Low Salt Concentrations Research Articles

Comparative study of the effect of moderate and strong sodium chloride salinization on growth and photosynthetic apparatus of cultivated cereals

In a controlled environment, the effect of moderate (100 mM) and strong (200 mM) sodium chloride salinity on seed germination, seedling growth and the state of the photosynthetic apparatus (PSA) of barley (Hordeum vulgare L.) varieties Nur and wheat (Triticum aestivum L.) varieties Zlata was studied. It was found that with moderate salinization, the seeds of both species successfully germinated, but the growth of shoots and the accumulation of aboveground biomass were inhibited, which was partly due to a slowdown in the rate of photosynthesis. With strong salinity, distinct interspecific differences were observed in the response of plants. In particular, the number of germinated seeds decreased in barley, while in wheat it remained at the control level. In barley, shoot growth was inhibited to a greater extent, whereas in wheat, the accumulation of aboveground biomass was. The content of pigments in barley plants decreased, and the content of wheat increased. At the same time, stomatal conductivity decreased in both species and the rate of photosynthesis slowed down. It is concluded that based on the energy of germination and germination of seeds, it is possible to determine the salt resistance of species only to a high level of salinity (200 mM NaCl). Morphometric indicators of shoot growth make it possible to assess the resistance of plants to salinity already at lower salt concentrations (100 mM NaCl). For a more accurate comparative assessment of the salt resistance of species (varieties, varietals, genotypes) of cereals, not one, but several indicators should be used, reflecting not only the growth potential of plants, but also photosynthetic activity.

BURONG TILAPIA: FACTORS ON THE FERMENTATION PROCESS AND ITS MICROBIOTA

Fermented fish products hold significant prominence in the Philippines. However, its potential risks for human consumption are faced as a result of inadequate awareness of microbiological standards in its preparation. This study investigated the microbiota and fermentation process of burong tilapia, how this is influenced by fermentation factors such as salt content, temperature, and proper sanitation, and how it can impact food safety for human consumption. This study revealed that the population of aerobic microorganisms in burong tilapia was relatively high with the Aerobic Plate Count result of 2.1 x 107 CFU/g, indicating significant bacterial presence. On the other hand, a relatively low level of E. coli and Yeast and Molds count was detected having <25 CFU/g and <10 CFU/g, respectively. Moreover, it was found that low salt content, non-ideal temperature conditions and failure to strictly observe sanitation practices, all influenced the growth and proliferation of unwanted microorganisms. These results emphasize how crucial it is to optimize fermentation factors in order to guarantee both the food quality and safety of fermented fish products for human consumption. Furthermore, this case study highlights that consumer education is needed in promoting awareness and acceptance of fermented fish products in the market.

Evaluation of Probiotic Potential and Functional Properties of Lactobacillus Strains Isolated from Dhan, Traditional Algerian Goat Milk Butter

Goat milk butter, locally known as “Dhan,” from the Sfisfa region of Algeria, holds significant cultural and economic value. This study investigates the probiotic properties of lactic acid bacteria (LAB) present in Dhan, focusing particularly on Lactobacillus strains. Molecular identification using 16S rRNA revealed a dominance of Levilactobacillus brevis and Lactiplantibacillus plantarum, forming a substantial part of the bacterial profile. Three LAB isolates (DC01-A, DC04, and DC06) were selected from fresh samples, and rigorous analyses were performed to evaluate their probiotic properties. Safety assessments confirmed the absence of gelatinase, DNase, and haemolytic activities in all isolates. The isolates demonstrated high tolerance to bile salts and acidic conditions, along with the ability to survive simulated gastrointestinal digestion. Notably, strain DC06 exhibited exceptional survival at low pH (1.5) and high bile salt concentrations (0.15–0.3%). All isolates showed substantial growth in MRS medium with 2% phenol, although growth was significantly decreased at 5% phenol. Furthermore, our strains exhibited high adhesion rates to various solvents, demonstrating their potential for strong interaction with cell membranes. Specifically, adhesion to chloroform was observed at 98.26% for DC01-A, 99.30% for DC04, and 99.20% for DC06. With xylene, the adhesion rates were 75.94% for DC01-A, 61.13% for DC04, and 76.52% for DC06. The LAB strains demonstrated impressive growth in ethanol concentrations up to 12%, but their tolerance did not exceed this concentration. They also exhibited robust growth across temperatures from 10 °C to 37 °C, with strains DC04 and DC06 able to proliferate at 45 °C, though none survived at 50 °C. Additionally, the isolates showed significant resistance to oxidative stress induced by hydrogen peroxide (H2O2) and displayed medium to high autolytic activity, with rates of 50.86%, 37.53%, and 33.42% for DC01-A, DC04, and DC06, respectively. The cell-free supernatant derived from strain DC04 exhibited significant antimicrobial activity against the tested pathogens, while strain DC06 demonstrated moderate antioxidant activity with the highest DPPH scavenging rate at 68.56%, compared to the probiotic reference strain LGG at 61.28%. These collective findings not only suggest the probiotic viability of LAB strains found in Dhan but also highlight the importance of traditional food practises in contributing to health and nutrition. Consequently, this study supports the potential of traditional Dhan butter as a functional food and encourages further exploration of its health benefits.

