Hofmeister Sequence Research Articles

Regulating room temperature phosphorescence of carbazole quaternization pyridine in polymer through Hofmeister effect

AbstractHofmeister effect is a famous physical chemistry phenomenon that was reported a hundred years ago, which firstly refers to the action of certain salts to decrease the solubility of proteins while others increase. The Hofmeister effect on the luminescent properties of cationic organic fluorophore is still obscure, especially for their room temperature phosphorescence (RTP). Herein, hydrophilic groups (quaternization pyridine) were introduced into carbazole molecules to obtain a series of carbazole derivatives (named CZ‐Py+) with different counter anions in the Hofmeister series. These carbazole derivatives displayed tunable fluorescent color from cyan to yellow in the solid state following the Hofmeister sequence and anti‐Hofmeister behavior in an aqueous solution. Moreover, RTP material with tunable emission color and lifetime was achieved by doping CZ‐Py+ with Hofmeister series anion in polymethyl methacrylate and polyvinyl alcohol, which displayed good performance in time getting information encryption and anti‐counterfeiting.

Insights into the assembly process and properties of regenerated cellulose beads prepared in alkali/urea aqueous solutions

Taking the perspective of cellulose molecular chain assembly via the “bottom-top” route, we delve into the influence of both the cellulose solution and the coagulation bath on the assembly process and structure of regenerated cellulose beads (RCBs). The results show that cellulose molecular weight, mass fraction, and the presence of surfactant have an impact on RCBs. Contrary to traditional views where the structures of material are determined by solvent-nonsolvent exchange rate, ion-cellulose binding capacity also affects RCBs. Overall, the influence of ions follows the Hofmeister sequence. Kosmotropes promote the assembly of cellulose chains and elementary fibers, leading to “salting out” effects, reduced pore size of RCBs, increased crystallinity, and enhanced mechanical properties. In contrast, chaotropes induce “salting in” effects, resulting in opposite outcomes. The average pore size of RCBs coagulated in NaSCN solution was approximately 15-folds larger than those prepared in sodium citrate solution. Anions have a greater impact than cations, and both “salting out” and “salting in” effects strengthen with concentration. Temperature variations primarily affect solvent and nonsolvent exchange speed during cellulose regeneration. These findings provide new insights into regulating RCBs, enabling tailored performance for different applications.

Three-dimensional (3D) bioprinting of medium toughened dipeptide hydrogel scaffolds with Hofmeister effect

Short peptide self-assembled hydrogels as 3D bioprinting inks show excellent biocompatibility and diverse functional expansion, and have broad application prospects in cell culture and tissue engineering. However, the preparation of biological hydrogel inks with adjustable mechanical strength and controllable degradation for 3D bioprinting still faces big challenges. Herein, we develop dipeptide bio-inks that can be gelled in-situ based on Hofmeister sequence, and prepare hydrogel scaffold by using a layer-by-layer 3D printing strategy. Excitingly, after the introduction of Dulbecco's Modified Eagle's medium (DMEM), which is necessary for cell culture, the hydrogel scaffolds show an excellent toughening effect, which matches the needs of cell culture. It’s notable that in the whole process of preparation and 3D printing of hydrogel scaffolds, no cross-linking agent, ultraviolet (UV), heating or other exogenous factors are involved, ensuring high biosafety and biocompatibility. After two weeks of 3D culture, millimeter-sized cell spheres are obtained. This work provides an opportunity for the development of short peptide hydrogel bioinks without exogenous factors in 3D printing, tissue engineering, tumor simulant reconstruction and other biomedical fields.

