Anion-π Interactions Research Articles

Light-Induced Activation of C–X Bond via Carbonate-Assisted Anion−π Interactions: Applications to C–P and C–B Bond Formation

We have presented a carbonate anion assisted photochemical protocol for the C-X bond activation. Anion-π interactions have been leveraged to generate aryl radicals from easily accessible aryl halides that are further utilized in C-P and C-B bond formation reactions with excellent reactivity and broad functional group tolerance. Spectroscopic investigations and DFT studies were conducted for mechanistic insights. This inexpensive method alleviates the use of a photocatalyst and the need of preactivation of the substrate for the light-induced activation of C-X bonds.

An anomalous anion transfer order in graphene oxide membranes induced by anion-π interactions.

Selective transport of anions across membranes has become an important goal in chemistry and biology. Here, we found an anomalous anion transfer order within the graphene oxide membrane: Cl- > Br- > F- > I-. This is at odds with the conventional ranking of the transfer order, which usually decreases as the radii of the anions increase, i.e., F- > Cl- > Br- > I-. The abnormal transportation of F- can be ascribed to the strong anion-π interactions between F- and graphene oxide sheets. Such unexpectedly strong anion-π interaction resulted in the lower movement of F- in the graphene oxide membrane and caused the anomalous anion transfer order. Our findings not only provide experimental evidence of anion-π interactions, but also improve our understanding of anion-π interactions in the selective transport of anions across a two-dimensional membrane.

Anion-π interaction inside the polyanionic Mo132O372 cage with hydrophobic inner space.

In this paper, we provide experimental evidence to indicate that the polyanionic Mo132O372 cage with a hydrophobic inner nanospace has a unique capability to participate in anion-π interactions by showing a preference for electron-deficient mono-substituted benzenes over non-electron-deficient guests in inclusion.

Inner and Interfacial Environmental Nanoarchitectonics of Supramolecular Assemblies Formed by Amphiphiles: from Emergence to Application.

The inner and interfacial environments of self-assemblies provide fascinating nano-space for selective and efficient chemical reactions and processes. In biological systems, various chemical reactions, molecular recognition, and transport occur precisely and selectively by virtue of effective molecular interactions on biological membranes and proteins. Considering these advantages and the concept of nanoarchitectonics, we demonstrated that the photochromism of a lophine dimer was accelerated by using confined nano-spaces formed by surfactant micelles. The photoresponsive micelles were used for the rapid controlled release of a model drug upon ultraviolet light irradiation. Furthermore, selective ion recognition inside the self-assembled molecular films at the interfaces was investigated. The anion-π interaction between the anion and an electron-deficient aromatic ring was evaluated on a solid substrate modified with a naphthalenediimide (NDI) analog. Force curve measurements afforded a quantitative analysis of anion-π interactions on the NDI film. The strength of anion-π interactions is regulated by the electric fields on the electrode. An optical probe was developed to visualize the distribution of Cs ions in the soil, plant bodies, and aqueous media using an optode system. Advances in the development of molecular functional systems are expected based not only on molecular structures but also on the spaces and environments produced by them.

Facile synthesis and anion binding studies of fluorescein/benzo-12-crown-4 ether based bis-dipyrromethane (DPM) receptors.

Two novel fluorescein as well as benzo-12-crown-4 ether functionalized dipyrromethane receptors (DPM3 and DPM4) have successfully been synthesized. The anion (used as their TBA salts) binding studies of thus prepared DPM3 and DPM4 receptors were evaluated by the UV-visible spectrophotometric titrations. Binding affinities as well as the stoichiometry were determined through the UV-visible titrations data with the involvement of the BindFit (v0.5) package available online at https://supramolecular.org. Moreover, binding events were validated by means of the comparison of the partial 1H-NMR spectrum of the simple host molecule with that of the host-guest complex, and the 1 : 1 stoichiometry were further confirmed by the Job's method of continuous variation. From the results, we observed the binding constant (Ka) values of DPM3/DPM4 with various tested anions in the range of 516.07 M-1 to 63789.81 M-1, depending upon the nature/shape/size of the anions. Moreover, the anion-π interactions were confirmed by the partial 1H-NMR spectral data, and further supported by the literature reported systems. The authors hope that such types of valued receptors will be benefitted in future for the recognizing/binding of a variety of biologically important anions.

