scholarly journals “Thermal Peroxidation” of Dietary Pentapeptides Yields N-Terminal 1,2-Dicarbonyls

2021 ◽  
Vol 8 ◽  
Author(s):  
Maria Bikaki ◽  
Nikolai Kuhnert
Keyword(s):  
Lipid Peroxidation ◽  
Reaction Mechanism ◽  
Thermal Degradation ◽  
Primary Amine ◽  
Elevated Temperatures ◽  
Degradation Products ◽  
Degradation Mechanism ◽  
Reaction Products ◽  
Unsaturated Lipids

In this contribution we investigate the thermal degradation of dietary-relevant pentapeptides. Most unsaturated lipids degrade by the well-known peroxidation mechanism. Here we show a degradation mechanism of peptides analogous to lipid peroxidation, forming a series of novel degradation products with possible toxicological relevance. At elevated temperatures above 180°C, pentapeptides with an N-terminal phenylalanine moiety react via a debenzylation to form 1,2-dicabonyl compounds, replacing the N-terminal primary amine. We propose a radical-based reaction mechanism that leads via a common peroxoaminal intermediate to two distinct types of reaction products with a terminal α-1,2 diamide or an α-amide-aldehyde functionality.

Thermal degradation of EDTA chelates in aqueous solution

1982 ◽  
Vol 60 (10) ◽  
pp. 1207-1213 ◽  
Author(s):  
Ramunas J. Motekaitis ◽  
X. B. Cox III ◽  
Patrick Taylor ◽  
Arthur E. Martell ◽  
Brad Miles ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Thermal Degradation ◽  
Elevated Temperatures ◽  
Degradation Products ◽  
Iminodiacetic Acid ◽  
Reaction Products ◽  
Degradation Rates ◽  
Lower Temperature Range ◽  
Higher Temperature ◽  
Lower Temperature

The thermal degradation of Ca(II), Mg(II), Zn(II), Fe(II), and Ni(II) chelates of EDTA was investigated in alkaline aqueous solution at elevated temperatures (230–310 °C). The kinetics of decomposition were followed by nmr, titrimetry, and spectrophotometry. Reaction products were identified through nmr and by gas chromatography. The relative order of degradation rates, as measured by the loss of EDTA, was found to be Mg(II) > Ca(II) > Zn(II) > Fe(II) > Ni(II). The main degradation products formed in the lower temperature range (~250 °C) are iminodiacetic acid, hydroxyethyliminodiacetic acid, and ethylene glycol. Higher temperature products are primarily dimethylamine and carbon dioxide. The rates of degradation of Ca(II), Mg(II), and Zn(II) EDTA chelates are considerably enhanced when either phosphate is present or a glass-lined autoclave is employed.

scholarly journals Empirical Kinetic Modelling and Mechanisms of Quercetin Thermal Degradation in Aqueous Model Systems: Effect of pH and Addition of Antioxidants

2021 ◽  
Vol 11 (6) ◽  
pp. 2579
Author(s):  
Abdessamie Kellil ◽  
Spyros Grigorakis ◽  
Sofia Loupassaki ◽  
Dimitris P. Makris
Keyword(s):  
Thermal Degradation ◽  
Empirical Model ◽  
Degradation Products ◽  
Degradation Kinetics ◽  
Kinetic Modelling ◽  
Degradation Mechanism ◽  
Antioxidant Properties ◽  
Biological Significance ◽  
Model Systems ◽  
Molar Ratio

Quercetin (Qt) is a natural flavonoid of high biological significance, and it occurs in a wide variety of plant foods. Although its oxidation by various means has been extensively studied, its behavior with regard to thermal treatments remains a challenge. The study described herein aimed at investigating Qt thermal decomposition, by proposing an empirical sigmoidal model for tracing degradation kinetics. This model was employed to examine the effect of addition of antioxidants on Qt thermal degradation, including ascorbic acid, L-cysteine, and sulfite. Furthermore, degradation pathways were proposed by performing liquid chromatography-tandem mass spectrometry analyses. Upon addition of any antioxidant used, the sigmoidal course of Qt thermal degradation was pronounced, evidencing the validity of the empirical model used in the study of similar cases. The antioxidants retarded Qt degradation in a manner that appeared to depend on Qt/antioxidant molar ratio. No major differentiation in the degradation mechanism was observed in response to the addition of various antioxidants, and in all cases protocatechuic acid and phloroglucinol carboxylic acid were typical degradation products identified. Furthermore, in all cases tested the solutions resulted after thermal treatment possessed inferior antioxidant properties compared to the initial Qt solutions, and this demonstrated the detrimental effects of heating on Qt. The empirical model proposed could be of assistance in interpreting the degradation behavior of other polyphenols, but its validity merits further investigation.

