The presence of nitrobenzene compounds (NBCs) in the environment has imparted severe threats to public health. Herein, highly selective extraction of polar NBCs from aqueous samples is achieved by ...rational design of novel extractants. The extraction efficiencies to NBCs are much higher than other analytes (e.g., BTEX, phenols) with subtle differences in structures and molecular dimensions. This extractant (termed as PF-CROSS) was designed by constructing micropores in nanoparticles and reserving electron-donating phenolic hydroxyl groups within the hydrophobic cavities. Owing to the shielding of the phenolic hydroxyl groups from water by the hydrophobic cavities, the polar interactions and π-π electron donor-acceptor specific interactions between the NBCs and PF-CROSS presented, which were confirmed based on Fourier transform infrared (FTIR) spectroscopy, and were further demonstrated to play important roles in selective extraction of NBCs through theoretical modeling. Moreover, the steric effect provided by the micropores further enhanced the extraction selectivity. By fabricating PF-CROSS into solid-phase microextraction fibers, the detection limits of developed method reached as low as 0.32–5.39 ng L−1 for NBCs in water samples. This study provides an efficient and cost-effective extraction phase for highly sensitive detection of NBCs, which is also promising for the recycling of NBCs in the future.
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•The novel hierarchical porous phenolic resin nanoparticles are rationally design.•PF-CROSS shows high extraction selectivity and efficiency to nitrobenzene compounds.•π-π EDA interactions, polar interactions, and steric effects affect the extraction.•The developed method is applied for determination of NBCs with high sensitivity.
Capillary pressures in a carbon paper gas diffusion layer (GDL) having hydrophilic and hydrophobic pores of a polymer electrolyte membrane fuel cell (PEMFC) are investigated by both lattice Boltzmann ...simulations and experimental measurements. The simulated and measured capillary pressures as a function of water saturation for water drainage and imbibition processes in the GDL are presented and compared. It is shown that the pore-scale simulated drainage and imbibition capillary pressure curves are in good agreement with that obtained by experiment, both indicating the coexistence of hydrophilic and hydrophobic properties in the polytetrafluoroethylene (PTFE) treated carbon paper GDLs. The fitted capillary pressure curves, obtained from this paper, can provide more accurate predictions of the capillary pressure in carbon paper GDLs with non-uniform porosity and wettability than the standard Leverett–Udell relationship which was obtained for soil with more uniform porosity and wettability.
Basic understanding of the barrier properties of biological membranes can be obtained by studying model systems, such as planar lipid bilayers. Here, we study water pores in planar lipid bilayers in ...the presence of transmembrane voltage. Planar lipid bilayers were exposed to fast and slow linearly increasing voltage and current signals. We measured the capacitance, breakdown voltage, and rupture time of planar lipid bilayers composed of 1-pamitoyl 2-oleoyl phosphatidylcholine (POPC), 1-pamitoyl 2-oleoyl phosphatidylserine (POPS), and a mixture of both lipids in a 1:1 ratio. Based on the measurements, we evaluated the change in the capacitance of the planar lipid bilayer corresponding to water pores, the radius of water pores at membrane rupture, and the fraction of the area of the planar lipid bilayer occupied by water pores.planar lipid bilayer capacitance, which corresponds to water pores, water pore radius at the membrane rupture, and a fraction of the planar lipid bilayer area occupied by water pores. The estimated pore radii determining the rupture of the planar lipid bilayer upon fast build-up of transmembrane voltage are 0.101 nm, 0.110 nm, and 0.106 nm for membranes composed of POPC, POPS, and POPC:POPS, respectively. The fraction of the surface occupied by water pores at the moment of rupture of the planar lipid bilayer The fraction of an area that is occupied by water pores at the moment of planar lipid bilayer rupture is in the range of 0.1-1.8%.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Biological membranes are essential components of the living systems and processes occurring with their participation are related mainly to electric phenomena, such as signal transduction, the ...existence of membrane potentials, and transport through the membrane. It is well known that the universal model of the cell membrane structure is the lipid bilayer, which constitutes the environment for integral and surface membrane proteins. Thus, much attention has been given to the study of the organization and properties of these structures concerning both experimental and theoretical aspects. As systematic examinations are impeded by the complexity of the natural membranes, the best approach to conducting detailed physical and chemical studies of biological membranes is to use simplified well-defined model lipid membranes. Among the most commonly used are liposomes, planar lipid membranes, membranes on solid substrates, and lipid monolayers on the free surface.Studies of the electrical properties of model lipid membranes have been carried out for many years. However, there are still many issues that have not been verified experimentally and for which the existing results are incomplete or inconsistent. Therefore, the main objective of this book was to collect recent scientific and review articles on the electrical properties of model lipid membranes. This objective has been successfully achieved, for which I express heartfelt appreciation to all authors and reviewers for their excellent contributions.
