Interaction Of Cations Research Articles

Superior Multielectron-Transferring Energy Storage by π-d Conjugated Frameworks.

Reversible multielectron-transfer materials are of considerable interest because of the potential impact to advance present electrochemical energy storage technology by boosting energy density. To date, a few oxide-based materials can reach an electron-transfer number per metal-cation (eM ) larger than 2 upon a (de)intercalation mechanism. However, these materials suffer from degradation due to irreversible rearrangements of the cation-oxygen bonds, and are based on precious metals, for example, Ir and Ru. Hence, a design of the non-oxide-based reversible multielectron-transfer materials with abundant elements can provide a promising alternative. Herein, it is demonstrated that the bis(diimino)copper framework can show eM = 3.5 with cation/anion co-redox mechanism together with a dual-ion mechanism. In this study, the role of the cation-anion interactions is unveiled by using an experiment/theory collaboration applied to a series of the model non-oxide abundant electrode systems based on different metal-nitrogen bonds. These models provide designer multielectron-transfer due to the tunable π-d conjugated electronic structures. It is found that the Cu-nitrogen bonds show a unique reversible rearrangement upon Li-intercalation, and this process responds to acquire a significant reversible multielectron-transfer. This work provides new insights into the affordable multielectron-transfer electrodes and uncovers an alternative strategy to advance the electrochemical energy storage reactions.

Theoretical Insight into the Phosphate-Targeted Silver’s Antibacterial Action: Differentiation between Gram (+) and Gram (−) Bacteria

Although silver is one of the first metals finding broad applications in everyday life, specific key points of the intimate mechanism of its bacteriostatic/bactericidal activity lack explanation. It is widely accepted that the antimicrobial potential of the silver cation depends on the composition and thickness of the bacterial external envelope: the outer membrane in Gram-negative bacteria is more prone to Ag+ attack than the cell wall in Gram-positive bacteria. The major cellular components able to interact strongly with Ag+ (teichoic acids, phospholipids, and lipopolysaccharides) contain mono/diesterified phosphate moieties. By applying a reliable DFT/SMD methodology, we modeled the reactions between the aforementioned constituents in typical Gram-positive and Gram-negative bacteria and hydrated Ag+ species, thus disclosing the factors that govern the process of metal-model ligand complexation. The conducted research indicates thermodynamically possible reactions in all cases but still a greater preference of the Ag+ toward the constituents in Gram-negative bacteria in comparison with their counterparts in Gram-positive bacteria. The observed tendencies shed light on the specific interactions of the silver cation with the modeled phosphate-containing units at the atomic level.

FingeRNAt—A novel tool for high-throughput analysis of nucleic acid-ligand interactions

Computational methods play a pivotal role in drug discovery and are widely applied in virtual screening, structure optimization, and compound activity profiling. Over the last decades, almost all the attention in medicinal chemistry has been directed to protein-ligand binding, and computational tools have been created with this target in mind. With novel discoveries of functional RNAs and their possible applications, RNAs have gained considerable attention as potential drug targets. However, the availability of bioinformatics tools for nucleic acids is limited. Here, we introduce fingeRNAt—a software tool for detecting non-covalent interactions formed in complexes of nucleic acids with ligands. The program detects nine types of interactions: (i) hydrogen and (ii) halogen bonds, (iii) cation-anion, (iv) pi-cation, (v) pi-anion, (vi) pi-stacking, (vii) inorganic ion-mediated, (viii) water-mediated, and (ix) lipophilic interactions. However, the scope of detected interactions can be easily expanded using a simple plugin system. In addition, detected interactions can be visualized using the associated PyMOL plugin, which facilitates the analysis of medium-throughput molecular complexes. Interactions are also encoded and stored as a bioinformatics-friendly Structural Interaction Fingerprint (SIFt)—a binary string where the respective bit in the fingerprint is set to 1 if a particular interaction is present and to 0 otherwise. This output format, in turn, enables high-throughput analysis of interaction data using data analysis techniques. We present applications of fingeRNAt-generated interaction fingerprints for visual and computational analysis of RNA-ligand complexes, including analysis of interactions formed in experimentally determined RNA-small molecule ligand complexes deposited in the Protein Data Bank. We propose interaction fingerprint-based similarity as an alternative measure to RMSD to recapitulate complexes with similar interactions but different folding. We present an application of interaction fingerprints for the clustering of molecular complexes. This approach can be used to group ligands that form similar binding networks and thus have similar biological properties. The fingeRNAt software is freely available at https://github.com/n-szulc/fingeRNAt.

