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1
Griffith, William P., e Maria Suriaatmaja. "Studies on transition-metal nitrido and oxo complexes. Part 20. Oxoruthenates and oxo-osmates in oxidation catalysis; cis-[Os(OH)2O4]2- as a catalytic oxidant for primary amines and for alcohols". Canadian Journal of Chemistry 79, n. 5-6 (1 maggio 2001): 598–606. http://dx.doi.org/10.1139/v00-181.
Testo completoAbstract (sommario):
cis-[Os(OH)2O4]2 with [Fe(CN)6]3 and other co-oxidants has been studied as a catalytic reagent for the oxidative dehydrogenation of primary aromatic and aliphatic amines to nitriles, the oxidation of primary alcohols to carboxylic acids and of secondary alcohols to ketones. Electronic and Raman spectroscopy have been used to elucidate the nature of the oxoruthenates and oxo-osmates present in a number of reported organic oxidations catalyzed by ruthenium and osmium species.Key words: oxidation catalysis, ruthenium, osmium, amine dehydrogenation, alcohol oxidation.
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Francioso, Antonio, Alessia Baseggio Conrado, Carla Blarzino, Cesira Foppoli, Elita Montanari, Simone Dinarelli, Alessandra Giorgi, Luciana Mosca e Mario Fontana. "One- and Two-Electron Oxidations of β-Amyloid25-35 by Carbonate Radical Anion (CO3•−) and Peroxymonocarbonate (HCO4−): Role of Sulfur in Radical Reactions and Peptide Aggregation". Molecules 25, n. 4 (20 febbraio 2020): 961. http://dx.doi.org/10.3390/molecules25040961.
Testo completoAbstract (sommario):
The β-amyloid (Aβ) peptide plays a key role in the pathogenesis of Alzheimer’s disease. The methionine (Met) residue at position 35 in Aβ C-terminal domain is critical for neurotoxicity, aggregation, and free radical formation initiated by the peptide. The role of Met in modulating toxicological properties of Aβ most likely involves an oxidative event at the sulfur atom. We therefore investigated the one- or two-electron oxidation of the Met residue of Aβ25-35 fragment and the effect of such oxidation on the behavior of the peptide. Bicarbonate promotes two-electron oxidations mediated by hydrogen peroxide after generation of peroxymonocarbonate (HCO4−, PMC). The bicarbonate/carbon dioxide pair stimulates one-electron oxidations mediated by carbonate radical anion (CO3•−). PMC efficiently oxidizes thioether sulfur of the Met residue to sulfoxide. Interestingly, such oxidation hampers the tendency of Aβ to aggregate. Conversely, CO3•− causes the one-electron oxidation of methionine residue to sulfur radical cation (MetS•+). The formation of this transient reactive intermediate during Aβ oxidation may play an important role in the process underlying amyloid neurotoxicity and free radical generation.
3
Zhao, Rong, Denghu Chang e Lei Shi. "Recent Advances in Cyclic Diacyl Peroxides: Reactivity and Selectivity Enhancement Brought by the Cyclic Structure". Synthesis 49, n. 15 (12 giugno 2017): 3357–65. http://dx.doi.org/10.1055/s-0036-1588458.
Testo completoAbstract (sommario):
Preliminarily studies on cyclic diacyl peroxides have shown novel and superior reactivities compared with their acyclic diacyl peroxide counterparts in many reaction types. After summarizing the methods available for the preparation of cyclic diacyl peroxides and describing their structural features, this review brings together an overview of their reactivities with respect to oxidations and decarboxylations, and demonstrates the advantages of reactions with cyclic diacyl peroxides, which include metal-free, additive-free, milder conditions, higher yields and better selectivities.1 Introduction2 Methods of Preparation of Cyclic Diacyl Peroxides3 Structures and Stabilities of Cyclic Diacyl Peroxides4 Oxidation Reactions4.1 Oxidative Additions to Alkenes4.2 Oxidation Reactions of Heteroatoms4.3 Oxidation Reactions of 1,3-Dicarbonyl Compounds4.4 Hydroxylations of Arenes5 Decarboxylations6 Conclusion
4
Silva, D. M. de, e S. D. Aust. "Ferritin and ceruloplasmin in oxidative damage: review and recent findings". Canadian Journal of Physiology and Pharmacology 71, n. 9 (1 settembre 1993): 715–20. http://dx.doi.org/10.1139/y93-107.
Testo completoAbstract (sommario):
The oxidation of biomolecules such as lipid, protein, and DNA is associated with a variety of toxicities and pathologies. In an all-encompassing definition these oxidative processes have been referred to as "oxidative stress." Although the direct reaction between molecular oxygen and most biomolecules is spin forbidden, this reaction can be efficiently catalyzed by transition metals such as iron and copper. Iron especially has been demonstrated to be a potent catalyst of biological oxidations. This review focuses on the relationship between iron and copper with respect to the copper protein ceruloplasmin, which may play a role in iron homeostasis by catalyzing the oxidation of iron as it is placed in ferritin.Key words: iron, copper, ferritin, ceruloplasmin.
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Lathbury, David, e Andy Wells. "Oxidation and Oxidative Reactions". Organic Process Research & Development 19, n. 11 (20 novembre 2015): 1536. http://dx.doi.org/10.1021/acs.oprd.5b00341.
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Cryle, Max J., Jeanette E. Stok e James J. De Voss. "Reactions Catalyzed by Bacterial Cytochromes P450". Australian Journal of Chemistry 56, n. 8 (2003): 749. http://dx.doi.org/10.1071/ch03040.
Testo completoAbstract (sommario):
The cytochromes P450 are a large family of oxidative haemoproteins that are responsible for a wide variety of oxidative transformations in a variety of organisms. This review focuses upon the reactions catalyzed specifically by bacterial enzymes, which includes aliphatic hydroxylation, alkene epoxidation, aromatic hydroxylation, oxidative phenolic coupling, heteroatom oxidation and dealkylation, and multiple oxidations including C–C bond cleavage. The potential for the practical application of the oxidizing power of these enzymes is briefly discussed.
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Sardarly, А. М. "PHASE COMPOSITION AND OXIDATION DEGREE OF VANADIUM IN CATALYSTS FOR OXIDATIVE DEHYDROGENATION OF PROPANE". Chemical Problems 20, n. 4 (2022): 358–65. http://dx.doi.org/10.32737/2221-8688-2022-3-358-365.
Testo completoAbstract (sommario):
The phase composition of vanadium and vanadium-antimony-containing samples of γ-Al2O3 and the degree of oxidation of vanadium in them were examined by XRD and EPR methods, respectively. The data of XRD and EPR spectroscopy show the formation of highly dispersed vanadium-oxygen and vanadiumantimony-oxygen structures on the surface of the support. It is shown that the EPR spectra of the studied samples are due to "isolated" vanadium ions with an oxidation state of +4 in nonstoichiometric vanadium-oxygen and vanadium-antimony-oxygen formations with a square pyramid local environment structure with a characteristic V=O double bond. The EPR spectra of two types of paramagnetic centers of vanadium, which differ in the distortion of the square-pyramidal structure of the local environment of the vanadium ion, were identified. It was established that the number of ions with an oxidation state of +4 in V,Sb-containing samples depends on the V/Sb ratio in them.
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SIMANDAN, Tiberiu, Jing SUN e Thomas A. DIX. "Oxidation of DNA bases, deoxyribonucleosides and homopolymers by peroxyl radicals". Biochemical Journal 335, n. 2 (15 ottobre 1998): 233–40. http://dx.doi.org/10.1042/bj3350233.
