Catalytic epoxidation of β-pinene with aqueous hydrogen peroxide

Epoxidation of β-pinene with 35–38% aqueous hydrogen peroxide in a new catalytic system containing manganese sulfate, salicylic acid, sodium bicarbonate and polar solvent (DMF, acetonitrile, methanol) is described. The method of quantitavive determination of β-pinene and its epoxide is developed.     

Iron-catalyzed hydroxylation of β-ketoesters with hydrogen peroxide as oxidant

The hydroxylation of β-ketoesters was studied using simple iron catalysts and 30 wt % hydrogen peroxide as the terminal oxidant. The highest activity and yield were achieved in the presence of iron(III) chloride. Cyclic β-ketoesters could be smoothly hydroxylated in 75-90% yield. For linear β-ketoester and β-ketoamide, the chloro-substituted products were obtained.     

Analytical sensing of hydrogen peroxide on Ag nanoparticles–multiwalled carbon nanotube-modified glassy carbon electrode

A sensor based on silver nanoparticles (NPs)/multiwalled carbon nanotube (CNT)-modified glassy carbon electrode (GCE) was prepared and employed for accurate and rapid determination of hydrogen peroxide (H₂O₂). In summary, by using a mechanochemical method, multiwalled CNTs dispersed in ethanol and used for modification of GCE. After that, by using a double-pulse technique, silver NPs are electrodeposited on surface of multiwalled CNTs/ GCE. Parameters that are affected by electrocatalytic reduction of H₂O₂ on the modified electrode, such as multiwalled CNT concentration and double-pulse parameters, were optimized using Minitab software. The optimal modified electrode was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and cyclic voltammetry. The proposed H₂O₂ sensor exhibited excellent characteristics for the sensing of H₂O₂, such as wide linear range from 0.1 to 10 mM, a low detection limit of 2 μM, high repeatability, and no interference by a number of substances.     

Synthesis of the iron phthalocyaninate radical cation μ-nitrido dimer and its interaction with hydrogen peroxide

The iron phthalocyaninate μ-nitrido dimer radical cation, as well as the μ-nitrido dimer complexes of iron phthalocyaninate, was found to have high catalytic activity in the oxidation of organic compounds. It was concluded that this compound is of interest as a model of active intermediates—catalase and oxidase enzymes.     

NMR and molecular modelling studies on the interaction of fluconazole with β-cyclodextrin

Background  

Fluconazole (FLZ) is a synthetic, bistriazole antifungal agent, effective in treating superficial and systemic infections caused by Candida species. Major challenges in formulating this drug for clinical applications include solubility enhancement and improving stability in biological systems. Cyclodextrins (CDs) are chiral, truncated cone shaped macrocyles, and can easily encapsulate fluconazole inside their hydrophobic cavity. NMR spectroscopy has been recognized as an important tool for the interaction study of cyclodextrin and pharmaceutical compounds in solution state.     

Synthesis of ɛ-caprolactone with stable hydrogen peroxide adducts

Oxidation of cyclohexanone to ?-caprolactone with stable industrially manufactured hydrogen peroxide derivatives: adduct with urea (urea hydrogen peroxide), sodium perborate, sodium percarbonate (Persol), magnesium monoperphthalate (Dismozon) was studied. Oxidation with urea hydrogen peroxide is the most efficient in hexafluoroisopropanol in the case of preliminary removal of urea in the form of an oxalate. Oxidation with sodium perborate and percarbonate provides high yields in trifluoroacetic acid. The lowest cost process consists in interaction with sodium monoperphthalate (Persol and phthalic anhydride) in an aqueous medium.     

Enantioselective formation of quaternary centers on β-ketoesters with chiral palladium QUIPHOS catalyst

Asymmetric formation of quaternary centers by allylic alkylation of β-ketoesters using the chiral palladium QUIPHOS catalyst has been achieved. The results obtained not only depend on the reaction conditions but also on the structural features of both β-ketoesters and allylating agents. Enantiomeric excesses of up to 95% have been observed.     

