Anion Binding Properties Research Articles

Pulsed Electrodeposition of Ultrathin Polyaniline Films and Mechanistic Understanding of their Anion-Mediated Electrochemical Behavior

Electrode materials which undergo anion insertion are of interest for next-generation energy storage devices and electrochemical water desalination. Polyaniline (PANI) is a robust and well-studied electrode material for anion insertion, but to date we have been unable to establish the electrochemical and anion-binding performance of PANI at nanoscale thicknesses because these thicknesses are not obtainable using standard PANI deposition procedures. Here, we report a new pulsed electrodeposition procedure for the controlled growth of PANI thin films with nanometer-scale thickness control. Using this pulsing technique, we deposit nanoscale (<100 nm) thin films of PANI onto stainless steel (SS) disks and gold electrochemical quartz crystal microbalance (EQCM) crystals. We examine the charge rate and anion-binding properties as a function of nanoscale thickness, and reveal previously undescribed insights into the charge storage and anion binding mechanisms of PANI. In particular, we identify that PANI films of <10 nm thickness provide rapid chloride ion uptake for desalination applications, and that thicker ∼100 nm PANI films are able to achieve rapid charge storage in sulfate solutions due to SO42−/HSO4− embedded within the PANI acting as a proton donor/acceptor. The results we report will inform the use of PANI thin films for energy storage and desalination applications.

Anion binding with biphenyl-bis-urea derivatives: solution and solid-state studies

Bis-urea derivatives1–3, featuring a biphenyl spacer, were synthesized, characterized and investigated about their anion binding properties in DMSO solution and in the solid state.

Halogenated isophthalamides and dipicolineamides: the role of the halogen substituents in the anion binding properties.

A novel family of amide-based receptors is herein described. Specifically, the role of the halogen substituents at the aryl moieties in the anion binding properties of a series of halogenated isophthalamides and dipicolineamides (L1-L6) was investigated both in solution and in the solid state in order to evaluate the incidence of all possible different and combined weak host-guest interactions. Only L5 and L6 bearing pentafluorophenyl rings as substituents have some affinities for the set of anions studied. In particular, in the case of L5 an interesting behaviour with the formation of a non-symmetric adduct with benzoate and dihydrogen phosphate was hypothesised by 1H- and 19F-NMR spectroscopy studies in solution and confirmed by theoretical calculation. The study of the crystal structures of the receptors demonstrated that the steric hindrance determined by the halogen substituents in the receptor molecules influences the accessibility of the anions to the isophthalamide or dipicoline amide NH moieties, thus modulating the affinity for the anion guests.

Anion binding and fluoride ion induced conformational changes in bisurea receptors

Two types of bisurea receptors, containing either 2,6-substituted phenyl or 2,6-substituted pyridine, are prepared, and their anion binding properties are investigated.

Selective anion transport mediated by strap-extended calixpyrroles

Synthetic anion receptors that facilitate transmembrane chloride transport are of interest as potential therapeutic agents for cancer and cystic fibrosis. Transporters selective for chloride over protons are desired for therapeutic applications to avoid autophagy inhibition and cytotoxicity. Examples of such compounds are rare because the majority of anion transporters can interact with the carboxylate head groups of fatty acids leading to proton leakage. In this paper, we report the synthesis, anion binding and transmembrane anion transport properties of two novel bis-triazole-functionalized calixpyrroles with extended straps, and compare them to previously reported shorter-strap analogues known to exhibit high Cl [Formula: see text] H[Formula: see text] selectivity. We demonstrate improved chloride transport activities of the strap-extended compounds that likely benefit from increased lipophilicity, and reduced Cl [Formula: see text] H[Formula: see text] selectivity due to the larger anion binding cavities facilitating interaction with fatty acids. The results are instructive for future design of ideal anion transporters with potent activity and high selectivity against proton leakage.

Tuning the anion binding properties of lanthanide receptors to discriminate nucleoside phosphates in a sensing array.