Thermal Degradation of Ionic Liquids at Elevated Temperatures

2004 ◽  
Vol 57 (2) ◽  
pp. 145 ◽  
Author(s):  
Krisztian J. Baranyai ◽  
Glen B. Deacon ◽  
Douglas R. MacFarlane ◽  
Jennifer M. Pringle ◽  
Janet L. Scott
Keyword(s):  
Thermal Stability ◽  
Ionic Liquids ◽  
Thermal Degradation ◽  
Elevated Temperatures ◽  
Degradation Products ◽  
Operating Temperature ◽  
Imidazolium Cation

Ionic liquids based on the imidazolium cation are found to degrade, yielding volatile degradation products, at temperatures significantly lower than previously reported and thus a parameter Tz/x (the maximum operating temperature) is developed to provide a more appropriate estimate of thermal stability.

Bayesian inference for a novel hierarchical accelerated degradation model considering the mechanism variation

2020 ◽  
Vol 234 (5) ◽  
pp. 708-720
Author(s):  
Hongyu Wang ◽  
Xiaobing Ma ◽  
Yu Zhao
Keyword(s):  
Activation Energy ◽  
Thermal Degradation ◽  
Elevated Temperatures ◽  
Degradation Mechanism ◽  
Polymeric Materials ◽  
Arrhenius Model ◽  
Degradation Model ◽  
Degradation Data ◽  
Degradation Tests ◽  
High Level

For highly reliable products, accelerated thermal degradation tests are efficient to provide feedback on reliability information. In accelerated thermal degradation tests, the degradation data collected at the elevated temperatures are used to extrapolate the performance of products at the normal temperature. An important tool in such extrapolation is the Arrhenius model, in which the activation energy is generally assumed to be constant. However, in some practical accelerated thermal degradation tests of polymeric materials, a variation of the underlying degradation mechanism is induced when the temperature rises to a certain high level, resulting in a change in the activation energy. Motivated by this phenomenon, we propose a two-stage Arrhenius model. The two stages correspond to the lower and higher temperature ranges with different activation energies. Then, this new model is incorporated to the degradation model, yielding a novel hierarchical model for the accelerated thermal degradation test data from polymeric materials involving a mechanism variation. Furthermore, the Bayesian method is adopted for parameter inference, and the lifetime distribution is obtained subsequently. A practical example of polysiloxane rubbers demonstrates the effectiveness of the proposed model.

scholarly journals The thermal degradation of poly(iso-butyl methacrylate) and poly(sec-butyl methacrylate)

2000 ◽  
Vol 65 (12) ◽  
pp. 867-875 ◽  
Author(s):  
Katarina Novakovic ◽  
Lynne Katsikas ◽  
Ivanka Popovic
Keyword(s):  
Thermal Degradation ◽  
Methyl Methacrylate ◽  
Elevated Temperatures ◽  
Degradation Mechanism ◽  
Butyl Methacrylate ◽  
Poly Methyl Methacrylate ◽  
Order Of Magnitude

The non-oxidative thermal degradation of poly(iso-butyl methacrylate) and poly(sec-butyl methacrylate) was investigated by studying changes in the polymer residue. Due to the different number of ?-hydrogens in their ester substituents, these two polymeric isomers behave differently when subjected to elevated temperatures. Poly(iso-butyl methacrylate) degrades quantitatively by depolymerisation with zip lengths of the same order of magnitude as those of poly(methyl methacrylate). Poly(sec-butyl methacrylate) degrades by a combined degradation mechanism of depolymerisation and de-esterification. De-esterification becomes a significant thermolysis route at temperatures higher than 240?C.

scholarly journals The Preparation and Identification of Characteristic Flavour Compounds of Maillard Reaction Products of Protein Hydrolysate from Grass Carp (Ctenopharyngodon idella) Bone

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Yunliang Li ◽  
Xiaojing Wang ◽  
Yang Xue ◽  
Siyu Ruan ◽  
Anqi Zhou ◽  
...  
Keyword(s):  
Thermal Degradation ◽  
Maillard Reaction ◽  
Grass Carp ◽  
Degradation Products ◽  
Protein Hydrolysate ◽  
Ctenopharyngodon Idella ◽  
Maillard Reaction Products ◽  
Reaction Products ◽  
Grass Carp Ctenopharyngodon Idella ◽  
Thermal Degradation Products