Dry-Cured Ham, 'Kraški Pršut', from Heavy Pig Production-A Pilot Study Focusing on the Effect of Ham Weight and Salting.

A pilot study was conducted with the aim of adapting the processing of "Kraški pršut", dry-cured ham, for thighs from heavy pigs. The focus was on the effect of ham weight and salting duration on the quality of dry-cured ham. From a pool of thighs harvested from heavy pigs, a total of 32 green hams were selected (from 16 carcasses) based on weight (two classes; L-lighter, H-heavier) and we used left and right ham for either the standard or a shortened salting phase. Salting duration consisted of phase 1 (7 days for all hams) and phase 2 (7 or 14 days for L, 10 or 17 days for H, in the case of shortened and standard salting, respectively). Equivalent conditions for all hams were maintained during the remaining phases, with a total maturation period of 18 months. The analysis focused on chemical, physical and rheological properties, sensory attributes, and consumer perceptions. The H hams had lower processing losses, resulting in higher moisture and water activity, lower salt content in internal biceps femoris muscle, and a softer texture (instrumental and sensory) than L hams. The salting duration mainly affected weight losses in the salting phase and, consequently, salt content, which was lower in the shortened salting phase, while no effects were observed on texture. The sensory panel perceived weight's effect on hardness, with L hams being perceived as harder, and salting's effect on sourness, with hams submitted to longer salting perceived as sourer than H hams. Consumer testing indicated a general preference for softer and less salty hams. Overall, the results show that the applied reduction in salting duration was not substantial, and future trials should explore further optimization in terms of salting and resting phases.

Genome-wide identification of shaker K+ channel gene family in sugar beet (Beta vulgaris L.) and function of BvSKOR in response to salt and drought stresses

Potassium (K+) is the most abundant cation in plants, which is absorbed by roots and distributed throughout the plants and within plant cells, and is involved in various cellular processes. Shaker K+ channel plays crucial roles in the absorption and distribution of K+ and in the response to abiotic stress in plants. Herein, a total of six shaker K+ channel genes, BvKAT1, BvKAT3, BvAKT1, BvAKT2, BvAKT5, and BvSKOR, were identified in the genome of sugar beet (Beta vulgaris L.). The coding domain sequences (CDS) of these genes ranged from 2232 to 2739 bp, and protein lengths were varied from 743 to 912 aa. The shaker K+ channel genes contained hormone-related and light responsiveness cis-acting regulatory elements. The phylogenetic analysis showed that BvSKOR was highly conserved and contained six transmembrane structures. The expression patterns of BvSKOR under salt and osmotic stress were analyzed by qRT-PCR, and found that the expression level of BvSKOR under low concentration salt and osmotic stress at short period of treatment were significantly higher than that of the control group. The function of BvSKOR was further verified in tobacco (Nicotiana tabacum), and the results showed that under salt and osmotic stress, the roots of transgenic plants were significantly stronger than those of wild type (WT) plants, and the relative water content (RWC), chlorophyll, proline, soluble sugar, soluble proteins contents and antioxidant enzyme activity were significantly higher than those of WT plants. These results indicated that overexpression of BvSKOR can significantly enhance the salt and drought tolerance in transgenic tobacco plants. This study could provide theoretical support and genetic resources for genetic improvement of crops stress resistance.