Comparison between Ab Initio Molecular Dynamics and OPLS-Based Force Fields for Ionic Liquid Solvent Organization.

OPLS-based force fields (FFs) have been shown to provide accurate bulk-phase properties for a wide variety of imidazolium-based ionic liquids (ILs). However, the ability of OPLS to reproduce an IL solvent structure is not as well-validated given the relative lack of high-level theoretical or experimental data available for comparison. In this study, ab initio molecular dynamics (AIMD) simulations were performed for three widely used ILs: the 1-butyl-3-methylimidazolium cation with chloride, tetrafluoroborate, or hexafluorophosphate anions, that is, [BMIM][Cl], [BMIM][BF4], and [BMIM][PF6], respectively, as a basis for further assessment of two unique IL FFs: the ±0.8 charge-scaled OPLS-2009IL FF and the OPLS-VSIL FF. The OPLS-2009IL FF employs a traditional all-atom functional form, whereas the OPLS-VSIL FF was developed using a virtual site that offloads negative charge to inside the plane of the ring with careful attention given to reproducing hydrogen bonding. Detailed comparisons between AIMD and the OPLS FFs were made based on radial distribution functions (RDFs), combined distribution functions (CDFs), and spatial distribution functions (SDFs) to examine cation-anion interactions and π+-π+ stacking between the imidazolium rings. While both FFs were able to correctly capture the general solvent structure of these popular ILs, the OPLS-VSIL FF quantitatively reproduced interaction distances more accurately. In addition, this work provides further insights into the different short- and long-range structure patterns of these popular ILs.

Mediating anion-cation interactions to improve aqueous flow battery electrolytes

The limited solubility of electrolyte active materials has impeded the development of energy dense aqueous redox flow batteries. Here, we report on the solubilizing effect urea has on metal-organic complexes chelated by aminopolycarboxylate ligands. Upon addition of urea, solubility enhancements of up to 60% or 125% are observed for chromium ethylenediaminetetraacetate (CrEDTA) and chromium 1,3-propylenediaminetetraacetate (CrPDTA) salts, respectively, resulting in maximum solubilities of e.g., 1.5 м for KCrPDTA and 2.2 м for NaCrEDTA. We investigate the mechanism behind enhanced solubility of aminopolycarboxylate chelates, revealing strong hydrogen bonding between urea and anions, resulting in eutectic-like destabilization of the solid phase. We study the impact of urea on the electrochemical performance of near neutral pH flow batteries and demonstrate 50% higher anolyte capacities, up to 40 Ah L−1, than previously reported for this promising class of materials. In capacity balanced full cells, using ferrocyanide catholytes, we observe excellent Coulombic efficiencies >99.6% and voltage efficiencies >78% at average discharge voltages of ca. 1.5 V when cycling at 100 mA cm−2. Peak discharge power densities of >400 mW cm−2 further highlight the potential of our facile and cost-effective approach. Finally, we discuss avenues for future work to further exploit the solubilizing effect described herein.

Calculation of the spin-lattice relaxation time and the activation energy near the IV–III phase transition in pyridinium fluorosulfonate (C5NH6)FSO3

The spin-lattice relaxation time T1 H for protons nuclei is calculated in term of the pseudospin–phonon (PS) coupled and the energy fluctuation (EF) models close to the IV–III solid–solid phase transition of in (C5NH6)FSO3. This calculation was performed by associating the observed second moment of the 1H as the order parameter below T C and the disorder parameter above T C. Values of the activation energy for the cation reorientation in this crystal are also deduced by using both models. In addition, the observed dielectric permittivity of this crystal is analyzed within the framework of the Landau theory and values of the spontaneous polarization (P S) are determined as a function of temperature. The normalized values of P S are used in the PS and EF models to extract the activation energy for the reorientation of the dipole moment of this compound arising from cation–anion interaction. Our results show that the PS and EF models can describe the observed behavior of the spin-lattice relaxation time adequately for the IV–III solid–solid transition in (C5NH6)FSO3.

