Solute Retention Research Articles

Modification of sand with Fe-Zn oxides: an alternative strategy to improve adsorption of phosphate from artificial wastewater treatment

ABSTRACT In this work, Fe-decorated quartz sand (FS), Fe-Mn bimetallic cation-decorated quartz sand (FMS) and Fe-Zn bimetallic cation-decorated quartz sand (FZS) were synthesised from ordinary quartz sand (QS). Iron, iron-manganese and iron-zinc oxides were stably formed on the surfaces of FS, FMS and FZS, respectively. The specific surface area of FZS (1.0497 m2/g) increased to more than 320% against that of QS (0.2482 m2/g). The obtained samples were evaluated for the removal of phosphate from artificial wastewater. Parameters that can affect adsorption process include solution phosphate concentration, pH and retention time, which were investigated by bath adsorption experiments. Under the optimal experimental conditions (pH value 4.0, initial concentration of phosphate 15 mg/l, temperature 25°C, retention time 150 min and adsorbent dose 5 g), the removal efficiency of phosphate by FS was higher than that of QS, FS and FMS and the maximum phosphate adsorption capacity (qmax) provided by FZS is 0.18 mg/g. Furthermore, the kinetics of phosphate adsorption fit well with the pseudo-second-order model, indicating that adsorption of phosphate on the Fe-Zn co-decorated quartz sand occurred through chemisorption, and the Langmuir adsorption isotherm model (R2 = 9944) is more suitable for adsorption capacity prediction than the Freundlich adsorption isotherm model (R2 = 0.9427). The results show that quartz sand can be modified effectively, which has great practical application potential in water treatment.

Surface-bubble-modulated liquid chromatography: an experimental strategy for identification of molecular processes of solute retention in reversed-phase separation systems.

Molecular level understanding of the chemistry at the aqueous/hydrophobe interface is crucial to separation processes in aqueous media, such as reversed-phase liquid chromatography (RPLC) and solid-phase extraction (SPE). Despite significant advances in our knowledge of the solute retention mechanism in these reversed-phase systems, direct observation of the behavior of molecules and ions at the interface in reversed-phase systems still remains a major challenge and experimental probing techniques that provide the spatial information of the distribution of molecules and ions are required. This review addresses surface-bubble-modulated liquid chromatography (SBMLC), which has a stationary gas phase in a column packed with hydrophobic porous materials and enables one to observe the molecular distribution in the heterogeneous reversed-phase systems consisting of the bulk liquid phase, the interfacial liquid layer, and the hydrophobic materials. The distribution coefficients of organic compounds referring to their accumulations onto the interface of alkyl- and phenyl-hexyl-bonded silica particles exposed to water or acetonitrile-water and into the bonded layers from the bulk liquid phase are determined by SBMLC. The experimental data obtained by SBMLC show that the water/hydrophobe interface exhibits an accumulation selectivity for organic compounds, which is quite different from that of the interior of the bonded chain layer, and the overall separation selectivity of the reversed-phase systems is determined by the relative sizes of the aqueous/hydrophobe interface and the hydrophobe. The solvent composition and the thickness of the interfacial liquid layer formed on octadecyl-bonded (C18) silica surfaces are also estimated from the bulk liquid phase volume determined by the ion partition method employing small inorganic ions as probes. It is clarified that various hydrophilic organic compounds as well as inorganic ions recognize the interfacial liquid layer formed on the C18-bonded silica surfaces as being different from the bulk liquid phase. The behavior of some solute compounds exhibiting substantially weak retention in RPLC or the so-called negative adsorption, such as urea, sugars, and inorganic ions, can rationally be interpreted with a partition between the bulk liquid phase and the interfacial liquid layer. The spatial distribution of solute molecules and the structural properties of the solvent layer on the C18-bonded layer determined by the liquid chromatographic methods are discussed in comparison to the results obtained by other research groups using molecular simulation methods.

