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Degradation Reactions (degradation + reaction)
Selected AbstractsSurface modification of PHBV films with different functional groups: Thermal properties and in vitro degradationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010Yu Ke Abstract Polyacrylamide was photografted on solution-cast poly(3-hydroxybutyric acid- co -3-hydroxyvaleric acid) (PHBV) films (amide-PHBV), on which amide groups were transformed into amine groups through Hofmann degradation reaction (amine-PHBV), followed by collagen coupling reaction to prepare collagen-modified PHBV (collagen-PHBV). Amide-, amine-, and collagen-PHBV had higher water absorption and d -spacing values than PHBV, and melting temperatures and enthalpies decreased in the order of collagen-PHBV < amine-PHBV < amide-PHBV < PHBV. Thermal decomposition kinetics of PHBV component in the films has been investigated by means of nonisothermal thermogravimetric and derivative thermogravimetric studies. Applying the Avrami-Erofeev equation with index of 2/5 as the probable kinetic function, the suitable activation energy was calculated by the Friedman method through linear fitting (correlation coefficient > 0.98). The activation energy of PHBV was lower than that of amide-PHBV but higher than that of amine- and collagen-PHBV. Being incubated in phosphate-buffered saline at 37°C, the modified PHBV films showed more weight loss than PHBV during 360 days; however, pH of degradation fluids was nearly neutral as the initial pH was recorded at 7.2. The modified PHBV films with different functional groups may provide an improved biodegradation rate for various cytocompatible biomaterials constructs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Synthesis of PLLA-MPEG Diblock Copolymers by Microwave-Assisted Copolymerization of L -Lactide and Methoxy Poly(ethylene glycol)MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 10 2007Chao Zhang Abstract PLLA-MPEG diblock copolymers with a controlled number-average molar mass ranging from 7,330 to 117,610 g,·,mol,1 and an L -lactide conversion ranging from 65.1 to 97.3% were synthesized effectively in 20 min at 100,°C by MPEG-initiated ROP of L -lactide under microwave irradiation. Prolonged microwave irradiation time led to the degradation of the copolymers because the ROP reaction and the thermal degradation reaction occurred simultaneously at the later stage of the reaction process. The differential scanning calorimetric and thermogravimetric study indicated that higher melting temperatures and thermal stability were obtained for PLLA-MPEG diblock copolymers with longer PLLA segments. [source] Preparation of Bismuth Oxide Quantum Dots and their Photocatalytic Activity in a Homogeneous SystemCHEMCATCHEM, Issue 9 2010Prof. Hua Zhang Abstract Colloidal oil-soluble Bi2O3 quantum dots (QDs) are synthesized through an alcoholysis route in organic media. Water-soluble Bi2O3 QDs are then obtained from the initial oil-soluble QDs through phase transfer by surface modification with mercaptopropionic acid. X-ray diffraction and transmission electron microscopy studies show that the crystallinity is enhanced and particles grow larger after phase transfer. The water-soluble Bi2O3 QDs exhibit excellent photocatalytic activity for the degradation of methyl orange at a wide range of pH values. After several cycles, the Bi2O3 QDs retain high degradation efficiency. Simulation according to the first-order reaction dynamics indicates that the degradation reaction may follow complicated quasi-homogeneous photocatalysis. [source] Catalytic effects of copper oxides on the curing and degradation reactions of cyanate ester resinJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Shinn-Gwo Hong Abstract The catalytic effect of copper oxides on the curing and degradation behaviors of the cyanate ester resin is studied with infrared spectroscopy, attenuated total reflection infrared spectroscopy (ATR), differential scanning calorimetry (DSC), and thermogravimetry analysis (TGA). The result of infrared spectroscopy and DSC analyses indicates that accelerated curing effects from different additives are in the order of zinc octoate > cuprous oxide > cupric oxide. The exothermic characteristics of the cyanate ester resin during cure are drastically affected by the presence of the copper oxides. In addition, it is obtained from TGA analyses that the thermal stability and degradation mechanism of cyanate ester resins are also significantly affected by the addition of copper oxides whereas the extent of degradation from the cupric oxide is greater than that from the cuprous oxide. These results are attributed to the differences in catalytic effects and surface areas of two copper oxides on the cyanate ester resin in contact during the thermal exposure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 442,448, 2007 [source] Degradation of cellulosic