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When a liquid film is thinning, the charge and the potential of its surfaces change simultaneously due to the interaction between the two surfaces. This phenomenon is an example for charge regulation and has been known for half a century for systems featuring aqueous solutions in contact with metals, salts, biological surfaces covered by protolytes, etc. Few studies, however, investigated regulation in foam and emulsion films, where the charge is carried by soluble ionic surfactants. This work presents an analysis of the phenomenon for surfactants that follow the classical Davies adsorption isotherm. The electrostatic disjoining pressure Πel was analyzed, and the Davies isotherm was shown to lead to Πel ∝ h−1/2 behavior at a small film thickness h. As usual, the charge regulation regime (constant chemical potential of the surfactant) corresponded to a dependence of Πel on h between those for constant charge and constant electric potential regimes. The role of the background electrolyte was also studied. At the water–air interface, many ionic surfactants exhibit a surface phase transition. We show that the interaction between the two surfaces of a foam film can trigger the phase transition (i.e., the film changes its charge abruptly), and two films of different h values can coexist in equilibrium with each other—one covered by surfactant in the 2D gaseous state and another in the 2D liquid state. [ABSTRACT FROM AUTHOR]

Biological ion channels are renowned for their exceptional ion transport selectivity and adaptability to environmental changes, posing a significant challenge for synthetic mimicry. Herein, an innovative covalent–organic‐framework membrane featuring aligned benzothiadiazole units within its oriented 1D nanochannels is reported. These densely arrayed dipolar benzothiadiazole units enhance selective ion adsorption and facilitate membrane charge regulation. Consequently, the membrane can dynamically adjust its permselectivity toward ions, transitioning seamlessly between cation‐selective, ambipolar, and anion‐selective states. This versatility affects both the type of ions transported and the transport efficiency, supporting reversible and controlled membrane operation, as illustrated by the capacity to regulate the magnitude and direction of osmotic power. When interacting with multivalent anions, highly negatively charged channels of the membrane exhibit outstanding cation permselectivity and conductivity. Specifically, upon exposure to PO43− ions, the membrane achieves a remarkable osmotic power of 155 W m−2 and an energy conversion efficiency of 46.1% under salinity gradients of 0.5 and 0.01 m NaCl. Notably, introducing multivalent cations can reverse the polarity of the membrane. This work underscores the potential of exploiting ion‐dipolar interactions for the development of adaptive, ion‐selective membranes with promising applications in electrochemical sensing, energy conversion, and more. [ABSTRACT FROM AUTHOR]

Developing highly effective electrocatalysts capable of bifunctionally facilitating hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is paramount for advancing water electrolysis. Herein, the authors report heterogeneous NiO‐Ni3Se4 nanosheet arrays grown on Ti3C2Tx MXene (NiO‐Ni3Se4/MXene) with asymmetrical charge distribution as bifunctional electrocatalysts to enhance the electrocatalytic performance for overall water splitting. Impressively, the meticulously engineered NiO‐Ni3Se4/MXene exhibits remarkable catalytic activities for the HER and the OER with low overpotentials of 50 mV and 260 mV at 10 mA cm−2, respectively. Moreover, the electrolyzer equipped with NiO‐Ni3Se4/MXene as both the cathode and anode demonstrates outstanding performance, reaching 10 mA cm−2 at a low cell voltage of 1.54 V and maintaining exceptional long‐term durability for over 50 h. The combination of theoretical calculations and experiments unveils the charge transfer induced at heterointerfaces in the NiO‐Ni3Se4 heterogeneous, leading to asymmetrical charge distributions, which modulate the adsorption/desorption of the reaction intermediates and enhance the reaction kinetics. This study presents a promising approach for rationalizing heterogeneous electrocatalysts with exceptional performance. [ABSTRACT FROM AUTHOR]

This article reviews the state of the art of the studies on charge regulation (CR) effects in flexible weak polyelectrolytes (FWPE). The characteristic of FWPE is the strong coupling of ionization and conformational degrees of freedom. After introducing the necessary fundamental concepts, some unconventional aspects of the the physical chemistry of FWPE are discussed. These aspects are: (i) the extension of statistical mechanics techniques to include ionization equilibria and, in particular, the use of the recently proposed Site Binding-Rotational Isomeric State (SBRIS) model, which allows the calculation of ionization and conformational properties on the same foot; (ii) the recent progresses in the inclusion of proton equilibria in computer simulations; (iii) the possibility of mechanically induced CR in the stretching of FWPE; (iv) the non-trivial adsorption of FWPE on ionized surfaces with the same charge sign as the PE (the so-called "wrong side" of the isoelectric point); (v) the influence of macromolecular crowding on CR. [ABSTRACT FROM AUTHOR]

[Display omitted] 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. 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. 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. [ABSTRACT FROM AUTHOR]

Sedimentation is a ubiquitous phenomenon across many fields of science, such as geology, astrophysics, and soft matter. Sometimes, sedimentation leads to unusual phenomena, such as the Brazil-nut effect, where heavier (granular) particles reside on top of lighter particles after shaking.We show experimentally that a Brazil-nut effect can be realized in a binary colloidal system of long-range repulsive charged particles driven purely by Brownian motion and electrostatics without the need for activity. Using theory, we argue that not only the mass-per-charge for the heavier particles needs to be smaller than the mass-per-charge for the lighter particles but also that at high overall density, the system can be trapped in a long-lived metastable state, which prevents the occurrence of the equilibrium Brazil-nut effect. Therefore, we envision that our work provides valuable insights into the physics of strongly interacting systems, such as partially glassy and crystalline structures. Finally, our theory, which quantitatively agrees with the experimental data, predicts that the shapes of sedimentation density profiles of multicomponent charged colloids are greatly altered when the particles are charge-regulating with more than one ion species involved. Hence, we hypothesize that sedimentation experiments can aid in revealing the type of ion adsorption processes that determine the particle charge and possibly the value of the corresponding equilibrium constants. [ABSTRACT FROM AUTHOR]

