Interaction Of Ions In Solution Research Articles

Osmotic Coefficients of Gabapentin Drug in Aqueous Solutions of Deep Eutectic Solvents: Experimental Measurements and Thermodynamic Modeling

Most of the applications for aqueous deep eutectic solvent (DES) solutions are directly related to molecular interactions, which can be studied using thermodynamic properties. In this regard, the activity coefficient and osmotic coefficient studies have provided evidence for understanding the depth of ion pair formation, ion solvent, and ion–ion interactions in solutions. In this study, the osmotic coefficients for binary gabapentin (GBP)/water and ternary GBP/DES (ChCl/EG and ChCl/U) aqueous solutions were calculated using vapor pressure osmometry measurements at T = 298.15 K and pressure 872 hPa. Water activities, osmotic coefficients, and vapor pressure depressions were all calculated for binary solutions. The Pitzer equation was used to correlate the osmotic coefficient values. Activity coefficients for GBP in the binary systems were determined by the obtained parameters of this equation. The standard deviation for the osmotic coefficient value in the binary system with the Pitzer equation is 0.0059. In ternary solutions, two different DES concentrations (about molality 1 and 3) were used to investigate the effect of concentration on osmotic coefficients. For ternary solutions, it was also possible to obtain quantities like water activity and osmotic coefficient data. Finally, the predicted values of water activity using the Lin and ECA models were applied to compare the results of water activity in the studied systems. The results showed that the ECA and Lin models have 0.00045 and 0.0011 average standard deviation, respectively.

Nicotine – Metal ion interactions in solutions: Potentiometric, cyclic voltammetry investigations and quantum chemical calculations

The experimental protonation and complex formation equilibrium constants of nicotine (NIC) with trivalent (iron (III), and chromium (III)) and divalent (copper (II), and nickel (II)) metal ions have been investigated at 310.15 oK in water solutions at ionic strength of 13.60g·dm−3 NaNO3 using pH-potentiometric and cyclic voltammetry techniques, and by means of Hyperquad 2008 estimation model program. Also, the dissociation constants of NIC and the equilibrium constants of its binary complexes with the studied metal ions in 13.60g·dm−3 NaNO3 water solutions were observed at different temperatures such as (298.15, 310.15, 318.15 and 328.15) K. The theoretical calculations of overall protonation and stability constants of the metal ion-nicotine complex species in aqueous solutions were predicted as the Gibbs energy change associated with the nicotine protonation, and metal ion – nicotine complex formation equilibria using ab initio and density function theory calculations by applying Gaussian 09 software molecular modeling. The usage of the experimental potentiometry/spectrophotometry techniques and theoretical predictions provides a complete picture of the microscopic equilibria of the studied systems (metal ions -nicotinate). Precisely, this theoretically predications could be useful to control the most real protonation constants of nicotine ligand in which the binding sites changes due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of different metal ions towards nicotine in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ions - nicotine complex species in solutions were estimated using HySS 2009 software.

Time-domain NMR relaxometry as an alternative method for analysis of chitosan-paramagnetic ion interactions in solution

Chitosan (CHI)-paramagnetic ion interactions in aqueous solution as affected by pH were studied using time-domain NMR (TD-NMR) relaxometry. Longitudinal (T1) and transverse (T2) relaxation times of CHI solutions with Fe3+, Cu2+, and Mn2+ were measured using a single-shot pulse sequence named CP-CWFPx-x. The results indicate that CHI interacted with Fe3+ ions or iron oxide nanoparticles, maintaining the metal ion in solution at pH ranging from 3 to 5. Above this pH, CHI coagulated and removed Fe ions or nanoparticles, resulting in a clear supernatant. CHI probably interacted with Cu ions at pH 6.2 through the deprotonated CHI-NH2 groups maintaining the relaxation effect in alkaline solution, whereas Mn2+ did not interact with CHI strongly enough to produce a complex of high stability. The proposed method can also be further exploited in the study of interactions paramagnetic ions with others CHI and CHI derivatives as well as of other water-soluble polysaccharides.

Hydrogen-Bonding and Ion−Ion Interactions in Solutions of Triflic Acid and 1-Ethyl-3-methylimidazolium Triflate

Ion-ion and hydrogen-bonding interactions in solutions of 1-ethyl-3-methylimidazolium trifluoromethansulfonate ([C(2)mim]Tf) and triflic acid (HTf) are investigated with infrared and Raman spectroscopy. Bands indicative of highly aggregated triflate anions appear in the vibrational spectra of solutions containing a large fraction of triflic acid. These species most likely consist of triflate anions that are at least threefold coordinated by positive ions (i.e., {[C(2)mim](x)H(y)Tf}(x+y-1) where x + y > or = 3). Such coordination environments would be consistent with a larger, extended aggregate of Tf(-), [C(2)mim](+), and H(+) ions that may be charged or neutral. Evidence for hydrogen bonding between the protons and the oxygen atoms of the triflate atoms and between the hydrogen atoms of the [C(2)mim](+) and triflate anion is identified in the infrared and Raman spectra.

