Role Of Counterions Research Articles

Effect of Water Models on The Stability of RNA: Role of Counter-Ions

Various force fields and water model potentials influence significantly RNA conformations. The polyanionic nature of RNA attracts the water molecules and the counter ions which in turn affects their stability. The interfacial water's structural and dynamic aspects affect the RNA's base-pair opening and denaturation by breaking or making inter/intra-hydrogen bonds. Herein, we employed an MD simulations study using SPC/E and modified TIP3P water models in combination with different force fields CHARMM and AMBER to find their influence on the hydration shell of the SARS-CoV-2 RNA genome at different temperatures. AMBER-mTIP3P model was found to give more dynamic and transient conformations for RNA. The lower dielectric constant of the SPC/E model helps in the formation of the ion-contact pair near the negatively charged phosphate group (Na+-PO4−) leading to strong RNA-ion interaction and strong hydration shells having higher hydrogen bond lifetime. The Na+ ion survival probability at the interface was found to be more in the SPC/E model. At lower temperatures, the water molecules inside these hydration shells were found to be inhomogeneous, with lower void space, higher-coordinated, and non-tetrahedral. The higher dielectric constant of the mTIP3P model screened out the attraction between the ion pairs leading to a more homogenous solvation shell having a lesser hydrogen bond lifetime and more diffusive water. The distribution of the ions near the RNA structure is confirmed by metadynamics simulations. Both water models were found to disrupt the base pair orientation due to the formation of water bridges between the O2ʹ group of RNA and the water molecules.

Destabilisation of water-in-crude oil emulsions using inorganic acids: The role of counter-ions and malonic acid

The quantitative role of pH with regards to the stabilisation of water-in-crude oil emulsions is not well established in literature. In this work, we report an observation wherein the prevention of stable emulsion formation occurs abruptly at a specific pH when water-in-crude oil emulsions are generated using inorganic acids (HCl, H2SO4 and HNO3) and crude oils with comparatively low asphaltene contents. Subsequent analysis of the aqueous phase indicated the emulsion prevention coincided with both increasing partitioning of metal cations and total organic content (TOC). Analysis of the TOC highlighted the presence of elevated concentrations of malonic acid and its derivatives which emphasises its importance in the demulsification process. The effect of elevated concentrations of malonic acid was investigated and determined to increase the rate of emulsion destabilisation when initially dissolved in the aqueous phase. Therefore, the role of malonic acid on emulsion stability is hypothesised to be due to its partitioning into the aqueous phase as a counter-ion to dissolved metals. These results highlight malonic acid as being a key chemical species to consider when assessing the stability of a water in crude oil emulsion.

Native hybrid carrageenans from Sarcopeltis skottsbergii and Sarcothalia crispata: The role of counterions on their gelling properties

Carrageenans are red seaweed polysaccharides of great importance as gelling agents in the food texture market. The hybrid kappa/iota-carrageenan is extracted from certain cold-water species and its unique properties have given rise to growing demand for this biopolymer. Gelation of these polysaccharides is affected by the valency and, sometimes, the identity of counterions. The main objectives of this work were to investigate the role of potassium and calcium ions on the gelation of the native hybrid carrageenans from Sarcopeltis skottsbergii and Sarcothalia crispata from the South American Atlantic coast, and to optimize the structural properties of these gels. Response surface methodology was used to analyze the effects of carrageenan concentration, salt concentration, and KCl:CaCl2 ratio, on the rheology, texture, syneresis after 50 % deformation, and color of these gels. Both native carrageenans presented high extraction yield (42.73 ± 0.20 g/100 g for S. skottsbergii and 20.43 ± 7.64 g/100 g for S. crispata) and formed either weak or strong gels upon the addition of salt. Carrageenan and salt concentrations increased gel strength, but also increased turbidity. Moreover, KCl fraction also increased gel strength, attributed to the predominance of the kappa diad in these carrageenans, whose gelation is favored by potassium ions. All samples showed syneresis after deformation, being minimized with higher carrageenan and salt contents. Optimal compositions predicted by the selected models to maximize gel strength and minimize syneresis and haze, were 1.13 % carrageenan, 0.39 M salt and a proportion of 0.85 KCl for S. skottsbergii, and 1.16 % carrageenan, 0.36 M salt and a proportion of 0.85 KCl for S. crispata. Predicted responses for these optimal compositions were in accordance with the observed responses. Considering the worldwide growing demand for kappa/iota-carrageenan in the food industry, S. skottsbergii and S. crispata from the South Atlantic represent a potential source of these biopolymers.