The charge plays an important role in cellulose nanocrystal (CNC) self-assembly to form liquid crystal structures, which has rarely been systematically explored. In this work, a novel technique combining atomic force microscopy force and atomistic molecular dynamics simulations was addressed for the first time to systematically investigate the differences in the CNC self-assembly caused by external positive and negative charges at the microscopic level, wherein sodium polyacrylate (PAAS) and chitosan oligosaccharides (COS) were used as external positive and negative charge additives, respectively. The results show that although the two additives both make the color of CNC films shift blue and eventually disappear, their regulatory mechanisms are, respectively, related to the extrusion of CNC particles by PAAS and the reduction in CNC surface charge by COS. The two effects both decreased the spacing between CNC particles and further increased the cross angle of CNC stacking arrangement, which finally led to the color variations. Moreover, the disappearance of color was proved to be due to the kinetic arrest of CNC suspensions before forming chiral nematic structure with the addition of PAAS and COS. This work provides an updated theoretical basis for the detailed disclosure of the CNC self-assembly mechanism. [ABSTRACT FROM AUTHOR]

Charged channels are considered an effective design for achieving efficient monovalent cation transport; however, it remains challenging to establish a direct relationship between charge microenvironments and ionic conductivity within the pores. Herein, we report a series of crystalline covalent organic frameworks (COFs) with identical skeletons but different charge microenvironments and explore their intra-pore charge-driven ion transport performance and mechanism differences. We found that the charged nature determines ion-pair action sites, modes, host-guest interaction, thereby influencing the dissociation efficiency of ion pairs, the hopping ability of cations, and the effective carrier concentration. The order of transport efficiency for Li + , Na + , and H + follows anion > zwitterion > cation > neutrality. Ionic COFs exhibit up to 11-fold higher ionic conductivity than neutral COFs. Notably, the ionic conductivity of anionic COF achieves 2.0 × 10 -4  S cm -1 for Li + at 30 °C and 3.8 × 10 -2  S cm -1 for H + at 160 °C, surpassing most COF-based ionic conductors. This COF platform for efficient ion migration and stable battery cycling in lithium-metal quasi-solid-state batteries has also been verified as proof of concept. This work offers new insights into the development and structure-activity relationship studies of the next generation of solid-state ionic conductors., (© 2025 Wiley-VCH GmbH.)

[Display omitted] • Surfactants increase ionization of PMA and solubilize water-insoluble isotactic PMA. • Conformational transition of PMA isomers is shifted to higher degrees of ionization. • The Gibbs free energy change of the conformational transition is affected. • PMA-surfactant binding changes from hydrophobic to electrostatics upon pH increase. • Imposing monomer attraction leads to a good agreement between experiments and model. By forming strong complexes with oppositely charged polyelectrolytes, cationic surfactants significantly affect their solution properties. We investigated the effect of bound surfactant on the titration behavior of two isomer forms of poly(methacrylic acid), PMA, atactic and isotactic PMA, aPMA and iPMA, respectively, which are known for the cooperative change in chain conformation in water. The bound surfactant micelles increase the initial degree of ionization, α, of carboxyl groups on PMA, shift the conformational transition to higher α and make it narrower, and exclude the complexed chains from the solution. The titration curves were analyzed in the framework of the Henderson-Hasselbalch theory and the Gibbs free energy change of the conformational transition was calculated. The results were discussed in the context of a complex influence of surfactant on the PMA chain conformation in solution. It is proposed that the PMA-surfactant interaction changes from a so-called hydrophobic mode, which is responsible for the solubilization of the unionized and water-insoluble iPMA at low α, to a predominantly electrostatic one at high α, which leads to the precipitation of both aPMA and iPMA from solution. Constant pH simulations using simple coarse-grained models for the PMA polymers and individual surfactants were performed to rationalize the titration behavior of PMAs in the absence and presence of surfactant. By inducing an attractive interaction between PMA monomers, an excellent agreement between the experimental and numerical titration curves was obtained. Such agreement becomes poorer upon the addition of surfactant; however, the main features of the PMA titration curves are preserved, which supports the role of hydrophobic interactions in PMA-surfactant association at low pH values and that of electrostatics at higher pH. [ABSTRACT FROM AUTHOR]

A bacterial biofilm (BF) is composed of microbial communities growing on the surface and extracellular substances secreted by itself, which is one of the main reasons for bacterial multidrug resistance. Analysis and treatment methods based on different principles have been widely used in BF research. Studies have proved that the communication behavior in bacterial BF is also controlled by electrochemical flow. Therefore, it is very effective to study the treatment strategy of new charge regulated anti-BF. Based on the electrical characteristics of bacteria and BF microenvironment, this article summarizes the progress of charge regulation in BF control and prospects the control methods based on the combination of charge regulation and other technologies. [ABSTRACT FROM AUTHOR]

