Chaotropic Anions Research Articles

Competitive effects of anion mobility and viscous forces on the interactions of hyaluronic acid and alginic acid with hofmeister salts

The specific ion effect takes into account the hydration, mobility, and kosmotropic/chaotropic effects. However, another important aspect to consider is the solution viscosity, which influences ion mobility. A limited number of publications have considered the impact of specific ion effects on polyelectrolytes. However, none of the studies have considered the viscous effect of polyelectrolytes. This study aims to investigate the impact of kosmotropic and chaotropic anions on negatively charged alginic acid and hyaluronic acid using dynamic light scattering, rheology, and molecular dynamic simulations. Different concentration regimes and the change in the chain conformations in these regimes, along with the viscosity scaling and impact of the salts on the polyelectrolytes, have been discussed. An interesting finding regarding the solution viscosity was reported. The solution viscosity leads to the reversal of the diffusivity and viscosity trend of the polymer with kosmotropes and chaotropes. A threshold is also identified above which viscous forces dominate. Specific ion effects dominate below the threshold. It was concluded that the specific ion effect shows a competitive nature with the viscous forces in the case of a high-viscosity polyelectrolyte solution, which becomes an important aspect to consider for unveiling such interactions. Prior knowledge of the conformations of polymers can be used for designing drug delivery/nutrient delivery systems and for understanding phase separation behavior. Considering the viscosity of polymer solution becomes an important factor which, in turn, impacts the anion's mobility and ultimately influences the polymer conformations.

An Experimentally Derived Prediction Model for Diffusion and Electrostatically Controlled Physical Interactions of Polyampholytes and Salts

AbstractThe interactions of salts with polyampholytes are well established using the Hofmeister series. However, the effect of these salts on the diffusivities of polyampholytes is unknown. This article discusses these electrostatically driven physical interactions using two developed prediction models. Sodium and Potassium salts are considered with 3 chaotropic anions and 2 kosmotropic anions. A dimensionless parameter has been developed to predict the trend for these salt interactions. Another model has been developed to predict these interactions for different salt mixtures. The effect of these salts and the mixtures on the second virial coefficient is also studied, and statistical clustering using the k‐means method has been defined, which can provide insight towards the changes in the solution properties of polyampholytes with these salt mixtures. At lower pH, the salt first screens the repulsions in the polyampholytes followed by a re‐expansion phenomenon.

Standard partial molar volumes of single aqueous ions composing ionic liquids. Measurement and evaluation of temperature dependent values. Parsing and LSER correlation with molecular descriptors based on DFT/COSMO approach

The densities of highly dilute aqueous solutions (m < 0.2 mol·kg−1) of 50 common ionic liquids (ILs) or related salts were accurately measured at seven equidistant temperatures in the range of (288.15 to 318.15) K and ambient pressure. The examined set of ILs/salts composed of 31 ions was judiciously selected to cover wide ranges of ion sizes and chemical structures and allow reliable evaluation of ionic contributions. The data were duly analyzed to infer related thermodynamic properties and information on the behavior of these systems on a molecular level. Appropriate means of mathematical statistics were used to estimate data uncertainties, assign weights to data correlations, and judge the significance of the results obtained. The standard partial molar volumes V¯∞ of the ILs/salts at infinite dilution were evaluated through fitting the concentration dependence of respective apparent molar volumes to Redlich-Meyer equation and their temperature dependence was correlated to quadratic polynomial. The data presented were compared whenever possible with those available in the literature; good agreement was often found, although some data from the literature were also considerably dispersed or in error. Standard partial molar volumes of ILs/salts obeying ionic additivity were split by least-squares optimization into temperature-dependent single-ion values based on the Conway-Millero extrathermodynamic assumption. The ionic additivity of BV parameter was also identified. Its magnitude for anions is typically greater than that for cations, supporting the fact that an anion dominates the volumetric behavior of aqueous ILs. As the BV,anion and the second temperature derivative ∂2V¯anion∞/∂T2 were found to correlate, the two solute’s water structure making/breaking ability indicators appear to speak consistently. Enhanced values of standard partial molar expansion were observed for both strongly kosmotropic and chaotropic anions and a plausible explanation of this phenomenon was suggested. To correlate and analyze the effect of ionic structure on V¯ion,298∞, Linear Solvation Energy Relationship (LSER) methodology with the recently proposed four quantum chemistry computed descriptors based on DFT/COSMO approach was employed providing excellent fit (SD = 2.48 cm3·mol−1, R2 = 0.9996).

