Charge density-dependent strength of hydration and biological structure

Thermal Stability of bivalent cation/phosphoinositide domains in model membranes

As key mediators in a wide array of signaling events, phosphoinositides (PIPs) orchestrate the recruitment of proteins to specific cellular locations at precise moments. This intricate spatiotemporal regulation of protein activity often necessitates the localized enrichment of the corresponding PIP. We investigate the extent and thermal stabilities of phosphatidylinositol-4-phosphate (PI(4)P), phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2 and phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P3) clusters with calcium and magnesium ions. We observe negligible or minimal clustering of all examined PIPs in the presence of Mg2+ ions. While PI(4)P shows in the presence of Ca2+ no clustering, PI(4,5)P2 forms with Ca2+ strong clusters that exhibit stablity up to at least 80°C. The extent of cluster formation for the interaction of PI(3,4,5)P3 with Ca2+ is less than what was observed for PI(4,5)P2, yet we still observe some clustering up to 80°C. Given that cholesterol has been demonstrated to enhance PIP clustering, we examined whether bivalent cations and cholesterol synergistically promote PIP clustering. We found that the interaction of Mg2+ or Ca2+ with PI(4)P remains extraordinarily weak, even in the presence of cholesterol. In contrast, we observe synergistic interaction of cholesterol and Ca2+ with PI(4,5)P2. Also, in the presence of cholesterol, the interaction of Mg2+ with PI(4,5)P2 remains weak. PI(3,4,5)P3 does not show strong clustering with cholesterol for the experimental conditions of our study and the interaction with Ca2+ and Mg2+ was not influenced by the presence of cholesterol.

Competitive Effects of Anions on Protein Solvation by Aqueous Ionic Liquids

The present study utilizes molecular dynamics simulations to examine how different anions compete for protein solvation in aqueous solutions of ionic liquids (ILs). Ubiquitin is used as model protein and studied in IL mixtures sharing the same cation, 1-ethyl-3-methylimidazolium (EMIM), and two different anions in the same solution, from combinations of dicyanamide (DCA), chloride (Cl), nitrate (NO3), and tetrafluoroborate (BF4). Our findings reveal that specific interactions between anions and the protein are paramount in IL solvation, but that combinations of anions are not additive. For example, DCA exhibits a remarkable ability to form hydrogen bonds with the protein, resulting in a significantly stronger preferential binding to the protein than other anions. However, the combination of DCA with NO3, which also forms hydrogen bonds with the protein, results in a smaller preferential solvation of the protein than the combination of DCA with chloride ions, which are weaker binders. Thus, combining anions with varying affinities for the protein surface modulates the overall ion accumulation through nonadditive mechanisms, highlighting the importance of the understanding of competition for specific interaction sites, cooperative binding, bulk-solution affinity, and overall charge compensations, on the overall solvation capacity of the solution. Such knowledge may allow for the design of novel IL-based processes in biotechnology and material science, where fine-tuning protein solvation is crucial for optimizing performance and functionality.

Dynamic Ion Correlations and Ion-Pair Lifetimes in Aqueous Alkali Metal Chloride Electrolytes

Electrolytes are central to many technological applications, as well as life itself. The behavior and properties of electrolytes are often described in terms of ion pairs, whereby ions associate as either contact ion pairs (in which ions are "touching") solvent-separated ion pairs (in which ions' solvent shells overlap) or solvent-solvent-separated ion pairs (in which ions' solvent shells are distinct). However, this paradigm is generally restricted to statistically averaged descriptions of solution structure and ignores temporal behavior. Here we elucidate the time-resolved dynamics of these ion-ion interactions in aqueous metal chloride electrolytes using the partial van Hove correlation function, based on polarizable molecular dynamics simulations. Our results show that the existence and persistence of ion pairs in aqueous metal chloride electrolytes should not be assumed a priori, but in fact are ion specific features of the solution with lifetimes on subpicosecond time scales.

Effects of Ionic Interferents on Electrocatalytic Nitrate Reduction: Mechanistic Insight

Nitrate, a prevalent water pollutant, poses substantial public health concerns and environmental risks. Electrochemical reduction of nitrate (eNO3RR) has emerged as an effective alternative to conventional biological treatments. While extensive lab work has focused on designing efficient electrocatalysts, implementation of eNO3RR in practical wastewater settings requires careful consideration of the effects of various constituents in real wastewater. In this critical review, we examine the interference of ionic species commonly encountered in electrocatalytic systems and universally present in wastewater, such as halogen ions, alkali metal cations, and other divalent/trivalent ions (Ca2+, Mg2+, HCO3-/CO32-, SO42-, and PO43-). Notably, we categorize and discuss the interfering mechanisms into four groups: (1) loss of active catalytic sites caused by competitive adsorption and precipitation, (2) electrostatic interactions in the electric double layer (EDL), including ion pairs and the shielding effect, (3) effects on the selectivity of N intermediates and final products (N2 or NH3), and (4) complications by the hydrogen evolution reaction (HER) and localized pH on the cathode surface. Finally, we summarize the competition among different mechanisms and propose future directions for a deeper mechanistic understanding of ionic impacts on eNO3RR.

Facile Preconcentration of Cell-Free DNA in Human Plasma by Ion-Specific Poly Ionic Sorbents Featuring an Anion Exchange Mechanism

The expanding horizon of diagnostic and therapeutic applications involving nucleic acids (NA) requires novel tools for purification, including minimal sample preparation. In this work, thin-film microextraction devices featuring five poly ionic sorbents were examined as anion exchange extraction phases for the rapid purification of NAs. Each sorbent is composed of a nonionic cross-linker and a methacrylate monomer containing a core tetra-alkyl ammonium moiety with an alkyl, anionic, or cationic residue. Extraction devices were produced through the application of the prepolymer sorbent mixture onto a functionalized nitinol metal support followed by photoinduced free-radical polymerization. The miniaturized extraction devices (10 mm × 3.5 mm) were directly immersed into aqueous samples to isolate NAs via electrostatic interactions with the polycation. The ammonium methacrylate (AMA) monomer containing a propyl trimethylammonium group (AMA-C3N(CH3)3) exhibited the highest affinity for DNA, with 80 ± 10% of DNA being isolated. Recovery of DNA from the sorbents required the introduction of ions in an aqueous solution to exchange the anionic biopolymer from the polycationic moiety. An investigation of three anion species revealed that the AMA-C3N(CH3)3 sorbent showed the highest recoveries, with the perchlorate anion producing a preconcentration factor of 4.36 ± 0.86 while requiring only 250 mM NaClO4. A directly compatible quantitative polymerase chain reaction assay was developed to quantify the recovery of spiked DNA with lengths of 830, 204, and 98 base pairs in heat-treated human plasma. The AMA-C3N(CH3)3 sorbent was uninhibited by the complex human plasma matrix and enabled high preconcentration factors for the spiked DNA at a biologically relevant concentration of 10 pg/mL. While Qiagen's circulating cell-free DNA MinElute extraction kit enabled higher preconcentration of all analytes, the methodology described in this work requires fewer steps, less user intervention, and minimal equipment requirements to isolate DNA, making it more amenable for high-throughput and low resource applications.