Synthesis, characterization, and in vitro antibacterial activity of some new pyridinone and pyrazole derivatives with some in silico ADME and molecular modeling study

A new series of pyridine-2-one and pyrazole derivatives were designed and synthesized based on cyanoacrylamide derivatives containing 2,4-dichlro aniline and 6-methyl 2-amino pyridine as an aryl group. Condensation of cyanoacrylamide derivatives 3a–d with different active methylene (malononitrile, ethyl cyanoacetate cyanoacetamide, and ethyl acetoacetate) in the presence of piperidine as basic catalyst afforded the corresponding pyridinone derivatives 4a–c, 5, 9, and 13. Furthermore, the reaction of cyanoacrylamide derivatives 3a–d with bi-nucleophile as hydrazine hydrate and thiosemicarbazide afforded the corresponding pyrazole derivatives 14a,b and 16. The newly designed derivatives were confirmed and established based on the elemental analysis and spectra data (IR, 1H NMR, 13C NMR, and mass). The in vitro antibacterial activity was evaluated against four bacterial strains with weak to good antibacterial activity. Moreover, the results indicated that the most active derivatives 3a, 4a, 4b, 9, and 16 might lead to antibacterial agents, especially against B. subtilis and P. vulgaris. The DFT calculations were performed to estimate its geometric structure and electronic properties. In addition, the most active pyridinone and pyrazole derivatives were further evaluated for in silico physicochemical, drug-likeness, and toxicity prediction. These derivatives obeyed all Lipinski’s and Veber’s rules without any violation and displayed non-immunotoxin, non-mutagenic, and non-cytotoxic. Molecular docking simulation was performed inside the active site of Topoisomerase IV (PDB:3FV5). It displayed binding energy ranging from -14.97 kcal/mol to -18.86 kcal/mol with hydrogen bonding and arene–cation interaction. Therefore, these derivatives were suggested to be good antibacterial agents via topoisomerase IV inhibitor.Graphical abstract

Concerted Rolling and Penetration of Peptides during Membrane Binding.

Peptide binding to membranes is common and fundamental in biochemistry and biophysics and critical for applications ranging from drug delivery to the treatment of bacterial infections. However, it is largely unclear, from a theoretical point of view, what peptides of different sequences and structures share in the membrane-binding and insertion process. In this work, we analyze three prototypical membrane-binding peptides (α-helical magainin, PGLa, and β-hairpin tachyplesin) during membrane binding, using molecular details provided by Markov state modeling and microsecond-long molecular dynamics simulations. By leveraging both geometric and data-driven collective variables that capture the essential physics of the amphiphilic and cationic peptide-membrane interactions, we reveal how the slowest kinetic process of membrane binding is the dynamic rolling of the peptide from an attached to a fully bound state. These results not only add fundamental knowledge of the theory of how peptides bind to biological membranes but also open new avenues to study general peptides in more complex environments for further applications.

A Single-Molecule Insight into the Ionic Strength-dependent, Cationic Peptide Nucleic Acids-Oligonucleotides Interactions.

To alleviate solubility-related shortcomings associated with the use of neutral peptide nucleic acids (PNA), a powerful strategy is incorporate various charged sidechains onto the PNA structure. Here we employ a single-molecule technique and prove that the ionic current blockade signature of free poly(Arg)-PNAs and their corresponding duplexes with target ssDNAs interacting with a single α-hemolysin (α-HL) nanopore is highly ionic strength dependent, with high salt-containing electrolytes facilitating both capture and isolation of such complexes. Our data illustrate the effect of low ionic strength in reducing the effective volume of free poly(Arg)-PNAs and augmentation of their electrophoretic mobility while traversing the nanopore. We found that unlike in high salt electrolytes, the specific hybridization of cationic moiety-containing PNAs with complementary negatively charged ssDNAs in a salt concentration as low as 0.5 M is dramatically impeded. We suggest a scenario in which reduced charge screening by counterions in low salt electrolytes enables non-specific, electrostatic interactions with the anionic backbone of polynucleotides, thus reducing the ability of PNA-DNA complementary association via hydrogen bonding patterns. We applied an experimental strategy with spatially-separated poly(Arg)-PNAs and ssDNAs, and present evidence at the single-molecule level suggestive of the real-time, long-range interactions-driven formation of poly(Arg)-PNA-DNA complexes, as individual strands entering the nanopore from opposite directions collide inside a nanocavity.

