Variation Of Ionic Strength Research Articles

Multifaceted Cargo Recruitment and Release from Artificial Membraneless Organelles.

Liquid-liquid phase separation (LLPS) drives membraneless organelles (MLOs) formation for organizing biomolecules. Artificial MLOs (AMLOs) have been constructed mostly via the LLPS of engineered proteins capable of regulating limited types of biomolecules. Here, leveraging a minimalist AMLO, driven by LLPS of polymer-oligopeptide hybrids, enrichment, recruitment, and release of multifaceted cargoes are quantitatively shown, including small fluorescent molecules, fluorophore-containing macromolecules, proteins, DNAs, and RNAs. Cargoes show up to 105 -fold enrichment, whilst recruitment and release are triggered by variations of temperature, pH, and/or ionic strength. Also, the first efficacious, rapid, and reversible control of aggregation-induced emission with over 30 folds of modulation of overall fluorescence intensity is achieved, by intensifying the aggregation of luminogens in AMLO. The AMLO is a simple yet versatile platform for potential drug delivery and biosensor applications.

New strumming sleight for old tunes: Exploration on the sorption mechanisms of Cd(II) by hydroxyapatite synthesized with different molar Ca/P ratios

Hydroxyapatite (HAP) has been widely used for the preconcentration and stabilization of various heavy metal pollutants in both the water and soil environment. Nonetheless, there still exists a gap between its synthesis conditions, physicochemical properties and removal performances. Under such a research background, three HAP materials were synthesized via a modified co-precipitation approach by varying initial Ca/P molar ratios (i.e., 4/3, 5/3 and 6/3) and used for capturing toxic cadmium (Cd(II)) from an aqueous solution. According to the experimental results, the three synthesized HAP samples were all the Ca-deficient type and the actual Ca/P molar ratio was in the increasing order of HAP4/3 < HAP5/3 < HAP6/3. In particular, the HAP4/3 sample exhibited higher Cd(II) removal performance due to its higher specific surface area (SSA) value and abundant Ca-deficient sites. More than 93% of Cd(II) was removed within an extremely short period of 5 min and a complete removal was achieved at a prolonged contact time of 24 h. The sorption behavior of Cd(II) was independent of ionic strength variation and scarcely influenced by various inorganic electrolyte ions, low molecular weight organic acids (LMWOAs) and competing heavy metal ions. The desorption data of Cd(II)-containing HAP phases, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses pointed to a predominant removal mechanism of lattice incorporation with a minor contribution of inner-sphere surface complexation. The experimental findings demonstrated the significant application potential of Ca-deficient HAP material for the cost-effective treatment of Cd(II)-polluted water systems.

Cellulose Nanocrystals' Assembly under Ionic Strength Variation: From High Orientation Ordering to a Random Orientation.

We discuss the effect of the ionic strength and effective charge density on the final structural organization of cellulose nanocrystals (CNCs) after drying suspensions with different ionic strengths in terms of quantitative characteristics of the orientation order, rarely considered to date. We observed that increasing the ionic strength in the initial suspension results in continuous shrinking of the helical pitch length that shifts the photonic band gap to a far UV region from the visible range (from 400 to 250 nm) because of the increase in the helical twisting power from 4 to 6 μm-1 and doubling of the twisting angle between neighboring monolayers from 5.5 to 9°. As our estimation of the Coulombic interactions demonstrates, the reduction of the Debye charge screening length below a critical value of 3 nm results in the loss of the long-range helicoidal order and the transition to a disordered morphology with random packing of nanocrystals. Subsequently, very high orientation ordering with the 2D orientation factor, S, within the range 0.8-0.9, close to the theoretical limit of 1, gradually decreased to a very low value of S = 0.1-0.2, a characteristic of random organization at high ionic strength. We suggest that the loss of the chiral ordering is a result of the reduction of repulsive forces, promoting direct physical contact with the reduced contact area during Brownian motion, combined with increased repulsive Coulombic interactions of nanocrystals at nonparallel local packing. Notably, electrolyte addition enhances chiral interactions to the point where the helical twisting power is too large and the resulting nanocrystal bundles can no longer compactly pack without creating unfavorably large free volume. We propose that the Debye charge screening length in suspensions can be used as a universal parameter for CNCs under different conditions and can be used to assess expected ordering characteristics in the solid films.