The role of counterion and concentration on the thermal behavior and structure of dioctadecyldimethylammonium bromide and chloride in water

Cationic dioctadecyldimethylammonium bromide and chloride (DODAB and DODAC) lipids assemble in water as unilamellar vesicles or more complex bilayer structures depending on the lipid concentration, counter-ion, solvent characteristics, etc. By using differential scanning calorimetry (DSC) and cryogenic transmission electron microscopy (cryo-TEM) techniques we investigated the structural and thermal properties of these two widely investigated molecules at 1–20 mM in water. Changes in the DSC thermogram profile indicate that DODAB bilayers undergo more structural changes than DODAC, while Cryo-TEM micrographs show that, in this range of concentration, DODAB assembles as more complex bilayer structures than DODAC, which assemble predominantly as unilamellar vesicles. These findings thus indicate that DODAC is preferable to DODAB at 1–20 mM for the preparation of unilamellar vesicles.

Role of Counterions in the Structural Stabilisation of Redox-Active Metal-Organic Frameworks.

The crystal structures of metal-organic frameworks (MOFs) are typically determined by the strong chemical bonds formed between the organic and inorganic building units. However, the latest generation of redox-active frameworks often rely on counterions in the pores to access specific charge states of the components. Here, we model the crystal structures of three layered MOFs based on the redox-active ligand 2,5-dihydroxybenzoquinone (dhbq): Ti2 (Cl2 dhbq)3 , V2 (Cl2 dhbq)3 and Fe2 (Cl2 dhbq)3 with implicit and explicit counterions. Our full-potential first-principles calculations indicate that while the reported hexagonal structure is readily obtained for Ti and V, the Fe framework is stabilised only by the presence of explicit counterions. For high counterion concentrations, we observe the formation of an electride-like pocket in the pore center. An outlook is provided on the implications of solvent and counterion control for engineering the structures and properties of porous solids.

Noncoordinating Secondary Sphere Ion Modulates Supramolecular Clustering of Lanthanides

The role of counterions in molecular recognition of lanthanides is underexplored, especially when they exhibit weak interactions with the metal cations. Here, we report a complementary and comprehensive investigation integrating theoretical calculations with X-ray absorption fine structure spectroscopy, dynamic light scattering, and small-angle X-ray scattering to reveal atomic-scale structural features beyond the immediate coordination sphere of a system used for rare-earth element separations. Our results indicate the formation of an unusual T-shaped outer-sphere lanthanide complex, containing two ligands and two nitrate ions in the first coordination sphere, whereas the third nitrate is weakly coordinated and resides in the second shell. This unique structural arrangement causes inhomogeneous charge distribution, leading to self-assembly of the complexes into larger nanoclusters through sterically directed electrostatic interactions in the nonpolar medium. Our findings point to the importance of "noncoordinating" anions in defining the degree of supramolecular aggregation and ion cluster assembly.

Tuning the Selectivity of Liquid Products during CO Electroreduction

The electrochemical carbon dioxide reduction (eCO2RR) into value-added chemicals and fuels offers a sustainable route to close the anthropogenic carbon cycle and store the renewable sources' excess energy into chemical bonds. Typically, eCO2RR/eCORR studies employ reactant reduction in the cathode and oxygen evolution reaction in the anode. The membrane (membrane electrode assembly configuration) facilitates the ion transport between the two electrodes and chemically isolate the occurring electrochemical half-reactions. It should be noted that investigators have conceptualized the use of ion-exchange membranes in order to improve the reaction energy efficiency and rate. However, the impact of membrane properties on reaction selectivity, stability, and efficiency remains unexplored.Herein, we investigated the role of anion exchange membrane on the CO reduction performance using a membrane electrode assembly configuration. This talk will provide insights into the ion-exchange membrane's role in the electrocatalytic reduction of CO. We will show how the membrane properties determine the product crossover, product selectivity, and stability. For example, we will discuss: i) the impact of membrane thickness on the product crossover and applied potential, ii) the role of the membrane on the cell stability, iii) the possibility of various membrane functional groups to tune the reaction selectivity and stability, and iv) the role of counter-ion, ion exchange capacity (IEC), and membrane reinforcement on the cell performance. This work will provide a first step toward designing an ion-exchange membrane with the desired characteristics for CO electroreduction.

