Effect Of Counterions Research Articles

Aerobic oxidation of benzylic alcohols catalysed by new (aryl‐BIAN)copper(I) complexes: Their synthesis and structural characterization

A new neutral dimeric Ar‐BIAN Cu(I) complex (where Ar‐BIAN = bis(aryl‐imino)acenaphthene) of formulation [CuBr(4‐iPrC6H4‐BIAN)]2 (2) was obtained by reacting CuBr and ligand 4‐iPrC6H4‐BIAN (L2) in refluxing acetonitrile under an argon atmosphere. When the ligand used was 2,4,6‐Me3C6H2‐BIAN (L1), we obtained 1 in which the expected dimer (1a) is present, but we could also observe, in solution, the presence of the bis‐chelate dimer [Cu(2,4,6‐Me3C6H2‐BIAN)2][CuBr2] (1b) bearing CuBr2− as counter‐ion; attempts to separate them failed. When the ligand used was 2‐iPrC6H4‐BIAN (L3), we obtained 3 in which the expected dimer (3a) is in equilibrium, in solution, with its bis‐chelate isomer [Cu(2‐iPrC6H4‐BIAN)2][CuBr2] (3b). The solid‐state molecular structures of compounds 2 and 3b were determined by single crystal X‐ray diffraction. The electrochemical behaviour of complexes: 1 (1a, and 1b), 2, and 3 (3a and 3b) and the known compound [Cu(2‐iPrC6H4‐BIAN)2][BF4] (7) were investigated by cyclic voltammetry. The new complexes 1 (1a, 1b), 2, and 3 (3a, 3b) were tested as catalysts for the aerobic oxidation of benzylic alcohols into aldehydes; they all catalyse the reaction, with good results; the catalytic studies were extended to the similar known complexes [CuBr(2,6‐iPr2C6H3‐BIAN)]2 (4), [CuI(2,6‐iPr2C6H3‐BIAN)]2 (5), [CuCl(2,6‐iPr2C6H3‐BIAN)]2 (6) and (7), in order to study the effect of different bridging halides or counter ions in the catalytic activity. We found that compound 4 exhibited a high catalytic activity comparable to the best results published so far. The oxidation products, benzaldehydes, were detected and further confirmed by NMR spectroscopy, and the conversion rate was determined after GC‐FID analysis.

Unraveling the role of counter anions on optical and microwave absorption characteristics of flexible copolymers

Engineering the structural architecture of materials is critical for the transmittance of visible light and absorb microwave radiation in various stealth and electronic applications. Transparent copolymers comprising of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) were synthesized at different compositions using reversible addition-fragmentation chain transfer (RAFT) polymerization. The copolymers exhibited a high percentage of light transmittance (>90%) within the visible range owing to the majority fraction of MMA units. The amine functionalities in the synthesized copolymers were ionized at room temperature by treating with dilute acids such as hydrochloric acid (HCl), trifluoroacetic acid (TFA), nitric acid (HNO3), tetrafluoroboric acid (HBF4), and hexafluorophosphoric acid (HPF6). The quaternization of the side-chain amine groups have resulted in a series of copolymer salts with an ion-pair complex. The investigation of the counter anion effect on the conductivity of the materials has been carried out to produce the highly transparent and conductive MMA-based copolymers. The presence of partially mobile Cl⁻ counter anions in the copolymers can result in conductance as high as 0.939 mS cm−1. Moreover, the optically transparent MMA-based copolymer salts have witnessed a high microwave absorption due to multiple reflections from structural and physical anisotropies.

