Counterion Exchange Research Articles

Orthogonal Phase Transfer of Oppositely Charged FeII4L6 Cages.

Coordination cages and their encapsulated cargo can be manoeuvred between immiscible liquid layers in a process referred to as phase transfer. Among the stimuli reported to drive phase transfer, counterion exchange is the most widespread. This method exploits the principle that counterions contribute strongly to the solubility preferences of coordination cages, and involves exchanging hydrophilic and hydrophobic counterions. Nevertheless, phase transfer of anionic cages remains relatively unexplored, as does selective phase transfer of individual cages from mixtures. Here we compare the phase transfer behaviour of two FeII4L6 cages with the same size and geometry, but with opposite charges. As such, this study presents a rare example wherein an anionic cage undergoes phase transfer upon countercation exchange. We then combine these two cages, and demonstrate that their quantitative separation can be achieved by inducing selective phase transfer of either cage. These results represent unprecedented control over the movement of coordination cages between different physical compartments, and are anticipated to inform the development of next-generation supramolecular systems.

Self-Assembled Triangular Prismatic Cages with Kinetic Inertness.

Two triangular prismatic cages were synthesized by combining a trishydrazide and two bisformyl precursors in strongly acidic water, where the dynamic nature of hydrazone was turned ON. An anionic guest was used as the template to drive the cage formation. Performing counterion exchange removed both the template and the Brønsted acid. The removal of the latter afforded the cages' kinetic inertness by turning OFF the reversibility of hydrazone. The cages can thus be used for recognizing various guests in water without observable degradation, driven by the hydrophobic effect. Upon being accommodated within the cage cavities, an anthracene derivative was protected from UV-stimulated oxidation, which would occur otherwise in the bulk solution without the protection from the host.

Quaternized poly(phenylene oxide) membranes for natural gas processing

This research explores the efficacy of quaternary ammonium-functionalized polymeric membranes in enhancing gas separation performance under different humidity levels. We synthesized brominated polyphenylene oxide and used it to prepare selective layers of thin film composite membranes. After coating, we implemented an in situ quaternization process for the brominated layer, followed by the subsequent exchange of bromine to chlorine counter ions. The spectroscopic characterization (FTIR and EDX) confirmed the inclusion of quaternary ammonium groups and the counter ion exchange. Under dry conditions, the quaternization followed by ion exchange significantly improved the CO2/CH4 selectivity to 30 while decreasing permeance. Under 90 % relative humidity, the membranes achieved 68 Barrer CO2 permeability and a CO2/CH4 selectivity of 178, compared to 56 Barrer and a selectivity of 11 for the brominated (non-quaternized) polymer membranes. The subsequent exchange of the counter ions, specifically replacing bromine ions by chlorine, markedly enhanced the performance of the membrane. This pivotal modification promotes the CO2 permeance and augments its CO2 selectivity over methane when evaluated in highly humid and challenging environments.

Synthesis, reactivity, and catalytic application of tetraphenylcyclobutadiene iridium complexes

Reaction of [(coe)2IrCl]2 (coe = cyclooctene) with AgPF6, arene (toluene, p-xylene, mesitylene), and diphenylacetylene, followed by counter anion exchange to BARF–, gives cyclobutadiene iridium complexes [(C4Ph4)Ir(arene)]BARF in 10–22% yield. Replacement of toluene in [(C4Ph4)Ir(toluene)]BARF by various ligands (trimethyl-phosphite, 1,3,5-triaza-7-phosphaadamantane, tert-butyl isonitrile) provides access to the half-sandwich cyclobuta-diene iridium complexes [(C4Ph4)Ir(L)3]BARF. Complex [(C4Ph4)Ir(toluene)]BARF in combination with [NBnEt3]Cl catalyses the insertion reaction between phenyl diazoacetate and various amines.

