Oxidation of Dibenzothiophene Catalyzed by Hemoglobin and Other Hemoproteins in Various Aqueous-Organic Media

Biocatalytic oxidation of dibenzothiophene (a model of organic sulfur in coal) with hydrogen peroxide was investigated. It was found that various hemoproteins, both enzymic (e.g., horseradish peroxidase) and nonenzymic (e.g., bovine blood hemoglobin), readily oxidized dibensothiophene to its S-oxide and, to a minor extent, further to its S-dioxide (sulfone). This process catalyzed by hemoglobin (a slaughterhouse waste protein) was studied in a number of monophasic aqueousorganic mixtures. Although hemoglobin was competent as an oxidation catalyst even in nearly dry organic solvents (with protic, acidic solvents being optimal), the highest conversions were observed in predominantly aqueous media. The hemoglobin-catalyzed oxidation of dibenzothiophene at low concentrations of the protein stopped long before all the substrate was oxidized. This phenomenon was caused by inactivation of hemoglobin by hydrogen peroxide that destroyed the heme moiety. The maximal degree of the hemoglobin-catalyzed dibenzothiophene oxidation was predicted, and found, to be strongly dependent on the reaction medium composition.     

Hemoglobin,horseradish peroxidase,and heme-bovine serum albumin as biocatalyst for the oxidation of dibenzothiophene

Hemoglobin, horseradish peroxidase, and bovine serum albumin incubated heme-catalyzed the oxidation of dibenzothiophene into sulfoxide in the presence of hydrogen peroxide. This reaction was carried out in an aqueous buffer containing 25% of water-miscible organic solvents. The observation of this transient state of hemoproteins during sulfoxidation showed heme degradation. None of the compounds usually involved in a classical peroxidative activity mechanism were detected. Furthermore, this activity did not appear to be based on a Fenton-type reaction. The highest degrees of sulfoxidation were obtained with hemoglobin. Under the best conditions of reaction, 100% of dibenzothiophene were converted into dibenzothiophene sulfoxide by hemoglobin. Heat-denatured hemoproteins did keep their sulfoxidation activity. With hemoglobin, a k_cat of 0.22 min^-1 was determined. Nearly the same values were obtained with heat-denatured hemoglobin and bovine serum albumin-adsorbed heme. With horseradish peroxidase, only 4% of conversion was attained. This percentage could be slightly increased by using a less pure peroxidase or heat-denatured peroxidase.     

NMR spectroscopy can characterize proteins encapsulated in a sol-gel matrix

Proteins encapsulated within sol-gel matrices (SG) have the potential to fill many scientific and technological roles, but these applications are hindered by the limited means of probing possible structural consequences of encapsulation. We here present the first demonstration that it is possible to obtain high-resolution, solution NMR measurements of proteins encapsulated within a SG matrix. With the aim of determining the breadth of this approach, we have encapsulated three paramagnetic proteins with different overall charges: the highly acidic human Fe3+ cytochrome b5 (cyt b5); the highly basic horse heart cytochrome c (cyt c); and the nearly neutral, sperm whale cyanomet-myoglobin. The encapsulated anionic and neutral proteins (cyt b5; myoglobin) undergo essentially free rotation, but show minor conformational perturbations as revealed by shifts of contact-shifted peaks associated with the heme and nearby amino acids.     

Biomolecular materials based on sol-gel encapsulated proteins

The proteins copper-zinc superoxide dismutase (CuZnSOD), cytochrome c, myoglobin, hemoglobin, and bacterio-rhodopsin are encapsulated in stable, optically transparent, porous, silica glass matrices prepared by the sol-gel method such that the biomolecules retain their characteristic reactivities and spectroscopic properties. The resulting glasses allow transport of small molecules into and out of the glasses at reasonable rates but retain the protein molecules within their pores. The transparency of the glasses enables the chemical reactions of the immobilized proteins to be monitored by means of changes in their visible absorption spectra. Silica glasses containing the immobilized proteins have similar reactivities and spectroscopic properties to those found for the proteins in solution. The enzymes glucose oxidase and peroxidase were also encapsulated in transparent silica glass matrices. Upon exposure to glucose solutions, a colored glass is formed that can be used as the active element in a solid state optically based glucose sensor.     