Anion-π catalysis on carbon allotropes.

Anion-π catalysis, introduced in 2013, stands for the stabilization of anionic transition states on π-acidic aromatic surfaces. Anion-π catalysis on carbon allotropes is particularly attractive because high polarizability promises access to really strong anion-π interactions. With these expectations, anion-π catalysis on fullerenes has been introduced in 2017, followed by carbon nanotubes in 2019. Consistent with expectations from theory, anion-π catalysis on carbon allotropes generally increases with polarizability. Realized examples reach from enolate addition chemistry to asymmetric Diels-Alder reactions and autocatalytic ether cyclizations. Currently, anion-π catalysis on carbon allotropes gains momentum because the combination with electric-field-assisted catalysis promises transformative impact on organic synthesis.

Synthesis and Characterization of a Cd(II) complex: Anion interaction and Fabrication of Cadmium oxide nanoparticles

A framework of Cd(II), {[Cd2(toua)(4,4′-bpy)](NO3)2·3H2O}n (1) is constructed using a heteroatom based linker 3,6,9-trioxaundecanedioic acid (H2toua) and a nitrogen based ligand, 4,4′-bipyridine (4,4′-bpy). Compound 1 was characterized by elemental analysis, FTIR and UV-Visible spectroscopy. The thermal stability of 1 was determined using thermogravimetric analysis (TGA). Spectroscopic studies revealed the presence of nitrate as an anion that makes compound 1 suitable for anion interaction study. This study was performed using different sodium salts such as chloride, oxalate, hydroxide, acetate, bromate, sulphate, thiosulfate, carbonate and bicarbonate respectively and it was found that among all these anions, the compound exhibit anion-π interactions selectively with acetate, sulphate, and thiosulfate. Furthermore, CdO nanoparticles with hexagonal morphology was obtained upon direct calcination of compound 1 at 700 °C. These as-synthesized CdO nanoparticles showed selective behavior towards a cationic dye (methylene blue) over an anionic dye (Eosin yellow).

Design and optimization of a novel Y-Fe-GO magnetic adsorbent for simultaneous removal of tetracycline and arsenic and adsorption mechanisms

Composite pollution containing antibiotics and heavy metals is still a challenge for the field of wastewater treatment. In this study, a novel magnetic Y-Fe modified GO adsorbent (YMGO) was designed and prepared for the simultaneous and effective removal of tetracycline (TC) and arsenic with superior separation ability. The adsorbents were optimized by varying the ratios of Y(III):Fe(III):Fe(II), of which the adsorption of both TC and As(V) by YMGO-2 was higher than many other reported adsorbents. The scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results verified that the Y-Fe based particles were successfully and homogenously in-situ generated on GO matrix. More importantly, the presence of TC or As(V) showed significantly adverse effect on the adsorption of As(V) or TC in the composite system, compared with the adsorption in single TC/As(V) system. 2D Fourier transform infrared correlation spectroscopy (2D-FTIR-COS) and XPS analyses indicated that the hydrogen bond (HB), π-π electron-donor–acceptor (EDA), n-π, and cation bonding bridge interactions were involved in the adsorption of TC, while ion-exchange between As(V) and Y/Fe-OH groups played important roles in the uptake of As(V). Notably, in combined system, the interaction of As(V) with Y/Fe cations outperformed the anion-π interaction formed between As(V) and TC, leading to a significant suppression of TC adsorption. Whereas the competition for Y/Fe cations by TC caused a reduction in As(V) adsorption. Furthermore, the YMGO-2 exhibited excellent magnetic separation performance and reusability for both TC and As(V). This study can provide a powerful material for the simultaneous treatment of TC and As(V) containing wastewater and a mechanistic insight into the co-removal of combined pollutants.