The development of synthetic receptors for the selective binding and discrimination of anions in water requires an understanding of how anions interact with these synthetic receptors. Molecules designed to differentiate nucleoside phosphate anions (e.g. ATP, ADP, GTP, GDP, UDP) under physiological conditions could underpin exciting new sensing tools for biomedical research and drug discovery, but it is very challenging due to the similarities in anion structure, size and charge. We present a series of lanthanide-based anion receptors and establish key structural elements that impact on nucleoside phosphate anion binding and sensing. Structural evidence of anion binding using X-ray crystallographic and NMR data, supported by DFT calculations indicate the binding modes between the lanthanide complexes and certain phosphoanions, revealing a bidentate (α-, γ-) binding mode to ATP. We further use four of the receptors to allow discrimination of eight nucleoside phosphate anions in the first array-based assay using lanthanide complexes, taking advantage of the multiple emission bands and long emission lifetimes associated with luminescent lanthanide complexes.

Synthesis of Butadiynyl-Strapped Corona[6]arenes and Their Selective Anion Binding Properties.

A number of butadiynylene-strapped O6-corona[6]arenes were synthesized straightforwardly through intramolecular oxidative homocoupling of O6-corona[6]arenes, which contained at least two N-propargyl-phthalimide segments. The mono-macrocyclic reactants were prepared from the reaction between 3,6-dichlorotetrazine and N-propargyl-3,6-dihydroxyphthalimide and another 1,4-dihydroxybenzene derivative with roughly a 3:2:1.3-1.5 ratio in a one-pot reaction manner. The synthesized butadiynylene-strapped corona[3]arene[3]tetrazines acted as highly selective electron-deficient macrocyclic hosts to form 1:1 complexes with thiocyanate in solution, and the association constant (Ka) was up to 1390 M-1. The anion-π noncovalent interactions provided the driving force for host-guest complexation.

Strategic Stereoselective Halogen (F, Cl) Insertion: A Tool to Enhance Supramolecular Properties in Polyols.

To improve the supramolecular properties of organic compounds, chemists continuously need to identify new tools. Herein, the influence of the stereoselective insertion of halogen atoms (F or Cl) on different supramolecular properties is analyzed. Inserting anti-halohydrins in polyols considerably strengthens the H-bonding networks and other supramolecular interactions. This behavior resulted in improved anion binding, H-bonding catalysis, or organogel properties of the designed polyols with strong perspectives for applications in other classes of substrates.

Anthracene-Based Receptors with a Turn-on Fluorescence Response for Nitrate.

Herein we describe the design, synthesis, and anion binding properties of bicyclic receptors with two or three anthracenes, which show a turn-on fluorescence response in the presence of nitrate and chaotropic anions in a buffered aqueous solution. The receptor with two anthracenes binds nitrate with 103 M-1 affinity and stabilizes it in the inner cavity though electrostatic, hydrogen bonding, and anion-π interactions.

π-Metalated [15]Paracyclophanes: Synthesis and Binding to Oxo-Anions via Anion-π Interactions.

The host-guest properties of [15]paracyclophane ([15]PCPs) are engendered by π-metalation, which exhibits fantastic regioselectivity toward a macrocyclic molecule. The synthesis and characterization of mono-, di-, and trimetalated [15]PCPs are discussed in this article, and the anion binding behavior of 3Ru-[15]PCP-II6+, one of the trimetalated [15]PCPs, driven by anion-π interactions, is comprehensively demonstrated in both solution and the solid state. The anion binding properties of 3Ru-[15]PCP-II6+ in solution are investigated by 1H NMR titrations, showing selectivity toward ReO4- in both organic and aqueous solutions. The binding mode is unexpected; the anionic guest stacks over the host rather than threads it. This selectivity for ReO4- is also supported by water-nitromethane extraction experiments, which demonstrate that its partition from water into the organic phase by 3Ru-[15]PCP-II·6OTf is maintained to some extent in the presence of excess Cl-, SO42-, H2PO4-, NO3-, and ClO4-.

Synthesis and anion binding properties of phthalimide-containing corona[6]arenes.

Functionalized O6-corona[3]arene[3]tetrazines were synthesized efficiently and conveniently by means of a macrocyclic condensation reaction between N-functionalized 3,6-dihydroxyphthalimides and 3,6-dichlorotetrazine under mild conditions in a one-pot reaction manner. The novel macrocycles exist as a mixture of rapidly interconvertible conformers in solution while in the solid state they adopt the conformation in which three phthalimide units are cis,trans-orientated. Acting as electron-deficient macrocyclic hosts, the synthesized O6-corona[3]arene[3]tetrazines self-regulated conformational structures to complex anions in the gas phase and in the solid state owing to the anion–π noncovalent interactions between anions and the tetrazine rings.