Experimental study on high-pressure adsorption of hydrogen on activated carbon

A systematic measurement of H2 adsorption on activated carbon over a wide scope of conditions was completed for the first time using a novel cryostat developed by the present authors. The equilibrium temperatures covered 77-298 K with the space of about 20 K, and the equilibrium pressures increased from 0 to about 7MPa. A set of adsorption/desorption isotherms was obtained by a standard volumetric method. This set of experimental data was fitted to all the well-known models of type-I isotherms, and Dubinin-Astakhov (D-A) equation was found to be the best-fit one On the basis of D-A model one can predict adsorption with relative error of ±4%. A 3-dimensional adsorption surface was also constructed, and the isosteric heat of adsorption was analytically determined. Except in the low pressure area, the calculated values agreed well with the experimental ones. Finally, the troubles encountered in applying D-A equation to supercritical adsorption is discussed.     

Non-enzymatic sensing of hydrogen peroxide using a glassy carbon electrode modified with a composite consisting of chitosan‐encapsulated graphite and platinum nanoparticles

We report on a non-enzymatic hydrogen peroxide (H₂O₂) sensor which makes use of a nanocomposite consisting of platinum nanoparticles (PtNPs) and chitosan-encapsulated graphite (graphite-CS). The composite was prepared by sonication of pristine graphite in chitosan (CS) in 5 % acetic acid. The PtNP decorated graphite-CS (graphite-CS/PtNPs) composite was prepared by electrodeposition of PtNPs on the graphite-CS modified glassy carbon electrode. The graphite-CS/PtNP composite was characterized by scanning electron microscopy, elemental analysis and FTIR spectroscopy. The modified electrode displays an enhanced reduction peak current for H₂O₂ when compared with electrodes modified with graphite/PtNPs and PtNPs. The modified electrode exhibits excellent electrocatalytic activity towards the reduction of H₂O₂, and the amperometric response is linear over the concentration range from 0.25 to 2890 μM. The sensitivity and the detection limit are 0.465 μA?μM￣¹ ? cm￣² and 66 nM, respectively. The sensor shows fast response (3 s) in detecting H₂O₂. It is also highly selective in the presence of potentially interfering compounds, and may therefore be used as a feasible platform for sensing H₂O₂ in real samples.

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Graphical abstract Preparation of graphite-CS/PtNP composite, and its application to electrochemical reduction of H₂O₂.

     

Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-aniline complex

Sn-aniline complex was prepared by a simple procedure.Cyclic and acyclic ketones were oxidized into lactones or esters with very high selectivity and yield with 30% hydrogen peroxide in the presence of Sn-aniline complex.     

Selective oxidation of sulfides to sulfoxides with cyanuric chloride and urea–hydrogen peroxide adduct

Although a number of methods have been developed for the selective oxidation of sulfides to sulfoxides, the need remains for alternative efficient, reliable strategies that can be generally applied to various sulfides and that use readily available reagents under mild reaction conditions. Herein, we report the use of urea–hydrogen peroxide adduct (UHP) and cyanuric chloride in CH₃CN at room temperature to convert sulfides to sulfoxides in excellent yields. In particular, this protocol produced sulfoxides with aromatic rings bearing electron-withdrawing groups in excellent yields.     

Catalytic oxidation and determination of β-NADH using self-assembly hybrid of gold nanoparticles and graphene

A self-assembly hybrid of gold nanoparticles on graphene modified electrodes for low-potential NADH detection has been achieved. We used the natural polymer chitosan (Chit) to assist the stabilization of graphene in aqueous solution, and immobilize the electronegative Au nanoparticles (NPs) through electrostatic attraction. The synergy of Au NPs with graphene for catalytic oxidation of NADH made the overpotential ca. 220 mV less positive than that on the bare electrode, and remarkably increased the oxidation current. The amperometric sensors based on such modified electrodes for detection of NADH exhibited a good linearity from 1.5 to 320 μM, and showed high sensitivity with a low detection limit of 1.2 μM (S/N = 3). It could also exclude common interfering electroactive compounds like ascorbic acid and possessed good reproducibility and operational stability. Such eminent performance of the Au-RGO/Chit film together with the ability of graphene to significantly enhance the electron transfer between enzymes and the electrode suggested its promise for constructing novel graphene based dehydrogenase biosensors.     

Compared effects of “solid-based” hydrogen peroxide pretreatment on disintegration and properties of waste activated sludge

The effects of two solid-based hydrogen peroxides sodium percarbonate(SPC) and calcium peroxide(CP)on waste activated sludge(WAS) disintegration were investigated. Both oxidants achieved efficient WAS disintegration for the synergistic effect of alkaline and oxidation. The strong alkaline condition led to the leakage of ammonia and the existence of abundant calcium ions accelerated the fixation of phosphorus via precipitation in CP WAS disintegration process. However, the spongy-like layer and l...     