Ions effect on tunable coacervate and its relevance to the Hofmeister series

Ion induced self-assembly allows a better understanding of the natural self-assemblies such as proteins, colloids and polymers, etc. However, little is known about ions mediated tunable coacervates. Herein, we show that the Hofmeister series of ions can be used to explain the tunable coacervates induced by different types of ions. The assembly of benzenesulfonate and polyetheramine undergoes the transformation from bilayer vesicles to the network structure of bottom coacervate with the increased concentration of inorganic salt, and the tunable coacervates of surfactants was found to be highly dependent on the ion species in solution. The affinity and compatibility of cations and surfactant follows Li+ > Na+ > K+, which determines the disturbance range of water molecules in the hydration shell of surfactant, resulting in different states of the final aggregates varying from precipitate, upper coacervate to bottom coacervate. The chaotropic anions (e.g., I−) have more pronounced dehydration effect on surfactants compared with kosmotropic anions (e.g., F−), and the ability of anions induced the transition from the bottom to the upper coacervate follows I−> Br− > Cl− >F−. Since the structural transformation of bottom coacervate requires conformational entropy, the release of water molecules is thermodynamically favorable for the transition of coacervates, which is also verified by the fact that the occurrence of dehydration drives the bottom coacervate upward to the upper coacervate during the heating process. These results provide a close link between the Hofmeister series and the controllable coacervates, which is of importance for further progress in ion specificity effects and creates a basic physicochemistry skeleton to understand this important phenomenon.

Low-Frequency Spectra of Hydrated Ionic Liquids with Kosmotropic and Chaotropic Anions.

In this study, we investigated the water concentration dependence of the intermolecular vibrations of two hydrated ionic liquids (ILs), cholinium dihydrogen phosphate ([ch][dhp]) and cholinium bromide ([ch]Br), using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES). The anions of the former and latter hydrated ILs are kosmotropic and chaotropic, respectively. We found that the spectral peak of ∼50 cm-1 shifted to the low-frequency side in hydrated [ch][dhp], indicating the weakening of its intermolecular interactions. In contrast, no change in the peak frequency of the low-frequency band at ∼50 cm-1 was observed with increasing water concentration in hydrated [ch]Br. The vibrational density of states (VDOS) spectra generated from molecular dynamics (MD) simulations were in qualitative agreement with the experimental results. Decomposition analysis of the VDOS spectra for each component revealed that the red shift of the low-frequency band in the hydrated [ch][dhp] upon water addition was essentially due to the contributions of anions and water rather than that of the cholinium cation. We also found from the low-frequency spectra of the two hydrated ILs that they differed in the concentration dependence of the 180 cm-1 band, which is assigned as a hindered translational motion of water molecules combined to form O···O stretching motions. From the relationship between the peak frequency of the low-frequency band and the bulk parameter, which is the square root of the surface tension divided by the density, we found that the peak frequency in the hydrated IL with kosmotropic [dhp]- depends on the bulk parameter, similar to the case for an aqueous solution of the typical deep eutectic solvent reline. However, the peak frequency of the hydrated IL with chaotropic Br- is constant with the bulk parameter.

