pH对无机陶瓷膜微滤中药水提液膜过程的影响研究

目的研究中药水提液pH的变化对无机陶瓷膜微滤中药水提液膜过程的影响。方法调节甘草水提液的pH值为2、3、4、5、6、7、8，在温度、压力、膜面流速恒定的条件下分别过0.2μmAl2O3无机陶瓷膜，测定不同pH的甘草水提液的膜稳定通量及指标性成分甘草酸的转移率。结果不同pH条件下的甘草水提液的膜稳定通量及指标性成分甘草酸的转移率随着pH的增大有逐渐增大的趋势.在pH=4左右显著增加，pH=7时膜稳定通量最大，甘草酸的含量最高，pH=8的甘草酸转移率最高。结论pH值对无机陶瓷膜微滤甘草水提液的膜过程有很大的影响。     

镍铬合金烤瓷全冠腐蚀性分析

对不同两地加工厂生产的镍铬合金烤瓷熔附金属全冠(porcelain-fused-to-metal crown,PFM冠)进行了为期一年的体外腐蚀性对比研究、分析该产品应用近30年来烤瓷全冠中镍的析出量及其市场的规范化程度.将两厂家生产的镍铬PFM冠样品共40个,随机分为4组(10天组、1月组、6月组、12月组),分别浸泡于ISO/TR10271标准(37℃,pH 6.8)配制的人工唾液中,于10天、1月、6月、12月用电感耦合等离子体发射光谱仪(ICP-AES)测定浸提液中析出的镍离子浓度,同步采用X射线能量散谱仪(EDS)、正置式金相显微镜分析、观察样品元素构成及金相显微组织结构.结果显示两厂样品的镍离子析出量在一年组差异具有统计学意义(F=9.360,P=0.000).能谱分析显示两厂样品主要成分都为Ni、Cr、Mo,但含量不同;其金相结构均为树枝状共晶结构,但B厂样品较A厂夹杂物多,枝晶粗、排列紊乱、晶间相多.一年内两厂的镍铬合金烤瓷冠在抗腐蚀性能方面存在差异性,远期效果有待进一步观察.     

OH-根对掺铒碲酸盐玻璃光谱性质的影响

制备了5种浓度下系列不同OH^−根含量的掺铒碲酸盐玻璃样品, 测试了样品的红外吸收光谱, 分析了在不同通氧除水时间下玻璃的红外吸收系数变化情况. 测试了样品的吸收光谱, 利用Judd-Ofelt理论计算了不同铒掺杂浓度和OH^−根含量样品的光谱参量Ω _i (i = 2, 4, 6). 根据McCumber理论计算了铒离子在1532 nm处的吸收截面和Er³⁺:⁴I_13/2®⁴I _15/2跃迁峰值发射截面. 测试了样品中 Er³⁺: ⁴I_13/2®⁴I_15/2跃迁对应的荧光光谱和⁴I_13/2能级荧光寿命, 讨论了OH^−根对不同铒掺杂浓度下碲酸盐玻璃光谱性质的影响. 研究结果表明, OH^−根仅对荧光寿命和荧光峰值强度存在影响, 在Er₂O₃浓度小于1.0 mol%时, OH^−根是发生荧光猝灭的主要影响因素, 而高于这一浓度后Er³⁺离子本身的能量转移对荧光猝灭起主要作用. 而OH^−根对其他光谱性质(荧光半高宽、吸收光谱、受激发射截面等)基本没有影响.     

质子传导陶瓷膜在催化脱氢反应中的应用

有机化合物催化脱氢是一种吸热、体积增大的可逆反应过程,通过特定的膜将反应过程中生成的氢气不断地移出反应区,可促使反应向产物方向移动,从而提高反应转化率、减少副反应并最终达到降低反应温度、提高产率的目的。质子传导陶瓷膜可以以质子传递方式选择性透过氢,具有成本低、选择高,耐高温、热稳定及化学稳定性能好、不易中毒等特点,非常适合于脱氢膜反应器。本文对质子传导陶瓷膜材料、透氢机理、膜制备、膜反应器及其用于脱氢反应的研究现状与进展情况进行了综述。     

Solute traffic across mammalian peroxisomal membrane – single channel conductance monitoring reveals pore-forming activities in peroxisomes

