Chloride Ion Pair Research Articles

Structure and interactions of CO2 with reline (a 1:2 choline chloride – Urea mixture) according to quantum chemical calculations and molecular dynamics simulation

Quantum chemical DFT calculations [B3LYP+GD3/6-311++g(2d,2p)] of the structure and interactions in various complexes of CO2 molecule with a choline cation, a chloride anion, urea molecules, a choline chloride ion pair and a 1:2 choline chloride – urea complex were carried out. The contributions of Coulomb and van der Waals interactions were calculated. The QTAIM method was used to evaluate the strength of various bonds. A molecular dynamics simulation of CO2 molecules in reline in the NPT ensemble (1 atm, 298 K) was also carried out. The radial distribution functions of the particle centers of mass, local mole fraction functions, spatial distribution functions, and density profiles were calculated. Stronger interactions, compared to the other DES components, were observed in case of the chloride anion and the CO2 molecule according to the DFT calculations. However, in the system, stronger interactions were observed between the chloride anion and the system components, namely NHCl and OHCl hydrogen bonds. This made the chloride anion inaccessible and unable to interact with the CO2 molecule, according to the MD simulation results. Additionally, the presence of a fairly extensive surface layer containing DES and CO2 molecules was shown.

Ionic Pairing and Selective Solvation of Butylmethylimidazolium Chloride Ion Pairs in DMSO-Water Mixtures: A Comprehensive Examination via Molecular Dynamics Simulations and Potentials of Mean Force Analysis.

Ionic liquids (ILs) with dimethyl sulfoxide (DMSO) and water act as a promising solvent medium for the dissolution of cellulose in an efficient manner. To develop a proper solvent system, it is really important to understand the thermodynamics of the molecular solutions consisting of ILs, DMSO, and water. The ion-pairing propensity of the ILs in the presence of DMSO and water plays a crucial role in governing the property of the solvent mixtures. Employing all-atom molecular dynamics simulations, we estimate the potentials of mean force between BMIM+ and Cl- ions in DMSO-water mixtures. Analysis reveals a significant increase in the thermodynamic stability of both contact ion pair (CIP) and solvent-assisted ion pair (SAIP) states with a rising DMSO mole fraction. Thermodynamic assessments highlight the entropic stabilization of CIP states and SAIP states in pure water, in DMSO-water mixtures, and in pure DMSO. The structural analysis reveals that in comparison to the DMSO local density, the local water density is relatively very high around ion pairs, more specifically in the solvation shell of a chloride ion. Preferential binding coefficients also consistently indicate exclusion of DMSO from the ion pair in DMSO-water mixtures. To enhance our understanding regarding the solvent molecules kinetics around the ion pairs, the survival probabilities of DMSO and water are computed. The calculations reveal that the water molecules prefer a prolonged stay in the solvation shell of Cl- ions.

Competitive ion-exchange reactions of Pb(II) (Pb2+/PbCl+) and Ra(II) (Ra2+) on smectites: Experiments, modeling, and implication for 226Ra(II)/210Pb(II) disequilibrium in the environment.

In this study, new experimental data for the adsorption of lead onto a swelling clay mineral with a tetrahedral charge (beidellite) at the ultratrace level (<10−10 M) are presented. The data were interpreted using an ion-exchange multisite model that considers the sorption of major cations (including H+), which always compete with trace elements for sorption onto mineral surfaces in natural environments. The ability of the proposed model to predict experimental Kd values under various conditions of ionic strength (fixed by NaCl solutions) and aqueous cation compositions (including Pb2+ and PbCl+) was tested. The proposed model was applied to experimental data previously published for other types of swelling clay minerals, and the results were compared with the results obtained using previously published models. The preferential adsorption of chloride ion pairs, as well as the effect of the swelling clay crystal chemistry on lead adsorption, were assessed. Finally, the selective adsorption behavior of 226Ra compared to 210Pb was demonstrated, which has implications for the study of many environmental processes using isotope partitioning.

