脂肪酶催化合成L-抗坏血酸脂肪酸酯和D-异抗坏血酸脂肪酸酯

用固定化脂肪酶Lipozyme 435作催化剂,分别用直接酯化法和酯交换法合成L-抗坏血酸脂肪酸酯和D-异抗坏血酸脂肪酸酯.产物结构经IR、1HNMR、13CNMR和MS表征.结果表明,对于同一目标化合物,相似条件下,直接酯化法的效果优于酯交换法,原料脂肪酸和脂肪酸甲酯均可回收循环使用.     

高效液相色谱法同时测定水果蔬菜中L-抗坏血酸、D-异抗坏血酸、脱氢抗坏血酸及总维生素C的含量

建立了同时测定水果或蔬菜中L-抗坏血酸、D-异抗坏血酸、脱氢抗坏血酸及总维生素C含量的高效液相色谱分析方法。用偏磷酸提取水果或蔬菜样品中L-抗坏血酸、D-异抗坏血酸和脱氢抗坏血酸,提取液中的L-抗坏血酸、D-异抗坏血酸可直接进行检测,脱氢抗坏血酸在磷酸钠溶液中(p H 7.0~7.2)用L-半胱氨酸还原成L-抗坏血酸,之后测定以L-抗坏血酸表达总维生素C含量,脱氢抗坏血酸含量由总维生素C含量减去L-抗坏血酸含量获得。采用C18色谱柱分离,以甲醇-磷酸盐缓冲溶液(p H 3.5)为流动相,在245 nm下检测,外标法定量。结果表明,在0.5~50 mg/L的浓度范围内L-抗坏血酸和D-异抗坏血酸的线性关系良好,相关系数大于0.999,检出限分别为42.0,19.4μg/kg,脱氢抗坏血酸的检出限为262μg/kg。低、中、高3个浓度的加标水平下,3种物质的加标回收率为82.8%~111.3%,相对标准偏差(RSD)小于15%。该方法操作简单,灵敏度高,准确性好,适用于水果和蔬菜中维生素C的测定。     

D-异抗坏血酸饱和脂肪酸酯的合成

用浓H2SO4作为反应介质和催化剂,通过直接酯化法或酯交换法合成了5个D-异抗坏血酸脂肪酸(癸酸,月桂酸,豆蔻酸,棕榈酸和硬脂酸)酯,其结构经1H NMR和IR表征.实验结果表明,就粗产物的产率和纯度而言,直接酯化法均比酯交换法高.     

异VC豆蔻酸酯的合成

异VC(D-异抗坏血酸)和VC(L-异抗坏血酸)互为同分异构体,它们分子中因含有连烯二醇结构单元,具有还原性,均可作为水溶性食品抗氧化剂.此外,在它们的分子结构中,C6上有伯醇羟基、C5上有仲醇羟基.化学修饰后的衍生物既保留着具有亲水性和还原性的异VC(或VC)结构部分,同时又增加了亲油性的长碳链烃基部分,属于两性分子,可望作为油脂或含油脂食品的抗氧化剂、食品加工过程中的表面活性剂和乳化剂等.VC的化学修饰及其衍生物的性能和应用方面的研究,在国内外非常活跃[1-8],而对于异VC,相关的工作则少见报道.     

高效液相色谱法测定毛樱桃中维生素C含量

建立了高效液相色谱(HPLC)测定毛樱桃中维生素C的主要成分L-抗坏血酸和D-异抗坏血酸的方法. 以0.05 mol/L磷酸溶液∶甲醇(体积比为98∶2)作为流动相,紫外检测波长245 nm,柱温25 ℃,流速0.70 mL/min. 获得L-抗坏血酸、D-异抗坏血酸标准曲线线性较好(r为1.0),精密度(RSD)为0.6%. L-抗坏血酸加标回收率为90.83%~92.52%,D-异抗坏血酸加标回收率为91.93%~92.99%. 试验结果表明,方法测定维生素C操作简单、提取速度快、灵敏度高、回收率好,测得L-抗坏血酸的含量为8.24 mg/100 g,D-异抗坏血酸未检测出. 方法可适用于检测其他与毛樱桃相似的果蔬中L-抗坏血酸、D-异抗坏血酸的含量.     

D-异抗坏血酸缩醛的合成

以对甲苯磺酸为催化剂,N,N-二甲基乙酰胺为溶剂,环己烷为带水剂,直链饱和脂肪族醛与D-异抗坏血酸反应合成了7个D-异抗坏血酸缩醛(3a～3g),其结构经1H NMR,IR和MS表征.实验结果表明,3a～3g均为两个非对映异构体的混合物,其比例接近1:1.     

HILIC色谱柱拆分抗坏血酸对映体及其在药物分析中的应用

采用HILIC色谱柱,利用高效液相色谱分离L-抗坏血酸和D-异抗坏血酸,考察了流动相的组成、柱温和流速对分离L-抗坏血酸和D-异抗坏血酸的影响.结果表明:流动相为乙腈-0.1%磷酸(93∶7),流速为0.8 m L·min~(-1),柱温为20℃,检测波长为243 nm的条件下,分离效果最优,分离度为7.79.该方法进一步应用于3种维生素C实际样品中抗坏血酸含量的测定,3种样品中均仅有L-抗坏血酸检出,其含量在96.62~985.8 mg·g~(-1)之间,相对标准偏差在0.65%~0.94%之间.     

