Oxidation Of Guaiacol Research Articles

Development of a Detection Kit Based on G-Quadruplex DNAzyme for Detection of Lead(II) Ion in Food Samples

The biocatalytic function of G-quadruplex DNAzyme has been first used to design a detection kit for colorimetric detection of Pb2+ in food samples by coupling guaiacol (GA) as an effective and ideal colorimetric signal indicator. Addition of Pb2+ enabled the G-rich DNA to bind hemin to fabricate the Pb2+-promoted DNAzyme, which can catalyze the H2O2-mediated oxidation of colorless GA to produce amber tetraguaiacol, causing a visible color change. Both standard curve and colorimetric card were constructed in the present detection kit for the quantitative analysis of Pb2+. Under optimum conditions, the working range of the kit was 10–100 nM with a detection limit of 1 nM Pb2+. And the performance of the colorimetric card method of the kit could discriminate Pb2+ from 5 to 80 nM. The shelf-life of the kit was 6 months at 4 °C, and the effectiveness and reliability of the kit on the determination of Pb2+ were evaluated in real food samples. Therefore, the good performance characteristics of the DNAzyme-based detection kit indicate that it holds a promising application for sensitive and low-cost detection of Pb2+ ions in foods.

Visual and Raman spectroscopic observations of hot compressed water oxidation of guaiacol in fused silica capillary reactors

Using fused silica capillary reactors (FSCRs), we investigated the decomposition of guaiacol during hot compressed water oxidation (HCWO), with H2O2 added in stoichiometric ratios from 100 to 300%. Reactions were performed between 180 and 300°C for durations from 2 to 10min while the concurrent generation of CO2 during the oxidation process was followed by Raman spectroscopy and the phase behavior of guaiacol in HCW, with or without H2O2, was observed visually under a polarized microscope configured with a heating/cooling stage. We found that complete conversion of guaiacol and 100% yield of CO2 were achieved with a 150% stoichiometric ratio of oxidizer after 10min at 200 and 300°C, respectively. Based on the global reaction kinetics for the complete conversion of guaiacol to CO2, the reaction is considered to be first order. The activation energy and pre-exponential factor for CO2 formation are 18.62kJmol−1 and 12.81s−1, respectively.

Low-temperature oxidation of guaiacol to maleic acid over TS-1 catalyst in alkaline aqueous H2O2 solutions

To mitigate the negative environmental impact of greenhouse gas (GHG) emission originated from the use of fossil fuels, the chemical world is switching to utilize renewable biomass resources. Co-producing value-added chemicals is important for an integrated biorefinery to improve economics of biofuels. Lignin derived compounds, e.g. guaiacol, are common by-products of fast pyrolysis of lignocellulosic biomass. In this paper, the feasibility of low-temperature selective oxidation of guaiacol to value-added dicarboxylic acids, e.g. maleic acid, was investigated using titanium silicalite/hydrogen peroxide (TS-1/H 2 O 2 ) reaction system. Under the reaction conditions (80 °C and the initial pH = 13.3), the molar yields of maleic acid from guaiacol were approximately 20%–30%. The effects of catalyst amount, initial pH values, reaction time, and temperature on the yields of maleic acid were investigated. A possible reaction mechanism of TS-1 catalyzed aromatic ring opening was proposed. A novel oxidative ring opening method was developed for the conversion of guaiacol to maleic acid with a TS-1 catalyst in alkaline aqueous H 2 O 2 solutions.

Activity of Guaiacol Peroxidase of Solanum Lycopersicum In presence of Detergents and Chaotropic Agents

Browning of damaged tissues in fresh fruits and vegetables results mainly from the oxidation of phenolic compounds to quinones by peroxidase. The activation of Peroxidase by sodium dodesyl sulphat investigated, but reports on the effect of detergents and chaotropic agents on activity of Peroxidase are scarce. Here the effect of some detergents and chaotropic agent on activity of enzyme in soluble and in partial purified fraction was investigated. Sarkosyl inhibited activity of enzyme for oxidation of guaiacol and H2O2, although has inhibitory effect in higher concentrations. Other ionic, Nonionic detergents and Chaotropic agents showed inhibitory effect on activity of Peroxidasein partial purified fraction. Inhibitory effect of Urea, GnHcl, NP-40, Triton x-100 and Sodium cholate in presence of these substrates investigated so GnHcl and NP40 showed that they are potent inhibitor of peroxidase and sodium cholate showed that it is a weak inhibitor of guaiacol peroxidase. Results identified and confirmed the differences in structure and conformation of enzyme in soluble and in partial purified fraction for oxidation of different substrates. KEYWORD: Catechol, Pyrogallol, Purification, Sarkosyl

