Interaction of nanoparticles with lipid membrane

A nanoscale range of surface feature curvatures where lipid membranes lose integrity and form pores has been found experimentally. The pores were experimentally observed in the l-alpha-dimyristoyl phosphatidylcholine membrane around 1.2-22 nm polar nanoparticles deposited on mica surface. Lipid bilayer envelops or closely follows surface features with the curvatures outside of that region. This finding provides essential information for the understanding of nanoparticle-lipid membrane interaction, cytotoxicity, preparation of biomolecular templates and supported lipid membranes on rough and patterned surfaces.     

In-plane homogeneity and lipid dynamics in tethered bilayer lipid membranes (tBLMs)

Tethered bilayer lipid membranes (tBLMs) were prepared by the self-assembly of thiolated lipidic anchor molecules on gold, followed by phospholipid precipitation via rapid solvent exchange. They were characterized by their in-plane structure, dynamics and dielectric properties. We find that the in-plane homogeneity and resistivity of the tBLMs depend critically on a well-controlled sample environment during the rapid solvent-exchange procedure. The in-plane dynamics of the systems, assessed by fluorescence correlation spectroscopy (FCS) as the diffusivity of free, labeled phospholipid dissolved in the membrane, depend on the density of the lipidic anchors in the bilayer leaflet proximal to the substrate as well as on details of the molecular structure of the anchor lipid. In DOPC tBLMs in which tethers are laterally dilute (sparsely tethered bilayer lipid membranes, stBLMs), measured diffusivities, D ≈ 4 μm(2) s(-1), are only slightly greater than those reported in physisorbed bilayers (M. Przybylo, J. Sykora, J. Humpolíckova, A. Benda, A. Zan and M. Hof, Langmuir, 2006, 22, 9096-9099). However, when we distinguish label diffusion in the proximal and in the distal bilayer leaflets, we observe distinct diffusivities, D ≈ 2 μm(2) s(-1) and 7 μm(2) s(-1), respectively. The value observed in the distal leaflet is identical to that in free membranes. stBLMs completed with phytanoyl lipids (DPhyPC) show consistently lower label diffusivity than those completed with unsaturated chains (DOPC). As the length of the tether chain increases, a reduction in the apparent diffusivity is observed, which we interpret as an increased propensity of the proximal bilayer leaflet to host free lipid. We also investigated preparation conditions that control whether the tBLMs are laterally homogeneous, as assessed by optical microscopy. In laterally heterogeneous bilayers, the label diffusivity varies only by a factor of ~2 to 4, indicating that the regions in the bilayers with different label solubilities do not correspond to distinct phases, such as a fluid phase coexisting with a gel phase.     

Radial sizing of lipid nanotubes using membrane displacement analysis

We report a novel method for the measurement of lipid nanotube radii. Membrane translocation is monitored between two nanotube-connected vesicles, during the expansion of a receiving vesicle, by observing a photobleached region of the nanotube. We elucidate nanotube radii, extracted from SPE vesicles, enabling quantification of membrane composition and lamellarity. Variances of nanotube radii were measured, showing a growth of 40-56 nm, upon increasing cholesterol content from 0 to 20%.     

微型支撑双层类脂膜pH电极的研制

把对氢质子敏感的四氯对位苯醌 (TCPBQ)置于在不锈钢丝末端的双层类脂膜 (s -BLM)里 .然后将这种固体支撑的s -BLM作为工作电极 ,Ag -AgCl电极作为参比电极 ,在各种pH水溶液里测得的电动势与pH的关系符合Nernst公式 .这种s -BLM电极易于制备 ,尺寸很小 (直径只有 0 .2mm) ,能在两天内保持稳定 .用这种电极对常规pH计难以测定的水包油型乳状液的pH作了测定 ,得到较好的结果 .     

Comparison of the effect of lipid A analog E5531 and the lipid A from Escherichia coli on phospholipid membrane properties

The effect of the lipid A analog E5531 on the phospholipid membrane was compared with that of the lipid A from Escherichia coli (EC). E5531 decreased the phase transition temperature of dipalmitoylphosphatidylcholine (DPPC) membrane and increased the fluidity and micropolarity. On the other hand, the effect of EC on the membrane was contradictory. These results suggested that the reason for the difference of biological effects of these two lipid A would be caused by the differences from the effect on the cell membranes.     