Testo completoAbstract (sommario):
DNA base oxidation is considered to be a key event associated with disease initiation and progression in humans. Peroxyl radicals (ROO•) are important oxidants found in cells whose ability to react with the DNA bases has not been characterized extensively. In this paper, the products resulting from ROO• oxidation of the DNA bases are determined by gas chromatography/MS in comparison with authentic standards. ROO• radicals oxidize adenine and guanine to their 8-hydroxy derivatives, which are considered biomarkers of hydroxyl radical (HO•) oxidations in cells. ROO• radicals also oxidize adenine to its hydroxylamine, a previously unidentified product. ROO• radicals oxidize cytosine and thymine to the monohydroxy and dihydroxy derivatives that are formed by oxidative damage in cells. Identical ROO• oxidation profiles are observed for each base when exposed as deoxyribonucleosides, monohomopolymers and base-paired dihomopolymers. These results have significance for the development, utilization and interpretation of DNA base-derived biomarkers of oxidative damage associated with disease initiation and propagation, and support the idea that the mutagenic potential of N-oxidized bases, when generated in cellular DNA, will require careful evaluation. Adenine hydroxylamine is proposed as a specific molecular probe for the activity of ROO• in cellular systems.
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Wang, Xi, e Yingwei Li. "Nanoporous carbons derived from MOFs as metal-free catalysts for selective aerobic oxidations". Journal of Materials Chemistry A 4, n. 14 (2016): 5247–57. http://dx.doi.org/10.1039/c6ta00324a.
Testo completoAbstract (sommario):
A new kind of metal-free catalyst comprised of highly graphitized N-doped nanoporous carbons from direct carbonization of metal–organic frameworks (MOFs) turns out to be an excellent metal-free catalyst for a series of liquid-phase oxidation reactions including aerobic oxidations of cyclohexane and toluene as well as oxidative coupling of amines.
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Christoffers, Jens, e Mathias S. Wickleder. "Synthesis of Aromatic and Aliphatic Di-, Tri-, and Tetrasulfonic Acids". Synlett 31, n. 10 (17 marzo 2020): 945–52. http://dx.doi.org/10.1055/s-0039-1691745.
Testo completoAbstract (sommario):
Oligosulfonic acids are promising linker compounds for coordination polymers and metal-organic frameworks, however, compared to their carboxylic acid congeners, often not readily accessible by established synthetic routes. This Account highlights the synthesis of recently developed aromatic and aliphatic di-, tri- and tetrasulfonic acids. While multiple electrophilic sulfonations of aromatic substrates are rather limited, the nucleophilic aromatic substitution including an intramolecular variant, the Newman–Kwart rearrangement, allows the flexible introduction of up to four sulfur-containing moieties at an aromatic ring. Sulfonic acids are then accessed by oxidation of thiols, thioethers, or thioesters either directly with hydrogen peroxide or in two steps with chlorine (generated in situ from N-chlorosuccinimide/hydrochloric acid) to furnish sulfochlorides which are subsequently hydrolyzed. In the aliphatic series, secondary alcohols as starting materials are converted into thioethers, thioesters, or thiocarbonates by nucleophilic substitutions, which are also subsequently oxidized to furnish sulfonic acids.1 Introduction2 Electrophilic Aromatic Substitution3 Nucleophilic Aromatic Substitution3.1 Intermolecular SNAr3.2 Intermolecular with Subsequent Oxidation3.3 Intramolecular with Subsequent Oxidation4 Nucleophilic Aliphatic Substitution with Subsequent Oxidation5 Oxidation5.1 Oxidation of Thiocarbonates5.2 Oxidation of Thioethers5.3 Oxidation of Thioesters6 Thermolysis of Neopentylsulfonates7 Functionalization via Diazonium Ions8 Conclusion
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Chen, Chuck T., Marc-Olivier Trépanier, Kathryn E. Hopperton, Anthony F. Domenichiello, Mojgan Masoodi e Richard P. Bazinet. "Inhibiting Mitochondrial β-Oxidation Selectively Reduces Levels of Nonenzymatic Oxidative Polyunsaturated Fatty Acid Metabolites in the Brain". Journal of Cerebral Blood Flow & Metabolism 34, n. 3 (11 dicembre 2013): 376–79. http://dx.doi.org/10.1038/jcbfm.2013.221.
Testo completoAbstract (sommario):
Schönfeld and Reiser recently hypothesized that fatty acid β-oxidation is a source of oxidative stress in the brain. To test this hypothesis, we inhibited brain mitochondrial β-oxidation with methyl palmoxirate (MEP) and measured oxidative polyunsaturated fatty acid (PUFA) metabolites in the rat brain. Upon MEP treatment, levels of several nonenzymatic auto-oxidative PUFA metabolites were reduced with few effects on enzymatically derived metabolites. Our finding confirms the hypothesis that reduced fatty acid β-oxidation decreases oxidative stress in the brain and β-oxidation inhibitors may be a novel therapeutic approach for brain disorders associated with oxidative stress.
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Masferrer-Rius, Eduard, e Robertus J. M. Klein Gebbink. "Non-Noble Metal Aromatic Oxidation Catalysis: From Metalloenzymes to Synthetic Complexes". Catalysts 13, n. 4 (19 aprile 2023): 773. http://dx.doi.org/10.3390/catal13040773.
Testo completoAbstract (sommario):
The development of selective aromatic oxidation catalysts based on non-noble metals has emerged over the last decades, mainly due to the importance of phenol products as intermediates for the generation of pharmaceuticals or functional polymers. In nature, metalloenzymes can perform a wide variety of oxidative processes using molecular oxygen, including arene oxidations. However, the implementation of such enzymes in the chemical industry remains challenging. In this context, chemists have tried to mimic nature and design synthetic non-noble metal catalysts inspired by these enzymes. This review aims at providing a general overview of aromatic oxidation reactions catalyzed by metalloenzymes as well as synthetic first-row transition-metal complexes as homogeneous catalysts. The enzymes and complexes discussed in this review have been classified based on the transition-metal ion present in their active site, i.e., iron, copper, nickel, and manganese. The main points of discussion focus on enzyme structure and function, catalyst design, mechanisms of operation in terms of oxidant activation and substrate oxidation, and substrate scope.
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Uchuskin, Maxim, Igor Trushkov e Anton Makarov. "Furan Oxidation Reactions in the Total Synthesis of Natural Products". Synthesis 50, n. 16 (16 luglio 2018): 3059–86. http://dx.doi.org/10.1055/s-0037-1610021.
Testo completoAbstract (sommario):
Recent developments on the transformations of furans under oxidative conditions toward the total synthesis of complex natural compounds are discussed. Reactions and methods are classified according to the type of oxidant used. Comparisons are then made between all the strategies to provide a comprehensive overview. This review covers the most prominent work published from 2011 until 2017.1 Introduction2 Reagents and Methods for Oxidation of the Furan Ring2.1 Singlet Oxygen2.2 Peroxides and Hydroperoxides2.3 Quinones2.4 Halogen-Based Oxidants2.5 Chromium-Based Oxidants3 The Achmatowicz Reaction3.1 Halogen-Based Oxidants3.2 Hydroperoxides3.3 Enzymatic Oxidation4 Conclusion
14
YANO, Yumihiko, e Norio TAMURA. "Oxidations by Oxidation-Active Flavin Mimics." Journal of Synthetic Organic Chemistry, Japan 50, n. 10 (1992): 899–907. http://dx.doi.org/10.5059/yukigoseikyokaishi.50.899.
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Dyck, Yan Felix Karl, Daniel Rehm, Jan Felix Joseph, Karsten Winkler, Volker Sandig, Wolfgang Jabs e Maria Kristina Parr. "Forced Degradation Testing as Complementary Tool for Biosimilarity Assessment". Bioengineering 6, n. 3 (21 luglio 2019): 62. http://dx.doi.org/10.3390/bioengineering6030062.
