Jixi Guo

Syntheses, crystal structures and luminescent properties of four Zn(II) coordination polymers with pyrazolone derivatives and 4,4′-bipyridine

Four new Zn(II) coordination polymers, {[Zn(L1)(4,4′-bipy)]·0.52CH3OH}n (1), {[Zn(L2)(4,4′-bipy)]·CH3OH}n (2), {[Zn3(L3)3(4,4′-bipy)0.5]·3CH3OH}n (3), {[Zn(L4)(4,4′-bipy)]·2CH3OH}n (4) (H2L1 = N-(1,3-diphenyl-4-propylene-5-pyrazolone) p-nitrobenzoylhydrazide, H2L2 = N-(1-phenyl-3-benzyl-4-propylene-5-pyrazolone) p-nitrobenzoylhydrazide, H2L3 = N-(1,3-diphenyl-4-propylene-5-pyrazolone) isoniazid, H2L4 = N-(1-phenyl-3-benzyl-4-propylene-5-pyrazolone) isoniazid, 4,4′-bipy = 4,4′-bipyridine) have been synthesized by the reactions of zinc acetate with the corresponding 4-acyl pyrazolone derivatives and 4,4′-bipyridine. The X-ray diffraction analyses revealed that complexes 1 and 2 exhibit 1D zigzag chain structures. The ligands (H2L1 and H2L2) serve as divalent tridentate chelating agents to coordinate with Zn(II) atoms. Complex 3 displays a complicated pillared-layer 3D framework and the ligands H2L3 adopt two different kinds of coordination modes. In the case of complex 4, the octahedral Zn(II) atoms are connected by the tetradentate ligands to form a 1D chain, then the 4,4′-bipyridine molecules further connect the 1D chains along the axial direction to generate a 2D network structure. The effect of the coordination groups and substituents at the 3-position of the ligands on the structure of the complexes have been discussed. Additionally, the luminescent properties of the complexes have been investigated in the solid state.

Solid-state photochromism of pyrazolones with highly improved sensitivity, fatigue resistance and reversible fluorescent switching properties

Photochromic compounds derived from pyrazolones, which undergo reversible photoisomerization reactions in pure solid state, were synthesized toward the end of designing novel solid-state photonic switches. The materials exhibit high sensitivity, excellent fatigue resistance and reversible fluorescent switching properties with distinguishable contrast signals under alternating UV irradiation and heating. The mechanism of the photochromic reactions was verified by FT-IR and XPS. The detailed analysis of the spectra and crystal structure of the materials revealed that their photochromism resulted from tautomerization between their enol and keto forms accompanied by proton transfer.

Selenium status and cardiovascular diseases: meta-analysis of prospective observational studies and randomized controlled trials.

Background/Objectives:Selenium was thought to have a role in cardiovascular disease (CVD) owing to its antioxidant properties; however, evidence from observational studies and randomized controlled trials (RCTs) has been inconsistent and controversial. We thus conducted a meta-analysis to assess the discrepancies between observational and randomized trial evidence.Subjects/Methods:We searched MEDLINE and EMBASE for eligible prospective studies regarding the relationship between selenium and CVD up to 15 December 2013 and finally included 16 prospective observational studies and 16 RCTs. Random effects model was used to estimate the pooled relative risk (RR). Generalized least-squares trend test and restricted cubic spline model were performed to assess a linear and a nonlinear dose–response relationship.Results:Our meta-analysis of prospective studies showed a nonlinear relationship of CVD risk with blood selenium concentrations across a range of 30–165 μg/l and a significant benefit of CVD within a narrow selenium range of 55–145 μg/l. Our meta-analyses of RCTs showed that oral selenium supplements (median dose: 200 μg/day) for 2 weeks to 144 months significantly raised the blood selenium concentrations by 56.4 μg/l (95% confidence interval (CI): 40.9, 72.0 μg/l), whereas oral selenium supplements (median: 100 μg/day) for 6 to 114 months caused no effect on CVD (RR=0.91; 95% CI: 0.74, 1.10).Conclusions:Our meta-analysis in prospective studies demonstrated a significant inverse association between selenium status and CVD risk within a narrow selenium range and a null effect of selenium supplementation on CVD was observed in RCTs. These findings indicate the importance of considering selenium status, dose and safety in health assessment and future study design.

Coal derived porous carbon fibers with tunable internal channels for flexible electrodes and organic matter absorption

Coal-derived porous carbon fibers (CPCFs) were prepared by single-nozzle electrospinning the aqueous solution of acid treated coal and polyvinyl alcohol followed by thermal treatment in an inert atmosphere. The production yield of CPCFs was about 92% from coal. The structural, textural, and surface properties of CPCFs were investigated by means of spectroscopy, microscopy, and Brunauer–Emmett–Teller (BET) techniques. The results showed that the flexible CPCFs had an abundant pore structure and large specific surface area. The electrochemical performance of supercapacitor electrodes with these fiber mats was studied. The binder free electrodes showed a capacitance of 170 F g−1 at a current density of 1 A g−1 in 6 M aqueous KOH electrolyte. The electrodes also showed stable cycling performance without any decrease in the specific capacitance after 20000 charge/discharge cycles at a current density of 2 A g−1. Besides, the CPCFs were superhydrophobic and showed outstanding performance in oil-absorption and good circulation for the removal of dyes from water. These outstanding properties potentially make the flexible CPCFs a promising candidate for energy storage and environmental protection.