Effects of fermentation conditions (salt concentration, temperature, and pH) on Lactobacillus strains for induction of interleukin-12 in the exposed murine splenocytes

The present work aimed to assess the stresses of temperature, salt concentration, and pH on Lactobacillus gasseri 54C, Lactiplantibacillus plantarum ATCC 14917, and 11SH in fermented culture medium and their effects on interleukin-12 (IL-12) induction in murine splenocytes. First, the strains were fermented under different microbial stress conditions at salt concentrations (2, 4, and 6% w/v), temperatures (30 and 42°C), and pH levels (4, 5, and 6), as well as their combined conditions. Then, they were heat-killed, lyophilized, and exposed to murine splenocytes. The IL-12 induction was measured using the immunoassay method. It was indicated that the induction of IL-12 depended on the culture conditions, as it was increased by the fermentation strains under microbial stresses with the higher temperature (42°C), lower salt concentration (%2), and lower pH level (4). It seems that the bacterial cells' integrity is essential to stimulate the induction of IL-12.

Evaluation of the Glass Transition Temperature and Intermolecular Interaction of Poly(ethylene oxide) with Addition of Lithium Perchlorate or/and Titanium Dioxide

The high crystallinity of poly (ethylene oxide) (PEO) has urged the need for adding salt or nanofiller. The effect of the glass transition temperature (Tg) and intermolecular interaction of PEO upon the addition of salt or nanofiller become a debatable topic due to the lacking of the understanding of the role of salt or nanofiller in PEO. Hence, the evaluation of the Tg and intermolecular interaction of PEO with addition of lithium perchlorate (LiClO4) salt or/and titanium dioxide (TiO2) nanofiller are presented and discussed. The solid polymer electrolytes with addition of nanofiller are prepared by solution casting technique. The optimum composition of PEO and LiClO4 salt is used as host matrix and TiO2 as nanofiller. The Tg and intermolecular interaction of the polymer-based electrolytes have been studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. PEO-LiClO4 serves as the classical model of polymer-salt systems with good polymer-salt molecular interaction at low salt concentration (WS ≤ 0.107) whereas TiO2 without any surface treatment when added to PEO, serves as a classical model of polymer-nanofiller systems with weak polymer-nanofiller molecular interaction. Results have shown that LiClO4 salt gives notable effect on the Tg and intermolecular interaction of PEO. Whereas, TiO2 do not provide a substantial effect on the Tg and intermolecular interaction of PEO-based polymer electrolytes. This work provides a better understanding and knowledge of the effect of addition of salt or/and nanofiller in the Tg and intermolecular interaction of the PEO systems.

Exploring Fresh Lettuce (Lactuca sativa) as a Dairy-Free Probiotic Source

Probiotics are living microorganisms that, when given in appropriate amounts, have optimistic effects on body. This study explores the potential of fresh lettuce (Lactuca sativa) leaves as a probiotic source for individuals with dairy allergies. Gram staining and the catalase test were used to identify the bacteria that were recovered from lettuce leaves as gram-positive, catalase-negative strains. The resistance to antibiotics and their capacity to tolerate low pH and bile salt concentrations both essential for surviving the digestive tract were evaluated. The bacteria showed a high tolerance to bile salts and low pH, but they were susceptible to ampicillin, streptomycin, gentamycin, chloramphenicol, and neomycin. Tests for gas production in the presence of glucose revealed no gas production. Molecular techniques such as PCR and 16S rRNA gene sequencing revealed the presence of Enterococcus lactis, Enterococcus durans, Lactobacillus paracasei, and Lactobacillus casei

How Salt and Temperature Drive Reentrant Condensation of Aβ40.

