Oxidation Of 4-methylcatechol Research Articles

Effect of pH and temperature on antioxidant enzymes activities in Morinda citrifolia L. (Mengkudu) leaves extract

Morinda citrifolia L. (Mengkudu) leaf is not well-known for its benefits compared to M. citrifolia fruit. It can be considered a good source in healing disease and anti-cancer properties due to the high content of antioxidant enzymes. The objective of this study was to determine the antioxidative activities of M. citrifolia leaves extracted at different pH (pH 3 to pH 9) and temperatures (20°C to 80°C), based on four types of antioxidant enzymes test, namely catalase (CAT), peroxidase (POD), polyphenol oxidase (PPO) and superoxide dismutase (SOD). Another analytical test is the protein determination of M. citrifolia leaves using Bovine Serum Albumin as standard. All of the tests were conducted using spectroscopy methods. Catalase (CAT) activity was monitored by reduction of absorbance due to the decomposition of hydrogen peroxide and peroxidase (POD) activity was observed by an increment of absorbance caused by the oxidation of 4-methylcatechol by hydrogen peroxide. Polyphenol oxidase (PPO) was monitored by an increment of absorbance due to the oxidation of 4-methylcatechol and superoxide dismutase (SOD) activity was determined using the NBT-based method, which monitors the amount of enzyme causing 50% inhibition of photochemical reduction of NBT. Results indicated that CAT activity and POD activity were significantly highest (p<0.05) at pH6, 0.51 U/mg for CAT, 2.58 U/mg for POD, while SOD activity was significantly higher at pH7, 0.47 U/ mg. However, no significant difference (p>0.05) was observed for PPO activity in pH treatment. For different temperature treatments, CAT activity was significantly highest (p<0.05) at 50°C, 0.36 U/mg, while PPO activity and SOD activity were found to be significantly highest (p<0.05) at 30°C, 0.64 U/mg for PPO and 0.43 U/mg for SOD. However, all-temperature treatments given did not significantly affect POD activity. Morinda citrifolia leaves have a good antioxidant potential and can be practised in the treatment of diseases associated with oxidative stress.

Synthesis, structure, polyphenol oxidase mimicking and bactericidal activity of a zinc-schiff base complex

Focusing on the important biological functions of metallo-enzymes and metallo-therapeutics in living world, this research work demonstrates the synthesis, crystal structure, supramolecular architecture, 4-methylcatechol oxidation and bactericidal activity of an interesting zinc-Schiff base complex, [Zn(HL)2Cl2] (1), [Schiff base (HL) = 2-(2-methoxybenzylideneamino)phenol]. Crystal structure analysis of the zinc-Schiff base reveals that zinc centre exists in a distorted tetrahedral geometry. The Schiff base adopts three donor centres, however it gets protonated to exist in a zwitter ionic form and behaves as a monodentate coordinator in 1. This zinc-Schiff base complex has been examined towards the bio-mimetic oxidation of 4-methylcatechol (4-MC) in methanol and portrays its good efficacy with good turnover number, 1.45 × 103 h−1. Electro-chemical study, electron paramagnetic resonance analysis and electrospray ionization mass spectrometry results for the zinc-Schiff base complex in presence of 4-MC ensures that the catalytic reaction undergoes through enzyme-substrate binding, and generation of radical in the course of catalysis drives the catalytic oxidation of 4-MC. Antibacterial study has also been performed against few clinical pathogens (Bacillus SP, Enterococcus, and E. coli). Scanning electron microscope and EDAX analysis for the pathogen with little dose of zinc complex confirms the destruction of bacterial cell membrane with 1.44% occurrence of zinc in the selected zone of inhibition area. This observation holds a great promise to develop future antibacterial agent.