离子液体耦合有机过氧化物脱除二苯并噻吩的研究

以12-磷钨酸为催化剂,研究了离子液体耦合有机过氧化物脱除二苯并噻吩(DBT)。研究结果表明,单独使用离子[bmim]BF4、[bmim]PF6液体为萃取剂,脱硫率为27.78%~38.76%。以由等体积的H2O2与甲酸制成有机过氧化物为氧化剂,不使用催化剂和离子液体,温度70℃,反应时间6 h,DBT氧化为二苯并噻吩砜的比例为76.6%。在催化剂作用下,将离子液体与氧化剂耦合使用时,脱硫率明显提高。当催化剂与DBT的摩尔比为0.20∶1,氧化剂与DBT的体积比为10∶1,[bmim]PF6离子液体与DBT的体积比为1∶1,在70℃反应6 h后,脱硫率可达98.60%。耦合体系重复使用五次后,氧化脱硫活性没有明显降低。     

模拟油品氧化脱硫及反应动力学研究

在H₂O₂/WO₃/ZrO₂氧化体系中对以甲苯为溶剂、二苯并噻吩(DBT)为模型含硫化合物的模拟油品(硫的质量分数为1540×10^-6)进行了氧化脱硫研究,考察了反应温度、反应时间、氧化剂加入量、催化剂用量对DBT转化率的影响。实验结果表明,在反应温度50℃,反应时间90min,氧化剂加入量油/H₂O₂的体积比为20∶1和催化剂用量0.02g/mL的适宜氧化脱硫条件下,96%以上的DBT氧化为容易分离脱除的二苯并噻吩砜(DBTOs);同时研究了DBT氧化反应动力学,得知DBT氧化反应为一级反应,表观活化能E_a为55.37kJ/mol,指前因子A为3.35×10⁷min^-1。     

Selective oxidation of organic sulfides by mononuclear and dinuclear peroxotungsten(VI) complexes

Clean conversion of a variety of sulfides and dibenzothiophene (DBT) to the corresponding sulfoxide or sulfone could be achieved in high yields at room temperature using mononuclear as well as dinuclear diperoxo complexes of tungsten as oxidants, by a variation of reaction conditions. The compounds could also effectively catalyze oxidation of sulfides by H₂O₂ to selectively yield sulfone with reasonably good turnover frequency (TOF).     

分子氧为氧化剂磷钒酸盐为催化剂超深度氧化脱除柴油中的二苯并噻吩

一种“双帽Keggin型”磷钒酸盐在温和的反应条件下以分子氧为氧化剂氧化二苯并噻吩至二苯并噻吩砜的反应中表现出很高的催化活性. 用溶剂萃取或者选择吸附等方法可轻易地将反应产生的二苯并噻吩砜从油品中除去. 这提供了一种新型的分子氧为氧化剂的超深度氧化脱硫方法.     

Mimicking biological electron transport in sol-gel glass: photoinduced electron transfer from zinc cytochrome C to plastocyanin or cytochrome C mediated by mobile inorganic complexes

