Pyridinium Cations Research Articles

Tunable Intermolecular Charge Transfer in Ionic Liquid Crystalline Derivatives of the [closo-B10H10]2– Anion

A new paradigm of ionic liquid crystals exhibiting low-energy charge transfer bands is demonstrated. Thus, four series of ion pairs of 1,10-disubstituted derivatives of the [closo-B10H10]2– anion and substituted pyridinium cations were prepared and their thermal and photophysical properties were investigated. All pyridinium ion pairs form a smectic A (SmA) phase with clearing temperatures above 200 °C and intermolecular charge transfer (CT) band in the solid and fluid states and in CH2Cl2 solutions. The CT band maximum is in the range of 320–510 nm and its position correlates with the difference in frontier molecular orbital (FMO) energies of the ions (highest occupied molecular orbital (HOMO) of the anions and the lowest unoccupied molecular orbital (LUMO) of the cations), which, in turn, correlate well with the substituent σp parameters. Experimental results are augmented with extensive density functional theory (DFT) calculations and X-ray diffraction (XRD) analyses.

Thermal Stability and Specific Heat Estimation of Pyridinium Cation-Based Surfactant Ionic Liquids Using TGA-DSC

Background:In recent years, the ultimate goal has been to learn how to select ionic liquids specifically for materialistic or molecular level applications of these neoteric materials. Progress has been initiated, but much more is needed to optimize the full potential of ionic liquids in every aspect of modern-day science.Methods:A number of engineering parameters need to be determined for the challenging flourishing of ionic liquids in sustainable commercial applications.Results & Discussion:In particular, the general absence of specific heat capacity (Cp) data is a substantial obstacle to the design of chemical reactors and heat transfer systems if any ionic liquid-based processes are to be developed beyond the laboratory scale. The specific heat capacities of ionic liquids and their mixtures have significant importance in chemical engineering work, accompanying the design and operation of reactors and heat-related operations required for the commercialization of ionic liquids and technologies associated with them.Conclusion:In this work, thermal profiles of the surfactant or sponge ionic liquids have been explored very aptly to measure the specific heat capacity (Cp) of the pyridinium cation- based surfactant or sponge ionic liquids.

From a Dense Structure to Open Frameworks: The Structural Plethora of Alkali Metal Iron Fluorophosphates.

By employing the pyridinium hexafluorophosphate task-specific ionic liquids 1-butyl-4-methylpyridinium hexafluorophosphate ([C4mpyr][PF6]) and 1-ethylpyridinium hexafluorophosphate ([C2pyr][PF6]) as the reaction medium, mineralizer, structure-directing agent, and, in the case of the smaller pyridinium cation, even a structural component, it was possible to obtain five new alkali metal iron phosphates featuring interconnected FeX6 octahedra and PX4 (X = F, O, or OH) tetrahedra. NaFe(PO3F)2 (1) is a dense 3D structure, RbFe(PO3F)(PO2(OH)F)(PO2(OH)2) (2) features 1D strands, (C2pyr)LiFe(PO3F)3(PO2F2)F (3) has 2D layers, and LiFe(PO3F)(PO2F2)F (4) as well as Cs0.75Fe(PO2.75(OH)0.25F)(PO2F2)2 (5) are 3D open frameworks. While in 1–2 as well as in 4 and 5, FeX6 octahedra and PX4 (X = F, O, or OH) tetrahedra alternate, 3 features octahedra dimers, Fe2X11 (X = F, O, or OH). The magnetic behavior of all compounds is governed by antiferromagnetic interactions. Interestingly, 3 exhibits a broad maximum in the temperature dependence of the magnetic susceptibility, characteristic of a low-dimensional magnetic system consistent with the presence of Fe–Fe dimers in its crystal structure.