Testo completoAbstract (sommario):
Oxidation of monoclonal antibodies (mAbs) can impact their efficacy and may therefore represent critical quality attributes (CQA) that require evaluation. To complement classical CQA, bevacizumab and infliximab were subjected to oxidative stress by H2O2 for 24, 48, or 72 h to probe their oxidation susceptibility. For investigation, a middle-up approach was used utilizing liquid chromatography hyphenated with mass spectrometry (LC-QTOF-MS). In both mAbs, the Fc/2 subunit was completely oxidized. Additional oxidations were found in the light chain (LC) and in the Fd’ subunit of infliximab, but not in bevacizumab. By direct comparison of methionine positions, the oxidized residues in infliximab were assigned to M55 in LC and M18 in Fd’. The forced oxidation approach was further exploited for comparison of respective biosimilar products. Both for bevacizumab and infliximab, comparison of posttranslational modification profiles demonstrated high similarity of the unstressed reference product (RP) and the biosimilar (BS). However, for bevacizumab, comparison after forced oxidation revealed a higher susceptibility of the BS compared to the RP. It may thus be considered a useful tool for biopharmaceutical engineering, biosimilarity assessment, as well as for quality control of protein drugs.
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Tonda, Rachel, Arlene Lamptey e Brenda Reid. "PSV-15 Variability in the Oxidative Status of Fats and Oils Used in Livestock Diets in North America". Journal of Animal Science 99, Supplement_1 (1 maggio 2021): 197–98. http://dx.doi.org/10.1093/jas/skab054.322.
Testo completoAbstract (sommario):
Abstract Lipids are essential energy sources in nearly every animal’s diet. However, lipids used in feed formulations today are highly variable in both composition and susceptibility to oxidation – a major source of decreased lipid quality. Feeding oxidized lipids negatively influences animal health and performance, yet data on the oxidative status of commercially used lipids is limited. Herein, the oxidative stability results of lipid samples submitted to Kemin Customer Laboratory Services (CLS) for analysis since 2018 is summarized. Of the 392 samples evaluated, corn oil (n=122), choice white grease (CWG; n=101) and soybean oil (n=66) were the most common. Current oxidation status was assessed by measuring active oxidation markers, including peroxide values (PV; target < 5 meq/kg) and secondary oxidative molecules (hexanal and 2,4-decadienal; target < 50 ppm total). Resistance to future oxidation was evaluated by Oxidative Stability Index (OSI) at 100° C. Lipid PVs ranged from 0 meq/kg to 47.8 meq/kg, with an average PV of 3.4 meq/kg. Total secondary oxidatives averaged 28 ppm, ranging from below the limit of quantitation (5 ppm) to 313 ppm. Based on current oxidative markers, 39% of samples showed no signs of oxidation, 40% had early signs of oxidation, 16% were undergoing active oxidation and 5% were severely oxidized. Lipid OSI times ranged from 0.2 to 144 hours, averaging 17.4 hours. Fifty percent of samples had OSI times of < 10 hours. Further, 46% of animal fats had an OSI < 5 hours, indicating enhanced susceptibility of these fats to future oxidation. In conclusion, >60% of samples showed signs of oxidation, and significant variability in the oxidative status of commercial lipids was observed. To optimize nutritional efficiency and minimize adverse effects of oxidation on overall health of livestock, managing lipid quality – including understanding oxidation risks – should be a major consideration for producers.
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Blacken, Grady R., Yi Wang, Jose A. Lopez e Xiaoyun Fu. "Cysteine 93 of Hemoglobin Beta Chain Is the Major Target of Oxidation During Red Blood Cell Storage." Blood 114, n. 22 (20 novembre 2009): 4040. http://dx.doi.org/10.1182/blood.v114.22.4040.4040.
Testo completoAbstract (sommario):
Abstract Abstract 4040 Poster Board III-976 Red blood cells (RBC) stored for prolonged time periods under blood banking conditions are known to accumulate irreversible damage that ultimately affects their viability and function. Among the consequences of this RBC storage lesion are enhanced hemolysis and oxidative stress after transfusion. Stored RBCs accumulate reactive oxygen species (ROS) and surface-associated hemichrome, a partially denatured form of oxidized hemoglobin. In this work, we examined whether the ROS created during RBC storage lead to characteristic oxidative modifications to hemoglobin (Hb) and RBC membrane proteins. To characterize Hb modifications leading to hemichrome formation, we oxidized human hemoglobin A with varied concentrations of hydrogen peroxide (H2O2), an oxidant relevant to RBC storage. The reaction was quenched with excess methionine and the protein digested with trypsin. The resulting peptides were analyzed by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). Methionine and cysteine residues are the major targets of oxidation. Oxidation of methionine to methionine sulfoxide and cysteine to cysteine sulfonic/sulfinic acids is accompanied by a mass shift related to the covalent modifications of each residue, which are readily detected by LC-ESI-MS/MS. We found that HBβ-Cys-93 was oxidized to a maximum of approximately 70% after treatment with 200 αM H2O2. This cysteine occurs adjacent to the FeII-coordinating His-92 and is thus exposed to the heme-FeII center. In contrast, HBβ-Cys-112 and HBα-Cys-104, which are buried and located away from the heme-FeII center, were oxidized to only 2% and 0%, respectively. The enhanced oxidation of the heme-FeII proximal HBβ-Cys-93 suggests that ROS are generated through a FeII-dependent mechanism such as Fenton's reaction. Oxidation of each of the three Hb methionines reached 20% upon treatment with 200 μM H2O2. Among these Met residues, HBα-Met-32 is located near the heme-FeII, center, while both Hbα-Met-76 and HBβ-Met-55 are near the protein/solvent interface. Thus, Cys and Met oxidations in Hb appear to be dependent on proximity to either the heme-FeII center or the protein/solvent interface. To test whether these Hb residues are also sensitive to oxidation during storage we acquired 3 RBC units stored for 3 days and 3 RBC units stored for 45 days, from the Puget Sound Blood Center. The cytosolic Hb was extracted by hypotonic lysis and digested with trypsin prior to LC-ESI-MS/MS analysis. We observed that oxidation of HBβ-Cys-93 was dramatically increased from 10% on day 3 to 29% on day 45 (p < 0.02). HBα-Met-32 was also oxidized to a small extent (5% on day 3 to 7.5 % on day 45, p<0.04). The two buried Cys residues were unoxidized, whereas two surface proximal Met residues were oxidized, but not in a significantly storage-time-dependent manner. These data implicate the redox active heme-FeII center in enhanced ROS production and oxidative stress in stored RBCs. Our observations suggest that HBβ-Cys-93 oxidation is a specific and sensitive marker for oxidative stress during storage. Moreover, we have correlated these progressive oxidations with increases in microvesiculation and hemolysis, storage-time-dependent changes that have been well documented. Future studies will evaluate the storage-time-dependence in other oxidative and post-translational modifications to RBC membrane proteins and correlate these findings with functional consequences such as microvesiculation and hemolysis. Disclosures: No relevant conflicts of interest to declare.
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Wazir, Hazrati, Shyan Yea Chay, Mohammad Zarei, Farah Salina Hussin, Nor Afizah Mustapha, Wan Zunairah Wan Ibadullah e Nazamid Saari. "Effects of Storage Time and Temperature on Lipid Oxidation and Protein Co-Oxidation of Low-Moisture Shredded Meat Products". Antioxidants 8, n. 10 (16 ottobre 2019): 486. http://dx.doi.org/10.3390/antiox8100486.
Testo completoAbstract (sommario):
Studies on the oxidative changes in meat-based, low-moisture, ready to eat foods are complicated due to complex food system and slow lipid-protein oxidative deterioration. The current study evaluates the oxidative changes over six months of storage on shredded beef and chicken products (locally known as serunding) for physicochemical analysis, lipid oxidation (conjugated dienes and malondialdehydes) and protein co-oxidation (soluble protein content, amino acid composition, protein carbonyl, tryptophan loss and Schiff base fluorescence) at 25 °C, 40 °C and 60 °C. The lipid stability of chicken serunding was significantly lower than beef serunding, illustrated by higher conjugated dienes content and higher rate of malondialdehyde formation during storage. In terms of protein co-oxidation, chicken serunding with higher polyunsaturated fatty acids (PUFA) experienced more severe oxidation, as seen from lower protein solubility, higher protein carbonyl and Schiff base formation compared to beef serunding. To conclude, chicken serunding demonstrates lower lipid and protein stability and exhibits higher rate of lipid oxidation and protein co-oxidation than beef serunding. These findings provide insights on the progression of lipid oxidation and protein co-oxidation in cooked, shredded meat products and could be extrapolated to minimize possible adverse effects arising from lipid oxidation and protein co-oxidation, on the quality of low-moisture, high-lipid, high-protein foods.
