On the influence of ionic strength on the equilibrium constant of copper-murexide interaction

The concentration formation constant for the 1:1 complex between copper(II) and murexide in aqueous solutions has been measured as a function of ionic strength by spectrophotometry at 25 degrees . There is an inverse relationship between the K(c) values and ionic strength. The formation constant at infinite dilution was found to be 6.16 x 10(4). The distance of closest approach for the Cu(2+) ion was estimated as 4.3 +/- 0.3 A.     

On the influence of ionic strength on the equilibrium constant of an ion-molecule reaction

Concentration formation constants for the 18-crown-6-sodium ion complex in anhydrous methanol solutions were measured as a function of the ionic strength of the solution. The K_c values remained reasonably constant for I_c ? 0.05 mol dm^?3 At higher ionic strengths the K_c values begin to decrease. The infinite-dilution formation constant was 2.2 × 10⁴.     

The investigation of complex formation equilibria at constant ionic strength

The inert salts used for the investigations of complex formation are briefly discussed in relation to the effects of their ions on the equilibria studied. In general, some association with the inert salt ions cannot be completely avoided. In case of very stable complexes measured at low ionic strength, their effects can be quantified even though they are not caused by the anion if NO(-)(3) or ClO(-)(4) are used. In the case of weak complexes, when ionic strengths I > or =1 are used, the concentration of the complex of interest can be 1000 times lower than that of the associates of the same cation with the anion of the inert salt causing difficulties with the investigation of the latter systems. If the experimental results for K(1) of the alkaline-earth metal ions with fluoride in sodium perchlorate and sodium nitrate are correct, as their equilibrium constants have very similar values, it follows that the behavior of two anions is very similar. However, if NO(-)(3) associates with the above cations, as found, the same behavior is expected for ClO(-)(4). A more accurate analysis can only be done if activity coefficients in these solutions are known.     

Critical evaluation of methane-hydrocarbon high-pressure experimental vapour-liquid equilibrium data using equations of state

Legret, D., Richon, D. and Renon, H., 1984. Critical evaluation of methane-hydrocarbon high-pressure experimental vapour-liquid equilibrium data using equations of state. Fluid Phase Equilibria, 17: 323–350.An evaluation of literature vapour-liquid equilibrium data for methane-hydrocarbon systems is presented, based on the application of cubic equations of state. Lists of interaction parameters and data sets are presented.     

A new approach to experimental data evaluation from tree ring analysis

Summary A different approach is outlined for the correlation between the element values determined and the annual growth of tree rings in order to assess the total burden. Oxygen flask combustion and ion-chromatographic analysis has been applied to the determination of P, Cl and S in annual growth rings of Pinus pinea L. in Southern Sardinia (Italy). The high sensitivity of the method permits the analysis of individual growth rings using a minimum amount of material for the complete combustion. The preliminary investigation shows that a net increase of S, P and Cl over the last decade is evident both in concentration and in total quantity.     

Ion pair chromatography: A new approach to dynamic equilibrium

Summary This work describes the dynamic equilibrium of an ionpair, reverse-phase liquid chromatography system. A given adsorbed quantity of an anionic surfactant can lead to different capacity factors and selectivity for anionic solutes.This paper was presented as a poster-communication at the 7^th International Symposium on Column Liquid Chromatography, Baden-Baden, May 3–6, 1983.     

On the liquid junction potential for the determination of equilibrium constants by means of the potentiometric technique without constant ionic strength

A modified method for the calculation of liquid junction potentials based on the Henderson equation is proposed. The estimation of the activity coefficients and the conductivities is performed by means of the Modified Bromley Methodology [G. Borge, R. Castaño, M.P. Carril, M.S. Corbillón, J.M. Madariaga, Fluid Phase Equilibria 121 (1996) 85–98;G. Borge, N. Etxebarria, L.A. Fernández, M.A. Olazabal, J.M. Madariaga, Fluid Phase Equilibria 121 (1996) 99–109.] and the Extended Falkenhagen Equation [A. De Diego, Conductivity of concentrated electrolytic solutions: study of the dependence with concentration and temperature, Ph.D. Thesis, University of the Basque Country, Bilbao, 1996.]. The efficiency of the method has been tested in potentiometric titrations without constant ionic strength. Its applicability to potentiometric titrations with constant ionic strength is also discussed.     

Dependence of equilibrium constants ofL-valine on ionic strength according to Guggenheim,Scatchard and Pitzer models

Summary A systematic study of the dependence of acid-base stoichiometric constants on the ionic strength has been carried out for the aminoacidL-valine in ClK and BrK solutions. The observed dependence has been interpreted by using Guggenheim, Scatchard and Pitzer models for the activity coefficients of the species involved in the equilibria.