The construction of biocompatible and trackable‐imaging single‐atom nanozymes (SAzymes) with efficient catalytic activities is particularly desirable. Here, cobalt/titanium oxide (Co/TiO2) SAzymes are presented with cobalt atomically dispersed on nanoporous hollow TiO2 using a cation‐exchange strategy. Significantly, by varying the calcination conditions, the enzyme‐like activity can be enhanced tenfold. It is determined that different calcination treatments result in valence state shifts of the Co active site due to changes in the amounts of defects, which affects the catalytic kinetics. Moreover, Co/TiO2 SAzymes exhibit good intrinsic biocompatibility and excellent tolerance toward the biological medium, while the hollow structure facilitates the loading of drugs and imaging agents for image‐guided chemo‐chemodynamic therapy via intravenous injection. This study not only provides a paradigm shift for the preparation of biocompatible SAzymes but also presents new insights for modulating the catalytic activity of SAzymes. [ABSTRACT FROM AUTHOR]

[Display omitted] We describe the deposition behavior of monodispersed silica nanoparticles on polystyrene spherical particles by using modified pairwise DLVO (Derjaguin-Landau-Verwey-Overbeek) interaction force profiles at pH values between two and twelve. Our modified model contains a new nonlinear charge regulation parameter that considers redistribution of ions, which allows us to realistically express the electrical double layer (EDL) interaction forces. Silanol-terminated silica nanoparticles (7.6 ± 0.4 nm), l -lysine-covered silica nanoparticles (7.8 ± 0.4 nm), and polyallylamine hydrochloride-covered polystyrene (PAH/PS) particles (348 ± 1 nm) were synthesized. Then, each type of silica nanoparticle was deposited on the PAH/PS particles at a range of pH values. Our new regulation parameter describes the realistic redistribution of charges governed by pH, total salt concentration, ionic strength of solution, and separation distance of particles. We find that this regulation parameter can be roughly approximated from the absolute values of theoretically calculated surface charge density and potential distributions, as well as experimentally measured ζ-potentials. Morphological analysis using electron microscopy of the experimental systems shows that the modified pairwise DLVO interaction forces exceptionally describe the deposition behavior of the silica nanoparticles physically adsorbed on the PAH/PS particle substrates. [ABSTRACT FROM AUTHOR]

Peptide amphiphiles are a class of molecules that can self-assemble into a variety of supramolecular structures, including high-aspect-ratio nanofibers. It is challenging to model and predict the charges in these supramolecular nanofibers because the ionization state of the peptides are not fixed but liable to change due to the acid-base equilibrium that is coupled to the structural organization of the peptide amphiphile molecules. Here, we have developed a theoretical model to describe and predict the amount of charge found on self-assembled peptide amphiphiles as a function of pH and ion concentration. In particular, we computed the amount of charge of peptide amphiphiles nanofibers with the sequence C16 − V2A2E2. In our theoretical formulation, we consider charge regulation of the carboxylic acid groups, which involves the acid-base chemical equilibrium of the glutamic acid residues and the possibility of ion condensation. The charge regulation is coupled with the local dielectric environment by allowing for a varying dielectric constant that also includes a position-dependent electrostatic solvation energy for the charged species. We find that the charges on the glutamic acid residues of the peptide amphiphile nanofiber are much lower than the same functional group in aqueous solution. There is a strong coupling between the charging via the acid-base equilibrium and the local dielectric environment. Our model predicts a much lower degree of deprotonation for a position-dependent relative dielectric constant compared to a constant dielectric background. Furthermore, the shape and size of the electrostatic potential as well as the counterion distribution are quantitatively and qualitatively different. These results indicate that an accurate model of peptide amphiphile self-assembly must take into account charge regulation of acidic groups through acid–base equilibria and ion condensation, as well as coupling to the local dielectric environment.

The interaction of polypeptides and proteins with an inorganic surface is intrinsically dependent on the interfacial behavior of amino acids and sensitive to solution conditions such as pH, ion type, and salt concentration. A faithful description of amino‐acid adsorption remains a theoretical challenge from a molecular perspective due to the strong coupling of local thermodynamic nonideality and inhomogeneous ionization of both the adsorbate and substrate. Building upon a recently developed coarse‐grained model for natural amino acids in bulk electrolyte solutions, here we report a molecular theory to predict amino‐acid adsorption on ionizable inorganic surfaces over a broad range of solution conditions. In addition to describing the coupled ionization of amino acids and the underlying surface, the thermodynamic model is able to account for both physical binding and surface associations such as hydrogen bonding or bidentate coordination. It is applicable to all types of natural amino acids regardless of the solution pH, salt type and concentration. The theoretical predictions have been validated by extensive comparison with experimental data for the adsorption of acidic, basic, and neutral amino acids at rutile (α‐TiO2) surfaces. [ABSTRACT FROM AUTHOR]

MOF-derived and Zn-modulated cobalt nanoparticle catalyst (CZ-Co@NC-800) achieves excellent indoor HCHO elimination at room temperature. [Display omitted] • MOF-derived and Zn-modulated new cobalt catalyst was designed and prepared. • Large specific surface area bringing about more O 2 active sites. • Residual Zn metal affects the electronic structure of catalysts. • The catalyst achieves a short reaction path and high activity of HCHO removal. The indoor low-concentration formaldehyde (HCHO) removal in cobalt-based catalysts is still a "hot potato". In this work, metal–organic-frameworks (MOF)-derived and Zinc (Zn)-modulated new cobalt nanoparticles catalyst (CZ-Co@NC-800) was designed and prepared. The CZ-Co@NC-800 performed outstanding elimination activities for ~1 ppm HCHO at 25 °C. In the static test condition, it achieves complete HCHO removal in 3 h at a relative humidity (RH) of ~55%. Moreover, 90.18% HCHO removal ratio is held after five recycle tests. In the dynamic test condition, it remains the characteristic to eliminate around 95.89% of HCHO within 8 h under an RH of ~55% and a gas hourly space velocity (GHSV) of ~150,000 mL·h−1g−1. Such advanced results should be ascribed to large specific surface area bringing about more cobalt active sites; and it is also because residual Zn metal affects the electronic structure of CZ-Co@NC-800 and enhance the surface charge transfer rate, thus the activation and dissociation ability of oxygen is promoted. Besides, a short HCHO reaction path over CZ-Co@NC-800 which was clarified by the In situ DRIFTs is also a reason for excellent catalytic performance. This work represents a crucial addition to expand the family of cobalt-based catalysts for indoor HCHO elimination. [ABSTRACT FROM AUTHOR]