Efficient Conversion of Elemental Sulfur to Robust Ultrabright Fluorescent Sulfur Quantum Dots Using Sulfur-Ethylenediamine Precursor

The direct utilization of abundant and cheap elemental sulfur (S) to synthesize sulfur quantum dots (SQDs) with satisfactory yield and photoluminescence quantum yield (PLQY) remains a big challenge. Here, we report a simple and effective method for mass-producible synthesis of ultrabright fluorescent SQDs based on one-pot solvothermal treatment of S-ethylenediamine (S-EDA) solution. The PLQY of synthesized SQDs and the corresponding S-to-SQDs conversion efficiency (CE) can reach as high as 87.8% and 15.9%, respectively, both of which are the highest values to date. In addition, the SQDs simultaneously show good water solubility, superior storage stability, stable fluorescence against ionic strength variation and pH change, and low toxicity, which enable them promising for numerous applications such as fabrication of fluorescent polymer composite and ink. Furthermore, SQDs also present strong two-photon emission, and their use for two-photon fluorescence imaging is reported here for the first time. This work thus highlights enormous opportunities not only for bringing SQDs from laboratory research to real applications but also for the value-added utilization of S resource.

Improving the colloidal stability and emulsifying property of flaxseed 11S globulin by heat induced complexation with soy 7S globulin

Flaxseed protein contains mainly 11S globulin (FG). It suffers significant aggregation upon heating, ionic strength and pH variation which hinders its application in food products. This study aims at improving the colloidal stability of FG by fabricating a flaxseed 11S globulin-soy 7S globulin (SG) complex and exploring its potential application in stabilizing emulsion. Results showed that SG could limit the thermal aggregation of FG by forming a stable FG-SG complex above 80 °C at neutral pH. Increasing temperature and heating time would promote the exposure of hydrophobic sites and facilitate the complexation that was irreversible. The complex showed enhanced stability against ionic strength and pH variation and was able to stabilize high internal phase emulsion (HIPE) with oil volume fraction up to 85% by a minimal protein concentration of 20 g/L which however could not be achieved solely by flaxseed 11S globulin. The HIPEs showed long term stability in a wide range of pH and ionic strength. This study paves way for enhancing the functionalities of oilseed 11S globulin simply through thermal induced complexation with 7S globulin from another plant source.

A multiparametric fluorescence assay for screening aptamer\u2013protein interactions based on microbeads

For improving aptamer-ligand binding we have developed a screening system that defines optimal binding buffer composition. Using multiplex assays, one buffer system is needed which guarantees the specific binding of all aptamers. We investigated nine peer-reviewed DNA aptamers. Non-specific binding of aptamers is an obstacle. To address this, we investigated 16 proteins as specificity controls bound covalently to encoded microbeads in a multiplex assay. Increasing the NaCl concentration decreased the binding for all aptamers. Changing pH values by one unit higher or lower did not influence the aptamer binding significantly. However, pH < 5 led to non-specific binding for all aptamers. The PfLDH-aptamer selected in the absence of divalent cations exhibited doubling of its binding signal by the addition of Ca2+ and Mg2+. We confirmed Ca2+ and Mg2+ dependency of the aptamers for streptavidin and thrombin by observing a 90% and 50% binding decrease, respectively. We also achieved a doubling of binding for the streptavidin aptamer when replacing Ca2+ and Mg2+ by Mn2+. A buffer suitable for all aptamers can have considerable variations in pH or ionic strength, but divalent cations (Ca2+, Mg2+, Mn2+) are essential.