Cancer Cell Membrane Labeling Fluorescent Doppelganger Enables In Situ Photoactivated Membrane Dynamics Tracking via Two-Photon Fluorescence Imaging Microscopy

Various suborganelles are delimited by lipid bilayers, in which high spatial and temporal morphological changes are essential to many physiological and pathological processes of cells. However, almost all the amphiphilic fluorescent molecules reported until now are not available for in situ precise tracking of membrane dynamics in cell apoptosis. Here, the MO (coumarin pyridine derivatives) was devised by engineering lipophilic coumarin and cationic pyridine salt, which not only lastingly anchored onto the plasma membrane in dark due to appropriate amphipathicity and electrostatic interactions but also in situ reflected the membrane damage and heterogeneity with secretion of extracellular vesicles (EVs) under reactive oxygen species regulation and was investigated by two-photon fluorescence lifetime imaging microscopy. This work opens up a new avenue for the development of plasma membrane staining and EV-based medicines for the early diagnosis and treatment of disease.

One-pot hydrothermal synthesis of a mononuclear cobalt(II) complex and an organic-inorganic supramolecular adduct: Structures, properties and hirshfeld surface analyses

Through the hydrothermal reaction of cobalt(II) perchlorate hexahydrate with 5-bromo-6-methyl-pyridine-2-carboxylic acid (5-Br-6-Me-Hpyc) and 1,4-bis(4-pyridyl)benzene (1,4-bpb) coligands, a cobalt(II) complex [Co(5-Br-6-Me-pyc)2(H2O)]·2H2O (1) and an organic-inorganic adduct [H2(1,4-bpb)]·2ClO4 (2) have been co-synthesized in the same medium. Structural analyses indicated that the cobalt(II) ion in 1 is penta-coordinated by one water and two bidentate chelate 5-Br-6-Me-pyc anionic ligands to obtain an asymmetric mononuclear species. While in 2, the two pyridyl groups of 1,4-bpb acquire two protons forming a bivalent cation pyridinium, which combine two perchlorate anions via N–H⋯O hydrogen bonds to fabricate an interesting anion-cation supramolecular adduct 2. The magnetism for 1, fluorescence for 2 as well as the hirshfeld surface structures for them have been carefully described and discussed.

The influence of a solvent environment on direct non-covalent interactions between two molecules: A symmetry-adapted perturbation theory study of polarization tuning of π–π interactions by water

High-level quantum chemical computations have provided significant insight into the fundamental physical nature of non-covalent interactions. These studies have focused primarily on gas-phase computations of small van der Waals dimers; however, these interactions frequently take place in complex chemical environments, such as proteins, solutions, or solids. To better understand how the chemical environment affects non-covalent interactions, we have undertaken a quantum chemical study of π–π interactions in an aqueous solution, as exemplified by T-shaped benzene dimers surrounded by 28 or 50 explicit water molecules. We report interaction energies (IEs) using second-order Møller–Plesset perturbation theory, and we apply the intramolecular and functional-group partitioning extensions of symmetry-adapted perturbation theory (ISAPT and F-SAPT, respectively) to analyze how the solvent molecules tune the π–π interactions of the solute. For complexes containing neutral monomers, even 50 explicit waters (constituting a first and partial second solvation shell) change total SAPT IEs between the two solute molecules by only tenths of a kcal mol−1, while significant changes of up to 3 kcal mol−1 of the electrostatic component are seen for the cationic pyridinium–benzene dimer. This difference between charged and neutral solutes is attributed to large non-additive three-body interactions within solvated ion-containing complexes. Overall, except for charged solutes, our quantum computations indicate that nearby solvent molecules cause very little “tuning” of the direct solute–solute interactions. This indicates that differences in binding energies between the gas phase and solution phase are primarily indirect effects of the competition between solute–solute and solute–solvent interactions.