Specific anion effects on urease activity: A Hofmeister study

The effects of a range of electrolytes on the hydrolysis of urea by the enzyme urease is explored. The autocatalytic behavior of urease in unbuffered solutions and its pH clock reactions are studied. The concentration dependence of the experimental variables is analyzed in terms of specific ion-enzyme interactions and hydration. The results offer insights into the molecular mechanisms of the enzyme, and on the nature of its interactions with the electrolytes. We found that urease can tolerate mild electrolytes in its environment, while it is strongly inhibited by both strong kosmotropic and strong chaotropic anions. This study may cast light on an alternative therapy for Helicobacter pylori infections and contribute to the design of innovative materials and provide new approaches for the modulation of the enzymatic activity.

Thermo-pH-Salt Environmental Terpolymers Influenced by 2-((Dimethylamino)methyl)-4-methylphenyl Acrylate: A Comparative Study for Tuning Phase Separation Temperature.

This study offers a comparison between three different types of thermoresponsive (TR) and thermo-pH-salt (TPR) multiresponsive polymers including homopoly(N-isopropylacrylamide) (PNIPAAm), copolymers with three different monomers, 2-hydroxyethyl methacrylate (HEMA), N,N-dimethylacrylamide (DMAAm), and styrene (S) at three different concentrations (5, 10, and 20 mol %), and a PNIPAAm terpolymer with 5, 10, and 20 mol % 2-((dimethylamino)methyl)-4-methylphenyl acrylate (DMAMCA) and 10 mol % HEMA, DMAAm, and S monomers. All polymers were chemically analyzed with 1H NMR and Fourier transform infrared spectroscopy (FT-IR) as well as gel permeation chromatography (GPC) for the molecular weights and dispersity and differential scanning calorimeter (DSC) for the glass transition temperatures. The cloud point, also known as the phase separation temperature (Cp), was determined for all polymers by a turbidity test using a UV-vis spectrophotometer; a micro-differential scanning calorimeter was used for measuring the cloud point in deionized water. The influence of a tertiary amine cationic group of DMAMCA changed the behavior of TR copolymers into TPR by shifting the cloud point of the TPR to higher values in acidic solutions (lower pH) and to lower values in alkaline solutions. The Cp was measured at different concentrations of Hofmeister kosmotropic and chaotropic anion salt solutions in a range of pH solutions for the terpolymers. It demonstrated the same behavior as mentioned in pH solutions besides the effect of salt ions. By measuring the Tc and Cp of these polymers, we can exploit various applications of stimuli-responsive materials for sensors and biomedical technology.

Is "Water in Salt" Electrolytes the Ultimate Solution? Achieving High Stability of Organic Anodes in Diluted Electrolyte Solutions Via a Wise Anions Selection.

The introduction of the water-in-salt (WIS) electrolytes concept to prevent water splitting and widen the electrochemical stability window, has spurred extensive research efforts toward development of improved aqueous batteries. The successful implementation of these electrolyte solutions in many electrochemical systems shifts the focus from diluted to WIS electrolyte solutions. Considering the high costs and the tendency of these nearly saturated solutions to crystallize, this trend can be carefully re-evaluated. Herein we show that the stability of organic electrodes comprising the active material perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), is strongly influenced by the solvation character of the anions rather than the concentration of the electrolyte solution. Even though the charging process of PTCDA involves solely insertion of cations (i.e., principal counter-ions), surprisingly, the dominant factor influencing its electrochemical performance, including long-term electrode stability, is the type of the co-ions (i.e., electrolytic anions). Using systematic electrochemical analysis combined with theoretical simulations, we show that the selection of kosmotropic anions results in fast fading of the PTCDA anodes, while a selection of chaotropic anions leads to excellent stability, even at electrolytes concentrations as low as 0.2 M. These findings provide a new conceptual approach for designing advanced electrolyte solutions for aqueous batteries.