Oxygenation of Substituted (Phenylthio)acetic Acids by Acidic Bromate: A Kinetic and Mechanistic Study and Validity of Linear Free-Energy Relationships

Kinetics and mechanistic investigations on the oxygenation of (phenylthio)acetic acid and its substituted compounds using bromate in acid medium have been carried out. The reaction exhibited first-order in [bromate], 1.6 order in [H2SO4], less than one order in [substrate] and displayed solvent isotopic effect of 1.75 (kD2O/kH2O). The reaction rate is not affected by ionic strength variation, however, enhanced by lowering dielectric constant of the medium. Structural modifications in the aryl moiety of the substrate resulted in a change of reactivity, where electron-seeking substituents decreased the reaction rate. The order of reactivity among the studied substrates is paramethoxy &gt; para-methyl &gt; -H &gt; para-chloro ≈ para-bromo &gt; para-nitro(phenylthio)acetic acid and showed an excellent correlation between rate constant and the Hammett substituent constant (σ value). The reaction constant (ρ) value is negative (-1.37 at 303 K) and decreased by increase in the reaction temperature. Proposed mechanism involves decomposition of the complex formed between acid bromate and the substrate. Based on the proposed mechanism, an appropriate rate law has been derived and tested for its validity. Activation parameters and isokinetic temperature have been evaluated and discussed. The validity of linear free-energy relationships have been discussed thoroughly.

Reductive Removal of Pertechnetate and Chromate by Zero Valent Iron Under Variable Ionic Strength Conditions

Reductive Removal of Pertechnetate and Chromate by Zero Valent Iron Under Variable Ionic Strength Conditions

OXIDATION OF VANILLIN BY IODATE IN AQUEOUS ACETIC ACID MEDIUM: A KINETIC AND MECHANISTIC STUDY

The kinetics and mechanism of the oxidation of vanillin by iodate in aqueous acetic acid medium is studied. The reaction exhibits first order in [Iodate], fractional order in [vanillin] and [acid]. Variation of ionic strength had no effect on the reaction rate. Increase in the reaction rate by a decrease in the dielectric constant of the medium is observed. The reaction was studied at four different temperatures and the related activation and thermodynamic parameters were calculated. The product of oxidation was confirmed as vanillic acid by spectral analysis. Based on the results a plausible mechanism has been proposed and the appropriate rate law has been derived.

Effects of abiotic factors on the stability and infectivity of polyvalent coliphage.

Bacteriophage has attracted growing interest as a promising therapeutic agent for pathogenic bacteria, especially for antibiotic-resistant bacteria. However, the various abiotic conditions could impact the stability of phages and further threat host-virus interactions. Here, we investigated the stability and lytic activity of virulent polyvalent coliphage (named PE1) by double-layer plaque assay. PE1 can efficiently infect both the drug-sensitive Escherichia coli K12 and multidrug-resistant E. coli NDM-1 even after prolonged storage at 4 °C for up to two months. Results showed that PE1 exhibits an outstanding stability to infect E. coli strains under a wide range of thermal (4 °C-60 °C) and pH (4-11) conditions, which covers the thermal and pH variations of most wastewater treatment plants. Moreover, PE1 exhibited high resistibility to heavy metals exposure including Cu2+, Cd2+, Co2+, and Cr3+ at the concentrations below 0.5 mM, and an excellent resistant ability to the variation of ionic strength, which still retained strong infectious ability even treated with saturated sodium chloride solution (350 g/L). This work shows that polyvalent phage PE1 has a strong adaptive capacity to various abiotic factors and should be a good candidate of being an antibacterial agent, especially for antibiotic-resistant bacteria control in sewage.

Polymers as Encapsulating Agents and Delivery Vehicles of Enzymes.