Precise counter anion modulation of the self-assembly behavior-endowed ultrasensitive and specific dual-mode visualization of nitrate

Pt(II) polypyridine complex-based probe exhibits promising performance in anion detection by the change of the absorption and emission properties based on supramolecular self-assembly. However, whether one can develop a modulation strategy of the counter anion to boost the detection sensitivity and anti-interference capability of the Pt(II) complex-based probe remains a big challenge. Here, an effective modulation strategy was proposed by precisely regulating the interaction energy through adjusting the type of the counter anions, and a series of probes have been synthesized by counter anion (X = Cl-, ClO4-, PF6-) exchange in [Pt(tpy)Cl]·X (tpy=2,2′:6′,2′’-terpyridine), and thus the colorimetric-luminescence dual-mode detection toward nitrate was achieved. The optimal [Pt(tpy)Cl]·Cl probe shows superior nitrate detection performance including a limit of detection (LOD) (8.68 nM), rapid response (<0.5 s), an excellent selectivity and anti-interference capability even facing 14 common anions. Moreover, a polyvinyl alcohol (PVA) sponge-based sensing chip loaded with the probe enables the ultra-sensitive detection of nitrate particles with an ultralow detection limit of 7.6 pg, and it was further integrated into a detection pen for the accurate recognition of nitrate particles in real scenarios. The proposed counter-anion modulation strategy is expected to start a new frontier for the exploration of novel Pt(II) complex-based probes.

Auxiliary strategy for the general and practical synthesis of diaryliodonium(III) salts with diverse organocarboxylate counterions.

Diaryliodonium(III) salts are versatile reagents that exhibit a range of reactions, both in the presence and absence of metal catalysts. In this study, we developed efficient synthetic methods for the preparation of aryl(TMP)iodonium(III) carboxylates, by reaction of (diacetoxyiodo)arenes or iodosoarenes with 1,3,5-trimethoxybenzene in the presence of a diverse range of organocarboxylic acids. These reactions were conducted under mild conditions using the trimethoxyphenyl (TMP) group as an auxiliary, without the need for additives, excess reagents, or counterion exchange in further steps. These protocols are compatible with a wide range of substituents on (hetero)aryl iodine(III) compounds, including electron-rich, electron-poor, sterically congested, and acid-labile groups, as well as a broad range of aliphatic and aromatic carboxylic acids for the synthesis of diverse aryl(TMP)iodonium(III) carboxylates in high yields. This method allows for the hybridization of complex bioactive and fluorescent-labeled carboxylic acids with diaryliodonium(III) salts.

Heterogeneous Structure, Mechanisms of Counterion Exchange, and the Spacer Salt Effect in Complex Molten Salt Mixtures Including LaCl3.

Complex molten chloride salt mixtures of uranium, magnesium, and sodium are top candidates for promising nuclear energy technologies to produce electricity based on molten salt reactors. From a local structural perspective, LaCl3 is similar to UCl3 and hence a good proxy to study these complex salt mixtures. As fission products, lanthanide salts and their mixtures are also very important in their own right. This article describes from an experimental and theory perspective how very different the structural roles of MgCl2 and NaCl are in mixtures with LaCl3. We find that, whereas MgCl2 becomes an integral part of multivalent ionic networks, NaCl separates them. In a recent article (J. Am. Chem. Soc. 2022, 144, 21751-21762) we have called the disruptive behavior of NaCl "the spacer salt effect". Because of the heterogeneous nature of these salt mixtures, there are multiple structural motifs in the melt, each with its particular free energetics. Our work identifies and quantifies these; it also elucidates the mechanisms through which Cl- ions exchange between Mg2+-rich and La3+-rich environments.

Stimuli-Responsive Nanostructured Viologen-Siloxane Materials for Controllable Conductivity.