A transferable force-field for alkali metal nitrates

We present a new rigid-ion force-field for the alkali metal nitrates that is suitable for simulating solution chemistry, crystallisation and polymorphism. We show that it gives a good representation of the crystal structures, lattice energies, elastic and dielectric properties of these compounds over a wide range of temperatures. Since all the alkali metal nitrates are fitted together using a common model for the nitrate anion, the force-field is also suitable for simulating solid solutions. We use the popular Joung and Cheatham model for the interactions of the alkali metal cations with water and obtain the interaction of the nitrate ion with water by fitting to a hydrate.

Molecular Dynamics Simulation of Privileged Biflavonoids as SARS-CoV2 3CLpro Targeting Agents

According to the limited medications for COVID-19, natural products gained increasing attention. Scientific indications revealed the effect of biflavonoids (BFs) against respiratory syndrome viruses. The functional importance of 3-chymotrypsin-like protease (3CLpro) in forming viral RNA raises its potential to be targeted in SARS-CoV2. This study is devoted to the computational analysis of privileged BFs within the SARS-CoV2 3CLpro active site. Docking and molecular dynamics (MD) simulations were collectively used to explore the most probable binding modes and stable ligand–enzyme chemical interactions. Despite the structural resemblance, a wide range of binding affinities was retrieved for BFs ([Formula: see text][Formula: see text]kcal/mol). Garciniaflavone C ([Formula: see text][Formula: see text]kcal/mol), 7,7[Formula: see text], 4[Formula: see text]-tri-O-methylagathisflavone ([Formula: see text][Formula: see text]kcal/mol) and 8,8[Formula: see text]-biapigenil ([Formula: see text][Formula: see text]kcal/mol) were top enzyme binders. The stability of acquired complexes was analyzed through 50-ns all-atom MD simulations. Garciniaflavone C, 7,7[Formula: see text], 4[Formula: see text]-tri-O-methylagathisflavone and 8,8[Formula: see text]-biapigenil showed 29%, 22% and 23% persevered binding residues, respectively. SARS-CoV2-garciniaflavone C complex was mediated by several nonpolar interactions. MD simulations assigned H-bond interaction between the catalytic dyad residue Cys145 and garciniaflavone C. 7,7[Formula: see text], 4[Formula: see text]-tri-O-methylagathisflavone participated in a [Formula: see text]-cation interaction to His41. Solvent accessible surface area distribution indicated the sufficiency of MD simulation time (50[Formula: see text]ns) to screen equilibrated complex systems. Although a detailed pharmacological mechanism is to be elucidated, our findings indicated superior binding stability of 7,7[Formula: see text], 4[Formula: see text]-tri-O-methylagathisflavone within SARS-CoV2 active site. While the biological function of the majority of BF derivatives remains to be elucidated, results of the current study revealed key structural features and potentials of privileged BFs for further structure-guided optimization toward potent SARS-CoV2 3CLpro inhibitors.

Studies of radial distribution function and second virial coefficient for surfactant decyltrimethylammonium bromide in aqueous solutions at 298.15 K: Evidence for cation–cation hydrophobic interactions effect

Excess internal pressure of solution and excess partial molar volume of solute data embedded in the parameter reversible isothermal work (W) have been used to calculate the ion–ion pair correlation functions (gij(r), r being distance) and the thermodynamic properties of aqueous solutions of decyltrimethylammonium bromide (C10TAB) in concentration range 0.01 – 0.14 mol∙kg–1. It is observed that gij(r) exhibits a peak at critical micelle concentration (cmc), while the virial coefficient term (gij(r) – 1) also goes through a maximum. Using Friedman's methodology and McMillan–Mayer theory of solutions, these results have been examined. With the help of concept of Gurney cosphere around the ions, the overlap of solvation shells (water molecules) as the concentration of ions increases have been used to probe water– structure effects as water–structure making/breaking. Coefficients Aij are estimated (Coulombic term, a core repulsive term, a cavity formation term and overlap of cosphere term) at various concentrations of ionic surfactant and at a radial distance of 20 Å for a micellar entity. Further analysis indicates that gij parameter (that is, representing cation–cation interaction g++) dominate over g+– (representing ion–solvent interaction) in solution phase. Thus for a self–assembly process (formation of micelle with aggregation number) in a solution phase is being characterized by a peak in gij(r) function at cmc and aggregation number of ≈ 38, area under the peak, while the virial coefficient variation indicates a dominance of cation–cation interaction and cosphere water–structural effects. It is emphasized that the approach adopted by us to use excess PV work to estimate gij(r) is better to understand the thermodynamic process involved in self–assemblies and micelle formation.

