Hofmeister Series Effect Research Articles

Focusing on Hofmeister series: Composition, structure and functional properties of pea protein extracted with food-related anions

Hofmeister series effects have important impacts on hydration and stability of proteins during dissolution. However, Hofmeister anions in plant protein extraction are not yet clear. Here, the effects on pea protein extraction of some common food-compatible anions (CO 3 2− , Citrate 3− , SO 4 2− , C 3 H 5 O 3 − (lactate), CH 3 COO − , and Cl − ) in their Na-form were investigated. Native gel electrophoresis of dialyzed proteins revealed that CO 3 2− , Citrate 3− , and SO 4 2− decreased the intensity of 11S legumin fraction compared to C 3 H 5 O 3 − , CH 3 COO − , and Cl − . Also, pea protein extracted by the first three anions showed a higher denaturation state and exposed more hydrophobic regions to the aqueous solvent, as shown by the circular dichroism and fluorescence probe measurements, respectively. Accordingly, the techno-functional properties of the obtained proteins varied, depending on the Hofmeister order of each anion. A notable exception was represented by the proteins extracted by carbonate (a salting-out salt), whose small particle size and high solubility at pH 7 were more akin to that of the proteins extracted by salting-in salts. An effect which may be due to the synergistic effect of bicarbonate (the main ionic species present at pH 8) and chloride (necessary to bring, as HCl, carbonate solution to pH 8). In summary, Hofmeister anions are suitable for plant protein extraction, providing a promising approach to confer tunable properties to pea proteins and enhance their usability and application fields. • Structure and functional properties of pea protein are impacted by Hofmeister effect. • Na 2 CO 3 solution resulted in a highest extraction yield of pea protein. • NaCl extraction promotes the protein secondary structure folding. • Na 2 CO 3 solution had a more impact on protein conformation than others salt. • NaCl extracted pea protein had highest gelling temperature.

Effect of imidazolium based ionic liquids on CO-association dynamics and thermodynamic stability of Ferrocytochrome c

Analysis of kinetic and thermodynamic parameters measured for CO-association reaction of Ferrocytochrome c (Ferrocyt c) under variable concentrations of 1-butyl-3-methylimidazolium with varying anion ([Bmim]X) (X = Cl−, I−, Br−, HSO4−) at pH 7 revealed that the low concentration of [Bmim]X (≤0.5 M) constrains the CO-association dynamics of Ferrocyt c and typically follows the order: [Bmim]HSO4 > [Bmim]Cl > [Bmim]Br > [Bmim]I. At relatively higher concentrations (>0.5), the chaotropic action of [Bmim]+ dominates which consequently increases the thermal-fluctuations responsible to denature the protein and thus accelerates the speed of CO-association reaction. Analysis of thermal denaturation curves of Ferrocyt c measured at different concentrations of [Bmim]X revealed that the [Bmim]X decreases the thermodynamic stability of protein and typically follows the order: [Bmim]I > [Bmim]Br > [Bmim]Cl > [Bmim]CH3COO > [Bmim]HSO4, demonstrating that the effect of [Bmim]X on thermodynamic stability of protein is not in accordance to Hofmeister series effect of anions because instead of increasing the kosmotropic anion carrying [Bmim]X ([Bmim]CH3COO and [Bmim]HSO4) also decreases the thermodynamic stability of protein.

Counteranions in the Stimulation Solution Alter the Dynamics of Exocytosis Consistent with the Hofmeister Series.

We show that the Hofmeister series of ions can be used to explain the cellular changes in exocytosis observed by single-cell amperometry for different counteranions. The formation, expansion, and closing of the membrane fusion pore during exocytosis was found to be strongly dependent on the counteranion species in solution. With stimulation of chaotropic anions (e.g., ClO4–), the expansion and closing time of the fusion pore are longer, suggesting chaotropes can extend the duration of exocytosis compared with kosmotropic anions (e.g., Cl–). At a concentration of 30 mM, the two parameters (e.g., t1/2 and tfall) that define the duration of exocytosis vary with the Hofmeister series (Cl– < Br– < NO3– ≤ ClO4– < SCN–). More interestingly, fewer (e.g., Nfoot/Nevents) and smaller (e.g., Ifoot) prespike events are observed when chaotropes are counterions in the stimulation solution, and the values can be sorted by the reverse Hofmeister series (Cl– ≥ Br– > NO3– > ClO4– > SCN–). Based on ion specificity, an adsorption-repulsion mechanism, we suggest that the exocytotic Hofmeister series effect originates from a looser swelling lipid bilayer structure due to the adsorption and electrostatic repulsion of chaotropes on the hydrophobic portion of the membrane. Our results provide a chemical link between the Hofmeister series and the cellular process of neurotransmitter release via exocytosis and provide a better physical framework to understand this important phenomenon.

Stability of collagen in ionic liquids: Ion specific Hofmeister series effect.

In protein-ionic liquids (ILs) interactions, anions play an important role. In this work, imidazolium-based ILs (IILs) with varying anions namely dicyanamide (DCA), hydrogen sulfate (HS), dimethyl phosphate (DP), acetate (A), sulfate (S) and dihydrogen phosphate (DHP) have been chosen with the aim of understanding the role of anions in bringing about the destabilization effect on collagen based on the kosmotropicity and chaotropicity of ions. Imidazolium-based ILs destabilized the triple helical structure of collagen, thereby proving as strong denaturants for collagen and this was confirmed by various spectroscopic techniques viz., CD, FT-IR, viscosity and impedance measurements. The solution studies were in accordance to the changes in the dimensional stability of RTT collagen fibres at the fibrillar level. Imidazolium cations with varied anions have exhibited destabilizing effect on collagen in order of ions in Hofmeister series; IDP < IDHP < IA < IDCA < IS < IHS. Presumably, these notable effect and changes were facilitated by electrostatic interactions between the anions and amine functional groups of collagen.