Theory predicts that the net charge (Z) of a protein can be altered by the net charge of a neighboring protein as the two approach one another below the Debye length. This type of charge regulation suggests that a protein's charge and perhaps function might be affected by neighboring proteins without direct binding. Charge regulation during protein crowding has never been directly measured due to analytical challenges. Here, we show that lysine specific protein crosslinkers (NHS ester‐Staudinger pairs) can be used to mimic crowding by linking two non‐interacting proteins at a maximal distance of ~7.9 Å. The net charge of the regioisomeric dimers and preceding monomers can then be determined with lysine‐acyl "protein charge ladders" and capillary electrophoresis. As a proof of concept, we covalently linked myoglobin (Zmonomer = −0.43 ± 0.01) and α‐lactalbumin (Zmonomer = −4.63 ± 0.05). Amide hydrogen/deuterium exchange and circular dichroism spectroscopy demonstrated that crosslinking did not significantly alter the structure of either protein or result in direct binding (thus mimicking crowding). Ultimately, capillary electrophoretic analysis of the dimeric charge ladder detected a change in charge of ΔZ = −0.04 ± 0.09 upon crowding by this pair (Zdimer = −5.10 ± 0.07). These small values of ΔZ are not necessarily general to protein crowding (qualitatively or quantitatively) but will vary per protein size, charge, and solvent conditions. [ABSTRACT FROM AUTHOR]

We investigate the effects of electric double layers and flexoelectricity on the surface anchoring in general nematic fluids. Within a simplified model, we demonstrate for a nematic electrolyte how the surface anchoring strength can be affected by the surface charge, bulk ion concentration and/or flexoelectricity, effectively changing not only the magnitude of the anchoring but also the anchoring type, such as from planar to tilted. In particular, we envisage possible tuning of the anchoring strength by the salt concentration in the regime where sufficiently strong electrostatic anchoring, as controlled by the (screened) surface charge, can compete with the non-electrostatic anchoring. This effect is driven by the competing energetic-torque couplings between nematic director and the emergent electrostatic potential, due to surface charge, ions and flexoelectricity. Our findings propose a way of influencing surface anchoring by using electrostatic effects, which could be used in various aspects, including in the self-assembly of colloidal particles in nematic fluids, optical and display patterns, and sensing. [ABSTRACT FROM AUTHOR]

A combination of constant pH method and single chain in mean field simulations is employed to probe the influence of charge regulation and charge heterogeneities on the bridging characteristics of dissociable polyelectrolytes on globular proteins. By adopting a coarse‐grained representation of proteins as spherical particles, the influence of charge patches on the polyelectrolyte bridging probabilities near protein isoelectric points and in regimes in which the net charge of the protein is the same sign as that of the polyelectrolytes is probed. The results demonstrate that in the presence of dissociable polyelectrolytes, the probability of bridging of proteins capable of charge regulation is higher relative to proteins which are completely dissociated. For homogeneously charged proteins and/or proteins with weak charge heterogeneities, partially dissociated polyelectrolytes are seen to exhibit enhanced bridging characteristics compared to completely dissociated polyelectrolytes. In contrast, for proteins exhibiting strong charge heterogeneities, dissociable polyelectrolytes are seen to exhibit weaker bridging compared to completely dissociated polyelectrolytes. [ABSTRACT FROM AUTHOR]

Enhancing the surface charge density through interface modification is crucial for the design of triboelectric energy harvesting devices (triboelectric nanogenerator, TENG). Based on the electron transfer theory, loading electron-accepting elements (F, S) on the material surface will enhance the negative charge, and loading electron-donating elements (N) will enhance the positive charge. However, this paper finds a new electron-transfer regulation effect that is completely contrary to that mentioned above both in contact electrification of material-identical solid materials and liquid-solid interface. In the contact electrification of identical materials, the electron-accepting element S enhances the positive charge, while the electron-donating element N enhances the negative charge. More liquid-solid interfacial contact electrification experiments based on the droplet-triboelectric nanogenerator (Droplet-TENG) show that if the solid material is negatively charged after contacting with water droplet, loading the element S on the solid will enhance the negative charge, and loading the element N will enhance the positive charge. Unexpectedly, if the solid material is positively charged after contacting with water droplet, loading the element S on the solid will enhance the positive charge, and loading the element N will enhance the negative charge. Namely, in the contact electrification of material-identical solid materials and special liquid-solid interface, element S actually becomes "electron-donating" and element N actually becomes "electron-accepting". We infer that the effect of elements on electron-transfer is directly related to the fundamental electron transfer direction of the material. This work can provide totally new perspective for the regulation of interfacial triboelectric behavior and material surface design of TENG. [Display omitted] • In contact electrification, the element S is "electron-donating" and the element N is "electron-accepting". • The effect of elements on electron-transfer is related to the fundamental electron transfer direction of the materials. • The electron-transfer effects of element S and element N under different charging systems are comprehensively studied. [ABSTRACT FROM AUTHOR]