Within the framework of liquid-liquid phase separation (LLPS), biomolecular condensation orchestrates vital cellular processes, and its dysregulation is implicated in severe pathological conditions. Recent studies highlight the role of intrinsically disordered proteins (IDPs) in LLPS, yet the influence of microenvironmental factors has remained a puzzling factor. Here, via computational simulation of the impact of solution conditions on LLPS behavior of neurologically pathogenic IDP Aβ40, we chanced upon a salt-driven reentrant condensation phenomenon, wherein Aβ40 aggregation increases with low salt concentrations (25-50 mM), followed by a decline with further salt increments. An exploration of the thermodynamic and kinetic signatures of reentrant condensation unveils a nuanced interplay between protein electrostatics and ionic strength as potential drivers. Notably, the charged residues of the N-terminus exhibit a nonmonotonic response to salt screening, intricately linked to the recurrence of reentrant behavior in hydrophobic core-induced condensation. Intriguingly, our findings also unveil the reappearance of similar reentrant condensation phenomena under varying temperature conditions. Collectively, our study illuminates the profoundly context-dependent nature of Aβ40s liquid-liquid phase separation behavior, extending beyond its intrinsic molecular framework, where microenvironmental cues wield significant influence over its aberrant functionality.

Reentrant Condensation of Polyelectrolytes Induced by Diluted Multivalent Salts: The Role of Electrostatic Gluonic Effects.

We explore the reentrant condensation of polyelectrolytes triggered by multivalent salts, whose phase-transition mechanism remains under debate. We propose a theory to study the reentrant condensation, which separates the electrostatic effect into two parts: a short-range electrostatic gluonic effect because of sharing of multivalent ions by ionic monomers and a long-range electrostatic correlation effect from all ions. The theory suggests that the electrostatic gluonic effect governs reentrant condensation, requiring a minimum coupling energy to initiate the phase transition. This explains why diluted salts with selective multivalency trigger a polyelectrolyte phase transition. The theory also uncovers that strong adsorption of multivalent ions onto ionic monomers causes low-salt concentrations to induce both collapse and reentry transitions. Additionally, we highlight how the incompatibility of uncharged polyelectrolyte moieties with water affects the polyelectrolyte phase behaviors. The obtained results will contribute to the understanding of biological phase separations if multivalent ions bound to biopolyelectrolytes play an essential role.

Studying the Influence of Salt Concentrations on Betalain and Selected Physical and Chemical Properties in the Lactic Acid Fermentation Process of Red Beetroot

This study emphasizes the significance of optimizing salt content during the fermentation of red beetroot to produce healthier and high-quality fermented products. It investigates the impact of different salt levels on fermentation, analyzing various parameters such as pH levels, dry matter content, total acidity, salt content, color changes, pigment content, and lactic acid bacteria count. This study identifies the most favorable salt concentration for bacterial growth during fermentation and storage as 2–3%. It was evaluated that salt levels fluctuated significantly during fermentation, with nearly 50% of the added salt absorbed by the beetroot tissues, mainly when lower salt concentrations were used. The fermentation process had a negative effect on the content of betalain pigments, as well as yellow pigments, including vulgaxanthin-I. It was also found that fermentation and storage affected the proportions of red pigments, with betacyanins proving to be more stable than betaxanthins, and that salt addition affected negatively pH and total acidity while causing an increase in yellow color. The pH was negatively correlated with the duration of the process, the amount of red pigment, and bacterial count. The results indicate that lower salt levels can lead to favorable physicochemical and microbiological parameters, allowing for the production of fermented red beetroot with reduced salt content without compromising quality.

Adsorption of polyelectrolytes in the presence of varying dielectric discontinuity between solution and substrate.

