共查询到17条相似文献，搜索用时 162 毫秒
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研究了没食子酸辛酯标准样品的制备、均匀性和稳定性及其定值试验.将没食子酸辛酯工业品用无水乙醇溶解,再用纯水稀释后重结晶,得到高纯度的没食子酸辛酯标准样品.没食子酸辛酯含量测定采用液相色谱面积归一化法.所研制的没食子酸辛酯标准样品通过了均匀性检验和稳定性检验(6个月).经定值检测,该标准样品的质量分数为99.4720％,不确定度为0.03％. 相似文献
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利用黑曲霉(Aspergillus niger)细胞作为全细胞生物催化剂,研究了催化没食子酸生成没食子酸丙酯的条件,探讨了有机溶剂、细胞预处理、底物浓度、反应时间和水分含量等因素在酶催化没食子酸丙酯合成中的影响,结果表明,苯是最佳溶剂,而菌丝体的含水量在80％时得率最高.在此基础上,选择菌丝量、没食子酸浓度、正丙醇体积分数和反应时间进行了正交试验,在200 r/min、40℃的转化条件下得到的较佳催化组合为:25 mL锥形瓶中加入10 mL苯、0.5g菌丝、7 mmol(0.012 7 g)没食子酸、7.3 ％(0.73 mL)正丙醇组成的有机催化体系中,反应18h,没食子酸丙酯得率达到36.4％.该过程无需要纯化或者固定化酶,实现了没食子酸丙酯低成本、高得率的催化. 相似文献
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微乳凝胶固定化单宁酶催化没食子酸酯的合成 总被引：1，自引：0，他引：1
没食子酸酯是一类优良的抗氧化剂,为了避免化学合成方法带来的弊端,建立了微乳凝胶(MBGs)固定化单宁酶催化系统,催化没食子酸(GA)与不同的脂肪醇进行酯化.Na2SO4-Na2SO4·10H2O盐水合对可有效调控有机相固定化酶催化系统中水的活度,其调控能力与盐水合对的总量有关.在反应系统中加入盐-盐水舍对(Na2SO4-Na2S04·10H2O)可以明显提高GA的转化率.当pH值6、温度28℃、振摇速度150 r/min时,在生产没食子酸丙酯(PG)、没食子酸丁酯(BG)的MBGs反应系统中,加入总量1.8 g,比例为1:1的Na2SO4-Na2SO4·10H2O,GA的转化率可分别达到78.2%和85%,比对照样分别提高93.0%、129.7%;在生产没食子酸戊酯(AG)的MBGs反应系统中,加入总量2.4 g,比例为1:1的Na2SO4-Na2SO4·10H2O,GA的转化率为72.4%.比对照样提高103.7%. 相似文献
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在实验室条件下,以没食子酸和甘油为原料合成了1-没食子酸甘油酯(GG),做为油脂或油脂食品的抗氧化剂,保护油脂不因氧化腐败,延长贮存时间。合成途径是在日本高砂光正等人工作基础上进行了若干改进,使得率由45.7％提高到72.9％。以菜子油和豆油做底物,丙酯(PG)和2,6-二特丁基对甲酚(BHT)做对比抗氧化剂,用增重法评价其抗氧化性能,柠檬酸和酒石酸做增效剂,评价其增效作用,研究了浓度和分散度对诱导期的影响,探讨了结构因素对性能的影响。实验室结果表明:在本实验条件下,活性次序是GG>PG>BHT,随着浓度的增加,活性增大顺序是GG>PG>BHT。酒石酸对GG有增效作用,柠檬酸无效。溶解度对诱导期没有影响,说明了性能差异产生的原因。通过研究为简化合成途径,进行工业化生产提供了依据,并在此基础上为合成新型抗氧化剂找到一种可行方法。 相似文献
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利用取之不尽、用之不竭的可再生资源生产生物柴油和有机化工产品是未来维持社会经济可持续发展的重要途径。从动物油脂和植物油生产的柴油称为生物柴油(Biodiesel)。它是一种长链脂肪酸的单烷基酯。天然油脂多由直链脂肪酸的甘油三酯组成,与甲醇酯交换后,分子量降至与柴油接近,从而使其具有更接近于柴油的性能,故 相似文献
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基于阳离子型萜烯基环氧树脂多元醇的双组分水性聚氨酯的交联反应与性能 总被引：1，自引：0，他引：1
利用阳离子型萜烯基环氧树脂多元醇与聚异氰酸酯(EC385)配合制备双组分水性聚氨酯.通过纳米粒径分析表明,水性阳离子型萜烯基环氧树脂多元醇对EC385具有良好的分散性能,两者混合后,当固含量为30%～32%时,体系具有较理想的施工黏度.FT-IR分析表明,两者交联反应速率较快,室温(25 ℃)下5 h可完全反应.交联产物具有优异的柔韧性、附着力、抗冲击性能以及耐水、耐碱、耐污染、抗粘连性能;以一缩二乙二醇、1,4-丁二醇为扩链剂、提高-NCO与-OH物质的量之比可增强交联产物的硬度及耐醇性. 相似文献
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无色松香季戊四醇酯的稳定化研究 总被引：1，自引：1，他引：0
以无色松香季戊四醇酯的热稳定性、耐候性和储存稳定性为考察指标,对抗氧剂和光稳定剂的稳定化作用进行了研究.结果表明,将0.3%的抗氧剂K-B与0.4%的光稳定剂与紫外线吸收剂LD UV-20添加于无色松香季戊四醇酯中,其热稳定性、耐候性和储存稳定性得到明显改善:在180℃下加热8h,产品颜色小于加纳色号1;距离400W紫外灯40cm下照射15h,产品的增重率为0.213%、颜色为3～4(加纳色号);在40℃下储存30天,其颜色及其中的氢过氧化物浓度基本不变.采用氧化诱导期(OIT)法对试样的抗氧化能力进行了评价,所得结果与上述结论一致. 相似文献
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利用天然可再生资源没食子酸(GA)与氢化萜烯基环氧树脂(HTME)在一定条件下反应制备了环氧树脂基多元醇(HTME - GA多元醇).通过研究合成反应的影响因素,确定了HTME - GA多元醇的合成反应条件:以GA物质的量12.5倍的正丙醇为反应溶剂,以占HTME与GA总质量2%的季铵盐为催化剂,HTME与GA共沸回流反应3h.经FT - IR、NMR光谱表征了HTME - GA多元醇的化学结构,比较了该多元醇与聚己二异氰酸酯HN90T、改性聚己二异氰酸酯EC385的交联反应特性及交联产物性能.实验结果表明,HTME - GA多元醇与EC385的交联产物具有优良的机械力学性能,与HN90T的交联产物具有较好的耐液体介质性能和硬度,但后者柔韧性较差.随着NCO与OH物质的量比的增大,交联产物的硬度和耐液体介质性能提高. 相似文献