Is “Water in Salt” Electrolytes the Ultimate Solution? Achieving High Stability of Organic Anodes in Diluted Electrolyte Solutions Via a Wise Anions Selection

AbstractThe introduction of the water‐in‐salt (WIS) electrolytes concept to prevent water splitting and widen the electrochemical stability window, has spurred extensive research efforts toward development of improved aqueous batteries. The successful implementation of these electrolyte solutions in many electrochemical systems shifts the focus from diluted to WIS electrolyte solutions. Considering the high costs and the tendency of these nearly saturated solutions to crystallize, this trend can be carefully re‐evaluated. Herein we show that the stability of organic electrodes comprising the active material perylene‐3,4,9,10‐tetracarboxylic dianhydride (PTCDA), is strongly influenced by the solvation character of the anions rather than the concentration of the electrolyte solution. Even though the charging process of PTCDA involves solely insertion of cations (i.e., principal counter‐ions), surprisingly, the dominant factor influencing its electrochemical performance, including long‐term electrode stability, is the type of the co‐ions (i.e., electrolytic anions). Using systematic electrochemical analysis combined with theoretical simulations, we show that the selection of kosmotropic anions results in fast fading of the PTCDA anodes, while a selection of chaotropic anions leads to excellent stability, even at electrolytes concentrations as low as 0.2 M. These findings provide a new conceptual approach for designing advanced electrolyte solutions for aqueous batteries.

Manipulating chaotropic anion enables lacked H-bond aqueous electrolyte for lithium-ion hybrid capacitor

Aqueous electrochemical energy storages have multiple advantages especially safety performance in the energy storage process. The high concentration aqueous electrolytes with a wide electrochemical stable voltage window (ESW) solves the key problems of aqueous electrochemical energy storages. It effectively breaks the limitation of H2O molecule decomposition to realize aqueous electrochemical energy storage with high operating voltage. However, the slow ion transport and high cost limit their application in power-type storages. Here, the lacked H-bond aqueous electrolyte (LHE) is proposed by investigating the structures and properties of aqueous electrolytes with various chaotropic anions. The LHE achieves high conductivity, low viscosity, and low cost while ensuring a wide ESW. These excellent properties originate from the OTf− effect on the solvation structure of cations and the number of H-bonds. An aqueous Li-ion hybrid capacitor (LHC) with the LHE exhibits high operating voltage of 2.5 V and high ESW utilization of 92.6 %. The aqueous cathode electrolyte interphase formed by anions on the cathode surface also achieved a long cycle life for the LHC. It has guided the development of novel electrolytes for electrochemical energy storage.

Modulation of Insulin Amyloid Fibrillization in Imidazolium-Based Ionic Liquids with Hofmeister Series Anions.

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

Elucidating the effect of the Hofmeister effect on formation and rheological properties of soy protein/κ-carrageenan hydrogels

Hydrogels derived from soy protein isolates (SPI) offer numerous advantages such as sustainability, biodegradability, and non-toxicity. However, the weak mechanical properties of SPI-based hydrogels limit their practical applications. To address this issue, a soaking strategy employing the Hofmeister effect was proposed to prepare SPI-based hydrogels. In this work, we looked at the possibilities of enhancing the rheological and mechanical characteristics of SPI-based hydrogels utilizing the Hofmeister series. SPI hydrogels were fabricated by introducing κ-carrageenan (SPIK). The SPIK hydrogels were soaked in different concentrations of Hofmeister salts (SO42−, Cl−, and SCN−). The results showed that the mechanical properties of SPIK hybrid hydrogels soaked with kosmotropic anion (SO42−) were obviously enhanced. The neutral ion (Cl−) soaked SPIK hybrid hydrogels showed no apparent difference in mechanical properties compared to the control, while the mechanical properties of chaotropic anion soaked SPIK hybrid hydrogels were weakened and the SPIK hybrid hydrogels were softened. The rheological test results showed that the order of anion effect on the G′ of the SPIK hybrid hydrogels were SO42− > Cl− > SCN−. Meanwhile, the G′ of the SPIK hybrid hydrogel containing SO42− was remarkably higher than the other samples. Moreover, the effect of different ratios of water, salt, and SPI on the SPIK hybrid hydrogel properties, structure, and microstructure was evaluated using a hybrid design. The results of rheological regression analysis showed a strong interaction between protein and salt. Frequency scan tests, strain scan tests, and texture analyzer measurements revealed that the SPIK hybrid hydrogels exhibited superior rheological and mechanical properties when the salt to SPI concentration ratio was 2:1, for both SO42− and Cl− ions. Overall, our results reveal the influence of the Hofmeister effect on SPI-based hydrogels.