Biomimetic studies of electron-transport chains are important for establishing the molecular mechanisms of long-range communications between proteins. We mimic these biological assemblies by encapsulating metalloproteins in sol-gel silica glass and letting mobile inorganic complexes shuttle electrons between the immobilized proteins. We present two examples of such rudimentary electron-transport chains. In both of them the immobilized electron donor is the zinc-substituted cytochrome c, Zncyt; the immobilized electron acceptor is either cupriplastocyanin, pc(II), or ferricytochrome c, cyt(III); and the mobile charge carrier Q/Q(-) is the redox couple FeEDTA(-)(/2)(-) or Ru(NH(3))(6)(3+/2+). The redox processes are photoinduced: Zncyt is excited by the laser pulse and converted to the triplet state, (3)Zncyt, which is a strong reducing agent. Visible absorption, circular dichroism, and electron paramagnetic resonance spectra of the metalloproteins show that encapsulation in sol-gel glass does not affect their intrinsic redox properties. The rigid silica glass spatially separates the proteins from each other. In this matrix, the electron-transfer reactions between (3)Zncyt and pc(II) and between (3)Zncyt and cyt(III), which occur fast in solution, are completely suppressed in the absence of a charge carrier Q/Q(-). The reactivity of FeEDTA(-) and Ru(NH(3))(6)(3+) (as quenchers Q of (3)Zncyt) is minimally affected by the interior of the sol-gel glass. In the glass, the second-order rate constants for the excited-state electron transfer, from (3)Zncyt to Q, are (8.9 +/- 0.6) x 10(6) and (8.0 +/- 2.4) x 10(6) M(-)(1) s(-)(1) for FeEDTA(-) and Ru(NH(3))(6)(3+), respectively. This reaction is followed by the ground-state back electron transfer, from Q(-) to Zncyt(+). In the "monoprotein" glasses Zncyt/Q, the respective second-order rate constants for this back electron-transfer reaction are (4.9 +/- 0.2) x 10(7) and (7.8 +/- 2.7) x 10(7) M(-)(1) s(-)(1). In the "diprotein" glasses Zncyt/Q/pc(II) and Zncyt/Q/cyt(III), containing also the acceptor protein pc(II) or cyt(III), Zncyt(+) decays on two time scales. The faster and major component of this decay is analogous to the only mode of the decay in the Zncyt/Q glasses and is a second-order process. Between 25 and 40% of the initially formed Zncyt(+), however, lives longer (k(slow) =1.1 +/- 0.2 s(-)(1)) and decays by a first-order process. We attribute the lengthening of the Zncyt(+) lifetime to a partial escape of the photogenerated Q(-) into the glass pores, where it reacts with the immobilized pc(II) or cyt(III). Indeed, the visible absorption spectra show the photoinduced reduction of pc(II) and cyt(III). Evidently, the small inorganic complexes, FeEDTA(-)(/2)(-) and Ru(NH(3))(6)(3+/2+), move through the glass pores, react with the encapsulated metalloproteins, and establish the interprotein electron transfer. Each interprotein reaction now occurs in two steps: a mobile charge carrier Q receives an electron from (3)Zncyt, and Q(-) then delivers an electron to pc(II) or cyt(III). Ultimately, the energy of visible light is converted to reducing equivalents for plastocyanin and cytochrome c. The sequential electron transfer described here resembles the events in a rudimentary electron-transport chain. Our findings demonstrate the promise of integrating proteins, with their optimally adjusted redox sites, in photocatalytic materials.     

Supramolecular complex of cytochrome c with lariat ether: solubilization, redox behavior and catalytic activity of cytochrome c in methanol

A variety of lariat ethers were employed to solubilize water-soluble cytochrome c in methanol, in which alcohol, ether, ester, amine, and amide functionalities were attached as cation-ligating side arms to 18-crown-6, 15-crown-5, and 12-crown-4 rings. Among these lariat ethers, the alcohol-armed 18-crown-6 derivative offered the highest solubilization efficiency for cytochrome c via supramolecular complexation. The resulting cytochrome c-lariat ether complexes were electrochemically and spectroscopically characterized and confirmed to have redox-active heme structures of 6-coordinate low-spin population in methanol. Some of them catalyzed the oxidation of pinacyanol chloride with hydrogen peroxide in methanol and exhibited higher activities than unmodified cytochrome c and its poly(ethylene glycolated) derivative. Since the supramolecular complexation between lariat ether and cytochrome c includes extremely simple procedures, it provides a facile preparation method of effective biocatalysts working in organic solvents from metalloproteins.     

Optical biosensing of nitric oxide using the metalloprotein cytochrome c'

The metalloprotein cytochrome c' was extracted and purified from the bacterium Paracoccus denitrificans in order to develop a specific biosensing system for nitric oxide (NO). The metalloprotein was encapsulated in a porous silicate sol-gel glass to enable spectroscopic changes in the haem centre as a function of NO ligation to be quantified using absorption measurements. Spectroscopic evidence suggested that, between 2 and 4 d after encapsulation, the cytochrome c' protein changed conformation in the locality of the haem moiety, possibly from a five to a six coordinate haem centre. Such conformational changes were also observed when the cytochrome c' was stored in solution, although over a 2-3 month period. The conformational changes occurring in the protein altered the spectral characteristics of the reduced, oxidised and nitrosyl complex of the cytochrome c' and appear to change the binding affinity of the protein towards NO. However, the encapsulated (reconformed) cytochrome c' was shown to retain its selectivity towards NO with good reproducibility (seven consecutive measurements of NO produced an intensity value with a relative standard deviation of 0.28%). An NO calibration curve, using the in situ release of NO from the donor diethylamine NONOate, was obtained for the encapsulated cytochrome c' with an approximate working range of 10-400 mumol l-1.     