Squaramide-substituted calix[4]pyrrole: Synthesis and ion binding studies

Squaramide-substituted calix[4]pyrrole 2 was synthesized and its anion-binding properties were investigated. On the basis of UV spectroscopy, 1H NMR spectroscopic and computational DFT model analyses, compared with the parent calix[4]pyrrole 1, compound 2 shows significantly enhanced binding affinities for anions in CH2Cl2, and it was concluded that this increase in affinity is ascribed to participation of the squaramide unit in anion binding.

Anion-binding properties of π-electron deficient cavity in tetraoxacalix[2]arene[2]triazine by a computational study

Host-guest inclusion complex formation of tetraoxacalix[2]arene[2]triazine (1) with anions X(CH3COO−, ClO4−, BrO4−, IO4−, SO42−, SO32−, CO32−, SiO32−) was studied by DFT calculations at M062X/6-311+G** level, together with their equilibrium geometries, binding energies and electronic structures. MESP, NCI-RDG and AIM topography analysis were performed to explore underlying interactions. The inclusion complexes in 1:1 ratio were stabilized through a cooperative effect of non-covalent interactions, including anion-π, σ-interactions, hydrogen bonds and van der Waals interactions. The recognition process of anions within 1 was spontaneous both thermodynamically and dynamically. The structure of molecule 1 changed slightly after encapsulation, reflected in IR and NMR spectra. After complexation, the red shifts of CH stretching and triazine rings bending in IR were attributed by hydrogen bonds and anion-π interactions. Anions encased in the host cavity exhibited magnetic shielding; those bifurcate hydrogen bonds could cause chemical shifts signals in 1H NMR spectra.

Meso-Bis(ethynyl) Versus meso-Bis(aryl) Calix[4]pyrroles: Dimensionally Well-Modulated Receptors That Can Regulate the Anion Binding Domains.

meso-Substituted calix[4]pyrroles 2-6 containing a direct meso-ethynyl linker displayed high binding affinities and unique conformational features on halide anion binding. A general conformational bias for the equatorial alignments of the meso-(aryl)ethynyl groups was observed in the host-halide complexes which was attributed to the repulsive anion-alkyne interactions and released steric strain. Such conformational features of host-halide complexes persisted even in the case of calix[4]pyrrole 6 bearing cationic meso components, which displayed the highest binding affinity for chloride anions among known meso-aryl calix[4]pyrroles. Synthetic details, conformational features, and comparative halide anion binding properties of this series of calix[4]pyrroles are described.

Tailoring the Binding Properties of Phosphazane Anion Receptors and Transporters.

The binding and sensing of anions is an important cross-disciplinary field, which impacts broad areas such as biology, supramolecular chemistry and catalysis. To date, however, this area has been dominated by organic architectures which function as H-bonding, anion receptor molecules. Inorganic anion receptors have largely been based on Lewis acidic metals, with very few examples of H-bonding counterparts of organic systems having been systematically studied. This paper develops strategies for enhancing the anion binding properties of phosphazanes of the type [(RNH)(E)P(μ-N tBu)]2 (E = O, S, Se) which are bench-stable, H-bond receptors that can be regarded as inorganic analogues of squaramides (a key class of organic anion receptor). The distinct advantages of these inorganic receptors over organic counterparts is the ease by which their functionality and electronic character can be altered (by means of the R group, chalcogenide, or metal present). Se substitution at the P centers, the presence of electron-withdrawing R groups, and metal coordination to the soft donor centers can be used to modulate and enhance anion binding. The water stability and superior anion binding properties of the seleno-phosph(V)azanes give them applications as synthetic anion transporters through phospholipid layers.