Self-regeneration of activated carbon modified with palladium catalyst for electrochemical dechlorination

Catalyst regeneration and the retention of high catalytic activity are still the critical issues in environmental application.A novel fluidized gas-liquid-solid electrochemical reactor was developed to simultaneously remove chlorinated pollutants and in situ regenerate the spent catalyst.Activated carbon modified with palladium catalyst (AC-Pd) was prepared for electrochemical dechlorination.For the 4-chloropbenol wastewater of initial concentration 200 mg L~(-1),the removal efficiency could nearly reach 100% in less than 30 min.Catalytic activity of AC-Pd catalyst was preserved effectively even in consecutive cycling run without special regeneration.OH radicals,generated by electrochemical reaction,played a critical role in self-regeneration of AC-Pd.High catalytic activity of spent AC-Pd catalyst provided an attractive alternative in wastewater treatment.     

Compared effects of “solid-based” hydrogen peroxide pretreatment on disintegration and properties of waste activated sludge

The effects of two solid-based hydrogen peroxides sodium percarbonate(SPC) and calcium peroxide(CP)on waste activated sludge(WAS) disintegration were investigated. Both oxidants achieved efficient WAS disintegration for the synergistic effect of alkaline and oxidation. The strong alkaline condition led to the leakage of ammonia and the existence of abundant calcium ions accelerated the fixation of phosphorus via precipitation in CP WAS disintegration process. However, the spongy-like layer and l...     

An amperometric penicillin biosensor with enhanced sensitivity based on co-immobilization of carbon nanotubes, hematein, and β-lactamase on glassy carbon electrode

An amperometric penicillin biosensor with enhanced sensitivity was successfully developed by co-immobilization of multi-walled carbon nanotubes (MWCNTs), hematein, and β-lactamase on glassy carbon electrode using a layer-by-layer assembly technique. Under catalysis of the immobilized enzyme, penicillin was hydrolyzed, decreasing the local pH. The pH change was monitored amperometrically with hematein as a pH-sensitive redox probe. MWCNTs were used as an electron transfer enhancer as well as an efficient immobilization matrix for the sensitivity enhancement. The effects of immobilization procedure, working potential, enzyme quantity, buffer concentration, and sample matrix were investigated. The biosensor offered a minimum detection limit of 50 nM (19 μg L⁻¹) for penicillin V, lower than those of the conventional pH change-based biosensors by more than two orders of magnitude. The electrode-to-electrode variation of the response sensitivity was 7.0% RSD.     

Combination self-assembly of β-sheet peptides and carbon nanotubes: functionalizing carbon nanotubes with bioactive β-sheet block copolypeptides

Understanding the self-assembly behavior of β-sheet peptides is important, not only in constructing bioactive peptide nanostructures, but also in inhibiting uncontrollable protein aggregation in protein-misfolding diseases. Here, the first systematic investigation of combination self-assembly between β-sheet block copolypeptides and CNTs is presented, demonstrating the presence of several different association modes during the combination self-assembly process. Bioactive β-sheet block copolypeptides can self-assemble by themselves, or can be used to functionalize CNT hybrids depending on the situation. This behavior may be important both for fabricating bioactive peptide/CNT hybrids and for controlling/inhibiting protein-misfolding diseases.     

Electrocatalytic determination of propranolol hydrochloride at carbon paste electrode based on multiwalled carbon-nanotubes and γ-cyclodextrin

A carbon paste electrode based on γ-cyclodextrin–carbon nanotube composite (γ-CD–CNT–CME) was developed for the determination of propranolol hydrochloride (PRO). The electrochemical behaviour of PRO was investigated employing cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse adsorptive stripping voltammetry (DPAdSV). Surface morphology of the electrode has been studied by means of scanning electron microscopy. The results revealed that the oxidation of PRO is facilitated at γ-CD–CNT–CME. Under the optimized conditions in Britton–Robinson buffer pH 1.5, the peak currents were found to vary linearly with their concentrations in the range of 1.42 × 10^?7 to 4.76 × 10^?5 M. A detection limit (S/N = 3) of 4.01 × 10^?8 M was obtained for PRO by means of DPAdSV. The proposed method was employed for the determination of PRO in pharmaceutical formulations, urine and blood serum samples.