Bilirubin and hemoglobin interferences in direct colorimetric cholesterol reactions using enzyme reagents

The interferences of bilirubin and hemoglobin were tested in two cholesterol procedures in which enzymes were used as chemical reagents. Both procedures used similar approaches with cholesterol esterase to free cholesterol from its esters and cholesterol oxidase to generate hydrogen peroxide from the total free cholesterol resulting. From that common start, one procedure then used catalase to generate formaldehyde from methanol and the peroxide produced from cholesterol, and the formaldehyde was then reacted with acetylacetone to produce a yellow chromogen, while the other procedure used peroxidase to catalyze a reaction directly between peroxide and 4-aminoantipyrine plus phenol to generate a pink chromogen. Bilirubin and hemoglobin were shown to produce some interference by reacting competitively with peroxide in both systems and by contributing residual absorbance at the wavelengths of measurement of each of the chromogens. Since bilirubin showed a spectral change, static blanking with sample blanks caused overcorrections. However, the elimination of a sample blank for either procedure could result in a favorable compensating error because the residual color of bilirubin could substitute in part at least for the lost reactivity of the peroxide used up in reaction with the bilirubin of the sample.     

Kinetics of oxidation of bilirubin and its protein complex by hydrogen peroxide in aqueous solutions

A comparative study of oxidation reactions of bilirubin and its complex with albumin was carried out in aqueous solutions under the action of hydrogen peroxide and molecular oxygen at different pH values. Free radical oxidation of the pigment in both free and bound forms at pH 7.4 was shown not to lead to the formation of biliverdin, but to be associated with the decomposition of the tetrapyrrole chromophore into monopyrrolic products. The effective and true rate constants of the reactions under study were determined. It was assumed that one possible mechanism of the oxidation reaction is associated with the interaction of peroxyl radicals and protons of the NH groups of bilirubin molecules at the limiting stage with the formation of a highly reactive radical intermediate. The binding of bilirubin with albumin was found to result in a considerable reduction in the rate of the oxidation reaction associated with the kinetic manifestation of the protein protection effect. It was found that the autoxidation of bilirubin by molecular oxygen with the formation of biliverdin at the intermediate stage can be observed with an increase in the pH of solutions.     

The kinetics of oxidation of bilirubin and ascorbic acid in solution

The results of a comparative study of the oxidation of bilirubin, ascorbic acid, and their mixture in aqueous solutions under the action of air oxygen and hydrogen peroxide are presented. The observed and true rate constants for the oxidation reactions were determined. It was shown that the oxidation of tetrapyrrole pigment occurred under these conditions bypassing the stage of biliverdin formation to monopyrrole products. Simultaneous oxidation of bilirubin and ascorbic acid was shown to be accompanied by the inhibition of ascorbic acid oxidation by bilirubin, whereas ascorbic acid itself activated the oxidation of bilirubin.     

Bilirubin/rat serum albumin interaction

Essential differences are demonstrated between bilirubin binding to rat serum proteins and to albumin in human serum. Acidimetric titration of rat serum with and without added bilirubin shows that binding of bilirubin acid in the range of pH from 6.8 to 8.8 takes place with release of less than one hydrogen ion per molecule of bound bilirubin. With human serum, two hydrogen ions are released, indicating binding of bilirubin dianion. The binding equilibrium of N-[4-[(4-aminophenyl)-sulfonyl]phenyl]-acetamide (MADDS) to rat serum albumin is influenced slightly by cobinding of bilirubin whereas MADDS and bilirubin bind competitively to human serum albumin. Finally, the rate of oxidation of bilirubin with hydrogen peroxide and peroxidase is decreased moderately by addition of rat serum albumin and strongly by the human protein, indicating that biliribin in its complex with rat serum albumin is subject to oxidation while the complex with human serum albumin is protected. These differences should be considered when rats are used as a model in experimental studies aiming at prevention of bilirubin encephalopathy in human neonates.     

Kinetics and Mechanism of Bilirubin Oxidation by Benzoyl Peroxide in Dimethyl Sulfoxide

The kinetics of the redox reaction of bilirubin by the action of benzoyl peroxide in dimethyl sulfoxide was analyzed. It is shown that the first reaction product is biliverdin, which oxidizes to purpurin and further to choletelin. The kinetic and activation parameters of the oxidation reactions were obtained. A kinetic model of the process was proposed. An assumed route of the reaction is related to the exchange interaction of CH protons of methylene and methine spacers with free radicals in the rate‐limiting step with the further destruction of the “ridge‐tile” pigment conformation. The mechanism steps are confirmed by quantum‐chemical calculations and HPLC. It is found that in organic solvents the end products of bilirubin oxidation are not monopyrrolic derivatives. The data obtained will be useful in constructing antioxidant action models of the pigment.     

