Search Results (31)

Specific ion effects are widespread and have been studied for over a century, yet they remain poorly understood. Terms like “kosmotropes” and “chaotropes” are convenient rules of thumb but the frequent reversal of the Hofmeister series implies their limitations. Polarizability is often used to classify ions, with kosmotropes considered low in polarizability and chaotropes high. However, for polyatomic ions, this framework becomes misleading. The anisotropic nature of polarizability in polyatomic ions plays a decisive role in shaping their behavior. In this work, we study pseudohalides (KOCN, KSCN, and KSeCN) aqueous solutions to explore these effects. We evaluate properties of these anions through experimental measurements of conductivity, density, viscosity, infrared spectra, and polarizability. Our results demonstrate that, even for linear isoelectronic polyatomic ions, the anisotropy of polarizability governs their hydration behavior. Full article

Specific ion effects on the structure and function of many biological macromolecules, their associations, colloidal systems, interfacial phenomena, and even “simple” electrolytes solutions are ubiquitous. The molecular origin of such phenomena is discussed either as a salt-induced change of the water structure (the hydrogen bond network) or some specific (solvent mediated) interactions of one or both of the ions of the electrolyte with the investigated co-solute (macromolecules or colloidal particles). The case of hydrogels is of high interest but is only marginally explored with respect to other physico-chemical systems because they are formed through the interactions of gelling agents in the presence of water and the added electrolyte. In addition, hydrogels in a physiological environment, in which they are used for biomedical applications, may be subjected to fluctuations in their ionic environment. In this review, specific ion effects on the properties of hydrogels (made from macromolecules or small-molecular-weight gelators) are reviewed and discussed. In particular, the importance of specific ion binding to the molecules constituting the gel network versus the effect of the same ions on the structure of water is discussed. Full article

The interactions and structural organization of water molecules play a crucial role in a wide range of physical, chemical, and biological processes. The ability of water to form hydrogen bonds (H-bonds) underpins its unique properties and enables it to respond dynamically to various environmental factors. These interactions at the molecular level may affect vital processes like protein folding, enzyme activity, and cellular organization. The presence of solutes and spatial constraints can alter the H-bonding network of water, and these effects are ubiquitous in the biological environment. In this study, we analyzed the fluorescence of 2-acetyl-6-(dimethylamino)naphthalene (ACDAN) fluorescence emission in water solutions containing kosmotropic and chaotropic salts and in agar hydrogels. Recently, this dye has proven invaluable in studying water network structure and dynamics, as its fluorescence signal changes based on the local dielectric environment, revealing variations in the dipolar relaxation of water. Our results show that ACDAN spectral response correlates with the degree of water ordering, providing important insights into solute–water interactions and water dynamics in free and confined environments. Full article

The Hofmeister series categorizes ions based on their effects on protein stability, yet the microscopic mechanism remains a mystery. In this series, NaCl is neutral, Na₂SO₄ and Na₂HPO₄ are kosmotropic, while GdmCl and NaSCN are chaotropic. This study employs CD and NMR to investigate the effects of NaCl, Na₂SO₄, and Na₂HPO₄ on the conformation, stability, binding, and backbone dynamics (ps-ns and µs-ms time scales) of the WW4 domain with a high stability and accessible side chains at concentrations ≤ 200 mM. The results indicated that none of the three salts altered the conformation of WW4 or showed significant binding to the four aliphatic hydrophobic side chains. NaCl had no effect on its thermal stability, while Na₂SO₄ and Na₂HPO₄ enhanced the stability by ~5 °C. Interestingly, NaCl only weakly interacted with the Arg27 amide proton, whereas Na₂SO₄ bound to Arg27 and Phe31 amide protons with Kd of 32.7 and 41.6 mM, respectively. Na₂HPO₄, however, bound in a non-saturable manner to Trp9, His24, and Asn36 amide protons. While the three salts had negligible effects on ps-ns backbone dynamics, NaCl and Na₂SO₄ displayed no effect while Na₂HPO₄ significantly increased the µs-ms backbone dynamics. These findings, combined with our recent results with GdmCl and NaSCN, suggest a microscopic mechanism for the Hofmeister series. Additionally, the data revealed a lack of simple correlation between thermodynamic stability and backbone dynamics, most likely due to enthalpy–entropy compensation. Our study rationalizes the selection of chloride and phosphate as the primary anions in extracellular and intracellular spaces, as well as polyphosphate as a primitive chaperone in certain single-cell organisms. Full article