Development of a cationic aggregate induced emission fluorescent probe for detection of aromatase

Tetraphenylethylene with electron withdrawing pyridinium cations and cyano groups were designed and synthesized. Cyanoprobe 2 has a typical Aggregate Induced Emission effect under physiological conditions, while cation probe 1 cannot aggregate luminescence due to its higher hydrophilicity. When interacting with aromatase, probe 1 showed obvious fluorescence change, but probe 2 did not. Under the same conditions, or even under the interference of various factors, probe 1 can recognize aromatase with high sensitivity. Probe 1 can rapidly light up aromatase-expressing cells. Probe 1 have the properties of aromatase inhibitors, which can inhibit the growth of tumor cells. The design ideas of cationic AIE fluorescent probes in this paper are expected to be applied to other targets.

Structure, optical and magnetic properties of the pyridinium cobaltate (C6H9N2)2[CoCl4

The reaction of 2-amino-4-methylpyridine (L) with CoCl2·6H2O in hydrochloric acid gave the chlorocobaltate (HL)2[CoCl4] in 82% yield. X-ray diffraction of the blue crystalline material showed isolated [CoCl4]2– tetrahedra in the structure, connected to the aromatic 2-amino-4-methyl pyridinium cations through H bonding while the cations show π-stacking. FT-IR spectroscopy in conjunction with Hirshfeld surface analysis confirmed the importance of the 2-amino function in the cations for the hydrogen bonding. The material is thermally stable up to 270 °C. Intense UV–vis absorptions in the range 200–400 nm were assigned to π–π* transitions in the pyridinium cation, weaker features in the range 600–750 nm were due to ligand-field transitions in the d7 high-spin system [CoCl4]2–. Excitation at 370 nm led to an intense blue-green emission at λem = 473 nm attributable to excited π–π* states. The molar susceptibility measured over a range of 5–300 K reveals paramagnetic behavior at high temperature range with an effective magnetic moment of µeff = 4.74 µB indicating a significant spin–orbit coupling contribution adding to the spin-only value of 3.87 µB expected for Co(II) with 3d7 high spin configuration.

Effects of the Cationic Structure on the Adsorption Performance of Ionic Polymers toward Au(III): an Experimental and DFT Study.

Ionic polymers have been proven to be promising adsorbents in recovering Au(III) due to their advantages of simple synthesis and high adsorption efficiency. However, the unclarity of the relationship between the adsorption ability of ionic polymers and their cationic structures hinders further optimization of their adsorption performance. This study synthesized a series of ionic polymers with pyridinium, imidazolium, piperidinium, pyrrolidinium, and triethylammonium cations to discover the effects of the cationic structure on their adsorption properties. Experimental results show that the existence of anion-π interaction between aromatic cations and [AuCl4]- makes the aromatic cations-anion interaction stronger, which does not enhance the adsorption performance of the aromatic-based ionic polymer. This is due to the charge delocalization in the aromatic ring, resulting in a lower electrostatic potential (ESP) of aromatic cations than that of aliphatic cations with a localized charge. The higher the ESP of cations, the better the adsorption performance of the corresponding ionic polymer. This study serves as a deep understanding of the cationic structure-adsorptive performance relationship of the ionic polymer at the molecular level and further provides a theoretical guidance to optimize the adsorption performance of ionic polymers.

Efficient removal of 2,4-D from solution using a novel antibacterial adsorbent based on tiger nut residues: adsorption and antibacterial study.