Mouse liver peroxisomes were isolated by centrifugation in a self-generated Percoll gradient followed by an Optiprep density gradient centrifugation. Peroxisomes contributed 90–96% of the total protein content in the fraction, as confirmed by marker enzyme assays, protein pattern in SDS-PAGE, immunoblotting, and electron microscopy. Solubilized peroxisomal membrane proteins were reconstituted into a planar lipid bilayer. A single-channel conductance monitoring of the reconstituted lipid bilayer revealed the presence of two pore-forming components with a conductance in 1 M KCl of 1.3 nS and 2.5 nS. Control experiments with fractions enriched in mitochondria, lysosomes, and fragments of endoplasmic reticulum showed that the peroxisomal channel-forming activities were not due to admixture of isolated peroxisomes with other cellular organelles. The peroxisomal channels were well preserved in membrane preparations but became unstable after solubilization from the membranes by detergent. Received 27 May 2005; received after revision 23 September 2005; accepted 11 October 2005     

Recombinant G protein-coupled receptors from expression to renaturation: a challenge towards structure

G protein-coupled receptors (GPCRS) represent a class of integral membrane proteins involved in many biological processes and pathologies. Fifty percent of all modern drugs and almost 25% of the top 200 bestselling drugs are estimated to target GPCRs. Despite these crucial biological implications, very little is known, at atomic resolution, about the detailed molecular mechanisms by which these membrane proteins are able to recognize their extra-cellular stimuli and transmit the associated messages. Obviously, our understanding of GPCR functioning would be greatly facilitated by the availability of high-resolution three-dimensional (3D) structural data. However, expression, solubilization and purification of these membrane proteins are not easy to achieve, and at present, only one 3D structure has been determined, that of bovine rhodopsin. This review presents and compares the different successful strategies which have been applied to solubilize and purify recombinant GPCRs in the perspective of structural biology experiments. Received 21 November 2005; received after revision 20 January 2006; accepted 2 February 2006 An erratum to this article is available at .     

膜分离处理印染废水研究进展

印染废水具有水量大、色度高、成分复杂、环境污染严重等特点。膜分离技术处理印染废水具有选择性好、生产效率高和处理成本低等特点。基于对近年来的文献调研,综述了膜分离技术在印染废水处理中的研究进展情况,指出了膜分离法处理印染废水还存在的主要问题和未来发展方向,并对膜分离技术处理印染废水应用前景作了展望。     

Changes in erythrocyte membrane lipid composition affect the transient decrease in membrane order which accompanies insulin receptor down-regulation

We have recently demonstrated, using electron paramagnetic resonance (EPR) spectroscopy, that insulin receptor internalization in response to insulin incubation (down-regulation) in human erythrocytes is accompanied by a transient decrease in membrane order, as measured by the 2T order parameter. Since membrane lipids play such an important role in receptor internalization, we investigated the possible effects that an alteration of the normally-occurring lipid profile might have on down-regulation and the concomitant transient decrease in membrane order. Consequently, human erythrocytes enriched with cholesterol and erythrocytes from cirrhotic patients were examined, because both of these groups of cells have a higher cholesterol/phospholipid molar ratio (CH/PL) than controls. The 5-nitroxystearate spin label, which inserts into the lipid bilayer of cell membranes, was used to monitor changes in 2T for a 3-h period at 37°C. We report here that both cholesterol-enriched and cirrhotic erythrocytes do not down-regulate, as demonstrated by binding assays, and that they do not show the typical transient decrease in membrane order observed in controls. The results seem to indicate that a more ordered membrane inhibits internalization of the insulin receptor in erythrocytes, and that an increase in membrane disorder is necessary for insulin receptor down-regulation.     

In vitro modulation of rat adipocyte ghost membrane fluidity by cholesterol oxysterols

