Intrinsic Permeability Research Articles

Removing emerging perfluoroalkyl ether acids and fluorotelomer sulfonates from water by nanofiltration membranes: Insights into performance and underlying mechanisms

Although nanofiltration (NF) has been widely reported for removing long-chain per- and polyfluoroalkyl substances (PFAS) from water, little is known about the correlations between removal efficacy and PFAS/membrane characteristics, especially for emerging PFAS with shorter polyfluoroalkyl chain or containing fluoroether moieties. A systematic study of treatment of structurally diverse PFAS by NF can help predict the behavior of more unknown compounds during NF process. In this study, we conducted filtration experiments with five commercial NF membranes. Results show that seven legacy PFAS, three emerging perfluoroalkyl ether acids (PFEA) and two fluorotelomer sulfonates (FTS) can be removed simultaneously during the NF process, with rejection ranging from 66.0% to > 99.9%. The removal efficiency of five membranes decreased successively as DK > NF90 > XN45 > NF270 > DL. Rejection of FTS and PFEA by DK membranes were 88.3% to 97.1% and 81.7% to > 99.9%, respectively. Correlation analysis revealed that PFAS molecular structure and membrane characteristics significantly affect PFAS rejection. PFAS molecular weight (MW) and hydrophobicity (logKow) and membrane intrinsic structural characteristics (e.g., molecular weight cut-off (MWCO), water permeability, and salt selectivity) are among the most significant parameters impacting PFAS removal. The findings imply that both steric hindrance and hydrophobic interactions contribute to PFAS rejection. Moreover, the mass of PFAS adsorbed on the membrane was positively correlated with their molecular parameters (i.e., MW and logKow) and weakly correlated with membrane properties, suggesting that the adsorption and rejection of PFAS have similar driving forces. This study provides critical insights into the application of NF for emerging PFAS removal for both the scientific community and private industry, concerning water purification processes and remediation of thousands of PFAS-impacted sites.

Effective stress effect and slippage effect of gas migration in deep coal reservoirs

The deep coal reservoir is in a high in-situ stress regime, and the drop in pore pressure during the coalbed methane extraction can induce significant slippage effect and effective stress change. Both of them play a competitive role in permeability evolution. In our research, coal seepage experiments under variable bulk stress and pore pressure paths are performed to investigate the slippage effect and effective stress effect during gas migration in deep coal seams. The results show that the gas flow pattern changes from effective stress–control to slippage effect–control during the increase of bulk stress. Because of the dual pore structure and rich clay, coal presents microscopically inhomogeneous assemblage in mechanical and seepage properties. It makes the effective stress coefficient (ESC) for permeability, κ, always greater than 1, up to 1.94–2.64. By substituting the elastic modulus of the bedding for that of the clay in the coal, the clay-particle model can be used to explain the κ > 1. The linear-Klinkenberg equation is no longer applicable to the correction of gas slippage effect in deep coal reservoir, but conforms to the double-slip-Klinkenberg equation. Slippage effect weakens the stress sensitivity of permeability. As the effective stress increases, the slippage coefficient b increases accordingly, and the slippage effect becomes more pronounced. The gas flow pattern in deep coal reservoir is basically in the region of slippage flow, and the slippage effect cannot be ignored in gas migration. Furthermore, the anisotropy of κ is weakened in deep coal reservoirs, and the intrinsic permeability of coal, k∞, has the strongest stress sensitivity to σ3.

Periodic Flow Through Regenerator Fillers Made from Packed Spherical Microparticles

Periodic flow of gases at cryogenic temperatures through microporous structures occur in the regenerators of Stirling-type cryocoolers. For computational fluid dynamics simulation of such flows using the Darcy–Brinkman–Forchheimer model, permeability and inertial coefficients are needed. Experimental pore-level characterization of such regenerators is difficult due to their microporous structure, and the occurrence of near-zero instantaneous flow rates and extraction of these parameters from experimental data can involve significant uncertainty. In this work, by three-dimensional direct simulation, the hydrodynamic parameters are found for flow through a metallic fill powder common to some recent cryocooler regenerators that operate at very low temperatures. The intrinsic permeability and the Forchheimer coefficients are found for parameter ranges of interest to pulse-tube cryocoolers and are compared with reported extracted experimental values. The permeability and Forchheimer coefficients are correlated to be suitable for application in computational fluid dynamics codes.

