Enhanced Photocatalytic Hydrogen‐Production Performance of Graphene–ZnxCd1−xS Composites by Using an Organic S Source

In response to the increasing concerns over energy and environmental sustainability, photocatalytic water‐splitting technology has attracted broad attention for its application in directly converting solar energy to valuable hydrogen (H₂) energy. In this study, high‐efficiency visible‐light‐driven photocatalytic H₂ production without the assistance of precious‐metal cocatalysts was achieved on graphene–Zn_xCd_1?xS composites with controlled compositions. The graphene‐Zn_xCd_1?xS composites were for the first time fabricated by a one‐step hydrothermal method with thiourea as an organic S source. It was found that thiourea facilitates heterogeneous nucleation of Zn_xCd_1?xS and in situ growth of Zn_xCd_1?xS nanoparticles on graphene nanosheets. Such a scenario results in abundant and intimate interfacial contact between graphene and Zn_xCd_1?xS nanoparticles, efficient transfer of the photogenerated charge carriers, and enhanced photocatalytic activity for H₂ production. The highest H₂‐production rate of 1.06 mmol h^?1 g^?1 was achieved on a graphene–Zn_0.5Cd_0.5S composite photocatalyst with a graphene content of 0.5 wt %, and the apparent quantum efficiency was 19.8 % at 420 nm. In comparison, the graphene–Zn_xCd_1?xS composite photocatalyst prepared by using an inorganic S source such as Na₂S exhibited much lower activity for photocatalytic H₂ production. In this case, homogeneous nucleation of Zn_xCd_1?xS becomes predominant and results in insufficient and loose contact with the graphene backbone through weak van der Waals forces and a large particle size. This study highlights the significance of the choice of S source in the design and fabrication of advanced graphene‐based sulfide photocatalytic materials with enhanced activity for photocatalytic H₂ production.     

Synthesis,Crystal Structure,and Photocatalytic Properties of a Zinc(II) Coordination Polymer Based on 3‐Hydroxy‐2‐pyridinecarboxylic Acid

The zinc(II) compound, [Zn₃(HL)₆]_n ( 1 ) (H₂L = 3‐hydroxypyridine‐2‐carboxylic acid) was synthesized by a solvothermal reaction of Zn(NO₃)₂ · 6H₂O and 3‐hydroxypyridine‐2‐carboxylic acid as raw materials. The structure of complex 1 was determined by single‐crystal X‐ray diffraction analysis and further characterized by elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, as well as powder X‐ray diffraction. X‐ray structure analysis demonstrates that the complex crystallizes in the monoclinic system, space group P2₁/n. There are three zinc ions in the asymmetric unit, which are either five‐coordinate or six‐coordinate. The asymmetric units are further bridged by the carboxylate of the organic ligands, featuring a 2D framework. The solid state diffuse‐reflectance UV/Vis spectra reveals that complex 1 has semiconducting nature with the energy bandgap (E_g) estimated to be 3.11 eV. The photocatalytic properties of complex 1 in degradation of organic dyes were further investigated. Results showed that the complex could degrade 54 % of the dye methylene blue solution within 120 min under UV irradiation light and reused for five times without the decline of the photocatalytic activity.     

Comparison of the structure of (E)‐2‐(2‐benzylidenehydrazinylidene)quinoxaline with those of its chloro‐ and bromobenzylidene analogues

(E)‐2‐(2‐Benzylidenehydrazinylidene)quinoxaline, C₁₅H₁₂N₄, crystallized with two molecules in the asymmetric unit. The structures of six halogen derivatives of this compound were also investigated: (E)‐2‐[2‐(2‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(3‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(4‐chlorobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁ClN₄; (E)‐2‐[2‐(2‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄; (E)‐2‐[2‐(3‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄; (E)‐2‐[2‐(4‐bromobenzylidene)hydrazinylidene]quinoxaline, C₁₅H₁₁BrN₄. The 3‐Cl and 3‐Br compounds are isomorphous, as are the 4‐Cl and 4‐Br compounds. In all of these compounds, it was found that the supramolecular structures are governed by similar predominant patterns, viz. strong intermolecular N—H...N(pyrazine) hydrogen bonds supplemented by weak C—H...N(pyrazine) hydrogen‐bond interactions in the 2‐ and 3‐halo compounds and by C—H...Cl/Br interactions in the 4‐halo compounds. In all compounds, there are π–π stacking interactions.     