We examine the interactions between polyelectrolytes (PEs) and uncharged substrates under conditions corresponding to a dielectric discontinuity between the aqueous solution and the substrate. To this end, we vary the relevant system characteristics, in particular the substrate dielectric constant ɛs under different salt conditions. We employ coarse-grained molecular dynamics simulations with rodlike PEs in salt solutions with explicit ions and implicit water solvent with dielectric constant ɛw = 80. As expected, at low salt concentrations, PEs are repelled from the substrates with ɛs < ɛw but are attracted to substrates with a high dielectric constant due to image charges. This attraction considerably weakens for high salt and multivalent counterions due to enhanced screening. Furthermore, for monovalent salt, screening enhances adsorption for weakly charged PEs, but weakens it for strongly charged ones. Meanwhile, multivalent counterions have little effect on weakly charged PEs, but prevent adsorption of highly charged PEs, even at low salt concentrations. We also find that correlation-induced charge inversion of a PE is enhanced close to the low dielectric constant substrates, but suppressed when the dielectric constant is high. To explore the possibility of a PE monolayer formation, we examine the interaction of a pair of like-charged PEs aligned parallel to a high dielectric constant substrate with ɛs = 8000. Our main conclusion is that monolayer formation is possible only for weakly charged PEs at high salt concentrations of both monovalent and multivalent counterions. Finally, we also consider the energetics of a PE approaching the substrate perpendicular to it, in analogy to polymer translocation. Our results highlight the complex interplay between electrostatic and steric interactions and contribute to a deeper understanding of PE-substrate interactions and adsorption at substrate interfaces with varying dielectric discontinuities from solution, ubiquitous in biointerfaces, PE coating applications, and designing adsorption setups.

Study on Preparation and Properties of Pickering Emulsions Prepared by Carboxymethyl Starch‐Xanthan Gum Nanoparticles

AbstractIn this work, carboxymethyl starch‐xanthan gum nanoparticles (CXN) with different ratios are prepared by ethanol precipitation method. The effects of different ratios, NaCl content, and pH on the particle size and zeta potential of the nanoparticles are investigated, as well as the rheological properties and stability of the CXN emulsions. The results show that with the increase of xanthan gum (XG), the particle size, and zeta potential of the nanoparticles decrease and the prepared emulsions have higher shear stress and viscosity, as well as greater thermal and storage stability. Changes in pH and NaCl concentration significantly affect the particle size and zeta potential values of the nanoparticles. Excess acids or bases increase the viscosity of the emulsions. At low salt concentrations (0.05 M), the emulsion viscosity increases significantly, after which the emulsion viscosity decreases with increasing salt concentration. Neutral pH conditions at room temperature are not conducive to the stability of the emulsions. At high temperatures (100 °C), high salt concentrations, excessive acids or bases can destabilize emulsions. This study provides a new way to reduce the particle size of nanoparticles and a feasible strategy for developing long‐term stable Pickering emulsion.

A Comprehensive Study on the Parameters Affecting Magnesium Plating/Stripping Kinetics in Rechargeable Mg Batteries

AbstractMg metal anode‐based battery is a more sustainable, lower cost, and higher energy density alternative to Li‐ion. However, this battery chemistry also faces several challenges associated with the high charge density of Mg2+, including achieving high reversibility and low voltage hysteresis for Mg metal plating/stripping. While significant improvements are achieved in last decades, they involve rather complex electrolyte formulations and/or Mg salts difficult to produce, and the use of unpractical substrates such as platinum. Here, significant improvement in terms of Mg plating kinetics is achieved in electrolytes containing commercial magnesium bis(trifluoromethanesulfonyl)imide salt (Mg(TFSI)2) by using titanium substrate with similar crystal structure and lattice parameter as Mg leading to lower nucleation overpotential. Low salt concentration electrolyte and addition of dibutyl magnesium (Mg(butyl)2) also enable the formation of thinner interphase, richer in solvent based decomposition products, further improving Mg plating kinetics. This work highlights the complex role of Mg(butyl)2, often considered as a simple drying agent, and how it impacts ion solvation favoring the mobility of electroactive cationic species, paving the way toward better electrolyte design with improved cation transference number.