Physical property characterization of the Waipapa greywacke: an important geothermal reservoir basement rock in New Zealand

Greywacke basement rocks in New Zealand host conventional geothermal reservoirs and may supply important hotter and deeper geothermal energy resources in the future. This work combines petrological analyses and physical property measurements of Waipapa greywacke, a basement unit hosting New Zealand geothermal reservoirs, in order to understand better how structurally controlled flow networks develop and channel geothermal fluids within it. Results show intact Waipapa greywacke has high tensile and triaxial compressive strengths, and low intrinsic permeability (~ 10–21 m2). Permeability of intact Waipapa greywacke does not increase significantly during triaxial loading to failure and is accompanied by minimal changes ultrasonic wave velocities. These data taken together suggest that microcrack development during brittle deformation is very limited. Upon failure, the permeability increases by two orders of magnitude and shows similar permeability to tests performed on synthetic, single, mode I fractures in intact Waipapa greywacke. Permeability persists in Waipapa greywacke fractures under confining pressures of at least 150 MPa. It is concluded that Waipapa greywacke rocks will not allow fluid flow through the matrix of the rock and that substantial geothermal fluid flow will only occur through macrofracture networks.

Permeability extraction from multiple well logs using particle swarm optimization based factor analysis

In this paper, we present an innovative factor analysis algorithm for hydrocarbon exploration to estimate the intrinsic permeability of reservoir rocks from well logs. Unlike conventional evaluation methods that employ a single or a limited number of data types, we process simultaneously all available data to derive the first statistical factor and relate it to permeability by regression analysis. For solving the problem of factor analysis, we introduce an improved particle swarm optimization method, which searches for the global minimum of the distance between the observed and calculated data and gives a quick estimation for the factor scores. The learning factors of the intelligent computational technique such as the cognitive and social constants are specified as hyperparameters and calculated by using simulated annealing algorithm as heuristic hyperparameter estimator. Instead of the arbitrary fixation of these hyperparameters, we refine them in an iterative process to give reliable estimation both for the statistical factors and formation permeability. The estimated learning parameters are consistent with literature recommendations. We demonstrate the feasibility of the proposed well-log analysis method by a Hungarian oilfield study involving open-hole wireline logs and core data. We determine the spatial distribution of permeability both along a borehole and between more wells using the factor analysis approach, which serves as efficient and reliable multivariate statistical tool for advanced formation evaluation and reservoir modeling.

Towards the estimation of concrete intrinsic permeability

This paper presents the development and evaluation of a practical, adequate, and appropriate means of estimating the intrinsic permeability of concrete. The study is based on the author's own experimental results and observations reported in literature. A correlation model between effective and intrinsic permeability is developed, and a means of estimating intrinsic permeability for planned concrete elements from material and mix properties is investigated. The multiplicative effect of compressive strength and coarse aggregate content is shown. Although various multiple linear regression models are considered, it is shown that practical simple linear regression models can be considered for the estimation of intrinsic permeability of existing or planned concrete elements.

High-reliability data processing and calculation of microstructural parameters in hydroxyapatite scaffolds produced by vat photopolymerization

The accurate determination of mass transport and microstructural properties within highly-porous trabecular bone specimens and substitutes still represents a challenge due to the complex arrangement in the three-dimensional space, where adjacent pores can be hardly identified due to the open-cell disordered structure resulting from the reciprocal alternation of struts and voids. In the present study, the complete set of mass transport properties of hydroxyapatite (HA) scaffolds produced by digital light processing (DLP)-based vat photopolymerization was determined by applying the recent Ergun-Wu resistance model. Input data include the intrinsic permeability of the scaffolds, obtained by acoustic experimental measurements, and the equivalent pore diameter, calculated as a function of total porosity and average trabecular size from accurate micro-computed tomography (μ-CT) scans. The results, corroborated by an accurate and robust statistical analysis, were compared with previous literature data and confirmed a feasible and concrete application of DLP-derived HA scaffolds in clinical practice.

