Influence of dipalmitoylphosphatidylcholine (or dioleoylphosphatidylcholine) and phospholipase A2 enzyme on the properties of emulsions

The properties of n-tetradecane emulsions with dipalmitoylphosphatidylcholine (DPPC) or dioleoylphosphatidylcholine (DOPC) in 1M ethanol were investigated at 20 and 37°C. The zwitterionic phospholipids having the same headgroup bound to the apolar tail composed of two saturated or unsaturated chains were used as stabilizing agents. Both phospholipids may self-organize into aggregates, which possess different sizes and surface affinities. Electrokinetic properties of the systems at natural pH or pH 8 were investigated taking into account the effective diameter of the droplets as well as the zeta potentials using the dynamic light scattering technique. The effect of both phospholipids decreases the initially negative zeta potential of the n-tetradecane emulsion and is more evident in the case of DPPC especially at a physiological temperature near its main temperature transition. The change of zeta potential by DOPC is visible at both temperatures probably as an effect of a loose packing of this phospholipid on n-tetradecane droplets, because of the presence of double bonds in its molecule. Also, the role of ethanol dipoles on the stability of oil/phospholipid emulsions is obvious. The other aim of paper was the characterization of the phospholipase A(2) influence on DOPC hydrolysis in the emulsion environment in order to emphasize the importance of such methodology. The present work is the first study that explores the effects of both electrolyte ions and ethanol molecules on DOPC hydrolysis by phospholipase. The effect of enzyme on the n-tetradecane/DOPC emulsions was investigated at pH 8 with Na(+) or Ca(2+) ions, which occur in the physiological fluids. The effective diameters do not always correlate with the zeta potentials. A possible reason of such behavior might a mechanism different from the electrostatic stabilization. The particular role of Ca(2+) ions in the emulsions with phospholipids was confirmed. Those investigations provide insight into the properties of the PLA(2) hydrolysis process enhanced by added ethanol. It is believed that the enzyme effect on the phospholipid aggregation behavior at the oil-water interface will be helpful for understanding other biological phenomena.     

Comparison of n-tetradecane/electrolyte emulsions properties stabilized by DPPC and DPPC vesicles in the electrolyte solution

The properties of n-tetradecane/electrolyte emulsions with DPPC or DPPC vesicles in the electrolyte solution were investigated. The DPPC molecules form different aggregates, which possess different surface affinity, size and structure, and therefore we assumed some differences in the adsorption at the oil droplet/water interface. The n-tetradecane emulsions in 1:1, 1:2 and 1:3 electrolytes were prepared by mechanical stirring in the presence of DPPC at natural pH. Electrokinetic properties of the systems were investigated taking into account the effective diameter and multimodal size distribution of the droplets as well as the zeta potentials using the dynamic light scattering technique. The zeta potential of the droplets was negative in all systems with NaCl. In the emulsions with CaCl(2) at a higher concentration of electrolyte and emulsions with LaCl(3) with all investigated concentrations, positive values were observed. Similar measurements were performed for DPPC vesicles in the electrolyte solution. The pH and ionic strength changes induce those in the electrical charge of DPPC layer or vesicle surface. This is due to the fact that the DPPC molecule contains -PO(-) and -N(CH(3))(3) groups, which are in equilibrium with H(+) and OH(-), as well as other ions present in the solution, i.e. Na(+), Ca(2+), La(3+) or Cl(-). In the n-tetradecane/electrolyte emulsion stabilized by DPPC or DPPC vesicles the zeta potential may be also related to acid-base interactions. The effect of the ions from the solution on the DPPC layer adsorbed on n-tetradecane droplets or DPPC vesicles is discussed.     

Investigation of the electrokinetic properties of paraffin suspension. 1. In inorganic electrolyte solutions

Although electrical properties of nonionogenic hydrophobic surface (solid or liquid) in water and/or electrolyte solutions have been studied for many decades, they are still not well recognized, especially as for the nature of the charge and potential origin. Similarly, water structure at such a surface is still extensively studied. One such system is paraffin wax/water (electrolyte). The zeta potentials and the particle diameters of this system were investigated in this paper. To obtain the suspension of paraffin in water or electrolyte solution (NaCl or LaCl3), the mixture was heated to ca. 70 degrees C and then stirred during cooling. For thus obtained suspensions, the zeta potential was determined as a function of time at 20 degrees C. Also the pH effect on the zeta potentials was investigated. The zeta potentials were calculated from Henry's equation. The results obtained by us are in agreement with those obtained earlier by others. They confirm that although H+/OH- are not surface charge creating ions, OH- ions to some extent are zeta potential determining for the paraffin surface. By use of the potentials and diameters, the electric charge for a spherical particle in the shear plane was calculated. These values are small in the range of 10(-3) C/m2. On the basis of the findings of water structure near hydrophobic surface and the calculated charges, it is concluded that in fact the potential may be created by immobilized and oriented water dipoles.     