A series of substituted (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐phenylprop‐2‐en‐1‐ones

In the molecular structures of a series of substituted chalcones, namely (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐phenylprop‐2‐en‐1‐one, C₂₁H₁₅FO₂, (I), (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐fluorophenyl)prop‐2‐en‐1‐one, C₂₁H₁₄F₂O₂, (II), (2E)‐1‐(4‐chlorophenyl)‐3‐(2‐fluoro‐4‐phenoxyphenyl)prop‐2‐en‐1‐one, C₂₁H₁₄ClFO₂, (III), (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐methylphenyl)prop‐2‐en‐1‐one, C₂₂H₁₇FO₂, (IV), and (2E)‐3‐(2‐fluoro‐4‐phenoxyphenyl)‐1‐(4‐methoxyphenyl)prop‐2‐en‐1‐one, C₂₂H₁₇FO₃, (V), the configuration of the keto group with respect to the olefinic double bond is s‐cis. The molecules pack utilizing weak C—H...O and C—H...π intermolecular contacts. Identical packing motifs involving C—H...O interactions, forming both chains and dimers, along with C—H...π dimers and π–π aromatic interactions are observed in the fluoro, chloro and methyl derivatives.     

Triterpenoide. XIX. 3β‐Hydroxy‐11‐oxo‐18α‐olean‐12‐en‐28‐säure‐methyl­ester und 3,11‐Dioxo‐18α‐olean‐12‐en‐28‐säure‐methyl­ester

The X‐ray crystal structure analyses of 3β‐hydroxy‐11‐oxo‐18α‐olean‐12‐en‐28‐oic acid methyl ester ethanol solvate, C₃₁H₄₈O₄·C₂H₆O, (I), and 3,11‐dioxo‐18α‐olean‐12‐en‐28‐oic acid methyl ester, C₃₁H₄₆O₄, (II), are described. These two compounds differ only in the structure of ring A. In (I), ring A has a chair conformation, while in (II), it has a twisted boat conformation. In both compounds, ring C has a slightly distorted sofa conformation, rings B, D and E are in chair conformations, and rings D and E are trans‐fused. The asymmetric unit of (I) contains one mol­ecule of ethanol linked by hydrogen bonds with two different mol­ecules of (I).     

Two‐Phase System Utilizing Hydrophobic Metal–Organic Frameworks (MOFs) for Photocatalytic Synthesis of Hydrogen Peroxide

Much effort has been devoted to photocatalytic production of hydrogen peroxide (H₂O₂) as an alternative to fossil fuels. From an economic point of view, reductive synthesis of H₂O₂ from O₂ coupled with the oxidative synthesis of value‐added products is particularly interesting. We herein report application of MIL‐125‐NH₂, a photoactive metal–organic framework (MOF), to a benzylalcohol/water two‐phase system that realized photocatalytic production and spontaneous separation of H₂O₂ and benzaldehyde. Hydrophobization of the MOF enabled its separation from the aqueous phase. This resulted in enhanced photocatalytic efficiency and enabled application of various aqueous solutions including extremely low pH solution which is favorable for H₂O₂ production but fatal to MOF structure. In addition, a highly concentrated H₂O₂ solution was obtained by simply reducing the volume of the aqueous phase.     

Two 9‐[(E)‐nitrophenylvinyl]‐9H‐carbazoles

The crystal structures of 9‐[(E)‐(4‐nitrophenyl)vinyl]‐9H‐carbazole and 9‐[(E)‐(3‐nitrophenyl)vinyl]‐9H‐carbazole, both C₂₀H₁₄N₂O₂, are determined mainly by van der Waals forces and π–π interactions between the carbazole and benzene systems. However, the packing modes are different. In the 4‐nitro derivative, the molecules in the weakly bound stack are related by a unit‐cell translation, while in the 3‐nitro derivative there are centrosymmetric pairs of molecules joined by π–π interactions and also pairs of molecules, related by another centre of symmetry, connected by eight relatively short C—H...O interactions.     