Solubilities of Amino Acids in the Presence of Chaotropic Anions

This work addresses the effect of chaotropic anions (thiocyanate and tosylate) on the solubility of glycine, L-leucine, L-phenylalanine, and L-aspartic acid in aqueous solutions at 298.2 K. The salts used were NaSCN, KSCN, NH4SCN, and NaC7H7SO3 (sodium tosylate), with salt concentrations ranging from 0 to 2 molal. The pH of the saturated solutions was registered, and solid-phase studies were also performed. All the thiocyanate salts and sodium tosylate induced a salting-in effect, except in the systems composed of glycine in aqueous sodium tosylate solutions at 0.5 and 1 molal. For L-leucine, L-phenylalanine, and L-aspartic acid the salting effect of anions followed the order tosylate− > SCN− > NO3-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mathrm{NO}}_{3}^{-}$$\\end{document} > Cl−, in good agreement with the behavior predicted by the Hofmeister series. Differently, the relative solubility of glycine in aqueous nitrate solutions was higher than in those containing thiocyanate, followed by the chloride and, closing the rank, the solutions containing the tosylate anion, suggesting that the solubility change in this case is achieved by a different mechanism.

Ion-Specific Water–Macromolecule Interactions at the Air/Aqueous Interface: An Insight into Hofmeister Effect

The specificity of ions in inducing conformational changes in macromolecules is introduced as the Hofmeister series; however, the detailed underlying mechanism is not comprehensible yet. We utilized surface-specific sum frequency generation (SFG) vibrational spectroscopy to explore the Hofmeister effect at the air/polyvinylpyrrolidone (PVP)/water interface. The spectral signature observed from the ssp polarization scheme reveals ion-specific ordering of water molecules following the Hofmeister series attributed to the ion-macromolecule interactions. Along with this, the presence of ions does not reflect any significant influence on the structure of the PVP macromolecule. However, the ppp-SFG spectra in the CH-stretch region reveal the impact of ions on the orientation angle of vinyl chain CH2-groups, which follows the Hofmeister series: SO42- > Cl- > NO3- > Br- > ClO4- > SCN-. The minimal orientation angle of CH2-groups indicates significant reordering in PVP vinyl chains in the presence of chaotropic anions ClO4-, and SCN-. The observation is attributed to the ion-specific water-macromolecule interactions at the air/aqueous interface. It is compelling to observe the signature of spectral blue shifts in the OH-stretch region in the ppp configuration in the presence of chaotropic anions. The origin of spectral blue shifts has been ascribed to the existence of weaker interactions between the interfacial water molecules and the backbone CH- and CH2-moieties of the PVP macromolecules. The ion-specific modulation in water-macromolecule interactions is endorsed by the relative propensity of anion's adsorption toward the air/aqueous interface. The experimental findings highlight the existence and cooperative participation of ion-specific water-macromolecule interactions in the mechanism of the Hofmeister effect, along with the illustrious ion-water and ion-macromolecule interactions.