Vertical vibration of a rigid strip footing on a half-space of unsaturated porous soil

This study presents an analytical solution to the compliance coefficient of rigid strip footings lying on an unsaturated porous soil half-space when subjected to vertical vibration. Using the Fourier transform techniques, the complex interaction between unsaturated soils and rigid strip foundations is transformed into a mixed boundary-value problem based on the developed framework of Biot’s model. The wavenumber domain auxiliary function and boundary conditions are used to convert the governing equations to a pair of dual integral equations. To yield the compliance function, the integral equations are transformed into a system of inhomogeneous linear equations by utilizing hypergeometric polynomials and Bessel functions. The proposed analytical solution is verified against existing solutions to interactions between foundations and saturated soil or single-phase soil by adjusting the parameters in the unsaturated soil model. Additionally, the impacts of soil skeleton saturation, intrinsic permeability, and Poisson’s ratio of unsaturated soil on the dynamic compliance coefficient of rigid strip footings are examined. It is shown that the Poisson’s ratio of the soil skeleton and the soil saturation at critical saturation have a significant effect on the dynamic compliance coefficient, but have a negligible effect on the intrinsic permeability.

Functionalized two-dimensional g-C3N4 nanosheets in PIM-1 mixed matrix membranes for gas separation

The virtuous of two-dimensional (2D) nanomaterials in high aspect ratio and tunable surface functionality have geared towards their implementation in mixed matrix membranes (MMMs) for advanced gas separation. In this study, the effects of functionalized 2D nanosheets in the MMMs for gas separation were investigated. The graphitic carbon nitride (g-C3N4) nanosheets were modified with various functional groups namely sulfuric acid group, aliphatic amino group, aromatic amino group, and sulfonic group via four different synthesis approaches. Polymers of intrinsic microporosity (PIMs, e.g., PIM-1) was selected as the continuous polymer phase due to its intrinsic high permeability and comparable selectivity towards different gas pair. The sulfonic acid functionalized g-C3N4 MMMs (e.g., PIM-1/g-C3N4-D) imparted high separation properties ascribed to the great CO2 affinity induced by the sulfonic acid groups. In particular, PIM-1/g-C3N4-D (99:1) MMM demonstrated promising CO2 separation performance, with CO2 permeability of 3740 Barrer and CO2/N2 selectivity of 19.8. Moreover, at 5 wt% loading of g-C3N4-D, the H2/N2 and O2/N2 separation of the MMMs had exceeded the 2008 Robeson upper bound, thanks to the periodic triangular ultramicropores in g-C3N4 that favor precise sieving of small gases. These results pave the way in using the developed membranes in practical H2 purification, air separation and CO2 capture.

Lattice Boltzmann Model for Oil/Water Two-Phase Flow in Nanoporous Media Considering Heterogeneous Viscosity, Liquid/Solid, and Liquid/Liquid Slip

Summary Due to intermolecular interactions, the oil/water two-phase flow behaviors in shale nanoporous media are complex and diverse, which cannot be characterized by a conventional continuum flow equation. In this work, we propose a nanoscale multirelaxation-time multicomponent and multiphase lattice Boltzmann method (MRT-MCMP-LBM) based on pseudopotential format to simulate oil/water two-phase flow at the pore scale. The nanoscale effect of liquid/solid slip, liquid/liquid slip, and heterogeneous viscosity due to liquid/solid and liquid/liquid molecular interactions is fully taken into account. We use the Laplace test, contact angle, and phase separation to calibrate the desired interfacial tension (IFT) and wettability. Then, the proposed model is verified by comparing to molecular simulation and theoretical results. Although the liquid/solid slip can increase the oil/water flow capacity, it can reduce the relative permeability due to the increased intrinsic permeability. The oil/water interfacial slip can increase the relative permeability of the nonwetting phase, which can be greater than unity because the effect of oil/water interfacial slip is greater than that of nonwetting-phase/wall slip. We also calibrate the microscopic parameters of oil and water flow in inorganic and organic pores by comparing their velocity profiles to those from molecular dynamics (MD) simulations. The oil/water two-phase flow in shale nanoporous media indicates that with a higher total organic carbon (TOC) content, oil relative permeability is lower due to the more significant adverse nanoscale effect. The proposed model can be potentially applied to simulate shale oil/gas/water multicomponent and multiphase (MCMP) flow, imbibition, CO2 huff ‘n’ puff, and geological sequestration.

