Accumulation and separation of membrane-bound proteins using hydrodynamic forces

The separation of molecules residing in the cell membrane remains a largely unsolved problem in the fields of bioscience and biotechnology. We demonstrate how hydrodynamic forces can be used to both accumulate and separate membrane-bound proteins in their native state. A supported lipid bilayer (SLB) was formed inside a microfluidic channel with the two proteins streptavidin (SA) and cholera toxin (CT) coupled to receptors in the lipid bilayer. The anchored proteins were first driven toward the edge of the lipid bilayer by hydrodynamic forces from a flowing liquid above the SLB, resulting in the accumulation of protein molecules at the edge of the bilayer. After the concentration process, the bulk flow of liquid in the channel was reversed and the accumulated proteins were driven away from the edge of the bilayer. Each type of protein was found to move at a characteristic drift velocity, determined by the frictional coupling between the protein and the lipid bilayer, as well as the size and shape of the protein molecule. Despite having a similar molecular weight, SA and CT could be separated into monomolecular populations using this approach. The method also revealed heterogeneity among the CT molecules, resulting in three subpopulations with different drift velocities. This was tentatively attributed to multivalent interactions between the protein and the monosialoganglioside G(M1) receptors in the lipid bilayer.     

Resonance-mode electrochemical impedance measurements of silicon dioxide supported lipid bilayer formation and ion channel mediated charge transport

A single-chip electrochemical method based on impedance measurements in resonance mode has been employed to study lipid monolayer and bilayer formation on hydrophobic alkanethiolate and SiO(2) substrates, respectively. The processes were monitored by temporally resolving changes in interfacial capacitance and resistance, revealing information about the rate of formation, coverage, and defect density (quality) of the layers at saturation. The resonance-based impedance measurements were shown to reveal significant differences in the layer formation process of bilayers made from (i) positively charged lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-ethylphosphocholine (POEPC), (ii) neutral lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) on SiO(2), and (iii) monolayers made from POEPC on hydrophobic alkanethiolate substrates. The observed responses were represented with an equivalent circuit, suggesting that the differences primarily originate from the presence of a conductive aqueous layer between the lipid bilayers and the SiO(2). In addition, by adding the ion channel gramicidin D to bilayers supported on SiO(2), channel-mediated charge transport could be measured with high sensitivity (resolution around 1 pA).     

Equilibrium sampling of persistent and bioaccumulative compounds in soil and sediment: comparison of two approaches to determine equilibrium partitioning concentrations in lipids

The equilibrium sampling in silicone is increasingly applied to measure freely dissolved concentrations and chemical activities within bioaccumulation research of hydrophobic organic chemicals. Two equilibrium methods were applied to PCB-contaminated soil and sediment, and directly calibrated with respect to equilibrium partitioning concentrations in lipids (C(lipid,partitioning)): (i) Solid phase microextraction in the headspace above the sample (HS-SPME) required optimization for its application to PCBs, and it was calibrated above external partitioning standards in olive oil. (ii) Equilibrium sampling with internally coated glass jars with varying thicknesses of silicone (PDMS) resulted in proportionality between coating and analyte mass, which confirmed several validity criteria. C(lipid,partitioning) was here determined as product of PDMS concentration and PDMS to lipid partition ratio. The results of the two methods were in good agreement and thus validated each other. Finally, the coated glass jar method was applied to field sediment containing invertebrates, which lead to C(lipid,partitioning) that were about two times higher than measured lipid-normalized concentrations in the organisms. Temperature differences and animal lipid structure were discussed as possible reasons for this discrepancy. Both methods combine high analytical performance, reduced equilibration times and new calibration possibilities, which makes them suited for bioaccumulation research and environmental monitoring.     

Enhanced performance of printed organic diodes using a thin interfacial barrier layer

Printed, organic diodes with a thin organic interfacial layer forming a Schottky barrier were fabricated and characterized. Experiments indicated that the thickness of the barrier layer is <10 nm. The interfacial layer reduces the reverse current of the diode by 2 orders of magnitude without significantly affecting the forward characteristics above 1 V. As a result, printed organic diodes with a rectification ratio of 5 orders of magnitude were fabricated. The diodes enable applications where low reverse currents are needed.     