Tetraalkylammonium counterion effects on lauroyl β-alanine: A chemical trapping study

The use of acyl amino acid surfactants has gained significant interest due to increasing environmental pressure from both the government and customers. Understanding the ion-specific effects (SIE) in these surfactant systems not only contributes to their practical applications in complex systems but also provides a theoretical basis for investigating SIE in protein systems. In this study, we synthesized four types of lauroyl β-alanine tetraalkylammonium salts (TAA-LA) with tetramethylammonium (TMA-LA), tetraethylammonium (TEA-LA), tetrapropylammonium (TPA-LA), and tetrabutylammonium (TBA-LA) as counterions. The SIE on their surface activities, aggregation behaviors, and interfacial molarities were examined. The critical micelle concentration of TAA-LA decrease with an increase in the size of the counterions. Chemical trapping revealed that the interfacial molarity of water and carboxylate groups followed the order TBA-LA > TPA-LA > TEA-LA > TMA-LA, whereas the interfacial amide bond molarity followed the reversed order. These results were consistent with their differences in aggregation behaviors. Specifically, LA bearing smaller TAA+ counterions formed uni-lamellar vesicles (ULVs) spontaneously, while LA with TBA+ self-assembled into double-lamellar vesicles (DLVs) of comparable sizes. Both CT and MD confirmed that TBA-LA DLVs with relatively smaller “average curvature” were more hydrated than other TAA-LA ULVs. Our results suggested that TBA+ tends to break the intermolecular hydrogen bond between amide bonds, which results in looser interfacial packing and larger “average curvature”. Our findings provide new insights into the tetraalkylammonium counterion effects on acyl amino acid surfactants and elucidate the SIE on protein systems at the molecular level.

Solution‐Phase Tuning of Emission of Divalent Europium

AbstractThe key to developing smart light‐emitting systems lies in the ability to tune luminescence with only modest changes in the chemical environment. Divalent europium‐based luminophores are unique materials that access emissions ranging from the blue to red regions of the visible spectrum. Early studies demonstrate the tunability of the emission of EuII in solid‐state host lattices, and recent research has shown that altering counter anions, solvents, and ligands also enables tuning of the emission of EuII. These findings are supported by numerous publications, and mechanistic studies shed light on the underlying theories behind the tunable emissions of EuII. The purpose of this article is to present the most recent hypotheses and understanding regarding the effect of counter anions, solvents, and ligands on luminescence properties of EuII based systems.

The Organic Ammonium Counterion Effect on Slow Magnetic Relaxation of the [Er(hfac)4]− Complexes

The first mononuclear anionic erbium complex [Er(hfac)4]− (hfac = hexafluoroacetylacetone) with an organic ammonium cation [(CH3)4N+] as the counterion was synthesized and structurally and magnetically characterized. The coordination geometries around the Er ions are square antiprisms with pseudo-D4d symmetry. The complex shows distinct field-induced slow magnetization relaxation, which is described by a combination of Orbach (Ueff/kB~28.54(8) K.) and direct mechanisms. Quantum chemical calculations were performed to analyze the magnetic properties of the complex under consideration.

Insights into Synergistic Effects of Counterion and Ligand on Diastereoselectivity Switch in Gold-Catalyzed Post-Ugi Ipso-Cyclization.

The concept of diastereoselectivity switch in gold catalysis is investigated, which primarily depends on the effects of ligand and counterion. The origins of gold-catalyzed post-Ugi ipso-cyclization for the diastereoselective synthesis of spirocyclic pyrrol-2-one-dienone have been explored with density functional theory calculations. The reported mechanism emphasized the importance of the cooperation of ligand and counterion in diastereoselectivity switch, leading to the stereocontrolling transition states. Furthermore, the nonbonding interactions primarily between the catalyst and the substrate play a significant role in the cooperation of ligand and counterion. This work would be useful to further understand the reaction mechanism of gold-catalyzed cyclization and the effects of ligand and counterion.

