XPS study of the surface properties and Ni particle size determination of Ni‐supported catalysts

The surface properties of Ni/MgAl₂O₄ catalysts doped with Ce or Pr were analyzed by XPS after treatment in an inert and reductive atmosphere at 400 °C. The Ce‐promoted solids presented the Ce³⁺/Ce⁴⁺ couple on the surface even after treatment in a reductive atmosphere, H₂(5%)/Ar. The promotion effect of Ce on these solids could be associated with their participation on the carbon deposition‐removal mechanism. Pr‐doped catalysts showed a very high concentration of Pr³⁺ under a reductive atmosphere and the redox behavior associated with the carbon removal could be partially inhibited or become slower. The size of the Ni⁰ particles after both an inert and a reductive atmosphere was estimated by XPS intensity ratio using the model proposed by Davis. The results obtained from the Davis model showed that an important increase occurred in Ni particle size after treatment in H₂(5%)/Ar for the Pr‐promoted solids. The metal sintering under reductive atmosphere could be the reason for the higher loss of activity of the Pr‐doped solids under reforming conditions. Copyright © 2014 John Wiley & Sons, Ltd.     

Chemiluminescence determination of citrate and pyruvate and their mixtures by the stopped-flow mixing technique

A novel kinetic chemiluminescent method using the stopped-flow mixing technique has been investigated for the rapid and sensitive determination of citrate and pyruvate. The method is based on a tris(2,2′-bipyridiyl)ruthenium(III) (Ru(bpy)₃³⁺) chemiluminescence (CL) reaction. Ru(bpy)₃³⁺ was generated in the mixing chamber by oxidising tris(2,2′-bipyridyl)ruthenium(II) with cerium(IV). After selecting the best operating parameters, calibration graphs were obtained over the concentration ranges 0.38-38 μg ml⁻¹ and 8.7-1300 ng ml⁻¹ for citrate and pyruvate, respectively. The limits of detection were 0.1 μg ml⁻¹ for citrate and 0.3 ng ml⁻¹ for pyruvate. Based on the differential rate of the chemiluminescent reaction corresponding to citrate and pyruvate, a very simple kinetic procedure was developed for the simultaneous determination of both compounds. Mixtures of citrate and pyruvate in ratios between 15:1 and 1.5:1 were satisfactorily resolved. The proposed method was successfully applied to the determination of citrate in pharmaceutical formulations, pyruvate in animal blood serum and both compounds in human urine.     

Lewis Acid-Promoted Reduction of Bis(triorganotin) Oxides to Hexaorganoditins

Hexalkylditin is prepared by a Lewis acid-promoted (MgCl₂) reductive reaction of bis(trialkyltin) oxide using magnesium metal as reducing agent. Hexabutyl- and hexaphenylditin are synthesized with 95% and 80% yield separately and a radical mechanism is proposed for the reaction condition. Unsymmetric ditin, Bu₃Sn-SnPh₃, was first synthesized by this reductive method.     

The Electrochemical Behavior of α‐Ketoglutarate at the Hanging Mercury Drop Electrode in Acidic Aqueous Solution and Its Practical Application in Environmental and Biological Samples

The voltammetric behavior of α‐ketoglutarate (α‐KG) at the hanging mercury drop electrode (HMDE) has been investigated in acetate buffer solution. Under the optimum experimental conditions (pH 4.5, 0.2 M NaAc‐HAc buffer solution), a sensitive reductive wave of α‐KG was obtained by linear scan voltammetry (LSV) and the peak potential was ?1.18 V (vs. SCE), which was an irreversible adsorption wave. The kinetic parameters of the electrode process were α=0.3 and k_s=0.72 1/s. There was a linear relationship between peak current i_{p, α‐KG} and α‐KG concentration in the range of 2×10^?6–8×10^?4 M α‐KG. The detection limit was 8×10^?7 M and the relative standard deviation was 2.0% (C_α‐KG=8×10^?4 M, n=10). Applications of the reductive wave of α‐KG for practical analysis were addressed as follows: (1) It can be used for the quantitative analysis of α‐KG in biological samples and the results agree well with those obtained from the established ultraviolet spectrophotometric method. (2) Utilizing the complexing effect between α‐KG and aluminum, a linear relationship holds between the decrease of peak current of α‐KG Δi_p and the added Al concentration Cequation/tex2gif-inf-5.gif in the range of 5.0×10^?6–2.5×10^?4 M. The detection limit was 2.2×10^?6 M and the relative standard deviation was 3.1% (Cequation/tex2gif-inf-6.gif=4×10^?5 M, n=10). It was successfully applied to the detection of aluminum in water and synthetic biological samples with satisfactory results, which were consistent with those of ICP‐AES. (3) It was also applied to study the effect of Al^III on the glutamate dehydrogenase (GDH) activity in the catalytically reaction of α‐KG+NH +NADH?L ‐glutamate+NAD⁺+H₂O by differential pulse polarography (DPP) technique. By monitoring DPP reductive currents of NAD⁺ and α‐KG, an elementary important result was found that Al could greatly affect the activity of GDH. This study could be attributed to intrinsic understanding of the aluminum's toxicity in enzyme reaction processes.     

