Cell model of biporous medium (membrane)

The hydrodynamic permeability of biporous medium (membrane) modeled by the set of porous particles located in the porous medium with other rheological properties is calculated using the cell method. All known boundary conditions on the cell surface, i.e., the Happel, Kuwabara, Kvashnin, and Cunningham boundary conditions, are considered. Significant limiting cases that lead to new or already known results are studied.     

Hydrodynamic permeability of a membrane composed of porous spherical particles in the presence of uniform magnetic field

This work concerns the flow of an incompressible viscous fluid past a porous sphere in presence of transverse applied uniform magnetic field, using particle-in-cell method. The Brinkman equations are used in porous region and the Stokes equations for non-porous region. At the fluid-porous interface, the stress jump boundary condition for tangential stresses along with continuity of normal stress and velocity components are used. Four known boundary conditions on the hypothetical surface are considered and compared: Happel’s, Kuwabara’s, Kvashnin’s and Cunningham’s (Mehta-Morse’s condition). The hydrodynamic drag force experienced by a porous spherical particle in a cell and hydrodynamic permeability of membrane built up by porous spherical particles are evaluated. The patterns of streamlines are also obtained and discussed. The effect of stress jump coefficient, Hartmann number, dimensionless specific permeability of the porous particle and particle volume fraction on the hydrodynamic permeability and streamlines are discussed. Some previous results for hydrodynamic drag force and dimensionless hydrodynamic permeability have been verified.     

Electrically modulated membrane permeability

Double tracer flux experiments using the neutral solutes ³H₂O and ¹⁴C-sucrose have demonstrated that an applied electric field can change the permeability of a charged membrane supporting a gradient in pH or salt concentration. The field selectively changed the membrane's permeability to ¹⁴C-sucrose, while permeability to ³H₂O was minimally affected. Membrane ultrastructure and permeability were shown to depend on the membrane's fixed charge density and intramembrane salt content. The applied field, in turn, served to change the pH or salt concentration inside the membrane by means of an electrodiffusion process. This modulated electrostatic repulsion forces between membrane molecules and fibrils, thereby changing the interstitial separation distances which determine the effective pore size of the membrane. The proposed mechanism was tested using a theoretical model for membrane transport along with independent measurements of field-related transport properties. Our results suggest that the electric field acts as a switch to control the swelling state and the resulting pore size of the membrane.     

Modeling the pharmacodynamics of passive membrane permeability

Small molecule permeability through cellular membranes is critical to a better understanding of pharmacodynamics and the drug discovery endeavor. Such permeability may be estimated as a function of the free energy change of barrier crossing by invoking the barrier domain model, which posits that permeation is limited by passage through a single “barrier domain” and assumes diffusivity differences among compounds of similar structure are negligible. Inspired by the work of Rezai and co-workers (JACS 128:14073–14080, 2006), we estimate this free energy change as the difference in implicit solvation free energies in chloroform and water, but extend their model to include solute conformational affects. Using a set of eleven structurally diverse FDA approved compounds and a set of thirteen congeneric molecules, we show that the solvation free energies are dominated by the global minima, which allows solute conformational distributions to be effectively neglected. For the set of tested compounds, the best correlation with experiment is obtained when the implicit chloroform global minimum is used to evaluate the solvation free energy difference.     

Modulation of membrane permeability by carbon dioxide

Promoting drug delivery across the biological membrane is a common strategy to improve bioavailability. Inspired by the observation that carbonated alcoholic beverages can increase the absorption rate of ethanol, we speculate that carbon dioxide (CO₂) molecules could also enhance membrane permeability to drugs. In the present work, we have investigated the effect of CO₂ on the permeability of a model membrane formed by 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine lipids to three drug-like molecules, namely, ethanol, 2′,3′-dideoxyadenosine, and trimethoprim. The free-energy and fractional-diffusivity profiles underlying membrane translocation were obtained from μs-timescale simulations and combined in the framework of the fractional solubility-diffusion model. We find that addition of CO₂ in the lipid environment results in an increase of the membrane permeability to the three substrates. Further analysis of the permeation events reveals that CO₂ expands and loosens the membrane, which, in turn, facilitates permeation of the drug-like molecules. © 2019 Wiley Periodicals, Inc.     