A New Lipase Isolated from Oleaginous Seeds from <Emphasis Type="Italic">Pachira aquatica</Emphasis> (Bombacaceae)

A new lipase from seeds of Pachira aquatica was purified to homogeneity by SDS-PAGE obtaining an enzyme with a molecular weight of approximately 55 kDa. The purified lipase exhibited maximum activity at 40 degrees C and pH 8.0, for an incubation time of 90 min. Concerning temperature stability, at the range from 4 to 50 degrees C, it retained approximately 47% of its original activity for 3 h. The enzyme activity increased in the presence of Ca(++) and Mg(++), but was inhibited by Hg(++), Mn(++), Zn(++), Al(+++) and various oxidizing and reducing agents. The lipase was highly stable in the presence of organic solvents, and its activity was stimulated by methanol. The values of K(m) and V(max) were 1.65 mM and 37.3 micromol mL(-1) min(-1), respectively, using p-nitrophenylacetate as substrate. The enzyme showed preference for esters of long-chain fatty acids, but demonstrated significant activity against a wide range of substrates.     

Purification and characterization of a cyclomaltodextrin glucanotransferase from Paenibacillus campinasensis strain H69-3

A cyclomaltodextrin glucanotransferase (E.C. 2.4.1.19) from a newly isolated alkalophilic and moderately thermophilic Paenibacillus campinasensis strain H69-3 was purified as a homogeneous protein from culture supernatant. Cyclomaltodextrin glucanotransferase was produced during submerged fermentation at 45 degrees C and purified by gel filtration on Sephadex G50 ion exchange using a Q-Sepharose column and ion exchange using a Mono-Q column. The molecular weight of the purified enzyme was 70 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the pI was 5.3. The optimum pH for enzyme activity was 6.5, and it was stable in the pH range 6.0-11.5. The optimum temperature was 65 degrees C at pH 6.5, and it was thermally stable up to 60 degrees C without substrate during 1 h in the presence of 10 mM CaCl(2). The enzyme activity increased in the presence of Co(2+), Ba(2+), and Mn(2+). Using maltodextrin as substrate, the K(m) and K(cat) were 1.65 mg/mL and 347.9 micromol/mg x min, respectively.     

Analysis of methyl tert.-butyl ether and its degradation products by direct aqueous injection onto gas chromatography with mass spectrometry or flame ionization detection systems.

A method was developed to analyze methyl tert.-butyl ether (MTBE) and its degradation products by gas chromatography with mass spectrometry (GC-MS) or flame ionization detection (FID) with direct aqueous injection. The column had dimensions of 30 m x 0.25 mm with film thickness 0.25 microm and a stationary phase of FFAP (nitroterephthalic acid-modified polyethylene glycol). The optimized GC conditions for non-acid components were as follows: carrier gas flow-rate,l mL/min; oven temperature, 35 degrees C for 5.5 min, ramped to 90 degrees C at 25 degrees C/min, then ramped to 200 degrees C at 40 degrees C/min and held at 200 degrees C for 8 min. The conditions for the acid components were: carrier gas flow-rate, 1 mL/min; oven temperature, 110 degrees C for 2 min, ramped to 150 degrees C at 10 degrees C/min, then ramped to 200 degrees C at 40 degrees C/min. The injection port contained a silanized-glass reverse-cup liner filled with Carbofrit. The minimum concentrations for the linear range for the selective ion monitoring mode were 30 to 100 microg/L, depending on the analytes. The minimum detection limit was 1 mg/L for MTBE and tert.-butanol when using FID. More components could be analyzed with the FFAP-type column than with the cyanopropylphenyl-dimethyl polysiloxane-type column.     