High-yield preparation of rod-like CaSO<Subscript>4</Subscript>/Fe<Superscript>0</Superscript> magnetic composite for effective removal of Cu<Superscript>2+</Superscript> in wastewater

In this study, a simple approach was described for the fabrication of CaSO₄/Fe⁰ composite used as a novel adsorbent for the reductive removal of Cu²⁺ from aqueous solutions. The magnetic CaSO₄/Fe⁰ composite was prepared by a solid state reaction at 550 °C in the H₂ atmosphere using CaSO₄·2H₂O/α-FeOOH as a precursor. The structure and morphology of the as-synthesized magnetic composite were characterized by X-ray diffraction, field emission scanning electron microscopy and a superconducting quantum interference device, respectively. Results showed that the CaSO₄/Fe⁰ composite with a rod-like shape could be easily acquired from the CaSO₄·2H₂O/α-FeOOH precursor with the ratio of 1:0.5 at 550 °C in the H₂ atmosphere for 1 h. The CaSO₄/Fe⁰ composite exhibited enhanced performance relevant to the reductive removal of Cu²⁺. The removal amount of Cu²⁺ increased linearly with increasing of concentration of Cu²⁺ in wastewater. Possible removal mechanisms were proposed as follows: (1) the formation of Cu₂O by fast reduction of Cu²⁺ with Fe⁰ nanoparticles on interface of CaSO₄/Fe⁰ composite, (2) proper adsorption of Cu²⁺ on the surface of CaSO₄/Fe⁰ composite, (3) the hydrous iron oxide (HIO) such as Fe (OH)₃ and FeOOH in situ generated on the rest of CaSO₄/Fe⁰ composite could further adsorb Cu²⁺ from wastewater.     

Mechanism of the Kolbe-Schmitt reaction with lithium and sodium phenoxides

The mechanisms of the carboxylation reactions of lithium and sodium phenoxides are investigated by means of the DFT method with a CEP-31 + G(d) basis set. The introduction of diffusion functions does not affect the outcome of the calculations. As a consequence, the results of this investigation are in good agreement with the findings obtained by means of the LANL2DZ basis set. Lithium phenoxide yields only salicylic acid in the Kolbe-Schmitt reaction. The reaction of sodium phenoxide can proceed in the ortho and para positions, but the para-substituted product can be expected at a very low concentration in the reaction mixture. The deviation of lithium and sodium phenoxides from the mechanisms of carboxylations of other alkali metals is a consequence of the small ionic radii of lithium and sodium. The text was submitted by the authors in English.     

Non‐natural Cofactor and Formate‐Driven Reductive Carboxylation of Pyruvate

A non‐natural cofactor and formate driven system for reductive carboxylation of pyruvate is presented. A formate dehydrogenase (FDH) mutant, FDH*, that favors a non‐natural redox cofactor, nicotinamide cytosine dinucleotide (NCD), for generation of a dedicated reducing equivalent at the expense of formate were acquired. By coupling FDH* and NCD‐dependent malic enzyme (ME*), the successful utilization of formate is demonstrated as both CO₂ source and electron donor for reductive carboxylation of pyruvate with a perfect stoichiometry between formate and malate. When ¹³C‐isotope‐labeled formate was used in in vitro trials, up to 53 % of malate had labeled carbon atom. Upon expression of FDH* and ME* in the model host E. coli, the engineered strain produced more malate in the presence of formate and NCD. This work provides an alternative and atom‐economic strategy for CO₂ fixation where formate is used in lieu of CO₂ and offers dedicated reducing power.     