Drying of mortar at ambient temperature studied using high resolution neutron tomography and numerical modeling

The drying of cement-based materials, naturally occurring in most civil engineering contexts, affects their thermal, hydraulic and mechanical properties and is a leading contributor to the loss of their durability potential. The techniques conventionally employed to study this moisture transfer, such as gravimetry weight loss and point-wise sensor-based measurements, are often destructive and cannot characterize the local driving phenomena in 4D (3D+time), essential given the highly heterogeneous nature of the involved processes. Conversely, full-field techniques, and notably neutron tomography, are non-invasive and ideal for measuring the moisture transport process due to the high attenuation of neutron by hydrogen.In this study, the moisture distribution of a set of cylindrical mortar samples was characterized at different hydric states, as imposed through drying in a thermo-hydrically controlled environment (T=20 °C, RH=35%). The lateral surfaces of the samples were sealed to impose a unidirectional moisture flow. The main phases of the mortar (aggregates, cement paste and voids), visible at the 30μm resolution adopted, were separated, and saturation profiles were deduced and validated against the mortar mixture ratios and weight loss measurements.Besides the intrinsic interest of the spatio-temporal evolution of the local extracted saturation, these hydric gradients are essential to calibrate numerical models, as the commonly used Finite Element model presented here. A minimization algorithm was developed for this purpose to automate, optimize and ensure a more objective numerical–experimental calibration procedure. This has allowed the identification of key hydric parameters such as the convective exchange coefficient and the intrinsic permeability.

Numerical analysis of soil desaturation by an air injection method

A numerical analysis is conducted to evaluate the effective radius of air advance (Reff) in coarse-grained, saturated, sandy deposits improved by means of air injection (i.e., soil desaturation). It is well-known that the cyclic resistance to liquefaction of a saturated sandy deposit is highly affected by the presence of gas in the void space. A parametric study is performed to investigate the soil’s main hydraulic parameters and air-injection conditions of the transient gas affecting Reff and controlling the desaturation process. The effects of the a) soil-water characteristic curve, b) intrinsic permeability, c) injection pressure, and d) duration of air injection are investigated. It is shown that the injection pressure and soil’s intrinsic permeability are the main factors influencing the extent of Reff. The analysed cases showed that, for a fixed injection pressure, the soil will achieve a maximum value for Reff. This threshold value is reached more rapidly when the soil’s intrinsic permeability increases. The results aim to shorten existing knowledge gaps and contribute to the development of design methodologies for air-injection desaturation techniques.

Impact of cholesterol and sphingomyelin on intrinsic membrane permeability

Transwell experiments with Caco-2 or MDCK cells are the gold standard for determining the intestinal permeability of chemicals. The intrinsic membrane permeability (P0), that can be extracted from these experiments, might be comparable to P0 measured in black lipid membrane (BLM) experiments and P0 predicted by the solubility-diffusion model. Unfortunately, the overlap between experimental P0,Caco-2/MDCK and P0,BLM data is very small. So far, differences between both approaches have been attributed to the cholesterol and sphingomyelin content of cell membranes, but the database is too sparse to thoroughly test this theory. To create a diverse dataset, we measured P0,BLM of ten chemicals in BLM experiments using DPhPC and DPhPC/cholesterol/sphingomyelin membranes. The results were compared to predicted BLM data and experimental Caco-2/MDCK data obtained from literature. While P0,BLM of all chemicals was well predicted by the solubility-diffusion model, P0,Caco-2/MDCK was only predictable for rather hydrophilic compounds with logarithmic hexadecane/water partition coefficients below −0.5. The effect of cholesterol and sphingomyelin on P0,BLM was negligibly small.