Highly porous ultrathin polyamide membranes for fast separation of small molecules from organic solvents

Membranes with permselective performance as well as high stability in harsh solvents are urgently desired for energy-efficient precise chemical separations. In this work, we utilize an adamantane diamine as a molecular building block to fabricate thin-film composite polyamide membranes for high-performance organic solvent nanofiltration (OSN). The bulky, cage-like adamantane structure acts as a molecular-level steric hindrance unit to inhibit polymer chain packing which generating interconnected micropores within the interfacially polymerized polyamide layer. This translates into high membrane methanol permeance of 20.6 L m-2 h-1 bar-1 and 94.7% retention to organic dye molecules with molecular weight down to 327 g mol-1. Furthermore, the membrane demonstrates high stability in different organic solvents taking advantage of the crosslinked rigid structure, which shows constant solute retention throughout a 180 h continuous filtration experiment with a DMF solution containing methyl orange as feed solution. Employing rigid and bulky molecular features in selective layer is thus demonstrated to significantly promote the polyamide membrane permeability and solvent resistance without compromising the overall selectivity.

Theoretical study on solute migration and band broadening occurring in pressure-enhanced liquid chromatography

Upon recently studying the use of pressure gradients during liquid chromatography (LC), it was noted that pressure differentials across a column can have a significant impact on peak shape, not just retention as has been noted several times before. Theoretical models and thought experiments were performed here to more carefully study these effects. Two situations have been elucidated. The first is one that reflects a protein reversed phase separation wherein solute retention increases with pressure. In this condition, it has been found that a positive pressure gradient will result in band broadening while a negative pressure gradient will help yield sharper peaks. The second case that has come to be better appreciated is when solute retention decreases with pressure, which can occur in protein ion exchange (IEX) and hydrophobic interaction chromatography (HIC). In this situation, a positive pressure gradient will conversely result in peak sharpening, and a negative pressure gradient will introduce band broadening. These observations have facilitated making new fundamental understandings on pressurized separations which has in turn made it possible to begin envisioning new ways of and reasons for applying pressure enhanced LC methods.

Anionic amphiphilic copolymers as potential agents for enhanced oil recovery

To develop “smart fluids” for enhanced oil recovery from reservoir rocks, comb-type amphiphilic copolymers were synthesized through free radical polymerization (FRP) of: (i) the hydrophilic, anionic monomer 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) that offer a hydrophilic character to the final copolymers; (ii) the weakly acidic hydrophilic monomer acrylic acid (AA); (iii) the hydrophobic monomer dodecyl methacrylate (DMA). The polymers were characterized by Proton Nuclear Magnetic Resonance (1H NMR), Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR), fluorescence probing, Dynamic Light Scattering (DLS) and electrophoresis. Stable polymer solutions were prepared without and with the presence of salts (NaCl, CaCl2, MgSO4). The dynamic air/water surface and oil/water interfacial tensions were measured by the pendant drop method, and their steady-state values were estimated with fitting to asymptotic relations predicting the long-time behavior. Moreover, the wettability of water/air and water/oil to glass or poly(methyl methacrylate) (PMMA) surface was quantified by measuring the contact angles. Oil-in-water Pickering emulsions were prepared by mixing n-dodecane with polymer solutions and their stability was evaluated macroscopically with optical inspection, and microscopically by measuring the oil drop size distribution and shear viscosity. Polymer solutions and Pickering emulsions were tested as agents for the displacement of the residual n-dodecane from a glass-etched pore network. The long-lasting retention of polymer solution in the pore network makes the solid surface more hydrophilic, facilitating the fission of oil ganglia into smaller ones which are mobilized easier, resulting in a final EOR efficiency between 10% and 18%. When using an emulsion as displacing fluid, the viscosity ratio and capillary number increase by orders of magnitude, the viscous forces prevail against the capillary ones, and the growth pattern becomes a frontal drive leading to a high EOR efficiency of ∼94%.