Light-regulated permeability of rhodopsin-phospholipid membrane vesicles.

Abstract—Light absorption by rhodopsin in receptor cell membranes initiates the excitation of the receptor cell. Rhodopsin-phospholipid membrane vesicles were studied to localize initial transduction events. Rhodopsin-phospholipid recombinant membranes are thermally stable and light sensitive and may be chemically regenerated after bleaching in the same manner as receptor cell membranes. Rhodopsin-containing vesicles prepared from unsaturated phosphatidylcholine (PCho) or PCho and phosphatidylethanolaminc display kinetics for the metarhodopsin I to II transition which are comparable to those of receptor cell membranes. NMR spectroscopy was used to examine the permeability of the membrane vesicles to added shift (Eu³⁺) or relaxation reagents (Mn²⁺, Co²⁺). Unexposed rhodopsin-phospholipid vesicles are sealed to ion movement and become permeable after light exposure. Selected ions (Ca²⁺, Mn²⁺, Co²⁺) may be photoreleased from the interior of loaded membrane vesicles. The quantity released is proportional to the initial ionic concentration. The number of ions released/rhodopsin bleached is dependent on the light intensity, and high yields (40–160) of Ca²⁺/rhodopsin bleached are observed at low levels of light bleaching. The present results indicate that rhodopsin spans the phospholipid bilayer membrane, and are consistent with an increase in the permeability of the membrane initiated by light excitation of rhodopsin.     

Restoring permeability barrier function to outer membrane

A recent issue of Cell published two papers resulting from the collaboration between the Kahne and Silhavy laboratories [1,2]. These studies, possibly initiated as an effort to identify the target of action of vancomycin with lipophilic substitutions, resulted in the discovery of a protein complex involved in the assembly of outer membrane proteins.     

Gas permeability of high-temperature-resistant silicone polymer-vycor glass membrane

A high-temperature-resistant heterogeneous poly (dimethyl siloxane) membrane was prepared in situ by using monomer gas-phase polymerization in microporous media without employing prepolymerization. The permeation rates for various gases were measured at penetrant pressure up to 233 cmHg and at temperatures between 20°C and 200°C. The permeation rates for low-soluble gases, such as He, H₂, N₂, CO, O₂, and Ar, increased with increasing temperature. On the other hand, the permeation rates for highly soluble gases, such as C₂H₄ and CO₂, decreased with increasing temperature. For all gases, the permeation rate increases or decreases linearly with the increase of temperature. The turning points were observed for all gases in the temperature range of 140-160°C. Permeation rates of most gases decreased with the increase of temperature above the turning point, excepting those of helium and hydrogen.     

Erythrocyte membrane permeability for a series of diols

Erythrocyte membrane permeability coefficients for a series of diols have been defined by the method developed. The method is based on the physical and mathematical modeling of hypotonic hemolysis process. There have been also determined membrane permeability coefficients for erythrocytes treated with p-chloromercuribenzenesulfonic acid monosodium salt (pCMBS), which is known to block aqueous protein channels. Permeating process is shown to be conditioned both by hydrophilic/hydrophobic properties of the molecules and their geometrical parameters. The obtained results propose that, when exceeding the molecules diameter over a value of 4 A, the permeability coefficient reduces due to decreasing of flow through the aqueous protein pores of a constant size. Permeability coefficients for comparatively hydrophobic molecules are almost directly proportional to the coefficients of partition between hydrophobic and hydrophilic phases, by pointing to a lipid way of permeation of these molecules through erythrocyte membranes.     

Membrane structure and its correlation with membrane permeability

Methods for the investigation of pore and molecular structure of synthetic membranes are reviewed. Membranes are classified as coarse-porous, fine-porous, and solution-diffusion membranes, on one hand; and homogeneous, asymmetric, and composite on the other, Pore structure of synthetic membranes can be elucidated in detail only by electron and raster electron microscopic investigations. Inspection of molecular structure requires diversely specific test probes such as low-energy neutron scattering and/or diffraction, and gas sorption and permeability measurements, as well as thermodynamic and thermomechanical analysis. Other methods used to elucidate pore and molecular structure of synthetic membranes are discussed and, concurrently, membrane structure is correlated with membrane permeability.     