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Li, Yong Zhi, Zeng Wu Zhao, Bao Wei Li, Wen Fei Wu e Shuo Li. "Oxidation of U71Mn Steel under Pure Oxygen". Advanced Materials Research 562-564 (agosto 2012): 68–71. http://dx.doi.org/10.4028/www.scientific.net/amr.562-564.68.
Testo completoAbstract (sommario):
Isothermal oxidations of U71Mn steels under pure oxygen, between 1027K and 1473K, are experimentally analyzed in this study. The results showed that Oxidation kinetics at different temperature from 1173K to 1473K are similar: mass increase per unit area as function of oxidation time follows parabolic role. Oxidation rate constants of the steel under pure oxygen, from 1173K to 1473K, keep exponential law as function of oxidation time.
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Blair, Megan C., Michael D. Neinast e Zoltan Arany. "Whole-body metabolic fate of branched-chain amino acids". Biochemical Journal 478, n. 4 (24 febbraio 2021): 765–76. http://dx.doi.org/10.1042/bcj20200686.
Testo completoAbstract (sommario):
Oxidation of branched-chain amino acids (BCAAs) is tightly regulated in mammals. We review here the distribution and regulation of whole-body BCAA oxidation. Phosphorylation and dephosphorylation of the rate-limiting enzyme, branched-chain α-ketoacid dehydrogenase complex directly regulates BCAA oxidation, and various other indirect mechanisms of regulation also exist. Most tissues throughout the body are capable of BCAA oxidation, and the flux of oxidative BCAA disposal in each tissue is influenced by three key factors: 1. tissue-specific preference for BCAA oxidation relative to other fuels, 2. the overall oxidative activity of mitochondria within a tissue, and 3. total tissue mass. Perturbations in BCAA oxidation have been implicated in many disease contexts, underscoring the importance of BCAA homeostasis in overall health.
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Grilo, Filipa S., e Selina C. Wang. "Walnut (Juglans regia L.) Volatile Compounds Indicate Kernel and Oil Oxidation". Foods 10, n. 2 (4 febbraio 2021): 329. http://dx.doi.org/10.3390/foods10020329.
Testo completoAbstract (sommario):
Kernel oxidation susceptibility and pellicle darkening are among the biggest concerns regarding walnut quality. Monitoring oxidation is crucial to preserve quality from production to consumption. Chemical oxidation parameters (peroxide value and UV absorbances), fatty acid profile, tocopherols, phenols, and volatiles in ‘Chandler’ and ‘Howard’ kernels were studied at different time points during 28 weeks of storage to evaluate potential oxidation markers. During storage, peroxide value, UV absorbances, and volatiles concentration increased; oxidative stability, phenols, and tocopherols decreased, while fatty acid profile was unaffected. ‘Chandler’ had a lower peroxide value, K232, and K268; and higher kernel and oil oxidative stability compared to ‘Howard’. Phenols and tocopherols decreased 1.2-fold in ‘Chandler’ and 1.3-fold in ‘Howard’. Using multivariate analysis, samples were discriminated in three groups according with their oxidative levels. Increases of volatiles in oil and kernel were associated with higher oxidative levels. Pentanal, 2-methylpropanal, hexanal, (E)-2-pentenal, 3-octanone, octanal, (Z)-2-penten-1-ol, hexanol, (E)-2-octenal, 1-octen-3-ol, benzaldehyde, (E,E)-2,4-nonadienal, and hexanoic acid in kernels were adequate at distinguishing oxidation levels and as oxidative markers in walnuts. Kernel volatiles is a useful measurement for walnut oxidation during storage without any prior fat extraction.
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Mária Nagy, Zoltán Győri e Mária Borbélyné Varga. "Methods for detention of lipid rancidity". Acta Agraria Debreceniensis, n. 50 (16 dicembre 2012): 117–20. http://dx.doi.org/10.34101/actaagrar/50/2576.
Testo completoAbstract (sommario):
There are various methods available for measurement of lipid oxidation in foods.Changes in chemical, physical, or organoleptic properties of fats and oils during oxidation may be monitored to assess the extent of lipid oxidation. However, there is no uniform and standard method for detecting all oxidative changes in all food systems. The available methods to monitor lipid oxidation in foods and biological systems may be divided into two groups. The first group measures primary oxidative changes and the second determines secondary changes that occur in each system.
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Yang, Lingwei, Xueren Xiao, Liping Liu, Jie Luo, Kai Jiang, Xinxing Han, Changhao Zhao, Jun Zhang e Guolin Wang. "Dynamic oxidation mechanism of carbon fiber reinforced SiC matrix composite in high-enthalpy and high-speed plasmas". Journal of Advanced Ceramics 11, n. 2 (11 gennaio 2022): 365–77. http://dx.doi.org/10.1007/s40145-021-0540-8.
Testo completoAbstract (sommario):
AbstractThis work employed an inductively coupled plasma wind tunnel to study the dynamic oxidation mechanisms of carbon fiber reinforced SiC matrix composite (Cf/SiC) in high-enthalpy and high-speed plasmas. The results highlighted a transition of passive/active oxidations of SiC at 800–1600 °C and 1–5 kPa. Specially, the active oxidation led to the corrosion of the SiC coating and interruption of the SiO2 growth. The transition borders of active/passive oxidations were thus defined with respect to oxidation temperature and partial pressure of atomic O in the high-enthalpy and high-speed plasmas. In the transition and passive domains, the SiC dissipation was negligible. By multiple dynamic oxidations of Cf/SiC in the domains, the SiO2 thickness was not monotonously increased due to the competing mechanisms of passive oxidation of SiC and dissipation of SiO2. In addition, the mechanical properties of the SiC coating/matrix and the Cf/SiC were maintained after long-term dynamic oxidations, which suggested an excellent thermal stability of Cf/SiC serving in thermal protection systems (TPSs) of reusable hypersonic vehicles.
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Silva, Raphael S. F., Mauro B. de Amorim, Maria do Carmo F. R. Pinto, Flávio S. Emery, Marília O. F. Goulart e Antonio V. Pinto. "Chemoselective oxidation of benzophenazines by m-CPBA: n-oxidation vs. oxidative cleavage". Journal of the Brazilian Chemical Society 18, n. 4 (2007): 759–64. http://dx.doi.org/10.1590/s0103-50532007000400014.
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Domínguez, Rubén, Mirian Pateiro, Paulo E. S. Munekata, Wangang Zhang, Paula Garcia-Oliveira, Maria Carpena, Miguel A. Prieto, Benjamin Bohrer e José M. Lorenzo. "Protein Oxidation in Muscle Foods: A Comprehensive Review". Antioxidants 11, n. 1 (28 dicembre 2021): 60. http://dx.doi.org/10.3390/antiox11010060.
Testo completoAbstract (sommario):
Muscle foods and their products are a fundamental part of the human diet. The high protein content found in muscle foods, as well as the high content of essential amino acids, provides an appropriate composition to complete the nutritional requirements of humans. However, due to their special composition, they are susceptible to oxidative degradation. In this sense, proteins are highly susceptible to oxidative reactions. However, in contrast to lipid oxidation, which has been studied in depth for decades, protein oxidation of muscle foods has been investigated much less. Moreover, these reactions have an important influence on the quality of muscle foods, from physico-chemical, techno-functional, and nutritional perspectives. In this regard, the loss of essential nutrients, the impairment of texture, water-holding capacity, color and flavor, and the formation of toxic substances are some of the direct consequences of protein oxidation. The loss of quality for muscle foods results in consumer rejection and substantial levels of economic losses, and thus the control of oxidative processes is of vital importance for the food industry. Nonetheless, the complexity of the reactions involved in protein oxidation and the many different factors that influence these reactions make the mechanisms of protein oxidation difficult to fully understand. Therefore, the present manuscript reviews the fundamental mechanisms of protein oxidation, the most important oxidative reactions, the main factors that influence protein oxidation, and the currently available analytical methods to quantify compounds derived from protein oxidation reactions. Finally, the main effects of protein oxidation on the quality of muscle foods, both from physico-chemical and nutritional points of view, are also discussed.