Investigation of ion pairs in electrochemical ferrocene methanol –Ferrocenium methanol system in presence of supporting electrolyte

Density functional theory (DFT) has been applied to consider ion pair formation in ferrocenium methanol and ferrocene methanol aqueous solutions in the presence of a supporting electrolyte. Based on DFT calculation, the free energy of all species is calculated to evaluation the equilibrium constant. Henry constant of electrochemical ion pair species has been calculated based on transfer Gibbs free energy and combination free energy. DFT calculation in water solvent has been extended to calculate electrode potential as a function of supporting electrolyte. Polarizable continuum model (PCM) is applied for calculating HOMO and LUMO orbitals for ferrocenium methanol - chloride ion pair. DFT-PCM calculation has been done to get chemical structure of ion pair and all electrochemical species. DFT-PCM calculation shows that ion pair reaction between ferrocenium methanol and Cl− ion is an exothermic process. Theoretical DFT calculation results regarding chemical bond length and standard electrical potential of ferrocenium methanol to ferrocene methanol versus standard hydrogen electrode are agreement to the experimental result.

Intriguing Chloride: Involvement of Chloride Ions in Proton Transfers.

The proton transfer from carbon to a chloride ion and the proton transfer to a molecule of water promoted by chloride ions in the acid-catalyzed formation of hydroxamic acids from aldehydes and substituted nitrosobenzenes in mixed solvents have been proposed based on experimental and theoretical investigations. The formation of uncommon contact ion pairs consisting of the nitrosocarbinolic cation intermediate and a chloride anion, followed by the proton transfer from a C-H moiety of the cation intermediate, has been proposed. The influence of chloride on the proton transfer to a water molecule of the solvent-separated nitrosocarbinolic-cation–chloride ion pair was investigated too. The insights are based on the obtained kinetic and other evidence with regard to (1) influences of chloride anions on the observed reaction rates and primary kinetic isotope effects (PKIE) in the reaction; (2) the observed variation of the PKIE-s and rates of the reaction when perchlorate anions are present along with the chloride ions; and (3) the consideration of a model of the nitrosocarbinolic-cation-intermediate—chloride ion pair and transition structure for the proposed proton transfers based on the ab initio calculations.

Aminophosphine-Based InP Quantum Dots for the Detection of Zn2+ and Cd2+ Ions in Water

Water is considered a pivotal molecule for colloidal III–V indium phosphide (InP) quantum dots (QDs) and significantly affects the QD crystal growth and photoluminescence (PL) stability. Herein, we demonstrate a positive aspect of water for aminophosphine-based InP QDs, that is an enhanced PL quantum yield (QY) of ∼50 times and red-shifted optical absorption (∼15 nm) after a water post-treatment of InP QDs occurring in seconds at room temperature. The phenomenon is caused by water-activated ligand exchange between the oleylammonium chloride ion pair ([OAmH+]–Cl–, X-type bound ion pair ligand) and oleylamine (OAm, L-type ligand), followed by QD surface passivation by existing Zn2+ metal ions. A similar phenomenon is also observed for intentionally added Cd2+, which increases PLQY ∼15 times together with 55 nm red-shift in the optical absorption. Taking advantage of the rapid PL response and feasible preparation process, an InP QD fluorescent probe has been demonstrated for selectively detecting Zn2+ or Cd2+ in water. The water-activated surface phenomenon for aminophosphine-based InP QDs may provide insight into the QD surface dynamics and environmental sensing applications.

The study of structure and interactions of glucose-based natural deep eutectic solvents by molecular dynamics simulation

In the current study, molecular dynamics simulations were conducted to investigate the structural and dynamical properties of glucose-based Deep Eutectic Solvents (DESs) at different molar ratios (the mixture of glucose and choline chloride with the molar ratios of 1:3, 1:1 and 3:1). Accordingly, the interaction energies of different species and structural properties such as atom–atom radial distribution functions (RDFs), the hydrogen-bonding network between species, and spatial distribution functions (SDFs) were computed to understand effective interactions in the eutectic mixture formation. It was found that the insertion of glucose molecules reduced the accumulation of chloride anions around choline cations, eventually decreasing the interaction between the choline chloride ion pairs. Moreover, the possible explanations for the thermos-physical properties of DESs, such as the shear viscosity and density, have been provided. Dynamical properties of DES were evaluated by calculating the mean-square displacement (MSD) and the velocity autocorrelation function (VACF) for the centers of the mass of the ions and glucose molecules. MSD analysis results were then used to calculate the self-diffusion parameter by applying the Einstein relation. The simulation results indicated that increasing the temperature led to easing the migration of the molecules and decreasing the dependence of the movement of the molecules on each other. This growing trend of migration may lead to an increase in the self-diffusion coefficient of molecules. Structural analysis revealed that a ratio of 1:1 of glucose: choline chloride could provide the best condition to maintain the low melting point of the mixture due to the strong hydrogen-bonded network between the two species.