Poly(diallylmethylammonium) proton conducting membranes with high ionic conductivity at intermediate temperatures

High temperature proton exchange membrane fuel cells are being lately investigated because of their high energy efficiency, their superior heat/water management, CO tolerance, and electrode reaction kinetics. To further advance this technology, the polymer membrane portfolio and performance should be improved for intermediate or high temperature operation (>100 °C). In this work we present new poly(diallylmethylammonium) proton conducting membranes with high ionic conductivity at 120 °C. First, new protic ionic liquids, hereafter called DAMAH+X−, were synthesized leading to diallylmethylammonium monomers with different counter-anions. By radical cyclopolymerization through thermal and photoinitiation mechanisms, self-standing protic polymeric membranes of poly(diallylmethylammonium X−) were obtained. Membranes showed good thermal stability (>250 °C) and mechanical properties without the need of additives such as (protic) ionic liquids, solvents or inorganic charges. Great attention was paid to understand the effect of the different counter-anions on the membrane properties. As a general trend, fluorinated anions coming from strong acids confer high ionic conductivity and allow to reduce the hygroscopic properties on the protic polymeric membranes. Proton structural and dynamical stability at different temperatures and humidification conditions were investigated by Neutron Scattering (QENS and NR). The optimized poly(diallylmethylammonium X−) shows similar ionic conductivity values than Nafion 212 under varying relative humidity conditions at 80 °C. Furthermore, it shows a high ionic conductivity value of 1.9 × 10−3 S cm−1 at 120 °C under dry conditions.

Bistable Aryl Azopyrazolium Ionic Photoswitches in Water.

We report a new class of arylazopyrazolium-based ionic photoswitches (AAPIPs). These AAPIPs with different counter ions have been accessed through a modular synthetic approach in high yields. More importantly, the AAPIPs exhibit excellent reversible photoswitching and exceptional thermal stability in water. The effects of solvents, counter ions, substitutions, concentration, pH, and glutathione (GSH) have been evaluated using spectroscopic investigations. The results revealed that the bistability of studied AAPIPs is robust and near quantitative. The thermal half-life of Z isomers is extremely high in water (up to years), and it can be lowered electronically by the electron-withdrawing groups or highly basic pH.

Spatial charge storage on the nitrogen-doped graphene for ultrafast supercapacitors with high EDLC capacity

The limited specific surface area of carbon substance restricts the raise of the electrochemistry double layer capacitance (EDLC). If the charge storage location could be extended from surface to space, the EDLC of carbon materials can be greatly improved. Here, an original spatial charge storage mechanism according to the counterion effect from Fe (CN)6 3− ions bridged by nitrogenous groups is proposed, which can provide additionally spatial charge storage for EDLCs. More importantly, the graphene designed based on this structure can achieve a high storage capacity of 334 F g−1 at 0.5 A g−1 (the rate retention is 64% at 50 A g−1) in 6 M KOH electrolyte, much higher than the sample without space charge storage effect (from 270 to 160 F g−1). This novel strategy for the design of graphene with multiple spatial active sites can be extended to other carbon materials, which can propose a new idea for the development of carbon materials in the field of energy storage.

The Interplay of Weakly Coordinating Anions and the Mechanical Bond: A Systematic Study of the Explicit Influence of Counterions on the Properties of (Pseudo)rotaxanes

Weakly coordinating anions (WCAs) have attracted much attention in recent years due to their ability to stabilise highly reactive cations. It may well be argued, however, that a profound understanding of what truly defines a WCA is still lacking, and systematic studies to unravel counterion effects are scarce. In this work, we investigate a supramolecular pseudorotaxane formation reaction, subject to a selection of anions, ranging from strongly to weakly coordinating, which not only aids in fostering our knowledge about anion coordination properties, but also provides valuable theoretical insight into the nature of the mechanical bond. We employ state-of-the-art DFT-based methods and tools, combined with isothermal calorimetry and 1H NMR experiments, to compute anion-dependent Gibbs free association energies ΔGa, as well as to evaluate intermolecular interactions. We find correlations between ΔGa and the anions' solvation energies, which are exploited to calculate physico-chemical reaction parameters in the context of coordinating anions. Furthermore, we show that the binding situation within the (pseudo)rotaxanes can be mostly understood by straight-forward electrostatic considerations. However, quantum-chemical effects such as dispersion and charge-transfer interactions become more and more relevant when WCAs are employed.

FAIR and scalable management of small-angle X-ray scattering data.