One Assay, Two Vital Values‐Estimating Intrinsic Permeability and Efflux Using MDCK‐MDR1 Assay

BackgroundIntestinal intrinsic permeability and transporter mediated efflux are two major determinants of oral absorption. Typically, wild type Madin‐Darby canine kidney cells (MDCK) and MDCK cells transfected with the human MDR1 gene (MDCK‐MDR1) are used to evaluate intrinsic permeability and efflux, respectively. The MDCK assay provides intrinsic permeability but lacks transporter mediated efflux. Conversely, the MDCK‐MDR1 assay provides efflux ratio and “apparent permeability”. However, the apparent permeability can differ significantly from intrinsic permeability due to efflux. Traditionally, both assays (MDCK, MDCK‐MDR1) are applied separately and sequentially, which can be time‐consuming and costly.In this study, we present a novel approach to estimate intrinsic permeability and efflux simultaneously using the MDCK‐MDR1 assay alone. Intrinsic permeability can be calculated using a scaling method by combining the 3 parameters (bi‐directional apparent permeability values and efflux ratio) determined from the MDCK‐MDR1 assay.MethodsTest compounds of varying permeability and efflux ratios were used to assess the validity of the hypothesis. Results from the MDCK, MDCK‐MDR1 and caco‐2 assays were analyzed. Efflux ratio is estimated by dividing the apparent permeability from the basolateral to apical direction (PappBA) by the apparent permeability from the apical to basolateral direction (PappAB). Different averaging methods were used to calculate intrinsic permeability from MDCK‐MDR1 assay, and the measured intrinsic permeability from the MDCK assay was used as a comparison to find the most accurate averaging method.ResultsOf the different scaling and averaging methods used for estimating intrinsic permeability from MDCK‐MDR1 assay, the best method we found was a “quotient” scheme where calculated intrinsic permeability was adjusted based on the magnitude of efflux ratio. With this adjustment, both the intrinsic permeability and efflux ratio can be reliably obtained from the MDCK‐MDR1 assay for compounds with a wide range of efflux ratios. The calculated intrinsic permeability from the MDCK‐MDR1 assays aligns within 2 fold of the permeability values determined from the MDCK assay. Results from the caco‐2 cell line were also evaluated and applicable to the method mentioned above. Several hypotheses were formulated regarding why the “quotient” method was a better fit than simple apparent permeability averaging.ConclusionThe strategy presented here provides an efficient and effective method to estimate both intrinsic permeability and efflux solely based on the MDCK‐MDR1 assay. Compared to the traditional approach of using MDCK and MDCK‐MDR1 assays separately, the method used here requires less time, cost, and compound for testing. This is particularly attractive for early drug discovery screening needs.

Estimation of uniaxial compressive strength and intrinsic permeability from ultrasounds in sedimentary stones used as heritage building materials

This paper combines ultrasonic parameters recorded from P- and S- waves and effective porosity to estimate uniaxial compressive strength, σC, and intrinsic permeability, k - two of the most crucial physical parameters used in stone conservation studies. The ultrasonic parameters have been chosen because they are sensitive to the microstructural properties of stones which influence both σC and k differently. Velocities of compressional or primary, Vp, and shear or secondary, Vs, elastic waves are related to porosity and the mineralogical composition; the waveform attenuation is related to the presence of vuggy macropores and pore and particle size; and the wavelength is related to the pore and particle size. Fifteen types of stones used in the Spanish built heritage were measured including calcarenites, sandstones, dolostones and travertines. Several simple and multiple predictive expressions for σC and k are fitted, which are quantified through the Pearson correlation coefficient, R. Curve fitting improves as the number of petrophysical parameters taken into account in the multiple linear regressions increases. The obtained Pearson's correlations values for σC are slightly higher than for k. The best correlation for σC (R = 0.921) and k (R = 0.903) is found when the predictive equation incorporates all of the elastic wave parameters obtained non-destructively, and the connected porosity. In general, effective porosity is statistically the most significant variable of the fitted regressions. The σC and k estimation from all the ultrasonic parameters, without considering connected porosity, shows a good correlation (R = 0.852 and 0.864, respectively). The addition of Vs to multiple regressions does not significantly improve the goodness of the fit. Consequently, the measurement of Vs is unnecessary as it is difficult and time-consuming. Finally, results also show that vuggy porosity (present in travertines) influences waveform attenuation and σC and k differently, relative to other microstructural properties; limiting the techniques use for stones with this type of porosity. Estimating σC and k using ultrasonic parameters exclusively is advantageous as the estimations can be obtained non-destructively using portable equipment, while also providing an acceptable goodness of fit.