Insight into Hofmeister effects on aggregation of 2:1 and 1:1 type clay minerals

Abstract2:1 and 1:1 types of clay minerals are ubiquitous in soil, and their different surface properties result in distinct environmental behaviours. In this study, dynamic light scattering (DLS) technology was adopted to determine the aggregation kinetics of 2:1 type (Montmorillonite [Mt]) and 1:1 type (Kaolinite [Ka]) clay minerals in different electrolytes. Hofmeister effects on their aggregation characteristics and mechanisms were explored. The results showed that the activation energy and critical coagulation concentration (CCC) for Mt and Ka aggregation followed Hofmeister sequences of Na+ > K+ > Cs+, Mg2+ > Ca2+ > Zn2+ ≈ Cd2+ > Cu2+> Pb2+. The analyses of physical insights into those differences revealed that the observed Hofmeister sequence was produced from the different non‐classical polarisation of cations and surface O atoms in the strong electric field of clay, which led to non‐electrostatic force adsorption of cations at the surface (or in the Stern layer). In this study, the effective charge coefficient γ was employed to characterise the intensity of the non‐electrostatic adsorption forces of cations arising from the non‐classical polarisation, and the γ values followed Na+ < K+ < Cs+, Mg2+ < Ca2+ < Zn2+ = Cd2+ < Cu2+ < Pb2+. For alkali and alkali earth metal cations with same valence, the more the electron layers, the ‘softer’ the electron cloud, the stronger the non‐classical polarisation effects in the electric field and the stronger ability to shield the electric field around the particle, which finally lead to the larger γ and lower CCC for clay minerals aggregation. For heavy metal cations, different s/p/d empty orbitals provided the basis for the difference in polarisation‐induced coordination between heavy metal cations with surface O atoms on clay. The results also showed that, the Hofmeister effects on Mt/Ka aggregation were different, it was from the differences in Hamaker constant and surface charge density for the two clay minerals.Highlights Mt and Ka aggregations exhibited different Hofmeister effects. Repulsive force among Mt particles was much larger than Ka. Cationic polarisation played critical role in particle interactions of Mt. Polarisation‐induced covalent adsorption of cations was observed at Mt surface.

AFM measurements of Hofmeister effects on clay mineral particle interaction forces

Interaction forces between clay minerals determine particle aggregation and dispersion of clay suspension. Strong Hofmeister effects have been found in surface reactions of clay mineral particles, clay aggregation kinetics, and clay aggregate stability. However, Hofmeister effects observed so far lack experimental evidence from direct measurements of clay mineral particle interaction forces. Through introducing a parameter of “effective radius” for clay mineral particle with a rough surface, AFM was successfully employed to determine the interaction forces between montmorillonite (with roughly surface) and mica (with smooth surface), and strong Hofmeister effects on particle interaction forces were directly observed. The directly measured repulsive forces between the two particles followed the sequence of Li+ > Na+ > K+ > Cs+, and the force strength in solution with 10−4 mol L−1 Li+ was about 3.6 times that in solution with 10−4 mol L−1 Cs+. Correspondingly, the determined average Stern potential of montmorillonite and mica decreased in the sequence of Li+ > Na+ > K+ > Cs+, and the Stern potential in solution with 10−4 mol L−1 Li+ was about 2.58 times that in solution with 10−4 mol L−1 Cs+. Analyses of AFM measurements showed that the cation surface adsorption energy determined the ability of cations to shield the electric field around clay mineral particles, which led to the Hofmeister sequence of the Stern potentials of clay mineral particle and the electrostatic repulsive forces between the two clay mineral particles.

Effect of electrolyte on regenerated cellulose film as gold nanoparticle carrier

The catalytic performances of gold nanoparticles immobilized on regenerated cellulose films were influenced by cellulose structure. Cellulose was regenerated in aqueous coagulants containing different electrolytes, to fabricate regenerated films with different coagulated network structure and property. Hofmeister sequence can be used to describe regeneration, namely more kosmotropic ions in the coagulants led to cellulose films with more homogeneous coagulated network structure, possibly due to the dehydration of cellulose caused by the ions. Gold nanoparticles were then immobilized on the films to prepare portable catalysts. The catalytic performance was influenced by cellulose structure. A linear relationship between the turnover frequency and the mesh size of cellulose films was observed. The results revealed that the catalytic performance can be controlled by cellulose structure, via altering the regeneration. This work provided not only the fundamental information about the intermolecular interactions between ions and macromolecules, but also an effective approach to construct powerful catalysts.