Spontaneous phase separation is a promising strategy for the development of novel electronic materials, as the resulting well-defined morphologies generally exhibit enhanced conductivity. Making these structures adaptive to external stimuli is challenging, yet crucial as multistate reconfigurable switching is essential for neuromorphic materials. Here, a modular and scalable approach is presented to obtain switchable phase-separated viologen-siloxane nanostructures with sub-5nm features. The domain spacing, morphology, and conductivity of these materials can be tuned by ion exchange, repeated pulsed photoirradiation and electric stimulation. Counterion exchange triggers a postsynthetic modification in domain spacing of up to 10%. Additionally, in some cases, 2D to 1D order-order transitions are observed with the latter exhibiting a sevenfold decrease in conductivity with respect to their 2D lamellar counterparts. Moreover, the combination of the viologen core with tetraphenylborate counterions enables reversible and in situ reduction upon light irradiation. This light-driven reduction provides access to a continuum of conducting states, reminiscent of long-term potentiation. The repeated voltage sweeps improve the nanostructures alignment, leading to increased conductivity in a learning effect. Overall, these results highlight the adaptivity of phase-separated nanostructures for the next generation of organic electronics, with exciting applications in smart sensors and neuromorphic devices.

Artificial Multi-Stimulus-Responsive E-Skin Based on an Ionic Film with a Counter-Ion Exchange Reagent.

Sensing pressure and temperature are two important functions of human skin that integrate different types of tactile receptors. In this paper, a deformable artificial flexible multi-stimulus-responsive sensor is demonstrated that can distinguish mechanical pressure from temperature by measuring the impedance and the electrical phase at the same frequency without signal interference. The electrical phase, which is used for measuring the temperature, is totally independent of the pressure by controlling the surface micro-shapes and the ion content of the ionic film. By doping the counter-ion exchange reagent into the ionic liquid before pouring, the upper temperature measuring limit increases from 35 to 50°C, which is higher than the human body temperature and the ambient temperature on Earth. The sensor shows high sensitivity to pressure (up to 0.495 kPa-1) and a wide temperature sensing range (-10 to 50°C). A multimodal ion-electronic skin (IEM-skin) with an 8 × 8 multi-stimulus-responsive sensor array is fabricated and can successfully sense the distribution of temperature and pressure at the same time. Finally, the sensors are used for monitoring the touching motions of a robot-arm finger controlled by a remote interactive glove and successfully detect the touching states and the temperature changes of different objects.

The Study of Antistaphylococcal Potential of Omiganan and Retro-Omiganan Under Flow Conditions.

Staphylococcus aureus is considered one of the leading pathogens responsible for infections in humans and animals. The heterogeneous nature of diseases caused by these bacteria is due to the occurrence of multiple strains, differentiated by several mechanisms of antibiotic resistance and virulence factors. One of these is the ability to form biofilm. Biofilm-associated bacteria exhibit a different phenotype that protects them from external factors such as the activity of immune system or antimicrobial substances. Moreover, it has been shown that the majority of persistent and recurrent infections are associated with the presence of the biofilm. Omiganan, an analog of indolicidin - antimicrobial peptide (AMP) derived from bovine neutrophil granules, was found to exhibit high antistaphylococcal and antibiofilm potential. Furthermore, its analog with a reversed sequence (retro-omiganan) was found to display enhanced activity against a variety of pathogens. Based on experience of our group, we found out that counterion exchange can improve the antistaphylococcal activity of AMPs. The aim of this study was to investigate the activity of both compounds against S. aureus biofilm under flow conditions. The advantage of this approach was that it offered the opportunity to form and characterize the biofilm under more controlled conditions. To do this, unique flow cells made of polydimethylsiloxane (PDMS) were developed. The activity against pre-formed biofilm as well as AMPs-treated bacteria was measured. Also, the incorporation of omiganan and retro-omiganan into the channels was conducted to learn whether or not it would inhibit the development of biofilm. The results of the microbiological tests ultimately confirmed the high potential of the omiganan and its retro-analog as well as the importance of counterion exchange in terms of antimicrobial examination. We found out that retro-omiganan trifluoroacetate had the highest biofilm inhibitory properties, however, acetates of both compounds exhibited the highest activity against planktonic and biofilm cultures. Moreover, the developed methodology of investigation under flow conditions allows the implementation of the studies under flow conditions to other compounds.

Mechanistic Insights into Anion-Induced Electrochromism of Ru(II)-Based Metallo-Supramolecular Polymer.