过氧化脲在氧化反应中的应用研究进展

氧化反应是重要的有机合成单元反应,常采用H2O2或过氧酸等为氧化剂.近年来,过氧化脲作为一种清洁环保的固态H2O2,以其性质稳定、H2O2含量高(36.2%)且释放可控等优点,在众多氧化反应中得到了广泛应用.对过氧化脲在氧化反应中的应用进行了总结和概述,重点介绍了环氧化、Baeyer-Villiger氧化、N-氧化、硫醚氧化成砜和亚砜、氧化卤化等反应.     

Differential selectivity in electrochemical oxidation of ascorbic acid and hydrogen peroxide at the surface of functionalized ormosil-modified electrodes

Functionalized ormosil-modified electrodes have been developed for electroanalytical applications. The functionalized ormosil-modified electrodes are made by encapsulating potassium ferricyanide/potassium ferrocyanide within ormosil film derived from an optimum composition of 3-aminopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and phenyltrimethoxy silane in acidic medium in absence of Nafion/crown ether (system 1), in the presence of Nafion (system 2) and in the presence of dibenzo-18-crown-6 (system 3). Another modified electrode (system 4) is also developed using the reaction product of potassium ferricyanide, 3-aminopropyltrimethoxysilane and either tetrahydrofuran (THF) or cyclohexanone followed by ormosil formation in the presence of 2-(3,4-epoxycyclohexyl)ethyl trimethoxysilane and phenyltrimethoxy silane in acidic medium. The electrochemical oxidation of hydrogen peroxide and ascorbic acid conducted at the surface of these four types of functionalized electrodes shows very interesting observations on the selective sensing of ascorbic acid and peroxide. The results based on cyclic voltammetry justify the relative performances on the kinetics of hydrogen peroxide oxidation and reduction. System 3 shows relatively much better oxidation kinetics of hydrogen peroxide as compared to other three systems with relatively weak reduction kinetics whereas system 4 shows relatively faster reduction kinetics of hydrogen peroxide as compared to other three systems. Similarly system 4 shows excellent response to ascorbic acid whereas system 3 shows insensitivity to ascorbic acid under similar experimental conditions. Typical response curve for the analysis of hydrogen peroxide and ascorbic acid using system 3 and system 4 respectively are reported. The results show that system 3 is the best for probing hydrogen peroxide with lowest detection limit of 0.5 μM without any interference from ascorbic acid as commonly encountered using many conventional and chemically modified electrodes.     

On the mechanisms of oxidation of organic sulfides by H2O2 in aqueous solutions

The mechanism of oxidation of organic sulfides in aqueous solutions by hydrogen peroxide was investigated via ab initio calculations. Specifically, two reactions, hydrogen transfer of hydrogen peroxide to form water oxide and the oxidation of dimethyl sulfide (DMS) by hydrogen peroxide to form dimethyl sulfoxide, were studied as models of these processes in general. Solvent effects are included both via including explicitly water molecules and via the polarizable continuum model. The former was found to have a much more significant effect than the latter. When explicit water molecules are included, a mechanism different from those proposed in the literature was found. Specific interactions including hydrogen bonding with 2-3 water molecules can provide enough stabilization for the charge separation of the activation complex. The energy barrier of the oxidation of DMS by hydrogen peroxide was estimated to be 12.7 kcal/mol, within the experimental range of the oxidation of analogous compounds (10-20 kcal/mol). The major reaction coordinates of the reaction are the breaking of the O-O bond of H2O2 and the formation of the S-O bond, the transfer of hydrogen to the distal oxygen of hydrogen peroxide occurring after the system has passed the transition state. Reaction barriers of the hydrogen transfer of H2O2 are an average of 10 kcal/mol or higher than the reaction barriers of the oxidation of DMS. Therefore, a two-step oxidation mechanism in which, first, the transfer of a hydrogen atom occurs to form water oxide and, second, the transfer of oxygen to the substrate occurs is unlikely to be correct. Our proposed oxidation mechanism does not suggest a pH dependence of oxidation rate within a moderate range around neutral pH (i.e., under conditions in which hydronium and hydroxide ions do not participate directly in the reaction), and it agrees with experimental observations over moderate pH values. Also, without including a protonated solvent molecule, it has activation energies that correspond to measured activation energies.     