Polyoxometalate-based metal-organic frameworks (POMOFs) with bifunctional Lewis-Brønsted acid were designed by confining polyoxometalates (POMs: phosphotungstic acid (PW), phosphomolybdic acid (PMo) or silicotungstic acid (SiW)) within the Zr-MOFs. The confined POMs not only have their own Brønsted acid, but can also regulate the Lewis acid strength of the POMOFs via charge regulation, ultimately allowing the POMOFs to display superior catalytic performance in the tandem catalysis of furfural (FAL) to γ-valerolactone (GVL). Among the three catalysts (POMOF-PW, POMOF-PMo and POMOF-SiW), a complete conversion of FAL was achieved, while POMOF-PW exhibited the highest GVL yield (58.1 %) at 160 °C within 23 h. The leaching experiment and structural characterization of the catalyst before and after recycling confirmed the stability of the catalyst structure. The humin originates from the polymerization of furan ring-containing compounds driven by Brønsted acid. The adsorption configuration of the substrate molecules on the catalyst offers a new explanation for the tandem reaction process, i.e. that perpendicular adsorption performs only the first step of the tandem reaction, while the coexistence of perpendicular and horizontal adsorption permits the entire reaction process. This work gives unique insights into the tandem reaction of FAL and can guide the design of efficient tandem reaction catalysts. A synthetic strategy has been developed to construct polyoxometalate-based metal-organic framework (POMOF) with bifunctional Lewis-Brønsted acid sites by chemically confining polyoxometalates (POM) in metal-organic framework (MOF) channels. Confined POM not only endows the catalyst with Brønsted acid sites, but also enhances the acid strength of the catalyst through charge regulation, which finally promotes the catalyst to exhibit excellent catalytic performance in the multi-step cascade catalysis from furfural (FAL) to γ-valerolactone (GVL). This work also provides insight into the origin and driving sites of the by-product humin, as well as the role of the adsorption configuration in the catalytic process. A look into the future of the multi-step tandem reaction of FAL to GVL is presented. [Display omitted] [ABSTRACT FROM AUTHOR]

Protein translocation through nanopores holds significant promise for applications in biotechnology, biomolecular analysis, and medicine. However, the interpretation of signals generated by the translocation of the protein remains challenging. In this way, it is crucial to gain a comprehensive understanding on how macromolecules translocate through a nanopore and to identify what are the critical parameters that govern the process. In this study, we investigate the interplay between protein charge regulation, orientation, and nanopore surface modifications using a theoretical framework that allows us to explicitly take into account the acid-base reactions of the titrable amino acids in the proteins and in the polyelectrolytes grafted to the nanopore surface. Our goal is to thoroughly characterize the translocation process of different proteins (GFP, β-lactoglobulin, lysozyme, and RNase) through nanopores modified with weak polyacids. Our calculations show that the charge regulation mechanism exerts a profound effect on the translocation process. The pH-dependent interactions between proteins and charged polymers within the nanopore lead to diverse free energy landscapes with barriers, wells, and flat regions dictating translocation efficiency. Comparison of different proteins allows us to identify the significance of protein isoelectric point, size, and morphology in the translocation behavior. Taking advantage of these insights, we propose pH-responsive nanopores that can load proteins at one pH and release them at another, offering opportunities for controlled protein delivery, separation, and sensing applications.

Producing metal-free leather is an effective approach to eliminate Cr pollution and achieve sustainable development of the leather industry. However, the high water sorption of the metal-free leather and the mismatching of the charge properties between the metal-free tanned leather and anionic post-tanning chemicals result in the unsatisfactory properties of the leather products, thereby restricting the industrial application of metal-free tanning technologies. Herein, a series of cationic amphiphilic acrylic copolymers (PSD) with different molar ratios of hydrophobic monomer to cationic hydrophilic monomer were synthesized and applied in the retanning of a metal-free tanned leather. PSD can effectively penetrate to the hierarchy of collagen fibril of leather and firmly bind to collagen carboxyls to form a thin hydrophobic coating on the fibril surface due to their small particle size (< 70 nm), excellent surface activity and cationic amine groups (3–27 μmol/g). Molecular dynamics (MD) simulations confirm that the primary driving force between PSD and collagen is electrostatic interaction. MD simulations and water resistance tests demonstrate that the amphiphilic PSD provides the metal-free leather with moderate hydrophobicity, which indicates the upgrade of the comprehensive properties of leather. PSD retanning enhances the uptake rate of anionic dyes and fatliquors (> 90 %) and endows the metal-free leather with excellent filling effect and bright color. The molar ratio of hydrophilic monomer and hydrophobic monomer plays an important role in the performance of PSD. The hydrophobic segments contribute to the hydrophobicity enhancement of leather, and the cationic hydrophilic segments in PSD contribute to the charge regulation of leather and robust binding of post-tanning chemicals. Hence, the multifunctional PSD retanning agents can fulfill the demands for versatile metal-free leather types and promise to boost the sustainable development of the leather industry. [Display omitted] • Multifunctional cationic amphiphilic acrylic copolymer (PSD) was synthesized. • The primary driving force between PSD and collagen is electrostatic interaction. • PSD coating on fibrils improves the hydrophobicity of metal-free leather. • PSD shows robust binding and excellent filling performance on metal-free leather. • PSD retanning endows metal-free leather with vibrant color. [ABSTRACT FROM AUTHOR]

An analytical study of the electroosmosis and electric conduction of electrolyte solutions in a fibrous medium composed of parallel charge-regulating cylinders with arbitrary electric double layer thickness is presented. A linearized charge regulation model was adopted for the association and dissociation reactions occurring at the amphoteric functional groups over the surfaces of the cylinders, and a unit cell model was employed to accommodate interactions among the cylinders. The electrokinetic equations governing the ionic concentration, electric potential, and liquid flow fields were solved at low zeta potential for the cylinders. Explicit formulas for the electroosmotic mobility and effective electric conductivity in the fiber matrix were obtained. The results indicate that the charge regulation characteristics, such as the equilibrium constants of the reactions occurring at the cylinders’ surfaces and the bulk concentration of the charge-determining ions, influence the surface charge density and potential, electroosmotic mobility, and effective electric conductivity substantially.