Silicon-on-insulator based nanopore cavity arrays for lipid membrane investigation

We present the fabrication and characterization of nanopore microcavities for the investigation of transport processes in suspended lipid membranes. The cavities are situated below the surface of silicon-on-insulator (SOI) substrates. Single cavities and large area arrays were prepared using high resolution electron-beam lithography in combination with reactive ion etching (RIE) and wet chemical sacrificial underetching. The locally separated compartments have a circular shape and allow the enclosure of picoliter volume aqueous solutions. They are sealed at their top by a 250?nm thin Si membrane featuring pores with diameters from 2?μm down to 220?nm. The Si surface exhibits excellent smoothness and homogeneity as verified by AFM analysis. As biophysical test system we deposited lipid membranes by vesicle fusion, and demonstrated their fluid-like properties by fluorescence recovery after photobleaching. As clearly indicated by AFM measurements in aqueous buffer solution, intact lipid membranes successfully spanned the pores. The nanopore cavity arrays have potential applications in diagnostics and pharmaceutical research on transmembrane proteins.     

Non-Brownian diffusion of membrane molecules in nanopatterned supported lipid bilayers

Molecules associated with the outer surface of living cells exhibit complex, non-Brownian patterns of diffusion. In this report, supported lipid bilayers were patterned with nanoscale barriers to capture key aspects of this anomalous diffusion in a controllable format. First, long-range diffusion coefficients of membrane-associated molecules were significantly reduced by the presence of the barriers, while short-range diffusion was unaffected. Second, this modulation was more pronounced for large molecular complexes than for individual lipids. Surprisingly, the quantitative effect of these barriers on long-range lipid diffusion could be accurately simulated using a simple, continuum-based model of diffusion on a nanostructured surface; we thus describe a metamaterial that captures the properties of the outer membrane of living cells.     

A microfluidic vesicle screening platform: monitoring the lipid membrane permeability of tetracyclines

For many drugs including antibiotics such as tetracyclines it is crucial that the molecule has the ability to quickly and passively permeate lipid membranes. Hence, the understanding of the permeability in relation to the molecular structure is an important aspect to rationally design novel pharmaceutically active compounds with high bioavailability. Here, we present a versatile method to study the kinetics of tetracycline permeation across liposome membranes on a microchip. Liposomes are immobilized onto the glass surface in a stripe pattern via an avidin-biotin bond and covered by microchannels to allow continuous delivery of tetracycline and buffer. The fluid flow provides a constant concentration profile and thereby resembles the drug transport via blood in the human body. Total internal reflection fluorescence (TIRF) microscopy was used to image the formation of a fluorescent drug-europium complex inside the liposomes. The permeation rates of various tetracyclines were investigated and the results compared to a conventional method (water-octanol partitioning). The findings largely confirm the correlation between membrane permeability and lipophilicity of the permeating molecules (Overton's rule). However, slight deviations reveal that lipophilicity is an important but not the exclusive parameter for the prediction of permeation. The method is fast enough to study the permeation of unstable tetracyclines such as rolitetracycline. Additionally, with the use of different cholesterol concentrations, the influence of membrane composition on the permeation rate can be investigated conveniently. The microfluidic approach can be easily applied to investigate the kinetics of other processes such as ligand-membrane receptor association and dissociation, provided that the process can be visualized by means of fluorescence spectroscopy.     

计算流体力学在纳滤膜分离技术研究中应用

介绍了计算流体力学(CFD)在膜分离过程模拟中的基本原理,探讨了CFD在膜隔网优化设计、纳滤膜污染机理研究、纳滤膜对无机离子截留等领域中的应用,并对CFD在纳滤膜分离技术研究中的应用前景进行了展望.     

计算流体力学在膜技术及膜生物反应器研究中的应用

介绍了计算流体力学(CFD)的基本原理、内容和特点,综述了CFD在膜技术领域中的研究和发展,特别讨论了其在膜生物反应器(MBR)技术中的研究和应用,并对其应用前景进行了展望.     

Biotinylated lipid membrane patterns supported by proteins for the recognition of streptavidined polystyrene microspheres

Human serum albumin (HSA) patterns constructed on glass substrate by the micro-contact printing (microCP) technique are fabricated to support phospholipids membranes functionalized with biotinylated lipid. The experiment results indicate that this kind of lipid membrane has been assembled on HSA patterns with good stability. And the streptavidin-coated PS microspheres can be deposited on such lipid patterns with high efficiency. In this way, it may create a route to change the biological interface in the fabrication of biosensor.     

The effect of the membrane fluidity on pharmacokinetics for lipid A analog E5531

The effect of the dispersing procedure on the aggregate size, membrane fluidity and the pharmacokinetics were evaluated for the lipid A analog E5531. The size of the aggregates prepared by the pH-jump method (pH 11.0 → 7.3) was decreased, reaching 20 nm with increasing dispersing time in 0.003 N NaOH (pH 11.0). The membrane fluidity of the aggregates increased with increasing dispersing time. When prepared by the normal dilution method (pH 7.3 → 7.3), the size of the aggregates remained constant at 150 nm and the membrane fluidity was smaller compared to samples prepared by the pH-jump method. Using samples with different degrees of hydration and different membrane fluidities prepared by the pH-jump method, the pharmacokinetics after intravenous administration into rats were evaluated, and the data obtained confirmed that the membrane fluidity was correlated with the pharmacokinetics in rat. In addition, E5531 vials were stable for 24 months at room temperature when used within 24 hr after reconstitution.     