Electrochemically Induced Diels-Alder Reactions of Some Substituted o-quinones with 1,3-cyclopentadiene: An Interesting Finding in the Diels–Alder Reactions

The electrochemical oxidation of 4-methylcatechol (1a), 4-tert-butylcatechol (1b), and 3-methylcatechol (5) has been studied in the presence of 1,3-cyclopentadiene (3) in an ethanol/water (60:40 v/v) mixture using cyclic voltammetry, controlled-potential coulometry, and preparative electrolysis. The electrochemically generated benzoquinones took part, as dienophiles, in a Diels-Alder reaction with 3 to form methanotetrahydronaphtoquinones through an EC mechanism. The cycloaddition of 3-methyl-o-benzoquinone (5a) to 3 is highly regioselective, affording product 6, a novel regioisomer. It is proposed that the cycloaddition would occur with the benzoquinones adsorbed on the carbon electrode surface. The controlled potential electrolyses were carried out in a one-compartment cell.

Chemistry of Manganese and Interaction with Iron and Copper in Wine

Iron (Fe) plays a key role in wine oxidation. The reduction potential of the Fe(III)/Fe(II) redox couple in wine conditions allows Fe(II) to react with O2 and Fe(III) to react with polyphenols with the assistance of sulfite. Copper (Cu) accelerates Fe(II) oxidation and thus can greatly accelerate wine oxidation. Some studies suggest that manganese (Mn), which is present at concentrations similar to those of Fe in wine, may also participate in the catalytic process. This study was therefore undertaken to examine the possible interaction of Mn with Fe and Cu in wine. The reduction potential of the Mn(III)/Mn(II) redox couple is considerably higher than that of the Fe couple. As a result, Fe(III), H2O2, and O2 cannot oxidize Mn(II). Furthermore, Mn(III) is a stronger oxidant than Fe(III) and rapidly oxidizes tartaric acid. Thus, Mn cannot redox-cycle in the same way as the Fe couple. Despite this, Mn(II) accelerates Fe(II) oxidation in an air-saturated wine model, and it is proposed that Mn(II) reacts with an intermediate Fe(III)-superoxo complex to generate Mn(III). This accelerates the oxidation of 4-methylcatechol (4-MeC; a model polyphenol) in the presence of Fe and Cu in the model wine. Mn is a powerful catalyst of sulfite autoxidation, involving a radical chain reaction initiated by traces of Fe. As a radical scavenger, 4-MeC prevents chain propagation and, as with Fe, polyphenols prevent Mn-catalyzed sulfite autoxidation in wine. Results show that Mn accelerates the air oxidation of white wine, which is most evident at high Fe and Cu concentrations.

Oxidative calcium release from catechol.

Oxidation of 4-methylcatechol previously exposed to aqueous calcium chloride was shown by ion chromatography to be associated with release of calcium ions. The catechol was oxidised to the corresponding orthoquinone by the use of tyrosinase from Agaricus bisporus. The oxidative release of calcium from the catechol is ascribed to the diminution of the available hydroxyl functions able to act as chelating groups. Our results suggest that the redox status of melanin may regulate calcium binding and influence calcium levels in pigmented cells.

Facile and one-pot, electro-organic synthesis of a new bis-quinone by the ECCE mechanism in green media

Abstract Electrochemical oxidation of 4-methyl catechol (1a) is investigated in the presence of 1,3-indandione (3) as nucleophile in phosphate buffer solution (0.2 mol/L, pH 6) mixed with ethanol as organic green solvent (50/50) using cyclic voltammetry and controlled-potential coulometry. The results indicated that quinones derived from electro-oxidation of 1a, participated in a 1,4-Michael addition reaction with 1,3-indandione (3) under ECCE mechanism. In this direction, a new bis-quinone was synthesized in high yield and good purity using a facile and convenient electrochemical pathway by carbon anode electrodes in an undivided cell.