26
Xiao, Ling, Yu Li, Xuan Wang e Chao Yu. "Study on aging mechanism of special neoprene in hot air". IOP Conference Series: Earth and Environmental Science 1171, n. 1 (1 aprile 2023): 012038. http://dx.doi.org/10.1088/1755-1315/1171/1/012038.
Testo completoAbstract (sommario):
Abstract The accelerated aging tests of the special neoprene material in hot air were carried in laboratory. The aging mechanism was analyzed by using FTIR, DSC and TG spectra. The results showed that the thermal oxidative aging in air was a self-catalyzed oxidating reaction, the cross-linking reaction firstly in the process of thermo-oxidation, and the degradation reaction occurs at the later stage of aging.
27
Han, Wei, e Binbin Liu. "Iron-Catalyzed Wacker-Type Oxidation". Synlett 29, n. 04 (29 gennaio 2018): 383–87. http://dx.doi.org/10.1055/s-0036-1591532.
Testo completoAbstract (sommario):
Compared with the widespread use of Pd-catalyzed Wacker-type oxidation of olefins, iron catalysis for this transformation is almost virgin territory. Our work on an iron-catalyzed Wacker-type oxidation through reductive activation of dioxygen is discussed here. This novel single-electron-transfer process not only addresses the issues of the Pd-catalyzed two-electron Wacker-type oxidation, but also possesses unprecedented functional-group tolerance and chemoselectivity. Importantly, the catalytic system uses ambient air as the sole oxidant, and it permits late-stage oxidations of complex molecules.
28
Petersen, J. Claine, e P. Michael Harnsberger. "Asphalt Aging: Dual Oxidation Mechanism and Its Interrelationships with Asphalt Composition and Oxidative Age Hardening". Transportation Research Record: Journal of the Transportation Research Board 1638, n. 1 (gennaio 1998): 47–55. http://dx.doi.org/10.3141/1638-06.
Testo completoAbstract (sommario):
The kinetic data and chemistry of asphalt oxidative age hardening suggested a sequential, dual mechanism for asphalt oxidation. The dual mechanism rationalizes conflicts between earlier mechanistic investigations and explains the hyperbolic-like, time-versus-property plots characteristic of asphalt oxidative aging. The oxidation kinetics provide further confirmation of the asphalt microstructural model. It is proposed that the rapid initial oxidation rate of asphalt results from reaction of oxygen with limited amounts of highly reactive hydrocarbons. Final oxidation products of this initial reaction are sulfoxides and, most likely, ring aromatization. During this initial reaction, a slower oxidation reaction of asphalt benzylic carbons is initiated; final products are ketones and sulfoxides. The ratio of ketones to sulfoxides formed and the rate of age hardening were found to be dependent on temperature and oxygen pressure. Low-temperature oxidative aging, as occurs in pavements, was found significantly more sensitive to variations in temperature and asphalt composition than 100°C pressure vessel aging.
29
Burgoyne, Joseph R., e Philip Eaton. "Contemporary techniques for detecting and identifying proteins susceptible to reversible thiol oxidation". Biochemical Society Transactions 39, n. 5 (21 settembre 2011): 1260–67. http://dx.doi.org/10.1042/bst0391260.
Testo completoAbstract (sommario):
Elevated protein oxidation is a widely reported hallmark of most major diseases. Historically, this ‘oxidative stress’ has been considered causatively detrimental, as the protein oxidation events were interpreted simply as damage. However, recent advances have changed this antiquated view; sensitive methodology for detecting and identifying proteins susceptible to oxidation has revealed a fundamental role for this modification in physiological cell signalling during health. Reversible protein oxidation that is dynamically coupled with cellular reducing systems allows oxidative protein modifications to regulate protein function, analogous to phosphoregulation. However, the relatively labile nature of many reversible protein oxidation states hampers the reliable detection and identification of modified proteins. Consequently, specialized methods to stabilize protein oxidation in combination with techniques to detect specific types of modification have been developed. Here, these techniques are discussed, and their sensitivity, selectivity and ability to reliably identify reversibly oxidized proteins are critically assessed.
30
Kusuhara, S., M. Ito, T. Sato, W. Yokoi, Y. Yamamoto, K. Harada, H. Ikemura e K. Miyazaki. "Intracellular GSH of Streptococcus thermophilus shows anti-oxidative activity against low-density lipoprotein oxidation in vitro and in a hyperlipidaemic hamster model". Beneficial Microbes 9, n. 1 (29 gennaio 2018): 143–52. http://dx.doi.org/10.3920/bm2017.0065.
Testo completoAbstract (sommario):
Streptococcus thermophilus YIT 2001 (ST-1), a lactic acid bacterial strain, was shown to have inhibitory effects on the oxidation of low-density lipoprotein (LDL) and the development of aortic fatty lesions in an animal model, and lower the serum levels of malondialdehyde-modified LDL, an oxidative modification product of LDL, in a clinical trial. This study aimed to identify the intracellular active component of ST-1 associated with anti-oxidative activity against LDL oxidation. High-performance liquid chromatography-electrospray ionisation mass spectrometry analysis after fractionation of the cellular extract by reversed-phase chromatography demonstrated that the active fraction contained reduced glutathione (GSH). GSH showed anti-oxidative activity in a dose-dependent manner, while this activity disappeared following thiol derivatisation. ST-1 had the strongest anti-oxidative activity against LDL oxidation and the highest level of intracellular GSH among five strains of S. thermophilus. In addition, the anti-oxidative activity of ST-1 after thiol derivatisation decreased by about half, which was similar to that of three other strains containing poor or no intracellular GSH or thiol components. Moreover, anti-oxidative activity against LDL oxidation was observed in hyperlipidaemic hamsters fed with high GSH ST-1 cells but not in those given low GSH cells. These findings suggest that intracellular GSH in ST-1 may provide beneficial effects via anti-oxidative activity against LDL oxidation and excess oxidative stress in the blood.
31
Fruehwirth, Sarah, Sandra Egger, Dennis Kurzbach, Jakob Windisch, Franz Jirsa, Thomas Flecker, Miriam Ressler, Agnes T. Reiner, Nesrin Firat e Marc Pignitter. "Ingredient-Dependent Extent of Lipid Oxidation in Margarine". Antioxidants 10, n. 1 (13 gennaio 2021): 105. http://dx.doi.org/10.3390/antiox10010105.
Testo completoAbstract (sommario):
This study reports the impact of margarine-representative ingredients on its oxidative stability and green tea extract as a promising antioxidant in margarine. Oil-in-water emulsions received much attention regarding factors that influence their oxidative stability, however, water-in-oil emulsions have only been scarcely investigated. Margarine, a widely consumed water-in-oil emulsion, consists of 80–90% fat and is thermally treated when used for baking. As different types of margarine contain varying additives, their impact on the oxidative stability of margarine during processing is of pressing importance. Thus, the influence of different ingredients, such as emulsifiers, antioxidants, citric acid, β-carotene and NaCl on the oxidative stability of margarine, heated at 80 °C for 1 h to accelerate lipid oxidation, was analyzed by the peroxide value and oxidation induction time. We found that monoglycerides influenced lipid oxidation depending on their fatty acyl chain. α-Tocopheryl acetate promoted lipid oxidation, while rosemary and green tea extract led to the opposite. Whereas green tea extract alone showed the most prominent antioxidant effect, combinations of green tea extract with citric acid, β-carotene or NaCl increased lipid oxidation in margarine. Complementary, NMR data suggested that polyphenols in green tea extracts might decrease lipid mobility at the surface of the water droplets, which might lead to chelating of transition metals at the interface and decreasing lipid oxidation.