Biomolecular condensates are characterized by interphase electric potentials

Biomolecular condensates form via processes that combine phase separation and reversible associations of multivalent macromolecules. Condensates can be two- or multi-phase systems defined by coexisting dense and dilute phases. Here, we show that solution ions can partition asymmetrically across coexisting phases defined by condensates formed by intrinsically disordered proteins or homopolymeric RNA molecules. Our findings were enabled by direct measurements of the activities of cations and anions within coexisting phases of protein and RNA condensates. Asymmetries in ion partitioning between coexisting phases vary with protein sequence, condensate type, salt concentration, and ion type. The Donnan equilibrium set up by asymmetrical partitioning of solution ions generates interphase electric potentials known as Donnan and Nernst potentials. Our measurements show that the interphase potentials of condensates are of the same order of magnitude as membrane potentials of membrane-bound organelles. Interphase potentials quantify the degree to which microenvironments of coexisting phases are different from one another. Importantly, and based on condensate-specific interphase electric potentials, which are membrane-like potentials of membraneless bodies, we reason that condensates are mesoscale capacitors that store charge. Interphase potentials lead to electric double layers at condensate interfaces. This helps explain recent observations of condensate interfaces being electrochemically active.

Biophysical Principles Emerging from Experiments on Protein-Protein Association and Aggregation

Protein-protein association and aggregation are fundamental processes that play critical roles in various biological phenomena, from cellular signaling to disease progression. Understanding the underlying biophysical principles governing these processes is crucial for elucidating their mechanisms and developing strategies for therapeutic intervention. In this review, we provide an overview of recent experimental studies focused on protein-protein association and aggregation. We explore the key biophysical factors that influence these processes, including protein structure, conformational dynamics, and intermolecular interactions. We discuss the effects of environmental conditions such as temperature, pH and related buffer-specific effects, and ionic strength and related ion-specific effects on protein aggregation. The effects of polymer crowders and sugars are also addressed. We list the techniques used to study aggregation. We analyze emerging trends and challenges in the field, including the development of computational models and the integration of multidisciplinary approaches for a comprehensive understanding of protein-protein association and aggregation.

Bioinspired Dopamine and N-Oxide-Based Zwitterionic Polymer Brushes for Fouling Resistance Surfaces

Biofouling is a great challenge for engineering material in medical-, marine-, and pharmaceutical-related applications. In this study, a novel trimethylamine N-oxide (TMAO)-analog monomer, 3-(2-methylacrylamido)-N,N-dimethylpropylamine N-oxide (MADMPAO), was synthesized and applied for the grafting of poly(MADMPAO) (pMPAO) brushes on quartz crystal microbalance (QCM) chips by the combination of bio-inspired poly-dopamine (pDA) and surface-initiated atom transfer radical polymerization technology. The result of ion adsorption exhibited that a sequential pDA and pMPAO arrangement from the chip surface had different characteristics from a simple pDA layer. Ion adsorption on pMPAO-grafted chips was greatly inhibited at low salt concentrations of 1 and 10 mmol/L due to strong surface hydration in the presence of charged N+ and O- of zwitterionic pMPAO brushes on the outer layer on the chip surface, well known as the "anti-polyelectrolyte" effect. During BSA adsorption, pMPAO grafting also led to a marked decrease in frequency shift, indicating great inhibition of protein adsorption. It was attributed to weaker BSA-pMPAO interaction. In this study, the Au@pDA-4-pMPAO chip with the highest coating concentration of DA kept stable dissipation in BSA adsorption, signifying that the chip had a good antifouling property. The research provided a novel monomer for zwitterionic polymer and demonstrated the potential of pMPAO brushes in the development and modification of antifouling materials.

Addition of sodium malonate alters the morphology and increases the critical flux during tangential flow filtration of precipitated immunoglobulins

Recent studies have demonstrated that one can control the packing density, and in turn the filterability, of protein precipitates by changing the pH and buffer composition of the precipitating solution to increase the structure/order within the precipitate. The objective of this study was to examine the effect of sodium malonate, which is known to enhance protein crystallizability, on the morphology of immunoglobulin precipitates formed using a combination of ZnCl2 and polyethylene glycol. The addition of sodium malonate significantly stabilized the precipitate particles as shown by an increase in melting temperature, as determined by differential scanning calorimetry, and an increase in the enthalpy of interaction, as determined by isothermal titration calorimetry. The sodium malonate also increased the selectivity of the precipitation, significantly reducing the coprecipitation of DNA from a clarified cell culture fluid. The resulting precipitate had a greater packing density and improved filterability, enabling continuous tangential flow filtration with minimal membrane fouling relative to precipitates formed under otherwise identical conditions but in the absence of sodium malonate. These results provide important insights into strategies for controlling precipitate morphology to enhance the performance of precipitation-filtration processes for the purification of therapeutic proteins.

Can Aluminum Cations Promote Nucleation for THF Hydrate Growth?

Rapid nucleation of tetrahydrofuran (THF) hydrate is essential for developing a THF hydrate-based cold storage technology. Earlier works have hypothesized the role of aluminum complexes in initiating the nucleation of clathrate hydrates using aluminum metal electrodes and substrates. This study investigates if the nucleation promotional effect of hydrate can be achieved using the aluminum salt, AlCl3, due to the formation of aluminum aqua complexes in water. Metal chlorides NaCl and MgCl2 are also utilized to evaluate the effect of cation type in initiating nucleation, i.e., the effect of charge/radius ratio. The induction time is measured in a stirred reactor at various subcoolings and concentrations of 0.05, 0.1, 0.5, 1, and 2 wt %. The nucleation time is studied in two reactor configurations based on the nature of salt introduction in the THF solution, i.e., salt premixed in solution and salt injected inside the solution. The sudden rise in the reactor temperature due to hydrate formation is used as an indicator of hydrate formation. Results indicate that AlCl3 promotes hydrate nucleation as AlCl3 reduces induction time by 92.2% at 0.05 wt % concentration compared with water. Nearly instantaneous nucleation is also achieved by directly injecting AlCl3. MgCl2 and NaCl do not show a similar effect on induction time as AlCl3. The pH and Raman spectra measurements with and without salts are carried out to explain the effect of cations on the THF-water solution.