Preparation of 3-arylmethylindoles as selective COX-2 inhibitors

The 3-arylmethylation of indoles using TMSOTf/Et₃SiH with a wide variety of substituted benzaldehydes has been accomplished. Under these mild Lewis acid mediated reductive conditions, it was demonstrated that indoles bearing both 6-MeSO₂ and 2-methyl substituents could be 3-arylmethylated in good to excellent yields to afford the corresponding 3-arylmethyl indoles, effective as selective COX-2 inhibitors. In addition, the viability of this method for the reductive alkylation of indoles by ketones was demonstrated and shown to be C-3 regioselective. For indoles bearing both a 6-MeSO₂ and 2-cyano substituent where this indole reductive alkylation methodology was unsuccessful, an unprecedented Pd(0) mediated arylorganozinc coupling with the requisite substituted 3-methylcarbonatomethylindole proved successful in affording the desired 2-cyano-6-MeSO₂-3-arylmethylindoles effective as selective COX-2 inhibitors.     

Non-natural Cofactor and Formate-Driven Reductive Carboxylation of Pyruvate

A non-natural cofactor and formate driven system for reductive carboxylation of pyruvate is presented. A formate dehydrogenase (FDH) mutant, FDH*, that favors a non-natural redox cofactor, nicotinamide cytosine dinucleotide (NCD), for generation of a dedicated reducing equivalent at the expense of formate were acquired. By coupling FDH* and NCD-dependent malic enzyme (ME*), the successful utilization of formate is demonstrated as both CO₂ source and electron donor for reductive carboxylation of pyruvate with a perfect stoichiometry between formate and malate. When ¹³C-isotope-labeled formate was used in in vitro trials, up to 53 % of malate had labeled carbon atom. Upon expression of FDH* and ME* in the model host E. coli, the engineered strain produced more malate in the presence of formate and NCD. This work provides an alternative and atom-economic strategy for CO₂ fixation where formate is used in lieu of CO₂ and offers dedicated reducing power.     

铜催化异噁唑还原环清洁高效合成1-氨基-2-乙酰基蒽醌简

以水为反应介质,水合肼为还原剂,研究了痕量铜催化3-甲基蒽醌-[1,2-c]-异噁唑还原开环反应以清洁高效合成1-氨基-2-乙酰基蒽醌,考察了不同种类过渡金属硝酸盐的催化性能,发现Cu（NO₃）₂性能最好. 加入 2.6% 的催化剂和1.3倍的水合肼,在室温反应 2 h,底物转化率和目标产物选择性分别可达到 97.2%和 95%,TON达到38. 产品结构经氢核磁谱和质谱得以确证,主要副产为羟基取代的1-氨基-2-乙酰基蒽醌. 此外,提出了铜催化 3-甲基蒽醌-[1,2-c]-异噁唑还原开环反应合成 1-氨基-2-乙酰基蒽醌的可能反应机理.     

A method for lactate and pyruvate determination in filter-paper dried blood spots

Lactic acidemia is commonly associated with severe diseases in pediatric patients. Quantitation of blood lactate and pyruvate is important for the diagnosis and clinical management. A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method using dried blood spots (DBS) was developed and could be used for simultaneous quantification of blood lactate and pyruvate. The applicability of the developed method was tested and confirmed by the regression analysis between LC–MS/MS method and enzymatic assay. Lactate and pyruvate were extracted from DBS obtained from 580 full-term, 120 pre-term infants (gestations ranging from 24 to 36 weeks), and 65 patients with suspected lactic acidemia, with methanolic internal standard (IS) solutions of sodium l-lactate-¹³C₃ and pyruvate-¹³C₃. An API-2000 LC–MS/MS system with multiple reaction monitoring (MRM) mode was applied. The within-run and between-run precisions (CV%) were determined and the results were 1.9% and 3.9% for lactate (n = 20) and 5.7% and 7.3% for pyruvate (n = 20). The linearity of lactate (r = 0.9986) and pyruvate (r = 0.9973) based on the IS was excellent. The parameter r squared (r²) of linear regression between LC–MS/MS method and enzymatic assay was 0.9405 for lactate and 0.9447 for pyruvate, respectively, and the agreement between these methods was consistent and acceptable. The stability of lactate and pyruvate on DBS was also confirmed. The LC–MS/MS method we developed is a specific, sensitive, and reproducible method for measuring blood lactate and pyruvate concentrations. The use of DBS in this method makes it particularly attractive for pediatric patients.     