Molecular Dynamics Simulation of Association Processes in Aqueous Solutions of Maleate Salts of Drug-like Compounds: The Role of Counterion.

The study of the formation of microstructures during the interaction of a protonated drug-like compound (API) with a maleic acid monoanion sheds light on the assembly processes in an aqueous solution at the molecular level. Molecular dynamics (MD) simulations coupled with density functional theory (DFT) calculations made it possible to find initial hydrogen bonding motifs during the assembly process, leading to the formation of heterodimers and trimers. The process of trimer formation [protonated API—maleic acid monoanion—protonated API] proceeds through the formation of three intermolecular H-bonds by the CO2− group of the maleic acid monoanion in both systems. The total enthalpy/energy of these H-bonds is more than 70 kJ/mol. Thus, the maleic acid monoanion plays a key role in the processes of association in aqueous solution, and the interaction of the maleic acid monoanion with API is more preferable than the interaction of API molecules with each other. DFT computations in the discrete continuum approximation reveal the spectral features of heterodimers and trimers, and the ATR-IR spectra confirmed these findings. MD simulations followed by DFT calculations made it possible to describe the initial stages of the formation of pharmaceutical cocrystals in an aqueous solution.

Role of Counterions in the Adsorption and Micellization Behavior of 1:1 Ionic Surfactants at Fluid Interfaces─Demonstrated by the Standard Amphiphile System of Alkali Perfluoro-n-octanoates.

In our latest communication, we proved experimentally that the ionic surfactant’s surface excess is exclusively determined by the size of the hydrated counterion.[Lunkenheimer, Langmuir,2017, 33, 10216−1022410.1021/acs.langmuir.7b00786]28925711. However, at this stage of research, we were unable to decide whether this does only hold for the two or three lightest ions of lithium, sodium, and potassium, respectively. Alternatively, we could also consider the surface excess of the heavier hydrated alkali ions of potassium, rubidium, and cesium, having practically identical ion size, as being determined by the cross-sectional area of the related anionic extended chain residue. The latter assumption has represented state of art. Searching for reliable experimental results on the effect of the heavier counterions on the boundary layer, we have extended investigations to the amphiphiles’ solutions of concentrations above the critical concentration of micelle formation (cmc).We provided evidence that the super-micellar solutions’ equilibrium surface tension will remain constant provided the required conditions are followed. The related σcmc-value represents a parameter characteristic of the ionic surfactant’s adsorption and micellization behavior. Evaluating the amphiphile’s surface excess obtained from adsorption as a function of the related amphiphile’s σcmc-value enables you to calculate the radius of the hydrated counterion valid in sub- and super-micellar solution likewise. The σcmc-value is directly proportional to the counterion’s diameter concerned. Taking additionally into account the radii of naked ions known from crystal research, we succeeded in exactly discriminating the hydrated alkali ions’ size from each other. There is a distinct sequence of hydration radii in absolute scale following the inequality, Li+ > Na+ > K+ > (NH4)+ > Rb+ > Cs+. Therefore, we have to extend our model of counterion effectiveness put forward in our previous communication. It represents a general principle of the counterion effect.

Slow glycosylation: Activation of trichloroacetimidates under mild conditions using lithium salts and the role of counterions

Glycosylations were carried out with the two glycosyl donors 4-O-acetyl-2,3-O-isopropylidene-1-O-trichloroacetimidoyl-α-l-rhamnopyranose and 2,3,4-tri-O-benzyl-1-O-trichloro-acetimidoyl-α-l-rhamnopyranose in combination with the two alcohols 1-adamantanol and l-menthol as model glycosyl acceptors. As catalysts, the five lithium salts LiNTf2, LiI, LiClO4, LiPF6 and LiOTf were investigated. We demonstrated that both lithium and the respective counterions are playing a role in the activation of trichloroacetimidate glycosyl donors at rt. Under these very mild conditions, the glycosylations are slow and completed in two to eight days. Depending on the counterion, the rate and yield of the reaction differs; however, the selectivity of all investigated lithium salts is deficient.