The biophysics of water in cell biology: perspectives on a keystone for both marine sciences and cancer research

The biophysics of water, has been debated over more than a century. Although its importance is still underestimated, significant breakthroughs occurred in recent years. The influence of protein condensation on water availability control was documented, new findings on water-transport proteins emerged, and the way water molecules rearrange to minimize free energy at interfaces was deciphered, influencing membrane thermodynamics. The state of knowledge continued to progress in the field of deep-sea marine biology, highlighting unknown effects of high hydrostatic pressure and/or temperature on interactions between proteins and ligands in extreme environments, and membrane structure adaptations. The role of osmolytes in protein stability control under stress is also discussed here in relation to fish egg hydration/buoyancy. The complexity of water movements within the cell is updated, all these findings leading to a better view of their impact on many cellular processes. The way water flow and osmotic gradients generated by ion transport work together to produce the driving force behind cell migration is also relevant to both marine biology and cancer research. Additional common points concern water dynamic changes during the neoplastic transformation of cells and tissues, or embryo development. This could improve imaging techniques, early cancer diagnosis, and understanding of the molecular and physiological basis of buoyancy for many marine species.

Protein Thermodynamic Properties, Crystallisation, and the Hofmeister Series

The Hofmeister series is a series of ions ordered according to their ability to precipitate proteins. It has also been linked to a host of (bio)chemical phenomena. Several attempts over the years to correlate the series to the varying success of different salts in crystallising proteins have been largely inconclusive. A correlation, based on published data and crystallisation conditions for several proteins, is proposed here between some thermodynamic properties of proteins and the position in the Hofmeister series of the salts from which they preferentially crystallise. Namely, a high ratio between the entropic or enthalpic protein-solvent interactions contribution to thermodynamic stability and the total thermodynamic stability of a given protein, indicate the protein's high propensity to crystallise in solutions of highly kosmotropic salts. Low such ratios on the other hand, indicate that chaotropic salts can be equally successful, i. e. that the protein in question is rather indifferent to the Hofmeister character of the salt. Testing various model proteins for crystallisation against screens containing salts found at different points on the Hofmeister series, as well as further bibliographic analysis, have yielded results that appear to largely corroborate this hypothesis. These conclusions may conceivably be used as a crystallisation predictive tool.

Effect of Monovalent Cations on the Structure and Dynamics of Multimodal Chromatographic Surfaces

While multimodal (MM) chromatography is a promising approach for purifying proteins, the lack of a fundamental understanding of how ion-ligand interactions govern selectivity limits its use in the biopharmaceutical industry. This study uses molecular dynamics simulations to study the interactions between simple monovalent cations and two commonly used structurally similar multimodal chromatography ligands, the Capto ligand and Nuvia cPrime, immobilized on the surface. On the Capto ligand surface, ion presence and type play a key role in modulating the formation of phenyl rings and carboxylate clusters. The flexible linkage attaching the Capto ligand to the self-assembled monolayer (SAM) surface allowed multiple ligands to form interactions with the small cations, while large cations interacted less strongly, following the order Li+ > Na+ > K+ > Cs+. Thus, smaller cations resulted in greater ordering on the surface and lower ion diffusivities, while larger cations resulted in less ordering and higher ion diffusivities, following the order Li+ < Na+ < K+ < Cs+. In contrast, due to the rigid attachment of Nuvia cPrime to the SAM surfaces, the cations bound less strongly and had a much smaller effect on ligand clustering or ordering. Additionally, ions in the presence of the Nuvia cPrime surface had generally greater diffusivities than those in the presence of the Capto ligand. Overall, the interaction of cations with the multimodal ligands can lead to unique configurations on the SAM that likely contribute to differential behavior in biological separations.

The Current Understanding of Mechanistic Pathways in Zeolite Crystallization

Zeolite catalysts and adsorbents have been an integral part of many commercial processes and are projected to play a significant role in emerging technologies to address the changing energy and environmental landscapes. The ability to rationally design zeolites with tailored properties relies on a fundamental understanding of crystallization pathways to strategically manipulate processes of nucleation and growth. The complexity of zeolite growth media engenders a diversity of crystallization mechanisms that can manifest at different synthesis stages. In this review, we discuss the current understanding of classical and nonclassical pathways associated with the formation of (alumino)silicate zeolites. We begin with a brief overview of zeolite history and seminal advancements, followed by a comprehensive discussion of different classes of zeolite precursors with respect to their methods of assembly and physicochemical properties. The following two sections provide detailed discussions of nucleation and growth pathways wherein we emphasize general trends and highlight specific observations for select zeolite framework types. We then close with conclusions and future outlook to summarize key hypotheses, current knowledge gaps, and potential opportunities to guide zeolite synthesis toward a more exact science.

Ion-Induced PIP2 Clustering with Martini3: Modification of Phosphate-Ion Interactions and Comparison with CHARMM36

Phosphatidylinositol 4,5-bisphosphate (PIP2) is a critical lipid for cellular signaling. The specific phosphorylation of the inositol ring controls protein binding as well as clustering behavior. Two popular models to describe ion-mediated clustering of PIP2 are Martini3 (M3) and CHARMM36 (C36). Molecular dynamics simulations of PIP2-containing bilayers in solutions of potassium chloride, sodium chloride, and calcium chloride, and at two different resolutions are performed to understand the aggregation and the model parameters that drive it. The average M3 clusters of PIP2 in bilayers of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine and PIP2 bilayers in the presence of K+, Na+, or Ca2+ contained 2.2, 2.6, and 6.4 times more PIP2 than C36 clusters, respectively. Indeed, the Ca2+-containing systems often formed a single large aggregate. Reparametrization of the M3 ion-phosphate Lennard-Jones interaction energies to reproduce experimental osmotic pressure of sodium dimethyl phosphate (DMP), K[DMP], and Ca[DMP]2 solutions, the same experimental target as C36, yielded comparably sized PIP2 clusters for the two models. Furthermore, C36 and the modified M3 predict similar saturation of the phosphate groups with increasing Ca2+, although the coarse-grained model does not capture the cooperativity between K+ and Ca2+. This characterization of the M3 behavior in the presence of monovalent and divalent ions lays a foundation to study cation/protein/PIP2 clustering.