We engineered a tiger nut residue (TNR, a low-cost agricultural waste material) through a facile and simple process to take advantage of the introduced functional groups (cetylpyridinium chloride, CPC) in the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) in batch mode and further investigated its impingement on bacterial growth in a yeast-dextrose broth. The surface characterizations of the adsorbent were achieved through Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller method (BET), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). The batch adsorption studies revealed that solution pH, adsorbent dose, temperature, and salt affected the adsorptive capacity of TNR-CPC. The equilibrium data were best fitted by Langmuir isotherm model with a maximum monolayer adsorption capacity of 90.2mgg-1 at 318K and pH 3. Pseudo-second-order model best fitted the kinetics data for the adsorption process. Physisorption largely mediated the adsorption system with spontaneity and a shift in entropy of the aqueous solid-solute interface reflecting decreased randomness with an exothermic character. TNR-CPC demonstrated a good reusability potential making it highly economical and compares well with other adsorbents for decontamination of 2,4-D. The adsorption of 2,4-D proceeded through a probable trio-mechanism; electrostatic attraction between the carboxylate anion of 2,4-D and the pyridinium cation of TNR-CPC, hydrogen bonding between the hydroxyl (-OH) group inherent in the TNR and the carboxyl groups in 2,4-D and a triggered π-π stacking between the benzene structures in the adsorbate and the adsorbent. TNR-CPC reported about 99% inhibition rate against both gram-positive S. aureus and gram-negative E. coli. It would be appropriate to investigate the potential of TNR-CPC as a potential replacement to the metal oxides used in wastewater treatment for antibacterial capabilities, and its effects against airborne bacteria could also be of interest.

Oxidation Catalysis over Solid-State Keggin-Type Phosphomolybdic Acid with Oxygen Defects.

Keggin-type phosphomolybdic acid (PMo12O40), treated with pyridine (Py), forms a crystalline material (PyPMo-HT) following heat treatment under an inert gas flow at ∼420 °C. Although this material is known to have attractive catalytic properties for gas-phase oxidation, the origin of this catalytic activity requires clarification. In this study, we investigated the crystal structure of PyPMo-HT. PyPMo-HT comprises a one-dimensional array of Keggin units and pyridinium cations (HPy), with an HPy/Keggin unit ratio of ∼1.0. Two oxygen atoms were removed from the Keggin unit during crystal structure transformation, which resulted in an electron being localized on the Mo atom in close contact with the adjacent Keggin unit. Upon the introduction of molecular oxygen, electron transfer from this Mo atom resulted in the formation of an electrophilic oxygen species that bridged two Keggin units. The electrophilic oxygen species acted as a catalytically active oxygen species, as confirmed by the selective oxidation of propylene. PyPMo-HT showed excellent catalytic activity for the selective oxidation of methacrolein, with the methacrylic acid yield being superior to that obtained with PMo12O40 and comparable to that obtained with an industrial Keggin-type polyoxometalate (POM) catalyst. The oxidation catalysis observed over PyPMo-HT provides a deeper understanding of POM-based industrial catalytic processes.

Mitochondrial Targeting Long-Term Near-Infrared Imaging and Photodynamic Therapy Aggregation-Induced Emission Luminogens Manipulated by Thiophene.

In recent years, the development and application of integrated probes for theranostics have attracted more and more attention. However, few biological probes can meet the needs of in vivo and in vitro long-term near-infrared imaging and photodynamic therapy, especially with a certain subcellular organelle targeting ability. Here, 2-chlorophenothiazine as a pharmacophore is linked to the mitochondrial targeting group pyridine cation through an alkyl chain, which is further linked to triphenylamine-based aggregation-induced emission groups to obtain two aggregation-induced emission luminogens (AIEgens). Only the presence or absence of thiophene causes two AIEgens to exhibit different structure-oriented characteristics. Although they are different with respec to mitochondrial targeting, cellular imaging, and cytotoxicity, they all have excellent in vivo and in vitro long-term near-infrared imaging and photodynamic therapy capabilities.

Mitochondria-Targeted Photodynamic Cancer Therapy of Nanoscale Liposome-Encapsulating Boron Dipyrromethene Photosensitizers Conjugated with Pyridine Cations

Mitochondria-Targeted Photodynamic Cancer Therapy of Nanoscale Liposome-Encapsulating Boron Dipyrromethene Photosensitizers Conjugated with Pyridine Cations

Aprotic Ionic Liquids: A Framework for Predicting Vaporization Thermodynamics.