Symmetric and asymmetric ceramic-supported polyelectrolyte multilayer nanofiltration membranes

Polyelectrolyte multilayer based nanofiltration membranes can remove organic micropollutants from water. Such polyelectrolyte multilayer membranes (PEMMs) are often assembled on polymeric supports, but less research focuses on inorganic (ceramic) supports. In this work, we assembled symmetric and asymmetric, coatings of poly(allylamine (PAH) and poly(styrene sulfonate) (PSS) on ceramic supports. Symmetric membranes are assembled with the same salt concentration in the coating solution for each layer. Asymmetric membranes use very permeable layers (high salt concentration in coating solution) as base layers and dense top layers with lower permeability (low salt concentration in coating solution) as filtration layers. By reversing the coating order – first salt-free and after that high salt concentration, we obtained reverse asymmetric membranes. They consistently outperformed the symmetric and standard asymmetric design in removing organic micropollutants, reaching an average retention of 85 ± 13 % compared to 77 ± 14 % for the standard asymmetric membranes. We attribute this higher retention to a more efficient pore overcoating for the reverse asymmetric membranes. This work demonstrates that ceramic supports combined with reverse asymmetric PEMMs can be efficiently used for micropollutant removal from water.

Capacitive deionization and electrochemical performance of a hierarchical porous electrodes enabled by nitrogen and phosphorus doped CNTs and removable NaCl template

Capacitive Deionization (CDI) is an electrochemical desalination technique based on the electrical double layer, which accumulate salts from the water stream; however, achieving higher salt adsorption for low-concentration salt is hindered due to several obstacles, such as low adsorption capacity and slow kinetics on the electrode surface. In this study, we reported a novel electrode fabrication method designed to enhance the hydrophilicity of the electrode material and activate hierarchical porosity, making a more accessible adsorption surface area. This modification enables more than 210 % improvement in salt adsorption capacity, achieving 17.5 mg g-1 in a single pass process with good stability in an 850 mg/L NaCl solution at 1.2 V, surpassing most reported carbon-based electrodes under similar operating conditions. Electrode formulation consists of Nitrogen (N) and Phosphorus (P) doped hierarchical carbon nanotubes (CNTs) network blended with additional NaCl as a green and removable template to reach higher levels of porosity. The electrochemical sorption behavior of the sample was characterized over a voltage range of –0.5 to 0.7 V. Furthermore, the electrode materials were characterized utilizing various characterization methods, including Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Raman Spectroscopy, Fourier Transformed Infrared (FTIR), X-ray Photoelectron Spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) to explore the correlation between microstructure, morphology, and properties. Our finding reveals that not only N and P can affect adsorption, but also the novel cathode preparation method, which employs a removable NaCl templated hierarchical porous electrode, has a profound effect on the electrochemical and CDI results. This finding will open a new perspective in designing electrodes for all electrochemical systems.

Transcriptome Analysis Revealed the Response Mechanism of Pomegranate to Salt Stress

Pomegranate (Punica granatum) is a well-known fruit tree species and a significant pioneer ecological species on saline–alkali land with moderate resistance to salt stress. To explore its response mechanism to salt stress could provide valuable insights into the molecular and physiological strategies plants employ to adapt and survive in high-salt environments. In this study, changes in physiological parameters and gene expressions were examined following salt treatment. After 72 h of salt treatment, change patterns of SOD and POD differed between high and low salt concentrations. Similar changes were found in the contents of proline and total soluble sugar. RNA-Seq analysis of fifteen samples detected 32,630 genes from the pomegranate genome data. A total of 6571 DEGs, including 374 TFs, were identified across different treatments. Six special modules and 180 hub genes were obtained by WGCNA analysis. Functional annotation highlighted signaling pathways and the accumulation of primary and secondary metabolites as significant pathways. These findings could reveal the salt tolerance mechanism in pomegranate leaves, offering a theoretical foundation for enhancing plant salt tolerance through genetic engineering.

Different taste map for amiloride sensitivity, response frequency, and threshold to NaCl in the rostral nucleus of the solitary tract in rats.