Dual Effect of Secondary Solutes on Binding Equilibria: Contributions from Solute-Reactant Interactions and Solute-Water Interactions

This study examines the role of water in binding equilibria with a special focus on secondary solutes (cosolutes) that influence the equilibrium but are not constituents of the final product. Using a thermodynamic framework that includes an explicit term for the release of water molecules upon binding, this investigation reveals how solutes may alter equilibria by changing the activity of the reactants, reflected in ΔG°(obs), and by changing the chemical potential of the solvent, reflected in ΔGS. The framework is applied to four experimental binding systems that differ in the degree of electrostatic contributions. The model systems include the chelation of Ca2+ by EDTA and three host-guest reactions; the pairings of p-sulfonatocalix[4]arene with tetramethylammonium ion, cucurbit[7]uril with N-acetyl-phenylalanine-amide, and β-cyclodextrin with adamantane carboxylate are tested. Each reaction pair is examined by isothermal titration calorimetry at 25 °C in the presence of a common osmolyte, sucrose, and a common chaotrope, urea. Molar solutions of trehalose and phosphate were also tested with selected models. In general, cosolutes that enhance binding tend to reduce the solvation free energy penalty and cosolutes that weaken binding tend to increase the solvation free energy penalty. Notably, the nonpolar-nonpolar interaction between adamantane carboxylate and β-cyclodextrin is characterized by a ΔGS value near zero. The results with β-cyclodextrin, in particular, prompt further discussions of the hydrophobic effect and the biocompatible properties of trehalose. Other investigators are encouraged to test and refine the approach taken here to further our understanding of solvent effects on molecular recognition.

Water-in-Salt: Fast Dynamics, Structure, Thermodynamics, and Bulk Properties

We present concentration-dependent dynamics of highly concentrated LiBr solutions and LiCl temperature-dependent dynamics for two high concentrations and compare the results to those of prior LiCl concentration-dependent data. The dynamical data are obtained using ultrafast optical heterodyne-detected optical Kerr effect (OHD-OKE). The OHD-OKE decays are composed of two pairs of biexponentials, i.e., tetra-exponentials. The fastest decay (t1) is the same as pure water's at all concentrations within error, while the second component (t2) slows slightly with concentration. The slower components (t3 and t4), not present in pure water, slow substantially, and their contributions to the decays increase significantly with increasing concentration, similar to LiCl solutions. Simulations of LiCl solutions from the literature show that the slow components arise from large ion/water clusters, while the fast components are from ion/water structures that are not part of large clusters. Temperature-dependent studies (15-95 °C) of two high LiCl concentrations show that decreasing the temperature is equivalent to increasing the room temperature concentration. The LiBr and LiCl concentration dependences and the two LiCl concentrations' temperature dependences all have bulk viscosities that are linearly dependent on τcslow, the correlation time of the slow dynamics (weighted averages of t3 and t4). Remarkably, all four viscosity vs 1/τCslow plots fall on the same line. Application of transition state theory to the temperature-dependent data yields the activation enthalpies and entropies for the dynamics of the large ion/water clusters, which underpin the bulk viscosity.

Highly efficient synthesis of zeolite chabazite using cooperative hydration-mismatched inorganic structure-directing agents

Chabazite (CHA type) zeolite is notoriously difficult to synthesize in the absence of organic structure-directing agents owing to long synthesis times and/or impurity formation. The ability to tailor organic-free syntheses of zeolites is additionally challenging due to the lack of molecular level understanding of zeolite nucleation and growth pathways, particularly the role of inorganic cations. In this study, we reveal that zeolite CHA can be synthesized using six different combinations of inorganic cations, including the first reported seed- and organic-free synthesis without the presence of potassium. We show that lithium, when present in small quantities, is an effective accelerant of CHA crystallization; and that ion pairings can markedly reduce synthesis times and temperatures, while expanding the design space of zeolite CHA formation in comparison to conventional methods utilizing potassium as the sole structure-directing agent. Herein, we posit the effects of cation pairings on zeolite CHA crystallization are related to their hydrated ionic radii. We also emphasize the broader implications for considering the solvated structure and cooperative role of inorganic cations in zeolite synthesis within the context of the reported findings for chabazite.

Dehydration of biological membranes in a non-condensing environment

The study of the dehydration process in a cell membrane allows a better understanding of how water is bound to it. While in prior studies, cell dehydration was commonly analyzed under osmotic stress conditions, in the present work, we focus on the dehydration driven by evaporation in a restricted condensing environment. Using a thermogravimetry method, we studied the dehydration of Escherichia coli through isothermal evaporation in the presence of a gas flux. To figure out the loss of mass in this situation, we first evaluated the dynamics of water evaporation of a suspension of multilamellar liposomes. We found that the evaporation of liposomal suspensions composed of individual lipids is constant, although slightly restricted by the presence of liposomes, while the evaporation of liposomal suspensions composed of a mixture of different lipids follows an exponential decay. This is explained considering that the internal pressure at the air-water interface is proportional to the amount of bound water. The evaporation of water from a biomass sample follows this latter behaviour.

Binding of carboxylate and water to monovalent cations

The interactions of carboxylate anions with water and cations are important for a wide variety of systems, both biological and synthetic. To gain insight on properties of the local complexes, we apply density functional theory, to treat the complex electrostatic interactions, and investigate mixtures with varied numbers of carboxylate anions (acetate) and waters binding to monovalent cations, Li+, Na+ and K+. The optimal structure with overall lowest free energy contains two acetates and two waters such that the cation is four-fold coordinated, similar to structures found earlier for pure water or pure carboxylate ligands. More generally, the complexes with two acetates have the lowest free energy. In transitioning from the overall optimal state, exchanging an acetate for water has a lower free energy barrier than exchanging water for an acetate. In most cases, the carboxylates are monodentate and in the first solvation shell. As water is added to the system, hydrogen bonding between waters and carboxylate O atoms further stabilizes monodentate structures. These structures, which have strong electrostatic interactions that involve hydrogen bonds of varying strength, are significantly polarized, with ChelpG partial charges that vary substantially as the bonding geometry varies. Overall, these results emphasize the increasing importance of water as a component of binding sites as the number of ligands increases, thus affecting the preferential solvation of specific metal ions and clarifying Hofmeister effects. Finally, structural analysis correlated with free energy analysis supports the idea that binding to more than the preferred number of carboxylates under architectural constraints are a key to ion transport.

Anion-Specific Adsorption of Carboxymethyl Cellulose on Cellulose

Integration of fiber modification step with a modern pulp mill is a resource efficient way to produce functional fibers. Motivated by the need to integrate polymer adsorption with the current pulping system, anion-specific effects in carboxymethylcellulose (CMC) adsorption have been studied. The QCM-D adsorption experiments revealed that CMC adsorption to the cellulose model surface is prone to anion-specific effects. A correlation was observed between the adsorbed CMC and the degree of hydration of the co-ions present in the magnesium salts. The presence of a chaotropic co-ion such as nitrate increased the adsorption of CMC on cellulose compared to the presence of the kosmotropic sulfate co-ion. However, anion-specificity was not significant in the case of salts containing zinc cations. The hydration of anions determines the distribution of the ions at the interface. Chaotropic ions, such as nitrates, are likely to be distributed near the chaotropic cellulose surface, causing changes in the ordering of water molecules and resulting in greater entropy gain once released from the surface, thus increasing CMC adsorption.