Towards an atomistic understanding of apatite–collagen biomaterials: linking molecular simulation studies of complex-, crystal- and composite-formation to experimental findings

The investigation of the atomistic mechanisms of crystal nucleation constitutes a major challenge to both experiment and theory. Understanding the underlying principles of composite materials formation represents an even harder task. For the investigation of the mechanisms of crystal nucleation a profound knowledge of the ion–solvent and the ion–ion interactions in solution is required. Studying biocomposites like fluorapatite–collagen materials, we must furthermore account for the biomolecules and their effect on the growth process. Molecular simulation approaches directly offer atomistic resolution and hence appear particularly suited for detailed mechanistic analyses. However, the computational effort is typically immense and for a long time the investigation of crystal nucleation from atomistic simulations was considered as impossible. We therefore developed special simulation strategies, which allowed to considerably extent the limitations of computational studies in this field. In combination with advanced experimental investigations this provided new insights into the nucleation of biomimetic apatite–gelatin composites and the mechanisms of hierarchical growth at the micro- and mesoscopic scale. Along this line, molecular simulation studies reflect a powerful tool to achieve a profound understanding of the complex growth processes of apatite/collagen composites. Apart from reviewing related work we outline future directions and discuss the perspectives of simulation studies for the investigation of biomineralization processes in general.

Corrected Debye–Hückel Analysis of Surface Complexation: I. Bulk Salt Limit

Statistical mechanics in the framework of generalized van der Waals theory is used to clarify the mechanisms at work in surface complexation. As a first step this article will focus on a description of ion interactions in solution. A simple semiempirical theoretical framework is proposed on the basis of an extension of the Debye–Hückel theory of the screening mechanism. Ion size effects are accounted for within a restricted primitive model of the electrolyte leading to a shift in the Debye screening length. Remarkably the shift is found to be due only to hole correction of the electrostatic potential energy while the excluded volume effects vanish in the linear approximation. The treatment of diffuse screening is tested by application of the corrected Debye–Hückel theory to the calculation of bulk thermodynamic properties, such as the internal energy, the osmotic coefficient, and mean ionic activity coefficients. Calculations and comparisons with experimental data have been performed for 1 : 1, 2 : 1, 3 : 1, and 2 : 2 salt solutions. The accuracy is good indicating that the theory is suitable for the intended application in the study of surface complexation. Finally our theory is applied to electrolyte solutions in the solvent primitive model where the solvent is represented by neutral hard spheres. Our analysis indicates that, within the limits of our basic assumptions, the solvent hard spheres only enter the background contributions and leave the screening mechanism unaffected. The simulation results available indicate that this is largely, if not entirely, correct.

Adsorption sequence of the alkali cations at the tungsten trioxide–water interface

The stability of pyrogenic tungsten trioxide hydrosols is studied in the presence of various monovalent cations between pH 2 and 12. The hydrosol critical coagulation concentrations ( c*) are determined by extrapolation of the experimental log W–log c curves up to log W=0. The c* of K +, Rb +and Cs + slightly increase with the pH of the solution while the c* of Li + presents a pronounced maximum at pH 4.5. A less marked maximum is also observed at the same pH in the presence of Na +. The corresponding ionic adsorption sequence at the water–WO 3 interface deduced from these experimental data is Cs +>Rb +>K +>Na +>Li + in the pH domain under investigation. This overall behavior is successfully explained by the model proposed by Gierst who has generalized the Gurney concept describing the ion–ion interactions in solution to the ion–surface interactions. The results reported in this work are also compared with those obtained previously for other oxides; they confirm the validity and the generality of the conclusions already drawn concerning the ionic adsorption sequences at the oxide–water interface.

Kinetics of Calcite Precipitation from Seawater: II. The Influence of the Ionic Strength

