共查询到20条相似文献,搜索用时 15 毫秒
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Tom Verleyen Afaf Kamal‐Eldin Revilija Mozuraityte Roland Verh Koen Dewettinck Andre Huyghebaert Wim De Greyt 《European Journal of Lipid Science and Technology》2002,104(4):228-233
The competitive oxidation between α‐tocopherol and unsaturated fatty acyls at thermoxidation conditions (180 and 240 °C) was evaluated using purified triacylglycerols from nine fats and oils (refined coconut, palm, tallow, olive, high oleic sunflower, sunflower, corn, soybean, and flaxseed oil). α‐Tocopherol degraded faster in less unsaturated lipids and a linear correlation between the iodine value (x) and the residual tocopherol content (y) was obtained after 2 h of heating at 240 °C (y = 3.72x + 137.5, R2 = 0.9463). The formation of polar oxidation products was established and the results were explained by a non‐selective oxidation of unsaturated fatty acyls and α‐tocopherol by highly reactive alkoxyl and hydroxyl radicals generated by decomposition of hydroperoxides. 相似文献
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María Jesús Oliveras‐López José Javier Quesada Granados Francisco Martín Bermudo Herminia López‐García de la Serrana Maria del Carmen López Martínez 《European Journal of Lipid Science and Technology》2008,110(6):530-536
The aim of this study was to estimate the α‐tocopherol content in Picual extra‐virgin olive oils obtained from the 2004/2005 harvesting season and to evaluate the influence that different extraction processes and sample handling had on the final vitamin E content in the oils. A new experimental oil extraction carried out at 9 °C enabled us to obtain encouragingly high quantities of α‐tocopherol with an average quantity reaching 341.34 ± 50.17 mg/L (n = 13), with significant differences among the same oil types produced from the traditional two‐phase system at low (9 °C, p <0.01) and moderate (21.5 °C, p <0.001; 33 °C, p <0.0001) temperatures. The temperature at which extraction was carried out should be considered as a major factor to be taken into account. Additionally, we also developed a precise method for the extraction of α‐tocopherol from olive oil samples, which enables high recovery (96 ± 2%) for use in subsequent HPLC/DAD/fluorescence quantification. 相似文献
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Nedyalka V. Yanishlieva Afaf Kamal‐Eldin Emma M. Marinova Assya G. Toneva 《European Journal of Lipid Science and Technology》2002,104(5):262-270
A kinetic analysis was performed to evaluate the antioxidant behavior of α‐ and γ‐to‐copherols (5—2000 ppm) in purified triacylglycerols obtained from sunflower oil (TGSO) and soybean oil (TGSBO) at 100 °C. Different kinetic parameters were determined, viz. the stabilization factor as a measure of effectiveness, the oxidation rate ratio as a measure of strength, and the antioxidant activity which combines the other two parameters. In the low concentration range (up to 400 ppm in TGSBO and up to 700 ppm in TGSO) α‐tocopherol was a more active antioxidant than γ‐tocopherol whereas the latter was more active at higher concentrations. It has been found that the different activity of the tocopherols is not due to their participation in chain initiation reactions, but that the loss of antioxidant activity at high tocopherol concentrations is due to their consumption in side reactions. The rates of these reactions are higher in TGSBO than in TGSO. Both α‐tocopherol itself and its radicals participated more readily in side reactions than γ‐tocopherol and its radicals. Both α‐ and γ‐tocopherol reduce lipid hydroperoxides, thus generating alkoxyl radicals which are able to amplify the rate of lipid oxidation by participating in chain propagation reactions. 相似文献
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Temelkan Bakır Bilge Yıldoğan Beker İnci Sönmezoğlu Filiz İmer Reşat Apak 《European Journal of Lipid Science and Technology》2013,115(3):372-376