32
Yang, Moua, e Roy L. Silverstein. "Targeting Cysteine Oxidation in Thrombotic Disorders". Antioxidants 13, n. 1 (9 gennaio 2024): 83. http://dx.doi.org/10.3390/antiox13010083.
Testo completoAbstract (sommario):
Oxidative stress increases the risk for clinically significant thrombotic events, yet the mechanisms by which oxidants become prothrombotic are unclear. In this review, we provide an overview of cysteine reactivity and oxidation. We then highlight recent findings on cysteine oxidation events in oxidative stress-related thrombosis. Special emphasis is on the signaling pathway induced by a platelet membrane protein, CD36, in dyslipidemia, and by protein disulfide isomerase (PDI), a member of the thiol oxidoreductase family of proteins. Antioxidative and chemical biology approaches to target cysteine are discussed. Lastly, the knowledge gaps in the field are highlighted as they relate to understanding how oxidative cysteine modification might be targeted to limit thrombosis.
33
Kanvah, Sriram, e Gary B. Schuster. "Oxidative damage to DNA: Inhibition of guanine damage". Pure and Applied Chemistry 78, n. 12 (1 gennaio 2006): 2297–304. http://dx.doi.org/10.1351/pac200678122297.
Testo completoAbstract (sommario):
One-electron oxidation of DNA results in chemical damage to nucleobases, particularly guanine in multiple G sequences. Oxidation may be triggered by numerous events, including photosensitization. We describe studies of photoinduced oxidations of DNA triggered by irradiation of covalently linked anthraquinone derivatives under various conditions that affect the global structure of the DNA. These structural changes have subtle effects on the result of the one-electron oxidation.
34
Kuo, C. F., e I. Fridovich. "Free-radical chain oxidation of 2-nitropropane initiated and propagated by superoxide". Biochemical Journal 237, n. 2 (15 luglio 1986): 505–10. http://dx.doi.org/10.1042/bj2370505.
Testo completoAbstract (sommario):
The superoxide radical O2.-, whether produced by the xanthine/xanthine oxidase reaction or infused as KO2, solubilized by a crown ether in dry dimethyl sulphoxide, initiated a free-radical chain oxidation of anionic 2-nitropropane. Superoxide dismutase, but not catalase, inhibited oxidation of the nitroalkane. Xanthine oxidase suffered a syncatalytic inactivation, during the co-oxidation of 2-nitropropane, which was reversed by dialysis. Cyanide exacerbated this syncatalytic inactivation and rendered it irreversible. The frequently observed oxidations of nitroalkanes by flavoenzymes now need to be re-examined to clarify the extent to which O2.--initiated free-radical chain oxidation contributed to the overall nitroalkane oxidation.
35
Domínguez, Rubén, Mirian Pateiro, Mohammed Gagaoua, Francisco J. Barba, Wangang Zhang e José M. Lorenzo. "A Comprehensive Review on Lipid Oxidation in Meat and Meat Products". Antioxidants 8, n. 10 (25 settembre 2019): 429. http://dx.doi.org/10.3390/antiox8100429.
Testo completoAbstract (sommario):
Meat and meat products are a fundamental part of the human diet. The protein and vitamin content, as well as essential fatty acids, gives them an appropriate composition to complete the nutritional requirements. However, meat constituents are susceptible to degradation processes. Among them, the most important, after microbial deterioration, are oxidative processes, which affect lipids, pigments, proteins and vitamins. During these reactions a sensory degradation of the product occurs, causing consumer rejection. In addition, there is a nutritional loss that leads to the formation of toxic substances, so the control of oxidative processes is of vital importance for the meat industry. Nonetheless, despite lipid oxidation being widely investigated for decades, the complex reactions involved in the process, as well as the different pathways and factors that influenced them, make that lipid oxidation mechanisms have not yet been completely understood. Thus, this article reviews the fundamental mechanisms of lipid oxidation, the most important oxidative reactions, the main factors that influence lipid oxidation, and the routine methods to measure compounds derived from lipid oxidation in meat.
36
Lozano-Picazo, Carmen María, e Francisco Fernández-Belda. "Especies reactivas de oxígeno y su implicación en Biomedicina". Anales de Veterinaria de Murcia 34 (16 dicembre 2020): 17–26. http://dx.doi.org/10.6018/analesvet.332621.
Testo completoAbstract (sommario):
Las especies reactivas de oxígeno (ROS) actúan como regulador intracelular cuando se generan de forma controlada en puntos concretos de la célula. Modifican la función de proteínas mediante la oxidación reversible de cisteínas. Hay quinasas y fosfatasas de proteínas, factores de transcripción y canales iónicos que están regulados por ROS. Estrés oxidativo y daño celular aparecen cuando los mecanismos antioxidantes de protección son incapaces de mantener bajo el nivel intracelular de ROS. En estas condiciones, ROS inducen pérdida de viabilidad celular en patologías degenerativas de corazón y cerebro y promueven proliferación celular ilimitada en procesos tumorales. La alteración de la función mitocondrial juega un papel clave en la generación del estrés oxidativo y por tanto es una diana terapéutica preferente para evitar o aminorar los daños oxidativos producidos por ROS. Reactive oxygen species (ROS) act as intracellular regulator when they are generated under control in specific cell spots. They modify proteins function by cysteine reversible oxidation. There are protein kinases and phosphatases, transcription factors and ionic channels that are regulated by ROS. Oxidative stress and cell damage arise when the protection antioxidant mechanisms are unable to keep low the intracellular ROS level. Under these conditions, ROS induce cell viability loss in heart and brain degenerative pathologies and promote unlimited cell proliferation in tumor processes. Alteration of the mitochondrial function is a key player in the oxidative stress generation and therefore it is preferential therapeutic target for prevention or attenuation of the ROS-induced oxidative damage.
37
Hong, Yiming, Tiantian Fang, Meichao Li, Zhenlu Shen, Xinquan Hu, Weimin Mo, Baoxiang Hu, Nan Sun e Liqun Jin. "2,3-Dichloro-5,6-dicyano-1,4-benzoquinone-catalyzed aerobic oxidation reactions via multistep electron transfers with iron(ii) phthalocyanine as an electron-transfer mediator". RSC Advances 6, n. 57 (2016): 51908–13. http://dx.doi.org/10.1039/c6ra08921f.
Testo completo
38
Li, Gui-Yang, e J. L. Koenig. "A Review of Rubber Oxidation". Rubber Chemistry and Technology 78, n. 2 (1 maggio 2005): 355–90. http://dx.doi.org/10.5254/1.3547888.
Testo completoAbstract (sommario):
Abstract The aging of rubber caused by oxidative degradation leads to the deterioration in the physical and mechanical properties of vulcanized rubbers. In an effort to improve the oxidative stability of rubbers and elastomers, considerable amount of work has been carried out over the past 50 years (especially in the most recent 5 years) in order to understand degradation modes and effects in rubber due to the action of oxygen and ozone in the air. Different mechanisms have been proposed to interpret the experimental data relative to the oxidation of rubber. The diffusion limited theory has been widely used in the literature and verified by many experiments. Various instrumental techniques have been utilized to characterize the oxidation and degradation and their mechanisms in rubber compounds. Recently, FTIR imaging has demonstrated a unique combination of spectral and spatial resolution which allows not only the identification of the oxidation products but also their spatial distribution from the oxygen penetrating surfaces. This critical review will cover the major developments in our understanding of the oxidation of rubbers.