Ni-rich layered oxides LiNi x Co y Mn 1- x - y O 2 (NCMs, x > 0.8) are the most promising cathode candidates for Li-ion batteries because of their superior specific capacity and cost affordability. Unfortunately, NCMs suffer from a series of formidable challenges such as structural instability and incompatibility with commonly used electrolytes, which seriously hamper their practical applications on a large scale. Herein, the Al/Ta codoping modification strategy is proposed to improve the performance of the LiNi 0.83 Co 0.1 Mn 0.07 O 2 cathode, and the as-prepared Al/Ta-modified LiNi 0.83 Co 0.1 Mn 0.07 O 2 delivers exceptional cycling stability with a capacity retention of 97.4% after 150 cycles at 1C and an excellent rate performance with a high capacity of 143.2 mAh g -1 even at 3C. Based on the experimental study, it is found that the structural stability of NCM is strengthened due to the regulated coordination of oxygen by introducing a robust Ta-O covalent bond, which prevents the layered structure from collapsing. Moreover, the reconstructed rock-salt-like surface is capable of effectively inhibiting interfacial side reactions as well as the overgrowth of the cathode-electrolyte interface. Theoretically, the energy of Li/Ni mixing is significantly increased with the introduction of Al and Ta elements in Al/Ta codoped NCM, leading to inhibited adverse phase transition during cycling. A feasible pathway for designing and developing advanced Ni-rich cathode materials for Li-ion batteries is provided in this work.

Surprisingly, the local structure of electrolyte solutions in electric double layers is primarily determined by the solvent. This is initially unexpected as the solvent is usually a neutral species and not a subject to dominant Coulombic interactions. Part of the solvent dominance in determining the local structure is simply due to the much larger number of solvent molecules in a typical electrolyte solution.The dominant local packing of solvent then creates a space left for the charged species. Our classical density functional theory work demonstrates that the solvent structural effect strongly couples to the surface chemistry, which governs the charge and potential. In this article we address some outstanding questions relating double layer modeling. Firstly, we address the role of ion-ion correlations that go beyond mean field correlations. Secondly we consider the effects of a density dependent dielectric constant which is crucial in the description of a electrolyte-vapor interface.

Electrostatic interactions play a pivotal role in many (bio)molecular association processes. The molecular organization and function in biological systems are largely determined by these interactions from pure Coulombic contributions to more peculiar mesoscopic forces due to ion-ion correlation and proton fluctuations. The latter is a general electrostatic mechanism that gives attraction particularly at low electrolyte concentrations. This charge regulation mechanism due to titrating amino acid and nucleotides residues is discussed here in a purely electrostatic framework. By means of constant-pH Monte Carlo simulations based on a fast coarse-grained titration proton scheme, a new computer molecular model was devised to study protein–RNA interactions. The complexation between the RNA silencing suppressor p19 viral protein and the 19-bp small interfering RNA was investigated at different solution pH and salt conditions. The outcomes illustrate the importance of the charge regulation mechanism that enhances the association between these macromolecules in a similar way as observed for other protein-polyelectrolyte systems typically found in colloidal science. Due to the highly negative charge of RNA, the effect is more pronounced in this system as predicted by the Kirkwood-Shumaker theory. Our results contribute to the general physico-chemical understanding of macromolecular complexation and shed light on the extensive role of RNA in the cell's life. [ABSTRACT FROM AUTHOR]

Electrical manipulation of charged ions in electrolyte-gated transistors is crucial for enhancing the electric-double-layer (EDL) gating effect, thereby improving their sensing abilities. Here, indium-zinc-oxide (IZO) based thin-film-transistors (TFTs) are fabricated on flexible plastic substrate. Acid doped chitosan-based biopolymer electrolyte is used as the gate dielectric, exhibiting an extremely high EDL capacitance. By regulating the dynamic EDL charging process with special gate potential profiles, the EDL gating effect of the chitosan-gated TFT is enhanced, and then resulting in higher pH sensitivities. An extremely high sensitivity of ∼57.8 mV/pH close to Nernst limit is achieved when the gate bias of the TFT sensor sweeps at a rate of 10 mV/s. Additionally, an enhanced sensitivity of 2630% in terms of current variation with pH range from 11 to 3 is realized when the device is operated in the ion depletion mode with a negative gate bias of −0.7 V. Robust ionic modulation is demonstrated in such chitosan-gated sensors. Efficiently driving the charged ions in the chitosan-gated IZO-TFT provides a new route for ultrasensitive, low voltage, and low-cost biochemical sensing technologies. [ABSTRACT FROM AUTHOR]

It is known that when the electric double layers (EDLs) overlap, the ionic conductance in a nanochannel depends substantially on its surface charge property. Considering growing modern applications of nanochannel devices and demand of fast analysis, we for the first time develop an exact analytical model, referred to as the simplified analytical truncated model (ATM), for estimating the surface-charge-governed nanochannel conductance in the region of EDL overlap by taking into account the practical effects of the Stern layer, the existence of multi-component ionic species, surface site dissociation/association equilibrium reactions, and electroosmotic flow. Note that the derived ATM is suitable for long nanochannels and symmetric electrolytes. The present ATM is validated by excellent agreement with not only the reported full analytical multi-ion model but also existing experimental data of nanochannel conductance in the regime of overlapped EDLs. Results show that the developed ATM is capable of explicitly predicting the surface-charge-governed nanochannel conductance at any levels of pH under the condition of highly overlapped EDLs. The validated ATM provides a very useful receipt for experimentalists and is applicable to the design of next-generation nanochannel devices. [ABSTRACT FROM AUTHOR]