Review of Molecular Dynamics Simulations of Phosphonium Ionic Liquid Lubricants

Phosphonium ionic liquids (ILs) have various uses, including as environmentally benign lubricants and lubricant additives. The properties and behavior of these ILs depend on their chemical composition, i.e., cation and anion combination, and the operating conditions. One approach to understanding the relationships between composition, conditions, and lubricant-relevant properties is classical molecular dynamics simulation. Although this research area is still emerging, it is growing rapidly, so a review of the topic is timely. Here, we review force field-based molecular dynamics simulations of phosphonium ILs, with emphasis on physical, chemical, and thermal properties relevant to lubricants. Properties reported in previous studies are density, viscosity, self-diffusivity, ionic conductivity, heat capacity, and thermal stability, as well as interactions with other compounds, including \(\mathrm {H_2O}\) and \(\mathrm {CO_2}\), and solid surfaces. The effects of anion and cation, as well as conditions such as temperature, on these properties are identified and analyzed in terms of anion-cation structure, orientation, and interactions. Finally, trends are summarized and opportunities for future research are identified.Graphical Abstract

Principles of Cation-π Interactions for Engineering Mussel-Inspired Functional Materials.

Supramolecular assembly is commonly driven by noncovalent interactions (e.g., hydrogen bonding, electrostatic, hydrophobic, and aromatic interactions) and plays a predominant role in multidisciplinary research areas ranging from materials design to molecular biology. Understanding these noncovalent interactions at the molecular level is important for studying and designing supramolecular assemblies in chemical and biological systems. Cation-π interactions, initially found through their influence on protein structure, are generally formed between electron-rich π systems and cations (mainly alkali, alkaline-earth metals, and ammonium). Cation-π interactions play an essential role in many biological systems and processes, such as potassium channels, nicotinic acetylcholine receptors, biomolecular recognition and assembly, and the stabilization and function of biomacromolecular structures. Early fundamental studies on cation-π interactions primarily focused on computational calculations, protein crystal structures, and gas- and solid-phase experiments. With the more recent development of spectroscopic and nanomechanical techniques, cation-π interactions can be characterized directly in aqueous media, offering opportunities for the rational manipulation and incorporation of cation-π interactions into the design of supramolecular assemblies. In 2012, we reported the essential role of cation-π interactions in the strong underwater adhesion of Asian green mussel foot proteins deficient in l-3,4-dihydroxyphenylalanine (DOPA) via direct molecular force measurements. In another study in 2013, we reported the experimental quantification and nanomechanics of cation-π interactions of various cations and π electron systems in aqueous solutions using a surface forces apparatus (SFA).Over the past decade, much progress has been achieved in probing cation-π interactions in aqueous solutions, their impact on the underwater adhesion and cohesion of different soft materials, and the fabrication of functional materials driven by cation-π interactions, including surface coatings, complex coacervates, and hydrogels. These studies have demonstrated cation-π interactions as an important driving force for engineering functional materials. Nevertheless, compared to other noncovalent interactions, cation-π interactions are relatively less investigated and underappreciated in governing the structure and function of supramolecular assemblies. Therefore, it is imperative to provide a detailed overview of recent advances in understanding of cation-π interactions for supramolecular assembly, and how these interactions can be used to direct supramolecular assembly for various applications (e.g., underwater adhesion). In this Account, we present very recent advances in probing and applying cation-π interactions for mussel-inspired supramolecular assemblies as well as their structural and functional characteristics. Particular attention is paid to experimental characterization techniques for quantifying cation-π interactions in aqueous solutions. Moreover, the parameters responsible for modulating the strengths of cation-π interactions are discussed. This Account provides useful insights into the design and engineering of smart materials based on cation-π interactions.