Preparation, Characterization, and Chromatographic Evaluation of Nickel Oxide Deposited Silica Stationary Phase in Hydrophilic Interaction Liquid Chromatography

Nickel oxide deposited silica stationary phase was prepared by liquid phase deposition and characterized. Its chromatographic performance was evaluated using several compounds such as typical polar compounds and benzimidazoles as probes. The effects of mobile phase variables such as acetonitrile content, salt concentration, and pH on the chromatographic behavior, thermodynamics, and kinetics of these compounds were investigated to reveal the retention mechanism. The results showed that the prepared stationary phase exhibited a retention behavior of hydrophilic interaction liquid chromatography, and that multiple retention mechanisms including partitioning, adsorption, ion-exchange, electrostatic attraction, and coordination interactions contributed to solute retention. The coordination of nickel oxide electron-accepting sites and the electron-donating solutes resulted in the mixed-mode retention on stationary phase, which could be very useful for enhancing the chromatographic selectivity for the analytes. The batch-to-batch reproducibility was acceptable with the relative standard deviations of probe retention of less than 9.89%. The prepared nickel oxide deposited silica stationary phase was successfully employed for the separation of several compounds, and it showed better separation effect and different selectivity from silica column and commercial Zorbax NH2 column.

Optimizing the preparative capacity of two-dimensional liquid chromatography based on analytes retention behaviors

In this work, a solute retention optimization method (SRO) was proposed to exploit the purification potential of two-dimensional liquid chromatography (2D-LC). According to our findings, the complementarity of 2D-LC correlates with some specific impurities. In the two methods used in 2D-LC, the retention order of these impurities and target compound is completely opposite. Taking full advantage of the complementarity is crucial to enhance the saturation capacity (wmax) of 2D-LC by SRO. For the purpose of validating the effectiveness of SRO, a reverse-phase liquid chromatography (RPLC) coupled with hydrophilic interaction chromatography (HILIC) was developed to purify p-chlorobenzoic acid from substituted benzenes. By using the overloading effects of analytes as indicators, the wmax of RPLC × HILIC was determined by the bisection method, and finally defined by the extremely high loading volume of 4.9 mL. A touch-peak separation of impurities and the target compound occurred precisely during the secondary separation. The effectiveness of SRO was also verified by the greater purification efficiency of RPLC × HILIC than that of HILIC × RPLC. Subsequently, a RPLC × RPLC method was developed by SRO to prepare the reference materials of caffeine from tea extracts. Only by an analytical C18 column, 15.6 mg of caffeine with the purity of 98.3% was obtained at once with the recovery up to 82.3%. However, without the aid of SRO, the purity rapidly decreased to 62.0%. Compared to other methods, SRO-based 2D-LC offers certain advantages in terms of purity, recovery, and the purification efficiency, suggesting that it is particularly effective in developing preparative 2D-LC facing complex matrices.

Fractionation by ultrafiltration of an aqueous extract of chestnut obtained by pressurized hot water extraction

Different types, ceramic and polyethersulfone, ultrafiltration membranes were evaluated to purify a wood extract obtained in pressurized hot water conditions. Tests were performed at transmembrane pressure (TMP) from 0.4 to 2.0 bars with membrane molecular weight cut-offs ranging from 5 kDa to 100 kDa. The results showed the permeate fluxes were lower than 15 L.h-1.m-², except for the 100 kDa organic membrane, with no influence of the feed flowrate. The retention of total phenolic compounds highly depends on the membrane cut-off but the retention rates of gallic and ellagic acid were not directly link to the cut-off. The retention rate of gallic acid is lower than 10%, when ellagic acid had retention ranging from 75 to 95 % for the membrane 5 kDa. It is suggested that other phenomena could be involved in solute retention, i.e. Donnan effect or solubility, that could explain so large differences.

PS-C18-4: HIGH BODY MASS INDEX IS A RISK FACTOR FOR TRANSITION TO HEMODIALYSIS OR HYBRID THERAPY AND PERITONEAL DIALYSIS-RELATED INFECTION