High-performance carbon nanotube field-effect transistors with electron mobility of 39.4 cm2V−1s−1 using anion–π interaction doping

Single-walled carbon nanotube (SWNT) is desirable next generation semiconductor for flexible, transparent and even stretchable with exceptional electrical characteristics. Here, high-performance n-type semiconducting SWNT field-effect transistors (s-SWNT-FETs) are achieved by chemical doping using anion-π interaction between SWNT and anion of tetrabutylammonium fluoride (TBAF) salt. The Fermi level (EF) of SWNT shifts to the conduction band edge with increasing dopant concentration. The doped s-SWNT-FETs exhibit significant improvement in electron mobility (39.4 cm2V−1s−1) with high current on/off ratio (>104) compared to those of un-doped device. The doping using anion–π interaction leads to populate electron density of channel and reduces both channel and contact resistance by 99.0% and 99.6%. Excess carriers introduced by the doping compensate traps by shifting the EF toward conduction band edge. The doped device showed improved current stability after 10 h of bias stress test, while the current of undoped FET decreased by 40.4%. Finally, flexible FETs with TBAF doped s-SWNT network are demonstrated on polyethylene naphthalate substrate and show stable operation after 2000 times bending test.

Noncovalent Interactions in Halogenated Pyridinium Salts of the Weakly Coordinating Anion [Al(OTeF5 )4

The synthesis and the first structural characterization of the halogenated pyridinium salts [C5 F5 NH]+ , [C5 F4 ClNH]+ , [(C5 F5 N)2 H]+ , [(C5 Cl5 N)2 H]+ of the weakly coordinating anion (WCA) [Al(OTeF5 )4 ]- , showing noncovalent interactions in the solid state, are presented. The salts were characterized by the multinuclear NMR and IR spectroscopy as well as X-ray diffraction. Hirshfeld surface analysis and solid state structures reveal various intermolecular anion-π and σ-hole interactions between the corresponding halogenated pyridinium cations and the anion [Al(OTeF5 )4 ]- .

Unfurling Anion-π Interactions Involving Graphynes.

Ever since the inception of anion-π interactions, their nature and functional relevance have intrigued researchers. We address the twin challenge of elucidation of the role of extended conjugation and design of all-carbon neutral anion receptors by computations on the anion-π complexes of the halide ions with graphynes. Leveraging on the extended π-conjugation effects, we unfurl the functional relevance of graphynes as anion receptors using descriptors such as electrostatic potential, quadrupole moments, molecular polarizabilities and binding energies. Further, employing natural energy decomposition analysis, we assert that anion-π interactions are not merely dominated by electrostatic interactions. The polarization components do indeed play a crucial role in governing the binding of the anions to the graphynes.

C-6 fluorinated casuarines as highly potent and selective amyloglucosidase inhibitors: Synthesis and structure-activity relationship study

A series of C-6 fluorinated casuarine derivatives have been synthesized via organocatalytic stereoselective α-fluorination of iminosugar-based aldehydes or direct nucleophilic fluorination of polyhydroxylated pyrrolizidines. Glycosidase assays against various glycosidases allowed systematic structure-activity relationship (SAR) study using molecular docking calculations. Introduction of fluorine atom(s) at C-6 position removed the trehalase and maltase inhibitory activities of all casuarine derivatives, and greatly increased their specificity towards amyloglucosidase. Inhibition of the fluorinated casuarines depended on the configuration of C-6 fluorine, of which 6-deoxy-6-epi-6-fluoro-casuarine (24) was found approximately 40-fold potent than its parent compound 6-epi-casuarine (2) as a potent and specific inhibitor of amyloglucosidase. Molecular docking calculations showed that replacement of the C-6 hydroxyls by fluorine atom(s) removed the original interactions with trehalase, but helped to reinforce the binding with amyloglucosidase via newly established fluorine related hydrogen bonding or untypical anion-π interactions. To further investigate the quantitative SARs of casuarine derivatives, the CoMFA and CoMSIA models on amyloglucosidase were established, indicating the dominating effect of electrostatic field in amyloglucosidase inhibition. The 3D-QSAR models were validated to be reliable and can be used for further optimization of casuarine-related iminosugars, as well as design and development of anti-diabetic and immunomodulatory drugs.

A Combined DFT, Energy Decomposition, and Data Analysis Approach to Investigate the Relationship Between Noncovalent Interactions and Selectivity in a Flexible DABCOnium/Chiral Anion Catalyst System.