Synthesis,crystal structure studies and solvatochromic behaviour of two 2‐{5‐[4‐(dimethylamino)phenyl]penta‐2,4‐dien‐1‐ylidene}malononitrile derivatives

The synthesis, crystal structure studies and solvatochromic behavior of 2‐{(2E,4E)‐5‐[4‐(dimethylamino)phenyl]penta‐2,4‐dien‐1‐ylidene}malononitrile, C₁₆H₁₅N₃ (DCV[3]), and 2‐{(2E,4E,6E)‐7‐[4‐(dimethylamino)phenyl]hepta‐2,4,6‐trien‐1‐ylidene}malononitrile, C₁₈H₁₇N₃ (DCV[4]), are reported and discussed in comparison with their homologs having a shorter length of the π‐conjugated bridge. The compounds of this series have potential use as nonlinear materials with second‐order effects due to their donor–acceptor structures. However, DCV[3] and DCV[4] crystallized in the centrosymmetric space group P2₁/c which excludes their application as nonlinear optical materials in the crystalline state. They both crystallize with two independent molecules having the same molecular conformation in the asymmetric unit. The series DCV[1]–DCV[4] demonstrated reversed solvatochromic behavior in toluene, chloroform, and acetonitrile.     

Synthesis,Characterization, and Photocatalytic Properties of Bismuth (III)‐benzene‐1,3,5‐tricarboxylate

{[Bi(BTC)(H₂O)₂] · H₂O}_n (H₃BTC = 1,3,5‐benzenetricarboxylic acid) was synthesized by an eco‐friendly hydrothermal method and characterized by single‐crystal X‐ray diffraction, IR and UV/Vis spectroscopy, photoluminescence (PL), and thermogravimetric analyses. The complex featured a 3D metal‐organic framework with Bi₂ secondary building units. In the complex, the central Bi³⁺ is nine‐coordinate, three central Bi atoms and three BTC^3– anions are interconnected into a ring with the dimension of 7.95 × 9.89 Ų. Moreover, the complex is decomposed at over 388 °C, showing its highly thermal stability. Further, the complex exhibits photocatalytic activity for the degradation of methyl orange (MO) solution under UV light irradiation, and its structure can keep consistent with the original one after 9 h photocatalytic reaction, indicating that it is also very stable under UV light. Therefore, it could be anticipated the novel coordination complex will be a stable ultraviolet light catalyst.     

Novel asymmetric 3,5‐bis(arylidene)piperidin‐4‐one derivatives: synthesis,crystal structures and cytotoxicity

3,5‐Bis(arylidene)piperidin‐4‐one derivatives (BAPs) display good antitumour activity because of their double α,β‐unsaturated ketone structural characteristics. Reported BAPs have generally been symmetric and asymmetric BAPs have been little documented. Three asymmetric BAPs, namely (5E)‐3‐(4‐tert‐butylbenzylidene)‐5‐(4‐fluorobenzylidene)‐1‐methylpiperidin‐4‐one, C₂₄H₂₆FNO, ( 5 ), (5E)‐3‐(4‐tert‐butylbenzylidene)‐5‐(3,5‐dimethoxybenzylidene)‐1‐methylpiperidin‐4‐one, C₂₆H₃₁NO₃, ( 6 ), and (5E)‐3‐{3‐[(E)‐(2,3‐dihydroxybenzylidene)amino]benzylidene}‐5‐(2‐fluorobenzylidene)‐1‐methylpiperidin‐4‐one, C₂₇H₂₃FN₂O₃, ( 12 ), were generated by Claisen–Schmidt condensation. They are characterized by NMR and FT–IR spectroscopies, and elemental analysis. Single‐crystal structure analysis reveals that the two arylidene rings on both sides of the BAP structures adopt an E stereochemistry of the olefinic double bonds and the compounds are E,E isomers. Molecules of ( 5 ) and ( 12 ) generate one‐dimensional chains through intermolecular hydrogen bonds, while compound ( 6 ) generates a two‐dimensional network through hydrogen bonds. Preliminary cytotoxicities toward human liver hepatocellular carcinoma cell line (HepG2), human acute mononuclear granulocyte leukaemia (THP‐1) and human normal hepatical cell line (LO2) were evaluated.     