Hypothesis The adsorbed amount of the polyelectrolyte-like protein histatin 5 on a silica surface depends on the pH and the ionic strength of the solution. Interestingly, an increase in ionic strength affects the adsorbed amount differently depending on the pH of the solution, as shown by ellipsometry measurements (Hyltegren, 2016). We have tested the hypothesis that the same (qualitative) trends can be found also from a coarse-grained model that takes all charge–charge interactions into account within the frameworks of Gouy–Chapman and Debye–Hückel theories. Experiments Using the same coarse-grained model as in our previous Monte Carlo study of single protein adsorption (Hyltegren, 2016), simulations of systems with many histatin 5 molecules were performed and then compared with ellipsometry measurements. The strength of the short-ranged attractive interaction between the protein and the surface was varied. Findings The coarse-grained model does not qualitatively reproduce the pH-dependence of the experimentally observed trends in adsorbed amount as a function of ionic strength. However, the simulations cast light on the balance between electrostatic attraction between protein and surface and electrostatic repulsion between adsorbed proteins, the deficiencies of the Langmuir isotherm, and the implications of protein charge regulation in concentrated systems. [ABSTRACT FROM AUTHOR]

• Joint fluid DFT and surface reaction model could accurately predict surface charge density and ζ potential of rock. • The pore size effect became negligible with the increasing surfactant concentration. • The upper limit of charge regulation performance emerges as the surfactant concentration increases. • The ζ potential exhibits less negative with the increasing surfactant concentration due to the electrostatic screening. • The chain length effect is significant in cationic surfactants systems, while anionic surfactants' behavior is similar to simple salt. The surface charge density and ζ potential of rock play an essential role in chemical enhanced oil recovery (CEOR), but the electrochemical properties of rock surfaces are difficult to predict under different reservoir conditions. Therefore, a new method was proposed combining fluid density functional theory (fluid DFT) and the surface reaction model. The surface charge density and ζ potential of silica pores under different conditions were predicted, in which the effects of pH, pore size (d), surfactant chain length (N), surfactant type, and concentration on the charge regulation of silica pores were thoroughly investigated. The surface tends to be more negatively charged with increasing pH and surfactant concentration. Moreover, the pore size effect is not negligible in charge regulation, but there is a critical pore size (CPS) that decreases as the surfactant concentration and pH increase. The difference between anionic and cationic surfactants is also investigated, which display different behaviors under nanoconfinements. The anionic surfactants' behavior is similar to that of the simple salt. Furthermore, the ζ potential of silica pores increased as the surfactant concentration increased due to electrostatic screening, which is consistent with the results of molecular dynamics (MD) simulations and experiments. [ABSTRACT FROM AUTHOR]

The colloidal probe technique was used to measure the inner layer capacitance of an electrical double layer. In particular, the forces were measured between silica surfaces and sulfate latex surfaces in solutions of monovalent salts of different alkali metals. The force profiles were interpreted with Poisson-Boltzmann theory with charge regulation, whereby the diffuse layer potential and the regulation properties of the interface were obtained. While the diffuse layer potential was measured in this fashion in the past, we are able to extract the regulation properties of the inner layer, in particular, its capacitance. We find systematic trends with the type of alkali metal ion and the salt concentration. The observed trends could be caused by difference in ion hydration, variation of the binding capacitance, and changes of the effective dielectric constant within the Stern layer. Our results are in agreement with recent experiments involving the water-silica interface based on a completely independent method using X-ray photoelectron spectroscopy in a liquid microjet. This agreement confirms the validity of our approach, which further provides a means to probe other types of interfaces than silica.

Electrokinetic energy, where the pressure-driven transport of ions through nanofluidics yields streaming potential/current, is one of the next generation, sustainable, clean energies by converting hydraulic to electrical power. In this study, we develop an analytical model taking into account many practical effects, such as the Stern layer, buffer anions (e.g., HEPES, ACES, and lactic acid), electric double layers (EDLs) overlap, and surface equilibrium reactions, to investigate the buffer effect on the electrokinetic energy conversion in a long, pH-regulated nanochannel. Taking the nanochannel made of silica as an example, we for the first time show that introducing buffer anions into the working fluid can significantly enhance not only the maximum electrokinetic power output but also the corresponding conversion efficiency in a nanochannel under the condition of highly overlapped EDLs (e.g., low background salt concentration and/or small channel height). With buffer anions, the performance of electrokinetic energy, depending on the salt concentration, pH, and nanoscale channel height, can be enhanced at a degree as high as 1.5–26 times, as compared to the case without buffer anions. This work provides a useful receipt for estimating the electrokinetic energy in the nanochannel in the presence of buffer anions and the finding is of crucial importance for renewable energy applications. [ABSTRACT FROM AUTHOR]

Literature interpretations of the electrophoretic mobility of spherical polyelectrolytes are revisited using the capillary-electrophoresis data of Duval et al. (2006) for the extracellular polysaccharide succinoglycan as an example. Subtle changes in the polyelectrolyte mobility have recently been attributed to new electrokinetic theories that feature multi-component electrolytes, charge regulation, and the so-called polarization and relaxation phenomena. However, these calculations exhibit several unusual trends that have yet to be explained, and so the conclusions drawn from them are controversial. Here, independent computations strengthen conclusions drawn from the original model of Duval et al., i.e., the discrepancies between experiments and all the presently available electrokinetic theories reflect changes in the conformation of succinoglycan arising from changes in the electrolyte pH and ionic strength. [ABSTRACT FROM AUTHOR]