Enzymes are versatile biomolecules with broad applications. Since they are biological molecules, they can be easily destabilized when placed in adverse environmental conditions, such as variations in temperature, pH, or ionic strength. In this sense, the use of protective structures, as polymeric capsules, has been an excellent approach to maintain the catalytic stability of enzymes during their application. Thus, in this review, we report the use of polymeric materials as enzyme encapsulation agents, recent technological developments related to this subject, and characterization methodologies and possible applications of the formed bioactive structures. Our search detected that the most explored methods for enzyme encapsulation are ionotropic gelation, spray drying, freeze-drying, nanoprecipitation, and electrospinning. α-chymotrypsin, lysozyme, and β-galactosidase were the most used enzymes in encapsulations, with chitosan and sodium alginate being the main polymers. Furthermore, most studies reported high encapsulation efficiency, enzyme activity maintenance, and stability improvement at pH, temperature, and storage. Therefore, the information presented here shows a direction for the development of encapsulation systems capable of stabilizing different enzymes and obtaining better performance during application.

Influence of calcium chloride and pH on soluble complex of whey protein-basil seed gum and xanthan gum.

SummaryInteraction between biopolymers generates different rheological behaviors, which can be effective on the structure of food products. One way to control the polysaccharide–protein interaction is the variation of acidic and ionic strength. In this research, the different amounts of pHs (3–7) and calcium chloride (5–20 mM) were investigated on a soluble complex of whey protein concentrate (WPC) with xanthan gum (XG) and basil seed gum (BSG). The complex characteristic was investigated according to turbidity, viscosity behavior, and electrostatic interactions. The turbidity test showed that WPC:BSG and WPC:XG absorbance increased at pH 3.5 and 4.5, respectively, due to the formation of insoluble complex. pH 6 was the start point of the turbidity increment, which showed the formation of soluble complexes between WPC and polysaccharides. The FTIR analysis confirmed creation of soluble complex at pH 6. The absorbance raised with increasing the molar of CaCl2 to 10 mM, but no significant difference was observed by turbidity test in the range of CaCl2<10 mM. Also, the highest viscosity value was obtained by 10 mM CaCl2.

Application of Multivariate Approaches to the Hydro-chemical Assessment of the Ghodaghodi Lake, Sudurpaschim Province, Nepal

Wetlands are considered the most diverse and productive ecosystems in the world, providing life-sustaining ecological services. Hydrochemical variables of the Ghodaghodi Lake situated in Far west Nepal were studied using multivariate statistical approaches to investigate the characteristics of water quality of the lake. A total of 10water samples were collected and analyzed for water temperature, pH, electrical conductivity, total dissolved solids, total hardness, salinity, dissolved oxygen, major ions, and dissolved Si in the pre-monsoon season during 2017.The water quality assessment was carried out by applying sodium percentage, sodium adsorption ratio, permeability index, Kelly’s ratio, magnesium adsorption ratio, action ratio of soil structural stability, and water quality index. Multivariate statistical techniques were used to evaluate the geochemical and anthropogenic processes and to identify factors influencing the ionic concentrations. The results revealed that the water was slightly alkaline with low ionic strength and remarkable spatial variations. The hydrochemistry of the lake was mainly controlled by rock weathering as the dominant Ca2+-HCO3- facies. The principal component analysis provided three major components exhibiting the diverse sources of natural and anthropogenic chemicals, including agricultural fertilizers, leakage of sewages near the human settlements, etc. The measured hydrochemical parameters indicate that lake water lies within the safe drinking water and irrigational standards. However, special consideration should be taken to control the concentrations of NO3- due to increasing anthropic activities.