Purification and partial characterization of a lipase from Bacillus coagulans ZJU318

An extracellular lipase was purified from the fermentation broth of Bacillus coagulans ZJU318 by CM-Sepharose chromatography, followed by Sephacryl S-200 chromatography. The lipase was purified 14.7-fold with 18% recovery and a specific activity of 141.1 U/mg. The molecular weight of the homogeneous enzyme was (32 kDa), determined by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. The enzyme activity was maximum at pH 9.0 and was stable over a pH range of 7.0–10.0, and the optimum temperature for the enzyme reaction was 45°C. Little activity loss (6.2%) was observed after 1 h of incubation at 40°C. However, the stability of the lipase decreased sharply at 50 and 60°C. The enzyme activity was strongly inhibited by Ag⁺ and Cu²⁺, whereas EDTA caused no inhibition. SDS, Brij 30, and Tween-80 inhibited lipase, whereas Triton X-100 did not significantly inhibit lipase activity.     

高效液相色谱法测定吲哚美辛控释胶囊的血药浓度和生物利用度

采用ＯＤＳ柱,甲醇－稀磷酸溶液（７６２４）为流动相,２６０ｎｍ为检测波长,建立了测定血浆中吲哚美辛浓度的高效液相色谱法,并测定了吲哚美辛控释胶囊炎痛康的血药浓度。结果表明,血浆中吲哚美辛浓度在０．１２５～５．０ｍｇ／Ｌ范围内线性关系良好（ｒ＝０．９９９６）,检测限６２．５μｇ／Ｌ（Ｓ／Ｎ＝３１）,平均回收率为１００．４％,日内和日间ＲＳＤ均小于５％。１１位受试者单剂量口服炎痛康后的相对生物利用度为１０２．３８％。     

Stability of oil/water (ethanol,lysozyme or lysine) emulsions

Emulsions of n-tetradecane in water (0.1%^v/_^V) homogenized by ultrasounds (1 5 min) were stabilized by 0.5 or 1.0 M ethanol and in the presence of lysozyme (4 mg 100 ml⁻¹) or 1 mM lysine monohydrochloride (14.6 mg 100 ml⁻¹). The zeta potentials and multimodal size distributions of the droplets after 5, 15, 30, 60, 120 min, and 1 and 2 days were determined by dynamic light scattering technique using ZetaPlus apparatus (Brookhaven Instr., USA). Both parameters were determined on the same sample subsequently without any mixing. The effect of pH [4, 6.8 (natural), and 11] was also investigated. The most stable emulsions in 1 M ethanol solutions alone were at pH 6.8 and 11 (the effective diameter D_eff and 350 nm, respectively), while in 0.5 M at pH 4 (D_eff nm). The most stable emulsions with lysozyme were obtained at pH 4 and 1 M ethanol (D_eff nm), and with lysine at pH 6.8 and 0.5 M ethanol (D_eff nm). Except for the emulsions with lysozyme at pH 4 and 6.8, in the rest systems the zeta potentials were negative and ranged between −5 and −85 mV as a function of time and pH. The changes of zeta potential indicate that H⁺ ions are not much potential determining, while OH⁻ ions increase the negative zeta potentials. However, H⁺ ions affect functional groups of lysozyme molecules adsorbed on the alkane droplet, what appears in essential changes of zeta potential and even reversed sign of it in some systems. The results point that stability of these emulsions may also be determined by hydrogen bonding.     

高效液相色谱-电化学检测法测定脑组织中鬼臼甲叉甙

报道了用甲醇－水－乙酸（５６４１３,体积比）为流动相,在ＨｙｐｅｒｓｉｌＯＤＳ柱上以愈创木酚甘油醚为内标,采用电化学检测器（ＥＣＤ）测定人体脑组织中鬼臼甲叉甙含量。回收率９２．８７％,最低检测浓度为０．１ｍｇ／Ｌ,鬼臼甲叉甙在０．１～１０．０ｍｇ／Ｌ范围内呈线性,工作电压０．７０Ｖ。同时还对脑瘤患者脑组织中正常部位和肿瘤部分中鬼臼甲叉甙含量进行了测定。     

Production and Characterization of an Alkaline Thermostable Crude Lipase from an Isolated Strain of <Emphasis Type="Italic">Bacillus cereus</Emphasis> C<Subscript>7</Subscript>

A bacterial strain isolated from spoiled coconut and identified as Bacillus cereus was found capable of producing alkaline thermostable extracellular lipase. Optimum temperature, time, and pH for enzyme substrate reaction were found to be 60 °C, 10 min, and 8.0 respectively. Common surfactants except Triton X 100 and cetyltrimethylammonium bromide have no or very little inhibitory effects on enzyme activity. The enzyme was found to be stable in presence of oxidizing agents and protease enzyme. The maximum lipase production was achieved at 30–33 °C, pH 8.0 on 24 h of fermentation using 50 ml medium in a 250-ml Erlenmeyer flask. The superior carbon and nitrogen sources for lipase production were starch (2%) and ammonium sulfate (nitrogen level 21.2 mg/100 ml), peptone (nitrogen level 297 mg/100 ml), and urea (nitrogen level 46.62 mg/100 ml) in combination, respectively. The maximum enzyme activity obtained was 33 ± 0.567 IU/ml.     