Effect of compressive stress on the intrinsic permeability of concrete

Intrinsic permeability of concrete is a fundamental material property governing its durability and the development of pore pressure during fire exposure. Qualitative studies reported in literature suggests a slight decrease in effective permeability under typical service loading levels. However, the extent of this reduction has not been studied quantitatively in relation to typical observational variance. Moreover, no such results are reported for intrinsic permeability. This study shows that, under typical service compressive stress levels, the reduction in intrinsic permeability can be considered negligible.

Scientific Results of the Hydrate-01 Stratigraphic Test Well Program, Western Prudhoe Bay Unit, Alaska North Slope

The United States Department of Energy, the MH21-S Research Consortium of Japan, and the United States Geological Survey are collaborating to enable gas hydrate scientific drilling and extended-duration reservoir response testing on the Alaska North Slope. To feasibly execute such a test, a location is required that is accessible from existing roads and gravel pads and that can be occupied without disrupting ongoing industry operations. A review of potential locations meeting these criteria determined the likely occurrence of gas hydrate in two fine-grained marginal-marine sands of Tertiary age in the vicinity of the inactive “Kuparuk State 7-11-12” exploration pad in the western Prudhoe Bay Unit (PBU). Existing well and seismic data for that site were insufficient to preclude the potential for free gas occurrence within the deeper (and most prospective) target sand. Therefore, with support from the PBU Working Interest Owners, Alaska Department of Natural Resources, and Petrotechnical Resources Alaska, the Hydrate-01 Stratigraphic Test Well (STW) was drilled in December 2018 to confirm the suitability of the site for future gas hydrate scientific testing. The Hydrate-01 well was successfully drilled to −3290 ft (1003 m) subsea vertical depth at a bottom hole location of approximately 900 ft (∼275 m) east of the surface location. The drilling program featured acquisition of a full suite of logging while drilling data, the collection of side-wall pressure cores, and the installation of distributed temperature and distributed acoustic sensor fiber-optic cables. The log data acquired confirmed the occurrence of gas hydrate at high saturation in two target sands. Integrated evaluation of log and sidewall core data provide petrophysical and geomechanical property information that allow for potential reservoir response to depressurization to be simulated. The deeper “B1 sand” is deemed to be most favorable for reservoir response testing as a result of confirmed gas hydrate occurrence in sediments of high intrinsic permeability, location within 100 ft (30 m) of the base of gas hydrate stability, and minimal risk for direct communication with permeable water-bearing (hydrate-free) zones. The shallower “D1 sand” provides a secondary target that is differentiated by colder in situ temperatures and the interpreted direct hydraulic communication to a lower section of non-hydrate-bearing, water-saturated sand. The Hydrate-01 log data also confirm the occurrence of at least one sub-seismic fault in close proximity to the B1 sand reservoir. To better image the distribution of the gas-hydrate-bearing reservoir sections and associated faults, a three-dimensional (3D) vertical seismic profile was conducted in early 2019 using the distributed acoustic sensors installed as part of the Hydrate-01 STW completion. Detailed two-dimensional (2D) and 3D geologic models have been constructed to enable numerical simulations to inform the planning for potential future scientific tests of reservoir response to depressurization at the site.