Spectrophotometric Kinetic and Mechanistic Investigation of Chlorpromazine Radical Cation with Hexachloroiridate (IV) in Catalyzed Aqueous Acid Medium

AbstractThe kinetic mechanism of oxidation of Chlorpromazine (CPZ) (2‐chloro‐10‐(3‐dimethylaminopropyl) phenothiazine) by hexachloroiridate (IV) in acidic aqueous medium has been studied spectrophotometrically using UV‐visible spectrophotometer at λmax 525 nm (ϵ, 10200 dm3 mol−1 cm−1). The title reaction is overall second order being first order with respect to each reactant, but to be complicated at higher substrate concentrations. Oxidant has been found as strong electron transfer species to the formation of chlorpromazine radical cation and further respected sulfoxide. The rate also increases with increasing concentration of hydrogen ion and reaction is catalyzed by perchlorate medium. The oxidation is unaffected to variation in ionic strength. Various proposals have been suggested on the basis of reactivity of Ir[IV] and radical cation species. The activation parameters have been evaluated by employing Eyring equation. The oxidation product of CPZ has been confirmed spectrally and a suitable mechanism has been proposed.

Ionic strength-independent potentiometric cation concentration sensing on paper using a tetrabutylammonium-based reference electrode

Ion-selective electrodes (ISEs) are known not to strictly measure the concentration of ions, but their activities. The relationship between the two varies with ionic strength, which may result in measurement errors if samples of variable ionic strength are measured and concentration is chosen as the sensor output. Traditionally, concentration readings from potentiometric signals have been possible if the ionic strength of the solution matches that of the calibrant or is made constant by an ionic strength adjusting buffer. In this work, a direct concentration output is realized for a potassium-selective electrode by using a TBA+ (tetrabutylammonium)-selective membrane as the reference electrode and preloading a TBA+ salt in the solution channel. It is shown that the activity coefficients for K+ and TBA+ change similarly to effectively cancel out the influence of ionic strength, allowing for direct potentiometric concentration measurements with deviations from ideality of < 1 mV. The approach was realized on paper-based analytical devices (PADs). The potentiometric concentration data on paper were found to be independent of ionic strength and, owing to their geometric feature, of sample volume. K+ concentration in grape juice, infused water and green tea analyzed by the newly developed PADs showed good correspondence with Atomic Emission Spectroscopy (AES).

Adsorption of Organic Dyes on Magnetic Iron Oxide Nanoparticles. Part I: Mechanisms and Adsorption-Induced Nanoparticle Agglomeration.

This series of two papers is devoted to the effect of organic dye (methylene blue, MB; or methyl orange, MO) adsorption on the surface of either bare or citrate-coated magnetic iron oxide nanoparticles (IONPs) on their primary agglomeration (in the absence of an applied magnetic field) and secondary field-induced agglomeration. The present paper (Part I) is focused on physicochemical mechanisms of dye adsorption and adsorption-induced primary agglomeration of IONPs. Dye adsorption to oppositely charged IONPs is found to be mostly promoted by electrostatic interactions and is very sensitive to pH and ionic strength variations. The shape of adsorption isotherms is correctly reproduced by the Langmuir law. For the particular MB/citrated IONP pair, the maximum surface density of adsorbed MB seems to correspond to the packing density of an adsorbed monolayer rather than to the surface density of the available adsorption sites. MB is shown to form H-aggregates on the surface of citrate-coated IONPs. The effective electric charge on the IONP surface remains nearly constant in a broad range of surface coverages by MB due to the combined action of counterion exchange and counterion condensation. Primary agglomeration of IONPs (revealed by an exponential increase of hydrodynamic size with surface coverage by MB) probably comes from correlation attractions or π-stacking aromatic interactions between adsorbed MB molecules or H-aggregates. From the application perspective, the maximum adsorption capacity is 139 ± 4 mg/g for the MB/citrated IONP pair (pH = 4–11) and 257 ± 16 mg/g for the MO/bare IONP pair (pH ∼ 4). Citrated IONPs have shown a good potential for their reusability in water treatment, with the adsorption efficiency remaining about 99% after nine adsorption/desorption cycles.

EFFECTS OF PH, TEMPERATURE, IONIC STRENGTH AND ORGANIC MATTER ON TRICLOCARBAN SOLUBILITY

The solubility of triclocarban in ultrapure water and in several natural aqueous solutions is influenced by several environmental factors. In this study the variation of temperature, pH, ionic strength and concentration of the organic matter over the solubility of triclocarban was analysed. The results show that the solubility of triclocarban increases by increasing the contact time, longer than the time of equilibrium and the temperature. It is less influenced by the variations of pH and strongly influenced by the variation of ionic strength and by the natural organic matter into the studied aqueous matrices.