Co‐poly(aryl ether sulfone)s containing phthalimidine moiety in the main chain

Several new co‐poly(arylene ether sulfone)s have been prepared by the reaction of 4,4′‐fluorodiphenyl sulfone (FDS) with different bisphenols namely 4,4′‐isopropylidenediphenol (BPA), 4,4′‐hexafluoroisopropylidenediphenol (6F‐BPA), and N‐phenyl‐3,3‐bis(4‐hydroxyphenyl)phthalimidine(PA). The homo‐poly(arylene ether sulfone)s are named as 1a, 2a, and 3a. The copolymers namely 2b, 2c, 2d and 3b, 3c, 3d have been prepared, respectively, on reaction of FDS with BPA or 6F‐BPA using different molar ratios of PA such as 25, 50, and 75. The poly(aryl ether sulfone)s 1a containing PA unit in the main chain showed a very high glass transition temperature of 280°C and an outstanding thermal stability up to 510°C for 5% weight loss under synthetic air. Depending on the mole% of PA, the glass transition temperatures of the copolymers can be varied. The polymers were soluble in a wide range of organic solvents. Transparent thin films of these polymers exhibited tensile strengths upto 84 MPa and Young's modulus up to 3.16 GPa. The films of these polymers showed low water absorption of 0.24%. Copyright © 2009 John Wiley & Sons, Ltd.     

Water-soluble polymer anchored peroxotitanates as environmentally clean and recyclable catalysts for mild and selective oxidation of sulfides with H2O2 in water

Anchoring of peroxotitanium (pTi) species to linear water-soluble acrylic acid based polymers, poly(sodium acrylate) (PA) and poly(sodium methacrylate) (PMA) led to the successful synthesis of a pair of new, water-tolerant and recyclable catalysts of the type [Ti₂(O₂)₂O₂(OH)₂]^4-—L (L = PA or PMA), highly effective in chemoselective sulfoxidation of organic sulfides with 30% H₂O₂ in aqueous medium at ambient temperature. The catalytic protocol is high yielding (TOF up to 11,280 h^?1), operationally simple as well as environmentally clean and safe, being free from halide, or any other toxic auxiliaries. The catalysts are sufficiently stable to afford easy recyclability for at least 10 consecutive reaction cycles of sulfoxidation with consistent activity selectivity profile. Oxidation of dibenzothiophene (DBT) to respective high purity sulfoxide or sulfone could also be accomplished using the same catalysts by variation of reaction conditions.     

In-vitro protein interactions with a bioactive gel-glass

Recent theories suggest that the local adsorption of biologically active peptide growth factors onto the surface of an implant may contribute to the unique osteogenic nature of silica-containing bioactive ceramics. A sol-gel derived glass is used as a model of the in-vivo reaction product of 45S5 bioactive glass at relatively short times (<48 hrs.) to investigate protein adsorption/desorption behavior. The adsorption kinetics of three heme-class proteins (cytochrome c, myoglobin, and hemoglobin) are measured spectroscopically. The rate of adsorption is shown to increase with average pore size, which is determined by the silica content of the gel. Adsorption rate decreases as protein size is increased and as solution pH is decreased. Biological function of an adsorbed peroxidase enzyme on pre-reacted Bioglass^® is shown to be retained. Desorption during physiologic conditions is shown to be linear with time and pH dependant, while independent of gel bioactivity.     

Electrochemical redox reaction in a silica sol-gel glass with embedded organic electrolyte

The electrochemical redox reaction of ferrocene was studied in silica sol-gel glass with embedded organic electrolyte. This material has been prepared by mixing hydrolysed tetramethylorthosilicate sol with propylene carbonate LiClO₄ solution containing ferrocene and further gelation in a form of block or film. The electrochemical behaviour of encapsulated ferrocene was studied by cyclic voltammetry, chronoamperometry, differential pulse voltammetry and impedance spectroscopy on ultramicroelectrodes. The shape of the cyclic voltammograms corresponding to the electrooxidation of ferrocene in sol-gel block is similar to that obtained in liquid electrolyte and it does not depend on gel aging. The current substantially decreases during the first few days after gelation. Later it becomes weakly dependent on aging and the apparent diffusion coefficient of ferrocene in the gel block is about half of that in liquid electrolyte. The electrooxidation of ferrocene also occurs in film of the analogous sol-gel material cast on the surface of the electrode assembly.     