A Facile Method for Producing Selenocysteine‐Containing Proteins

Selenocysteine (Sec, U) confers new chemical properties on proteins. Improved tools are thus required that enable Sec insertion into any desired position of a protein. We report a facile method for synthesizing selenoproteins with multiple Sec residues by expanding the genetic code of Escherichia coli. We recently discovered allo‐tRNAs, tRNA species with unusual structure, that are as efficient serine acceptors as E. coli tRNA^Ser. Ser‐allo‐tRNA was converted into Sec‐allo‐tRNA by Aeromonas salmonicida selenocysteine synthase (SelA). Sec‐allo‐tRNA variants were able to read through five UAG codons in the fdhF mRNA coding for E. coli formate dehydrogenase H, and produced active FDH_H with five Sec residues in E. coli. Engineering of the E. coli selenium metabolism along with mutational changes in allo‐tRNA and SelA improved the yield and purity of recombinant human glutathione peroxidase 1 (to over 80 %). Thus, our allo‐tRNA^UTu system offers a new selenoprotein engineering platform.     

Biocatalytic Properties of a Recombinant <Emphasis Type="Italic">Fusarium proliferatum</Emphasis> Lactonase with Significantly Enhanced Production by Optimal Expression in <Emphasis Type="Italic">Escherichia coli</Emphasis>

The levo-lactonase gene of Fusarium proliferatum ECU2002 (EC3.1.1.25) was cloned and expressed in Escherichia coli JM109 (DE3) for biocatalytic resolution of industrially important chiral lactones, including DL-pantoyl lactone which was a key precursor to calcium d-pantothenate. By increasing the biomass concentration and lowering the inducer (isopropyl-β-d-thiogalactoside) concentration and induction temperature, the lactonase production was significantly enhanced up to 20 kU/L, which was 20 times higher than that of wild-type strain F. proliferatum ECU2002. The recombinant Fusarium lactonase was purified using immobilized metal affinity chromatography, and its SDS-PAGE revealed a molecular mass of 50 kDa for the recombinant protein, suggesting that the enzyme was a simplex protein. Furthermore, biocatalytic properties of the recombinant lactonase were investigated, including kinetic parameters, additive’s effect, and substrate specificity. The results reported in this paper provide a feasible method to make the whole cells of E. coli JM109 (DE3) expressing lactonase gene to be a highly efficient and easy-to-make biocatalyst for asymmetric synthesis of chiral compounds.     

Two derivatives of 1,5‐disubstituted tetrazoles: 1‐(4‐nitrophenyl)‐1H‐tetrazol‐5‐amine and {(E)‐[1‐(4‐ethoxyphenyl)‐1H‐tetrazol‐5‐yl]iminomethyl}dimethylamine

The geometric features of 1‐(4‐nitrophenyl)‐1H‐tetrazol‐5‐amine, C₇H₆N₆O₂, correspond to the presence of the essential interaction of the 5‐amino group lone pair with the π system of the tetrazole ring. Intermolecular N—H...N and N—H...O hydrogen bonds result in the formation of infinite chains running along the [110] direction and involve centrosymmetric ring structures with motifs R₂²(8) and R₂²(20). Molecules of {(E)‐[1‐(4‐ethoxyphenyl)‐1H‐tetrazol‐5‐yl]iminomethyl}dimethylamine, C₁₂H₁₆N₆O, are essentially flattened, which facilitates the formation of a conjugated system spanning the whole molecule. Conjugation in the azomethine N=C—N fragment results in practically the same length for the formal double and single bonds.     