The metallo-supramolecular polymer (MSP) is considered one of the most promising electrodes for electrochromic devices due to its intrinsically stable redox properties. Nevertheless, despite extensive work focusing on improving the electrochromic and electrochemical properties of MSPs, little experimental evidence exists from in-depth investigations on the anion-induced electrochromism of MSPs. Herein, Ru-based metallo-supramolecular polymer (polyRu) films with excellent electrochromic performance were fabricated through a novel electrochemical deposition method, and the electrochromic mechanism was further understood. The polyRu films possess fast reaction kinetics with a short switching time of 4.0 s (colored) and 2.8 s (bleached) and highly reversible redox properties due to the resulting impacts on the capacitive behaviors (containing surface, near-surface and intercalation pseudo-capacitance) of the perchlorate ions in the electrochromic process. Moreover, the electrochromic degradation of the polyRu films is considered to stem from the numerous nanopores in the film induced by ClO4- transport and the exchange of counter anions from Cl- to ClO4-. In addition, a physical model, revealing the transport of conduction ions and the evolution of the structure and properties of the polyRu film during the electrochromic process, is presented. It is observed that the charge balance of Ru3+ and Ru2+, achieved through the adsorption/desorption of ClO4- on the film, provides electrochromic and electrochemical reversibility to the polyRu film under positive/negative bias. Correspondingly, a transformation from polyRu·(Cl-)2n to polyRu·(ClO4-)x(Cl-)2n-x in the polyRu film is induced by a counter anion exchange from Cl- to ClO4-. Revealing the detailed perchlorate ion transfer kinetics and electrochromic mechanism in this film can offer new insights into the application of metallo-supramolecular polymers in electrochromic devices.

Ultrathin Mixed Ionic-Electronic Conducting Interlayer via the Solution Shearing Technique for High-Performance Lithium-Sulfur Batteries.

The commercialization of lithium-sulfur (Li-S) batteries has been hampered by diverse challenges, including the shuttle phenomenon and low electrical/ionic conductivity of lithium sulfide and sulfur. To address these issues, extensive research has been devoted to developing multifunctional interlayers. However, interlayers capable of simultaneously suppressing the polysulfide (PS) shuttle and ensuring stable electrical and ionic conductivity are relatively uncommon. Moreover, the use of thick and heavy interlayers results in an unavoidable decline in the energy density of Li-S batteries. We developed an ultrathin (750 nm), lightweight (0.182 mg cm-2) interlayer that facilitates mixed ionic-electronic conduction using the solution shearing technique. The interlayer, composed of carbon nanotube (CNT)/Nafion/poly-3,4-ethylenedioxythiophene:tetracyanoborate (PEDOT:TCB), effectively suppresses the shuttle phenomenon through the synergistic segregation and adsorption effects on PSs by Nafion and CNT/PEDOT, respectively. Furthermore, the electrical/ionic conductivity of the interlayer can be improved via counterion exchange and homogeneous Li+ ion flux/good wettability from SO3- functional group of Nafion, respectively. Enhanced sulfur utilization and reaction kinetics through polysulfide shuttle inhibition and facilitated electron/ion transfer by interlayer enable a high discharge capacity of 1029 mA h g-1 in the Li-S pouch cell under a high sulfur loading of 5.3 mg cm-2 and low electrolyte/sulfur ratio of 5 μL mg-1.

Unraveling the promoter effect and the roles of counterion exchange in glycosylation reaction.

The stereoselectivity of glycosidic bond formation continues to pose a noteworthy hurdle in synthesizing carbohydrates, primarily due to the simultaneous occurrence of SN1 and SN2 processes during the glycosylation reaction. Here, we applied an in-depth analysis of the glycosylation mechanism by using low-temperature nuclear magnetic resonance and statistical approaches. A pathway driven by counterion exchanges and reaction byproducts was first discovered to outline the stereocontributions of intermediates. Moreover, the relative reactivity values, acceptor nucleophilic constants, and Hammett substituent constants (σ values) provided a general index to indicate the mechanistic pathways. These results could allow building block tailoring and reaction condition optimization in carbohydrate synthesis to be greatly facilitated and simplified.