Investigation of the interionic interactions and spectroscopic features of 1-Octyl-3-methylimidazolium chloride, tetrafluoroborate, and hexafluorophosphate ionic liquids: An experimental survey and DFT modeling

This study presents the spectroscopic and electronic properties of some imidazole-based ionic liquids (ILs) consisting of 1-Octyl-3-methylimidazolium cation and chloride, tetrafluoroborate, and hexafluorophosphate anions from experimental and theoretical perspectives. The ground state structural and vibrational characteristics of the ionic liquids have been achieved through Density Functional Theory (DFT) calculations at the Becke's and the Lee–Yang–Parr (B3LYP) and 6–311++G(d,p) level of theory in Gaussian 16. The electronic and magnetic features of the ILs have been examined by using electronic absorption spectra and Nuclear Magnetic Resonance spectroscopy (NMR) techniques along with the calculations from Time-Dependent Density Functional Theory (TD-DFT) and using Gauge-Including Atomic Orbital (GIAO) method.The intra- and interionic noncovalent interactions in the ionic liquids have been revealed via the electron density analysis based on the Atoms in Molecules (AIM) approach, and decomposed as hydrogen bonding, van der Waals interactions, and steric effects via Reduced Density Gradient (RDG) analysis. To gain insight into the possible effects of anion-cation interaction on the physicochemical properties of ionic liquids, interionic interactions, reactivity properties, topological critical points, and electrostatic potential surfaces were obtained. These interactional characteristics were interpreted in terms of both the anion dependency and interaction type. Notably, the results of this study were evaluated together with the results obtained from our previous study on ILs consisting of the same anions with the 1-Hexyl-3-methylimidazolium cation to achieve the effects of the extension in the chain length of the cation in the presence of the same anion on the spectroscopic and electronic properties of ionic liquids.

A density functional theory study on the water aggregation behaviour of fatty acid-based anionic surface active ionic liquids

The hydrogen bond interactions between methyl-imidazolium cation (MIM+) and fatty acid anions (CmHnCOO–, where m = 1–6; n-3–13) of ionic liquids are studied in both gas phase and water phase using density functional theory. The structural properties show that the presence of N–H···O and C–H···O hydrogen bonds between [MIM]+ and [CmHnCOO]– (m = 1–6; n-3–13) ionic liquids. From the vibrational frequency analysis, it was found that the hydrogen bond interaction between [MIM]+ and [CmHnCOO]– (m = 1–6; n-3–13) ionic liquids are red-shifted in frequency. The natural bond orbital analysis show that the N–H···O hydrogen bond associated with the large charge transfer which has the higher stabilization energy (i.e. E(2) ~ 38 kcal/mol). Further, the cation/anion–water cluster (H2O)1–3 interactions show that the water molecules are preferred to interact with anions. In the case of ionic liquid–water cluster interaction, the water molecules occupies the interstitial space between cation and anion of ionic liquids which results in weakening the cation–anion interaction.

Implications of coordination chemistry to cationic interactions in honeycomb layered nickel tellurates

Honeycomb layered tellurates represent a burgeoning class of multi-functional materials with fascinating crystal-structural versatility and a rich composition space. Despite their multifold capabilities, their compositional diversity remains underexplored due to complexities in experimental design and syntheses. Thus, in a bid to expand this frontier and derive relevant insights into allowed metastable compositions, we employ a density functional theory (DFT) approach to predict in silico the crystal structures of new honeycomb layered tellurates embodied by the composition, A2Ni2TeO6 (A = alkali, hydrogen or coinage-metal cations). Here, alkali-metal atoms with vastly larger radii than K (for instance, Rb and Cs) are found to engender a prismatic coordination with the oxygen atoms from the honeycomb slabs whilst coinage-metal atoms (such as Ag, Au and Cu) display a propensity for linear coordination. Further, H2Ni2TeO6 is found to also render a linear coordination wherein the hydrogen atom preferentially establishes a stronger coordination with one of the oxygen atoms to form hydroxyl groups. All A cations in the studied A2Ni2TeO6 compositions form a honeycomb lattice. Conclusions on the possibility of a monolayer-bilayer phase transition in coinage metal atom tellurates can be drawn by considering the implications of conformal symmetry of the cation honeycomb lattice and metallophilicity. This work not only propounds new honeycomb layered tellurate compositions but also provides novel insight into the rational design of multifunctional materials for applications ranging from energy storage, catalysis and optics to analogue condensed matter systems of gravity.