程序升温大体积进样气相色谱-负化学离子源质谱法测定白菜和苹果中103种农药残留

采用程序升温大体积进样(PTV-LVI)和负化学离子源(NCI)技术建立了白菜和苹果中103种农药残留分析的气相色谱-质谱检测方法。PTV-LVI参数优化为: 初始温度45 ℃、分流排空流量20 mL/min、吹扫时间1 min和溶剂挥发温度60 ℃。样品采用QuEChERS方法进行快速处理,在NCI方式下进样10 μL,用基质标准溶液进行定量,结果表明103种农药的方法检出限均低于5 μg/kg。在5 μg/kg和10 μg/kg添加水平下,白菜和苹果中农药的平均回收率为58.5%～113.2%,相对标准偏差为3.3%～14.5%。该方法样品处理简单快速,相比普通分流/不分流进样和电子轰击电离气相色谱-质谱法,其灵敏度和选择性明显提高,适用于日常检测工作。     

Effect of microwave dielectric heating on intraparticle diffusion in reversed-phase liquid chromatography

The influence of microwave (MW) irradiation on the mass transfer kinetics in reversed-phase liquid chromatography (RPLC) was studied by placing a column in a microwave oven and measuring the incremental change in the temperature of the column effluent stream at various microwave energies and mobile phase compositions. The microwave energy dissipated in the column was set between 15 and 200 W and the mobile phase composition used varied from 100 to 70, 50, and 10% methanol in water at 1.2 mL/min. At all the mobile phase compositions considered, the effluent temperature increased with increasing microwave energy. At 70% methanol, the mobile phase flow rate was set at 1.2, 2.0, and 2.8 mL/min. At 1.2 mL/min, the effluent temperatures at the lowest (15 W) and highest (200 W) microwave energy inputs were 25 +/- 1 degrees C and 41 +/- 1 degrees C for pure methanol, 25 +/- 1 degrees C and 48 +/- 1 degrees C for 70% methanol, 25 +/- 1 degrees C and 50 +/- 1 degrees C for 50% methanol, and, 25 +/- 1 degrees C and 52 +/- 1 degrees C for 10% methanol, respectively. With 70% methanol and microwave energy inputs of 15, 30, and 50 W, the effluent temperature did not change with increasing flow rate; a considerable change was observed at 100, 150, and 200 W between 1.2 and 2.0 mL/min and none between 2.0 and 2.8 mL/min. Chromatographic elution band profiles of propylbenzene were recorded under linear conditions, in 70% methanol solutions, for microwave energy inputs of 0, 15 and 30 W, at constant temperature. The intraparticle diffusion coefficient, De, under microwave irradiation was ca. 20% higher than without irradiation. These preliminary results suggest that microwave irradiation may have a considerable influence on intraparticle diffusion in RPLC.     

固相微萃取-气相色谱/质谱分析栀子花的头香成分

 分别用固相微萃取和动态顶空法分离栀子鲜花的头香成分,用GC/MS技术分析鉴定,并用GC/MS总离子流色谱峰的峰面积进行归一化定量。在固相微萃取方法中,共鉴定了54种化学成分,占总峰面积的99.98%。主要成分(质量分数)依次为金合欢烯（64.86%）、罗勒烯（29.33%）、芳樟醇（2.74%）、惕各酸顺式叶醇酯（1.34%）和苯甲酸甲酯（0.25%）等。经与动态顶空法的分析结果比较发现,固相微萃取法不仅操作简便,而且具有较高的采样灵敏度,获得的化学成分的信息量多于动态顶空法。     

Production,purification, and characterization of a low-molecular-mass xylanase from Aspergillus sp. and its application in baking

An extracellular xylanase produced by a Mexican Aspergillus strain was purified and characterized. Aspergillus sp. FP-470 was able to grow and produce extracellular xylanases on birchwood xylan, oat spelt xylan, wheat straw, and corncob, with higher production observed on corncob. The strain also produced enzymes with cellulase, amylase, and pectinase activities on this substrate. A 22-kDa endoxylanase was purified 30-fold. Optimum temperature and pH were 60 degrees C and 5.5, respectively, and isoelectric point was 9.0. The enzyme has good stability from pH 5.0 to 10.0, retaining >80% of its original activity within this range. Half-lives of 150 min at 50 degrees C and 6.5 min at 60 degrees C were found. K(m) and activation energy values were 3.8 mg/mL and 26 kJ/mol, respectively, using birchwood xylan as substrate. The enzyme showed a higher affinity for 4-O-methyl-D-glucuronoxylan with a K(m) of 1.9 mg/mL. The enzyme displayed no activity toward other polysaccharides, including cellulose. Baking trials were conducted using the crude filtrate and purified enzyme. Addition of both preparations improved bread volume. However, addition of purified endoxylanase caused a 30% increase in volume over the crude extract.     