Objective: Obesity may negatively impact clinical outcomes of peritoneal dialysis (PD) patients. However, obesity is defined differently in Japan, and its impact on PD-related outcomes remains unclear. In current study, we aimed to examine the association of high body mass index (BMI) with the complete hemodialysis (HD) transfer, transition to HD and PD/HD hybrid therapy, peritonitis, catheter exit-site and tunnel infection (ESI/TI), and heart failure-related hospitalization. Design and method: This retrospective cohort study included 120 patients who underwent PD catheter insertion between January 2008 and June 2018. BMI ≧ 25 kg/m2, which was calculated from the height (m) and body weight (kg) at the time of PD catheter insertion, was defined as high BMI. Patients who develop solute retention or fluid overload with PD alone could choose to transfer first to PD/HD hybrid therapy, wherein patients usually undergo PD 5–6 days a week along with once-weekly HD, instead of directly transferring to HD alone. Association between high BMI and outcomes were analyzed by the log-rank test and the Cox proportional hazards models. Results: The follow-up duration was 46.2 (23.3–75.3) months. Time until transfer to HD and hybrid therapy was significantly shorter in the high BMI group than in the low one, whereas time until transfer to HD was not significantly different between both groups (P < 0.001 and 0.18, respectively). Peritonitis-free and ESI/TI-free survival were significantly shorter in the high BMI group than in the low one (P = 0.006 and 0.03, respectively). After adjusting for age, sex, diabetes mellitus, estimated glomerular filtration rate, BMI ≧ 25 kg/m2 remained as a significant risk factor for transferring to HD and PD/HD hybrid therapy, peritonitis, and ESI/TI (hazard ratio [HR] 2.60, P < 0.001; HR 2.08, P = 0.01; HR 2.64, P = 0.02, respectively). Conclusions: High BMI, defined as BMI ≧ 25 kg/m2, is a risk factor for transition to HD and PD/HD hybrid therapy, peritonitis, and ESI/TI. However, high BMI is not associated with early complete HD transfer in Japan, where PD/HD hybrid therapy is commonly used.

Geo-polymer sea sand cubes filled gabions

A gabion is derived from the Old Italian term “large cage.” Caged riprap is utilized for erosion prevention while building foundations or dams. Gabions are commonly used in civil engineering and landscaping projects as they provide a cost-effective erosion control and soil retention solution. They are also known for their flexibility and durability in various weather conditions. The present investigation aims to replace stones or cement mortar elements used in the gabions with the geo-polymer mortar cubes manufactured using the sea sand readily available at the construction site. The mortar cube specimens were prepared using industrial wastes such as ground-granulated blast-furnace slag (GGBS), fly ash (FA), polymerized in the presence of sodium hydroxide (NaOH) solution used as an alkali catalytic liquid and by sea sand as fine aggregate. The mortar cubes of three different mixes with the varied trial mixes of fly ash and GGBS along with the solution of NaOH with different molarities were cast. The cubes were air cured for 7 and 28 days, and the hardened properties were studied. The maximum 28-day compressive strength was found for 30% replacement of fly ash at 10 M solution, i.e., 16.13 MPa A model gabion of 0.5mX0.3mX0.3 m is prepared using a 'Netlon' mesh of geo-synthetic material to indicate the actual application in sea erosion control. The sea sand cubes are filled in the box to obtain a typical gabion filler.

Serum Metabolites Characterization Produced by Cats CKD Affected, at the 1 and 2 Stages, before and after Renal Diet.

Utilizing metabolomics, a tool for measuring and characterizing low-molecular-weight substances (LMWs), to identify eventual changes in response to dietary intervention is novel in cats with chronic kidney disease (CKD), a condition characterized by retention of uremic solutes. This study aims to assess the serum metabolomic profile of cats in early stages of CKD and to compare the serum metabolomic of CKD cats after 60 days of a renal diet to evaluate the effect of dietary intervention on these metabolites. Twenty-five domestic cats were included in the study. Fifteen cats with CKD stages 1 (n = 6) and 2 (n = 9) according to the International Renal Interest Society (IRIS) were included in the renal groups, and a control group consisting of 10 cats was included. All animals were enrolled on a maintenance diet for 30 days before the experimental period. The metabolomics analysis was performed by gas chromatography-mass spectrometry (GC-MS). Partial least squares discriminant analysis (PLS-DA) was performed on Metaboanalyst 4.0 software. Forty-three metabolites were identified. Citric acid and monostearin were altered in the CKD2 group when compared to CKD1 and the control group at T0. A total of seven serum metabolites differed after 60 days of the renal diet: glycine, fructose, glutamic acid, arachidonic acid, stearic acid, creatinine, and urea. Changes were seen in the serum metabolomic profile after 60 days of the renal diet, and some of the metabolites that changed in response to the diet have beneficial effects on health. Overall, metabolomics markers have the potential to identify early stages of CKD, providing insights into the possible pathophysiologic processes that contribute to the development and progression of CKD.