The formation of hydrophilic pores in a lipid bilayer during phase transition is described using the Smoluchowski equation with an additional term of the hydrophobic pore source. This term is added ...to account for defects in lipid packing during phase transition. We assume that the temporal sequence of the pores is a stochastic process, a non-stationary second-order Erlang flow. Flow characteristics depend on the equation solution and determine the formation times of the hydrophilic pores. The calculated distribution of the durations of intervals between hydrophilic pores is in a good agreement with experimental data published before. In the context of this model we describe the influence of poly(ethylene glycol) on the pore formation frequency.
During mixed-acid fermentation,
initially translocates formate out of the cell, but re-imports it at lower pH. This is performed by FocA, the archetype of the formate-nitrite transporter (FNT) family ...of pentameric anion channels. Each protomer of FocA has a hydrophobic pore through which formate/formic acid is bidirectionally translocated. It is not understood how the direction of formate/formic acid passage through FocA is controlled by pH. A conserved histidine residue (H209) is located within the translocation pore, suggesting that protonation/deprotonation might be linked to the direction of formate translocation. Using a formate-responsive
-based reporter system we monitored changes in formate levels
when H209 in FocA was exchanged for either of the non-protonatable amino acids asparagine or glutamine, which occur naturally in some FNTs. These FocA variants (with N or Q) functioned as highly efficient formate efflux channels and the bacteria could neither accumulate formate nor produce hydrogen gas. Therefore, the data in this study suggest that this central histidine residue within the FocA pore is required for pH-dependent formate uptake into
cells. We also address why H209 is evolutionarily conserved and provide a physiological rationale for the natural occurrence of N/Q variants of FNT channels.
•Electroosmosis of a viscoplastic fluid in a single hydrophobic cylindrical pore.•Solution of coupled Cauchy momentum equations and Poisson-Nernst-Planck equations.•Interfacial slip augments flow, ...conductance and ion selectivity.•Impact of yield stress and flow behavior index on ion current polarization.•Effect of surface hydrophobicity is pronounced for shear thinning liquid.
We have studied the electroosmotic flow (EOF) of a non-Newtonian viscoplastic fluid, modeled as a Herschel-Bulkley (H-B) fluid, through a single hydrophobic nanopore in a uniformly charged solid hydrophobic membrane separating two identical reservoirs. An interfacial slip velocity develops when the viscoplastic fluid is strained over a hydrophobic surface. It is well established in the context of Newtonian fluid that the interfacial slip at the charged surface augments the EOF. For the viscoplastic fluid, the EOF depends on the fluid behavioral index and the yield stress. We have illustrated the impact of the interfacial slip on the EOF, conductance and ion selectivity of the cylindrical nanopore at different yield stresses for both the shear thinning and the shear thickening cases of the H-B fluid. The slip velocity, characterized by the slip length, enhances the average flow and conductance of the pore and this impact is pronounced for the shear thinning case. The unyielded zone, which develops along the central line of the pore, contracts as the slip length is increased. The ion concentration polarization enhances for the shear thinning fluid, however, the slip length creates a marginal increment. The counterion selectivity of the pore is found to be significant for the Newtonian case as compared to the non-Newtonian fluid and the velocity slip enhances the ion selectivity further. We have determined an analytic solution for the EOF of a power-law fluid in a long hydrophobic tube. Our computed solution for the case of a long tube effectively coincides with this analytic solution. An increment in the pore length reduces its conductance but enhances the ion selectivity. The increment of the average EOF for the hydrophobic pore as compared to the no-slip case grows as the pore length is increased.