Role of Tartaric and Malic Acids in Wine Oxidation

Tartaric acid determines the reduction potential of the Fe(III)/Fe(II) redox couple. Therefore, it is proposed that it determines the ability of Fe to catalyze wine oxidation. The importance of tartaric acid was demonstrated by comparing the aerial oxidation of 4-methylcatechol (4-MeC) in model wine made up with tartaric and acetic acids at pH 3.6. Acetic acid, as a weaker Fe(III) ligand, should raise the reduction potential of the Fe couple. 4-MeC was oxidized in both systems, but the mechanisms were found to differ. Fe(II) readily reduced oxygen in tartrate model wine, but Fe(III) alone failed to oxidize the catechol, requiring sulfite assistance. In acetate model wine the reverse was found to operate. These observations should have broad application to model systems designed to study the oxidative process in foods and other beverages. Consideration should be given to the reduction potential of metal couples by the inclusion of appropriate ligands.

Electrochemical oxidation of catechols in the presence of ketene N, O-acetals: indole formation versus α-arylation

Anodic oxidation of catechols has been investigated in the presence of ketene N, O-acetals using cyclic voltammetry and constant current electrolysis methods. The results show that in the presence of ketene N, O-acetals, the anodic oxidation of 4-methylcatechol affords α-arylated products in satisfactory yields. Meanwhile, indoles can be synthesized from simple 3-substituted catechols or catechol itself following an ECEC mechanism. In addition, either α-arylation or indole formation could be the dominant pathway by simply modifying the composition of the electrolyte solution.

Thiol–Quinone Adduct Formation in Myofibrillar Proteins Detected by LC-MS

Protein oxidation in meat is considered to decrease meat tenderness due to protein disulfide cross-link formation of thiol-containing amino acid residues. An LC-MS method for detection of thiol-quinone adducts (RS-QH(2)) in myofibrillar proteins was developed to investigate the interaction between phenols, as protective antioxidants, and proteins from meat under oxidative conditions using aqueous solutions of (i) cysteine (Cys), (ii) glutathione (GSH), (iii) bovine serum albumin (BSA), or (iv) a myofibrillar protein isolate (MPI). The aqueous solutions were incubated at room temperature (30 min) with 4-methyl-1,2-benzoquinone (4MBQ) prepared from oxidation of 4-methylcatechol (4MC) by periodate resin or incubated at room temperature (5 h) with 4MC and Fe(II)/H(2)O(2). GSH, BSA, and MPI were hydrolyzed (6 N HCl, 110 °C, 22 h) after incubation, and the cysteine-quinone adduct, Cys-QH(2) (m/z 244.2) was identified according to UV and mass spectra after separation on an RP-C18 column. The thiol-quinone adduct was present in all thiol systems after incubation with 4MBQ or 4MC oxidized by Fe(II)/H(2)O(2). Direct reaction with 4MBQ resulted in each case in increased Cys-QH(2) formation compared to simultaneous oxidation of thiol source and 4MC with Fe(II)/H(2)O(2). The covalent bonds between quinones and thiol groups may act as a potential antioxidant by inhibiting disulfide protein cross-link formation.

Electrochemical Oxidation of 4-Methylcatechol in the Presence of β-Diketones

Abstract Electrochemical oxidation of 4-methylcatechol (1) in the presence of, benzoylacetone (2), dibenzoylmethane (3), 3-hydroxy-1H-phenalen-1-one (4), acetylacetone (5), dimedone (6), and 2-acetylcyclohexanone (7) as nucleophiles has been studied in detail by cyclic voltammetry and controlled-potential coulometry. The results indicate that the electrochemically generated quinone participates in Michael addition reaction with 2–7 via various mechanisms to produce new organic compounds. Furthermore, our studies show that the structure of intermediates play a crucial role in product selectivity under controlled-potential conditions. Various types of products were also obtained through the selective oxidation at the surface of a carbon electrode in an undivided cell.