Hydrogen-bonding and symmetry breaking in the protic ionic liquid 1-ethylimidazolium nitrate

The strong cation-anion interaction in the protic ionic liquid 1-ethylimidazolium nitrate, [C2im][NO3], is revealed in different regions of the infrared spectrum (IR). The IR band related to the anion asymmetric stretching mode νas(NO3) splits due to degeneracy lifting, the symmetry forbidden symmetric stretching mode νs(NO3) acquires significant IR activity, and the cation ν(NH) stretching mode produces a broad band characteristic of strong hydrogen bond (H-bond). At high temperatures (up to 120 °C), these spectral features remain in the IR spectrum, indicating the strong cation-anion interaction. The size of the νas(NO3) splitting, the relative strength of νs(NO3), and the intermolecular H-bond stretching mode ν(NH…O) seen in the far-IR range are all accounted for in a quantum chemistry calculation of an ionic pair. The complex spectral pattern in the high-frequency range of the IR spectrum, where NH and CH stretching modes occur in overlapping bands, can be explained using a simple model coupling the ν(N–H) and ν(NH…O) modes. The parameters of the model, including the dependence of the ν(NH) frequency on the N…O distance of the H-bond, are also derived from the ionic pair calculation. The IR spectrum thus gives experimental evidence that using an ionic pair to explore the H-bond influence on the electronic structure of [C2im][NO3] is reasonable.

The role of hydrogen‐bond in solubilizing drugs by ionic liquids: A molecular dynamics and density functional theory study

AbstractThe solvation mechanisms of aspirin and etomidate in four combinations of [Emim]+ and [BuGun]+ paired with [OAc]− and [NTf2]− were systematically studied by molecular dynamics simulations and DFT calculations. It was shown that the favorable solvation of aspirin and etomidate correlated well with hydrogen‐bond (H‐bond) basicity of anions and the H‐bond acidity of cations, respectively. Wherein, the H‐bond between aspirin and [OAc]− anion with high H‐bond basicity possessed covalent feature, so ILs containing [OAc]− anion has the best effective in solubilizing aspirin. However, H‐bond interactions between etomidate and cations exhibited an electrostatic dominant, and moderate cation–anion interaction could weaken it. Accordingly, for etomidate, the best ILs solvent comprised a weakly interacting anion and a cation with strong H‐bond acidity, that is, [BuGun][NTf2]. This solvation difference was because aspirin with carboxyl group displayed strongly H‐bond donating characteristic, whereas etomidate with no active hydrogen protons mainly formed H‐bond with cations. Additionally, we found that π–π stacking interactions were of secondary importance for the solubilization of etomidate, but little for aspirin. These simulations will be helpful for experimental design new ILs to solubilize some drugs with aspirin‐like or etomidate‐like structures.

Synthesis, NMR, vibrational spectroscopy, thermal and DFT studies of new DABCO hexafluorophosphate based ionic liquid

In this paper, a new ionic liquid; [C8DABCO+][PF6−] was prepared, its structure was well confirmed by 1H, 13C, 19F and 31P–NMR spectroscopies. Besides, thermal behaviour has been discussed through TGA and DTA in the temperature range from [-80 to 200 °C] and [25 to 700 °C] respectively. Theoretical studies were performed by DFT method to investigate the structural, electronic and topological properties. B3LYP/6–31G* calculations support the high solvation energy value of IL in aqueous solution (ΔGc= -122.9 kJ/mol) and it probably explain the high dipole moment value, the volume expansion in this medium (7.3 Å3) and also because the cation-anion interactions still remain in solution. Seven interactions were predicted by AIM calculations but only two cation-anion interactions have short distances. NBO studies reveal that IL is more stable in solution probably due to its higher solvation energy. The DOS spectrum in aqueous solution shows clearly that the orbitals belonging to the atoms of cage-like DABCO structure participle in both HOMO and LUMO and, hence, will confirm that DABCO is engaged in halogen interactions, as suggested from NBO analyses. These studies show that DABCO structure participates in the properties of [C8DABCO+][PF6−]. Complete assignments of IR and Raman spectra were reported.