The slippage effect of concrete gas permeability and the influence of its microstructure

Klinkenberg effect has a significant influence on the test results of gas permeability. To study the gas slippage effect of concrete and its microscopic mechanism, five kinds of concrete with different w/c ratios were designed, and the gas permeability coefficients were measured at seven additional gas pressures and five saturation degrees according to the Cembureau method, the effects of w/c ratio, saturation degree and additional gas pressure on slippage effect were investigated by the Grey Correlation Analysis (GCA) method. Meanwhile, based on the nuclear magnetic resonance (NMR) method, the influences of microstructure parameters on gas intrinsic permeability and slippage factor were studied. Results show that w/c ratio which reflects the microstructure characteristics of concrete, is the most important factor affecting the slippage effect. Moreover, a larger porosity indicates a more obvious slippage effect. The pores in concrete with size of 100–200 nm, have the greatest influence on the gas slippage effect.

Propidium uptake and ATP release in A549 cells share similar transport mechanisms

The lipid bilayer of eukaryotic cells’ plasma membrane is almost impermeable to small ions and large polar molecules, but its miniscule basal permeability in intact cells is poorly characterized. This report describes the intrinsic membrane permeability of A549 cells toward the charged molecules propidium (Pr2+) and ATP4−. Under isotonic conditions, we detected with quantitative fluorescence microscopy, a continuous low-rate uptake of Pr (∼150 × 10−21 moles (zmol)/h/cell, [Pr]o = 150 μM, 32°C). It was stimulated transiently but strongly by 66% hypotonic cell swelling reaching an influx amplitude of ∼1500 (zmol/h)/cell. The progressive Pr uptake with increasing [Pr]o (30, 150, and 750 μM) suggested a permeation mechanism by simple diffusion. We quantified separately ATP release with custom wide-field-of-view chemiluminescence imaging. The strong proportionality between ATP efflux and Pr2+ influx during hypotonic challenge, and the absence of stimulation of transmembrane transport following 300% hypertonic shock, indicated that ATP and Pr travel the same conductive pathway. The fluorescence images revealed a homogeneously distributed intracellular uptake of Pr not consistent with high-conductance channels expressed at low density on the plasma membrane. We hypothesized that the pathway consists of transiently formed water pores evenly spread across the plasma membrane. The abolition of cell swelling-induced Pr uptake with 500 μM gadolinium, a known modulator of membrane fluidity, supported the involvement of water pores whose formation depends on the membrane fluidity. Our study suggests an alternative model of a direct permeation of ATP (and other molecules) through the phospholipid bilayer, which may have important physiological implications.

Indications of ion dehydration in diffusion-only and pressure-driven nanofiltration

Recent insights into the permeation of small ions through polyamide membranes highlighted the role of ion dehydration in the transport and selectivity observed. However, such insights were a by-product of studies exploring different transport phenomena without a systematic methodology that focuses on ion dehydration itself. In this study, we quantified the intrinsic permeability and its underlying Eyring's enthalpy and entropy of activation for a systematic set of cations and anions in polyamide nanofiltration membranes to gain better understanding of ion dehydration. Our results in a diffusion-only system expose a distinct correlation between the hydration strength of the ions and the enthalpic barrier they experience during permeation, with a permeability order that is similar to the mobility order in solution. Smaller entropic losses are observed for smaller bare ions, indicating their higher freedom of motion after dehydration compared to larger bare ions. Comparing the measured activation enthalpies to quantum chemical calculations for the ions' hydration in solution suggests that ions are only partially dehydrated. Last, our simulated ion permeability at higher temperatures and experimental results in a pressure-driven system expose higher permeation rates with reversed ion-ion selectivity, indicating the activation of ion transport in the form of ion dehydration when additional energy is supplied. • Transport of monovalent ions is explored in diffusion-only and pressurized NF. • More strongly hydrated ions face higher enthalpic barrier during permeation. • Smaller bare ions face lower entropic losses during permeation. • Experimental barriers correlate to simulated stripping of 1–3 water molecules. • Diffusion-only and pressurized filtration expose reversed ion-ion selectivity.