Studies on taste bud cells and brain stem relay nuclei suggest that alternative pathways convey information regarding different taste qualities. Building on the hypothesis that amiloride (epithelial Na channel antagonist)-sensitive neurons respond to palatable salt (low-concentration) and amiloride-insensitive neurons respond to aversive salt (high-concentration), we investigated the histological distribution of taste-sensitive neurons in the rostral nucleus of the solitary tract in rats and their NaCl and amiloride sensitivities. We recorded neuronal activity in extracellular single units using multi-barrel glass micropipettes and reconstructed their locations on the rostrocaudal and mediolateral axes. Seventy-three taste-sensitive neurons were categorized into the best-taste category. The amiloride sensitivities of the 31 neurons were examined for 0.1, 0.2, 0.4, and 0.8 M NaCl. The neuronal distribution of amiloride-sensitive neurons was located in the lateral region, while amiloride-insensitive neurons were located in the medial region. The amiloride-sensitive neurons responded to low salt concentrations, signaling the NaCl levels required by body fluids. Amiloride-insensitive neurons were silent at low salt concentrations but may function as warning signals for high salt concentrations. Low-threshold and/or high-response neurons were located in the rostrolateral region. In contrast, high-threshold and/or low-response neurons were located in the caudal-medial region.

Mixtures of Intrinsically Disordered Neuronal Protein Tau and Anionic Liposomes Reveal Distinct Anionic Liposome-Tau Complexes Coexisting with Tau Liquid-Liquid Phase-Separated Coacervates.

Tau, an intrinsically disordered neuronal protein and polyampholyte with an overall positive charge, is a microtubule (MT) associated protein that binds to anionic domains of MTs and suppresses their dynamic instability. Aberrant tau-MT interactions are implicated in Alzheimer's and other neurodegenerative diseases. Here, we studied the interactions between full-length human protein tau and other negatively charged binding substrates, as revealed by differential interference contrast (DIC) and fluorescence microscopy. As a binding substrate, we chose anionic liposomes (ALs) containing either 1,2-dioleoyl-sn-glycero-3-phosphatidylserine (DOPS, -1e) or 1,2-dioleoyl-sn-glycero-3-phosphatidylglycerol (DOPG, -1e) mixed with zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) to mimic anionic plasma membranes of axons where tau resides. At low salt concentrations (0 to 10 mM KCl or NaCl) with minimal charge screening, reaction mixtures of tau and ALs resulted in the formation of distinct states of AL-tau complexes coexisting with liquid-liquid phase-separated tau self-coacervates arising from the polyampholytic nature of tau containing cationic and anionic domains. AL-tau complexes (i.e. tau-lipoplexes) exhibited distinct types of morphologies. This included large ∼20-30 μm tau-decorated giant vesicles with additional smaller liposomes with bound tau attached to the giant vesicles and tau-mediated finite-size assemblies of small liposomes. As the salt concentration was increased to near and above 150 mM for 1:1 electrolytes, AL-tau complexes remained stable, while tau self-coacervate droplets were found to dissolve, indicative of the breaking of (anionic/cationic) electrostatic bonds between tau chains due to increased charge screening. The findings are consistent with the hypothesis that distinct cationic domains of tau may interact with anionic lipid domains of the lumen-facing monolayer of the axon's plasma membrane, suggesting the possibility of transient yet robust interactions near relevant ionic strengths found in neurons.

Effect of fluorocarbons and inorganic salts on wetting and foaming characteristics of hydrocarbon surfactants

To improve the wetting and foaming properties of anionic SDS foam on coal dust, we experimentally investigated the effects of short-chain fluorocarbon surfactant FS-50 and inorganic salt NaCl on the wetting and foaming properties of SDS foam and the synergistic effect of the mixed system. The experimental results show that SDS and FS-50 can effectively improve the wetting properties of coal dust in a concentration of 0.05–0.16 wt% and a ratio of 3:1–1:2. In the mixed system, SDS provides sufficient hydrophilic base, FS-50 can effectively reduce the surface tension and have a certain agglomeration effect on coal dust to accelerate the settlement of coal dust and improve the wetting properties of coal dust. When the mixed ratio is lower than 1:1, the foaming volume and foam half-life of the surfactant solution are significantly reduced. The number of SDS molecules at the solution gas-liquid interface is reduced due to electronegative repulsion, and the FS-50 replenishes to the liquid surface faster due to stronger hydrophobicity, and it is difficult to form hydrogen bonds with water molecules, which reduces the foam stability. Low concentrations of inorganic salts can significantly improve the wetting performance of the SDS/FS-50 mixed system to coal dust, and high concentrations will reduce the foam stability of the mixed system.