and hemicellulosic substrates using a chelator-mediated Fenton reactionJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2006Valdeir Arantes Abstract The involvement of catechol and hydroxamate chelators, along with hydrogen peroxide and Fe3+, in the degradation of cellulosic and hemicellulosic substrates was examined with the purpose of improving our current knowledge of the non-enzymatic mechanisms involved in wood biodegradation by fungi. It could be demonstrated that a catechol chelator-mediated Fenton reaction not only clearly degraded hemicellulosic substrates but also significantly accelerated and increased the effectiveness of degradation reactions. On the other hand, when a hydroxamate chelator-mediated Fenton reaction was used, an inhibitory effect was observed. When cellulosic substrates underwent a chelator-mediated Fenton reaction, no significant difference in degradation was observed between catechol and hydroxamate chelator-mediated reactions. However, a catechol-mediated reaction did accelerate the degradation of cellulosic substrates at the beginning of reactions. In addition, it was observed that with a chelator-mediated Fenton reaction, oxidation of cellulose proceeds depolymerization. Copyright © 2005 Society of Chemical Industry [source] Accelerated stability model for predicting shelf-lifeJOURNAL OF CLINICAL LABORATORY ANALYSIS, Issue 5 2002Robert T. Magari Abstract Second- and higher-order degradation reactions sometimes cannot be approximated with linear or exponential relationships and need to be appropriately modeled. Events above the COULTER® HmX Analyzer white blood cell (WBC) counting threshold were recorded for the HmX PAK reagent system stored at five elevated temperatures. An accelerated stability model for a second-degree polynomial degradation pattern was used. The shelf-life of the reagent, along with 95% lower bound confidence intervals, is predicted using the same pattern of degradation as well as the Arrhenius approximation. Experiments indicated that the degradation of the HmX PAK reagent occurred in two phases, the lag phase and the degradation phase, in all tested temperatures. The phase durations are temperature-dependent, and the Arrhenius approximation is appropriate (P=0.639). The degradation of the reagent during the lag phase was experimentally undetectable. Changes of the reagent were nonsignificant for a predicted period of 164 days at 25°C. The rate of degradation increased significantly later on during the degradation phase. The lower bound of the 95% confidence interval of this prediction indicated that it would take at least 326 days before the HmX PAK reagent would have any performance issue related to aging at storage temperature. J. Clin. Lab. Anal. 16:221,226, 2002. © 2002 Wiley-Liss, Inc. [source] KINETICS OF HYDROXYMETHYLFURFURAL ACCUMULATION AND COLOR CHANGE IN HONEY DURING STORAGE IN RELATION TO MOISTURE CONTENTJOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2009L. BULUT ABSTRACT Quality reduction in honey during storage is indicated by hydroxymethylfurfural (HMF) accumulation and darkening of color. The effects of moisture content and temperature on HMF accumulation and color change in honey during storage were investigated. HMF accumulation and color change followed first- and zero-order reaction kinetics, respectively. The moisture content affected the rate of the two degradation reactions depending on the storage temperature. Reduction in moisture content caused an increase in rate constant for HMF accumulation at 20 and 30C, but there was no significant effect of moisture content at 40C. Rate constants for change in lightness and total color change values increased with increasing moisture content at 20 and 30C. The highest rate constant for change in color values was obtained at a moisture content of 18% at 40C. PRACTICAL APPLICATIONS Hydroxymethylfurfural accumulation and color change are two major quality degradations in honey during storage. This study shows that the rates of these two degradations are dependent on moisture content of honey. In addition, effect of moisture content on the rates of reactions was dependent on temperature of storage. Therefore, producers need to consider the effects of both moisture content and storage temperature in reducing quality loss in honey during storage. [source] Evaluation of the Photodegradation of Crystal Violet upon Light Exposure by Mass Spectrometric and Spectroscopic MethodsJOURNAL OF FORENSIC SCIENCES, Issue 2 2009Céline Weyermann Dr. rer. nat. Abstract:, Crystal violet is a very common dye in ballpoint ink. Recent research suggests that the degradation of triarylmethane dyes gives an indication of the age of a ballpoint pen entry on a document. The main problem for the quantitative evaluation of the degradation is that it is highly dependent on the exposure to light. Moreover additional factors, such as additives and