Whole‐Cell Biotransformation of Benzene to Phenol Catalysed by Intracellular Cytochrome P450BM3 Activated by External Additives

An Escherichia coli whole‐cell biocatalyst for the direct hydroxylation of benzene to phenol has been developed. By adding amino acid derivatives as decoy molecules to the culture medium, wild‐type cytochrome P450BM3 (P450BM3) expressed in E.coli can be activated and non‐native substrates hydroxylated, without supplementing with NADPH. The yield of phenol reached 59 % when N‐heptyl‐l ‐prolyl‐l ‐phenylalanine (C7‐Pro‐Phe) was employed as the decoy molecule. It was shown that decoy molecules, especially those lacking fluorination, reached the cytosol of E. coli, thus imparting in vivo catalytic activity for the oxyfunctionalisation of non‐native substrates to intracellular P450BM3.     

Two hydrazones derived from 1‐aryl‐3‐(p‐substituted phenyl)prop‐2‐en‐1‐one: synthesis,crystal structure,Hirshfeld surface analysis and in vitro biological properties

Two chalcones were synthesized by the aldolic condensation of enolizable aromatic ketones with substituted benzaldehydes under Claisen–Schmidt reaction conditions and then treated with 2,4‐dinitrophenylhydrazine to yield their corresponding hydrazones. The two (E,Z)‐2,4‐dinitrophenylhydrazone structures, namely (Z)‐1‐(2,4‐dinitrophenyl)‐2‐[(E)‐3‐(4‐methylphenyl)‐1‐phenylallylidene]hydrazine, C₂₂H₁₈N₄O₄, ( H1 ), and (Z)‐1‐[(E)‐3‐(4‐chlorophenyl)‐1‐(naphthalen‐1‐yl)allylidene]‐2‐(2,4‐dinitrophenyl)hydrazine, C₂₅H₁₇ClN₄O₄, ( H2 ), were isolated by recrystallization and characterized by FT–IR, UV–Vis, single‐crystal and powder X‐ray diffraction methods. The UV–Vis spectra of the hydrazones have been studied in two organic solvents of different polarity. It was found that ( H2 ) has a molar extinction coefficient larger than 40000. Single‐crystal X‐ray diffraction analysis reveals that the molecular zigzag chains of ( H1 ) and ( H2 ) are interconnected through noncovalent contacts. A quantitative analysis of the intermolecular interactions in the crystal structures has been performed using Hirshfeld surface analysis. All the synthesized chalcones and hydrazones were evaluated for their antibacterial and antioxidant activities. Results indicate that the studied compounds show significant activity against Gram negative Escherichia coli strain and the chalcone 3‐(4‐methylphenyl)‐1‐phenylprop‐2‐en‐1‐one, ( C1 ), was the most effective. In addition, only hydrazone ( H1 ) displayed a moderate DPPH (2,2‐diphenyl‐1‐picryl hydrazyl) scavenging efficiency.     

Bases,solvates and salts: new benzimidazole‐ and pyridine‐scaffolded ligands

The intermolecular interactions in the structures of a series of Schiff base ligands have been thoroughly studied. These ligands can be obtained in different forms, namely, as the free base 2‐[(2E)‐2‐(1H‐imidazol‐4‐ylmethylidene)‐1‐methylhydrazinyl]pyridine, C₁₀H₁₁N₅, 1 , the hydrates 2‐[(2E)‐2‐(1H‐imidazol‐2‐ylmethylidene)‐1‐methylhydrazinyl]‐1H‐benzimidazole monohydrate, C₁₂H₁₂N₆·H₂O, 2 , and 2‐{(2E)‐1‐methyl‐2‐[(1‐methyl‐1H‐imidazol‐2‐yl)methylidene]hydrazinyl}‐1H‐benzimidazole 1.25‐hydrate, C₁₃H₁₄N₆·1.25H₂O, 3 , the monocationic hydrate 5‐{(1E)‐[2‐(1H‐1,3‐benzodiazol‐2‐yl)‐2‐methylhydrazinylidene]methyl}‐1H‐imidazol‐3‐ium trifluoromethanesulfonate monohydrate, C₁₂H₁₃N₆⁺·CF₃O₃S^?·H₂O, 5 , and the dicationic 2‐{(2E)‐1‐methyl‐2‐[(1H‐imidazol‐3‐ium‐2‐yl)methylidene]hydrazinyl}pyridinium bis(trifluoromethanesulfonate), C₁₀H₁₃N₅²⁺·2CF₃O₃S^?, 6 . The connection between the forms and the preferred intermolecular interactions is described and further studied by means of the calculation of the interaction energies between the neutral and charged components of the crystal structures. These studies show that, in general, the most important contribution to the stabilization energy of the crystal is provided by π–π interactions, especially between charged ligands, while the details of the crystal architecture are influenced by directional interactions, especially relatively strong hydrogen bonds. In one of the structures, a very interesting example of the nontypical F…O interaction was found and its length, 2.859 (2) Å, is one of the shortest ever reported.     