The ability of thermoresponsive polymers to respond to temperature with a reversible conformational change makes them promising ‘smart’ materials for solutions in medical and biotechnological applications. In this work, two such polymers and structural isomers were studied: poly(N-isopropyl acrylamide) (PNiPAm) and poly(2-isopropyl-2-oxazoline) (PiPOx). We compare the critical solution temperatures (CST) of these polymers in D₂O and H₂O in the presence of Hofmeister series salts, as results obtained under these different solvent conditions are often compared. D₂O has a higher dipole moment and electronegativity than H₂O, which could significantly alter the CST transition. We used two complementary methods to measure the CST, dynamic light scattering (DLS) and differential scanning calorimetry (DSC) and found that the CST decreased significantly in D₂O compared to H₂O. In the presence of highly concentrated kosmotropes, the CST of both polymers decreased in both solvents. The influence of the kosmotropic anions was smaller than the water isotope effect at low ionic strengths but considerably higher at physiological ionic strengths. However, the Hofmeister anion effect was quantitatively different in H₂O than in D₂O, with the largest relative differences observed for Cl⁻, where the CSTs in D₂O decreased more than in H₂O measured by DLS but less by DSC. PiPOx was more sensitive than PNiPAm to the presence of chaotropes. It exhibited much higher transition enthalpies and multistep transitions, especially in aqueous solutions. Our results highlight that measurements of thermoresponsive polymer properties in D₂O cannot be compared directly or quantitatively to application conditions or even measurements performed in H₂O. Full article

N-Hydroxyurea (HU) is an important chemotherapeutic agent used as a first-line treatment in conditions such as sickle cell disease and $\beta$-thalassemia, among others. To date, its properties as a hydrated molecule in the blood plasma or cytoplasm are dramatically understudied, although they may be crucial to the binding of HU to the radical catalytic site of ribonucleotide reductase, its molecular target. The purpose of this work is the comprehensive exploration of HU hydration. The topic is studied using ab initio molecular dynamic (AIMD) simulations that apply a first principles representation of the electron density of the system. This allows for the calculation of infrared spectra, which may be decomposed spatially to better capture the spectral signatures of solute–solvent interactions. The studied molecule is found to be strongly hydrated and tightly bound to the first shell water molecules. The analysis of the distance-dependent spectra of HU shows that the E and Z conformers spectrally affect, on average, 3.4 and 2.5 of the closest H₂O molecules, respectively, in spheres of radii of 3.7 Å and 3.5 Å, respectively. The distance-dependent spectra corresponding to these cutoff radii show increased absorbance in the red-shifted part of the water OH stretching vibration band, indicating local enhancement of the solvent’s hydrogen bond network. The radially resolved IR spectra also demonstrate that HU effortlessly incorporates into the hydrogen bond network of water and has an enhancing effect on this network. Metadynamics simulations based on AIMD methodology provide a picture of the conformational equilibria of HU in solution. Contrary to previous investigations of an isolated HU molecule in the gas phase, the Z conformer of HU is found here to be more stable by 17.4 kJ·mol⁻¹ than the E conformer, pointing at the crucial role that hydration plays in determining the conformational stability of solutes. The potential energy surface for the OH group rotation in HU indicates that there is no intramolecular hydrogen bond in Z-HU in water, in stark contrast to the isolated solute in the gas phase. Instead, the preferred orientation of the hydroxyl group is perpendicular to the molecular plane of the solute. In view of the known chaotropic effect of urea and its N-alkyl-substituted derivatives, N-hydroxyurea emerges as a unique urea derivative that exhibits a kosmotropic ordering of nearby water. This property may be of crucial importance for its binding to the catalytic site of ribonucleotide reductase with a concomitant displacement of a water molecule. Full article

