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The oxidative dehydrogenation of phenol compounds, as well as polymer formation from these monomers, was studied by UV-vis and Mossbauer spectroscopy using a novel biological catalyst hematin. The mechanism of the polymerization r...
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The oxidative dehydrogenation of phenol compounds, as well as polymer formation from these monomers, was studied by UV-vis and Mossbauer spectroscopy using a novel biological catalyst hematin. The mechanism of the polymerization reaction was also followed in various pH environments. Phenol radicals were formed by a two-step electron transfer reaction catalyzed by hematin in the presence of peroxide, and polymer was formed from phenol radicals by a noncatalytic reaction. This mechanism partially explains the analogous catalytic polymerization activity of horseradish peroxidase. [References: 19]
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A facile synthesis of meso-unsubstituted but doubly fenced porphyrins is described The required pyrroles are made by the Barton-Zard method from 2,4,6-triisopropylbenzaldehyde and 2,6-diphenylbenzaldehyde. An X-ray structure confi...
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A facile synthesis of meso-unsubstituted but doubly fenced porphyrins is described The required pyrroles are made by the Barton-Zard method from 2,4,6-triisopropylbenzaldehyde and 2,6-diphenylbenzaldehyde. An X-ray structure confirms the type 1 pattern. [References: 19]
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The equilibrium binding constants and the binding site concentrations of an immobilised rabbit antiserum towards progesterone-11 alpha-hemisuccinate-bovine serum albumin were measured for different enzyme tracers. The enzyme trace...
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The equilibrium binding constants and the binding site concentrations of an immobilised rabbit antiserum towards progesterone-11 alpha-hemisuccinate-bovine serum albumin were measured for different enzyme tracers. The enzyme tracers obtained by linking progesterone to horseradish peroxidase (HRP) through different spacer arm structures were: progesterone-11 alpha-hemisuccinate-HRP (the homologous), progesterone-11 alpha-hemiglutarate-HRP, progesterone-11 alpha-hemiadipate-HRP, progesterone-11 alpha-hemisebacate-HRP, progesterone-11 alpha-hemisuccinamido-gamma-aminobutyrate-HRP and progesterone-11 alpha-hemisuccinamido-beta-alaninate-HRP. If compared with the homologous enzyme tracer (provided with a five atom spacer arm and with an affinity of 1x10(9) M-1) the affinity of enzyme tracers with spacer arms of at most six atoms showed a 10-fold decrease whereas about a two-fold decrease was observed with spacer arms of seven and nine atoms. When an amido group which simulates the link between the carboxylic group of the progesterone derivative and the proteic lysine in the immunogen was inserted into 9 and 10 atom spacer arms in the very same position of the immunogen a sharp affinity increase was observed (1.2x10(9) M-1 for progesterone-11 alpha-hemisuccinamido-beta-alanilate-HRP and 1.5x10(9) M-1 for progesterone-11 alpha-hemisuccinamido-gamma-aminobutyrate-HRP) These results showed that in order to reach and exceed the homologous tracer affinity, a four or five atom spacer arm elongation must be coupled to a suitable amido group insertion. An identical trend was observed for the antibody binding site concentrations indicating the presence of two main classes of binding sites in the antiserum used. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 6]
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p-Iodophenol, p-coumaric acid, phenol and aniline are enhancers of the luminol-H2O2-horseradish peroxidase chemiluminescence. These enhanced and unenhanced chemiluminescences were used to assay low concentrations of hydrogen perox...
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p-Iodophenol, p-coumaric acid, phenol and aniline are enhancers of the luminol-H2O2-horseradish peroxidase chemiluminescence. These enhanced and unenhanced chemiluminescences were used to assay low concentrations of hydrogen peroxide. The curves of chemiluminescence intensity maxima against hydrogen peroxide concentration were fitted to third order polynomial regressions, which permit a very good approach to the experimental results. Double the sensitivity (RSD less than or equal to 4.3%) and a slightly lower detection limit (e.g. 0.08 mu M with p-coumaric acid of 0.18 mu M without enhancer) were obtained with enhanced chemiluminescence than with unenhanced chemiluminescence. [References: 15]
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The polymerization of acrylamide in water initiated by a horseradish peroxidase-catalyzed redox system is studied. It combines hydrogen peroxide (as the oxidant) and 2,4-pentanedione (as the reductant). Several side reactions lead...