The peroxidation of linoleic acid (LA) in the absence and presence of either Cu(II) ions alone or Cu(II)‐ascorbate combination was investigated in aerated and incubated emulsions at 37°C and pH 7. LA peroxidation induced by either copper(II) or copper(II)‐ascorbic acid system followed pseudo‐first order kinetics with respect to primary (hydroperoxides) and secondary (aldehydes‐ and ketones‐like) oxidation products, detected by ferric‐thiocyanate and TBARS tests, respectively. α‐Tocopherol showed both antioxidant and prooxidant effects depending on concentration and also on the simultaneous presence of Cu(II) and ascorbate. Copper(II)‐ascorbate combinations generally led to distinct antioxidant behavior at low concentrations of α‐tocopherol and slight prooxidant behavior at high concentrations of α‐tocopherol, probably associated with the recycling of tocopherol by ascorbate through reaction with tocopheroxyl radical, while the scavenging effect of α‐tocopherol on lipid peroxidation was maintained as long as ascorbate was present. On the other hand, in Cu(II) solutions without ascorbate, the antioxidant behavior of tocopherol required higher concentrations of this compound because there was no ascorbate to regenerate it. Practical applications: Linoleic acid (LA) peroxidation induced by either copper(II) or copper(II)‐ascorbic acid system followed pseudo‐first order kinetics with respect to primary (hydroperoxides) and secondary (e.g., aldehydes and ketones) oxidation products. α‐Tocopherol showed both antioxidant and prooxidant effects depending on concentration and also on the simultaneous presence of Cu(II) and ascorbate. The findings of this study are believed to be useful to better understand the actual role of α‐tocopherol in the preservation of heterogenous food samples such as lipid emulsions. Since α‐tocopherol (vitamin E) is considered to be physiologically the most important lipid‐soluble chain‐breaking antioxidant of human cell membranes, the results can be extended to in vivo protection of lipid oxidation. 相似文献
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NataliyaS. Goulioukina GrigoriiN. Bondarenko SergeyE. Lyubimov VadimA. Davankov KonstantinN. Gavrilov IrinaP. Beletskaya 《Advanced Synthesis \u0026amp; Catalysis》2008,350(3):482-492
It was shown that the catalytic hydrogenation of α‐iminophosphonates by molecular hydrogen can serve as a convenient method for the synthesis of racemic and optically active α‐aminophosphonates. Up to 94% ee was achieved in the rhodium‐catalyzed enantioselective hydrogenation using chiral ligand (R)‐BINAP. 相似文献
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Koji Yonehara Yasuyuki Miyoshi Aki Tsukajima Takeo Akatsuka Makoto Saito 《Advanced Synthesis \u0026amp; Catalysis》2011,353(7):1071-1075
The methodology in this article is a palladium(II)/copper(II)‐ or palladium(II)‐catalyzed intermolecular cyclization of acrylic acid with alkenes to produce α‐methylene‐γ‐butyrolactone derivatives using molecular oxygen as an environmentally benign oxidant. In this system, the carboxylato, especially trifluoroacetato, or trimethylacetato ligand, plays a quite important role to afford a high catalytic activity by suppressing the deposition of palladium(0) black. 相似文献
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Gaetano Giammona Gennara Cavallaro Giovanna Pitarresi Elisa Pedone 《Polymer International》2000,49(1):93-98
In the present study the derivatization of two water‐soluble synthetic polymers, α,β‐poly(N‐2‐hydroxyethyl)‐DL ‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy), with glycidyltrimethylammonium chloride (GTA) is described. This reaction permits the introduction of positive charges in the macromolecular chains of PHEA and PAHy in order to make easier the electrostatic interaction with DNA. Different parameters affect the reaction of derivatization, such as GTA concentration and reaction time. PHEA reacts partially and slowly with GTA; on the contrary the reaction of PAHy with GTA is more rapid and extensive. The derivatization of PHEA and PAHy with GTA is a convenient method to introduce positive groups in their chains and it permits the preparation of interpolyelectrolyte complexes with DNA. © 2000 Society of Chemical Industry 相似文献
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Yohan Park Young Ju Lee Suckchang Hong Mi‐hyun Kim Myungmo Lee Taek‐Soo Kim Jae Kyun Lee Sang‐sup Jew Hyeung‐geun Park 《Advanced Synthesis \u0026amp; Catalysis》2011,353(18):3313-3318
A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers. 相似文献
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Xiang Li Siyu Li Suyan Sun Fan Yang Weiguo Zhu Yu Zhu Yusheng Wu Yangjie Wu 《Advanced Synthesis \u0026amp; Catalysis》2016,358(10):1699-1704
An efficient and generally applicable protocol for decarboxylative coupling of α,α‐difluoroarylacetic acids with ethynylbenziodoxolone (EBX) reagents has been developed, affording α,α‐difluoromethylated alkynes bearing various functional groups in moderate to excellent yields. Remarkably, this potassium persulfate (K2S2O8)‐promoted reaction employs water as solvent under transition metal‐free conditions, thus providing a green synthetic approach to α,α‐difluoromethylated alkynes.