Anions and Cations Affect Amino Acid Dissociation Equilibria via Distinct Mechanisms

Salts reduce the pKa of weak acids by a mechanism sensitive to ion identity and concentration via charge screening of the deprotonated state. In this study, we utilize constant pH molecular dynamics simulations to understand the molecular mechanism behind the salt-dependent dissociation of aspartic acid (Asp). We calculate the pKa of Asp in the presence of a monovalent salt and investigate Hofmeister ion effects by systematically varying the ionic radii. We observe that increasing the anion size leads to a monotonic decrease in Asp pKa. Conversely, the cation size affects the pKa nonmonotonically, interpretable in the context of the law of matching water affinity. The net effect of salt on Asp acidity is governed by an interplay of solvation and competing ion interactions. The proposed mechanism is rather general and can be applicable to several problems in Hofmeister ion chemistry, such as pH effects on protein stability and soft matter interfaces.

Adaptive Adhesions of Barnacle-Inspired Adhesive Peptides

The strategy of robust adhesion employed by barnacles renders them fascinating biomimetic candidates for developing novel wet adhesives. Particularly, barnacle cement protein 19k (cp19k) has been speculated to be the key adhesive protein establishing the priming layer in the initial barnacle cement construction. In this work, we systematically studied the sequence design rationale of cp19k by designing adhesive peptides inspired by the low-complexity STGA-rich and the charged segments of cp19k. Combining structure analysis and the adhesion performance test, we found that cp19k-inspired adhesive peptides possess excellent disparate adhesion strategies for both hydrophilic mica and hydrophobic self-assembled monolayer surfaces. Specifically, the low-complexity STGA-rich segment offers great structure flexibility for surface adhesion, while the hydrophobic and charged residues can contribute to the adhesion of the peptides on hydrophobic and charged surfaces. The adaptive adhesion strategy identified in this work broadens our understanding of barnacle adhesion mechanisms and offers valuable insights for designing advanced wet adhesives with exceptional performance on various types of surfaces.

Metal ion-mediated modulation of morphology, physicochemical properties, and digestibility of type 3 resistant starch microparticle

Short-chain glucan (SCG) derived from debranched amylopectin has emerged as a promising candidate for the production of resistant starch particle (RSP) due to its controllable self-assembly features. Here, we investigated the effect of metal cations with different valencies and concentrations on the morphology, physicochemical properties, and digestibility of RSP formed by the self-assembly of SCG. The effect of cations on the formation of RSP followed the valency in the following order: Na⁺, Ka⁺, Mg²⁺, Ca²⁺, Fe³⁺, and Al³⁺, of which 10 mM trivalent cations increased the particle size of RSP over 2 μm and considerably decreased the crystallinity by 49.5 % ~ 50.9 %, which were significantly different from that of mono- and divalent ones. Importantly, RSP formed with divalent cations switched the surface charge from -18.6 mV to 12.9 mV, which significantly increased the RS level, indicating that metal cations would be useful for regulating physicochemical properties and digestibility of RSP.

Specific Ion Effects at the Vapor-Formamide Interface: A Reverse Hofmeister Series in Ion Concentration Depth Profiles

Employing neutral impact collision ion scattering spectroscopy (NICISS), we have directly measured the concentration depth profiles (CDPs) of various monovalent ions at the vapor-formamide interface. NICISS provides CDPs of individual ions by measuring the energy loss of neutral helium atoms backscattered from the solution interface. CDPs at the vapor-formamide interface of Cl-, Br-, I-, Na+, K+, and Cs+ are measured and compared to elucidate the interfacial specific ion trends. We report a reverse Hofmeister series in the presence of inorganic ions (anion and cation) at the vapor-formamide interface relative to the water-vapor interface, and the CDPs are found to be independent of the counterion for most ions studied. Thus, ions at the surface of formamide follow a "Hofmeister paradigm" where the counterion does not impact the ion series. These specific ion trends are complemented with surface tension and X-ray absorption near-edge structure (XANES) measurements on formamide electrolyte solutions.

Polarizability Plays a Decisive Role in Modulating Association between Molecular Cations and Anions

Electrostatic interactions involving proteins depend on not only the ionic charges involved but also their chemical identities. Here we examine the origins of incompletely understood differences in the strength of association of different pairs of monovalent molecular ions that are relevant to protein-protein and protein-ligand interactions. Cationic analogues of the basic amino acid side chains are simulated, along with oxyanionic analogues of cation-exchange ligands and acidic amino acids. Experimentally observed association trends with respect to the cations, but not anions, are captured by a nonpolarizable model. An effective continuum correction to account for electronic polarizability can capture both trends better but at the expense of fidelity to the underlying free energy landscape for ion-pair association. A polarizable model proves decisive in capturing experimentally suggested trends with respect to both cations and anions; critically, the free energy landscape for ion-pair association is itself altered, thus altering configurational sampling.

DPA-Zinc around Polyplexes Acts Like PEG to Reduce Protein Binding While Targeting Cancer Cells

Gene therapy holds great promise as an effective treatment for many diseases of genetic origin. Gene therapy works by employing cationic polymers, liposomes, and nanoparticles to condense DNA into polyplexes via electronic interactions. Then, a therapeutic gene is introduced into target cells, thereby restoring or changing cellular function. However, gene transfection efficiency remains low in vivo due to high protein binding, poor targeting ability, and substantial endosomal entrapment. Artificial sheaths containing PEG, anions, or zwitterions can be introduced onto the surface of gene carriers to prevent interaction with proteins; however, they reduce the cellular uptake efficacy, endosomal escape, targeting ability, thereby, lowering gene transfection. Here, it is reported that linking dipicolylamine-zinc (DPA-Zn) ions onto polyplex nanoparticles can produce a strong hydration water layer around the polyplex, mimicking the function of PEGylation to reduce protein binding while targeting cancer cells, augmenting cellular uptake and endosomal escape. The polyplexes with a strong hydration water layer on the surface can achieve a high gene transfection even in a 50% serum environment. This strategy provides a new solution for preventing protein adsorption while improving cellular uptake and endosomal escape.

Dehydration-enhanced ion-pore interactions dominate anion transport and selectivity in nanochannels

State-of-the-art ion-selective membranes with ultrahigh precision are of significance for water desalination and energy conservation, but their development is limited by the lack of understanding of the mechanisms of ion transport at the subnanometer scale. Herein, we investigate transport of three typical anions (F-, Cl-, and Br-) under confinement using in situ liquid time-of-flight secondary ion mass spectrometry in combination with transition-state theory. The operando analysis reveals that dehydration and related ion-pore interactions govern anion-selective transport. For strongly hydrated ions [(H2O)nF- and (H2O)nCl-], dehydration enhances ion effective charge and thus the electrostatic interactions with membrane, observed as an increase in decomposed energy from electrostatics, leading to more hindered transport. Contrarily, weakly hydrated ions [(H2O)nBr-] have greater permeability as they allow an intact hydration structure during transport due to their smaller size and the most right-skewed hydration distribution. Our work demonstrates that precisely regulating ion dehydration to maximize the difference in ion-pore interactions could enable the development of ideal ion-selective membranes.