Preparation and Evaluation of the Oxidation Ability of Hematin-Appended 6-Amino-6-Deoxycellulose

The reaction of 6-amino-6-deoxycelluloe (1) with hematin in the presence of N,N′-carbonyldiimidazole and 1,8-diazabicyclo[5.4.0]undec-7-ene in N,N-dimethylformamide at 50°C for four days afforded hematin-appended 6-aminocellulose (2). Compound 2 was more stable than hematin, and retained the oxidation activity of hematin, even after being treated at 100°C for 3 h. Compound 2 showed good guaiacol oxidation activity in an aqueous 80% AcOH solution (pH 1.5), whereas hematin and horseradish peroxidase showed very low oxidation activities under the same conditions, suggesting that compound 2 is a useful biomimetic catalyst. However, no asymmetric induction was achieved in the catalytic oxidation of sinapyl alcohol (3) using compound 2.

The effect of the nature of hydrophilic ionic liquid on the catalytic activity of horseradish and soybean peroxidases

The kinetics of guaiacol oxidation by hydrogen peroxide and tert-butyl hydroperoxide catalyzed by horseradish and soybean peroxidases in the presence of 1-butyl-3-methylimidazolium acetate and tet-rafluoroborates of 1-butyl-3-methylimidazolium and N-butyl-4-methylpyridinium are studied and compared. The inhibiting effect of acetate ionic liquid on both peroxidases that occurred via the noncompetitive type is found; the Michaelis and inhibition constants have been calculated. Causes of different degrees of inhibition of the catalytic activity of plant peroxidases by ionic liquids are discussed. The advantages of their application compared to the polar molecular organic solvents are demonstrated.

Development of a Thyroperoxidase Inhibition Assay for High-Throughput Screening

High-throughput screening (HTPS) assays to detect inhibitors of thyroperoxidase (TPO), the enzymatic catalyst for thyroid hormone (TH) synthesis, are not currently available. Herein, we describe the development of a HTPS TPO inhibition assay. Rat thyroid microsomes and a fluorescent peroxidase substrate, Amplex UltraRed (AUR), were employed in an end-point assay for comparison to the existing kinetic guaiacol (GUA) oxidation assay. Following optimization of assay metrics, including Z', dynamic range, and activity, using methimazole (MMI), the assay was tested with a 21-chemical training set. The potency of MMI-induced TPO inhibition was greater with AUR compared to GUA. The dynamic range and Z' score with MMI were as follows: 127-fold and 0.62 for the GUA assay, 18-fold and 0.86 for the 96-well AUR assay, and 11.5-fold and 0.93 for the 384-well AUR assay. The 384-well AUR assay drastically reduced animal use, requiring one-tenth of the rat thyroid microsomal protein needed for the GUA 96-well format assay. Fourteen chemicals inhibited TPO, with a relative potency ranking of MMI > ethylene thiourea > 6-propylthiouracil > 2,2',4,4'-tetrahydroxy-benzophenone > 2-mercaptobenzothiazole > 3-amino-1,2,4-triazole > genistein > 4-propoxyphenol > sulfamethazine > daidzein > 4-nonylphenol > triclosan > iopanoic acid > resorcinol. These data demonstrate the capacity of this assay to detect diverse TPO inhibitors. Seven chemicals acted as negatives: 2-hydroxy-4-methoxybenzophenone, dibutylphthalate, diethylhexylphthalate, diethylphthalate, 3,5-dimethylpyrazole-1-methanol, methyl 2-methyl-benzoate, and sodium perchlorate. This assay could be used to screen large numbers of chemicals as an integral component of a tiered TH-disruptor screening approach.