Controlled Supramolecular Assemblies of Chiral Cyclometalated Gold (III) Amphiphiles in Aqueous Media.

Gold (III) cyclometalated based amphiphiles in aqueous media have been revealed with excellent supramolecular transformations to external stimuli to open new pathways for soft functional material fabrications. Herein, we report a new chiral cyclometalated gold (III) amphiphile (GA) assembling into lamellar nanostructures in aqueous media confirmed with transmission electron microscopy (TEM). Counterion exchange with D-, L-, or racemic-camphorsulfonates features the significant supramolecular helicity enhancements, enabling transformations of GA from lamellar structure to vesicles and to nanotubes with multi-equivalents of counterion. The limited cytotoxicity of GA in aqueous media exhibits good biocompatibility.

Aqueous supramolecular assemblies of luminescent cyclometalated gold (III) amphiphiles with biocompatibility

Gold (III) complex-based amphiphiles in aqueous media have recently been demonstrated with high structural sensitivity to external stimulations, enabling new prospect for soft functional material applications. Here we demonstrate an advanced supramolecular assembly system of gold (III) amphiphiles reversibly controlled by counterions exchange. More importantly, the luminescent properties of the gold (III) amphiphiles are enhanced by implementation of σ-donating mono-alkynyl ligand. Gold (III) amphiphiles demonstrate with good cytocompatibilities to human bone marrow-derived mesenchymal stem cells.

Interconversion of Highly Entangled Polyhedra into Concave Polyhedra by Nitrate-Induced Ternary Coordination.

Entangled (M3L2) n polyhedral complexes represent a unique class of supramolecular architectures that are stabilized by relatively weak metal-acetylene interactions in cooperation with conventional metal-pyridyl coordination. Counter-anion exchange of these complexes with a nitrate (NO3-) ion triggered formal metal insertion between the metal centers, and a heteroleptic ternary coordination mode with acetylenic, pyridyl, and nitrate donors was generated on the metal centers. As a result, the main frameworks of the polyhedral complexes M18L12 and M12L8 were formally extended into a new series of concave polyhedra having the compositions M21L12 and M13L8, respectively. This transformation also resulted in the local disconnection of the highly entangled trifurcate topology of the framework, providing clues toward the skeletal editing of extended and complex three-dimensional (3D) architectures.

Counterion-Dependent Material Properties of Phosphorylated Nanocellulose.

The material properties of cellulose nanofibers (CNFs) are governed by the surface chemical structure of the fibers. The chemical structure-property relationships for monovalent carboxylated CNFs are well understood. Here, we report the basic sheet properties of divalent phosphorylated CNFs with different phosphorus contents and counterion types. All examined sheet properties, including conditioned and wet tensile properties, electrical resistivities, and fire-retardant properties of the CNF sheets, were greatly enhanced by the counterion exchange from the initial sodium ions to calcium or aluminum ions. The phosphorus content had significant influences only on the conditioned tensile and fire-retardant properties. In comparison to CNF sheets with monovalent carboxy groups, the CNF sheets with divalent phosphate groups were superior in terms of their wet tensile properties and fire-retardant properties. Our research shows that the combination of the divalent phosphate introduction and counterion exchange provides a successful strategy for the practical application of CNF sheets as antistatic materials and flexible substrates for electronic devices.