Electrochemical determination of hydrogen peroxide using o -dianisidine as substrate and hemoglobin as catalyst

A new electrochemical method for the determination of microamounts of hydrogen peroxide utilizing o-dianisidine (ODA) as substrate and hemoglobin (Hb) as catalyst is described in this paper. Hb can be used as mimetic peroxidase and it can catalyse the reduction of hydrogen peroxide with the subsequent oxidation of ODA. The oxidative reaction product is an azo compound, which is an electroactive substance and has a sensitive second-order derivative polarographic reductive peak at the potential of -0.58 V (vs. SCE) in pH 80 Britton-Robinson (B-R) buffer solution. The conditions of Hb-catalytic reaction and polarographic detection of the reaction product were carefully studied. By using this polarographic peak and under optimal conditions, the calibration curve for the H₂O₂ was constructed in the linear range of 2.0 x 10^-7 ∼ 10 x 10^-4 mol/l with the detection limit of 5.0 x 10^-8 mol/l. This method can also be used to the determination of Hb content in the range of 20 x 10^-9 ∼ 30 x 10^-7 mol/l with a detection limit of 10 x 10^-9 mol/l. The proposed method was further applied to the determination of the content of H₂O₂ in fresh rainwater with satisfactory results. The catalytic reaction mechanism and the electrode reductive process of the reaction product were carefully studied.     

Extensive Studies on the AIEt3／THF-Promoted Diastereoselective Tandem Rearrangement／Reduction of a-Hydroxy （Amino） Heterocyclopropane： An Efficient Approach to 2-Quaternary 1,3-Diheteroatom Units

A facile and highly diastereoselective method for the construction of 2-quaternary 1,3-amino alcohols and 1,3-diols has been developed on the basis of the AlEt3/THF-promoted tandem rearrangement/reductive reaction of α-hydroxy (amino) aziridines (epoxides). The progressive achievement in this article included that both 2-epimers of the units could be constructed from the initially same substrate. Also a stereochemistry assignment we reported previously was corrected.     

Reactions of coordinated ligands,Part III(1). Kinetics of lodination of malonate and pyruvate in malonato(pentaammine)-cobalt(III), malonato-bis-(ethylenediamine)cobalt(III) and pyruvato(pentaammine)cobalt(III) ions

Summary The kinetics of iodination of malonate and pyruvate in the title complexes are reported at 35.0 °C and I=0.3 M. The reaction is first order in substrate and zeroth order in [I₂]. This result is commensurate with rate determining enolisation of the active methylene and methyl groups of the malonate and pyruvate respectively. The reaction is catalysed by H₂O, OH^– and by the buffer anions used. The rate data suggest that the malonate methylene group in the [Co(en)₂-O₂CCH₂CO₂]²⁺ chelate is considerably more active towards electrophilic substitution than is the case in [Co(NH₃)₅O₂CCH₂CO₂]²⁺.     

Fluoride‐Catalyzed Methylation of Amines by Reductive Functionalization of CO2 with Hydrosilanes

An effective and inexpensive organocatalyst tetrabutylammonium fluoride (TBAF) was developed for the reductive functionalization of CO₂ with amines to selectively afford formamides or methylamines by employing hydrosilanes. Hydrosilanes with different substituents show discriminatory reducing activity. Thus, the formation of formamides and further reduction products, that is, methylamines could be controlled by elegantly tuning hydrosilane types. Formamides were obtained exclusively under an atmospheric pressure of CO₂ with triethoxysilane. Using phenylsilane as a reductant, methylamines were attained with up to 99 % yield at 50 °C coupled to a complete deoxygenation of CO₂. The crucial intermediate silyl formate in the formylation step was identified and thereby a tentative mechanism involving the fluoride‐promoted hydride transfer from the hydrosilane to CO₂/formamide was proposed. Striking features of this metal‐free protocol are formylation and methylation of amines by reductive functionalization of CO₂ with hydrosilanes and mild reaction conditions.     

High Valence State Sites as Favorable Reductive Centers for High-Current-Density Water Splitting

Electrochemical water splitting is a promising approach for producing sustainable and clean hydrogen. Typically, high valence state sites are favorable for oxidation evolution reaction (OER), while low valence states can facilitate hydrogen evolution reaction (HER). However, here we proposed a high valence state of Co³⁺ in Ni_9.5Co_0.5−S−FeO_x hybrid as the favorable center for efficient and stable HER, while structural analogues with low chemical states showed much worse performance. As a result, the Ni_9.5Co_0.5−S−FeO_x catalyst could drive alkaline HER with an ultra-low overpotential of 22 mV for 10 mA cm⁻², and 175 mV for 1000 mA cm⁻² at the industrial temperature of 60 °C, with an excellent stability over 300 h. Moreover, this material could work for both OER and HER, with a low cell voltage being 1.730 V to achieve 1000 mA cm⁻² for overall water splitting at 60 °C. X-ray absorption spectroscopy (XAS) clearly identified the high valence Co³⁺ sites, while in situ XAS during HER and theoretical calculations revealed the favorable electron capture at Co³⁺ and suitable H adsorption/desorption energy around Co³⁺, which could accelerate the HER. The understanding of high valence states to drive reductive reactions may pave the way for the rational design of energy-related catalysts.     