Distributions of counterions on adsorption and aggregation behavior of Gemini quaternary ammonium salt

The counterions had a particular influence on various physical and chemical properties, which were significantly present in Gemini quaternary ammonium salt. To investigate this contribution three Gemini quaternary ammonium salt with different counterions, GC-S, GC-N and GC-Cl, were synthesized from dodecyl tertiary amines, epichlorohydrin, and corresponding acids. The structures were characterized by FT-IR and 1H NMR. Critical parameters such as surface tension, minimum interfacial tension, CMC, and maximum adsorption capacity were measured subsequently. The role of counterions on the adsorption properties was discussed with the help of two classical adsorption models. Their aggregation behavior was observed by TEM. The results showed that counterions with larger ionic radii were adsorbed near the cationic head group more easily, which facilitates the arrangement of surface-active molecules by reduced the repulsive force between them on the adsorption layer. Moreover, the diversity of counterions allowed the surfactants to aggregate in solution to form micelles with different aggregation structures. Cationic surfactants with different counterions were studied as corrosion inhibitors, and found to exhibit temperature-dependent inhibition effects.

The Role of Counterions in Intermolecular Radical Coupling of Ru-bda Catalysts

Intermolecular radical coupling (also interaction of two metal centers I2M) is one of the main mechanisms for O–O bond formation in water oxidation catalysts. For Ru(bda)L2 (H2bda = 2,2′-bipyridine-6,6′-dicarboxylate, L = pyridine or similar nitrogen containing heterocyclic ligands) catalysts a significant driving force in water solution is the hydrophobic effects driven by the solvent. The same catalyst has been successfully employed to generate N2 from ammonia, also via I2M, but here the solvent was acetonitrile where hydrophobic effects are absent. We used a classical force field for the key intermediate [RuVIN(bda)(py)2]+ to simulate the dimerization free energy by calculation of the potential mean force, in both water and acetonitrile to understand the differences and similarities. In both solvents the complex dimerizes with similar free energy profiles. In water the complexes are essentially free cations with limited ion paring, while in acetonitrile the ion-pairing is much more significant. This ion-pairing leads to significant screening of the charges, making dimerization possible despite lower solvent polarity that could lead to repulsion between the charged complexes. In water the lower ion pairing is compensated by the hydrophobic effect leading to favorable dimerization despite repulsion of the charges. A hypothetical doubly charged [RuVIIN(bda)py2]2+ was also studied for deeper understanding of the charge effect. Despite the double charge the complexes only dimerized favorably in the lower dielectric solvent acetonitrile, while in water the separated state is more stable. In the doubly charged catalyst the effect of ion-pairing is even more pronounced in acetonitrile where it is fully paired similar to the 1+ complex, while in water the separation of the ions leads to greater repulsion between the two catalysts, which prevents dimerization.Graphic

Mechanisms of bentonite colloid aggregation, retention, and release in saturated porous media: Role of counter ions and humic acid

In the subsurface environment, colloids play an important role in pollutant transport by acting as the carriers. Understanding colloid release, transport, and deposition in porous media is a prerequisite for evaluating the potential role of colloids in subsurface contaminant transport. In this work, the aggregation, retention, and release of bentonite colloid in saturated porous sand media were investigated by kinetic aggregation and column experiments, the correlation and mechanism of these processes were revealed by combining colloid filtration theory, interaction energy calculation and density functional theory. The results showed that the retention and release of colloids were closely related to the dispersion stability and filtration effect. Multivalent cations with higher mineral affinity reduced the colloid stability, and the dispersion stability and mobility of the colloid were greatly improved by humic acid due to the enhancement of electrostatic repulsion and steric hindrance effects. The primary minimum interaction was found to contribute more to irreversible colloid retention in a Ca2+ system, while the secondary energy minimum was found to be responsible for colloid release with the occurrence of transient solution chemistry. The deposited colloid aggregates could be redistributed and released when the solution chemistry became favorable towards dispersion. These findings provide essential insight into the environmental colloid fate as well as a vital reference for the risk of colloid-driven transport of contaminants in the subsurface aquifer environment.