Theoretical estimation of differential coefficients of ion-exchange membrane diffusion permeability

It has been shown that the differential coefficients of the diffusion permeability of MK-40 and Nafion 425 sulfonic cation-exchange membranes to solutions of diverse electrolytes can be calculated within the framework of the theory of generalized conductivity of structurally inhomogeneous membranes with the use of model transport-structural parameters. The calculation has been performed on the basis of experimentally measured concentration dependences of the specific electrical conductivities and diffusion fluxes of electrolytes through membranes into water. The results of the model calculation are in satisfactory agreement with the data obtained by an independent method without resorting to notions of the structural organization of a membrane.     

Development of rigid biporous polymeric adsorbent for protein chromatography

Summary A novel biporous poly (glycidyl methacrylate-triallyl isocyanurate-divinylbenzene) resin (denoted as Resin C) was prepared byin-situ co-polymerization with both superfine granules of sodium sulfate and the solvents toluene and n-heptane as porogenic agents. This material is based on a novel porogenic mode of a combination of both solid granules and solvents. The properties of Resin C were characterized, and then compared with both Resin A (where only solvents as porogen) and Resin B (where only solid granules are used as porogen). The biporous resin showed good mechanical performance, high dynamic adsorption capacity and column efficiency at high flow-rates. These factors indicate the biporous resin as a promising adsorbent for high-speed protein separation by chromatography.     

Gas permeability of combined membrane systems with mobile liquid carrier

Gas transfer in a membrane system called a selective membrane valve (SMV) is studied. The SMV is a system consisting of two mobile gas phases, one mobile liquid phase, and two membranes acting as interfaces between gas and liquid. Such a membrane system has supplementary variable parameters and is designated for the separation of multicomponent gas mixtures. System permeability for individual gases (CO₂, O₂, and H₂) and its dependence on a flow rate of a liquid phase are studied. Time dependences of the non-steady state transfer of CO₂ through the immobile layer of chemisorbent (aqueous K₂CO₃ solution) at its different concentrations are studied for the first time. Two theoretical models are developed: the model of gas transfer through a selective membrane valve system with a mobile liquid absorbent (in the absence of chemical interaction) and the model of a non-steady-state transfer of CO₂ through the immobile layer of aqueous potassium carbonate solution. The first model makes it possible to determine gas-to-liquid diffusion coefficients; the second model permits us to plot kinetic permeability curves and to calculate system permeability with allowance for the CO₂ transfer accompanied by reversible chemical reaction with the carrier. The model dependences agree well with the experimental data.     

Chlorine-induced permeability recovery for low-pressure membrane filtration of natural waters

Chlorine treatment is widely used by membrane filtration plants to recover the loss of membrane permeability encountered in low-pressure membrane (LPM) filtration of natural waters. However, there are few methodical studies in the literature addressing the efficacy of chlorine in cleaning membranes. Thus, the purpose of this study was to assess chlorine-induced permeability recovery (CIPR) of LPMs using the Ct concept (product of chlorine dose concentration and treatment time) commonly employed in the disinfection literature. The experimental work was conducted by evaluating the efficacy of CIPR for a membrane and water combination under variable Ct exposures and determining the presence of minimum effective Ct exposure and proper empirical models for the CIPR. The results showed that the efficacy of CIPR depended on both C and t. A minimum Ct exposure of approximately 2 × 10⁵ (min mg)/L was required for effective CIPR, and the relationship between the residual fouling and chlorine exposures was best fitted using a revised Chick–Watson model. These results may be explained by a conceptual model that considers CIPR as a sequential process of oxidation of organic foulants and diffusional detachment of the reaction products from membrane surfaces. Additional work is needed to validate the applicability of the model to other waters and membranes.