Visual demonstration and prediction of the Hofmeister series based on a poly(ionic liquid) photonic array

The Hofmeister effect and associated Hofmeister series (HS) are ubiquitous in physicochemical phenomena and have demonstrated fundamental importance in a myriad of fields ranging from chemistry to biology. Visualization of the HS not only helps to straightforwardly understand the underpinning mechanism, but also enables the prediction of new ion positions in the HS and directs the applications of the Hofmeister effect. Owing to the difficulties of sensing and reporting complete multiple and subtle inter- and intramolecular interactions involved in the Hofmeister effect, facile and accurate visual demonstration and prediction of the HS remain highly challenging. Herein, a poly(ionic liquid) (PIL)-based photonic array containing 6 inverse opal microspheres was rationally constructed to efficiently sense and report the ion effects of the HS. The PILs can not only directly conjugate with HS ions due to their ion-exchange properties, but also provide sufficient noncovalent binding diversity with these ions. Meanwhile, subtle PIL-ion interactions can be sensitively amplified to optical signals owing to their photonic structures. Therefore, synergistic integration of PILs and photonic structures gives rise to accurate visualization of the ion effect of the HS, as demonstrated by correctly ranking 7 common anions. More importantly, assisted by principal component analysis (PCA), the developed PIL photonic array can serve as a general platform to facilely, accurately, and robustly predict the HS positions of an unprecedented amount of important and useful anions and cations. These findings indicate that the PIL photonic platform is very promising for addressing challenges in the visual demonstration and prediction of HS and promoting a molecular-level understanding of the Hoffmeister effect.

Charge regulation indicates water expulsion from silica surface by cesium cations

HYPOTHESIS

Since the discovery of the Hofmeister effect in 1888, the varied propensity of ions to proteins, DNA and other surfaces has motivated research aimed at deciphering the underlying ion specific adsorption mechanism. Experimental and numerical studies have shown that in agreement with Collins' heuristic law of matching water affinity, weakly hydrated (chaotropic) ions adsorb preferentially to hydrophobic surfaces. Here, we show that this preference is driven by expulsion of bound water molecules from the surface by the adsorbing ions.

EXPERIMENTS

Using AFM spectroscopy of the force acting between two silica surfaces, we characterize surface charge regulation by adsorbed Na⁺ and Cs⁺ ions at different salt concentrations, pH values and temperatures. These data are analyzed in the framework of a recent theory of charge regulation, relating it to change in surface entropy.

FINDINGS

Upon binding to the silica, cesium cations expel water molecules from the surface to create additional adsorption sites for more ions. Cs⁺ adsorption is thus driven by the release of hydrating water molecules and the resulting increased surface entropy. The model indicates that on average, the binding of three cesium cations releases enough water molecules to make room for two additional bound cations. Na⁺ does not exhibit such behavior.

Crucial roles of ion-specific effects in the flotation of water-soluble KCl and NaCl crystals with fatty acid salts

HYPOTHESIS

Flotation of water-soluble KCl and NaCl minerals in brines is significant for K-fertilizer production, but its mechanism is controversial. Dissolved salt ions are expected to change the physicochemical properties of solvents, interfaces, and collector colloids, thereby affecting flotation significantly.

EXPERIMENTS

Flotation experiments of KCl and NaCl crystals in brines were conducted using potassium and sodium laurates as collectors. Contact angle (CA) and surface tension measurements, X-ray photoelectron spectroscopy (XPS) analysis, and molecular dynamics simulations (MD) were applied to gain a molecular understanding of changing interfacial properties and crystal-collector colloid interactions in the presence of dissolved ions in terms of salt flotation.

FINDINGS

While K⁺ ions activate the NaCl crystal flotation, Na⁺ ions depress the KCl crystal flotation, in agreement with the studies of CA, XPS, and MD results with these crystals. XPS results showed no collector adsorption at crystal surfaces which is a requirement of conventional flotation and presents a new theoretical challenge. We argue the crucial role of ion specificity: Na-laurate colloids adsorb at the bubble surface as a monolayer but solvent-separated from KCl crystals, inhibiting their flotation, or in interactive contact with NaCl crystals, enhancing their flotation. Increasing K⁺ concentration weakens NaCl crystal hydration, increasing Na-laurate colloid attraction with crystals for better flotation. The Contact Interactive Collector Colloid (CICC) and Solvent-separated Interactive Collector Colloid (SICC) hydration states are critical to salt crystal flotation via collector colloid-crystal attraction by dispersion forces.

Towards understanding the mechanism of 3D printing using protein: femtosecond laser direct writing of microstructures made from homopeptides

Femtosecond laser direct write (fs-LDW) is a promising technology for three-dimensional (3D) printing due to its high resolution, flexibility, and versatility. A protein solution can be used as a precursor to fabricate 3D proteinaceous microstructures that retain the protein's native function. The large diversity of protein molecules with different native functions allows diverse applications of this technology. However, our limited understanding of the mechanism of the printing process restricts the design and generation of 3D microstructures for biomedical applications. Therefore, we used eight commercially available homopeptides as precursors for fs-LDW of 3D structures. Our experimental results show that tyrosine, histidine, glutamic acid, and lysine contribute more to the fabrication process than do proline, threonine, phenylalanine, and alanine. In particular, we show that tyrosine is highly beneficial in the fabrication process. The beneficial effect of the charged amino acids glutamic acid and lysine suggests that the printing mechanism involves ions in addition to the previously proposed radical mechanism. Our results further suggest that the uneven electron density over larger amino acid molecules is key in aiding fs-LDW. The findings presented here will help generate more desired 3D proteinaceous microstructures by modifying protein precursors with beneficial amino acids. STATEMENT OF SIGNIFICANCE: Femtosecond laser direct write (fs-LDW) offers a three-dimensional (3D) printing capability for creating well-defined micro-and nanostructures. Applying this technology to proteins enables the manufacture of complex biomimetic 3D micro-and nanoarchitectures with retention of their original protein functions. To our knowledge, amino acid homo-polymers themselves have never been used as precursor for fs-LDW so far. Our studygainsseveral new insights into the 3D printing mechanism of pure protein for the first time. We believe that the experimental evidence presented greatly benefits the community of 3D printing of proteinin particular and the biomaterial science community in general. With the gained insight, we aspire toexpand the possibilitiesof biomaterial and biomedical applications of this technique.