Specific ion effects on the micellization of aqueous mixed cationic/anionic surfactant systems with various counterions

The micellization of cationic gemini surfactants with various counterions, [C12H25(CH3)2N(CH2)3N(CH3)2C12H25]X2, designated as 12-3-122+·2X−, with X−=F−, Cl−, Br−, Ac−, and NO3−, and anionic conventional surfactants alkali dodecylsulfonates with various counterions C12H25SO3Y, designated as Y+AS−, with Y+=Na+, K+, Rb+ in aqueous solutions has been investigated. The mixed micellization of some 12-3-122+·2X−/Y+AS−/H2O systems has also been investigated. For the single ionic surfactants, the critical micelle concentration (cmc) decreases in the Hofmeister sequence of the counterions, strong formation ability of ion pairs between surfactant ions and the corresponding counterions leads to strong micelle self-assembly ability and small cmc. For the 12-3-122+·2X−/Y+AS−/H2O systems, to our surprise, the cmc values of the 12-3-122+·2NO3−/Na+AS−/H2O systems with different compositions are much larger than those of the other 12-3-122+·2X−/Y+AS−/H2O systems with the same compositions. Significantly different from the single ionic surfactants, if there is weak formation ability of ion pairs between counterions X− and Y+, strong formation ability of ion pairs between surfactant ions and the corresponding counterions may increase the cmc for 12-3-122+·2X−/Y+AS−/H2O system. The dissociated Margules model has been used to correlate the mixed cmc values and fits the data well. The model parameters A12 and A21 can be used as measure of synergism between 12-3-122+·2X−and Y+AS−, and they reflect the two-body and three-body attractive interactions, and the interaction differences due to the specific ion effect of counterions X− and Y+.

In Situ Non-DLVO Stabilization of Surfactant-Free, Plasmonic Gold Nanoparticles: Effect of Hofmeister’s Anions

Specific ion effects ranking in the Hofmeister sequence are ubiquitous in biochemical, industrial, and atmospheric processes. In this experimental study specific ion effects inexplicable by the classical DLVO theory have been investigated at curved water-metal interfaces of gold nanoparticles synthesized by a laser ablation process in liquid in the absence of any organic stabilizers. Notably, ion-specific differences in colloidal stability occurred in the Hückel regime at extraordinarily low salinities below 50 μM, and indications of a direct influence of ion-specific effects on the nanoparticle formation process are found. UV-vis, zeta potential, and XPS measurements help to elucidate coagulation properties, electrokinetic potential, and the oxidation state of pristine gold nanoparticles. The results clearly demonstrate that stabilization of ligand-free gold nanoparticles scales proportionally with polarizability and antiproportionally with hydration of anions located at defined positions in a direct Hofmeister sequence of anions. These specific ion effects might be due to the adsorption of chaotropic anions (Br(-), SCN(-), or I(-)) at the gold/water interface, leading to repulsive interactions between the partially oxidized gold particles during the nanoparticle formation process. On the other hand, kosmotropic anions (F(-) or SO4(2-)) seem to destabilize the gold colloid, whereas Cl(-) and NO3(-) give rise to an intermediate stability. Quantification of surface charge density indicated that particle stabilization is dominated by ion adsorption and not by surface oxidation. Fundamental insights into specific ion effects on ligand-free aqueous gold nanoparticles beyond purely electrostatic interactions are of paramount importance in biomedical or catalytic applications, since colloidal stability appears to depend greatly on the type of salt rather than on the amount.