A model for the adsorption process of water dissolved elements flowing into reactive porous media: Characterization and sizing of water mining/filtering systems

This study presents a mathematical model describing the adsorption-desorption process of water dissolved elements onto reactive porous materials during filtering operations performed under dynamic flow conditions. The developed model is based on a reversible second order adsorption kinetic featuring the progressive reduction of the purifying capacity of the filtering material due to the gradual exhaustion of the active sites available for solute retention. It enables the simulation of the performances of water filtering systems through the use of parameters having a clear chemical-physical significance or it can be used for the estimation of these parameters to characterize the adsorption properties of the reactive material. Starting from the same adsorptive conceptual model used for the filtering system marked by ongoing flowing conditions, an adaptation for static systems was performed on the mathematical framework in order to process the same chemical physical parameters in both schemes. Adsorption laboratory tests were carried out to validate the developed model. Results show that the kinetic constants and adsorption capacities (a maximum of about 45 mg g−1 was obtained for the tested material) are highly comparable, both within the same experimental system, and between different experimental setup. This confirms the validity of the developed model which is able to perfectly fit the observed concentration data in all tested configurations.

Exploring tracer information in a small stream to improve parameter identifiability and enhance the process interpretation in transient storage models

Abstract. The transport of solutes in river networks is controlled by the interplay of processes such as in-stream solute transport and the exchange of water between the stream channel and dead zones, in-stream sediments, and adjacent groundwater bodies. Transient storage models (TSMs) are a powerful tool for testing hypotheses related to solute transport in streams. However, model parameters often do not show a univocal increase in model performances in a certain parameter range (i.e. they are non-identifiable), leading to an unclear understanding of the processes controlling solute transport in streams. In this study, we increased parameter identifiability in a set of tracer breakthrough experiments by combining global identifiability analysis and dynamic identifiability analysis in an iterative approach. We compared our results to inverse modelling approaches (OTIS-P) and the commonly used random sampling approach for TSMs (OTIS-MCAT). Compared to OTIS-P, our results informed about the identifiability of model parameters in the entire feasible parameter range. Our approach clearly improved parameter identifiability compared to the standard OTIS-MCAT application, due to the progressive reduction of the investigated parameter range with model iteration. Non-identifiable results led to solute retention times in the storage zone and the exchange flow with the storage zone with differences of up to 4 and 2 orders of magnitude compared to results with identifiable model parameters respectively. The clear differences in the transport metrics between results obtained from our proposed approach and results from the classic random sampling approach also resulted in contrasting interpretations of the hydrologic processes controlling solute transport in a headwater stream in western Luxembourg. Thus, our outcomes point to the risks of interpreting TSM results when even one of the model parameters is non-identifiable. Our results showed that coupling global identifiability analysis with dynamic identifiability analysis in an iterative approach clearly increased parameter identifiability in random sampling approaches for TSMs. Compared to the commonly used random sampling approach and inverse modelling results, our analysis was effective at obtaining higher accuracy of the evaluated solute transport metrics, which is advancing our understanding of hydrological processes that control in-stream solute transport.

Mass Transport of Dye Solutions through Porous Membrane Containing Tannic Acid/Fe3+ Selective Layer.

Tannic acid (TA)-Fe3+ membranes have received recent attention due to their sustainable method of fabrication, high water flux and organic solutes rejection performance. In this paper, we present a description of the transport of aqueous solutions of dyes through these membranes using the transport parameters of the Spiegler-Kedem-Katchalsky (SKK) model. The reflection coefficient (σ) and solute permeability (PS) of the considered TA-Fe3+ membranes were estimated from the non-linear model equations to predict the retention of solutes. The coefficients σ and PS depended on the porous medium and dye molecular size as well as the charge. The simulated rejections were in good agreement with the experimental findings. The model was further validated at low permeate fluxes as well as at various feed concentrations. Discrepancies between the observed and simulated data were observed at low fluxes and diluted feed solutions due to limitations of the SKK model. This work provides insights into the mass transport mechanism of dye solutions and allows the prediction of dye rejection by the TFC membranes containing a TA-Fe3+ selective layer using an SKK model.