We report a facile strategy to grow supramolecular copolymers on Au surfaces by successively exposing a surface-anchored monomer to solutions of oppositely charged peptide comonomers. Charge regulation on the active chain end of the polymer sufficiently slows down the kinetics of the self-assembly process to produce kinetically trapped copolymers at near-neutral pH. We thereby achieve architectural control at three levels: The β-sheet sequences direct the polymerization away from the surface, the height of the supramolecular copolymer brushes is well-controlled by the stepwise nature of the alternating copolymer growth, and 2D spatial resolution is realized by using micropatterned initiating monomers. The programmable nature of the resulting architectures renders this concept attractive for the development of customized biomaterials or chiral interfaces for optoelectronics and sensor applications. [ABSTRACT FROM AUTHOR]

ABSTRACT Spatial dependencies of monomer volume fraction profiles of pH responsive polyelectrolyte brushes were investigated using field theories and neutron reflectivity experiments. In particular, planar polyelectrolyte brushes in good solvent were studied and direct comparisons between predictions of the theories and experimental measurements are presented. The comparisons between the theories and the experimental data reveal that solvent entropy and ion-pairs resulting from adsorption of counterions from the added salt play key roles in affecting the monomer distribution and must be taken into account in modeling polyelectrolyte brushes. Furthermore, the utility of this physics-based approach based on these theories for the prediction and interpretation of neutron reflectivity profiles in the context of pH responsive planar polyelectrolyte brushes such as polybasic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and polyacidic poly(methacrylic acid) (PMAA) brushes is demonstrated. The approach provides a quantitative way of estimating molecular weights of the polymers polymerized using surface-initiated atom transfer radical polymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 956-964 [ABSTRACT FROM AUTHOR]

Hypothesis The adsorption of histatin 5 to hydrophilic silica surfaces is governed by electrostatic attractive forces between the positive protein and the negative surface. Hence pH and ionic strength control the adsorbed amount, which can be described by coarse-grained Monte Carlo simulations accounting for electrostatic forces and charge regulation of the protein. Experiments The amount of histatin 5 adsorbed to hydrophilic silica surfaces at different pH and ionic strengths was measured using null ellipsometry. The results were compared with coarse-grained Monte Carlo simulations of a single histatin 5 molecule and a surface with a fixed, smeared charge set according to experimental values for silica. The Langmuir isotherm was used to calculate the surface coverage from the simulation results. The effect of charge regulation of the protein was investigated. Findings Even though electrostatic attractive forces are important for the investigated system, a non-electrostatic short-ranged attraction with a strength of about 2.9 k B T per amino acid was needed in the simulations to get surface coverages close to experimental values. The importance of electrostatics increases with increasing pH. Charge regulation of the protein affected the results from the simulations only at high surface charge and low ionic strength. [ABSTRACT FROM AUTHOR]

The single alpha helix (SAH) is a recurring motif in biology. The consensus sequence has a di-block architecture that includes repeats of four consecutive glutamate residues followed by four consecutive lysine residues. Measurements show that the overall helicity of sequences with consensus E 4 K 4 repeats is insensitive to a wide range of pH values. Here, we use the recently introduced q-canonical ensemble, which allows us to decouple measurements of charge state and conformation, to explain the observed insensitivity of SAH helicity to pH. We couple the outputs from separate measurements of charge and conformation with atomistic simulations to derive residue-specific quantifications of preferences for being in an alpha helix and for the ionizable residues to be charged vs. uncharged. We find a clear preference for accommodating uncharged Glu residues within internal positions of SAH-forming sequences. The stabilities of alpha helical conformations increase with the number of E 4 K 4 repeats and so do the numbers of accessible charge states that are compatible with forming conformations of high helical content. There is conformational buffering whereby charge state heterogeneity buffers against large-scale conformational changes thus making the overall helicity insensitive to large changes in pH. Further, the results clearly argue against a single, rod-like alpha helical conformation being the only or even dominant conformation in the ensembles of so-called SAH sequences., (© 2023 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

To improve the development of gated nanofluidic devices for emerging applications, analytical expressions are derived to investigate the gate manipulation of surface charge property and ionic conductance in a pH-regulated nanochannel with overlapped electric double layers (EDLs). Results show that the EDL overlap effect is relatively significant at low pH and salt concentration when a negative gate potential is applied. If pH is low, the EDL overlap effect on the field control of zeta potential of the nanochannel is remarkable at large positive gate voltage, while that effect on ionic conductance is significant at large negative gate voltage. [ABSTRACT FROM AUTHOR]

The interface between a semiconductor material and an electrolyte solution has interesting and complex electrostatic properties. Its behavior will depend on the density of mobile charge carriers that are present in both phases as well as on the surface chemistry at the interface through local charge regulation. The latter is driven by chemical equilibria involving the immobile surface groups and the potential determining ions in the electrolyte solution. All these lead to an electrostatic potential distribution that propagate such that the electrolyte and the semiconductor are dependent on each other. Hence, any variation in the charge density in one phase will lead to a response in the other. This has significant implications on the physical properties of single semiconductor-electrolyte interfaces and on the electrostatic interactions between semiconductor particles suspended in electrolyte solutions. The present paper expands on our previous publication (Fleharty et al., 2014) and offers new results on the electrostatics of single semiconductor interfaces as well as on the interaction of charged semiconductor colloids suspended in electrolyte solution. [ABSTRACT FROM AUTHOR]