Possible Origin of the Inverse and Direct Hofmeister Series for Lysozyme at Low and High Salt Concentrations

Protein solubility studies below the isoelectric point exhibit a direct Hofmeister series at high salt concentrations and an inverse Hofmeister series at low salt concentrations. The efficiencies of different anions measured by salt concentrations needed to effect precipitation at fixed cations are the usual Hofmeister series (Cl(-) > NO(3)(-) > Br(-) > ClO(4)(-) > I(-) > SCN(-)). The sequence is reversed at low concentrations. This has been known for over a century. Reversal of the Hofmeister series is not peculiar to proteins. Its origin poses a key test for any theoretical model. Such specific ion effects in the cloud points of lysozyme suspensions have recently been revisited. Here, a model for lysozymes is considered that takes into account forces acting on ions that are missing from classical theory. It is shown that both direct and reverse Hofmeister effects can be predicted quantitatively. The attractive/repulsive force between two protein molecules was calculated. To do this, a modification of Poisson-Boltzmann theory is used that accounts for the effects of ion polarizabilities and ion sizes obtained from ab initio calculations. At low salt concentrations, the adsorption of the more polarizable anions is enhanced by ion-surface dispersion interactions. The increased adsorption screens the protein surface charge, thus reducing the surface forces to give an inverse Hofmeister series. At high concentrations, enhanced adsorption of the more polarizable counterions (anions) leads to an effective reversal in surface charge. Consequently, an increase in co-ion (cations) adsorption occurs, resulting in an increase in surface forces. It will be demonstrated that among the different contributions determining the predicted specific ion effect the entropic term due to anions is the main responsible for the Hofmeister sequence at low salt concentrations. Conversely, the entropic term due to cations determines the Hofmeister sequence at high salt concentrations. This behavior is a remarkable example of the charge-reversal phenomenon.

Catechols as Membrane Anion Transporters

We report that an amphiphilic bis-catechol (3) functions as a transmembrane anion transporter. Activity depends on the catechol's substitution and amphiphilicity. We also describe a liposomal assay that allows one to readily measure anion transport selectivity. This assay reveals that anion transport selectivity for this amphiphilic bis-catechol follows a Hofmeister sequence wherein anions that are easier to dehydrate are made more permeable to the membrane by 3.

Ion Specific Surface Forces between Membrane Surfaces

Entities such as ion distributions and forces between lipid membranes depend on effects due to the intervening salt solution that have not been recognized previously. These specific ion or Hofmeister effects influence membrane fusion. A typical illustrative example is this: measurements of forces between double-chained cationic bilayers adsorbed onto molecularly smooth mica surfaces across different 0.6-2 mM salt solutions have revealed a large degree of ion specificity [Pashley et al. J. Phys. Chem. 1986, 90, 1637]. This has been interpreted in terms of very specific anion "binding" to the adsorbed bilayers, as it would too for micelles and other self-assembled systems. However, we show here that inclusion of nonelectrostatic (NES) or ionic dispersion potentials acting between ions and the two surfaces explains such "ion binding". The observed Hofmeister sequence for the calculated pressure without any direct ion binding is given correctly. This demonstrates the importance of a source of ion specificity that has been ignored. It is due to ionic physisorption caused by attractive NES ionic dispersion potentials. There appear to be some far reaching consequences for interpretations of membrane intermolecular interactions in salt solutions.

Why forces between proteins follow different Hofmeister series for pH above and below pI

The relative effectiveness of different anions in crystallizing proteins follows a reversed Hofmeister sequence for pH < pI and a direct Hofmeister sequence for pH > pI. The phenomenon has been known almost since Hofmeister's original work but it has not been understood. It is here given a theoretical explanation. Classical electrolyte and double layer theory deals only with electrostatic forces acting between ions and proteins. Hydration and hydration interactions are dealt with usually only in terms of assumed hard core models. But there are, at and above biological salt concentrations, other non-electrostatic (NES) ion-specific forces acting that are ignored in such modeling. Such electrodynamic fluctuation forces are also responsible for ion-specific hydration. These missing forces are variously comprehended under familiar but generally unquantified terms, typically, hydration, hydrogen bonding, π-electron–cation interactions, dipole–dipole, dipole-induced dipole and induced dipole-induced dipole forces and so on. The many important body electrodynamic fluctuation force contributions are accessible from extensions of Lifshitz theory from which, with relevant dielectric susceptibility data on solutions as a function of frequency, the forces can be extracted quantitatively, at least in principle. The classical theories of colloid science that miss such contributions do not account for a whole variety of ion-specific phenomena. Numerical results that include these non-electrostatic forces are given here for model calculations of the force between two model charge-regulated hen-egg-white protein surfaces. The surfaces are chosen to carry the same charge groups and charge density as the protein. What emerges is that for pH < pI (where the anions are counter-ions) the repulsive double layer forces increase in the order NaSCN < NaI < NaCl, while at higher pH > pI (where anions are co-ions) the forces increase in the order NaCl < NaI < NaSCN. This is in excellent agreement with both solubility experiments and experiments using SAXS. The results are also consistent with cation effects observed in protein solutions. Our results may provide some insights into a long-standing problem in solution chemistry and biology.