Evidence Consistent with the Requirement of Cresolase Activity for Suicide Inactivation of Tyrosinase

Tyrosinase is a mono-oxygenase with a dinuclear copper catalytic center which is able to catalyze both the ortho-hydroxylation of monophenols (cresolase activity) and the oxidation of catechols (catecholase activity) yielding ortho-quinone products. Tyrosinases appear to have arisen early in evolution and are widespread in living organisms where they are involved in several processes, including antibiosis, adhesion of molluscs, the hardening of the exoskeleton of insects, and pigmentation. Tyrosinase is the principal enzyme of melanin formation in vertebrates and is of clinical interest because of the possible utilization of its activity for targeted treatment of malignant melanoma. Tyrosinase is characterised by an irreversible inactivation that occurs during the oxidation of catechols. In a recent publication we proposed a mechanism to account for this feature based on the ortho-hydroxylation of catecholic substrates, during which process Cu(II) is reduced to Cu(0) which no longer binds to the enzyme and is eliminated (reductive elimination). Since this process is dependent on cresolase activity of tyrosinase, a strong prediction of the proposed inactivation mechanism is that it will not be exhibited by enzymes lacking cresolase activity. We show that the catechol oxidase readily extracted from bananas (Musa cavendishii) is devoid of cresolase activity and that the kinetics of catechol oxidation do not exhibit inactivation. We also show that a species with the molecular mass of the putative cresolase oxidation product is formed during tyrosinase oxidation of 4-methylcatechol. The results presented are entirely consistent with our proposed mechanism to account for suicide-inactivation of tyrosinase.

Characterisation by liquid chromatography coupled to electrospray ionisation ion trap mass spectrometry of phloroglucinol and 4-methylcatechol oxidation products to study the reactivity of epicatechin in an apple juice model system

The reactivity of the (−)-epicatechin structure towards caffeoylquinic acid o-quinones was studied in an apple juice model solution. The approach consisted in considering separately the reactivities of the two phenolic moieties of an (−)-epicatechin molecule: phloroglucinol and 4-methylcatechol were chosen to represent A- and B-rings, respectively. The oxidation products were characterised by RP-HPLC coupled with electrospray ionisation Mass spectrometry (MS). The reactivities of the A- and B-rings were clearly different on the basis of the oxidation products formed. Both A- and B-rings could be involved in covalent bond formation, but electron transfers only occurred with the B-ring. Most of the (−)-epicatechin oxidation products were linked by A/B-ring linkage (“head-to-tail” intermolecular coupling). After this first dimerisation step, intramolecular reactions seemed to be favoured. Therefore, the complexity of oxidation products in apple juice does not only result from an extensive polymerisation of native phenolic compounds, but also from a multiplicity of small molecules in different oxidation states and isomeric forms.

Oxidation of 4-Methylcatechol: Implications for the Oxidation of Catecholamines

At alkaline pH, 4-methylcatechol oxidizes more rapidly than the related catecholamines: dopamine, norepinephrine, and epinephrine. This oxidation is not inhibited by superoxide dismutase or catalase, indicating that O2 itself is the oxidant, but the reduction potential of O2/O2-* is too low for it to oxidize 4-methylcatechol directly. Instead, O2 oxidizes the 4-methylcatechol semiquinone, which is formed by comproportionation of 4-methylcatechol and its o-quinone. Aniline reacts very quickly with the o-quinone and thus stops the comproportionation reaction that oxidizes 4-methylcatechol to the semiquinone. Oxidation of 4-methylcatechol then requires superoxide, and in the presence of aniline, oxidation of 4-methylcatechol by O2 is inhibited by superoxide dismutase. When catecholamines oxidize, the side chain amine inserts into the catechol o-quinone, forming a bicyclic compound. By eliminating the quinone, this ring closure prevents comproportionation and the consequent oxidation of catecholamines by O2. It also prevents reaction of the quinone with other compounds and the formation of potentially toxic products.