Ionic liquids (ILs) are recognized as an environmentally friendly alternative to replacing volatile molecular solvents. Knowledge of vaporization thermodynamics is crucial for practical applications. The vaporization thermodynamics of five ionic liquids containing a pyridinium cation and the [NTf2] anion were studied using a quartz crystal microbalance. Vapor pressure-temperature dependences were used to derive the enthalpies of vaporization of these ionic liquids. Vaporization enthalpies of the pyridinium-based ionic liquids available in the literature were collected and uniformly adjusted to the reference temperature T = 298.15 K. The consistent sets of evaluated vaporization enthalpies were used to develop the “centerpiece”-based group-additivity method for predicting enthalpies of vaporization of ionic compounds. The general transferability of the contributions to the enthalpy of vaporization from the molecular liquids to the ionic liquids was established. A small, but not negligible correction term was supposed to reconcile the estimated results with the experiment. The corrected “centerpiece” approach was recommended to predict the vaporization enthalpies of ILs.

Simple grinding for the synthesis of monomeric, dimeric, and trimeric pyridinium salts and its photophysical studies

AbstractSynthesis of water‐soluble‐substituted pyridinium cation which is attached with base sensitive fluorophore peripheral units with different inorganic counter anions under conventional/silica‐supported Muffle furnace methods. Solvent‐free synthetic approach has more merits than the conventional method, such as non‐toxic, shorter reaction time, easy workup procedure without purification process, and higher yields. Ultraviolet–visible spectra were recorded in neutral, acidic, and alkaline medium; it showed greater red shift in alkaline medium compared with neutral and acidic pH medium.

Pyridinium salt-based covalent organic framework with well-defined nanochannels for efficient and selective capture of aqueous 99TcO4−

Ionic covalent organic framework (COF) materials with high specific surface areas and well-defined pore structures are desired for many applications yet seldom reported. Herein, we report a cationic pyridinium salt-based COF (PS-COF-1) with a Brunauer-Emmett-Teller (BET) surface area of 2703 m2 g−1, state-of-the-art for an ionic COF. Aided by its ordered pore structure, chemical stability, and radiation resistance, PS-COF-1 showed exceptional adsorption properties toward aqueous ReO4− (1262 mg g−1) and 99TcO4−. Its adsorption performance surpassed its corresponding amorphous analogue. Importantly, PS-COF-1 exhibited fast adsorption kinetics, high adsorption capacities, and selectivity for 99TcO4− and ReO4− at high ionic strengths, leading to the successful removal of 99TcO4− under conditions relevant to low-activity waste streams at US legacy Hanford nuclear sites. In addition, PS-COF-1 can rapidly decontaminate ReO4−/99TcO4− polluted potable water (∼10 ppb) to drinking water level (0 ppb, part per billion) within 10 min. Density functional theory (DFT) calculations revealed PS-COF-1 has a strong affinity for ReO4− and 99TcO4−, thereby favoring adsorption of these low charge density anions over other common anions (e.g., Cl−, NO3−, SO42−, CO32−). Our work demonstrates a novel cationic COF sorbent for selective radionuclide capture and legacy nuclear waste management.

Risk-focused investigation on ionic liquids against their applied background in transdermal delivery

Ionic liquids (ILs) have recently been proposed as a new useful component for various transdermal and medical purposes. Before they are fully recognized and applied, systematic investigation on their safety should be focused. By using different animal and bionic skins, 12 ILs (composed of imidazole, pyridine, quaternary ammonium and quaternary phosphate cations and 5 common anions) and specific combinations between them were evaluated for their transdermal behaviors and potential adverse effects. 1-Butyl-3-methylimidazolium bromide ([C4mim][Br]) showed prominent permeability and permeation enhancement on stratum corneum among them by affecting skin barrier, lipid fluidity as well as keratin, which could be attributed to the appropriate molecular size, hydrogen-bonding ability, and octanol–water partition coefficient. Within our investigation, skin color change, loose edema and inflammatory cells infiltration were observed with hazard Category 2. It was also investigated whether the skin irritation could be improved by autoimmune function in the short term. The kinetics and computational analysis revealed that [C4mim][Br] inhibited tyrosinase activity in a reversible mixed manner. Combined with other toxicological assessment methods, this study provides a new thinking for further research on the design principles and risk assessment for such ‘green’ chemical mediums in the field of transdermal delivery.