This study aims at preparing the Maillard reaction products of protein hydrolysate from grass carp (Ctenopharyngodon idella) bone and identifying its characteristic flavour compounds. Meanwhile, bioactivities and amino acids composition of hydrolysates and its Maillard reaction products were compared with the thermal degradation reaction as one positive control. Single factor experiment was applied to optimize the enzymolysis parameters of grass carp bone protein using flavourzyme, under which the highest degree of hydrolysis (40.1%) was obtained. According to the response surface methodology, the top predicted value (70.45%) of degree of graft of Maillard reaction was obtained with initial pH of 7.07, temperature of 118.33°C, and time of 1.75 h. Moreover, the results of Maillard reaction products illustrated a significant increase in DPPH radical scavenging activity ( p < 0.05 ) compared to that of hydrolysate and its thermal degradation products, which was accompanied by the decreased ACE inhibitory activity. Besides, the umami-sweet taste amino acid ratio in free amino acids of Maillard reaction products climbed considerably compared to those of hydrolysate and its thermal degradation products, which proved that Maillard reaction is an effective way to improve the flavour taste of protein hydrolysate. The GC-MS results showed that 37, 40, and 62 kinds of volatile compounds were detected in hydrolysate, thermal degradation products, and Maillard reaction products, respectively. The Maillard reaction products contained more flavour volatile compounds of aldehydes, alcohol, ketone, pyrazine, and other compounds that contribute to pleasant aromas. These results suggested that the grass carp bone protein hydrolysate after Maillard reaction could potentially have a wide range of applications as antioxidant and flavour substances.

Characterization of dissolved material during the initial phase of softwood kraft pulping

TAPPI Journal ◽  
2013 ◽  
Vol 12 (1) ◽  
pp. 37-43 ◽  
Author(s):  
HANNU PAKKANEN ◽  
TEEMU PALOHEIMO ◽  
RAIMO ALÉN
Keyword(s):  
Mass Transfer ◽  
Molecular Mass ◽  
Initial Phase ◽  
Degradation Products ◽  
Kraft Pulping ◽  
Reaction Products ◽  
Cooking Temperature ◽  
Molecular Masses ◽  
Aliphatic Carboxylic Acids

The influence of various cooking parameters, such as effective alkali, cooking temperature, and cooking time on the formation of high molecular mass lignin-derived and low molecular mass carbohydrates-derived (aliphatic carboxylic acids) degradation products, mainly during the initial phase of softwood kraft pulping was studied. In addition, the mass transfer of all of these degradation products was clarified based on their concentrations in the cooking liquor inside and outside of the chips. The results indicated that the degradation of the major hemicellulose component, galactoglucomannan, typically was dependent on temperature, and the maximum degradation amount was about 60%. In addition, about 60 min at 284°F (140°C) was needed for leveling off the concentrations of the characteristic reaction products (3,4-dideoxy-pentonic and glucoisosaccharinic acids) between these cooking liquors. Compared with low molecular mass aliphatic acids, the mass transfer of soluble lignin fragments with much higher molecular masses was clearly slower.

Dielectric Breakdown in Printed Circuit Boards at Elevated Temperatures

1996 ◽  
Author(s):  
P. Singh ◽  
G.T. Galyon ◽  
J. Obrzut ◽  
W.A. Alpaugh
Keyword(s):  
Experimental Data ◽  
Thermal Degradation ◽  
Printed Circuit Boards ◽  
Printed Circuit Board ◽  
Elevated Temperatures ◽  
Dielectric Breakdown ◽  
Circuit Board ◽  
Circuit Boards ◽  
Printed Circuit ◽  
Data Matching

Abstract A time delayed dielectric breakdown in printed circuit boards, operating at temperatures below the epoxy resin insulation thermo-electrical limits, is reported. The safe temperature-voltage operating regime was estimated and related to the glass-rubber transition (To) of printed circuit board dielectric. The TG was measured using DSC and compared with that determined from electrical conductivity of the laminate in the glassy and rubbery state. A failure model was developed and fitted to the experimental data matching a localized thermal degradation of the dielectric and time dependency. The model is based on localized heating of an insulation resistance defect that under certain voltage bias can exceed the TG, thus, initiating thermal degradation of the resin. The model agrees well with the experimental data and indicates that the failure rate and truncation time beyond which the probability of failure becomes insignificant, decreases with increasing glass-rubber transition temperature.

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