L-抗坏血酸-2-单磷酸酯盐的研制

为了制备高效价的L-抗坏血酸-2-单磷酸酯,通过单因素及正交实验,对L-抗坏血酸与三偏磷酸钠在无催化剂存在下反应制备高效价的L-抗坏血酸-2-单磷酸酯的工艺进行了研究。结果表明:n(L-抗坏血酸):n(三偏磷酸钠)=1∶0.392、n(L-抗坏血酸)∶n(氢氧化钠)=1∶0.7、n(L-抗坏血酸)∶n(氢氧化钙)=1∶0.8,溶液pH值为9,反应温度为45℃,有效VC含量为41.8%,L-抗坏血酸-2-单磷酸酯的含量为38.3%。该工艺无需催化剂,三偏磷酸钠加入量少,有效VC和L-抗坏血酸-2-单磷酸酯含量高,反应液成冻快,适合闪蒸干燥以及分离提纯化妆品级L-抗坏血酸-2-单磷酸酯盐。     

亲水作用色谱法同时测定食品添加剂中D-异抗坏血酸、L-抗坏血酸和二氧化硫脲

食品添加剂样品用含1%(体积分数,下同)甲酸的100mmol·L~(-1)甲酸铵溶液溶解,经乙腈稀释后,用0.22μm微孔滤膜过滤,采用亲水作用色谱法同时测定滤液中D-异抗坏血酸、L-抗坏血酸和二氧化硫脲的含量。以InfinityLab Poroshell 120HILIC-Z色谱柱(3.0mm×100mm,2.7μm)为固定相,以含1%甲酸的100mmol·L~(-1)甲酸铵溶液和乙腈以体积比15∶85组成的混合液为流动相,用二极管阵列检测器测定。D-异抗坏血酸、L-抗坏血酸和二氧化硫脲的质量浓度均在1.0～100mg·L~(-1)内与其对应的峰面积呈线性关系,检出限(3S/N)均为1.0%。以空白样品为基体进行加标回收试验,所得回收率为94.7%～108%,测定值的相对标准偏差(n=6)小于8.0%。     

高效液相色谱法测定食品中抗坏血酸棕榈酸酯

提出了快速测定油脂食品、焙烤食品和方便米面食品中抗坏血酸棕榈酸酯的高效液相色谱法。以柠檬酸和异抗坏血酸为稳定剂,甲醇为样品提取剂,以甲醇-乙腈(1+1)及磷酸(1+99)溶液为流动相,经反相C18色谱柱梯度洗脱,在243 nm波长处,用光电二极管阵列检测器进行测定。抗坏血酸棕榈酸酯的质量浓度在0.50~100.0 mg.L-1范围内与其峰面积呈线性关系,测定下限(10S/N)为0.005 g.kg-1。加标回收率在85%~104%之间,相对标准偏差(n=6)在1.1%~3.9%之间。     

Monitoring of calcium stearate formation by thermogravimetry

Naphthenates are produced when naphthenic acids present in crude oil are mixed with brine. They deposit at oil/water interface and are insoluble in either of the phases causing a large problem to the oil industry. Generally, naphthenates precipitate jointly with others compounds such as sulfates and carbonates. This fact makes difficult their characterization. In this study, calcium stearate formation from stearic acid was investigated, under different conditions, as a previous model to understanding of calcium naphthenate precipitation. Medium reactions distinct were studied and the results indicated that the ethanol medium was the most efficient for the formation of solids because in this only case, the stearic acid was completely converted into stearate. Monitoring of the conversion was performed by thermogravimetry in spite of this technique not be typical in salts characterization. Nevertheless, the thermogravimetric analysis showed that is possible to identify differences between an organic acid, a salt of this acid and an inorganic salt, in the same sample. Infrared spectra was used in order to confirm the results obtained by thermogravimetry. However, this technique showed less efficiency and sensibility.     

Precipitation and Solubility of Calcium Soaps in Basic Aqueous Media

Measurements of the surface tension of aqueous media containing calcium salts of different fatty acids, whose structure only varied by the number of C=C unsaturations along their aliphatic chains, showed that their solubility increased as a function of this parameter going from near zero for calcium stearate to 4x10(-4) mol l(-1) for the linolenate homologue. The solubility product of the calcium soap corresponding to each tested fatty acid was estimated by using the anionic fatty acids adsorption isotherms in order to obtain the amount of dissolved ionic fatty acid at increasing concentration of calcium ions. These findings are discussed in terms of their serious repercussions on the operations related to flotation deinking in waste paper recycling. Copyright 2001 Academic Press.     