The Potentiometric Studies on the Effects of Various Functional Groups in Disiloxane as an Anion-Selective Ionophore

The potentiometric responses for various anions are investigated with membrane electrode (membrane 1) based on 1,3-diethyl-1,3-dihydroxy-1,3-bis(2-dimethylaminomethyl ferrocenyl) disiloxane. The nitrate ion-selective electrode based on compound 1 gave a good Nernstian response of 58.18 mV per decade for nitrate with the detection limit of −e5.66 of log [NO3−e]. Compound 1 has all those functional groups and the other two compounds have less functional group of ferrocenyl or ferrocenyl and hydroxide, respectively. Even though, potentiometric response to anions was excellent at pH 5, the selectivity pattern for all three membrane electrode based on series of disiloxane is almost like Hofmeister sequence at pH 5. However, the membrane electrode 1-3 exhibited very different response to anions at pH 7. In this pH, NH2 is not protonated and ionophore may act as neutral carrier. Hydrogen bond may enhance the responsibility to hydrogen acceptors and intramolecular electro-active site may increase the permeability of analyte to ionophore in membrane.

Symmetrical electrochemical cell for determination of coextraction constants of metal salts for ion-selective polymeric membranes

A symmetrical electrochemical cell has been developed to perform cyclic voltammetric study of a plasticised poly(vinyl chloride) (PVC) membrane. The plasticised PVC membrane of ca. 100 μm thickness was mounted in a specially laboratory-made electrochemical cell for voltammetric analysis on exposure to various sodium salt and metal chloride solutions. Symmetrical cyclic voltammograms were obtained when the sample and internal solutions contained same kind of metal salts. The coextraction constant of a metal salt for the plasticised PVC could be determined from either the positive or negative potential scans of a cyclic voltammetry. In addition, two coextraction constants could also be simultaneously obtained when the membrane was exposed to two different metal salts in the sample and internal solutions, respectively. It was observed that the more lipophilic of the cations or anions, the larger the coextraction constants of these ions for the plasticised PVC membrane. The results followed the Hofmeister sequence of ClO 4 −>NO 3 −>Br −>Cl −>OAc − for anions and the ease of extraction of cations was in the order of Cs +>K +>Na +>Li +. The proposed method provides a simpler, faster and more convenient method to obtain the coextraction constants of metal salts for plasticised polymeric membranes.

A perchlorate-selective membrane electrode based on a Cu(II) complex of the ligand 1,4,8,11-tetra(n-octyl)-1,4,8,11-tetraazacyclotetradecane.

The new cyclic polyazacycloalkane 1.4,8,11-tetra(n-octyl)-1,4,8,11-tetraazacyclotetradecane (L1) was synthesised and the copper(II) complex [Cu(L1)]2+ characterised. Different electrodes were prepared using the [Cu(L1)]2+ complex as ionophore, PVC as plastic matrix and o-nitrophenyl octyl ether (NPOE), bis(2-ethylhexyl) sebacate (BEHS) or dibutyl phthalate (DBP) as plasticizers. The electrode containing DBP showed a Nernstian response over a wide pH range and a fast response time (ca. 3 s) whereas NPOE and BEHS gave near-Nernstian slopes. Selectivity coefficients for the different anions with respect to perchlorate were calculated. The response of the electrodes basically followed the Hofmeister sequence, suggesting that interaction of the ionophore with the anions is via electrostatic forces rather than due to anion coordination to the axial sites of the square-planar [Cu(L1)]2+ complex.