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Drought-induced changes in flavonoids and other low molecular weight antioxidants in Cistus clusii grown under Mediterranean field conditions 总被引：2，自引：0，他引：2
Mediterranean plants have evolved a complex antioxidant defense system to cope with summer drought. Flavonoids, and particularly flavanols and flavonols, are potent in vitro antioxidants, but their in vivo significance within the complex network of antioxidant defenses remains unclear, especially in plant responses to stress. To gain insight into the role of flavonoids in the antioxidant defense system of Cistus clusii Dunal, we evaluated drought-induced changes in flavonoids in leaves and compared the response of these compounds with that of other low molecular weight antioxidants (ascorbic acid, tocopherols and carotenoids). Among the antioxidant flavonoids analyzed, epigallocatechin gallate was present in the greatest concentrations (up to about 5 micromol dm(-2)). Other flavanols, such as epicatechin and epicatechin gallate, were found at concentrations below 0.25 and 0.03 micromol dm(-2), respectively. Neither of the antioxidant flavonols analyzed, quercetin and kaempferol, were detected in C. clusii leaves. Epigallocatechin gallate, ascorbic acid and alpha-tocopherol concentrations increased to a similar extent (up to 2.8-, 2.6- and 3.3-fold, respectively) in response to drought, but the kinetics of the drought-induced increases differed. Epigallocatechin gallate, epicatechin and epicatechin gallate concentrations increased progressively during drought, reaching maximum values after 30 days of stress. Ascorbic acid concentrations increased twofold after 15 days of drought, and maximum values were attained after 50 days of drought. In contrast, alpha-tocopherol concentrations remained constant during the first 30 days of drought, but increased sharply by 3.3-fold after 50 days of drought. The maximum efficiency of photosystem II photochemistry and the extent of lipid peroxidation remained constant throughout the drought period, whereas the redox state of ascorbic acid and alpha-tocopherol shifted toward their reduced forms in response to drought, indicating that the concerted action of low molecular weight antioxidants may help prevent oxidative damage in plants. 相似文献
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系统调查了祁连山自然保护区森林病害种类，采到罹病林木11科22种（属），鉴定出林木病原107种，引起病害134种。病原分类分别为真菌83种、螨类6种、寄生植物3种、细菌1种，生理性病原14类。病害种类按寄生部位分，叶部病害74种，干部病害38种，枝梢病害17种，种实、根部病害较少。按树种分，青海云杉病害23种，青杄病害13种，人工栽培杨树病害18种，山杨病害18种，桦树病害10种，山柳病害8种，华北落叶松病害6种，祁连圆柏病害5种，油松病害5种，梅属植物病害5种，苹果属植物病害3种，小檗属植物病害4种，杜鹃类病害3种，忍冬病害2种，其他林木病害8种。 相似文献
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木塑复合材料耐候性能研究进展 总被引：1，自引：0，他引：1