发光反应型有机铵分子与CdSe纳米晶的组装

用巯基乙酸做稳定剂制备了水溶性CdSe纳米颗粒, 用十六烷基三甲基溴化铵(HTAB)、发光性(4-甲氧基均二苯乙烯基)二甲基乙基溴化铵 (MODAB)及末端含有双键的(4-甲基丙烯酰氧基均二苯乙烯基)二甲基乙基溴化铵(MSDAB)对该CdSe纳米颗粒进行了混合组装.通过改变三种有机分子的比例可以调控所得组装体的溶解性、聚合性及其发光性质.实验结果表明,当HTAB:MODAB:MSDAB=1:5.98～5.90:0.02～0.10(摩尔比)时,所得组装体具有较好的聚合性、溶解性和荧光性质.     

Physicochemical Studies on Cesium Soaps. I. Thermogravimetry and Infrared Absorption Spectra

The infrared absorption spectra of cesium stearate was compared with that of stearic acid, sodium stearate, and rubidium stearate. It is concluded that the fatty acids in the solid state exist with a dimeric structure through hydrogen bonding whereas the alkali metal soaps are ionic in nature. Thermogravimetric analysis shows that the decomposition reaction of the alkali metal soaps is kinetically of zero order and the activation energy for the process lies in the range of 2 to 6 kcal/mol.     

Vapor-liquid equilibria for binary mixtures of carbon dioxide and fatty acid ethyl esters

Vapor-liquid equilibria were measured and correlated using the Peng-Robinson equation of state for five binary systems of carbon dioxide and fatty acid ethyl esters (ethyl stearate, ethyl oleate, ethyl linoleate, ethyl eicosapentanoate, ethyl docosahexanoate) at 313.15 K, 323.15 K and 333.15 K. Solubility in CO₂ of fatty acid ethyl esters of equal chain length but of various degrees of unsaturation was compared. Although there was no distinct difference in solubility at lower pressures, at higher pressures (more than 15 MPa), those with a higher degree of unsaturation showed a slightly higher solubility. When the solubility in CO₂ of methyl esters and the corresponding ethyl esters were compared, it was noted that the former showed a slightly higher solubility at all system pressures measured in this work.     

液相分散法制备硬脂酸修饰铋纳米微粒

金属纳米微粒由于具有不同于普通材料的光、电、磁、热力学和化学反应等性能,在催化、信息存储、光电、微电子以及润滑等领域中有着广阔的应用前景。金属纳米微粒这些特殊的物理化学性能主要取决于制备工艺和具体的反应条件,因此研究具有特定性能的金属纳米微粒一直是纳米技术领域中的一个研究热点犤1,2犦,目前制备金属纳米微粒最常用的方法是液相法,它是通过在含有表面修饰剂的溶剂中还原相应的金属盐犤3,4犦或有机金属化合物热分解犤5,6犦来制备表面修饰的金属纳米微粒。虽然这种方法能够制备出多种具有特定性能的金属纳米微粒,但是这种方…     

Optimization of biodiesel production from castor oil

The transesterification of castor oil with ethanol in the presence of sodium ethoxide as catalyst is an exceptional option for the Brazilian biodiesel production, because the castor nut is quite available in the country. Chemically, its oil contains about 90% of ricinoleic acid that gives to the oil some beneficial characteristics such as its alcohol solubility at 30°C. The transesterification variables studied in this work were reaction temperature, catalyst concentration and alcohol oil molar ratio. Through a star configuration experimental design with central points, this study shows that it is possible to achieve the same conversion of esters carrying out the transesterification reaction with a smaller alcohol quantity, and a new methodology was developed to obtain high purity biodiesel.     

Determination of the solubility of vinyl stearate in water by a monolayer technique

Summary The surface activity of vinyl stearate has provided a method for determining its solubility in water to be 0,7±0,2×10^–6 mole/litre. The methods described above could be used to determine the solubility in water of any sparingly soluble surface active compound, such as stearic acid or cetyl alcohol, which formed a stable monolayer at theA/W interface. Method A could be used for compounds with a solubility as low as 10^–5 mole/litre where as for Method B solubilities as low as 10^–7 mole/litre could be measured.     

Propylene Glycol and Ethoxylated Surfactant Effects on the Phase Behavior of Water/Sucrose Stearate/Oil System

In this work, we studied the phase behavior as function of temperature of water/sucrose stearate/propylene glycol/oil and water/sucrose stearate/ethoxylated mono‐di‐glyceride/oil systems. The oils were R (+)‐limonene, isopropylmyristate, and caprylic‐capric triglyceride. It was found that adding propylene glycol and ethoxylated mono‐di‐glyceride to the water/sucrose stearate/R (+)‐limonene and water/sucrose stearate/isopropylmyristate systems decreases the temperature and surfactants concentration needed for the formation of a microemulsion phase region and no three phase region is observed. In the case of water/sucrose stearate/caprylic‐capric triglyceride system a three phase region is observed. In the caprylic‐capric based system, it was found that increasing the propylene glycol and ethoxylated mono‐di‐glyceride contents decrease the phase inversion temperature and increases the efficiency. In the case where the mixed surfactants (sucrose stearate and ethoxylated mono‐di‐glyceride) were present in the system, the efficiencies observed are higher than those observed in the system based on the mixture of sucrose stearate and propylene glycol.