Developing a potentiometric sunset yellow selective electrode and its applications

We developed a potentiometric ion-selective electrode (ISE) for detecting the food dye sunset yellow (SY). Sunset yellow-Methyltrioctylammonium chloride ion pairs were synthesized. The ion pair that was synthesized was employed as ionophorein the configuration of the electrode membrane. PVC membrane ion-selective electrodes in various compositions were produced using the ion pairs that were synthesized and then, potentiometric performance characteristics of these electrodes were investigated. It was determined that the electrode with the composition of 3.0 % sunset yellow-Methyltrioctylammonium (Sunset-MTOA) ion pair, 64.8 % nitrophenyloctyl ether (NPOE), 32.0 % polyvinylchloride (PVC) and 0.2 % potassium tetrakis (4-chlorophenylborate) (KTpClPB) demonstrated the best potentiometric performance properties. The linear range, slope, limit of quantification, pH range, and the response time of the electrode were determined as 1.0 × 10-5-5.0 × 10-2 M, 23.6 mV,1.0 × 10-5 M,6.4-9.1, and ≈ 5 sec, respectively. The electrode exhibited a highly repeatable potentiometric response

One water to bind a chloride-chloride ion pair: isolation of discrete [Cl2(H2O)]2- in the solid state.

A discrete dichloride ion pair in the form of a monohydrate, [Cl2(H2O)]2-, was isolated using the triaminocyclopropenium cation [C3(NHex2)(N(CH2CF3)2)2]+. Although this ion pair is calculated to be unstable in the gas phase, the ionic lattice and weak CH-Cl hydrogen bonds assist the stabilization of the cluster. The D2O and HDO isotopomers were also prepared and characterized.

Understanding Water Structure in an Ion-Pair Solvation Shell in the Vicinity of a Water/Membrane Interface.

The anomalous properties of interfacial water at the surface of a lipid membrane and their implications on nearby chemical processes are well recognized. However, we have found that ion pairing thermodynamics may not be significantly affected by interfacial water in a classical, nonpolarizable force field. To trace the root cause of such a counterintuitive finding, we performed atomistic molecular dynamics simulations to explore the impact of polarizable interactions and characterize the hydration structure of a sodium chloride (NaCl) ion pair at the surface of a model lipid membrane and in a bulk phase. Our study reveals that the effect of the aqueous interface on the first solvation shell of the ion pair and thus on the ion pairing thermodynamics becomes more pronounced in the polarizable model, and that the free energy profile along the interionic distance cannot capture the difference in the degree of solvent participation in ion pairing at the water/membrane interface. This study also forms the basis for the future design of a reaction coordinate that takes the behavior of the interfacial water into account.

Ion pairing and preferential solvation of butylmethylimidazolium chloride ion pair in water-ethanol mixtures by using molecular dynamics simulations

Constrained molecular dynamics simulations are used to compute the potentials of mean force (PMFs) of 1-butyl-3-methylimidazolium chloride (BMIM+−Cl−) ion pair in water-ethanol mixtures. From the PMFs of BMIM+−Cl− ion pair, we notice that, as the mole fraction of ethanol increases, the depths of the minima of the contact ion pair (CIP) and solvent assisted ion pair (SAIP) increase. The CIPs and SAIPs are stabilized by entropy in all the mixtures. As the mole fraction of ethanol changes from 1.0 to 0.8, the stabilities of CIPs and SAIPs are reduced significantly due to large enhancement in the local densities of water.

Shape-Selective Recognition of Quaternary Ammonium Chloride Ion Pairs.

