinone product is selectively captured by a stilbene based luminescent MOF to induce fluorescence response. By the tandem sensitization and filtration of enzymatic reaction and MOF adsorption, this method shows high sensitivity (DL=89 nm) and can distinguish DES from other similar-structured EDCs.

Luminescent Metal-Organic-Framework-Based Label-Free Assay of Polyphenol Oxidase with Fluorescent Scan.

Metal-organic frameworks (MOFs) are emerging in recent years as a kind of versatile fluorescent sensing materials, but their application to enzyme assays has rarely been studied. Here, the first example of a MOF-based label-free enzyme assay system is reported. A luminescent MOF was synthesized and applied to the activity analysis of polyphenol oxidase (PPO). With its distinct responses to the phenolic substrate and o-quinone product, this MOF could transduce the extent of PPO-catalyzed oxidation to fluorescence signal and enable the real-time monitoring of this reaction. Wide substrate adaptability and high sensitivity (detection limit=0.00012 U mL-1 ) were exhibited by this method, which meets the requirement of common bioanalysis. Interestingly, by the comparison with molecular capturing reagents, the heterogeneous nature of this MOF-based assay effectively preventing the interaction with the enzyme was proven, thus ensuring the authenticity of results.

Anticancer effect and mechanism of a Se-modified porphyrin Au(III) complex.

Au, Se and porphyrin are widely used components in the design of anticancer drugs, but their combination has never been referred to. In this work, a Se-modified porphyrin Au(III) complex, [AuTPP-Se]Cl, was designed and synthesized as a potential anticancer agent. This compound exhibits remarkable antiproliferative activity on all the six tested cancer cells. Its potency on HepG2 is even ten times higher than that of CDDP. The synergistic action among Au, Se and porphyrin components was validated. Mechanism study showed that both the induction of mitochondria-dependent apoptosis and the arrest of cell cycle contribute to the anticancer activity of [AuTPP-Se]Cl.

A barium based coordination polymer for the activity assay of deoxyribonuclease I.

A new coordination polymer which shows an unusual 2D inorganic connectivity was constructed. This compound exhibits distinct fluorescence quenching ability to the dye-labeled single-stranded DNA probes with different lengths, based on which an analytical method was developed for the activity assay of deoxyribonuclease I.

Solvent induced rapid modulation of micro/nano structures of metal carboxylates coordination polymers: mechanism and morphology dependent magnetism.

Rational modulation of morphology is very important for functional coordination polymers (CPs) micro/nanostructures, and new strategies are still desired to achieve this challenging target. Herein, organic solvents have been established as the capping agents for rapid modulating the growth of metal-carboxylates CPs in organic solvent/water mixtures at ambient conditions. Co-3,5-pyridinedicarboxylate (pydc) CPs was studied here as the example. During the reaction, the organic solvents exhibited three types of modulation effect: anisotropic growth, anisotropic growth/formation of new crystalline phase and the formation of new crystalline phase solely, which was due to the variation of their binding ability with metal cations. The following study revealed that the binding ability was critically affected by their functional groups and molecular size. Moreover, their modulation effect could be finely tuned by changing volume ratios of solvent mixtures. Furthermore, they could be applied for modulating other metal-carboxylates CPs: Co-1,3,5-benzenetricarboxylic (BTC), Zn-pydc and Eu-pydc etc. Additionally, the as-prepared Co-pydc CPs showed a fascinating morphology-dependent antiferromagnetic behavior.

A polypyridyl-pyrene based off-on Cd²âº fluorescent sensor for aqueous phase analysis and living cell imaging.

By retaining the quadrapyridyl receptor of polypyridylhexaazatriphenylene (a Cd(2+) sensor reported by us) and extending its chromophoric group with pyrene, a chemical sensor (1) was designed and synthesized in this work. This sensor exhibit selective off-on fluorescence response to Cd(2+) over other metal ions, and the detection limit is as low as 0.02 µM. The Cd(2+) sensing of 1 has high water toleration and can be carried out in the media with the water content up to 70%. Additionally, 1 was successfully applied to the in vivo imaging of intracellular Cd(2+) in living HaLa cells, and showed low cytotoxicity and cell membrane permeability in these experiments. These results suggest that 1 has potential application in the Cd(2+) analysis of environmental and biological samples.

Two hexaazatriphenylene based selective off-on fluorescent chemsensors for cadmium(II).