Developing strategies to study reactivity and selectivity in flexible catalyst systems has become an important topic of research. Herein, we report a combined experimental and computational study aimed at understanding the mechanistic role of an achiral DABCOnium cofactor in a regio- and enantiodivergent bromocyclization reaction. It was found that electron-deficient aryl substituents enable rigidified transition states via an anion-π interaction with the catalyst, which drives the selectivity of the reaction. In contrast, electron-rich aryl groups on the DABCOnium result in significantly more flexible transition states, where interactions between the catalyst and substrate are more important. An analysis of not only the lowest-energy transition state structures but also an ensemble of low-energy transition state conformers via energy decomposition analysis and machine learning was crucial to revealing the dominant noncovalent interactions responsible for observed changes in selectivity in this flexible system.

Halide ion directed templation effect of quadruple-stranded helicates

The allosteric effect, described as biological enzymes’ conformation change to accommodate specific substrates, plays an important role in metabolic regulation. However, well-organized aggregation of synthetic receptors into high-order supramolecular structures with different conformations and functions in response to a variety of external stimuli presents a formidable challenge. Herein, a series of quadruple-stranded helicates are created through the templation effect of halide ions in a library of metallo-macrocycles. Single-crystal X-ray diffraction unambiguously confirms that the four intertwined strands are bridged with halide ions via eight robust C–H···X¯ hydrogen bonds, four anion-π interactions, and two electrostatic contacts. The binding of I¯ results in a D 2 -symmetric helicate, while the Br¯ or Cl¯ adducts display asymmetric infrastructures. Furthermore, the templation effect exhibits non-thermodynamically controlled, high selectivity toward I¯ due to its nucleophilicity toward breaking up partial coordination bonds. • Halide ions create a templation effect, leading to quadruple-stranded helicates • Multiple non-covalent interactions support the quadruple-stranded helicates • The templation effect exhibits unusual nucleophilic selectivity toward halide ions • Over 90% of I¯ ions wereseparated in the presence of other competing halide anions Liu and Jang et al. report halide ion directed (I¯, Br¯, and Cl¯) templation effects, leading from metallo-macrocycles to quadruple-stranded helicates. Multiple non-covalent interactions co-stabilized the assemblies, which is reminiscent of allosteric proteins in nature.

1-Methyl-5-nitro-imidazolium chloride.

The title salt, C4H6N3O2 +·Cl-, exhibits multiple hydrogen-bonding inter-actions involving the nitro-imidazolium cation and the chloride anion. Strong hydrogen bonds between the amine hydrogen atom and the chloride anion link the ionic moieties. Of note, with respect to H⋯Cl inter-actions, the central aromatic hydrogen atom displays a shorter inter-action than the other aromatic hydrogen atom. Finally, inter-actions are observed between the nitro moiety and methyl H atoms. While no π-π stacking is observed, anion-π inter-actions are present. The crystal was refined as a two-component twin.

Inherently Chiral Cages via Hierarchical Desymmetrization.

A new type of cage inherent chirality was accessed by hierarchical desymmetrization of a D3h-symmetric prismlike cage motif. The dissymmetric C3v cage precursor C1 bearing two different phloroglucinol caps was first synthesized. The subsequent progressive substitutions on the three triazine arms by different nucleophiles furnished the desired C1-symmetric inherently chiral cages C3 and C4 with rich structural diversity. Resolution of the racemic cages was achieved by chiral chromatography, and the enantiopure cages were readily obtained on the gram scale. Convenient post-synthetic transformations of the chiral cages with retention of enantiomeric purity were also realized. The absolute configuration was determined by X-ray crystallography, and a chirality descriptor was provided to define the cage chirality. With the inherently chiral array of the electron-deficient triazine surfaces constituting three individual chiral V-shaped π cavities, regio- and enantioselective anion-π binding was probed for the first time with minimum interference of other interactions. As exemplified with chiral phosphate anions (CPAs), it was found that cage (-)-C3a preferably binds (S)-CPA- in the most electron-deficient cavity through synergistic anion-π interactions with considerable chiral selectivity.

Photochemical and Molecular Dynamics Studies of Halide Binding in Flavoenzyme Glucose Oxidase.