Anion modulation of calcium current voltage dependence and amplitude in salamander rods

Hofmeister anions were used to investigate the ability of Cl − replacement to produce inhibition and a hyperpolarizing activation shift in L-type Ca 2+ currents ( I Ca) of rod photoreceptors. Inhibition of I Ca largely followed the Hofmeister sequence: Cl −=Br −<NO − 3<I −<ClO − 4 (ClO − 4 caused the greatest suppression). Anion-induced hyperpolarizing activation shifts also followed the Hofmeister sequence: Cl −<Br −<NO − 3<I −<ClO − 4 (ClO − 4 caused the largest shift). Agreement with the Hofmeister sequence suggests that these effects are due to anion interactions at the membrane surface. Hofmeister anions also caused similar hyperpolarizing shifts in the voltage dependence of inwardly rectifying cation currents ( I h) and outward K + currents ( I K) consistent with the hypothesis that hyperpolarizing shifts arise from anion effects on membrane surface potential. Sulfate and phosphate inhibited rod I Ca and phosphate caused a significant leftward activation shift suggesting these anions are strongly adsorbed to the membrane. Because of the overlap between the physiological voltage range and the lower part of the I Ca activation curve, anion effects on amplitude and activation may influence synaptic transmission at the first retinal synapse.

Triphenyllead Chloride as a New Ionophore for an Iodide-Selective Membrane Electrode

ABSTRACT Triphenyllead chloride was found to act as an ionophore for iodide. An electrode constructed using this ionophore and tris(2-ethylhexyl) phosphate as a membrane solvent in a poly(vinyl chloride) membrane matrix exhibited a near-Nernstian response to iodide in the concentration range 1x10−5-1x10−2 M with a slope of-56 mV per concentration decade. The lower limit of detection was around 3 μM. The electrode displayed the following selectivity sequence: Γ > salicylate > SCN− ∼ Br− > Cl− > ClO4 − > CH3COO− > NO3 − > SO4 2− ∼ HPO4 2− > HCO3 −, which largely deviates from the Hofmeister sequence and also is not in accordance with the selectivity sequence of an electrode based on triphenyltin chloride. The pH dependence of the electrode response was not significant in the pH range 2-7. Diphenyllead dichloride also exhibited a similar selectivity sequence as triphenyllead chloride, but sensitivity to iodide was much lower than for triphenyllead chloride.

The role of the hydration of cations in their adsorption on oxides

Calculated radii of hydrated alkaline-earth and other divalent ions are in general agreement with their adsorption affinity sequence (Hofmeister sequence) on quartz or δ-MnO 2. An ion-exchange adsorption mechanism between hydrated ions in the outer Helmholtz layer and in the bulk solution explains the endothermic nature of the adsorption and the trends observed in the heat of adsorption. The results of the activation of the oleate flotation of quartz by the alkaline-earth ions can be accounted for by the surface- activator-oleate interaction. The limiting amounts of divalent cation adsorbed by silica at pH 6.0 and 323 K exhibit the Irving-Williams sequence. At the point of zero charge of silica or δ-MnO 2, specific adsorption of cations may be ascribed to the formation of surface coordination complexes. The free energy of specific adsorption is calculated for both powders using Grahame's equation and the estimated radii. The adsorption of cations on rutile or anatase shows opposite trends to those mentioned above, and this is possibly associated with the field strength of the TiO 2 surface.

Effect of electrolytes on rheological properties of Young-Il bentonite suspension

Dependence of the flow behavior of aqueous suspension of Young-Il bentonite on the concentration and the type of electrolytes was studied. Viscosity measurements were made with Rion Viscotester, using No. 3 rotor at 62.5 R.P.M. at 25°C. As electrolyte concentration increased, the apparent viscosity was observed to increase. Changes in viscosity were in general agreement with predicted results based on the Hofmeister sequence and the Schulze-Hardy rule.