Specific ion effects on the aggregation of polysaccharide-based polyelectrolyte complex particles induced by monovalent ions within Hofmeister series

Polysaccharide-based polyelectrolyte complex (PEC) particles have been utilized as carriers for drug delivery systems (DDS) and as building components for material development. Despite their versatility, the aggregation mechanism of PEC particles in the presence of salts remains unclear. To clarify the aggregation mechanism, the specific ion effects of monovalent salts within the Hofmeister series on the aggregation behavior of PEC particles composed of chitosan and chondroitin sulfate C, which are often used as DDS carriers and materials, were studied. Here, we found that weakly hydrated chaotropic anions promoted the aggregation of positively charged PEC particles. The hydrophobicity of the PEC particles was increased by these ions. Strongly hydrated ions such as Cl- are less likely to accumulate in these particles, whereas weakly hydrated chaotropic ions such as SCN- are more likely to accumulate. Molecular dynamics simulations suggested that the hydrophobicity of PECs might be strengthened by ions due to changes in intrinsic and extrinsic ion pairs and hydrophobic interactions. Based on our results, it is expected that the control of surface hydrophilicity or hydrophobicity is an effective approach for controlling the stability of PEC particles in the presence of ions.

Application of salts of chaotropic anions in the development of hplc methods for the determination of meldonium in dosage forms

The aim of the work was to create an approach for the development of HPLC methods for the determination of meldonium in dosage forms with the usage of salts of chaotropic anions in mobile phases.&#x0D; Material and methods. Analytical equipment: Shimadzu UPLC system LC-40 PDA; Shimadzu Nexera-i LC-2040C 3D-Plus, controlled by software Lab Solution version 5.97, electronic laboratory balance RAD WAG AS 200/C, pH-meter I-160MI. Meldonium dihydrate (purity 99.3 %) was purchased from Sigma-Aldrich (Switzerland), and Vasopro capsules 500 mg were purchased from a local pharmacy. Chromatographic conditions: Agilent Zorbax C-18 SB 150 mm x 4.6 mm 3.5 μm column was used (Agilent Technologies, USA). Mobile phases: 1) 0.25 % KPF6 w/v – 0.1 % v/v 85 %H3PO4 95 % – 5 % ACN, 2) 0.3 % bis-(trifluoromethane)sulfonimide lithium salt 97 % w/v – 0.1 %v/v 85 % H3PO4 80 % – 20 % acetonitrile. Flow rate - 1mL/min, T=32 °C, detection UV=at 4 channels - 190 nm, 195 nm, 200 nm, 205 nm.&#x0D; Results and discussion. We have proposed two approaches using two different salts of chaotropic anions - potassium hexafluorophosphate and bis-(trifluoromethane)sulfonimide lithium salt – for the HPLC method development. The chaotropic effects of these anions toward meldonium strongly influenced the analyte migratory behaviour. Both mobile phases involved, in addition to the use of a chaotrope, also the use of acetonitrile and pH adjustment with 0.1 % v/v 85 % H3PO4 solution. The detection wavelength (190 nm, 195 nm, 200 nm, 205 nm) was selected experimentally. The results were obtained for 8 concepts. Parameters of the chromatographic system confirm the conclusions and results of this investigation for the influence of chaotropic salts on N-containing molecules in an acidic pH medium, by increasing their retentivity and improving peak shape and uniformity homogeneity, even on the column without end-capping and base-deactivating. Validation of the analytical method was carried out following the requirements of SPhU. Conclusions. HPLC methods for the determination of meldonium in dosage forms have been developed, using positive impacts of chaotropic salts on the molecules containing N-atoms in their molecule on their retentions and peak symmetries on the chromatogram. The validation of the analytical methods showed their suitability for pharmaceutical analysis

Effect of Magnesium Salts with Chaotropic Anions on the Swelling Behavior of PNIPMAM Thin Films