Molecular versus ionic liquids: Development of a thermodynamic framework for predicting vaporization thermodynamics

Ionic liquids based on the pyridinium and quinolinium cations show good result in desulfurization of fuels. The knowledge of their vaporisation thermodynamics is of practical importance. The standard molar enthalpies of vaporization of pyridinium based ionic liquids were derived from the vapor pressure temperature dependences measured by the quartz-crystal microbalance method. We have collected available primary experimental results on vapour pressures, and enthalpies of phase transitions (solid-solid, crystal-gas, and liquid-gas) of analogous molecular species – substituted pyridines and quinolines. These data were evaluated using the structure-property correlations. The consistent sets of evaluated thermodynamic data on the molecular and ionic liquids were used to develop the “centerpiece” based group-additivity method for predicting enthalpies of vaporization of molecular and ionic compounds. The general transferability of the contributions to the enthalpy of vaporization from the molecular liquids to the ionic liquid has been established.

One-pot Sonogashira–Hydroarylation reaction catalyzed by anionic palladium complexes in an aqueous medium

It was found that anionic Pd(II) complexes of type [CA]2[PdCl4] and [CA]2[Pd2Cl6] (CA = imidazolium or pyridinium cation) are effective catalysts for copper-free Sonogashira coupling in an aqueous medium without additional ligands or co-catalysts. Both types of substrates, containing electron donor or electron acceptor groups, formed the corresponding products in good to excellent yield. The most active complex, [bmpy]2[Pd2Cl6] (bmpy = 1-butyl-4-methylpyridinium cation), was employed to the hydroarylation of the Sonogashira product in a one-pot process, using microwave radiation, NaBPh4 as a phenyl source and water as a proton donor. In these reactions the presence of electron donor substituents facilitated a higher conversion of diarylacetylenes to triarylethenes than electron acceptor groups.

Highly sensitive and disposable screen-printed ionic liquid/graphene based electrochemical sensors

In this work, a highly sensitive and disposable screen-printed ionic liquid-graphene electrode (SPIL-GE) was developed for electrochemical sensing. The paste for screen printing was facilely prepared by mixing IL with electrolytically exfoliated graphene in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (GP/PEDOT/PSS) and carbon paste (CP) via ball milling. The IL-GP paste was then screen printed to form working and counter electrodes (WE & CE) followed by screen printing of Ag/AgCl reference electrode and insulator layer on a polyethylene substrate. Electrode geometries were optimized for electrochemical sensing, arriving at an optimal design with an overall electrode length of 25 mm, and CE and WE active areas of 15.70 and 12.57 mm2, respectively. SPIL-GEs employing six ILs with imidazolium and pyridinium cations were assessed for electrochemical sensing of K3Fe(CN)6. The pyridinium-type IL, namely 3-methyl-1-propylpyridinium bis(trifluoromethyl sulfonyl)imide (PMPlm), was found to exhibit the highest CV peak currents compared with other ILs at an optimal PMPlm content of 1.0% (w/w). Characterization with scanning electron microscopy and Fourier-transform infrared spectroscopy confirmed the presence of PMPlm, GP/PEDOT/PSS and CP in SPIL-GEs. The electrochemical performance of the optimal SPIL-GE towards the three common analytes including ferri/ferro cyanide (Fe(CN)6)3-/4- redox couple, dopamine and hydroquinone were compared with the screen-printed carbon and graphene electrodes (SPCE & SPGE). From the results, the SPIL-GE demonstrated larger anodic currents with lower oxidation potentials for the three analytes than SPGE and SPCE, respectively. Therefore, the SPIL-GE could be a potential candidate for advanced electrochemical sensing applications.