Self-assembly of the blood protein fibrinogen is a highly relevant topic in materials science and medical research. This originates from fibrinogen’s beneficial material properties such as cell interaction and biocompatibility. Within recent decades, several enzyme-free strategies to create fibers and hydrogels out of fibrinogen have been presented, broadening the spectrum of fibrinogen-based material enormously. Herein, we describe a further method to obtain such a material by adding specifically MgSO₄ to fibrinogen. The key of this material is the combination of Mg²⁺ and a kosmotropic anion, for example sulfate or (hydrogen)phosphate. This effect is most likely related to occupancy of fibrinogen’s well-known binding sites for Mg²⁺, resulting in a significant increase in fiber yield and gel stability. Here, we shine light on the question of how electrostatic interactions via Mg²⁺ enhance fibrillogenesis and the gelation of fibrinogen and discuss first insights into the material’s properties. Full article

Amyloid fibrils have immense potential to become the basis of modern biomaterials. The formation of amyloid fibrils in vitro strongly depends on the solvent properties. Ionic liquids (ILs), alternative solvents with tunable properties, have been shown to modulate amyloid fibrillization. In this work, we studied the impact of five ILs with 1-ethyl-3-methylimidazolium cation [EMIM⁺] and anions of Hofmeisterseries hydrogen sulfate [HSO₄⁻], acetate [AC⁻], chloride [Cl⁻], nitrate [NO₃⁻], and tetrafluoroborate [BF₄⁻] on the kinetics of insulin fibrillization and morphology, and the structure of insulin fibrils when applying fluorescence spectroscopy, AFM and ATR-FTIR spectroscopy. We found that the studied ILs were able to speed up the fibrillization process in an anion- and IL-concentration-dependent manner. At an IL concentration of 100 mM, the efficiency of the anions at promoting insulin amyloid fibrillization followed the reverse Hofmeister series, indicating the direct binding of ions with the protein surface. At a concentration of 25 mM, fibrils with different morphologies were formed, yet with similar secondary structure content. Moreover, no correlation with the Hofmeister ranking was detected for kinetics parameters. IL with the kosmotropic strongly hydrated [HSO₄⁻] anion induced the formation of large amyloid fibril clusters, while the other kosmotropic anion [AC⁻] along with [Cl⁻] led to the formation of fibrils with similar needle-like morphologies to those formed in the IL-free solvent. The presence of the ILs with the chaotropic anions [NO₃⁻] and [BF₄⁻] resulted in longer laterally associated fibrils. The effect of the selected ILs was driven by a sensitive balance and interplay between specific protein–ion and ion–water interactions and non-specific long-range electrostatic shielding. Full article

In this work, we report the synthesis of novel triple hydrophilic statistical terpolymers consisting of three different methacrylate monomers with varying degrees of responsivity to solution conditions. Terpolymers of the type poly(di(ethylene glycol) methyl ether methacrylate-co-2-(dimethylamino)ethylmethacrylate-co-oligoethylene glycol methyl ether methacrylate), P(DEGMA-co-DMAEMA-co-OEGMA), and of different compositions, were prepared by using the RAFT methodology. Their molecular characterization was carried out using size exclusion chromatography (SEC) and spectroscopic techniques, including ¹H-NMR and ATR-FTIR. Studies in dilute aqueous media by dynamic and electrophoretic light scattering (DLS and ELS) show their potential responsiveness regarding changes in temperature, pH, and kosmotropic salt concentration. Finally, the change in hydrophilic/hydrophobic balance of the formed terpolymer nanoparticles during heating and cooling was studied using fluorescence spectroscopy (FS) in conjunction with pyrene giving additional information on the responsiveness and internal structure of the self-assembled nanoaggregates. Full article