Sol‐Gel Synthesis and Photocatalytic Study of Visible Light Active N‐Doped KSbWO6

KSbWO₆ was prepared by sol‐gel method. N‐doped KSbWO₆ (KSbWO_6–xN_x) was obtained by heating KSbWO₆ and urea at 400 °C. Both the compounds are characterized by powder X‐ray diffraction (XRD), TEM, SEM‐EDS, X‐ray photo electronic spectroscopy (XPS), and UV/Vis diffuse reflectance spectroscopy (UV‐DRS). A shift in the peak positions of powder XRD and XPS spectra was observed. The band gap energy (E_g) of KSbWO₆ and N‐doped KSbWO₆ was obtained from their diffused reflectance spectra.E_g was reduced from 3.17 eV to 2.56 eV upon nitrogen doping in KSbWO₆. The reduction of the E_g is attributed to the lifting of valence band of N‐doped KSbWO₆, due to the mixing of O 2p states with N 2p states. The photocatalytic activity of both the samples was studied by degradation of methylene blue (MB). The nitrogen doped KSbWO₆ shows higher photocatalytic activity compared to that of KSbWO₆.     

An Alkene‐Promoted Borane‐Catalyzed Highly Stereoselective Hydrogenation of Alkynes to Give Z‐ and E‐Alkenes

The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Z‐alkenes, the hydrogenation of alkynes to give E‐alkenes is still not well resolved. In particular, selective preparation of both Z‐ and E‐alkenes by the same catalytic hydrogenation system using molecular H₂ has rarely been reported. In this paper, a novel strategy of using simple alkenes as promoters for the HB(C₆F₅)₂‐catalyzed metal‐free hydrogenation of alkynes was adopted. Significantly, both Z‐ and E‐alkenes can be furnished by hydrogenation with molecular H₂ in high yields with excellent stereoselectivities. Further experimental and theoretical mechanistic studies suggest that interactions between H and F atoms of the alkene promoter, borane intermediate, and H₂ play an essential role in promoting the hydrogenolysis reaction.     

Preparation and Photocatalytic Activity of Mesoporous TiO2 Photocatalyst Co‐doped with Fe and H3PW12O40

The mesoporous titanium dioxide (MTiO₂) photocatalysts co‐doped with Fe and H₃PW₁₂O₄₀ were synthesized by template method using tetrabutyl titanate (Ti(OC₄H₉)₄), Fe(NO₃)k₃9H₂Oand H₃PW₁₂O₄₀ as precursors and Pluronic P123 as template. The as‐prepared photocatalyst was characterized by N₂ adsorption‐desorption measurements, X‐ray diffraction (XRD), scanning electron microscopy (SEM) and UV‐vis adsorption spectroscopy, and the photocatalytic activities of the prepared samples under UV and visible light were estimated by measuring the degradation rate of methyl blue (MB) (50 mg/L) in an aqueous solution. The characterizations indicated that the photocatalysts possessed a homogeneous pore diameter of ca. 10 nm with high surface area of ca. 150 m²/g. The results of MB photodecomposition showed that co‐doped mesoporous TiO₂ exhibited higher photocatalytic activities than un‐doped, single‐doped mesoporous TiO₂ under UV and visible light irradiation. It was shown that the co‐doped MTiO₂ could be activated by visible light and could thus be used as an effective catalyst in photo‐oxidation reactions. The synergistic effect of Fe and H₃PW₁₂O₄₀ co‐doping played an important role in improving the photocatalytic activity.