Oxidative chemistry of the natural antioxidant hydroxytyrosol: hydrogen peroxide-dependent hydroxylation and hydroxyquinone/ o-quinone coupling pathways

Oxidation of the natural antioxidant hydroxytyrosol ( 1 ) with peroxidase/H 2O 2 in phosphate buffer at pH 7.4 led to the formation of two main ethyl acetate-extractable products. These could be isolated by preparative TLC after reduction and acetylation, and were identified as the tetraacetyl derivative of 2-(2,4,5-trihydroxyphenyl)ethanol ( 3 ) and the heptaacetyl derivative of the pentahydroxybiphenyl 4 by 2D NMR and MS analysis. Similar oxidation of 4-methylcatechol gave, after the same work-up, the acetylated derivatives of 1,2,4-trihydroxy-5-methylbenzene ( 5 ) and the pentahydroxybiphenyl 6 . Mechanistic experiments suggested that hydrogen peroxide affects the course of the oxidation of 1 by adding to the first formed o-quinone to give a hydroxyquinone intermediate. This could bring nucleophilic attack to the o-quinone of 1 to give the dimer 4 . These results disclose novel oxidative pathways of 4-alkylcatechols and provide an improved chemical basis to enquire into the mechanism of the antioxidant action of 1 .

Properties of wheat bran polyphenol oxidase

Polyphenol oxidase (PPO) obtained from wheat bran catalyzed the oxidation of 4-methyl catechol. Phenolic compounds found naturally in crude extract played role as an endogeneous substrate and activity of crude extract needed correction. Activity versus enzyme concentration gave a linear plot at high substrate concentration whereas a nonlinear plot was obtained at low substrate concentration which proved the presence of endogeneous substrate. Adsorption on celite and extraction with polyvinylpyrrolidone (PVPP) caused the removal of phenols. Adsorption of PPO on celite yielded a 4-fold increase in specific activity whereas extraction with PVPP yielded a 2.5-fold increase in specific activity compared to the crude extract. The kinetics of PPO catalyzed oxidation obeyed Michaelis-Menten model; Km and Vmax values were found as 218 mM and 99 microM/min, respectively. The enzyme was inhibited by ethyl alcohol, dithiothreitol (DTT) and isoproterenol and exhibited heat stability up to a temperature of 90 degrees C. The optimum pH of the enzyme was found to be 5.0.

A diphenolase from persimmon fruits ( Diospyros kaki L., Ebenaceae)

A diphenolase from persimmon fruits ( Diospyros kaki L.), active against catechol, 4-methylcatechol, L-3,4-dihydroxyphenylalanine and 3-(3,4-dihydroxyphenyl)propionic acid, was characterized in detail in terms of pH and temperature optima, stability, kinetic parameters and inhibition behaviour toward some general PPO inhibitors. The substrate specificity of the persimmon PPO was very high for catechol and 4-methylcatechol. The enzyme was extremely stable at its optimum pH of 7.5 in the presence of 4-methylcatechol as the substrate and it retained over 90% of its original PPO activity after 24 h of incubation at 4 °C at that pH. Thermal properties of the persimmon enzyme, together with thermodynamic parameters, show that the persimmon enzyme is very heat-sensitive. Ascorbic acid, metabisulfite, azide and benzoic acid all inhibited the 4-methylcatechol oxidation by persimmon PPO, indicating its sensitivity toward the general PPO inhibitors, especially metabisulfite. All the data support the presence of a highly active diphenolase in persimmon fruits ( Diospyros kaki L.) having similar properties to other plant polyphenoloxidases.

Active Versus Laddered Municipal Bond Portfolio Management

Iron plays a key role in wine oxidation. The reduction potential of the Fe(III)/Fe(II) redox couple in wine conditions allows Fe(II) to react with O₂, and Fe(III) to react with polyphenols with the assistance of sulfite. Cu accelerates Fe(II) oxidation and so can greatly accelerate wine oxidation. Some studies suggest that Mn, which is present at similar concentrations to Fe in wine, may also participate in the catalytic process. This study was therefore undertaken to examine the possible interaction of Mn with Fe and Cu in wine. The reduction potential of the Mn(III)/Mn(II) redox couple is considerably higher than that of the Fe couple. As a result it is shown that Fe(III), H₂O₂ and also O₂ cannot oxidize Mn(II). Furthermore Mn(III) is a much stronger oxidant than Fe(III) and rapidly oxidizes tartaric acid. It is immediately apparent, therefore, that Mn cannot redox-cycle in the same way as the Fe couple. Despite this unpromising profile, Mn(II) is shown to accelerate Fe(II) oxidation in air saturated model wine and it is proposed that it reacts with an intermediate Fe(III)-superoxo complex to generate Mn(III). As a result it accelerates the oxidation of 4-methylcatechol (4-MeC, a model polyphenol) in the presence of Fe and Cu in model wine. Mn is a powerful catalyst of sulfite autoxidation, involving a radical chain reaction initiated by traces of Fe. As a radical scavenger, 4-MeC prevents chain propagation and so, as with Fe, polyphenols prevent Mn catalysed sulfite autoxidation in wine. Mn is shown to accelerate the air oxidation of a white wine, which is most evident with high Fe and Cu levels.