H2O2-dependent substrate oxidation by an engineered diiron site in a bacterial hemerythrin

The O2-binding carboxylate-bridged diiron site in DcrH-Hr was engineered in an effort to perform the H2O2-dependent oxidation of external substrates. A His residue was introduced near the diiron site in place of a conserved residue, Ile119. The I119H variant promotes the oxidation of guaiacol and 1,4-cyclohexadiene upon addition of H2O2.

ИССЛЕДОВАНИЕ ПРОДУКТОВ ФЕРМЕНТАТИВНОГО ОКИСЛЕНИЯ ГВАЯКОЛА В СИСТЕМЕ ВОДА – ДИМЕТИЛСУЛЬФОКСИД

The investigation on the reaction of enzymatic oxidation of guaiacol as lignin model compound with hydrogen peroxide in the presence of horseradish peroxidase in water – DMSO binary solvents was done. Using the method of gas chromatography – mass spectrometry the five dimeric products of guaiacol oxidative coupling are identified. The possibility of the using of peroxidase in the mixtures of water with DMSO in the range of solvent compositions up to 30% (w/w) DMSO is shown. For the solvent compositions up to 30% vol. of DMSO the absence of the solvent effect on guaiacol oxidation products is stated.

Post-harvest sugarcane residue degradation by autochthonous fungi

Several fungal species were isolated from different sources: post-harvest sugarcane residue, soil, decomposing forest litter and from mycelia obtained from the inner parts of fresh fungal fruiting bodies collected in Las Yungas region (Argentina). These isolates were first screened for their ability to produce carboxymethyl cellulose (CMC) degradation and guaiacol oxidation. After primary screening, seventeen isolates were further tested for their ligninolytic ability by assessing polyphenoloxidase, laccase, manganese peroxidase and endoxylanase activities. Based on their lignocellulolytic activities, five isolates (named Bjerkandera sp. Y-HHM2, Phanerochaete sp. Y-RN1, Pleurotus sp. Y-RN3, Hypocrea nigricans SCT-4.4 and Myrothecium sp. S-3.20) were selected for liquid and solid-state fermentation assays in culture media including sugarcane debris. Lignocellulolytic enzymes production, dry mass loss and phenol concentration in the water soluble fraction were then evaluated. Results suggest that native strains with lignocellulolytic activity are suitable to increase post-harvest sugarcane residue decomposition and support the use of these strains as an alternative to pre and post-harvest burning. Biological treatments using Phanerochaete sp. Y-RN1, Pleurotus sp. Y-RN3 and Myrothecium sp. S-3.20 could be used to degrade and increase the accessibility to lignocellulose components of sugarcane residue.

Influence of temperature, pH and metal ions on guaiacol oxidation of purified laccase from Leptographium qinlingensis

The bark beetle Dendroctonus armandi is able to kill living Pinus armandi and has caused serious damage to pine forest in Northern China. As the most important symbiotic fungus of D. armandi, Leptographium qinlingensis plays an important role in the invasion process of the bark beetle. The laccase secreted by it are involved in lignin degradation to provide utilizable nutrition for D. armandi, and catalyze some biochemical reactions, causing the damages of tree tissue. In present study, the extracellular laccase of L. qinlingensis was purified by using the ammonium sulfate precipitation and DEAE-cellulose (DE-52) column chromatography. Furthermore, the effects of temperature, pH value and metal ions on it were investigated and characterized. The purified enzyme exerted its optimal activity with guaiacol. The catalytic efficiencies K(m) and V(max) determined for substrate guaiacol were 15.4 μM and 372.9 IU mg⁻¹, respectively. The optimum pH and temperature for the purified enzyme was 4.4 and 45 °C, respectively, with the highest enzyme specific activity of 7,000 IU mg⁻¹. Moreover, the metal ions, Co²⁺, Mn²⁺, Ca²⁺, Mg²⁺, Fe²⁺ and Cd²⁺, especially Hg²⁺, showed significantly inhibition effects on its activity. To understand the characteristics of this laccase might provide an opportunity and theoretical basis to promote integrated pest management of D. armandi.