Specific ion effects on the particle size distributions of cell culture–derived influenza A virus particles within the Hofmeister series

Virus particle (VP) aggregation can have serious implications on clinical safety and efficacy of virus-based therapeutics. Typically, VP are suspended in buffers to establish defined product properties. Salts used to achieve these properties show specific effects in chemical and biological systems in a reoccurring trend known as Hofmeister series (HS). Hofmeister series effects are ubiquitous and can affect colloidal particle systems. In this study, influences of different ions (anions: SO4 2-, HPO4 2-, Cl-, Br-, NO3 -, I-; cations: K+, Na+, Li+, Mg2+, Ca2+) on particle size distributions of cell culture-derived influenza VP were investigated. For the experimental setup, influenza virus A/Puerto Rico/8/34 (H1N1) VP produced in adherent and suspension Madin Darby canine kidney cells were used. Inactivated and concentrated virus harvests were dialyzed against buffers containing the ions of interest, followed by differential centrifugal sedimentation to measure particle size distributions. VP from both cell lines showed no aggregation over a wide range of buffers containing different salts in concentrations ≥60 mM. However, when dialyzed to low salt or Ca2+ buffers, VP produced in adherent cells showed increased aggregation compared to VP produced in suspension cells. Additionally, changes in VP diameters depending on specific ion concentrations were observed that partially reflected the HS trend.

Column comparison and method development for the analysis of short-chain carboxylic acids by zwitterionic hydrophilic interaction liquid chromatography with UV detection

Short-chain carboxylic acids are relevant in pharmaceutical, food quality control, and biomedical analysis. In this study, 11 acids commonly found in drugs and in food products were selected. Wine was chosen as matrix for testing the method. The test compounds were used for comparing the selectivity of four 150 × 2.1 mm zwitterionic hydrophilic interaction LC (HILIC) columns (ZIC-HILIC 5 μm, 200 Å, and 3.5 μm, 100 Å, ZIC-pHILIC 5 μm, ZIC-cHILIC 3 μm, 100 Å) while varying the conditions to optimize for low UV wavelength detection and achieve high sensitivity. Retention using potassium phosphate and ammonium carbonate as mobile-phase components at pH 6.0, 7.5, and 8.5-8.9 was studied considering recent hypotheses on HILIC mechanism-related with the Hofmeister series effect and ion hydration. An isocratic method with UV detection at 200 nm and mobile phase consisting of 75% acetonitrile and 10 mM potassium phosphate at pH 6.0 applied to a ZIC-cHILIC column was found provisionally optimal and partially validated for the 11 analytes. Satisfactory results (R(2) from 0.9940 to >0.9999), and recoveries from 93-106% for all analytes evidenced the method as suitable for wine analysis. To the best of our knowledge, no previous study has reported on the direct ZIC-HILIC separation and UV detection of the acids considered here in wine.

Boundary lubrication by sodium salts: A Hofmeister series effect

Boundary lubrication plays an important role in the function of sliding surfaces in contact. Of particular interest in this study, boundary regime tribology is relevant for understanding textural attributes perceived during oral consumption of food, where the tongue squeezes and slides against the hard palate. This work investigates aqueous lubrication of a sliding/rolling ball-on-disc contact by sodium anions of the Hofmeister series in both water and guar gum solutions. Low concentrations (0.001M) of strongly kosmotropic salts provide reduced friction coefficients in both systems (water and guar gum solutions), although a different mechanism prevails in each. Surface-bound hydrated ions are responsible in the case of water, and salt-promoted adsorption of hydrated-polymer chains dominate with guar gum. In each system, friction decreases in accordance with the Hofmeister series: iodide, nitrate, bromide, chloride, fluoride, phosphate and citrate. The addition of salt has little impact on solution of bulk viscosity, and so this work demonstrates that significant boundary lubrication can be provided without surface modification and with lubricants of viscosity similar to that of water.

Influence of Monovalent Electrolytes on Rheological Properties of Gelled Colloidal Silica Suspensions

Rheological responses of the gelled (G) Snowtex 20 silica suspensions in the presence of LiCl, NaCl, and KCl have been investigated as functions of concentrations of silica and salt at pH 9.8 in terms of the Hofmeister series effect. The primary silica particle is isolated, and it is coagulated to form a gel above at 0.1, 0.3, and 0.5 M concentrations of LiCl, NaCl, and KCl, respectively, when the silica volume fraction φ is beyond 1.0%. The resulting G silica suspensions are classified into a strong‐link gel and their power‐law dependences of the critical strain as well as the storage modulus on the silica volume fraction were compared with the predictions by the fractal gel model. The resulting power‐law exponents of the critical strain are negative, this is in agreement with that predicted by the fractal model, and their magnitudes decrease with an increase in salt concentration, irrespective of the salt. Moreover, the magnitude of the power‐law exponent for the critical strain is well related to the Hofmeister series effect, namely it decreases in the order Li+, Na+, and K+, and the least hydrated K+ adsorbs in great enough in amount to create a less flexible network structure in the G silica suspension due to stronger attraction between the silica particles. Moreover, the stronger attraction, on the other hand, should be responsible for both the larger storage modulus and the higher power‐law exponent of the silica volume fraction dependence on the storage modulus. Therefore, the Hofmeister series effect is useful to understand the rheological properties of the G Snowtex 20 silica suspensions.