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Die Abhängigkeit von Gleichgewichtskonstanten desL-Valin von der Ionenstärke entsprechend den Modellen von Guggenheim, Scatchard und Pitzer

Zusammenfassung Es wurde anL-Valin in KCl- und KBr-Lösungen eine systematische Studie der Abhängigkeit der Säure-Base-Stöchiometrie von der Ionenstärke durchgeführt. Die beobachteten Abhängigkeiten wurden aufgrund der nach den Modellen von Guggenheim, Scatchard und Pitzer erhaltenen Aktivitätskoeffizienten der an den Gleichgewichten beteiligten Spezies interpretiert.

     

Non equilibrium thermodynamics and the city: a new approach to urban studies

A city can be conceived as a complex self-adaptive system. The multiple interactions among its structural elements and dynamic agents, its organization on multiple time-space scales, its exchanges with the external context, its irreversible dynamics, are signs of complexity. Some concepts from the evolutionary thermodynamics, such us the theory of dissipative structures, could be extended to the city in order to investigate its behaviour. This theoretical framework suggests to analyze the city in terms of entropy and negentropy production. An emergy analysis (spelled with an "m") of an urban region is presented in order to investigate how cities maintain their organization (and decrease their entropy) by virtue of constant energy inflows from the external environment. As a result, a non-homogeneous spatial pattern of emergy density is shown as an attempt to investigate the multiple relations and energy exchanges that take place in an urban region. This approach to urban studies introduces a new energy-based vision to understand cities.     

Thermodynamic properties and equilibrium constant of chemical reaction in nanosystem: An theoretical and experimental study

The theoretical relations of thermodynamic properties, the equilibrium constant and reactant size in nanosystem are described. The effects of size on thermodynamic properties and the equilibrium constant were studied using nanosize zinc oxide and sodium bisulfate solution as a reaction system. The experimental results indicated that the molar Gibbs free energy, the molar enthalpy and the molar entropy of the reaction decrease, but the equilibrium constant increases with decreasing reactant size. Linear trends were observed between the reciprocal of size for nano-reactant and thermodynamic variable, which are consistent with the theoretical relations.     

Electrokinetics at high ionic strength and hypothesis of the double layer with zero surface charge

A growing number of publications in the last two decades have suggested that the structure and other properties of the interfacial water layer can significantly affect the double layer (DL) because of changes in ion solvatation energy. Most interesting is the possibility that a double layer might in fact exist, even when there is no electric surface charge at all, solely because of the difference in cation and anion concentrations within this interfacial water layer. Dukhin, Derjaguin, and Yaroschuk suggested this possibility 20 years ago and developed a phenomenological theory. Recently, Mancui and Ruckenstein created more sophisticated microscopic model. In this article, we present our first experimental result regarding the verification of this "zero surface charge" DL model. The electroacoustic technique allows testing at high ionic strength (up to 2 M). As a first step, we confirm the surprising result of Johnson, Scales, and Healy regarding large zeta potential of alumina (8 +/- 1 mV) in 1 M KCl. As a second step, we suggest using nonionic surfactant Tween 80 for probing and modifying the structure of the interfacial layer at high ionic strength. The application of surfactant at moderate ionic strength (i.e., <0.1 mol/dm3), as might be expected, reduces the zeta potential simply by shifting the slipping plane. However, there is no influence of surfactant on the zeta potential observed at high ionic strength. It turns out that a high concentration of KCl simply eliminates surfactant adsorption. We develop a new technique for characterizing the adsorption of nonionic surfactant using an acoustic attenuation measurement. We hope that these methods in combination with a proper surfactant and electrolyte selection would allow us to gain more detailed information on the interface structure at high ionic strength.     

Static dielectric constant of room temperature ionic liquids: internal pressure and cohesive energy density approach

Measurements of the static dielectric constant (epsilon) of ionic liquids (ILs) are very difficult because of the decay of field by the ionic conductivity of ILs. Herein, we describe an easy method for the prediction of epsilon of various imidazolium-based ILs [C_n mim] from n, i.e. the ratio of internal pressure (P_i) and cohesive energy density (ced). A calibration curve of n vs epsilon for conventional organic solvents (mainly the linear alcohols) has been used to estimate the epsilon of the ILs. Estimated epsilon values for ILs having the anions [Cl]-, [BF 4]-, [PF 6]-, [TfO]-, and [Tf 2N]- showed a very good comparison with the literature results, whereas ILs having the anions [C_n OSO3]- tend to deviate from such correlation. Also, for a series of ILs having a common anion, the epsilon is shown to follow a very good correlation with the molecular volumes. Predicted values show that both the nature of the anion and alkyl chain length of the cation contribute significantly to the epsilon of the ILs. The method developed makes use of properties which can be either experimentally determined or estimated with good accuracy and can be extended to the other categories of ILs with ease and reasonable accuracy.     