Controlled Trafficking of Multiple and Diverse Cations Prompts Nucleic Acid Hydrolysis.

Recent in crystallo reaction intermediates have detailed how nucleic acid hydrolysis occurs in the RNA ribonuclease H1 (RNase H1), a fundamental metalloenzyme involved in maintaining the human genome. At odds with the previous characterization, these in crystallo structures unexpectedly captured multiple metal ions (K+ and Mg2+) transiently bound in the vicinity of the two-metal-ion active site. Using multi-microsecond all-atom molecular dynamics and free-energy simulations, we investigated the functional implications of the dynamic exchange of multiple K+ and Mg2+ ions at the RNase H1 reaction center. We found that such ions are timely positioned at non-overlapping locations near the active site, at different stages of catalysis, being crucial for both reactants' alignment and leaving group departure. We also found that this cation trafficking is tightly regulated by variations of the solution's ionic strength and is aided by two conserved second-shell residues, E188 and K196, suggesting a mechanism for the cations' recruitment during catalysis. These results indicate that controlled trafficking of multi-cation dynamics, opportunely prompted by second-shell residues, is functionally essential to the complex enzymatic machinery of the RNase H1. These findings revise the current knowledge on the RNase H1 catalysis and open new catalytic possibilities for other similar metalloenzymes including, but not limited to, CRISPR-Cas9, group II intron ribozyme and the human spliceosome.

Deciphering the Molecular Mechanism of Water Interaction with Gelatin Methacryloyl Hydrogels: Role of Ionic Strength, pH, Drug Loading and Hydrogel Network Characteristics.

Water plays a primary role in the functionality of biomedical polymers such as hydrogels. The state of water, defined as bound, intermediate, or free, and its molecular organization within hydrogels is an important factor governing biocompatibility and hemocompatibility. Here, we present a systematic study of water states in gelatin methacryloyl (GelMA) hydrogels designed for drug delivery and tissue engineering applications. We demonstrate that increasing ionic strength of the swelling media correlated with the proportion of non-freezable bound water. We attribute this to the capability of ions to create ion–dipole bonds with both the polymer and water, thereby reinforcing the first layer of polymer hydration. Both pH and ionic strength impacted the mesh size, having potential implications for drug delivery applications. The mechanical properties of GelMA hydrogels were largely unaffected by variations in ionic strength or pH. Loading of cefazolin, a small polar antibiotic molecule, led to a dose-dependent increase of non-freezable bound water, attributed to the drug’s capacity to form hydrogen bonds with water, which helped recruit water molecules in the hydrogels’ first hydration layer. This work enables a deeper understanding of water states and molecular arrangement at the hydrogel–polymer interface and how environmental cues influence them.

Size Modulation of Enzymatically Cross-Linked Sodium Caseinate Nanoparticles via Ionic Strength Variation Affects the Properties of Acid-Induced Gels

Enzymatic cross-linking by microbial transglutaminase is a prominent approach to modify the structure and techno-functional properties of food proteins such as casein. However, some of the factors that influence structure-function-interrelations are still unknown. In this study, the size of cross-linked sodium caseinate nanoparticles was modulated by varying the ionic milieu during incubation with the enzyme. As was revealed by size exclusion chromatography, cross-linking at higher ionic strength resulted in larger casein particles. These formed acid-induced gels with higher stiffness and lower susceptibility to forced syneresis compared to those where the same number of ions was added after the cross-linking process. The results show that variations of the ionic milieu during enzymatic cross-linking of casein can be helpful to obtain specific modifications of its molecular structure and certain techno-functional properties. Such knowledge is crucial for the design of protein ingredients with targeted structure and techno-functionality.