Unlike halides, where the kosmotropicity decreases from fluoride to iodide, the kosmotropic nature of halates apparently increases from chlorate to iodate, in spite of the lowering in the static ionic polarizability. In this paper, we present an experimental study that confirms the results of previous simulations. The lyotropic nature of aqueous solutions of sodium halates, i.e., NaClO₃, NaBrO₃, and NaIO₃, is investigated through density, conductivity, viscosity, and refractive index measurements as a function of temperature and salt concentration. From the experimental data, we evaluate the activity coefficients and the salt polarizability and assess the anions’ nature in terms of kosmotropicity/chaotropicity. The results clearly indicate that iodate behaves as a kosmotrope, while chlorate is a chaotrope, and bromate shows an intermediate nature. This experimental study confirms that, in the case of halates XO₃⁻, the kosmotropic–chaotropic ranking reverses with respect to halides. We also discuss and revisit the role of the anion’s polarizability in the interpretation of Hofmeister phenomena. Full article

Membrane chromatography is a modern, high-throughput separation method that finds important applications in therapeutic protein purification. Multimodal, salt-tolerant membranes are the most recent innovation in chromatographic membrane adsorbents. Due to the complex structure of their ligands and the bimodal texture of their carriers, their adsorption properties have not been sufficiently investigated. This work deals with the equilibrium and kinetic properties of a multimodal anion-exchange chromatography membrane, Sartobind STIC. Single- and two-component adsorption experiments were carried out with bovine serum albumin (BSA) and salmon DNA as model target and impurity components. The effect of the Hofmeister series ions and ionic strength on the BSA/DNA adsorption was investigated in micromembrane flow experiments. A significant difference was observed between the effects of monovalent and polyvalent ions when strong kosmotropic salts with polyvalent anions acted as strong displacers of BSA. On the contrary, DNA binding was rather high at elevated ionic strength, independent of the salt type. Two-component micromembrane experiments confirmed very high selectivity of DNA binding at a rather low sodium sulfate feed content and at pH 8. The strength of binding was examined in more than a dozen different desorption experiments. While BSA was desorbed relatively easily using high salt concentrations independent of buffer type and pH, while DNA was desorbed only in a very limited measure under any conditions. Separation experiments in a laboratory membrane module were carried out for the feed containing 1 g/L of BSA, 0.3 g/L of DNA, and 0.15 M of sodium sulfate. The negative flow-through mode was found to be more advantageous than the bind-elute mode, as BSA was obtained with 99% purity and a 97% yield. Membrane reuse was investigated in three adsorption-desorption-regeneration cycles. Full article

It is known from in vitro studies that macromolecular crowding in the cell effects protein structure, stability and function; but predictive studies are relatively unexplored. There are few reports where the effect of various crowder mixtures has been exploited to discern their combined effect on the structural stability of proteins. These studies are more significant because their effect can mimicked with in vivo conditions, where the environment is heterogeneous. Effects of two crowders, polyethylene glycol (PEG 400 Da), and its monomer ethylene glycol (EG) alone and in mixture on the structural stability of cytochrome c (cyt c) were determined using various spectroscopic and bioinformatics tools. The main conclusions of our study are (i) the monomer EG has a kosmotropic effect on the protein (stabilizes the protein), and has no significant effect on the tertiary structure; (ii) PEG 400 destabilizes the structure as well as the stability of the protein; and (iii) EG counteracts the destabilizing effect of PEG 400. From this investigation, it seems evident that proteins may fold or unfold in the crowded environment of the cell where various interactions assist them to maintain their structure for their functions. Bioinformatics approaches were also used to support all of the in vitro observations. Cyt c is functional protein; if the structure of the protein is modulated due to change in the environment its nature of function will also change. Our research addresses the question by modulating the environment around the protein, and the macromolecule (protein) conformation dynamics and interaction study via in vitro and in silico approaches which indirectly compares with that of the environment in-cellular milieu, which is highly crowded. Full article