On-line chemiluminescence detection for isoelectric focusing of heme proteins on microchips

In this paper we present a sensitive chemiluminescence (CL) detection of heme proteins coupled with microchip IEF. The detection principle was based on the catalytic effects of the heme proteins on the CL reaction of luminol-H2O2 enhanced by para-iodophenol. The glass microchip and poly(dimethylsiloxane) (PDMS)/glass microchip for IEF were fabricated using micromachining technology in the laboratory. The modes of CL detection were investigated and two microchips (glass, PDMS/glass) were compared. Certain proteins, such as cytochrome c, myoglobin, and horseradish peroxidase, were focused by use of Pharmalyte pH 3-10 as ampholytes. Hydroxypropylmethylcellulose was added to the sample solution in order to easily reduce protein interactions with the channel wall as well as the EOF. The focused proteins were transported by salt mobilization to the CL detection window. Cytochrome c, myoglobin, and horseradish peroxidase were well separated within 10 min on a glass chip and the detection limits (S/N=3) were 1.2x10(-7), 1.6x10(-7), and 1.0x10(-10) M, respectively.     

S-oxygenation of thiocarbamides IV: Kinetics of oxidation of tetramethylthiourea by aqueous bromine and acidic bromate

The kinetics and mechanism of oxidation of tetramethylthiourea (TTTU) by bromine and acidic bromate has been studied in aqueous media. The kinetics of reaction of bromate with TTTU was characterized by an induction period followed by formation of bromine. The reaction stoichiometry was determined to be 4BrO(3)(-) + 3(R)(2)C═S + 3H(2)O → 4Br(-) + 3(R)(2)C═O + 3SO(4)(2-) + 6H(+). For the reaction of TTTU with bromine, a 4:1 stoichiometric ratio of bromine to TTTU was obtained with 4Br(2) + (R)(2)C═S + 5H(2)O → 8Br(-) + SO(4)(2-) + (R)(2)C═O + 10H(+). The oxidation pathway went through the formation of tetramethythiourea sulfenic acid as evidenced by the electrospray ionization mass spectrum of the dynamic reaction solution. This S-oxide was then oxidized to produce tetramethylurea and sulfate as final products of reaction. There was no evidence for the formation of the sulfinic and sulfonic acids in the oxidation pathway. This implicates the sulfoxylate anion as a precursor to formation of sulfate. In aerobic conditions, this anion can unleash a series of genotoxic reactive oxygen species which can explain TTTU's observed toxicity. A bimolecular rate constant of 5.33 ± 0.32 M(-1) s(-1) for the direct reaction of TTTU with bromine was obtained.     

Effect of Organic Solvents on the Rate of Oxidation of Sulfoxides with Peroxy Acids

The reaction of sulfoxides with peroxy acids in various organic media was studied. The reaction mechanism involves the rapid formation of a sulfoxide­–peroxy acid intermediate which decomposes in the second stage to form carboxylic acid and the corresponding sulfone. The second stage is the rate-limiting step. The reaction medium significantly affects the rate of oxidation. The calculated activation parameters of the oxidation process indicate a compensation effect in the investigated reaction. Correlations between the main physicochemical parameters of solvents and the effective rate constants (k) of dimethyl sulfoxide oxidation with peroxy acids were found. Depending on the reaction conditions, the main factors affecting the k values are specific and nonspecific solvation of the reactants and structural factors.     

溶胶-凝胶法制备MoP/SiO2催化剂加氢脱硫催化活性的研究

以正硅酸乙酯为硅源,以钼酸铵和磷酸二氢铵为钼源和磷源,采用溶胶-凝胶法,经干燥、焙烧,程序升温还原制备得到二氧化硅负载磷化钼(MoP)催化剂。以噻吩、二苯并噻吩为模型化合物,对负载催化剂的加氢脱硫活性进行评价,考察了负载量、反应压力、反应温度等因素对催化活性的影响。实验结果表明,MoP/SiO₂催化剂Mo的最佳负载量为20%,升高反应压力和温度均有利于提高二苯并噻吩的转化率,但降低了产物中联苯的含量。     

Phase-vanishing methodology for efficient bromination, alkylation, epoxidation, and oxidation reactions of organic substrates

[reaction: see text] In cases where both reactants in a phase-vanishing reaction are less dense than the fluorous phase, an alternative to the U-tube method is to employ a solvent with greater density than the fluorous phase, such as 1,2-dibromoethane. This modification has been successfully applied to the methylation of a phenol derivative with dimethyl sulfate and to the m-CPBA-induced epoxidation of alkenes, N-oxide formation from nitrogen-containing compounds, and S-oxide or sulfone formation from organic sulfides.