Synthesis and catalytic activity of SBA-15 supported catalysts for styrene oxidation

Cu(II) and Mn(II) metals embedded on mesoporous SBA-15 were synthesized by co-precipitation technique.The support and catalysts were characterized by SEM–EDX,TEM,BET,XRD and ICP-AES methods.The catalytic activity of these catalysts was evaluated for styrene oxidation at various reaction conditions such as styrene to TBHP mole ratio,temperature,catalyst amount by using TBHP as an oxidizing agent.Major reaction products were styrene oxide and benzaldehyde and highest styrene conversion(97.3%) was observed at styrene to TBHP mole ratio of 1:4,temperature at 80 °C and 20 mg of catalyst.Further,the recyclability of the catalysts was observed and found that they can be recycled three times without major loss in their activity and selectivity.

A novel manganese tungstate nanorod catalyst for the oxidation of styrene with tert-butyl hydroperoxide as oxidant

Catalyst,solvent and process parameters are the keys for the selective oxidation of styrene and other olefins to value added intermediates.Hence MnWO_(4)was synthesized by the one-pot hydrothermal method using Pluronic F127 as a surfactant,characterized and evaluated for the oxidation of styrene and different olefins,using tert-butyl hydroperoxide(TBHP)as oxidant.X-ray diffractogram confirmed the phase purity of MnWO_(4)which became further evident from the near surface equimolar proposition of Mn and W in+2 and+6 oxidation states,respectively,as inferred from X-ray photoelectron spectra.N_(2)sorption followed typeⅣa isotherm with H_(3)hysteresis loop,starting at the relative pressure(P/P_(o))of 0.9,typically of mesoporous materials containing macropores as further confirmed by pore-size distribution.Transmission electron microscope images of MnWO_(4)revealed its nanorod morphology.In the absence of catalyst,styrene conversion was 35%with benzaldehyde as the sole product and addition of 75 g of MnWO_(4)increased the styrene conversion to 97.3%,and the styrene oxide selectivity from 0%to 85%demonstrated its activity and selectivity.For the maximum conversion and styrene oxide selectivity optimum temperature,styrene:TBHP molar ratio,catalyst amount and solvent were found to be 70℃,1:2,75 mg,and acetonitrile,respectively.MnWO_(4)catalyst retained its activity and selectivity for five recycles,confirming its recoverability and reusability.From the kinetic studies,pre-exponential factor and apparent activation energy were found to be 0.206 s^(-1)and 31.5 kJ·mol^(-1),respectively,and a reaction mechanism was proposed.MnWO_(4)catalyst was active for oxidation of alkenes,cycloolefins and alkenyl aromatics with high selectivity for epoxides.

Analysis of styrene oxide-hemoglobin adducts at different binding sites

An assay was described for measures of adducts of styrene oxide (SO) with molecules of hemoglobin(Hb) which have been modified at residues containing either carboxylic acid or sulfhydryl groups. The method employs two steps. In the first, SO carboxylic acid adducts are hydrolyzed in basic medium to liberate styrene glycol(SG). Then, the remaining residues are reacted with a reductive catalyst (Raney nickel) to liberate the two positional isomers of SO cysteine adducts, i.e., 1 phenylethanol (1 PE) and 2 phenylethanol (2 PE). The liberated products are derivatized with pentafluorobenzoyl chloride and measured by GC NICI MS. The assay was evaluated with SO adducts of Hb which had been produced in the blood of Sprague Dawley rats following (a) in vitro modification(0—300m mol/L SO) or (b) i.p administration of either SO(0—1 mmol/kg) or styrene (0—3 mmol/kg). Levels of each of the three analytes (SG, 1 PE, and 2 PE) increased with dose in hemoglobin. The ratios of cysteine adducts to carboxylic acid adducts varied significantly among experiments. Ratios of 2 PE to 1 PE were much more consistent (2 PE/1 PE=6.9 (SE=1.5)) suggesting that binding of SO to cysteine residues of blood proteins is greatly preferred at the α position rather than the β position both in vitro and in vivo. The lowest detectable adduct concentration, using 10 mg of protein, was 8 pmol/g protein for SG,5 pmol/g protein for 1 PE, and 0.6 pmol/g protein for 2 PE. No significant change of adduct level was found during storage of proteins at -80℃ for 1 year.

SYNTHESIS AND CHARACTERIZATION OF POLY(STYRENE - ETHYLENE OXIDE) DIBLOCK COPOLYMERS

Well - defined diblock copolymers Of styrene (St ) and ethylene oxide (EO )have been prepared by sequential living anionic polymerization of the twocomonomers in THF. Diphenyl methyl potassium has been used as initiator. Theblock copolymers were characterized in detail by methods Of size exclusion chromatography (SEC ) , 1H - Nab, FT - IR, dynamic mechanical analysis(Daal ) and WAXD.