Immobilization of α-amylase from Bacillus circulans GRS 313 on coconut fiber

A simple and inexpensive method for immobilizing alpha-amylase from Bacillus circulans GRS 313 on coconut fiber was developed. The immobilization conditions for highest efficiency were optimized with respect to immobilization pH of 5.5, 30 degrees C, contact time of 4 h, and enzyme to support a ratio of 1:1 containing 0.12 mg/mL of protein. The catalytic properties of the immobilized enzyme were compared with that of the free enzyme. The activity of amylase adsorbed on coconut fiber was 38.7 U/g of fiber at its optimum pH of 5.7 and 48 degrees C, compared with the maximum activity of 40.2 U/mL of free enzyme at the optimum pH of 4.9 and 48 degrees C. The reutilization capacity of the immobilized enzyme was up to three cycles.     

高效液相色谱-荧光检测法测定血浆中总同型半胱氨酸

 建立了测定血浆中总同型半胱氨酸的柱前衍生、高效液相色谱-荧光检测的分析方法。以Br omobimane作荧光剂,对巯基进行衍生。同型半胱氨酸的最低检测浓度为0.5 μmol/L,线性 浓度范围是2.5～80.0 μmol/L,回收率为94.0%～112.0%,批内、批间相对标准偏差都小于5. 6%。 关键词：     

表面活性剂对脂肪酶活性和选择性的影响

考察了几种表面活性剂对lipaseOF粗酶和纯化酶催化拆分酮基布洛芬的影响。除吐温-80,吐温-60和壬基酚聚氧乙烯醚外,大部分表面活性剂对酶活性有抑制作用,其中只有吐温-80能显著提高酶的立体选择性。酶的活性和选择性与表面活性剂浓度有关。在表面活性剂浓度为最佳(20mg/mL吐温-80或30mg/mL壬基酚聚氧乙烯醚)时lipaseOF粗酶的活性可分别提高13和15倍。加入80mg/mL吐温-80,粗酶和纯化酶的对映体选择率(E值)分别由1.1和8.0增至6.7和>100。     

气相色谱-质谱法测定大蒜挥发油的组成

采用改进的水蒸汽蒸馏法从山东金乡大蒜中提取挥发油。实验确定了气相色谱-质谱法分析大蒜油的条件,并对大蒜挥发油的化学成分进行了定性分析,共鉴定出20种物质。用峰面积归一化法对各物质的相对含量进行了测定,结果表明含硫化合物约占挥发油总成分的95%以上,其中含量最高的是大蒜新素,约占挥发油总量的三分之一。对低温储藏半年的挥发油进行分析的结果表明样品在低温下可稳定存放。     

固相萃取-气相色谱-质谱法测定利多卡因代谢物单乙基甘氨酰二甲苯胺的血药浓度

建立了固相萃取-气相色谱-质谱(GC-MS)测定利多卡因代谢物单乙基甘氨酰二甲苯胺(MEGX)血药浓度的方法。血清中的MEGX采用固相萃取小柱萃取、GC-MS测定。色谱条件为：HP-5MS毛细管柱(15 m×0.25 mm×0.1 μm),初始柱温100 ℃,保持1 min后以40 ℃/min速率升温至200 ℃,保持0.5 min;进样口温度250 ℃;分流进样,分流比1∶1,进样量2 μL;载气为氦气,流量为1.0 mL/min。质谱条件为:离子源温度230 ℃,电子轰击电离,电子能量70 eV,选择离子检测（m/z 58(MEGX)、 m/z 86(普鲁卡因,内标)）。结果表明,MEGX在血清中的浓度在1.562～25 ng/mL范围内的线性关系良好,相关系数0.9981,最低检测限为0.5 ng/mL,不同浓度MEGX的萃取回收率在80.1%～85.7%之间。实验证明该方法快速、准确,选择性好,灵敏度高,适合用于血清中微量MEGX的测定。