Photochromism and mechanism of pyrazolones in crystals: structural variations directly observed by X-ray diffraction

Structural changes of photochromic pyrazolones were first verified by an X-ray crystallographic method directly. A tautomeric transformation between enol and keto form isomers occurs, accompanied by proton transfer during the photochromic processes.

Synthesis, spectroscopic properties, and structures of copper(II) and manganese(II) complexes of pyridine-2,6-dicarboxylate and 1,10-phenanthroline

A binuclear copper(II) complex [Cu(PDC)(phen)]2 · 2CH3OH · 1.5H2O (1) and a seven-coordinate manganese(II) complex [Mn(PDC)(phen)2] · CH3OH (2) (PDC = pyridine-2,6-dicarboxylate, phen = 1,10-phenanthroline) have been synthesized hydrothermally and characterized by elemental analyses, spectroscopic studies (IR and UV), and single-crystal X-ray diffraction. In 1, the binuclear copper(II) compound consists of two kinds of Cu(II) centers with five- and six-coordination environments by PDC and phen. The two Cu(II) ions are bridged by one PDC. In 2, Mn(II) is seven-coordinate by two phen and one PDC.

Photochromism and fluorescence modulation of pyrazolone derivatives in the solid state

Two novel photochromic compounds derived from pyrazolones, which undergo a photochromic reaction in the solid state, have been synthesized and their photochromic and fluorescence properties were investigated. Their fluorescence emission can be efficiently modulated by photoisomerization of pyrazolones almost up to 90% upon UV light irradiation. Importantly, the fluorescence emission of 1 can be reversibly switched “on” and “off” upon alternative UV light irradiation and heating. These compounds exhibited photochromic coloration from white E-form to yellow brown K-form. On the basis of the molecular structure determined by X-ray single crystal analysis, there are intermolecular hydrogen bonds which provide suitable proton transfer channels for the enol–keto transformation. The colored K-form isomers, which are very stable at ambient temperature, may be due to the reverse reaction occurring at a high temperature.

Synthesis, infrared spectra, thermal analyses and structural studies of half-sandwich Fe(III)/Fe(II) complex containing pyridine-2,6-dicarboxylate and 1,10-phenanthroline.

A new pyridine-2,6-dicarboxylate iron(III)/iron(II) complex [Fe(phen)(3)][Fe(2)(PDC)(4)].3CH(3)OH was synthesized and characterized (where PDC=pyridine-2,6-dicarboxylate, phen=1,10-phenanthroline) by using elemental analysis, IR spectroscopy and thermal analyses (TGA and DTA). The molecular structure of the complex has been determined by single-crystal X-ray diffraction. The complex is mixed-ligands and the IR spectra display bands characteristic of coordinated mixed-ligand bases. All the IR results are in agreement with the X-ray crystal result. The bond lengths indicate that this complex has [Fe(phen)(3)](2+) cation where Fe(II) ion is in typical low-spin state, and in counter ions, [Fe(PDC)(2)](-) are both in high-spin state.

Synthesis, photochromic properties and thermal bleaching kinetics of pyrazolone phenylsemicarbazones containing a thiophene ring

Five novel pyrazolone derivatives containing a thiophene ring, 1-phenyl-3-(2-thiophenyl)-4-(3-bromobenzal)-5-hydroxypyrazole phenylsemicarbazone (1)/1-phenyl-3-(2-thiophenyl)-4-(3-chlorobenzal)-5-hydroxypyrazole phenylsemicarbazone (2)/1-phenyl-3-(2-thiophenyl)-4-benzal-5-hydroxypyrazole phenylsemicarbazone (3)/1-phenyl-3-(2-thiophenyl)-4-(4-bromobenzal)-5-hydroxypyrazole phenylsemicarbazone (4)/1-phenyl-3-(2-thiophenyl)-4-(4-chlorobenzal)-5-hydroxypyrazole phenylsemicarbazone (5), were synthesized. Among them, only two compounds (1 and 2) have excellent photochromic properties. Their structures, photochromic properties, thermal bleaching kinetics and the activation energies of the thermal bleaching process were investigated. The results show that the two compounds exhibit reversible enol–keto isomerization reaction under 365 nm light irradiation and heat, and high fatigue resistance.

Hierarchical porous carbon spheres constructed from coal as electrode materials for high performance supercapacitors

Hierarchical porous carbon spheres (PCS) are prepared by a simple one-pot spray pyrolysis of coal oxide solution without any further activation process. The specific surface area and total pore volume of the resultant carbon spheres are increased significantly with the increase of spray pyrolysis temperature. When evaluated as electrode materials for supercapacitors in 6 M KOH electrolyte, the PCS exhibits a high specific capacitance 227 F g−1 at a current density of 1 A g−1 and outstanding cycling stability after 10 000 charge/discharge cycles at a current density of 2 A g−1. In symmetric supercapacitor, the specific capacitance of the sample PCS-8 is 180 F g−1 at a current density of 0.2 A g−1 and has excellent rate capability. The proposed strategy offers a facile and green method to produce porous carbon spheres from coal, and has potential application in energy storage.