Most researchers associate the increase in the permeability of lipid bilayers of artificial and biological membranes observed in various experiments with the formation of hypothetical hydrophobic and ...hydrophilic pores. Although the existence of hydrophobic defects, as the first stage of the formation of a hydrophilic pore, was hypothesized decades ago from electroporation experiments, the difficulty of describing this stage is determined by the lack of experimental data confirming the existence or at least associated with hydrophobic pores. We explored the increase in the current variance through the lipid membrane, observed when approaching the phase transition from the side of high temperatures, and have associated it with capacitive currents arising in response to the formation of hydrophobic pores. Assuming that the number of hydrophobic pores in a membrane follows a Poisson distribution, and thus, the mean number of hydrophobic pores is equal to the variance of that number, we used the measurements of the membrane current variance to evaluate the number of hydrophobic pores. Analysis of experimental data within this model allows us to estimate the number of hydrophobic pores at or above the phase transition and shows that the number of hydrophobic pores in a membrane close to the phase transition increased 20 times compared to the number of hydrophobic pores existing in the membrane far from the melting transition.
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•Current variance on the membrane increases near the phase transition.•We attributed the increase in variance to the appearance of hydrophobic pores.•The hydrophobic pores number in the membrane at the phase transition was estimated.•We used the Smoluchowski equation to count the number of hydrophobic pores.
Proteolytic degradation of the ∼100-kDa isolated RTX (Repeat-in-ToXin) subdomain (CyaA-RTX) of the Bordetella pertussis CyaA-hemolysin (CyaA-Hly) was evidently detected upon solely-prolonged ...incubation. Here, a truncated CyaA-Hly fragment (CyaA-HP/BI) containing hydrophobic and acylation regions connected with the first RTX block (BI1015–1088) was constructed as a putative precursor for investigating its potential autocatalysis. The 70-kDa His-tagged CyaA-HP/BI fragment which was over-expressed in Escherichia coli as insoluble aggregate was entirely solubilized with 4 M urea. After re-naturation in a Ni2+-NTA affinity column, the purified-refolded CyaA-HP/BI fragment in HEPES buffer (pH 7.4) supplemented with 2 mM CaCl2 was completely degraded upon incubation at 37 °C for 3 h. Addition of 1,10-phenanthroline‒an inhibitor of Zn2+-dependent metalloproteases markedly reduced the extent of degradation for CyaA-HP/BI and CyaA-RTX, but the degradative effect was clearly enhanced by addition of 100 mM ZnCl2. Structural analysis of a plausible CyaA-HP/BI model revealed a potential Zn2+-binding His-Asp cluster located between the acylation region and RTX-BI1015–1088. Moreover, Arg997‒one of the identified cleavage sites of the CyaA-RTX fragment was located in close proximity to the Zn2+-binding catalytic site. Overall results demonstrated for the first time that the observed proteolysis of CyaA-HP/BI and CyaA-RTX fragments is conceivably due to their Zn2+-dependent autocatalytic activity.
Basic understanding of the barrier properties of biological membranes can be obtained by studying model systems, such as planar lipid bilayers. Here we study water pores in planar lipid bilayers in ...the presence of transmembrane voltage. Planar lipid bilayers were exposed to linearly increasing voltage. We measured the capacitance, breakdown voltage, and rupture time of planar lipid bilayers composed of 1-pamitoyl 2-oleoyl phosphatidylcholine (POPC), mixture of POPC + 50 mol % cholesterol, POPC + 80 mol % cholesterol, POPC and surfactant Octaethylene glycol monododecyl ether (Ci2E8), and archaeal lipids Aeropyrum pernix K1. Based on the measurements, we evaluated the change in the capacitance at the moment of the planar lipid bilayer rupture. We assumed the change in the capacitance corresponds to water pores formation. We evaluated the radius of water pores, and the fraction of the area of the planar lipid bilayer that is occupied by water pores. Water pores have larger radii and occupying greater area of the planar lipid bilayer in the planar lipid bilayers, where lipid molecules form hydrophilic pores upon exposure to the electric field (POPC and POPC with addition of Ci2E8), in comparison to the planar lipid bilayers, where lipid molecules form hydrophobic pores upon exposure to the electric field (mixture of POPC + holesterol (50 mol % in 80 mol %) and and archaeal lipids Aeropyrum pernix K1).
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