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Luca Deiana Gui‐Ling Zhao Shuangzheng Lin Pawel Dziedzic Qiong Zhang Hans Leijonmarck Armando Crdova 《Advanced Synthesis \u0026amp; Catalysis》2010,352(18):3201-3207
The first example of a highly enantioselective organocatalytic aziridination of α‐substituted α,β‐unsaturated aldehydes is presented. The reaction is catalyzed by simple chiral amines and gives access to highly functional terminal azirdines containing an α‐tertiary amine stereocenter in high yields and enantiomeric ratios (95.5:4.5–98:2). 相似文献
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Reynaldo Villalonga Leissy Gmez Hector L Ramírez Maria L Villalonga 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1999,74(7):635-638
Carboxymethylcellulose activated by periodate oxidation was covalently linked to porcine pancreatic α‐amylase (EC 3.2.1.1). The specific activity of the conjugate prepared was 54% of the native enzyme. The carbohydrate content was estimated to be 62% by weight as a result of the modification of 67% of the amino groups from the protein. In comparison with the native enzyme, the thermostability and pH stability were improved for α‐amylase by this modification. The conjugate was also more resistant to the action of denaturant agents such as urea and sodium dodecylsulfate. We conclude that modification of enzymes by the anionic polysaccharide carboxymethylcellulose might be a useful method for improving enzyme stability under various denaturing conditions. © 1999 Society of Chemical Industry 相似文献
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Krishna Bahadur SomaiMagar Yong Rok Lee 《Advanced Synthesis \u0026amp; Catalysis》2014,356(16):3422-3432
Efficient one‐step syntheses of α,β‐ and β,β‐dihaloenones were achieved by ruthenium(II)‐catalyzed reactions between cyclic or acyclic diazodicarbonyl compounds and oxalyl chloride or oxalyl bromide in moderate to good yields. This methodology offers several significant advantages, which include ease of handling, mild reaction conditions, one‐step reaction, and the use of an effective and non‐toxic catalyst. The synthesized compounds were further transformed into highly functionalized novel molecules bearing aromatic rings on the enone moiety using the Suzuki reaction.
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A Rapid Method for Simultaneous Analysis of Lignan and γ‐Tocopherol in Sesame Oil by Using Normal‐Phase Liquid Chromatography 下载免费PDF全文
Long‐Kai Shi Li Zheng Yin‐Feng Xiang Rui‐Jie Liu Ming Chang Qing‐Zhe Jin Xing‐Guo Wang 《Journal of the American Oil Chemists' Society》2018,95(1):13-19
A novel method for rapid and simultaneous analysis of three lignans and γ‐tocopherol in sesame oil has been established based on a one‐step solvent extraction followed by normal‐phase liquid chromatography. The briefness of the experimental procedure, use of 5 mL of n‐hexane/isopropanol (98:2, v/v) for extraction without any further cleanup process, short analysis time (10 min), and excellent sensitivity and selectivity demonstrated the advantages of this practical and efficient method. All the analytes exhibited satisfactory recoveries ranging from 95.4 to 103.4% at three spiked levels, with the relative SD ranging from 1.1 to 4.4%. The limits of quantitation of this method for four analytes were in the range of 0.3–1.0 μg g?1. The validated method was successfully applied to the coinstantaneous determination of lignan and γ‐tocopherol in five real sesame oil samples. Furthermore, the results of this study were compared with previously reported method and standard method. 相似文献
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Romain Blanc Laurent Commeiras Jean‐Luc Parrain 《Advanced Synthesis \u0026amp; Catalysis》2010,352(4):661-666
A new, highly efficient and mild N‐heterocyclic carbene (NHC)‐mediated organocatalytic procedure for the transfer of tin from tributyl(trimethylsilyl)stannane (Bu3SnSiMe3) onto aldehydes for the preparation of α‐silyloxyalkylstannanes and γ‐silyloxyallylstannanes has been developed. 相似文献
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Alessandro Palmieri Serena Gabrielli Roberto Ballini 《Advanced Synthesis \u0026amp; Catalysis》2010,352(9):1485-1492
A new class of nitro‐functionalized α,β‐unsaturated esters has been prepared by a regio‐ and diastereoselective Michael addition of nitroalkanes to β‐nitroacrylates, performed at room temperature, under carbonate on polymer as promoter, and in the presence of ethyl acetate as eco‐friendly solvent. Moreover, by the modular choice of the reaction conditions the method allows the synthesis of 1,3‐butadiene‐2‐carboxylates. 相似文献
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Xing‐Kuan Chen Chang‐Wu Zheng Sheng‐Li Zhao Zhuo Chai Ying‐Quan Yang Gang Zhao Wei‐Guo Cao 《Advanced Synthesis \u0026amp; Catalysis》2010,352(10):1648-1652
A highly enantioselective Michael addition of cyclic 1,3‐dicarbonyl compounds to β,γ‐unsaturated α‐keto esters catalyzed by amino acid‐derived thiourea‐tertiary‐amine catalysts is presented. Using 5 mol% of a novel tyrosine‐derived thiourea catalyst, a series of chiral coumarin derivatives were obtained in excellent yields (up to 99%) and with up to 96% ee under very mild conditions within a short reaction time. 相似文献