Polyphenol oxidase in reverse micelles of AOT/cyclohexane: A thermostability study

Polyphenol oxidase catalysing the oxidation of 4-methylcatechol in reverse micelles of AOT/cyclohexane had an optimum temperature 15 °C higher than in aqueous medium. However, the enzyme lost stability when it was preincubated in reverse micelles in the absence of substrate regardless of the temperature although the effect was more pronounced at higher temperatures. The thermostability of polyphenol oxidase is higher when it is injected in reverse micelles containing buffer than when injected in initially empty micelles. Moreover, the thermostability of polyphenol oxidase in reverse micelles is strongly dependent on the size of the micelles, the bigger the micelle the greater the stability. The thermoinactivation of the enzyme follows a monomolecular process characteristic of a conformational change so the protein is protected by ligands towards inactivation. p-Nitrophenol as competitive inhibitor and acetyl tyrosine ethyl ester as alternate substrate increase the half-life of the polyphenol oxidase by about 2.5 and 4 times respectively. This finding may allow the use of the enzyme at higher temperatures with a gain in its stability. © 2001 Society of Chemical Industry

Oxidation of Chlorogenic Acid, Catechins, and 4-Methylcatechol in Model Solutions by Combinations of Pear (Pyrus communis Cv. Williams) Polyphenol Oxidase and Peroxidase: A Possible Involvement of Peroxidase in Enzymatic Browning

To clarify the role of pear peroxidase (POD) in enzymatic browning, oxidation of 4-methylcatechol, chlorogenic acid, and (−)-epicatechin catalyzed by purified polyphenol oxidase (PPO), purified POD, or combinations of the two enzymes was followed by HPLC. It was shown that pear POD had no oxidative (oxygen dependent) activity. However, in presence of PPO, POD enhanced the phenol degradation. Moreover, when PPO was entirely inhibited by NaCl after different oxidation times, addition of POD led to a further consumption of the phenolic compound. Two mechanisms have been proposed to explain this additional consumption. First, our results have demonstrated that, whatever the substrate used, PPO oxidation generated H2O2, the amount of which varies with the phenolic structure. Second, quinonic forms are used by POD as peroxide substrate. These two mechanisms associated with the kinetic properties of pear PPO and POD are consistent with an effective involvement of pear POD in enzymatic browning. Keywords: Enzymatic browning; pear; peroxidase; polyphenol oxidase

Maillard reaction products inhibit apple polyphenoloxidase

The effects of Maillard reaction products (MRP) on apple polyphenol oxidase (PPO) were evaluated spectrophotometrically at 400 nm after oxidation of 4-methylcatechol. MRP, synthesized under different conditions including heating time, type of amino acids, pH and concentration of both amino acid and glucose, showed different effects on apple PPO. The inhibitory effects of MRP. heated for 7 h at 90 °C and synthesized from various amino acids with glucose, were as follows: arginine = histidine > ysteine > lysine. The MRP synthesized from glutamic acid or valine enhanced rather than inhibited PPO activity. Increasing the heating time of histidine-glucose solutions also enhanced the inhibitory effect. However, a slight decrease in the inhibitory effect was observed in the cysteine-glucose solutions after 3 h of heating. The MRP synthesized at low pH levels was a more effective inhibitor than the MRP synthesized at higher pH levels.