39
Li, Gui-Yang, e J. L. Koenig. "A Review of Rubber Oxidation". Rubber Chemistry and Technology 78, n. 3 (1 luglio 2005): 355–90. http://dx.doi.org/10.5254/1.3547889.
Testo completoAbstract (sommario):
Abstract The aging of rubber caused by oxidative degradation leads to the deterioration in the physical and mechanical properties of vulcanized rubbers. In an effort to improve the oxidative stability of rubbers and elastomers, considerable amount of work has been carried out over the past 50 years (especially in the most recent 5 years) in order to understand degradation modes and effects in rubber due to the action of oxygen and ozone in the air. Different mechanisms have been proposed to interpret the experimental data relative to the oxidation of rubber. The diffusion limited theory has been widely used in the literature and verified by many experiments. Various instrumental techniques have been utilized to characterize the oxidation and degradation and their mechanisms in rubber compounds. Recently, FTIR imaging has demonstrated a unique combination of spectral and spatial resolution which allows not only the identification of the oxidation products but also their spatial distribution from the oxygen penetrating surfaces. This critical review will cover the major developments in our understanding of the oxidation of rubbers.
40
Hopps, Eugenia, e Gregorio Caimi. "Protein Oxidation in Metabolic Syndrome". Clinical & Investigative Medicine 36, n. 1 (1 febbraio 2013): 1. http://dx.doi.org/10.25011/cim.v36i1.19399.
Testo completoAbstract (sommario):
Purpose: Oxidative stress plays a pivotal role in the pathogenesis of the metabolic syndrome and in the progression of its complications. Carbonylated proteins are a stable marker of severe oxidative stress because damage to the protein structure is irreversible and may cause an inhibition of their enzymatic activity or an increased susceptibility to proteolysis. There are few data regarding protein oxidation in metabolic syndrome, although elevated levels of carbonyl groups are often detected in subjects with obesity, diabetes mellitus, hypertension or dyslipidemia, well-known components of the metaboic syndrome. In particular, obesity, insulin resistance and diabetes mellitus are frequently associated with increased protein carbonylation. A relationship between insulin resistance, protein oxidative stress and inflammation has also been suggested as well as protein oxidation products are correlated with overexpression of resistin, TNF-α and IL-6. Conclusion: Therapeutic interventions based on lifestyle modifications and pharmacological agents in order to correct all the main risk factors influence oxidative stress and protein carbonylation.
41
Allen, Tara J., e Christopher D. Hardin. "Influence of glycogen storage on vascular smooth muscle metabolism". American Journal of Physiology-Heart and Circulatory Physiology 278, n. 6 (1 giugno 2000): H1993—H2002. http://dx.doi.org/10.1152/ajpheart.2000.278.6.h1993.
Testo completoAbstract (sommario):
The role of glycogen as an oxidative substrate for vascular smooth muscle (VSM) remains controversial. To elucidate the importance of glycogen as an oxidative substrate and the influence of glycogen flux on VSM substrate selection, we systematically altered glycogen levels and measured metabolism of glucose, acetate, and glycogen. Hog carotid arteries with glycogen contents ranging from 1 to 11 μmol/g were isometrically contracted in physiological salt solution containing 5 mM [1-13C]glucose and 1 mM [1,2-13C]acetate at 37°C for 6 h. [1-13C]glucose, [1,2-13C]acetate, and glycogen oxidation were simultaneously measured with the use of a 13C-labeled isotopomer analysis of glutamate. Although oxidation of glycogen increased with the glycogen content of the tissue, glycogen oxidation contributed only ∼10% of the substrate oxidized by VSM. Whereas [1-13C]glucose flux, [3-13C]lactate production from [1-13C]glucose, and [1,2-13C]acetate oxidation were not regulated by glycogen content, [1-13C]glucose oxidation was significantly affected by the glycogen content of VSM. However, [1-13C]glucose remained the primary (∼40–50%) contributor to substrate oxidation. Therefore, we conclude that glucose is the predominate substrate oxidized by VSM, and glycogen oxidation contributes minimally to substrate oxidation.
42
Van Hecke, Thomas, e Stefaan De Smet. "The Influence of Butter and Oils on Oxidative Reactions during In Vitro Gastrointestinal Digestion of Meat and Fish". Foods 10, n. 11 (17 novembre 2021): 2832. http://dx.doi.org/10.3390/foods10112832.
Testo completoAbstract (sommario):
Oxidative reactions during cooking and gastrointestinal digestion of meat and fish lead to the formation of various lipid- and protein oxidation products, some of which are toxic. In the present study, it was investigated how the addition of 3% butter or oils affect lipid- and protein oxidation during cooking and in vitro digestion of meat (chicken thigh, chicken breast, beef) and fish (mackerel, cod). These muscle foods were selected based on their differences in heme-Fe and PUFA contents, and n-6/n-3 PUFA ratio, and therefore varying potential to form oxidation products during digestion. Without additional fat, mackerel digests displayed the highest n-3 PUFA oxidation (4-hydroxy-2-hexenal, propanal, thiobarbituric reactive acid substances), and chicken digests the highest n-6 PUFA oxidation (4-hydroxy-2-nonenal, hexanal), whereas both lipid- and protein oxidation (protein carbonyl compounds) were low in cod and beef digests. Lipid oxidative reactions were generally not altered by the addition of butter to any muscle matrix, whereas the addition of fish oil and safflower oil in different ratios (3:0, 2:1, 1:2, 0:3) as n-3 PUFA and n-6 PUFA source respectively, stimulated oxidative reactions, especially during digestion of beef. Since beef was considered the muscle matrix with the highest potential to stimulate oxidation in the added fat substrate, in a second experiment, beef was cooked and digested with 3% butter or seven commercial vegetable oils (sunflower-, maize-, peanut-, rapeseed-, olive-, rice bran- or coconut oil), all labeled ‘suitable for heating’. No relevant oxidative reactions were however observed during digestion of beef with any of these commercial vegetable oils.
43
Pan, F., X. Wang, B. Wen, C. Wang, Y. Xu, W. Dang e M. Zhang. "Development of walnut oil and almond oil blends for improvements in nutritional and oxidative stability". Grasas y Aceites 71, n. 4 (30 dicembre 2020): 381. http://dx.doi.org/10.3989/gya.0920192.
Testo completoAbstract (sommario):
For the increase in oxidative stability and phytonutrient contents of walnut oil (WO), 5, 10, 20 and 30% blends with almond oil (AO) were prepared. The fatty acid compositions and the micronutrients of the oil samples such as tocopherol, phytosterol and squalene were measured by GC-MS and HPLC. It was found that the proportions of PUFAs/SFAs in blended oils with high AO contents were lowered, and the blends contained higher levels of tocopherols, phytosterols and squalene than those of pure WO. The 60 °C oven accelerated oxidation test was used to determine the oxidative stability of the blended oil. The fatty acid composition, micronutrients and oxidation products were determined. The results showed that the oxidation stability of the blended oil increased with an increasing proportion of AO. In addition, a significant negative correlation between micronutrient and oxidation products was observed as the number of days of oxidation increased.
44
Waldi, Muhamad, Helmi Bagas Samudra, Ahmad Maulana Arkan Leksana, Djoko Hadi Prajitno e Haris Tjahaya. "Cyclic Oxidation Behavior of HVOF Thermally Sprayed WC Cermet Based on AISI 1045 Steel". Majalah Ilmiah Pengkajian Industri 16, n. 2 (30 agosto 2022): 73–80. http://dx.doi.org/10.29122/mipi.v16i2.5311.
Testo completoAbstract (sommario):
Thermal spray coating technology High-Velocity Oxygen Fuel (HVOF) has become one of solution for metal protect and parts recondition that work in critical environments such as oxidative, erosive, and corrosive. One of the thermal spray coatings (TSC) application has been carried out to improve the oxidation resistance of the Induce Draft Fan (IDF) as a part on coal fired steam power plant unit. Cermet WC10Co4Cr and WC17Co are intended to sustain the AISI 1045 steel substrate against the oxidative environment. In this works, the cyclic oxidation at a temperature 500oC were conducted to reveal the oxidation resistance behavior of the coatings. Several mechanical tests are also presented including surface roughness of the coatings, coatings microhardness, and coatings adhesion. The coatings morphology was also characterized using SEM microscope, as well as X-ray diffraction (XRD) for phase analysis after the oxidation test. KeywordHVOF, Oxidation resistance, Induce draft fan.