Designing polyoxometalate-based metal-organic framework for oxidation of styrene and cycloaddition of CO_(2) with epoxides

A photoactive polyoxometalate-based metal-organic framework (POMOF),NiW-DPNDI,was synthesized by combination of Ni(Ⅱ) ions,[ZnW_(12)O_(40)]^(6–)anions,and N,N’-bis(4-pyridylmethyl)naphthalene diimide(DPNDI) molecules into one single framework.Ni W-DPNDI displays a three-dimensional structure by the strong anion···π interactions between the trapped[ZnW_(12)O_(40)]^(6–)anions and the electron-deficient naphthalenic ring centroids and theπ-πstacking interactions between DPNDI moieties.Ni W-DPNDI displayed a highly efficient hole-electron separation and ordered electron transfer under irradiation,thus ensuing its excellent photocatalysis in oxidation of styrene to produce benzaldehyde.In addition,it gave a high efficiency for styrene oxide under thermocatalytic conditions.Because the carbonic anhydrase (CA)-mimicking Ni sites and the negative electron-enriched[ZnW_(12)O_(40)]^(6–)anions are well aligned in the pores,it can promote the cycloaddition of CO_(2) with epoxides under mild conditions.

Synthesis of lathanum or La-B doped KIT-6 mesoporous materials and their application in the catalytic oxidation of styrene

La-doped and La-B-doped KIT-6 mesoporous materials were prepared by direct hydrothermal synthesis with pH-adjusting method and characterized by X-ray diffractometer(XRD),nitrogen sorption,FT-IR,UV-Vis,X-ray photoelectron spectroscopy(XPS) and ICP-AES.The catalytic performance for the oxidation of styrene by hydrogen peroxide,tert-butyl hydroperoxide or oxygen was investigated.The results showed that the introduction of heteroatoms did not destroy the mesostructure of KIT-6 with cubic Ia3d space group.La or ...

THE RING OPENING REACTION OF AN EPOXY COMPOUND ON THE TOP OF CHEMISORBED CYSTAMINE STUDIED BY THE SERS TECHNIQUE

Metal foils for Raman scattering were prepared by HNO_3 etching method. These foils werefound to exhibit a strong SERS effect and excellent thermal stability. SERS spectra of cystaminehave been taken to illustrate the usefulness of this sample preparation method in the studies ofchemisorption. The ring opening reactions of an epoxy compound have been observed on the topof chemisorbed cystamine on silver foils.

Synthesis of amorphous Pd-based nanocatalysts for efficient alcoholysis of styrene oxide and electrochemical hydrogen evolution

Amorphous nanomaterials with long-range disordered structures could possess distinct properties and promising applications,especially in catalysis,as compared with their conventional crystalline counterparts.It is imperative to achieve the controlled preparation of amorphous noble metal-based nanomaterials for the exploration of their phase-dependent applications.Here,we report a facile wet-chemical reduction strategy to synthesize various amorphous multimetallic Pd-based nanomaterials,including PdRu,PdRh,and PdRuRh.The phase-dependent catalytic performances of distinct Pd-based nanomaterials towards diverse catalytic applications have been demonstrated.Specifically,the usage of PdRu nanocatalysts with amorphous and crystalline face-centered cubic(fcc)phases can efficiently switch the ring-opening route of styrene oxide to obtain different products with high selectivity through alcoholysis reaction and hydrogenation reaction,respectively.Moreover,when used as an electrocatalyst for hydrogen evolution reaction(HER),the synthesized amorphous PdRh nanocatalyst exhibits low overpotential and high turnover frequency values,outperforming its crystalline fcc counterpart and most of the reported Pd-based HER electrocatalysts.

Evaluation of DNA adduct damage using G-quadruplex-based DNAzyme

Toxicity assessment is a major problem in pharmaceutical candidates and industry chemicals development.However,due to the lack of practical analytical methods for DNA adduct analysis,the safety evaluation of drug and industry chemicals was severely limited.Here,we develop a DNAzyme-based method to detect DNA adduct damage for toxicity assessment of drugs and chemicals.Among 18 structural variants of G4 DNAzyme,EA2 DNAzyme exhibits an obvious DNA damaging effect of styrene oxide(SO)due to its unstable structure.The covalent binding of SO to DNAzyme disrupts the Hoogsteen hydrogen bonding sites of G-plane guanines and affects the formation of the G4 quadruplex.DNA damage chemicals reduce the peroxidase activity of the G4 DNAzyme to monitor the DNA adduct damage by disrupting the structural integrity of the G4 DNAzyme.Our method for genotoxic assessment of pharmaceutical candidates and industrial chemicals can elucidate the complex chemical pathways leading to toxicity,predict toxic effects of chemicals,and evaluate possible risks to human health.