Two hexaazatriphenylene (HAT) derivatives, 2,3,6,7-tetramethyl-10,11-di(pyridin-2-yl)dipyrazino[2,3-f:2',3'-h]quinoxaline (1) and 2,3-dimethyl-6,7,10,11-tetra(pyridin-2-yl)dipyrazino[2,3-f:2',3'-h]quinoxaline (2), were designed and synthesized. Both 1 and 2 exhibited high off-on fluorescent selectivity for Cd(2+) over many other metal ions, and the detection limits were determined to be 0.6 and 5.0 µM, respectively. The stoichiometry and coordination mode of blue fluorescent 1-Cd(2+) and cyan fluorescent 2-Cd(2+) were determined with fluorescence titration fit, Job's plot analysis, (1)H NMR titration and X-ray crystallography, and the fluorescence enhancement mechanism was analyzed with density functional theory calculation.

A luminescent 2D coordination polymer for selective sensing of nitrobenzene.

A luminescent two-dimensional (2D) coordination polymer is demonstrated to be a selective sensing material for the straightforward detection of nitrobenzene via a redox fluorescence quenching mechanism.

C2-symmetrical hexaazatriphenylene derivatives as colorimetric and ratiometric fluorescence chemsensors for Zn2+.

Two C2-symmetrical hexaazatriphenylene (HAT) derivatives, 2,3-diphenyl-6,7,10,11-tetra(pyridin-2-yl)dipyrazino[2,3-f:2',3'-h]quinoxaline (1) and 2,3,6,7-tetraphenyl-10,11-di(pyridin-2-yl)dipyrazino[2,3-f:2',3'-h]quinoxaline (2), were designed and synthesized by the condensation reaction of 1,2-diamines and 1,2-diketones. Both compounds 1 and 2 exhibit sensitive, ratiometric and colorimetric fluorescence selectivity for Zn(2+) ion over alkali ions, alkaline earth ions and a wide range of transition metal ions upon excitation at 350 nm in acetonitrile/water. The interactions between 1 or 2 and Zn(2+) can be observed by naked eyes with an obvious color change of the solution from colorless to yellow. For fluorescence intensity of 2 toward Zn(2+), a good linearity (correlation coefficient R(2)=0.993) was established with a detection limit of 0.095 µM, which is more sensitive than that of 1 (0.2 µM). The binding modes of the free ligands 1 and 2 with Zn(2+) are discussed in context to their photophysical and electrochemical properties as well as single X-ray crystallographic structures of 1, 2 and 1-Zn.

Theoretical study of electronic structure and absorption spectra of diacid and zinc species of series of meso-phenylporphyrins.

DFT and TDDFT calculations with density functionals (PBE1PBE, B3LYP, and PBEPBE) have been employed in a study of HCl-acidified diacids of a series of meso-phenylporphyrins. This study aims to clarify the influence of conformational distortion, meso-phenyl substituents, and counterion Cl- on absorption spectra of porphyrin derivatives. Calculations indicate that all three factors increase the MO's level and decrease the Gouterman HOMO-LUMO gap; this, further, brings about the redshift of absorption band. In comparison with experimental methods, the PBE1PBE method produces a more credible description of UV-vis spectra than other two methods. TDDFT calculation with the PBE1PBE method indicates that the electronic effect of the meso-phenyl group is dominant for the spectral redshift of porphyrin diacid series as observed in zinc porphyrins. The redshift of the B band of porphyrin diacids is primarily caused by an electron-donating effect of the meso-phenyl group, whereas the Q band is more sensitive to the π electron delocalization effect. The counterion is indispensable in a theoretical study of electronic and spectral structure of porphyrin diacids.

Spectroscopic and theoretical studies on axial coordination of bis(pyrrol-2-ylmethyleneamine)phenyl complexes.

Metal (M = Zn(II), Ni(II), Cu(II)) complexes with tetradentate Schiff base ligand, bis(pyrrol-2-ylmethyleneamine)phenyl, has been synthesized and characterized by elemental analyses, 1H NMR, mass spectra and UV-vis spectra. The standard association constants (Ktheta) and the thermodynamic parameters (Delta(r)Hmtheta,Delta(r)Smtheta,Delta(r)Gmtheta) for axial coordination of imidazole derivatives with these Shiff base complexes were measured with UV-vis spectrophotometric titration. The decrease of enthalpy is found to be the drive of the axial coordination. Our Schiff base complexes can incorporate two axial ligands, except 2-Et-4-MeIm with two big substituents of great steric bulk according to stoichiometry of 1:1. ZnL displays high selectively binding to imidazole due to the steric bulk effect. Supporting density functional theory (DFT) calculations have been undertaken on B3LYP/6-31G(d) level.

5-{2-[(2-Hydroxy-5-methyl-phen-yl)(phenyl)methyl-eneamino]phenyl-imino-meth-yl}-pyrrole-2-carbaldehyde.

The title compound, C(26)H(21)N(3)O(2), is an unsymmetrical tetra-dentate Schiff base ligand. The hydr-oxy group forms an intra-molecular O-H⋯N hydrogen bond with an adjacent N atom. An inter-molecular N-H⋯O hydrogen bond creates centrosymmetric dimers in the crystal packing.