Computational evidence for sulfur participation in the first half-reaction of biotin-catalyzed carboxylations

Sulfur participation during the first half-reaction of biotin-dependent, enzyme-catalyzed carboxylations has been examined by ab initio molecular orbital (MO) calculations. Geometry optimization with the 6-31G¹ basis set on the model biotin structure 6, which contains a methyl in place of the side chain, shows that the highest occupied molecular orbital (HOMO) is localized on sulfur and the HOMO-1 is localized on the ureido moiety. Two modes of distortion of 6 were examined as possible enzymestabilized, transition state-like conformations that might show sulfur-ureido interactions. Puckering of ring-B through the use of a distance constraint between sulfur and the carbonyl carbon was found to be ineffective in establishing orbital overlap between sulfur and the ureido group. Twisting of 6 by constraining the methyl to be more pseudo-equatorial relative to the sulfur containing ring results in a loss of symmetry that allows the sulfur 3p orbital to interact with the orbital on the ureido moiety of A₂-like symmetry in a combined through-bond-through-space fashion. The net result is that in this twisted, transition state-like conformation, the ureido nitrogens now contribute to the HOMO and therefore have a lower ionization potential, which can be equated with increased nucleophilicity. Thus, N1 could be nucleophilic enough to initiate N1-carboxylation prior to N1-proton removal in the first half-reaction in biotin-dependent, enzyme-catalyzed carboxylations.     

Reductive Catalytic Difluorocarbene Transfer via Palladium Catalysis

A palladium-catalyzed reductive difluorocarbene transfer reaction that tames difluorocarbene to couple with two electrophiles has been developed, representing a new mode of difluorocarbene transfer reaction. The approach uses low-cost and bulk industrial chemical chlorodifluoromethane (ClCF₂H) as the difluorocarbene precursor. It produces a variety of difluoromethylated (hetero)arenes from widely available aryl halides/triflates and proton sources, featuring high functional group tolerance and synthetic convenience without preparing organometallic reagents. Experimental mechanistic studies reveal that an unexpected Pd^0/II catalytic cycle is involved in this reductive reaction, wherein the oxidative addition of palladium(0) difluorocarbene ([Pd⁰(L_n)]=CF₂) with aryl electrophile to generate the key intermediate aryldifluoromethylpalladium [ArCF₂Pd(L_n)X], followed by reaction with hydroquinone, is responsible for the reductive difluorocarbene transfer.     

Mechanism of Difluoroamine Deaminations

An alternative explanation of the reductive deamination with difluoroamine is suggested which does not involve the originally proposed formation of nitrogen monofluoride and Wolff-Kishner cleavage.The reductive deamination of amines by difluoroamine has been discussed in terms of intermediate formation of nitrogen monofluoride [1, 2]. Some steps in the proposed mechanism seem questionable and hence an alternative view of the reaction is presented.Bumgardner put forward a five step reaction scheme. The initial step was a proton transfer between difluoroamine and a more basic primary amine to form a salt with the difluoronitrogen (I) anion. This salt decomposed in a rate determining step to produce nitrogen monofluoride which inserted rapidly into the N-H bond of HNF₂. The product eliminated hydrogen fluoride with further amine to form a di-imine, which then extruded dinitrogen and left the alkane. The overall stoichiometry accords with.3RNH₂ + HNF₂ = RN = NH + 2RN₃⁺ F^- (1)There is only indirect evidence for the intermediacy of a fluoronitrene (NF) in reactions, based mainly on reaction products and their stereochemistry. Le Noble [3] inferred such an intermediate in the alkaline decomposition of HNF₂ from a large positive volume of activation obtained from the pressure variation of rate. The suggested rate determining step wasNF₂^-aq → NFg + F^- aqEven if this were the only explanation of a larger transition state, one has to transfer a mechanism obtained using a fully dissociated base in an aqueous medium to a relatively weak base in a non-aqueous medium.     

Auto‐Tandem Catalysis with Frustrated Lewis Pairs for Reductive Etherification of Aldehydes and Ketones

Herein we report that a single frustrated Lewis pair (FLP) catalyst can promote the reductive etherification of aldehydes and ketones. The reaction does not require an exogenous acid catalyst, but the combined action of FLP on H₂, R‐OH or H₂O generates the required Brønsted acid in a reversible, “turn on” manner. The method is not only a complementary metal‐free reductive etherification, but also a niche procedure for ethers that would be either synthetically inconvenient or even intractable to access by alternative synthetic protocols.