Synthetic receptors that recognize ion pairs are potentially useful for many technical applications, but to date there has been little work on selective recognition of quaternary ammonium (Q+) ion pairs. This study measured the affinity of a tetralactam macrocycle for 11 different Q+·Cl- salts in chloroform solution. In each case, NMR spectroscopy was used to determine the association constant ( Ka) and the structure of the associated complex. Ka was found to depend strongly on the molecular shape of Q+ and was enhanced when Q+ could penetrate the macrocycle cavity and engage in attractive noncovalent interactions with the macrocycle's NH residues and aromatic sidewalls. The highest measured Ka of 7.9 × 103 M-1 was obtained when Q+ was a p-CN-substituted benzylic trimethylammonium. This high-affinity Q+·Cl- ion pair was used as a template to enhance the synthetic yield of macrocyclization reactions that produce the tetralactam receptor or structurally related derivatives. In addition, a permanently interlocked rotaxane was prepared by capping the end of a noncovalent complex composed of the tetralactam macrocycle threaded by a reactive benzylic cation. The synthetic method provides access to a new family of rotaxanated ion pairs that can likely act as anion sensors, molecular shuttles, or transport molecules.

Molecular dynamics simulations of Ca2+[sbnd]Cl− ion pair in polar mixtures of acetone and water: Solvation and dynamical studies

The potentials of mean force (PMFs) have been used to assess the relative stabilities of contact ion pairs (CIPs), solvent assisted ion pairs (SAIPs) and solvent separated ion pairs (SSIPs) in acetone-water mixtures containing a calcium chloride ion pair. In the case of Cl−in (the second Cl− ion is placed within the solvation shell of Ca2+ ion), the CIPs are more stable than SAIPs for low mole fractions of acetone (xacetone) whereas the SAIPs are more stable than the CIPs for large values of xacetone. In the case of Cl−out (the second Cl− ion is placed outside the solvation shell of Ca2+ ion), the SAIPs are marginally more stable than CIPs in neat water and for low xacetone. However, CIPs become more stable than SAIPs with increase in xacetone. The Ca2+Cl− ion pair is preferentially solvated by water in all the mixtures.

Na+ Cl− ion pair association in water-DMSO mixtures: Effect of ion pair model potentials

Potentials of Mean Force (PMF) for the Na+Cl− ion pair in water–dimethyl sulfoxide (DMSO) mixtures for three DMSO mole fractions have been computed using constrained Molecular Dynamics (MD) simulations and confirmed by dynamical trajectories and residence times of the ion pair at various inter-ionic separations. The three ion-ion direct potentials used are 12-6-1, exp-6-1 and exp-8-6-1. The physical picture that emerges is that there is a strong contact ion pair (CIP) and strong to moderate solvent separated ion pair (SSIP) in these solutions. Analysis of local ion clusters shows that ions are dominantly solvated by water molecules. The 12-6-1 potential model predicts running coordination numbers closest to experimental data. The effect of the differences between the 12-6-1, Huggins-Mayer (exp-6-1) and Fumi-Tosi (exp-6-8-1) ion-ion potential models on the solvation structure of the sodium chloride ion pair in water-DMSO binary mixtures have been studied.

Thermodynamic stability of finely dispersed Na+Cl−(H2O) n aerosol particles in water vapor

Four qualitatively different thermodynamic states have been identified for hydrated sodium chloride ion pairs in water vapor. Two of the states are stable, and the other two are unstable. The stable states of a contact ion pair (CIP) and a solvent-separated ion pair (SSIP) represent sites of heterogeneous nucleation in supersaturated vapors. The unstable states form free energy barriers that separate the stable states. As the temperature is elevated, the SSIP states become more stable than the CIP states already in unsaturated water vapors. Hydrated ion pairs that contain hydroxonium ions instead of alkali metal cations are absolutely stable in the SSIP state already in the range of unsaturated vapors and low temperatures. Computer-assisted calculations of the free energy and work of hydration have been carried out by the Monte Carlo bicanonical statistical ensemble method in terms of a detailed model of interactions comprising polarization, many-particle covalent interactions, and charge transfer phenomena.

Solvation structure of sodium chloride (Na+–Cl−) ion pair in dimethyl sulfoxide–acetonitrile mixtures

Constrained molecular dynamics method has been used to compute the potentials of mean force (PMFs) of Na+-Cl− in dimethyl sulfoxide (DMSO)–acetonitrile (AN) binary mixtures. The PMFs are confirmed by calculating the residence times of the ion pair at various inter-ionic separations. Contact ion pairs (CIPs) are found to be more stable than the solvent shared ion pairs (SShIPs). The stabilities of CIPs generally increase with increase in the mole fraction of AN. The running coordination number analysis shows that the coordination number of Na+ in pure acetonitrile is 4.6, close to the experimental value by FTIR and refractometric study. The preferential solvation study through the excess coordination numbers shows that both Na+ and Cl− are preferentially solvated by DMSO, unlike the water–DMSO mixtures.