A modular research data management toolbox based on the programming language Python, the widely used computing platform Jupyter Notebook, the standardized data exchange format for analytical data (AnIML) and the generic repository Dataverse has been established and applied to analyze small-angle X-ray scattering (SAXS) data according to the FAIR data principles (findable, accessible, interoperable and reusable). The SAS-tools library is a community-driven effort to develop tools for data acquisition, analysis, visualization and publishing of SAXS data. Metadata from the experiment and the results of data analysis are stored as an AnIML document using the novel Python-native pyAnIML API. The AnIML document, measured raw data and plots resulting from the analysis are combined into an archive in OMEX format and uploaded to Dataverse using the novel easyDataverse API, which makes each data set accessible via a unique DOI and searchable via a structured metadata block. SAS-tools is applied to study the effects of alkyl chain length and counterions on the phase diagrams of alkyltrimethyl-ammonium surfactants in order to demonstrate the feasibility and usefulness of a scalable data management workflow for experiments in physical chemistry.

Molecular Influences on the Quantification of Lewis Acidity with Phosphine Oxide Probes.

Gutmann-Beckett-type measurements with phosphine oxide probes can be used to estimate effective Lewis acidity with 31P nuclear magnetic resonance spectroscopy, but the influence of the molecular structure of a given probe on the quantification of Lewis acidity remains poorly documented in experimental work. Here, a quantitative comparison of triethyl (E), trioctyl (O), and triphenyl (P) phosphine oxides as molecular probes of Lewis acidity has been carried out via titration studies in MeCN with a test set of six mono- and divalent metal triflate salts. In comparison to E, the bulkier O displays a similar range of chemical shift values and binding affinities for the various test metal ions. Spectral linewidths and speciation properties vary for individual cation-to-probe ratios, however, confirming probe-specific properties that can impact the data quality. Importantly, P displays a consistently narrower dynamic range than both E and O, illustrating how electronic changes at phosphorus can influence the NMR response. Comparative parametrizations of the effective Lewis acidities of a broader range of metal ions, including the trivalent rare earth ions Y3+, Lu3+, and Sc3+ as well as the uranyl ion (UO22+), can be understood in light of these results, providing insight into the fundamental chemical processes underlying the useful approach of single-point measurements for quantification of effective Lewis acidity. Together with a study of counteranion effects reported here, these data clarify the diverse ensemble of factors that can influence the measurement of Lewis acid/base interactions.

The counterion-mediated controllable coacervation of nano-ions with polyelectrolytes

Nano-ions can complex with polyelectrolytes for coacervates with hierarchical structures; however, the rational design of functional coacervations is still rare due to the poor understanding of their structure–property relationship from their complex interaction. Herein, 1 nm anionic metal oxide clusters, PW12O403-, with well-defined, mono-disperse structures are applied to complex with cationic polyelectrolyte and the system shows tunable coacervation via the alternation of counterions (H+ and Na+) of PW12O403-. Suggested from Fourier transform infrared spectroscopy (FT-IR) and isothermal titration studies, the interaction between PW12O403- and cationic polyelectrolytes can be modulated by the bridging effect of counterions via hydrogen bonding or ion–dipole interaction to carbonyl groups of polyelectrolytes. The condensed structures of the complexed coacervates are explored by small angle X-ray and neutron scattering techniques, respectively. The coacervate with H+ as counterions shows both crystallized and discrete PW12O403- clusters, with a loose polymer-cluster network in comparison to the system of Na+ which shows a dense packing structure with aggregated nano-ions filling the meshes of polyelectrolyte networks. The bridging effect of counterions helps understand the super-chaotropic effect observed in nano-ion system and provides avenues for the design of metal oxide cluster-based functional coacervates.

Designing Nanofluidic Diode from a Hybrid‐Bilayer Covalent Organic Framework: Molecular Simulation Investigation (Small 9/2023)

Molecular Simulation Investigations In article number 2206382, Mao Wang and Jianwen Jiang design a nanofluidic diode based on a hybrid-bilayer covalent organic framework. Through molecular simulation, remarkable diode behavior is observed. Further analysis reveals that the synergistic effect of counterions in the nanopore has a positive impact on rectification.