Reaction of hydrogen peroxide with tetraazamacrocyclic complex of iron(II) in the presence of nitrogeneous bases

The kinetics of hydrogen peroxide oxidation of Fe(II) to Fe(III) complexed with tetraazamacrocyclic ligand was studied, and a decrease in the reaction rate was observed in the presence of nitrogeneous bases, capable of forming hexacoordinated complexes with tetraazamacrocyclic compound of iron(II). The rate of reaction is proprotional to the concentration of the iron complex and hydrogen peroxide and inversely proportional to the concentration of the nitrogeneous base. A mechanism for the course of the reaction has been proposed, and the rate constants of the oxidation of the pentacoordinated iron(II) complexes have been calculated. It was shown that the addition of the fifth donor particle (in particular imidazole) activates the iron(II) atom with respect to the oxidation reaction. It was found that a tetraazamacrocyclic complex of iron(II) is capable of displaying a peroxidase type activity.Translated from Teoreticheskaya Eksperimental'naya Khimiya, Vol. 22, No. 3, pp. 309–316, May–June, 1986.     

Some new applications of the biamperostat catalytic-kinetic determination of copper, peroxidase, glucose oxidase, thyroxine and 5-chloro-7-iodo-8-hydroxyquinoline.

Biamperometrically observable reactions can be evaluated by the “potentiostat” method with a current-to-voltage transducer. Some further examples of the application of this “biamperostat” are described: the copper(II)-catalyzed autodecomposition of hydrogen peroxide, the horseradish peroxidase-catalyzed oxidation of iodide with hydrogen peroxide, the glucose oxidase-catalyzed oxidation of glucose with molecular oxygen and the iodine (in organic compounds )-catalyzed oxidation of arsenic(III) with cerium(IV). 1,10-Phenanthroline is determined indirectly by its inhibitory action on copper(II).     

Peroxygenase‐Catalyzed Oxyfunctionalization Reactions Promoted by the Complete Oxidation of Methanol

Peroxygenases catalyze a broad range of (stereo)selective oxyfunctionalization reactions. However, to access their full catalytic potential, peroxygenases need a balanced provision of hydrogen peroxide to achieve high catalytic activity while minimizing oxidative inactivation. Herein, we report an enzymatic cascade process that employs methanol as a sacrificial electron donor for the reductive activation of molecular oxygen. Full oxidation of methanol is achieved, generating three equivalents of hydrogen peroxide that can be used completely for the stereoselective hydroxylation of ethylbenzene as a model reaction. Overall we propose and demonstrate an atom‐efficient and easily applicable alternative to established hydrogen peroxide generation methods, which enables the efficient use of peroxygenases for oxyfunctionalization reactions.     

The spectrophotometric determination of vanadium in rocks

Vanadium in rock samples is determined, after alkaline fusion of the sample, by means of its catalytic action on the oxidation of aniline to aniline black by hydrogen peroxide. If necessary, chromium can be easily extracted to prevent interference. The sensitive procedure was applied to standard granite Gi and diabase Wi, and to the C.A.A.S. syenite i ; values of 16, 263 and 86 p.p.m., respectively, were obtained.     

A Sensitive Visible Spectrophotometric Method for Copper Using Bis-Substituted Thiocarbamoyl Trisulfides

Abstract

Bis-substituted thiocarbamoyl disulfides (thiuram disulfides) were investigated as chromogenic reagents for the analysis of copper in trichloroacetic acid solutions. It was found that hydrogen peroxide speeded color development, increased color stability and enhanced color intensity in a trichloroacetic acid-alcohol matrix. In the presence of hydrogen peroxide, all copper complexes had molar absorptivities exceeding 30,000. Bis-pentamethylene thiocarbamoyl disulfide was selected as the best commerically available reagent of those investigated. The procedure is almost interference free, silver and mercury being the most serious interference. The sensitivity is 6 × 10^?3 micrograms/cm².     

铜(Ⅱ)及其配合物催化胆红素氧化动力学的研究

本文用电化学，吸收光谱等方法对Ｃｕ（２＋）及其配合物与胆红素在碱性（ｐＨ１０）条件下的作用规律进行了研究．发现Ｃｕ（２＋）及其配合物对胆红素的氧化的催化作用依配合物的稳定性和配体齿数不同而异．在胆红素的氧化过程中，真正起氧化作用的是溶解氧．     

Redox‐Controlled Hydrogen Bonding: Turning a Superbase into a Strong Hydrogen‐Bond Donor

Herein the synthesis, structures and properties of hydrogen‐bonded aggregates involving redox‐active guanidine superbases are reported. Reversible hydrogen bonding is switched on by oxidation of the hydrogen‐donor unit, and leads to formation of aggregates in which the hydrogen‐bond donor unit is sandwiched by two hydrogen‐bond acceptor units. Further oxidation (of the acceptor units) leads again to deaggregation. Aggregate formation is associated with a distinct color change, and the electronic situation could be described as a frozen stage on the way to hydrogen transfer. A further increase in the basicity of the hydrogen‐bond acceptor leads to deprotonation reactions.     