Improvement and application of two extrapolation methods to FT-IR data

The applicability of two non-parametric extrapolation methods to FT-IR absorptance spectra is investigated. The first method minimizes those parts of the spectrum which do not satisfy a given constraint, while the second one changes them in each iteration through the true values.     

Studies on the equilibrium among poly(sodium 4‐styrenesulfonate), Cu2+, and iminodiacetic acid by ultrafiltration at constant ionic strength

The ultrafiltration technique evaluates the interactions of water‐soluble polymers with metal ions. Aqueous solutions containing poly(sodium 4‐styrenesulfonate) (PSS), Cu(NO₃)₂, NaNO₃, and iminodiacetic acid (IDAA) are examined by this technique. Cu²⁺ undergoes complex formation with IDAA and intreracts electrostatically with PSS. On the other hand, Na⁺ ions are in competition with Cu²⁺ for the electrostatic binding to PSS. The solutions are ultrafiltered keeping the ionic strength constant, so their compositions are allowed to change continuously. The concentration of Cu²⁺ bound to the polymer showed an exponential decay during filtration. The concentration of Cu²⁺ bound to the polymer before ultrafiltration is calculated by extrapolation. The concentration of the different species in solution is proposed as a function of the filtration factor. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2587–2593, 2002     

Iodine monochloride-amine complexes: an experimental and computational approach to new chiral electrophiles

Lactonizations are important steps in many synthetic sequences. Substrate-controlled reactions that use chiral auxiliaries or chiral alkenes have already been studied in depth. This study focuses on stereoselective reagent-controlled iodolactonizations, by application of a new method that uses complexes of iodine monochloride and various donor molecules. (R)-1,2,3,4-Tetrahydro-1-naphthylamine and other amines with similar structures were found to be efficient in the iodocyclization of 4-aryl-4-pentenoic acids. Calculations were performed on complexes of (R)-1,2,3,4-tetrahydro-1-naphthylamine with XCl (X = I, H) to identify possible reactive species in these iodocyclizations. Calculations were carried out at various levels of theory, including B3 LYP/6-31+G (d,p) by using a modified SDD basis set for iodine.     

Kinetic and equilibrium study of the reaction of nitroprusside and hydroxide ions: Influence of ionic strength using Pitzer model

A kinetic and equilibrium study of the addition reaction of hydroxide ions to nitroprusside has been carried out in this paper. Rate and equilibrium constants at different salt concentrations (up to 4 mol kg^?1) were obtained, and the influence of ionic strength was studied by means of Pitzer equations. This model is of special interest because it is able to explain the experimental behavior at high ionic strength, when Debye–Huckel limiting law is no longer valid. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 650–660, 2004     

A facile and specific approach to new liquid chromatography adsorbents obtained by ionic self-assembly

A new ionic-liquid monomer, 1-vinyl-3-octadecylimidazolium bromide ([C(18)VIm]Br), was prepared and polymerized on porous silica particles by means of a surface-initiated radical chain-transfer reaction. Further modification for functionalization was performed through the exchange of counteranions from bromide to methyl orange (MO). Two new silica-poly(octadecylimidazolium) (Sil-PImC(18)) hybrid materials (Sil-PImC(18)-Br and Sil-PImC(18)-MO) were synthesized and characterized by elemental analysis, thermogravimetric analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and solid-state (13)C CP/MAS NMR spectroscopy. Sil-PImC(18)-MO presented ultra-high shape selectivity for constrained isomers of polycyclic aromatic hydrocarbons (PAHs) both in reversed- and normal-phase HPLC when used as the stationary phase. Fundamental aspects of the molecular shape selectivity were evaluated by using Standard Reference Material (SRM) 869b; the column selectivity test mixture for liquid chromatography. The impact of this phase was also demonstrated by the separation of SRM 1647e (16 priority pollutant PAHs) and several steroid isomers. Enhanced selectivity could be explained by the highly oriented arrangement between the octadecylimidazolium chain and a rigid segment of MO. These findings may open a new window of research for the design of materials used in chromatographic supports, solid extraction, catalysis, and electrolytes by simple modifications of the counterions in the poly(ionic liquid) analogous phase.