substrate play an important role in this process. The aim of this work is to compare the degradation pathways of the pure dye in water and ethanol upon exposure to xenon light by UV/VIS spectrophotometry and laser desorption ionization. Significant differences have been observed in the products and the kinetics of the degradation. N-demethylation, an expected decomposition process, was found to take place only in aqueous solution and kinetics calculations showed that the degradation occurred 2.5 times faster in ethanol compared to water. The degradation of crystal violet in inks from four ballpoint pens on paper was also studied for entries made over 2,3 years. It was observed that degradation reactions were quenched by the presence of another dye due to competitive absorption. It was also observed that the thickness of a stroke (concentration of ink) influenced the degradation process. In the absence of light only one ballpoint pen showed slight degradation. A better understanding of the influence of the paper, ink composition, and storage conditions is necessary to interpret correctly the age of an ink based on the degradation of dyes. [source] Chemical degradation of peptides and proteins in PLGA: A review of reactions and mechanismsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 7 2008M.L. Houchin Abstract Biodegradable poly(lactide-co-glycolide) (PLGA) polymers have been studied extensively for the controlled release of peptide and protein drugs. In addition to polymer biodegradation, chemical degradation of the incorporated peptide/protein has also been reported in PLGA devices, and the role of the polymer in promoting these reactions has been debated. This review summarizes the peptide/protein chemical degradation reactions that have been reported in PLGA systems and their mechanisms. Reported methods for stabilizing peptides and proteins in PLGA devices are also discussed. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:2395,2404, 2008 [source] Thermally induced intramolecular oxygen migration of N -oxides in atmospheric pressure chemical ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2010Xin Wang N -Oxides are known to undergo three main thermal degradation reactions, namely deoxygenation, Cope elimination (for N -oxides containing a ,-hydrogen) and Meisenheimer rearrangement, in atmospheric pressure chemical ionization mass spectrometry (APCI-MS). The ions corresponding to these thermal degradants observed in the ensuing APCI mass spectra have been used to identify N -oxides as well as to determine the N -oxidation site when the analyte contains multiple tertiary amine groups. In this paper, we report a thermally induced oxygen migration from one N -oxide amine to another tert -amine group present in the same molecule through a six-membered ring transition state during APCI-MS analysis. The observed intramolecular oxygen migration resulted in the formation of a new isomeric N -oxide, rendering the results of the APCI-MS analysis more difficult to interpret and potentially misleading. In addition, we observed novel degradation behavior that happened after the Meisenheimer rearrangement of the newly formed N -oxide: a homolytic cleavage of the NO bond instead of elimination of an aldehyde or a ketone that usually follows the rearrangement. Understanding of these unusual degradation pathways, which have not been reported previously, should facilitate structural elucidation of N -oxides using APCI-MS analysis. Copyright © 2010 John Wiley & Sons, Ltd. [source] Analysis of electrochemical degradation products of sulphonated azo dyes using high-performance liquid chromatography/tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2006Dana Van, rková Electrochemical treatment of wastewaters containing azo dyes in the textile industry is a promising approach for their degradation. The monitoring of the course of the decomposition of azo dyes in wastewaters is essential due to the environmental impact of their degradation products. In this work, aqueous solutions of a simple azo dye with a low molecular weight (C.I. Acid Yellow 9) and more complex commercial dye (C.I. Reactive Black 5) were electrochemically treated in a laboratory-scale electrolytic cell in sodium chloride or ammonium acetate as supporting electrolytes. Ion-pairing reversed-phase high-performance liquid chromatography coupled with negative-ion electrospray ionization mass spectrometry is applied for the identification of electrochemical degradation products. In addition to simple inorganic salts, the formation of aromatic degradation products obtained due to the cleavage of azo bonds and further degradation reactions is shown, as well as chlorination where sodium chloride is the supporting electrolyte. Degradation mechanisms are suggested for the treatment with sodium chloride as the supporting electrolyte. Copyright © 2006 John Wiley & Sons, Ltd. [source] | |||||||||||||