Effects of ionic valence on aggregation kinetics of colloidal particles with and without a mixing flow

Hypothesis: The classical Schulze-Hardy rule states that the critical coagulation concentration (CCC) of colloidal particles is inversely proportional to the counter-ionic valence at powers ranging from 2 to 6. However, the inverse Schulze-Hardy rule has recently been proposed, suggesting that the CCC can also be inversely proportional to the co-ionic valence. Previous studies on these rules did not consider the effect of flow on aggregation kinetics and the CCC. This study aims to investigate the effect of multivalent counter-ions and co-ions on aggregation kinetics and the CCCs in systems with and without a mixing flow.Experiments: We measured the aggregation rate coefficients of polystyrene sulfate latex particles as a function of the salt concentration with different ionic species. Furthermore, we analyzed these measurements using theoretical models based on hydrodynamic pair-diffusion in a random flow and trajectory analysis in two steady flows. The analysis was conducted using zeta potentials determined through electrophoretic measurements.Findings: Although the trajectory analysis underestimates the CCCs, the hydrodynamic pair-diffusion model can capture the shift of critical coagulation concentrations in the mixing flow to higher values than those in Brownian aggregation and also shows a better agreement with the experimental results. This result suggests that combining random flow and Brownian diffusion is crucial for developing a consistent framework for predicting both Brownian aggregation and aggregation in a mixing flow.

Dynamic In Situ Monitoring of the Salt Counter-ion Effect on Surfactant Effectiveness Using Reconfigurable Janus Emulsions

A straightforward method for visualization and quantification of surfactant effectiveness within different electrolyte environments based on using reconfigurable Janus emulsions as novel optical probes is reported. More specifically, we investigated the effect of different types and concentrations of salt counter-ions on the surfactant surface excess of commercial ionic and non-ionic surfactants, namely sodium dodecyl sulfate (SDS) and Tween 80 via in situ monitoring the morphological reconfigurations of biphasic Janus emulsions comprising hydrocarbon and fluorocarbon oils. We find that significant variations in interfacial tensions of SDS-stabilized interfaces (up to 15 mN·m-1) can be evoked by titrating mono-, di-, and trivalent cationic counter-ions, which is coherent with the lyotropic (Hofmeister) series. In contrast, the salt counter-ion effect on the surfactant effectiveness was less pronounced for the non-ionic surfactant Tween 80 (∼3 mN·m-1). Our results reveal a facile in situ method for monitoring the central role of electrolyte type and concentration on surfactant effectiveness and, more broadly, illustrate that Janus emulsions serve as powerful optical probes to dynamically study the properties of surfactants at liquid interfaces. We demonstrate the utility of our findings for an electro-induced morphological reconfiguration of Janus droplet morphologies by dynamically tuning Cu2+ concentration in solution using an electrode setup. The latter provides a unique platform for liquid-phase, real-time, and continuous tuning of Janus droplet morphologies, e.g., for their application in sensing and dynamic optical device platforms.

Cationic cellulose Nanofibrils-based electro-actuators: The effects of counteranion and electrolyte

Cellulose-based electro-actuators have enormous potential in various applications, e.g. artificial muscles, soft grippers, medical devices, just to name a few, owing to their high mechanical strength, lightness and natural abundance. However, significant challenges remain in the fabrication of such electro-actuators featuring low operating voltage and fast response kinetics. We report here a facile fabrication route towards high-performance electro-actuators composed of CNFs films doped with ionic liquids or lithium salts and sandwiched by two thin film gold electrodes. Large bending motion at voltages as low as 3.0 V could be observed. The size effect of both anions and cations on the actuation was comprehensively investigated. CNF-TFSI@LiTFSI and CNF-BF4@EMIM-BF4 electro-actuators presented the best bending strain under an AC voltage of 3.0 V. This work provides new inspiration in the design of natural polymer-based high-performance electro-actuators.