Sensing hydrogen peroxide by carbon nanotube/horseradish peroxidase bio-nanocomposite

H2O2 is a product of reactions catalysed by several oxidase enzymes and it is essential in environmental and pharmaceutical analyses. The most commonly used enzyme in understanding the biological behaviour of catalysed oxidation of H2O2 is horseradish peroxidase (HRP). In our experiments HRP was bound to carboxyl-functionalized multiwalled carbon nanotubes (MWNT-COOH) by N-hydroxysuccinimide (NHS) and 1-[3-dimethylaminopropyl]-3-ethyl-carbodiimide (EDC) crosslinkers. The activity of this bio-nanocomposite and the limit of detection (LOD) for H2O2 were determined by measuring the fluorescence of tetraguaiacol (which chemical is the product of guaiacol oxidation after addition of H2O2 to the reaction mixture) as a function of time. The hydrogen peroxide biosensor we developed exhibited a detection limit of 1.2 µM H2O2 s−1 which resolution was better than the one measured in solution by about a factor of eight (it was 10 µM H2O2 s−1 in solution). An attempt has been made to measure the concentration of H2O2 in an electrochemical cell with HRP immobilized on the surface of an electrode made of indium tin oxide (ITO, a transparent conductive oxide) and MWNT.

Pre-existent Asymmetry in the Human Cyclooxygenase-2 Sequence Homodimer

Prostaglandin endoperoxide H synthase-2 (PGHS-2), also known as cyclooxygenase-2 (COX-2), is a sequence homodimer. However, the enzyme exhibits half-site heme and inhibitor binding and functions as a conformational heterodimer having a catalytic subunit (Ecat) with heme bound and an allosteric subunit (Eallo) lacking heme. Some recombinant heterodimers composed of a COX-deficient mutant subunit and a native subunit (i.e. Mutant/Native PGHS-2) have COX activities similar to native PGHS-2. This suggests that the presence of heme plus substrate leads to the subunits becoming lodged in a semi-stable Eallo-mutant/Ecat-Native∼heme form during catalysis. We examined this concept using human PGHS-2 dimers composed of combinations of Y385F, R120Q, R120A, and S530A mutant or native subunits. With some heterodimers (e.g. Y385F/Native PGHS-2), heme binds with significantly higher affinity to the native subunit. This correlates with near native COX activity for the heterodimer. With other heterodimers (e.g. S530A/Native PGHS-2), heme binds with similar affinities to both subunits, and the COX activity approximates that expected for an enzyme in which each monomer contributes equally to the net COX activity. With or without heme, aspirin acetylates one-half of the subunits of the native PGHS-2 dimer, the Ecat subunits. Subunits having an S530A mutation are refractory to acetylation. Curiously, aspirin acetylates only one-quarter of the monomers of S530A/Native PGHS-2 with or without heme. This implies that there are comparable amounts of two noninterchangeable species of apoenzymes, Eallo-S530A/Ecat-Native and Eallo-Native/Ecat-S530A. These results suggest that native PGHS-2 assumes a reasonably stable, asymmetric Eallo/Ecat form during its folding and processing.

Peroxidase-like activity of L29H myoglobin with two cooperative distal histidines on electrode using O2 as an oxidant

We recently showed that by introduction of a second distal histidine (Leu29 to His29 mutation) in the heme pocket of sperm whale myoglobin (Mb), L29H Mb mutant exhibits an enhanced peroxidase activity compared to wild type (WT) Mb using H2O2 as an oxidant. In this study, we further showed that when L29H Mb was immobilized in didecyldimethylammonium bromide (DDAB) on glassy carbon electrode (GCE), it can efficiently reduce O2 in aerobic buffer solution to H2O2, followed by electrode-driven oxidation of guaiacol, a common peroxidase substrate, which is more effective (∼3.6-fold at pH=7.0) than that of WT Mb with a single distal His64. Moreover, the peroxidase-like activity of immobilized L29H Mb was found to be affected by pH values, i.e., the slope of the plot of reduction peak vs. guaiacol concentration was increased from (0.83±0.04)×10−3μA/mM at pH=8.0 to (3.08±0.07)×10−3μA/mM at pH=6.0, which suggests that the distal histidines play a key role in reductive activation of O2 by providing protons. Since there is no native peroxidase with two distal histidines and native peroxidase usually uses H2O2 as an oxidant, this study is thus instructive for creating functional enzymes beyond those in nature.