Steric exclusion chromatography (SXC) is a promising purification method for biological macromolecules such as the Orf virus (ORFV) vector. The method’s principle is closely related to conventional polyethylene glycol (PEG) precipitation, repeatedly implementing membranes as porous chromatographic media. In the past decade, several purification tasks with SXC showed exceptionally high yields and a high impurity removal. However, the effect of varying process parameters, on the precipitation success and its limitations to SXC, is not yet well understood. For this reason, the precipitation behavior and SXC adaptation for ORFV were investigated for the PEG/ORFV contact time, the membranes pore size, and the type and concentration of ions. All three parameters influenced the ORFV recoveries significantly. A small pore size and a long contact time induced filtration effects and inhibited a full virus recovery. The application of salts had complex concentration-dependent effects on precipitation and SXC yields, and ranged from a complete prevention of precipitation in the presence of kosmotropic substances to increased efficiencies with Mg²⁺ ions. The latter finding might be useful to reduce PEG concentrations while maintaining high yields. With this knowledge, we hope to clarify several limitations of SXC operations and improve the tool-set for a successful process adaptation. Full article

A hyphenated pressurized hot water—aqueous two-phase extraction (PHW-ATPE) method was applied to extract solasodine from Solanum mauritianum (S. mauritianum). A central composite design (CCD) was applied to determine the optimal conditions for the extraction of solasodine. The parameters evaluated included the percentage concentration of salt (NaCl or Na₂CO₃) and temperature. The fit of the central composite design response surface model for PHW-ATPE to the data generated a model with a good quadratic fit (R² = 0.901). The statistically significant (p < 0.05) parameters, such as the linear and quadratic effects of the concentration of salt (%) powder, had a significant impact on the extraction of solasodine. The application of multiply charged salts such as Na₂CO₃ (kosmotrope) was shown to be a comparably better extractant of solasodine than NaCl (chaotrope) due to the salting-out effect. The optimized conditions for extraction of solasodine with NaCl or Na₂CO₃ were a temperature of 80 °C at a salt concentration of 20%. The maximum extraction of solasodine was 300.79 mg kg⁻¹ and 162.34 mg kg⁻¹ for Na₂CO₃ and NaCl, respectively. Full article

In this study, the protein stability of hen egg-white lysozymes (HEWL) by Fe₃O₄ and Fe₃O₄-coated trehalose (Fe₃O₄@Tre) magnetic nanoparticles (NPs) is investigated. For this purpose, the co-precipitation method was used to synthesize magnetic NPs. The synthesized NPs were characterized by XRD, FT-IR spectroscopy, FE-SEM, and VSM analysis. In addition, the stability of HEWLs exposed to different NP concentrations in the range of 0.001–0.1 mg mL⁻¹ was investigated by circular dichroism (CD) spectroscopy, fluorescence, and UV-Vis analysis. Based on the results, in the NP concentration range of 0.001–0.04 mg mL⁻¹ the protein structure is more stable, and this range was identified as the range of kosmotropic concentration. The helicity was measured at two concentration points of 0.02 and 0.1 mg mL⁻¹. According to the results, the α-helix at 0.02 mg mL⁻¹ of Fe₃O₄ and Fe₃O₄@Tre was increased from 35.5% for native protein to 37.7% and 38.7%, respectively. The helicity decreased to 36.1% and 37.4%, respectively, with increasing the concentration of Fe₃O₄ and Fe₃O₄@Tre to 0.1 mg mL⁻¹. The formation of hydrated water shells around protein molecules occurred by using Fe₃O₄@Tre NPs. Hence, it can be concluded that the trehalose as a functional group along with magnetic NPs can improve the stability of proteins in biological environments. Full article