Counterion effects on the alkali dissolution mechanism of quartz

In gold ore, quartz plays an important role in mineral formation by acting as the follower. Understanding counterion release, transport, and deposition in alkali solution is a prerequisite for evaluating the potential role of gold separate from quartz deposits in pretreatment. In this work, the aggregation, retention, and release of counterion in alkali solution media were investigated by kinetic research and pure mineral experiments, the correlation and mechanism of these processes were revealed by combining geochemical theory, interaction energy calculation, and quantum chemistry. The results showed that the retention and release of counterion were closely related to the dissolution and corrosion rate of quartz. The NH4+ and Fe2+ with higher mineral affinity reduced the quartz stability, and the dispersion stability and mobility of the quartz were greatly improved by an alkaline substance due to the enhancement of steric hindrance effects. Quantum chemical calculation results show that ammonium ion promotes the dissolution of quartz stronger than ferrous ion, which is mainly reflected in reducing the activation energy required for the formation of transition state (TS1), which can be verified by kinetic calculation. These findings provide essential insight into the extraction of gold coated by quartz as well as a vital reference for the experiment of gold-loaded quartz leaching in mineral processing.

Antimicrobial peptides alter lipid bilayer properties before disrupting membrane barrier property.

Antimicrobial peptides (AMPs) have been the subject of inquiry since the initial search for antibiotics in the ­first half of 20th century; the first antibiotic used in humans was the linear pentadecapeptide gramicidin. Much of this interest comes from the modest frequency of bacterial resistance against AMPs. Though AMPs differ in sequence and structure, the majority share three core physicochemical properties; they are short, cationic and amphipathic. Moreover, enantiomers of AMPs tend to have similar potencies. These common features have led to a focus on the bacterial membrane as a target for AMPs. High concentrations of AMPs cause gross bilayer defects, through pore formation or micellar breakdown. At lower concentrations, AMPs have effects on bacterial physiology that appear unrelated to membrane permeabilization, suggesting that they may act through bilayer-mediated regulation (BMR) of membrane protein function. If correct, this offers a mechanism of action that integrates the known membrane-modifying effects of AMPs with their ability to broadly alter bacterial physiology at sub-pore forming concentrations. We tested this hypothesis using melittin, gramicidin S, and indolicidin, three AMPs with distinct structures, that indeed alter bilayer properties at concentrations below those required for pore formation. Contrary to expectation, AMP induced BMR is attenuated in anionic bilayers despite increased AMP binding, suggesting an organizing effect of membrane-bound counterions. We further found that amphiphilic bilayer modifiers promote membrane permeabilization, suggesting that BMR may be responsible for the cooperativity of AMP-induced permeabilization. Two membrane-impermeant detergents, CHAPS and zwittergent, promote pore formation despite inhibiting AMP binding, suggesting a role for leaflet-specific lateral pressure differences. These results suggest a new mechanism by which AMPs exert their bactericidal effect, which may guide antibiotic design and provide a path for circumventing bacterial resistance.

Co2+, Ni2+ and Cu2+ complexes with phosphorylated derivatives of cyclen and diaza-18-crown-6: Effect of anion on the structure of complexes and their stability in solution

The effect of counterion A on the solid-state molecular structures and stability constants in solution for the complexes of the MA2 salts (M = Co2+, Ni2+, Cu2+, A = ClO4-, NCS-, NO3–) with phosphorylated cyclen and diaza-18-crown-6 derivatives has been studied. The synthesis, X-ray diffraction study, IR, and electronic absorption spectra of the complexes have been reported. The solid-state molecular structure of eight new complexes has been determined. The stability constants of the cobalt(II) complexes with 1,4,7,10-tetrakis[(diphenylphosphoryl)methyl]-1,4,7,10‑tetraazacyclododecane (L1) in acetonitrile have been estimated. A significant influence of the counterion of MA2 salt on the structure and stability of the complexes has been found. Salt anion affects both the number of formed complexes and the value of the stability constant of the complexes.