A Novel Ferrocene‐Based Calix[4]arene as an Efficient Optical and Electrochemical Sensor for Highly Selective Fluoride Recognition

AbstractA new tetra ferrocene‐triazole‐amide functionalized calix[4]arene as an effective optical and electrochemical anion sensor was successfully synthesized in high yield. The structure of the resulted compound ( 5,11,17,23‐tetra(ferrocenyl‐1H‐triazolo‐acetamido)‐25,26,27,28‐ tetrabutyloxycalix[4]arene, 6) was characterized with NMR spectra and elemental analysis. The anion binding properties of the compound in the presence of different anions were studied by various techniques (UV‐Vis, fluorescence, cyclic voltammetry (CV) and 1H NMR titration), which showed high selectivity and remarkable sensitivity toward fluoride ion (F−). The association constant (Ka) and the limit of detection (LOD) were determined to be 5.35×10+8 M−2 and 2.98×10−6 M, respectively. The results indicate this compound could act as an efficient sensor for fluoride anion in the presence of other common anions.

Investigating the Influence of Steric Hindrance on Selective Anion Transport

A series of symmetrical and unsymmetrical alkyl tren based tris-thiourea anion transporters were synthesised and their anion binding and transport properties studied. Overall, increasing the steric bulk of the substituents resulted in improved chloride binding and transport abilities. Including a macrocycle in the scaffold enhanced the selectivity of chloride transport in the presence of fatty acids, by reducing the undesired H+ flux facilitated by fatty acid flip-flop. This study demonstrates the benefit of including enforced steric hindrance and encapsulation in the design of more selective anion receptors.

Protonation and Anion Binding Properties of Aromatic Bis‐Urea Derivatives—Comprehending the Proton Transfer

AbstractInvited for the cover of this issue is the group of Vladislav Tomišić at the University of Zagreb and colleagues from the Ruđer Bošković Institute of Zagreb. The image depicts a urea derivative as a piece of jewelry, a part of which is being stolen, to represent proton transfer in the presence of basic anions. Read the full text of the article at 10.1002/chem.201805633.

Protonation and Anion Binding Properties of Aromatic Bis-Urea Derivatives-Comprehending the Proton Transfer.

A series of aromatic bis-urea derivatives was prepared and their proton dissociation, as well as anion binding properties in DMSO were investigated. To this end, UV/Vis and 1 H NMR spectroscopies and computational methods were employed. The synthesized molecules differed in the relative position of the urea moieties (ortho- and meta-derivatives) and in the functional groups (-H, -CH3 , -OCH3 , -NO2 ) in the para-position of the pendant phenyl groups. Remarkably high acidities of the compounds (logK1 H ≈14), were ascribed primarily to the stabilizing effect of the aromatic subunits. Quantum chemical calculations corroborated the conclusions drawn from experimental data and provided information from the structural point of view. Knowledge regarding protonation properties proved to be essential for reliable quantitative determination of anion binding affinities. Studied receptors were selective for acetate and dihydrogen phosphate among several anions. Formation of their complexes of 1:1 and 1:2 (ligand/anion) stoichiometries was quantitatively characterized. Proton transfer was taken into account in the course of data analysis, which was especially important in the case of AcO- . ortho-Receptors were proven to be more efficient acetate binders, achieving coordination with all four NH groups. The meta-analogues preferred dihydrogen phosphate, which acted as both hydrogen bond donor and acceptor. Cooperative binding was detected in the case of 1:2 H2 PO4 - complexes, which was assigned to formation of interanionic hydrogen bonds.

BN-Functionalized Benzotrithiophene-Based Azaborines: Synthesis, Structures, and Anion Binding Properties.

Facile synthesis of BN-functionalized azaborines (4a-4c) was accomplished via Suzuki coupling reactions followed by the electrophilic C-H borylation of benzotrithiophene (BTT). The core structure of BTT enables multiple modifications at the three thiophene rings. Molecular structures of 4a-4c were confirmed by NMR, high-resolution mass spectrometry, and X-ray crystallographic analysis. Their electronic properties were also examined through photophysical and electrochemical measurements as well as density functional theory computations. The red-shifted absorption and emission of these molecules were demonstrated upon fluoride titration in response to anion binding, leading to a remarkable decrease of the oxidation potential in the electrochemical differential pulse voltammetry scans. This work may provide a new pathway to robust redox-active materials for catalytic applications.