Addressing Specific (Poly)ion Effects for Layer-by-Layer Membranes

Layer-by-layer (LbL) assembly of the alternating adsorption of oppositely charged polyions is an extensively studied method to produce nanofiltration membranes. In this work, the concept of chaotropicity of the polycation and its counterion is introduced in the LbL field. In general, the more chaotropic a polyion, the lower its effective charge, charge availability, and hydrophilicity. Here, this is researched for the well-known PDADMAC (polydiallyldimethylammonium chloride) and PAH (poly(allylamine) hydrochloride), and the synthesized PAMA (polyallylmultimethylammonium), with two different counterions (I^- and Cl^-). Higher chaotropicity (PDADMAC > PAMA-I > PAMA-Cl > PAH) translates into a reduced charge availability and a more pronounced extrinsic charge compensation, resulting in more mass adsorption and a higher pure water permeability. PAMA-containing membranes show the most interesting results in the series. Due to its molecular structure, the chaotropicity of this polycation perfectly lies between PDADMAC and PAH. Overall, the chaotropicity of PAMA membranes allows for the formation of the right balance between extrinsic and intrinsic charge compensation with PSS. Moreover, modifying the nature of the counterions of PAMA (I^- or Cl^-) allows to tune the density of the multilayer and results in lower size exclusion abilities with PAMA-I compared to PAMA-Cl (higher MWCO and lower MgSO₄ retention). In general, the contextualization of the polyion interaction within the specific (poly)ion effects expands the understanding of the influence of the charge density of polycations without ignoring the chemical nature of the functional groups in their monomer units.

Experimental study on evaluation and optimization of heavy metals adsorption on a novel amidoximated silane functionalized Luffa cylindrica

This study aimed to synthesize an amidoximated Luffa cylindrica (AO-LC) bioadsorbent, and evaluate its efficiency in the adsorption of heavy metals from the aqueous solutions. For this purpose, NaOH solution was used to alkaline treatment of Luffa cylindrica (LC) fibers. The silane modification of LC was performed using 3-(trimethoxysilyl)propyl methacrylate (MPS). Polyacrylonitrile (PAN)/LC biocomposite (PAN-LC) was synthesized by PAN grafting onto the MPS-modified LC (MPS-LC). Finally, the AO-LC was obtained by the amidoximation of PAN-LC. The chemical structures, morphology, and thermal properties of biocomposites were characterized by the infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and field emission scanning electron microscopy. The results showed a successful grafting of MPS and PAN on the surface of LC. The order of heavy metals adsorption on AO-LC was: Pb²⁺ > Ag⁺ > Cu²⁺ > Cd²⁺ > Co²⁺ > Ni²⁺. The effects of operational parameters on the Pb²⁺ adsorption were studied using Taguchi experimental design method. Statistical analysis of the results showed that the initial Pb²⁺ concentration and the bioadsorbent dosage significantly affect the adsorption efficiency. The adsorption capacity and removal percentage of Pb²⁺ ions were obtained as 18.88 mg/g and 99.07%, respectively. The Langmuir isotherm and Pseudo-second order kinetics models were found to be better compatible with experimental data as a consequence of the isotherm and kinetics analysis.

Identification of Ion Pairs in Aqueous NaCl and KCl Solutions in Combination with Raman Spectroscopy, Molecular Dynamics, and Quantum Chemical Calculations

This work summarizes a theoretical analysis of the perturbation on Raman spectra in aqueous NaCl and KCl solutions with the aim to detect ion pairs. The experimental Raman spectra, both polarized and depolarized, are perturbed by these ions to a comparable extent or somewhat less by KCl than NaCl. This result appears to be contrary to the molecular dynamics (MD) simulation showing that the isolated and separated ions of KCl should have a larger perturbation than NaCl, as the solvation shell of K⁺ is larger than that of Na⁺. The apparent discrepancy signifies the ion pair formation which is more substantial for KCl than NaCl. The MD simulations and quantum chemical calculations revealed that KCl forms ion pairs more than NaCl and that the ion pair formation reduces the perturbation on the Raman spectra more for KCl. The present analysis shows that the perturbed Raman spectra provide a useful sign to evaluate the ion pair formation in aqueous solutions.

Separation Technologies for Whey Protein Fractionation

Whey is a by-product of cheese, casein, and yogurt manufacture. It contains a mixture of proteins that need to be isolated and purified to fully exploit their nutritional and functional characteristics. Protein-enriched fractions and highly purified proteins derived from whey have led to the production of valuable ingredients for many important food and pharmaceutical applications. This article provides a review on the separation principles behind both the commercial and emerging techniques used for whey protein fractionation, as well as the efficacy and limitations of these techniques in isolating and purifying individual whey proteins. The fractionation of whey proteins has mainly been achieved at commercial scale using membrane filtration, resin-based chromatography, and the integration of multiple technologies (e.g., precipitation, membrane filtration, and chromatography). Electromembrane separation and membrane chromatography are two main emerging techniques that have been developed substantially in recent years. Other new techniques such as aqueous two-phase separation and magnetic fishing are also discussed, but only a limited number of studies have reported their application in whey protein fractionation. This review offers useful insights into research directions and technology screening for academic researchers and dairy processors for the production of whey protein fractions with desired nutritional and functional properties.

Ion-Specific Antipolyelectrolyte Effect on the Swelling Behavior of Polyzwitterionic Layers

In this study, we systematically investigate the interactions between mobile ions generated from added salts and immobile charges within a sulfobetaine-based polyzwitterionic film in the presence of five salts (KCl, KBr, KSCN, LiCl, and CsCl). The sulfobetaine groups contain quaternary alkylammonium and sulfonate groups, giving the positive and negative charges. The swelling of the zwitterionic film in the presence of different salts is compared with the swelling behavior of a polycationic or polyanionic film containing the same charged groups. For such a comparative study, we design cross-linked terpolymer films with similar thicknesses, cross-link densities, and charge fractions, but with varying charged moieties. While the addition of salt in general leads to a collapse of both cationic and anionic films, the presence of specific types of mobile anions (Cl^-, Br^-, and SCN^-) considerably influences the swelling behavior of polycationic films. We attribute this observation to a different degree of ion-pair formations between the different types of anionic counterions and the immobile cationic quaternary alkylammonium groups in the films where highly polarizable counterions such as SCN^- lead to a high degree of ion pairing and less polarizable counterions, such as Cl^-, cause a low degree of ion pairing. Conversely, we do not observe any substantial effect of varying the type of cationic counterions (K⁺, Li⁺, and Cs⁺), which we assign to the lack of ion pairing between the weakly polarizable cations and the immobile anionic sulfonate groups in the films. In addition, we observe that the zwitterionic films swell with increasing ionic strength and the degree of swelling is anion dependent, which is in agreement with previous reports on the "antipolyelectrolyte effect". Herein, we explain this ion-specific swelling behavior with the different cation and anion abilities to form ion pairs with quaternary alkylammonium and sulfonate in the sulfobetaine groups.