45
Ni, Hong Jun, Lei Chen, De Qin She e Yin Nan Yuan. "Current Situation of the Study on Oxidative Stability of Biodiesel". Advanced Materials Research 887-888 (febbraio 2014): 484–87. http://dx.doi.org/10.4028/www.scientific.net/amr.887-888.484.
Testo completoAbstract (sommario):
As a high quality alternative of fossil diesel, biodiesel is widely concerned at domestic and abroad for its environmentally friendly and renewable. Oxidation stability is one of the important properties of biodiesel, which is also one of the quality criteria in storing and using. The oxidative mechanism and the influencing factors of Oxidation stability, oxidation stabilitys evaluation methods and the application of biodiesel antioxidants were reviewed. Then the direction of oxidation stability is put forward.
46
Kvasnica, Miroslav, Iva Tišlerová, Jan Šarek, Jan Sejbal e Ivana Císařová. "Preparation of New Oxidized 18-α-Oleanane Derivatives". Collection of Czechoslovak Chemical Communications 70, n. 9 (2005): 1447–64. http://dx.doi.org/10.1135/cccc20051447.
Testo completoAbstract (sommario):
19β,28-Epoxy-4,5-seco-3,5-cyclo-18α-olean-3(5)-ene (2) is an appropriate compound for oxidations, which lead to new oxidized compounds with potential biological activities. Several oxidations were used such as epoxidation, allylic oxidation, oxidative cleavage of double bond and other ones. From the starting compound epoxides 3a, 3b and unsaturated ketone 4 were prepared. This ketone was further oxidized to diketone 6 and anhydride 7. The double bonds of all unsaturated compounds were cleaved with ruthenium tetroxide to afford new A-seco oleananes. The structure and stereochemistry of the compounds were derived from IR, MS, 1H and 13C NMR spectra (1D and 2D COSY, TOCSY, NOESY, HSQC, HMBC).
47
Pandey, Kanti Bhooshan, Mohd Murtaza Mehdi, Pawan Kumar Maurya e Syed Ibrahim Rizvi. "Plasma Protein Oxidation and Its Correlation with Antioxidant Potential During Human Aging". Disease Markers 29, n. 1 (2010): 31–36. http://dx.doi.org/10.1155/2010/964630.
Testo completoAbstract (sommario):
Previous studies have indicated that the main molecular characteristic of aging is the progressive accumulation of oxidative damages in cellular macromolecules. Proteins are one of the main molecular targets of age-related oxidative stress, which have been observed during aging process in cellular systems. Reactive oxygen species (ROS) can lead to oxidation of amino acid side chains, formation of protein-protein cross-linkages, and oxidation of the peptide backbones. In the present study, we report the age-dependent oxidative alterations in biomarkers of plasma protein oxidation: protein carbonyls (PCO), advanced oxidation protein products (AOPPs) and plasma total thiol groups (T-SH) in the Indian population and also correlate these parameters with total plasma antioxidant potential. We show an age dependent decrease in T-SH levels and increase in PCO and AOPPs level. The alterations in the levels of these parameters correlated significantly with the total antioxidant capacity of the plasma. The levels of oxidized proteins in plasma provide an excellent biomarker of oxidative stress due to the relative long half-life of such oxidized proteins.
48
He, Zhongqi, Sunghyun Nam e K. Thomas Klasson. "Oxidative Stability of Cottonseed Butter Products under Accelerated Storage Conditions". Molecules 28, n. 4 (7 febbraio 2023): 1599. http://dx.doi.org/10.3390/molecules28041599.
Testo completoAbstract (sommario):
Cottonseed is a natural product of cotton (Gossypium spp.) crops. This work evaluated the oxidative stability of cottonseed butters through accelerated autoxidation by storage at 60 °C for 25 days. Three oxidative stability parameter values (peroxide value, p-anisidine value, and total oxidation value) were monitored over the storage time. These chemical measurements revealed that the storage stability of the butter products was dominated by primary oxidation of lipid (oil) components, while the secondary oxidation levels were relatively unchanged over the storage time. An analysis of the tocopherols (natural oxidants in cottonseed) suggested not only the protection function of the molecules against oxidation of the cottonseed butter during storage, but also the dynamic mechanism against the primary oxidation of lipid components. Attenuated total reflectance–Fourier-transform infrared spectroscopy (ATR–FTIR) data confirmed no changes in the major C functional groups of cottonseed butters over the storage time. On the other hand, characteristic minor peaks of conjugated dienes and trienes related to lipid oxidation were impacted by the accelerated storage. As each day of accelerated oxidation at 60 °C is equivalent to 16 days of storage at 20 °C, observations in this work should have reflected the oxidative stability behaviors of the cottonseed butters after about 13 months of shelf storage under ambient storage conditions. Thus, these data that were collected under the accelerated oxidation testing would be useful not only to create a better understanding of the autooxidation mechanism of lipid molecules in cottonseed butters, but also in developing or recommending appropriate storage conditions for cottonseed end products to prevent them from quality degradation.
49
Zografos, Alexandros, e Marina Petsi. "Advances in Catalytic Aerobic Oxidations by Activation of Dioxygen-Monooxygenase Enzymes and Biomimetics". Synthesis 50, n. 24 (15 ottobre 2018): 4715–45. http://dx.doi.org/10.1055/s-0037-1610297.
Testo completoAbstract (sommario):
Monooxygenases are not only some of the most versatile machineries in our lives, but also some of the most explored enzymes in modern organic synthesis. They provide knowledge and inspiration on how the most abandoned oxidant, dioxygen, can be activated and utilized to deliver selective oxidations. This review presents an outline in the mechanisms that Nature uses to succeed in these processes and recent indicative examples on how chemists use this knowledge to develop selective oxidation protocols based on dioxygen as the terminal oxidant.1 Introduction2 Monooxygenases2.1 Metal-Based Monooxygenases2.1.1 Cytochromes2.1.2 Copper-Dependent Monooxygenases2.1.3 Heme-Independent Iron Monooxygenases2.1.4 Pterin-Dependent Monooxygenases2.2 Metal-Free Monooxygenases2.2.1 Flavin-Dependent Monooxygenases2.2.2 Systems without Cofactors3 Biomimetic Aerobic Oxidations3.1 Aerobic Oxidations Based on Metal Catalysts3.1.1 Epoxidations and Allylic Oxidations3.1.2 Oxidations of Unactivated Carbon Atoms and Benzylic Oxidations3.1.3 Oxidations of Aryl Groups3.1.4 Heteroatom Oxidations3.2 Aerobic Oxidations Based on Organocatalysts3.2.1 Baeyer–Villiger Oxidations3.2.2 Oxidations of Aryl Groups3.2.3 Heteroatom Oxidations4 Conclusion
50
Williamson, Peter R., Kazumasa Wakamatsu e Shosuke Ito. "Melanin Biosynthesis in Cryptococcus neoformans". Journal of Bacteriology 180, n. 6 (15 marzo 1998): 1570–72. http://dx.doi.org/10.1128/jb.180.6.1570-1572.1998.
Testo completoAbstract (sommario):
ABSTRACT Pigment production by Cryptococcus neoformans is virulence associated. Dopamine- and 3,4-dihydroxyphenylalanine–melanin products were identified after acidic permanganate oxidation, alkaline hydrogen peroxide oxidation, or hydrolysis with hydriodic acid. These data provide direct chemical evidence for the formation of eumelanin polymers by catecholamine oxidation by laccase alone followed by oxidative coupling of dihydroxyindole.