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The polymerization of acrylamide in water initiated by a horseradish peroxidase-catalyzed redox system is studied. It combines hydrogen peroxide (as the oxidant) and 2,4-pentanedione (as the reductant). Several side reactions leading to the degradation of the enzyme through the formation of compound III are evidenced by polymerization experiments and UV spectroscopy; they can be avoided by adjusting the reactant concentrations. The oxidation of 2,4-pentanedione by a non-enzymic pathway is also detected by H-1 NMR. Its main effect is to reduce the concentration of the enol form of 2,4-pentanedione, and hence to modify the initiation rate. From this information, a schematic picture of the reactions involved in the enzyme-catalyzed redox system is drawn, so as to optimize the polymerization conditions. (C) 2000 Elsevier Science Ltd. All rights reserved. [References: 26]
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In this paper, horseradish peroxidase-mimicking DNAzyme (HRP-DNAzyme) and Prussian blue (PB)–gold (Au) nanocomposites were designed as versatile electrochemical sensing platforms for the amplified detection of DNA, Hg~(2+) and ad...
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In this paper, horseradish peroxidase-mimicking DNAzyme (HRP-DNAzyme) and Prussian blue (PB)–gold (Au) nanocomposites were designed as versatile electrochemical sensing platforms for the amplified detection of DNA, Hg~(2+) and adenosine triphosphate (ATP). By the conjugation of the target probe with the capture probe, a conformational change resulted in the formation of HRP-DNAzyme on the PB–Au modified electrode. The redox of HRP-DNAzyme (red) was efficiently carried out in the presence of H_2O_2, in which PB acted as a mediator stimulating the biocatalytic functions of HRP-DNAzyme and actuated a catalytic cycle bringing an amplified signal. Specific recognition of the target DNA, Hg~(2+) and ATP allowed selective amperometric detection of the target molecule. The detection limits of DNA, Hg~(2+) and ATP were 50 nM, 30 pM and 3 nM, respectively. The highlight of this work is that the catalytic cycle between PB–Au nanocomposites and HRP-DNAzyme was adequately utilized in the amplification platform for versatile sensing. The novel electrocatalytic biosensor involving only one-step incubation exhibited a wide linear range, low detection limit, and satisfactory selectivity and operational stability. The proposed approach provided an ease-of-use and universal reporting system with a simple design and easy operations.
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Optically pumped chemiluminescence of indole-3-acetic acid (IAA) was observed and studied. Rose Bengal (RB) was used as a photosensitizer. Long-lived chemiluminescence (CL) appeared after irradiation of the IAA/RB reaction mixture...
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Optically pumped chemiluminescence of indole-3-acetic acid (IAA) was observed and studied. Rose Bengal (RB) was used as a photosensitizer. Long-lived chemiluminescence (CL) appeared after irradiation of the IAA/RB reaction mixture by monochromatic light at 550 nm (the maximum of RB absorption) or by visible light. The CL spectrum had a maximum at 480 nm. The kinetics of the CL decay were single exponential. Single-exponential kinetics were characterized by two experimentally measured values: initial CL intensity and exponential lifetime of the CL decay. We studied the influence of five parameters: (1) the rate of irradiation fluence, (2) the time of irradiation, (3) RB concentration, (4) IAA concentration and (5) buffer pH on the initial CL intensity and the CL lifetime. Initial CL intensity was proportional to the rate of irradiation fluence and the concentration of RB. Saturation was observed in dependencies of initial CL intensity on the time of irradiation, the concentration of IAA and the buffer pH. The lifetime of the CL decay decreased with increasing pH and did not depend on the other four parameters. The mechanism explaining the experimental results was suggested and detailed kinetic analysis was performed to prove the proposed mechanism. Quantum yield of the CL and five rate constants that are involved in the mechanism were determined. [References: 28]
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A new type of sol-gel organic-inorganic hybrid material was developed and used for the fabrication of an amperometric hydrogen peroxide biosensor. This material was prepared from natural chitosan and recently introduced completely...
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A new type of sol-gel organic-inorganic hybrid material was developed and used for the fabrication of an amperometric hydrogen peroxide biosensor. This material was prepared from natural chitosan and recently introduced completely water-soluble precursor, tetrakis(2-hydroxyethyl) orthosilicates (THEOS), by the sol-gel process without the addition of organic solvents and catalysts. The gelation time for the sol-gel transition and dynamic rheological properties of the resultant gel matrix could be modulated by the amount of added THEOS. The structure of the hybrid gel was made up of a network and spherical particles, as confirmed by SEM observation. By electrochemical experiments, it was found that such a hybrid gel matrix could retain the native biocatalytic activity of the entrapped horseradish peroxidase and provide a fast amperometric response to hydrogen peroxide. The linear range for the determination of hydrogen peroxide was found to be from 1.0 X 10(-6) to 2.5 X 10(-4) mol/L with a detection limit of 4.0 X 10(-7) mol/L. The apparent Michaelis-Menten constant was determined to be 2.198 mmol/L. To improve the analytical characteristics of the fabricated biosensor, the effects of applied potential and pH value on the steady-state current were studied. Under the optimized experimental conditions, the fabricated biosensor was found to have good analytical performance, reproducibility, and storage stability.