木塑复合材料(WPC)的耐候性能决定了材料的户外使用寿命。文中介绍了国内外在WPC耐热氧老化、耐光氧老化、耐真菌腐朽及耐潮湿与冻融性能方面的研究进展。现有研究表明, 热氧老化与光氧老化均使得WPC发生褪色现象, 力学性能下降, 添加抗氧化剂与光稳定剂可分别改善二者对WPC的破坏作用。WPC中木粉含量较高时更易发生真菌腐朽现象, 添加化学防腐剂或其他助剂、木粉改性及涂饰可有效抑制真菌腐朽。WPC的吸水性是其热氧老化、光氧老化、真菌腐朽及冻融循环过程的催化剂。文中还总结了目前WPC耐候性能研究存在的主要问题, 并对其未来趋势进行了展望。 相似文献
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YANG Lei GAO Yan-hua ZU Yuan-gang LIU Xiao-na WANG Lei ZU Shu-chong 《林业研究》2006,17(4):329-331
Introduction Tea polyphenols, extracted from tea leaves, is a hydroxyl phenol compound. Of the components of green tea (Camellia sinensis), the content of (?)-epigallocatechin gallate (EGCG) is high, and this catechin has been extensively studied (Harold … 相似文献
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Characterization of proanthocyanidins from grape seeds 总被引：12，自引：0，他引：12
Gabetta B Fuzzati N Griffini A Lolla E Pace R Ruffilli T Peterlongo F 《Fitoterapia》2000,71(2):162-175
Leucoselect (grape seed selected proanthocyanidins) was analyzed. HPLC thermospray mass spectrometry (TSP-MS) allowed the detection of monomeric flavan-3-ols and dimeric proanthocyanidins. Fractionation over Sephadex LH-20 resin and analysis of the isolated fractions by gel permeation chromatography (GPC) and electrospray mass spectrometry (ESI-MS) led to the complete characterization of the proanthocyanidin constituents of Leucoselect. The analysis revealed the presence of approximately 15% of (+)-catechin (1) and (-)-epicatechin (2), 80% of (-)-epicatechin 3-O-gallate (3), dimers, trimers, tetramers and their gallates and 5% of pentamers, hexamers, heptamers and their gallates. 相似文献
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Reactivity of green tea catechins with formaldehyde 总被引：3，自引：0，他引：3
Akiko Takagaki Katsuhiko Fukai Fumio Nanjo Yukihiko Hara 《Journal of Wood Science》2000,46(4):334-338
In the reaction of green tea catechins with formaldehyde at room temperature (25°C), tea catechins were found to have reactivity. In particular, (-)-epicatechin gallate and (-)-epigallocatechin gallate, which have a galloyl moiety at the C-3 position, showed higher reactivity than (+)-catechin, (-)-epicatechin, or (-)-epigallocatechin. Reactivity of various kinds of simple phenolic compounds and flavonoids with formaldehyde was also examined. Among these compounds, only phloroglucinol showed reactivity to the same degree as that of nongalloylated catechins. These results suggest that factors for reactivity with formaldehyde at room temperature may be the presence of a phloroglucinolic A-ring structure and the absence of the electron-attractive group such as a carbonyl group in Cring. The comparison of the reactivity of 3-O-acylated catechins with that of 3-O-galloylated catechins indicated that only a galloyl group effectively enhanced reactivity with formaldehyde. 相似文献