Glucose oxidase (GOX), a characteristic flavoprotein oxidase with widespread industrial applications, binds fluoride (F- ) and chloride (Cl- ). We investigated binding properties of halide inhibitors of GOX through time-resolved spectral characterization of flavin-related photochemical processes and molecular dynamic simulations. Cl- and F- bind differently to the protein active site and have substantial but opposite effects on the population and decay of the flavin excited state. Cl- binds closer to the flavin, whose excited-state decays in <100 fs due to anion-π interactions. Such interactions appear absent in F- binding, which, however, significantly increases the active-site rigidity leading to more homogeneous, picosecond fluorescence decay kinetics. These findings are discussed in relation to the mechanism of halide inhibition of GOX by occupying the accommodation site of catalytic intermediates and increasing the active-site rigidity.

Novel Synthesis Methods of New Imidazole-Containing Coordination Compounds Tc(IV, V, VII)-Reaction Mechanism, Xrd and Hirshfeld Surface Analysis.

In this work, we have proposed two new methods for the synthesis of [TcO2L4]+ (where L = imidazole (Im), methylimidazole (MeIm)) complexes using thiourea (Tu) and Sn(II) as the reducing agents. The main and by-products of the reactions were determined, and possible reaction mechanisms were proposed. We have shown that the reduction of Tc(VII) with thiourea is accompanied by the formation of the Tc(III) intermediate and further oxidation to Tc(V). The reaction conditions’ changing can lead to the formation of Tc(VII) and Tc(IV) salts. Seven new crystal structures are described in this work: Tc(V) complexes, salts with Tc(VII) and Tc(IV) anions. For the halide salts of Tu the cell parameters were determined. In all of the obtained compounds, except for [TcO2(MeIm)4]TcO4, there are π–stacking interactions between the aromatic rings. An increase in the anion size lead to weakening of the intermolecular interactions. The halogen bonds and anion-π interactions were also found in the hexahalide-containing compounds. The Hirshfeld surface analysis showed that the main contribution to the crystal packing is created by the van der Waals interactions of the H···H type (42.5–55.1%), H···C/C···H (17.7–21.3%) and hydrogen bonds, which contribute 15.7–25.3% in total.

Synchronous regulation of bulk and interfacial defects by an ionic liquid for efficient and stable perovskite solar cells

Charge recombination at grain-boundary interfaces and charge extraction loss at perovskite-carrier transport layer interfaces are the two main causes for the performance deficiency in perovskite solar cells. Herein we reported the synthesis of an ionic liquid compound 9-bromo-6,7-diphenylpyrido[2,1-a]isoquinolin-5-ium hexafluorophosphate (DPPIQ+PF6−), which can synchronously react with perovskites at these two essential interfaces. Specifically, the PF6− anions are incorporated into the perovskite film bulk, immobilizing organic amine ions via hydrogen bonding, while the DPPIQ+ cations are mainly accumulated at the top film surface, binding the [PbI3]− through anion-π interactions. Reduced defect density and improved energy level alignment are achieved in the resultant perovskite solar cells. The best-performing DPPIQ+PF6− incorporated device shows a high power conversion efficiency of 23.41% and demonstrates 90% efficiency retention upon maximum-power-point tracking for 1260 h under continuous one-sun-intensity illumination.

DFT study of common anions adsorption at graphene surface due to anion-π interaction

Using density functional theory (DFT) calculations, we researched the different anions adsorption on the graphene and found that anions can be stably adsorbed on the graphene surface due to the anion-π interaction. The adsorption energy decreased as the order of HPO42- > SO42- > F- > CH3COO- > ClO3- > NO3- > ClO4- > SCN- > Cl- > Br-. The adsorption energy markedly increased as the valence of anion increased from negative monovalence (< -20kcal/mol) to negative bivalence (> -40kcal/mol). The energy decomposition analysis (EDA) showed that anion-π interaction is mainly induced by orbital effect. This work provides new insights for understanding Hofmeister effect at graphene interface from the molecular level and indicates that the anion-π interaction cannot be ignored at the interface, especially for the substrate with π-electron-rich carbon-based nanomaterials.