Poly(N-isopropylmethacrylamide) (PNIPMAM) is a stimuli-responsive polymer, which in thin film geometry exhibits a volume-phase transition upon temperature increase in water vapor. The swelling behavior of PNIPMAM thin films containing magnesium salts in water vapor is investigated in view of their potential application as nanodevices. Both the extent and the kinetics of the swelling ratio as well as the water content are probed with in situ time-of-flight neutron reflectometry. Additionally, in situ Fourier-transform infrared (FTIR) spectroscopy provides information about the local solvation of the specific functional groups, while two-dimensional FTIR correlation analysis further elucidates the temporal sequence of solvation events. The addition of Mg(ClO4)2 or Mg(NO3)2 enhances the sensitivity of the polymer and therefore the responsiveness of switches and sensors based on PNIPMAM thin films. It is found that Mg(NO3)2 leads to a higher relative water uptake and therefore achieves the highest thickness gain in the swollen state.

Chaotropic anion induced self-assembly of naphthalimide–glutathione nanohybrids: selective recognition of bisulphate anions in aqueous medium

Anion-induced self-assembly is one of the growing research fields as it provides a better understanding of natural self-assemblies such as DNA, proteins, peptides, etc.

Catalytic properties of Ce-MCM-41 prepared with ceric ammonium nitrate in the liquid-phase oxidation of benzyl alcohol

This work reports the influence of microstructural features in the catalytic performance, reaction kinetics and stability of a cerium-modified MCM-41 material prepared with ceric ammonium nitrate (Ce-MCM-CAN) in the liquid-phase oxidation of benzyl alcohol with tert-butyl hydroperoxide (TBHP) as oxidant. All the mentioned features were compiled and compared to other two Ce-MCM-41 catalysts prepared with CeCl3·7H2O and Ce(NO3)3·6H2O (Ce-MCM-Cl and Ce-MCM-NO3, respectively). Ce-MCM-CAN sample has offered a unique catalytic profile and considerable resistance towards conversion of isomorphous cerium sites in inactive agglomerated CeO2. In a typical catalytic essay at 80 °C and 24 h, Ce-MCM-CAN sample attains 54.6% of conversion, with 47.4 and 25.9% of benzaldehyde selectivity and yield, respectively. Nonetheless, kinetic essays demonstrates that the reaction continues after 24 h, mainly by reducing the aldehyde's selectivity and favoring the formation of benzoic acid, whereas Ce-MCM-Cl and Ce-MCM-NO3 samples has product formation stagnated after 20 h. After four catalytic cycles, the deactivation of Ce-MCM-CAN sample occurs mainly after the first cycle (reduction of 19.8% in conversion) with little influence in TBHP efficiency, while the other two model catalysts deactivate progressively after each cycle (reduction of 33.3 and 23.6% in conversion for Ce-MCM-Cl and Ce-MCM-NO3 samples, respectively) with loss of oxidant usage. Overall, the long-range ordering and pre-existing non-framework CeO2 nanoparticles in Ce-MCM-CAN sample is responsible for decreasing the deactivation rate. Such properties emerge from the counterbalanced synergy between chaotropic nitrate anions and condensation between [Ce(OH)4] species with silicate anions.

Suppressing the Hofmeister Anion Effect by Thermal Annealing of Thin-Film Multilayers Made of Weak Polyelectrolytes.

Thin films made of weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) have been fabricated on silicon wafers using the layer-by-layer (LbL) method. To study the influence of counteranion type on the growth and properties of PAH/PAA multilayers, the nature of the supporting sodium salt was varied from cosmotropic to chaotropic anions (F-, Cl-, and ClO4 -). Results of ellipsometry and AFM measurements indicate that the film thickness and surface roughness systematically increase on the order F- < Cl- < ClO4 -. Furthermore, we found that the hydrophobicity of the PAH/PAA multilayer also follows the described trend when a polycation is the terminating layer. However, the heating of PAH/PAA multilayers to 60 °C during the LbL assembly suppressed the influence of background anions on the multilayer formation and properties. On the basis of the obtained results, it could be concluded that thermal annealing induces changes at the polymer-air interface in the sense of reorientation and migration of polymer chains.