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The unfolding and refolding rates of the heme- and Ca2+-containing Coprinus cinereus peroxidase (CIP) have been measured at pH 12.1, in 4 M urea, and at 61.2 degrees C. The change in peroxidase activity paralleled the change in th...
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The unfolding and refolding rates of the heme- and Ca2+-containing Coprinus cinereus peroxidase (CIP) have been measured at pH 12.1, in 4 M urea, and at 61.2 degrees C. The change in peroxidase activity paralleled the change in the Soret band absorbance of the heme group. The unfolding rate constant (k(u)), was determined independently in thermolysin digestion and EDTA experiments at 59.4 degrees C. Both gave k(u) values of 1.5 ms(-1), and also showed that the presence of 4 mM EDTA made CIP unfolding practically irreversible. Unfolding and refolding rates could therefore be determined under identical conditions of denaturation having either EDTA or Ca2+ in excess. The refolding rates at high pH and in 4 M urea were measured by adding Ca2+ to the unfolded CIP, whereas refolding at 61.2 degrees C was evaluated by comparing the unfolding carried out under reversible (excess of Ca2+) and irreversible conditions (excess EDTA). The activation energies for the unfolding at 61.2 degrees C are approximately Delta G double dagger(u) 100, T Delta S double dagger(u) 200, and Delta H double dagger(u) 300 kJ/mol. Five different additives, glycerol, EtOH, Na2SO4, guanidinium chloride (GdmCl), and NaCl, all at 100 mM, were used as probes to evaluate the mechanism of base, urea, and heat on unfolding and refolding. Salts destabilized CIP at high pH, primarily by enhancing the unfolding rate but also by decreasing the refolding rate. Glycerol had the reverse effects and thus stabilized CIP at high pH. The unfolding rate in urea was only slightly affected by the additives, with the exception of GdmCl which enhanced the unfolding rate. The refolding rate was decreased in urea by EtOH and GdmCl, in contrast to glycerol and Na2SO4 which increased the refolding rate. At high temperature the unfolding was affected only slightly by the additives, except for GdmCl, and to a lesser extent NaCl, which enhanced the unfolding rate. The refolding rates were greatly decreased by Na2SO4, EtOH, and GdmCl, whereas glycerol and NaCl enhanced the process. It appears that 100 mM NaCl functions as a catalyst for the temperature-induced process, enhancing both the unfolding and refolding rates. The results indicate that the mechanisms of CIP unfolding and refolding are similar in urea and at high temperature but different at high pH.
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Sap (latex) that oozes out from mango during harvest, upon contact with the fruit, causes dark spots (sap-injury) on the peel and reduces consumer acceptance and shelf-life of fruit. In this investigation different components resp...
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Sap (latex) that oozes out from mango during harvest, upon contact with the fruit, causes dark spots (sap-injury) on the peel and reduces consumer acceptance and shelf-life of fruit. In this investigation different components responsible for sap-injury were identified. Mango saps from four Indian varieties were collected and separated into aqueous and nonaqueous phases. Whole sap, aqueous phase and nonaqueous phase were tested for their ability to cause sap-injury (browning) on mangoes. The nonaqueous phase caused maximum injury and the extent Of injury caused by nonaqueous phases from different varieties was varied. Limonene, ocimene and beta-myrcene, the major terpenoids identified in saps of Indian varieties, caused injury. Similar type of injury on mangoes was also caused by organic solvents. Damage on Totapuri mango fruit was significantly lower compared to other varieties, whereas Totapuri nonaqueous phase caused injury on all other varieties. The peel of Totapuri variety had very low level of polyphenol oxidase, peroxidase and polyphenols compared to other varieties. Thus, a clear relation was found between the peel polyphenol oxidase, peroxidase activities, the polyphenol content in the peel and the extent of injury. Further, nonaqueous phase applied on peels previously heat-treated at 95C for 5 min, neither caused injury nor showed any enzyme activity. Thus, the results indicated that the terpenoid components of sap and polyphenol oxidase, peroxidase, polyphenols of peel are involved in sap-injury.
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