Counterion-Induced Tailoring of Energy Transfer in Hydrothermally Grown Nanostructured ZnO for Photocatalysis

Morphological tailoring of zinc oxide (ZnO) nanostructures, viz., nanogranules, hexagonal pillars, and nanorods, has been demonstrated using the hydrothermal method by varying the precursor salts of zinc. Counterions of precursor salts, such as zinc chloride, zinc acetate, and zinc nitrate, are found to influence nucleation and growth of the nanostructures. Determination of crystalline and morphological properties of different nanostructures has been carried out by using X-ray diffraction and field emission scanning electron microscopy. The X-ray photoelectron spectroscopy technique is used for the investigation in a comparative surface study of ZnO nanostructures, and possible growth mechanisms of different nanostructures have been described. Bandgap and Urbach energies of the materials are also affected by the counterions of the precursor salts. Fourier transform infrared spectra of ZnO nanostructures show shifting of band positions of the functional group caused by variation of the precursor salt. Features of photoluminescence emission spectra of the ZnO nanostructures are ascribed to the association of different defect states due to the change of counterions. Moreover, the variation of precursor salts also influences the efficiency of Förster resonance energy transfer between the donor (ZnO) and acceptor (MB dye). ZnO with different nanostructures exhibits commendable photocatalysis degradation efficiency toward methylene blue dye (MB dye). Thus, the emission property and photocatalytic property of the ZnO nanostructures can be tuned by the variation of precursor salts. In this work, the role of counterions is established as a tool to control the ZnO nanostructures along with achieving control over the defect state emissions. This work not only establishes a relation between defects and photocatalysis, but also it deals with the variation of oxygen defects induced by the counterions of the zinc precursor salts.

The role of counterions in ionic liquid crystals.

Previous theoretical studies of calamitic (i.e., rod-like) ionic liquid crystals (ILCs) based on an effective one-species model led to indications of a novel smectic-A phase with a layer spacing being much larger than the length of the mesogenic (i.e., liquid-crystal forming) ions. In order to rule out the possibility that this wide smectic-A phase is merely an artifact caused by the one-species approximation, we investigate an extension that accounts explicitly for cations and anions in ILCs. Our present findings, obtained by grand canonical Monte Carlo simulations, show that the phase transitions between the isotropic and the smectic-A phases of the cation-anion system are in qualitative agreement with the effective one-species model used in the preceding studies. In particular, for ILCs with mesogens (i.e., liquid-crystal forming species) carrying charged sites at their tips, the wide smectic-A phase forms, at low temperatures and within an intermediate density range, in between the isotropic and hexagonal crystal phases. We find that in the ordinary smectic-A phase, the spatial distribution of the counterions of the mesogens is approximately uniform, whereas in the wide smectic-A phase, the small counterions accumulate in between the smectic layers. Due to this phenomenology, the wide smectic-A phase could be interesting for applications, which hinge on the presence of conductivity channels for mobile ions.

The Role of Counter-Ions in Peptides—An Overview

Peptides and proteins constitute a large group of molecules that play multiple functions in living organisms. In conjunction with their important role in biological processes and advances in chemical approaches of synthesis, the interest in peptide-based drugs is still growing. As the side chains of amino acids can be basic, acidic, or neutral, the peptide drugs often occur in the form of salts with different counter-ions. This review focuses on the role of counter-ions in peptides. To date, over 60 peptide-based drugs have been approved by the FDA. Based on their area of application, biological activity, and results of preliminary tests they are characterized by different counter-ions. Moreover, the impact of counter-ions on structure, physicochemical properties, and drug formulation is analyzed. Additionally, the application of salts as mobile phase additives in chromatographic analyses and analytical techniques is highlighted.

Zirconium retention for minimizing environmental risk: Role of counterion and clay mineral

Zr(IV) together with U(IV) are the major components of high-level radionuclide waste (HLRW) and spent nuclear fuel (SNF) from nuclear power plants. Thus, their retention in the waste disposal is of great importance for the environmental risk control. Here, the influence of clay minerals on the retention of Zr(IV), as component of the nuclear waste and as chemical analogues of U(IV), has been evaluated. Three clay minerals, two bentonites and one saponite, were hydrothermally treated with three zirconium salts. A structural study at long-range order by X-ray diffraction and short-range order by NMR was performed to evaluate the generation of new zirconium phases and degradation of the clay minerals. Three immobilization mechanisms were observed: i) cation exchange of ZrO2+ or Zr4+ by clay minerals, ii) the precipitation/crystallization of ZrO2, and, iii) the chemical interaction of zirconium with the clay minerals, with the formation of zirconium silicates.