The effects of cholesterol and cholesterol-derived oxysterols (cholestanone, cholestenone, coprostanone and epicoprostanol) on adipocyte ghost membrane fluidity were studied using a fluorescence depolarization method. The fluorescence anisotropy of the treated membranes was determined using 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). Cholestanone and cholesterol decreased membranes fluidity at both the concentrations tested (10 & 50 M) while the rest of the sterols did not exert any significant effect on membrane fluidity. In the presence of epinephrine, cholestanone partitioned more towards the lipid core but cholesterol partitioning was not affected. The fusion activation energies (E) obtained for membranes preincubated with cholestanone (8.6 kcal/mol) and cholesterol (8.2 kcal/mol) were not significantly different from that of untreated membranes (8.3 kcal/mol). Membranes preincubated with cholestanone and cholesterol did not exhibit any change in lipid phase throughout the temperature range (10–45°C) tested. The sterols were found to inhibit fisetin-induced phospholipid methylation in isolated rat adipocytes in the rank order of cholesterol > epicoprostanol > cholestanone=cholestenone=coprostanone, while basal methylations was unaffected. When adipocytes were preincubated with the sterols before the addition of fisetin, cholestanone and cholestenone showed 74% and 66% inhibition of maximal methylation respectively. These results indicated that cholesterol oxysterols interact differently with rat adipocyte membranes, with cholestanone interacting more with phospholipids located at the inner lipid bilayer (e.g. phosphatidylethanolamine) while cholesterol interacts more with phosphatidylcholine located at the outer lipid bilayer. This differential interaction may cause selective changes in membrane fluidity at different depths of the bilayer and thus may modulate the activities of membrane-bound proteins such as enzymes and receptors.     

Membrane protein folding on the example of outer membrane protein A of <Emphasis Type="Italic">Escherichia coli</Emphasis>

The biophysical principles and mechanisms by which membrane proteins insert and fold into a biomembrane have mostly been studied with bacteriorhodopsin and outer membrane protein A (OmpA). This review describes the assembly process of the monomeric outer membrane proteins of Gram-negative bacteria, for which OmpA has served as an example. OmpA is a two-domain outer membrane protein composed of a 171-residue eight-stranded -barrel transmembrane domain and a 154-residue periplasmic domain. OmpA is translocated in an unstructured form across the cytoplasmic membrane into the periplasm. In the periplasm, unfolded OmpA is kept in solution in complex with the molecular chaperone Skp. After binding of periplasmic lipopolysaccharide, OmpA insertion and folding occur spontaneously upon interaction of the complex with the phospholipid bilayer. Insertion and folding of the -barrel transmembrane domain into the lipid bilayer are highly synchronized, i.e. the formation of large amounts of -sheet secondary structure and -barrel tertiary structure take place in parallel with the same rate constants, while OmpA inserts into the hydrophobic core of the membrane. In vitro, OmpA can successfully fold into a range of model membranes of very different phospholipid compositions, i.e. into bilayers of lipids of different headgroup structures and hydrophobic chain lengths. Three membrane-bound folding intermediates of OmpA were discovered in folding studies with dioleoylphosphatidylcholine bilayers. Their formation was monitored by time-resolved distance determinations by fluorescence quenching, and they were structurally distinguished by the relative positions of the five tryptophan residues of OmpA in projection to the membrane normal. Recent studies indicate a chaperone-assisted, highly synchronized mechanism of secondary and tertiary structure formation upon membrane insertion of -barrel membrane proteins such as OmpA that involves at least three structurally distinct folding intermediates.     

Effect of suloctidil on blood viscosity in healthy volunteers after forearm occlusion

Summary The effect of suloctidil (1-(4-isopropylthiophenyl)-2-n-octylaminopropanol) on increased blood viscosity was studied in healthy volunteers after forearm occlusion. A significant reduction of blood viscosity was observed in subjects treated 1 day before, or immediately before, the ischaemic trial. It is concluded that the drug may preserve the deformability of erythrocytes during an ischaemic episode.     

Carbon tetrachloride modulates the rat hepatic microsomal UDP-glucuronyl transferase activity and membrane fluidity

Summary Modulations in rat hepatic microsomal UDP-glucuronyl transferase activity have been observed during carbon tetrachloride (CCl₄) poisoning, with a large decrease in the enzyme cooperativity and increase in the membrane fluidity, occurring 30 min after administration. The results strengthen the possibility that an increase in microsomal membrane fluidity may be an early key event in liver injury induced by CCl₄.Acknowledgments. This work was supported by funds of the University of Athens.     

Age-dependent changes of rat liver plasma membrane composition

Summary The chemical composition of liver plasma membrane was studied in Wistar rats aged between 3 and 24 months. Results obtained indicate a significant age-dependent positive correlation of both the protein:phospholipid and cholesterol:phospholipid ratios, whereas the protein:cholesterol ratio seems to remain unaffected. Phospholipid analysis of liver plasma membrane reveals that only the phosphatidylcholine content has a significant negative correlation with age; all other phospholipid species remain basically unchanged.Supported by a grant of the Italian National Research Council, Project Preventive and Rehabilitative Medicine, Subproject Mechanisms of Aging.