Physicochemical and transport parameters for a lipid coated regenerated cellulose membrane

Physicochemical and NaCl characteristic transport parameters determined for a lipid coated regenerated cellulose membrane are reported. The lipid studied consists of glyceryl triestearate, while l-α-phosphatidylcholine and sodium taurocholate were used as surfactants. The RC-support and the lipid-modified membrane were characterized by X-ray photoelectron spectroscopy (XPS) at three different take off angles and X-ray diffraction. Transport parameters (salt diffusion and electrical resistance) were determined from salt permeation and impedance spectroscopy measurements performed with the membranes in contact with a NaCl constant concentration (C_c = 0.01 M). These results show a reduction in the transport parameters across the lipid coated membrane due to the lipid presence as well as its stability under mass and ion fluxes, which supports its application in liquid systems.     

Molecular dynamics study of dipalmitoylphosphatidylcholine lipid layer self-assembly onto a single-walled carbon nanotube

Single-walled carbon nanotubes (SWNTs) are possible nano-injectors and delivery vehicles of molecular probes and drugs into cells. In order to explore the interaction between lipid membranes and carbon nanotubes, we investigate the binding mechanism of dipalmitoylphosphatidylcholine (DPPC) with SWNTs by molecular dynamics. In low concentration range simulations, the DPPC molecules form a supramolecular two-layered cylindrical structure wrapped around the carbon nanotube surface. The hydrophobic part of DPPC is adsorbed on the surface of the nanotube, and the hydrophilic top is oriented towards the aqueous phase. For higher concentration ranges, the DPPC molecules are found to form a supramolecular multi-layered structure wrapped around the carbon nanotube surface. At the saturation point a membrane-like structure is self-assembled with a width of 41.4 Å, which is slightly larger than the width of a cell membrane. Our study sheds light on the existing conflicting simulation data on adsorption of single-chained phospholipids.      

The effect of lipid A analog E5531 on membrane properties of dipalmitoylphosphatidylcholine

The effect of the lipid A analog E5531 on the phospholipid membrane was determined and compared with that of the lipid A from Escherichia coli (EC). E5531 decreased the phase transition temperature of dipalmitoylphosphatidylcholine (DPPC) membrane and increased the fluidity and permeability. On the other hand, EC increased the phase transition temperature and decreased the membrane fluidity and permeability. These results suggest that the reason for the difference of biological effects of E5531 and lipid A from EC would be caused by the differences from the effect on the cell membranes.     

Testing the hypothesis that amphiphilic antineoplastic lipid analogues act through reduction of membrane curvature elastic stress

The alkyllysophospholipid (ALP) analogues Mitelfosine and Edelfosine are anticancer drugs whose mode of action is still the subject of debate. It is agreed that the primary interaction of these compounds is with cellular membranes. Furthermore, the membrane-associated protein CTP: phosphocholine cytidylyltransferase (CCT) has been proposed as the critical target. We present the evaluation of our hypothesis that ALP analogues disrupt membrane curvature elastic stress and inhibit membrane-associated protein activity (e.g. CCT), ultimately resulting in apoptosis. This hypothesis was tested by evaluating structure–activity relationships of ALPs from the literature. In addition we characterized the lipid typology, cytotoxicity and critical micelle concentration of novel ALP analogues that we synthesized. Overall we find the literature data and our experimental data provide excellent support for the hypothesis, which predicts that the most potent ALP analogues will be type I lipids.     

Interaction of N-fluorescein-5-isothiocyanate pyrrolidine-C60 with a bimolecular lipid model membrane

In this letter we report the first synthesis of a fluorescein-functionalized fullerene, N-fluorescein-5-isothiocyanate pyrrolidine-C₆₀, and its influence on the electrical properties of a bimolecular lipid model membrane.     

催芽间高温高湿环境设计

通过对蒸气直接加热加湿的催芽间高温高湿环境的原理分析和讨论，提供了一种适用于高温高温环境的比较简单的空调方式和有关计算方法，其室内相对湿度接近饱和状态，而室内温度不低于空调房间的室外温度。     

Detection of noncharged organic substances by new measurement method using a lipid membrane sensor

This paper reports a new measurement method to detect ppb levels of noncharged organic substances using lipid/polymer membrane sensors. Noncharged organic substances have large influences on the adsorption of positively-charged lipids to negatively-charged membranes. Organic solvents (trichloroethylene) and endocrine disrupting chemicals (di-2-ethylhexylphthalate) were detected by utilizing the sensor output, which is the change of membrane potential caused by interactions among the lipid membrane, noncharged organic substances, and lipids in solution. This new potentiometric method has a possibility of detection of a trace amount of noncharged toxic substances.