Applications of transition-metal catalysts to textile and wood-pulp bleaching

From an economic perspective, textile and paper bleaching are amongst the most important oxidation processes. The removal of unwanted chromophores, be it stains on cloths or residual lignin in wood pulp, consumes more than 60 % of the world production of hydrogen peroxide. However, existing technologies have their limitations. At ambient temperature, hydrogen peroxide gives little stain bleaching and is used inefficiently. Hence the high product dosages and washing temperatures required limit its application to predominantly European markets, to the exclusion of the majority of the world's population. In paper manufacture, the use of chlorine-based oxidants results in the formation of chlorinated waste products, which show poor biodegradability. On the other hand, hydrogen peroxide requires higher temperatures, longer reaction times and is more expensive. Transition-metal catalysts offer an alternative. This review discusses the main classes of known bleach catalysts and their possible modes of action.     

CHEMICAL CHANGES LEADING TO CHEMILUMINESCENCE OF LUCIGENINE (DIMETHYLBIACRIDYLIUM NITRATE) AND OF SOME PHTHALAZINEDIONE DERIVATIVES

Abstract— Measurements of the redox potential of the chemiluminescent compound 10,10' dimethyl-9,9' biacridylium nitrate (-0.093 V) show that it is thermodynamically possible to reduce it with hydrogen peroxide or with ammonium hydroxide in alkaline solutions at equilibrium concentrations sufficiently high to account for the observed chemiluminescence. Reduction of the compound with ammonium hydroxide takes place much more slowly than the corresponding reaction with hydrogen peroxide so that when both redox couples (O₂/H₂O₂ and N₂H₄/NH₄OH) are present the hydrogen peroxide couple predominates if oxygen is supplied. It was shown that interference with the oxygen supply or its partial removal with nitrogen brings about an increase in chemiluminescence intensity in NH₄OH while increasing the concentration of oxygen diminished the intensity.
5-amino 2,3 phthalazine 1,4 dione (luminol) also appears to undergo a reduction following a two step oxidation. This is shown by the fact that when oxygen was supplied the chemiluminescence intensity was found to be directly proportional to the OH^- concentration while a typical titration curve with p K 11.7 is exhibited by the intensity when the oxygen supply is limited in mixtures of luminol and peroxydisulfate. The peroxide presumably arises in the first oxidation step. Amino peroxyphthalic anhydride is suggested as an intermediate which is reduced to the aminophthalate ion, the presumed emitter in the chemiluminescence.     

Highly selective sulfoxidation of allylic and vinylic sulfides by hydrogen peroxide using a flavin as catalyst

A highly chemoselective oxidation of allylic and vinylic sulfides to the corresponding sulfoxides has been developed using flavin 1 as the oxidation catalyst and hydrogen peroxide as the terminal oxidant. The sulfoxides were formed in good to excellent yields in a highly selective manner even when an excess of the oxidant was used. Sulfone formation was completely suppressed to <0.5% (in one single case 1.5% sulfone was detected). No epoxidation of double bonds or interference with other functional groups was observed under the reaction conditions. The general applicability was demonstrated by the selective oxidation of various allylic and vinylic sulfides having different electronic properties. A number of functionalities including hydroxy, acetoxy, amino, silyloxy, and formyl groups are tolerated under these mild reaction conditions.     

Oxidation of aldehydes to carboxylic acids in water catalyzed by cobalt(II) Schiff-base complex anchored to SBA-15/MCM-41

Cobalt(II) Schiff-base complexes were successfully anchored to SBA-15/MCM-41 and used as a catalyst for the oxidation of aldehydes to afford carboxylic acids in water under the action of hydrogen peroxide. Reaction conditions, such as different catalyst type, reaction temperature, reaction time, solvents media, and catalyst amount were studied systematically. High yield (up to 98%) of the process was reached. Such substrate-supported catalyst can be reused up to five times without significant loss of its catalytic activity which is not lower than 85%.     

Highly Sensitive Determination of DAO Activity by Oxidation of a Luminescence Reagent

A highly sensitive method for measuring the activity of the enzyme diamine oxidase (DAO) independent of the type of substrate is described. The principle of the assay is to determine the amount hydrogen peroxide generated as a reaction product during oxidation of diamines by DAO. PSatto™, a highly sensitive luminescence reagent, was used to generate a signal depending on the hydrogen peroxide concentration based on the action of horseradish peroxidase. DAO is specifically captured from a sample by an antibody immobilized to microwell plates, and the substrate is added to the bound enzyme. Various diamines were used as substrates; the peroxide produced is directly proportional to the amount of DAO bound to the specific antibodies. With this very sensitive method, it is possible to detect pmol amounts of generated hydrogen peroxide in plasma matrix corresponding to the biological activity of DAO.