5-Acetyl-4-(3-hydroxyphenyl)-6-methyl-1,2,3,4-tetrahydropyrimidin-2-one–tris(hydroxymethyl)ammonium chloride (2/1)

The asymmetric unit of the title compound, 2C13H14N2O3·C3H10NO3 +·Cl−, contains two independent mol­ecules (A and B) of the title pyrimidine derivative and one ion-pair of tris­(hy­droxy­meth­yl)ammonium chloride. The pyrimidine ring in each pyrimidine derivative has a half-chair conformation. Its mean plane is inclined to the benzene ring by 87.2 (3)° in mol­ecule A and 85.7 (2)° in mol­ecule B. In the crystal, the pyrimidine derivatives are connected to each other by N—H⋯O hydrogen bonds, forming chains propagating along the b-axis direction. The chains are linked via O—H—Cl hydrogen bonds, forming corrugated sheets lying parallel to the bc plane. The sheets are linked via C—H⋯O hydrogen bonds, forming a three-dimensional framework. The tris­(hy­droxy­meth­yl)ammonium chloride mol­ecules are located in the cages of the framework. There are also further C—H⋯O hydrogen bonds and C—H⋯π inter­actions present in the three-dimensional framework structure. Both the cation and chloride anion of the tris­(hy­droxy­meth­yl)ammonium chloride ion pair are disordered over two positions, with a refined occupancy ratio of 0.418 (8):0.582 (8) for the cation and 0.71 (4):0.29 (4) for the anion.

Solvation structure and dynamics of potassium chloride ion pair in dimethyl sulfoxide–water mixtures

Structure and dynamics of potassium chloride ion pair in mixtures of dimethyl sulfoxide (DMSO) and water have been investigated using constrained molecular dynamics. We have obtained the potentials of mean force (PMFs) between the K+ and Cl− ions at 298K over a wide concentration range of these mixtures. The results obtained are compared for relative stabilities of contact ion pair (CIP), solvent assisted ion pair (SAIP) and solvent separated ion pair (SSIP) in the mixtures with varying compositions. The stability of the CIPs decreases significantly as the mole fraction of water increases. The study of running coordination numbers at the first solvation shell suggests preferential solvation of ions by water in all the compositions and there is hardly any participation by DMSO molecules in the first solvation shell of the Cl− ion. The extent of association of potassium chloride ion pair in water, DMSO and their mixtures is determined by calculating the association constants. We have calculated the diffusion constants of ions and solvent molecules in the first solvation shell around K+ and Cl− in all the compositions. The diffusion constants of the shell molecules are the smallest in the DMSO mole fraction ranging from 0.2 to 0.5.

Potentials of mean force of sodium chloride ion pair in dimethyl sulfoxide–methanol mixtures

The constrained molecular dynamics technique has been used to simulate solutions of sodium chloride ion pair in pure methanol (MeOH), pure dimethyl sulfoxide (DMSO) and DMSO–MeOH mixtures with MeOH mole fractions (xMeOH) of 0.25, 0.50 and 0.75. The potentials of mean force (PMFs) of the sodium chloride ion pair have been computed for all the above compositions. The PMFs for the pure solvents indicate that contact ion pairs (CIPs) are more stable than the solvent separated ion pairs (SSIPs). In the mixtures, contact ion pairs (CIPs) dominate the PMF and solvent assisted ion pairs (SAIPs) persist in all the compositions. As the mole fraction of DMSO increases, the stability of CIP increases. In all three solvent mixtures, the Na+Cl− ion pair is preferentially solvated by MeOH molecules. These results have been confirmed by dynamical ion pair trajectories for long times. A study of the running coordination numbers in the CIP and SAIP/SSIP configurations shows that the number of DMSO and methanol molecules around the ion pair does not change significantly with composition beyond xMeOH=0.50.

Computational and experimental approaches to the molecular structure of the HCl adduct of Me3PO.

The reaction of anhydrous HCl(g) with trimethyl phosphane oxide yields trimethylhydroxy phosphonium chloride. A crystal structure analysis showed that the prevalent mesomeric structure in the solid state is the phosphonium chloride ion pair. Ab initio calculations in the gas phase cannot reproduce these findings, whereas higher correlated methods (CISD) and solvation models predict the experimental structure correctly.