Surface modification, counter-ion exchange effect on thermally annealed sulfonated poly (ether ether ketone) membranes for vanadium redox flow battery

In this work, we report new approaches to sulfonated poly ether ether ketone (SPEEK) membranes to improve its inhibition to vanadium ions along with polymer reinforcement. First approach includes facile thermal annealing of SPEEK membrane (SPEEK-T) which could reinforce the polymer matrix. Second approach was to exchange the labile proton of SPEEK with benzimidazole to protect the hydrolytic decomposition of sulfonic acid followed by thermal annealing (SPEEK-Benz), and third approach focused on creating barrier layer for vanadium ions by coating polyethyleneimine on SPEEK membrane followed by thermal treatment (SPEEK-PEI). The chemical stability study of the membranes revealed acceptable dimension change and VO2+ electrolyte sorption for all the membranes with least dimension change and weight gain of 5 % and 12 %, respectively, for SPEEK-PEI. Amongst four prepared membranes, SPEEK-PEI membrane displayed least diffusion coefficient of 8.04 × 10−7, 8.94 × 10−7, 4.20 × 10−7 cm2 min−1 for V3+, VO2+, and VO2+ ions respectively. VRFB assembled with SPEEK-PEI resulted highest Coulombic efficiency (CE) of 97 % and energy efficiency (EE) of 66 % over 50 charge/discharge cycles at 100 mA cm−2. Peak power density of 255, 248, 240 and 235 mW cm−2 at current density of 300 mA cm−2 was observed for SPEEK-PEI, SPEEK-Benz, SPEEK-T, and SPEEK-48, respectively; these values were higher than 225 mW cm−2 for Nafion®117 in identical experimental conditions. The excellent VRFB performance suggest that the developed new approaches have pronounced effect on the membrane properties and can be further improved to obtain an ideal VRFB separator. Furthermore, the surface modification approaches adopted in this work is facile, reproducible and scalable and can be further designed to develop high performance ion exchange membranes for separation/purification and energy.

Substrate-independent, robust and functional PVDF-g-IL coating based on tunable surface free energy

Substrate-independent and robust coatings with desired functions are highly demanded in many fields. The fabrication and fundamental theory of them, however, remain challenging for decades. Herein, we aim to elaborate it from a new perspective, in which the challenge has been attributed to the different or even conflicting requirements on surface free energy (SFE) at substrate/coating (bottom) and coating/air (top) interfaces. In this work, a novel strategy has been developed to tailor SFE continuously and reversibly based on counterion exchange. Polyvinylidene fluoride grafted with ionic liquids (PVDF-g-IL) coating with hierarchical surface roughness was fabricated via solution casting and vapor induced phase separation. In the as-prepared specimen, the surface free energy was calculated based on Neumann method. The resultant high SFE (from the counterion of [Cl−] and hierarchical roughness) contributes to the superior bondability of coating/substrate, corresponding to the excellent universality and robustness of PVDF-g-IL coating assessed via T-peeling test. After that, controlled counterion exchange between [Cl−] and [PFO−] (pentadecafluorooctanate anion) has been employed to tailor SFE at top interface. The consequent high/low magnitudes of SFE enable the super-hydrophilic/super-hydrophobic properties at solid/liquid interface while the tunable SFE dominates serial adsorption at multiple-phase interface.

An anionic porphyrinylphosphonate-based hydrogen-bonded organic framework: optimization of proton conductivity through the exchange of counterions.

Hydrogen-bonded organic frameworks (HOFs) possessing high crystallinity, simple synthetic procedure and easy regeneration provide high efficiency as multifunctional systems, including applications as proton conductors. Porphyrinylphosphonates having acidic moieties, which can form multiple hydrogen bonds, together with tunable physical-chemical properties of a macrocycle may significantly improve the proton conductivity of such materials. Herein, the synthesis, characterization and proton-conducting properties of a novel anionic HOF based on a new complex of palladium(II) with meso-tetrakis(4-(phosphonatophenyl))porphyrin, HOF-IPCE-1Pd, are reported. Directed structural transformation of the framework by the exchange of dimethylammonium counterions for ammonium cations along with the absorption of ammonia and water molecules led to the formation of a more hydrolytically stable structure of HOF-IPCE-1Pd-NH3, demonstrating the proton conductivity of 1.27 × 10-3 S cm-1 at 85 °C and 85% RH, which is one of the highest among all known HOFs based on porphyrins. It is noteworthy that the reversible absorbance of water/ammonia molecules preserves the crystal structure of HOF-IPCE-1Pd-NH3.