Unexpected Roles of Alkali-Metal Cations in the Assembly of Low-Valent Uranium Sulfate Molecular Complexes.

The directing effect of coordinating ligands in the formation of uranium molecular complexes has been well established, but the role of counterions in metal-ligand interactions remains ambiguous and requires further investigation. In this work, we describe the targeted isolation, through the choice of alkali-metal ions, of a family of tetravalent uranium sulfates, showing the influence of the overall topology and, unexpectedly, the UIV nuclearity upon the inclusion of such countercations. Analyses of the structures of uranium(IV) oxo/hydroxosulfate oligomeric species isolated from consistent synthetic conditions reveal that the incorporation of Na+ and Rb+ promotes the crystallization of 0D discrete clusters with a hexanuclear [U6O4(OH)4(H2O)4]12+ core, whereas the larger Cs+ ion allows for the isolation of a 2D-layered oligomer with a less condensed trinuclear [U3(O)]10+ center. This finding expands the prevalent view that counterions play an innocent role in molecular complex synthesis, affecting only the overall packing but not the local oligomerization. Interestingly, trends in nuclearity appear to correlate with the hydration enthalpies of alkali-metal cations, such that the alkali-metal cations with larger hydration enthalpies correspond to more hydrated complexes and cluster cores. These findings afford new insights into the mechanism of nucleation of UIV, and they also open a new path for the rational design and synthesis of targeted molecular complexes.

Role of Counterions and Nature of Spacer on Foaming Properties of Novel Polyoxyethylene Cationic Gemini Surfactants

Application of foam in various upstream operations, such as in enhanced oil recovery, has gained significant attention in recent years. A good foaming agent should generate a stable foam, must be thermally stable (>90 °C, typical reservoir temperature), must have a high tolerance to salinity, and should have low adsorption on the reservoir rock. In view of this, four thermally stable and salt-tolerant polyoxyethylene cationic gemini surfactants were synthesized with different spacers (mono phenyl and biphenyl) and different counterions (Br− and Cl−). Foaming properties were evaluated using initial foam generation, foam volume stability at a given time, bubble count, and average foam bubble radius. The effect of counterions and nature of spacers, with and without the presence of salts, on foaming properties was evaluated. It was found that number of phenyl rings (mono phenyl and biphenyl) had no significant effect on foamability and foam stability in the presence or absence of salts. However, the effect of counterions was prominent in deionized water. In deionized water, foam generated by gemini surfactants with bromide as a counterion was more stable compared to the foam generated using the surfactant containing chloride as the counterion. In saline solution, the type of counterion had no effect on the foamability or foam stability of the foam generated using synthesized cationic gemini surfactants. The foam volume stability decreased by the addition of salts; however, a further increase in salt concentration enhanced the foam volume stability. The synthesized surfactants showed good thermal stability, salt tolerance, and foaming properties and can be an attractive choice for upstream applications.

Counter Cations Affect Transport in Aqueous Hydroxide Solutions with Ion Specificity.

The anomalously high mobility of hydroxide and hydronium ions in aqueous solutions is related to proton transfer and structural diffusion. The role of counterions in these solutions, however, is often considered to be negligible. Herein, we explore the impact of alkali metal counter cations on hydroxide solvation and mobility. Impedance measurements demonstrate that hydroxide mobility is attenuated by lithium relative to sodium and potassium. These results are explained by ab initio molecular dynamics simulations and experimental vibrational hydration shell spectroscopy, which reveal substantially stronger ion pairing between OH- and Li+ than with other cations. Hydration shell spectra and theoretical vibrational frequency calculations together imply that lithium and sodium cations have different effects on the delocalization of water protons donating a hydrogen bond to hydroxide. Specifically, lithium leads to enhanced proton delocalization compared with sodium. However, proton delocalization and the overall diffusion process are not necessarily correlated.