Spatio-temporal skin strain distributions evoke low variability spike responses in cuneate neurons

A common method to explore the somatosensory function of the brain is to relate skin stimuli to neurophysiological recordings. However, interaction with the skin involves complex mechanical effects. Variability in mechanically induced spike responses is likely to be due in part to mechanical variability of the transformation of stimuli into spiking patterns in the primary sensors located in the skin. This source of variability greatly hampers detailed investigations of the response of the brain to different types of mechanical stimuli. A novel stimulation technique designed to minimize the uncertainty in the strain distributions induced in the skin was applied to evoke responses in single neurons in the cat. We show that exposure to specific spatio-temporal stimuli induced highly reproducible spike responses in the cells of the cuneate nucleus, which represents the first stage of integration of peripheral inputs to the brain. Using precisely controlled spatio-temporal stimuli, we also show that cuneate neurons, as a whole, were selectively sensitive to the spatial and to the temporal aspects of the stimuli. We conclude that the present skin stimulation technique based on localized differential tractions greatly reduces response variability that is exogenous to the information processing of the brain and hence paves the way for substantially more detailed investigations of the brain''s somatosensory system.     

Geographic aggregation of wind power—an optimization methodology for avoiding low outputs

This work investigates macro‐geographic allocation as a means to improve the performance of aggregated wind power output. The focus is on the spatial smoothing effect so as to avoid periods of low output. The work applies multi‐objective optimization, in which two measures of aggregated wind power output variation are minimized, whereas the average output is maximized. The results show that it is possible to allocate wind power so that the frequency of low outputs is substantially reduced, while maintaining the average output at around 30% of nameplate capacity, as compared with the corresponding output of 20% for the present allocation system. We conclude that in a future, fully electrically integrated Europe, geographic allocation can substantially reduce instances of low aggregate output, while impairing little on capacity factor and at the same time providing reduction in of short‐term jumps in output. Copyright © 2016 John Wiley & Sons, Ltd.     

The effect of a local mesh refinement on hydraulic modelling of river meanders

Large-scale river models are generally discretized by relatively large mesh cells resulting in bathymetry discretization errors and numerical effects. These hydraulic models are generally calibrated by altering the bed roughness to compensate for these errors and effects. Consequently, the calibrated roughness values are mesh-dependent while generally local mesh refinements are executed after model calibration to study the effects of river interventions. This study shows both the errors caused by bathymetry discretization and numerical effects for locally refined meshes. First, schematised river meanders with a flat bed in the transverse flow direction are analysed to isolate the induced numerical effects by the mesh. Afterwards, a case study is considered to verify if similar mesh influences are found in natural river meanders. Curvilinear, triangular and hybrid (combination of curvilinear and triangular cells) meshes are used with different resolutions. The analysis shows that in the schematised river meanders lower depth-averaged flow velocities and larger water depths are simulated with coarser meshes. In the case study, substantial differences in hydrodynamics between the meshes are obtained suggesting that the bathymetry discretization is more influential than the numerical effects. Finally, it was found that triangular meshes, and rivers with narrow meander bends, are most sensitive to mesh resolution. Especially in these cases, it is desirable to refine the mesh at the desired locations before model calibration.     

Formation of Amylose‐Lipid Complexes and Effects of Temperature Treatment. Part 1. Monoglycerides

The formation of amylose‐lipid complexes of form I (amorphous structure) and form II (crystalline structure) during heating was studied by differential scanning calorimetry (DSC) for a range of monoglycerides and for monoglyceride mixtures. The temperature treatment applied to amylose‐monoglyceride‐mixtures were either the first scan in DSC (10 °C/min, 15‐144 °C) or a prolonged heat treatment where the samples were kept at 100 °C for 24 h before being analysed in DSC. The temperature treatment influenced which type of complex was formed, and how much, whereas the thermal stability (as judged from the transition peak temperature) was only marginally influenced. It is shown in this study that all the investigated monoglycerides were able to give complex form I as well as complex form II, although the conditions for the formation differed between the monoglycerides. It was found that a simple DSC‐scan was enough for formation of complex form II for the shortest monoglycerides (glycerol monocaprin, glycerol monolaurin and glycerol monomyristin), whereas in case of the longer monoglycerides and monoglyceride mixtures the prolonged heat treatment was required for formation of complex form II. Moreover, the monoglyceride mixtures gave only form II at conditions where the individual components in the mixtures gave both form I and form II.