Evaluation of Nanofiltration Membranes for the Purification of Monosaccharides: Influence of pH, Temperature, and Sulfates on the Solute Retention and Fouling.

Furfural, acetic acid, and sulfates are found in the hemicellulose (HMC) fraction of lignocellulosic biomass. Separation of furfural, acetic acid, and sulfates from monosaccharides by four nanofiltration (NF) membranes was evaluated with a model solution of glucose, xylose, furfural, acetic acid, and sulfates. Results showed that Alfa Laval NF99HF is the most promising membrane to purify monosaccharides, with the retentions of xylose (85%), glucose (95%), and with the minimum sulfate retention. pH has the highest impact on the retention of all solutes and there is no significant effect of temperature on the retentions of sulphates and acetic acid. Lower pH and temperature are favored to maximize the monosaccharide retention and to remove acetic acid while retaining more furfural with the monosaccharides. Moreover, fouling tendency is maximized at lower pH and higher temperatures. According to the statistical analysis, the retentions of glucose, xylose, furfural, sulfates, and acetic acid are 95%, 90%, 20%, 88%, and 0%, respectively at pH 3 and 25 °C. The presence of sulfates favors the separation of acetic acid and furfural from monosaccharides.

Competitive control of multiscale aquifer heterogeneity on solute transport in an alluvial aquifer

Natural aquifers can contain multiscale medium heterogeneity, whose joint impact on solute transport, however, remains obscure. To fill this knowledge gap, this study selected an alluvial aquifer as the representative medium, where the spatial distribution of multiple hydrofacies (with a typically nonuniform hydraulic conductivity (K) within each facies) could represent both regional-scale (large-scale) and subhydrofacies-scale (local-scale) heterogeneities. To obtain first-hand data, a field tracer test was conducted in an alluvial aquifer located at the Tongzhou site in Beijing, China, where the breakthrough curves (BTCs) obtained at various aquifer depths indicated a significant influence of both regional- and subhydrofacies-scale heterogeneities on solute transport. Further numerical analysis revealed that the impact of regional-scale heterogeneity on solute transport increased with increasing discrepancy in K between adjacent hydrofacies. In comparison, subhydrofacies-scale heterogeneity embedded within each hydrofacies played an important role in controlling solute transport when the mean Ks value of adjacent hydrofacies became more similar. Bimodal transport at early stages was mainly impacted by multiscale preferential flow paths, while solute retention at later times was induced by immobile zones dominating late-time transport. Anomalous transport induced by multiscale heterogeneity could be captured by the dual heterogeneous domain model (DHDM), while the dual advection–dispersion equation (DADE) or fractal mobile-immobile (fMIM) model could only provide reasonable predictions at the early or later stage, respectively. This study sheds light on the control mechanism of multiscale heterogeneity on solute transport.

Effect of spacer alkyl chain length on retention among three imidazolium stationary phases under various modes in high performance liquid chromatography

The properties of ionic liquids (ILs) greatly influenced the retention of solutes on IL-functionalized stationary phases. In this work, three IL-functionalized stationary phases (Sil-C4Im, Sil-C7Im, and Sil-C10Im) were prepared by modifying silica gel with three ionic liquid silane reagents differing in spacer alkyl chain lengths, which refers to the alkyl chain between the imidazolium and the sulfur atom. The preparation was proved through a range of characterization techniques, including elemental analysis (EA), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). The effects of chromatographic conditions, such as acetonitrile content, salt concentration, pH, and column temperature, were studied to explore the retention mechanism of three stationary phases, which indicates that three IL-stationary phases provide interactions with solutes in reverse-phase liquid chromatography (RPLC), hydrophilic interaction liquid chromatography (HILIC), and ion exchange chromatography (IEC). The column efficiency is 83,686 plates/m for aminobenzoic acid, and the column also has excellent repeatability of retention time with relative standard deviations (RSDs) between 0.24% and 0.34% (n = 12). A variety of analytes, including five nucleosides and nucleobases, six alkylbenzenes, two polycyclic aromatic hydrocarbons (PAHs), and four inorganic anions, were separated well on three IL-functionalized stationary phases. It was found that the spacer alkyl chain length influenced selectivity by comparing the retention of the three IL-functionalized stationary phases.