Secondary organic aerosol formation from biomass burning intermediates: phenol and methoxyphenols

Abstract. The formation of secondary organic aerosol from oxidation of phenol, guaiacol (2-methoxyphenol), and syringol (2,6-dimethoxyphenol), major components of biomass burning, is described. Photooxidation experiments were conducted in the Caltech laboratory chambers under low-NOx (< 10 ppb) conditions using H2O2 as the OH source. Secondary organic aerosol (SOA) yields (ratio of mass of SOA formed to mass of primary organic reacted) greater than 25% are observed. Aerosol growth is rapid and linear with the primary organic conversion, consistent with the formation of essentially non-volatile products. Gas- and aerosol-phase oxidation products from the guaiacol system provide insight into the chemical mechanisms responsible for SOA formation. Syringol SOA yields are lower than those of phenol and guaiacol, likely due to novel methoxy group chemistry that leads to early fragmentation in the gas-phase photooxidation. Atomic oxygen to carbon (O : C) ratios calculated from high-resolution-time-of-flight Aerodyne Aerosol Mass Spectrometer (HR-ToF-AMS) measurements of the SOA in all three systems are ~ 0.9, which represent among the highest such ratios achieved in laboratory chamber experiments and are similar to that of aged atmospheric organic aerosol. The global contribution of SOA from intermediate volatility and semivolatile organic compounds has been shown to be substantial (Pye and Seinfeld, 2010). An approach to representing SOA formation from biomass burning emissions in atmospheric models could involve one or more surrogate species for which aerosol formation under well-controlled conditions has been quantified. The present work provides data for such an approach.

Cross-species analysis of thyroperoxidase inhibition by xenobiotics demonstrates conservation of response between pig and rat

Thyroperoxidase (TPO), the enzyme that catalyzes the synthesis of thyroid hormone, is a known target for thyroid-disrupting chemicals. In vivo toxicological evidence supporting TPO-inhibition as one molecular-initiating event that leads to thyroid disruption is derived largely from rat models; however, a significant fraction of research on the inhibition of TPO by xenobiotics has been conducted using porcine TPO. The current work tested the hypothesis that porcine and rat thyroid microsomes exposed to TPO-inhibiting chemicals would demonstrate different responses in a guaiacol oxidation assay. A primary objective of this work is to establish the degree of concordance between rat and porcine TPO inhibition data. Microsomes were isolated from both rat and pig thyroid glands, and the guaiacol oxidation assay was performed for a training set of 12 chemicals, including previously reported TPO inhibitors, thyroid-disrupting chemicals thought to perturb other targets, and several previously untested chemicals, to determine the relative TPO inhibition responses across species. Concentration–response curves were derived for methimazole (MMI), dibutylphthalate (DBP), diethylhexylphthalate (DEHP), diethylphthalate (DEP), 3,5-dimethylpyrazole-1-methanol (DPM), iopanoic acid (IOA), 2-mercaptobenzothiazole (MBT), sodium perchlorate (PERC), p-nonylphenol (PNP), 4-propoxyphenol (4POP), 6-propylthiouracil (PTU), and triclosan (TCS). MMI, PTU, MBT, DPM, 4POP, and at extremely high concentrations, PERC, inhibited TPO activity. Results demonstrated a strong qualitative concordance of response between the two species. All chemicals that inhibited TPO in porcine microsomes also inhibited TPO in rat microsomes. Hill model-derived IC50 values revealed approximate 1.5- to 50-fold differences in relative potency to MMI between species for positive chemicals. DPM, MBT, 4POP, and PTU exhibited greater relative potency to MMI using rat TPO versus porcine TPO, but rank order potency for inhibition was similar for the other test chemicals, with: PTU>MBT>DPM>4POP>PERC for rat TPO and MBT>PTU>DPM>4POP>PERC for porcine TPO. These data support the extrapolation of porcine TPO data to potential thyroid-disrupting activity in rodent models to evaluate TPO-inhibiting chemicals.