Cumulative Millisecond-Long Sampling for a Comprehensive Energetic Evaluation of Aqueous Ionic Liquid Effects on Amino Acid Interactions

The interactions of amino acid side-chains confer diverse energetic contributions and physical properties to a protein's stability and function. Various computational tools estimate the effect of changing a given amino acid on the protein's stability based on parametrized (free) energy functions. When parametrized for the prediction of protein stability in water, such energy functions can lead to suboptimal results for other solvents, such as ionic liquids (IL), aqueous ionic liquids (aIL), or salt solutions. However, to our knowledge, no comprehensive data are available describing the energetic effects of aIL on intramolecular protein interactions. Here, we present the most comprehensive set of potential of mean force (PMF) profiles of pairwise protein-residue interactions to date, covering 50 relevant interactions in water, the two biotechnologically relevant aIL [BMIM/Cl] and [BMIM/TfO], and [Na/Cl]. These results are based on a cumulated simulation time of >1 ms. aIL and salt ions can weaken, but also strengthen, specific residue interactions by more than 3 kcal mol^-1, depending on the residue pair, residue-residue configuration, participating ions, and concentration, necessitating considering such interactions specifically. These changes originate from a complex interplay of competitive or cooperative noncovalent ion-residue interactions, changes in solvent structural dynamics, or unspecific charge screening effects and occur at the contact distance but also at larger, solvent-separated distances. This data provide explanations at the atomistic and energetic levels for complex IL effects on protein stability and should help improve the prediction accuracies of computational tools that estimate protein stability based on (free) energy functions.

Recrystallization Mediates the Gelation of Amorphous Drugs: The Case of Acemetacin

Amorphization is widely used as an effective method of increasing the solubility of insoluble drugs. However, some amorphous drugs exhibit a much lower dissolution rate than their corresponding crystalline form due to their gelation. In this study, we reported the gels formed from amorphous acemetacin (ACM) for the first time. Gelation was promoted at conditions of lower pH, higher temperature and lower ionic strength. Solid-state characterizations suggested that ACM gels may be formed by recrystallization. This mechanism provides a new direction in facilitating the elimination of gelation for amorphous drugs. Moreover, it also provides the basis for the development of sustained-release formulations using the gelation properties.

Guanidinium–amino acid hydrogen-bonding interactions in protein crystal structures: implications for guanidinium-induced protein denaturation

Structural analysis of guanidinium–amino acid interaction pairs in protein crystal structures is coupled with an effective scheme for classifying the optimized pairs, to gain understanding of the guanidinium:protein hydrogen bonding modes.

The Lyotropic Nature of Halates: An Experimental Study

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.

Perturbative vibration of the coupled hydrogen-bond (O:H-O) in water

Perturbation Raman spectroscopy has underscored the hydrogen bond (O:H-O or HB) cooperativity and polarizability (HBCP) for water, which offers a proper parameter space for the performance of the HB and electrons in the energy-space-time domains. The OO repulsive coupling drives the O:H-O segmental length and energy to relax cooperatively upon perturbation. Mechanical compression shortens and stiffens the O:H nonbond while lengthens and softens the HO bond associated with polarization. However, electrification by an electric field or charge injection, or molecular undercoordination at a surface, relaxes the O:H-O in a contrasting way to the compression with derivation of the supersolid phase that is viscoelastic, less dense, thermally diffusive, and mechanically and thermally more stable. The HO bond exhibits negative thermal expansivity in the liquid and the ice-I phase while its length responds in proportional to temperature in the quasisolid phase. The O:H-O relaxation modifies the mass densities, phase boundaries, critical temperatures and the polarization endows the slipperiness of ice and superfluidity of water at the nanometer scale. Protons injection by acid solvation creates the H↔H anti-HB and introduction of electron lone pairs derives the O:⇔:O super-HB into the solutions of base or H₂O₂ hydrogen-peroxide. The repulsive H↔H and O:⇔:O interactions lengthen the solvent HO bond while the solute HO bond contracts because its bond order loss. Differential phonon spectroscopy quantifies the abundance, structure order, and stiffness of the bonds transiting from the mode of pristine water to the perturbed states. The HBCP and the perturbative spectroscopy have enabled the dynamic potentials for the relaxing O:H-O bond. Findings not only amplified the power of the Raman spectroscopy but also substantiated the understanding of anomalies of water subjecting to perturbation.

Refolding in the modern biopharmaceutical industry

Inclusion bodies (IBs) often emerge upon overexpression of recombinant proteins in E. coli. From IBs, refolding is necessary to generate the native protein that can be further purified to obtain pure and active biologicals. This work focusses on refolding as a significant process step during biopharmaceutical manufacturing with an industrial perspective. A theoretical and historical background on protein refolding gives the reader a starting point for further insights into industrial process development. Quality requirements on IBs as starting material for refolding are discussed and further economic and ecological aspects are considered with regards to buffer systems and refolding conditions. A process development roadmap shows the development of a refolding process starting from first exploratory screening rounds to scale-up and implementation in manufacturing plant. Different aspects, with a direct influence on yield, such as the selection of chemicals including pH, ionic strength, additives, etc., and other often neglected aspects, important during scale-up, such as mixing, and gas-fluid interaction, are highlighted with the use of a quality by design (QbD) approach. The benefits of simulation sciences (process simulation and computer fluid dynamics) and process analytical technology (PAT) for seamless process development are emphasized. The work concludes with an outlook on future applications of refolding and highlights open research inquiries.

Solubility of CO2 in Aqueous Formic Acid Solutions and the Effect of NaCl Addition: A Molecular Simulation Study

There is a growing interest in the development of routes to produce formic acid from CO₂, such as the electrochemical reduction of CO₂ to formic acid. The solubility of CO₂ in the electrolyte influences the production rate of formic acid. Here, the dependence of the CO₂ solubility in aqueous HCOOH solutions with electrolytes on the composition and the NaCl concentration was studied by Continuous Fractional Component Monte Carlo simulations at 298.15 K and 1 bar. The chemical potentials of CO₂, H₂O, and HCOOH were obtained directly from single simulations, enabling the calculation of Henry coefficients and subsequently considering salting in or salting out effects. As the force fields for HCOOH and H₂O may not be compatible due to the presence of strong hydrogen bonds, the Gibbs-Duhem integration test was used to test this compatibility. The combination of the OPLS/AA force field with a new set of parameters, in combination with the SPC/E force field for water, was selected. It was found that the solubility of CO₂ decreases with increasing NaCl concentration in the solution and increases with the increase of HCOOH concentration. This continues up to a certain concentration of HCOOH in the solution, after which the CO₂ solubility is high and the NaCl concentration has no significant effect.