Might nontransferrin-bound iron in blood plasma and sera be a nonproteinaceous high-molecular-mass FeIII aggregate?

The HFE (Homeostatic Fe regulator) gene is commonly mutated in hereditary hemochromatosis. Blood of (HFE)(-/-) mice and of humans with hemochromatosis contains toxic nontransferrin-bound iron (NTBI) which accumulates in organs. However, the chemical composition of NTBI is uncertain. To investigate, HFE(-/-) mice were fed iron-deficient diets supplemented with increasing amounts of iron, with the expectation that NTBI levels would increase. Blood plasma was filtered to obtain retentate and flow-through solution fractions. Liquid chromatography detected by inductively coupled plasma mass spectrometry of flow-through solutions exhibited low-molecular-mass iron peaks that did not increase intensity with increasing dietary iron. Retentates yielded peaks due to transferrin (TFN) and ferritin, but much iron in these samples adsorbed onto the column. Retentates treated with the chelator deferoxamine (DFO) yielded a peak that comigrated with the Fe-DFO complex and originated from iron that adhered to the column in the absence of DFO. Additionally, plasma from younger and older 57Fe-enriched HFE mice were separately pooled and concentrated by ultrafiltration. After removing contributions from contaminating blood and TFN, Mössbauer spectra were dominated by features due to magnetically interacting FeIII aggregates, with greater intensity in the spectrum from the older mice. Similar features were generated by adding 57FeIII to "pseudo plasma". Aggregation was unaffected by albumin or citrate at physiological concentrations, but DFO or high citrate concentrations converted aggregated FeIII into high-spin FeIII complexes. FeIII aggregates were retained by the cutoff membrane and adhered to the column, similar to the behavior of NTBI. A model is proposed in which FeII entering blood is oxidized, and if apo-TFN is unavailable, the resulting FeIII ions coalesce into FeIII aggregates, a.k.a. NTBI.

Relating uncharged solute retention of polyelectrolyte multilayer nanofiltration membranes to effective structural properties

A novel way of making Nanofiltration (NF) membranes is to apply the Layer-by-Layer method, where polyelectrolytes are alternatingly coated on top of a porous Ultrafiltration membrane to form a separation layer with a controllable thickness in the nanometer range, also known as Polyelectrolyte Multilayer (PEM). An important precondition to make use of the variety this fabrication method offers for membrane optimization is knowledge of design rules. Therefore, the structural properties of PEMs and their relation to both coating conditions and membrane performance is an ongoing field of research. In this work, the separation performance of NF PEM membranes, based on PDADMAC/PSS and PAH/PAA, towards uncharged molecules is related to PEM structure. The structure of the membrane is represented by a nanoporous film with distribution in pore size. As, up to date, no experimental technique is available to directly measure pore sizes in the nanometer range of a wet film, a representative pore size distribution is estimated via the use of a theoretical transport description fitted to experimental data. Here, the studied PEM systems showed distinctive differences in both film thickness (PDADMAC/PSS: 44nm/BL, PAH/PAA: 689nm/BL) and mean pore size (PDADMAC/PSS: 0.44 nm, PAH/PAA: 0.27 nm). Within the range of layer numbers, the pore size of both PEMs in the layer dominated regime was independent of layer number. This indicates that there is an optimum layer number for PEM NF membranes regarding uncharged solute retention. Surprisingly, despite forming much thicker layers the PAH/PAA system closes off the support membrane pores at a higher bilayer number.

Gut Microbiome and Kidney Disease: Reconciling Optimism and Skepticism.

Gut Microbiome and Kidney Disease: Reconciling Optimism and Skepticism.