To characterize the influence of ionic strength on the kinetics of calcite precipitation from seawater solutions we carried out a set of experiments at four different ionic strengths (I = 0.10; 0.34; 0.55; 0.93 m) in NaCl-CaCl2 solutions, at the temperature of 298.15K and a CO 2 partial pressure of 100 Pa. The constant addition technique was used in order to maintain [Ca 2+] at ≅10.5 mmol/kg, while the [CO 3 2−] was varied to isolate its role on the precipitation rate of calcite. Assuming that the calcite precipitation in this solution is dominated by the reaction: Ca 2++CO 3 2− ⇔ kb kf CaCO 3 (1) where k f and k b are, respectively, the forward and reverse reaction rate constants, the net precipitation rate, R, can be described at any ionic strength by R=k f (a Ca 2+ ) n1(a CO3 2− ) n2−k b (2) or, in its logarithmic form Log (R+k b)=Log K f+n 2 Log [CO 3 2−] (3) where n i are the partial reaction orders with respect to the participating ions, a and γ are, respectively, the ion activities and activity coefficients and, K f = k f(a Ca 2+ ) n1(γ CO3 2− ) n2, a constant at a given ionic strength. Results of this study indicate that, when the ionic strength is increased from 0.10 to 0.93 m, the partial reaction order with respect to the CO 3 2− concentration increases from 1 to 3 and the forward reaction rate constant, k f, increases by several orders of magnitude. This is interpreted as both a change in the calcite precipitation mechanism and a catalysis generated by the presence of inert electrolytes. Applying our model to the rate measurements carried out by Zhong and Mucci 1989 in seawater solutions at various salinities, under the compositional condition [Ca 2+] ≫ [CO 3 2−], we find that the partial reaction order with respect to the carbonate ion and the forward reaction rate constant increase as a function of the total ionic strength of the seawater solutions. A 50% increase of the total ionic strength of the parent solution results in an increase of the precipitation rate by 2 orders of magnitude. Finally, we propose that ion interactions in solution and a concomitant change of the precipitation mechanism may contribute to the development of nonequivalent kink sites of different sizes on the surface of the growing crystal but which still satisfy the symmetry. Variations in the amount of foreign ions adsorbed and incorporated into marine calcites could, therefore, be determined by the density of these less constrained sites, which, in turn, would be dependent on the total ionic strength of the solution.

Peptide-metal ion interactions in solution: Detection by laser desorption time-of-flight mass spectrometry and electrospray ionization mass spectrometry

The specific interaction of Cu(II) ions with metal-binding peptides in solution has been investigated by two different methods of soft ionization mass spectrometry, namely matrix-assisted ultraviolet laser desorption time-of-flight mass spectrometry (LDTOF) and electrospray ionization mass spectrometry (ES). The metal-binding peptide selected for these investigations is a 26-residue sequence found on the surface of the human plasma metal-transport protein histidine-rich glycoprotein. The peptide, (GHHPH)5 G, was synthesized and evaluated by ES and LDTOF before and after the addition of Cu(II) or Mn(II) ions in solution. In the absence of added metal ions, the peptide was observed to have a mass equal to within 0.5 Da of its calculated mass (2903.0 Da) by both LDTOF and ES. In the presence of Cu(II), up to five additional peaks were observed at mass increments of approximately 63.9 Da (LDTOF) or 62.3 Da (ES); Mn was not bound to the peptide under identical experimental conditions. By both LDTOF and ES, the maximum Cu-binding capacity observed (i.e., 5 g-atoms mol−1) demonstrated that up to 1 Cu could be bound per (GHHPH) internal repeat unit. This peptide-metal ion interaction stoichiometry was verified by direct titration in solution and, with immobilized peptide, by quantitative metal ion affinity chromatography. Thus, the ability to detect stable peptide-metal complexes did not appear to be differentially affected by the two different volatilization/ionization methods needed to generate charged intact molecular ions. The quantity and stoichiometry of bound Cu atoms was affected, however, by experimental conditions such as LDTOF matrix and ES solution composition. These results demonstrate the ability to verify directly the solution-phase binding capacity of metal-binding peptides by LDTOF and by ES. We conclude from these studies that other metallo-organic interactions may also be amenable to investigation by these rapid and sensitive techniques.

Effect of interion interactions on electrolyte properties near a phase separation boundary

The interaction of ions in solution and in the adsorbed state with themselves and with charges induced in the solid phase varies the isotherms of ion adsorption and the structure of the diffusion part of a double electric layer. This effect is treated within the Debye-Huckel approximation for a dilute solution of a strong electrolyte under conditions of local thermodynamic equilibrium.

The real standard potential on the aqueous hydrogen scale of the silver/silver chloride electrode in methanol: the surface potential of methanol

The compensating potential difference (cpd) has been measured for the voltaic cell constructed from a mercury jet reference electrode and a silver/silver chloride electrode in a methanolic solution of KCl, in the KC1 molality range 3×10 −5 < m 1 < 0.03. The results show that the surface potential of a KCl solution in methanol becomes steadily less negative with increasing KCl concentration. A quantitative electrostatic model for the interaction of ions in solution with the permanent dipole layer at the surface of a liquid is critically examined and we conclude that pure methanol has a surface potential of at least −90 mV although our data are consistent with a previously-recommended value of −230 mV. The standard real potential of the half-cell Cl − (methanol)|AgCl,Ag on the aqueous hydrogen scale is defined and found by extrapolation to be −0.321 ±0.001 V; this fixes the E XXX values on the real electrode potential scale in methanol at 298 K.