Detection of Subnanomolar Melamine Based on Electrochemical Accumulation Coupled with Enzyme Colorimetric Assay

Based on the synergetic effect of the electrochemical accumulation process and the signal amplification of enzymes, a new sensitive method has been developed for the detection of subnanomolar melamine. There are two steps involved in the sensor construction process: (1) accumulation of melamine on an electrode by cyclic voltammetric method and (2) chemical coupling of horseradish peroxidase (HRP) with the accumulated melamine through the linkage of glutaraldehyde. The coupled HRP catalyzes the oxidation of guaiacol to generate an amber-colored product. Quantitative analysis of melamine is performed by measuring the absorption intensities of the colored product. Under the optimal conditions, the method showed a wide linearity in the concentration range from 1.0 × 10(-11) to 1.0 × 10(-8) M for melamine detection. Moreover, it has been successfully applied to detect melamine in different infant formula powders and fish feed samples.

Thermus thermophilus HJ6 유래 내열성 laccase의 유전자 클로닝 및 효소학적 특성

The gene encoding Thermus thermophilus HJ6 laccase (Tt-laccase) was cloned, sequenced, and comprised of 1,389 nucleotides encoding a protein (462 amino acids) with a predicted molecular mass of 51,049 Da. The deduced amino acid sequence of Tt-laccase showed 99.7% and 44.3% identities to the Thermus thermophilus HB27 laccase and Synechococcus sp. RS9917 laccase, respectively. Tt-laccase gene was expressed as a fusion protein with six histidine residues in E. coli Rosetta-gami (DE3) cells, and the recombinant protein was purified to homogeneity. UV-Vis spectrum analysis revealed that the enzyme has copper atoms, a type I Cu(II) and a type III binuclear Cu(II). The optimum pH for the oxidation of guaiacol was 5.0 and the optimum temperature was <TEX>$90^{\circ}C$</TEX> The half-life of heat inactivation was about 120 min at <TEX>$90^{\circ}C$</TEX> The enzyme reaction was inhibited by sodium azide, L-cystein, EDTA, dithiothreitol, tropolone, and kojic acid. The enzyme oxidized various known laccase substrates, its lowest <TEX>$K_m$</TEX> value being for 4-hydroxyindole, highest <TEX>$k_{cat}$</TEX> value for syringaldazine, and highest <TEX>$k_{cat}/K_m$</TEX> for guaiacol.

Human Serum Albumin‐Based Peroxidase Having an Iron Protoporphyrin IX in Artificial Heme Pocket

Cooking up enzymes: Iron protoporphyrin IX (heme) is bound within a hydrophobic cavity in subdomain IB of human serum albumin (HSA). Site-specific mutations to introduce proximal and distal histidines into the heme pocket of HSA conferred a peroxidase activity to the prosthetic heme group. The catalytic activity of the recombinant HSA(mutant)-heme complex for guaiacol oxidation is 17-fold higher than that of HSA(wild type)-heme.

Amperometric determination of total phenolic content in wine by laccase immobilized onto silver nanoparticles/zinc oxide nanoparticles modified gold electrode

A method is described for construction of a highly sensitive amperometric biosensor for measurement of total phenolic compounds in wine by immobilizing laccase covalently onto nanocomposite of silver nanoparticles (AgNPs)/zinc oxide nanoparticles (ZnONPs) electrochemically deposited onto gold (Au) electrode. Scanning electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy were applied for characterization of the surface morphology of the modified electrode, and cyclic voltammetry was used to investigate the electrochemical properties of the proposed electrode toward the oxidation of guaiacol. The linearity between the oxidation current and the guaiacol concentration was obtained in a range of 0.1 to 500μM with a detection limit of 0.05μM (signal-to-noise ratio (S/N)=3) and sensitivity of 0.71μAμM–1cm–2. The electrode showed increased oxidation and reduced reduction current with the deposition of AgNPs/ZnONPs on it. RCT values of ZnONPs/Au, AgNPs/ZnONPs/Au, and laccase/AgNPs/ZnONPs/Au electrode were 220, 175, and 380Ω, respectively. The biosensor showed an optimal response within 8s at pH 6.0 (0.1M acetate buffer) and 35°C when operated at 0.22V against Ag/AgCl. Analytical recovery of added guaiacol was 98%. The method showed a good correlation (r=0.99) with the standard spectrophotometric method, with the regression equation being y=1.0053x−3.5541. The biosensor lost 25% of its initial activity after 200 uses over 5months.