Association Thermodynamic Parameters Research Articles

Electrical Conductivity and Thermodynamics of Ion Association of Ammonium Ionic Liquids in Acetone

The electrical conductivity of a number of tetraalkylammonium ionic liquids with tetrafluoroborate anion has been studied in acetone in the temperature range 298–313 K. Based on the obtained conductometric data for the compounds under study, the Lee–Wheaton method has been used to calculate the ion association constants (Ka), limiting molar electrical conductivities (λ0), and Gibbs association energy (ΔG0) in solutions. From the temperature dependence of equivalent electrical conductivity, the values of association enthalpy (ΔH0) and entropy (ΔS0) have been calculated. For all studied compounds, the Walden–Pisarzhevsky product has been calculated. Conclusions are drawn about the influence of the structure of the studied ionic liquids on the thermodynamic parameters of association in acetone solutions.

Theoretical and Experimental Salvation of Nano Copper Sulfate Interacted with 18-crown-6 in Water

Theoretical study of the electronic structure, NonLinear Optical (NLO) properties, and natural bonding orbital (NBO) analysis of 18-crown-6were investigated using Density Functional Theory DFT) calculations at the B3LYP/6-311G (d,p) level of theory. The optimized structure is a nonlinear compound indicated from the dihedral angles. Natural bonding orbital analysis has been analyzed in terms of the hybridization of each atom, natural charges (Core, Valence, and Rydberg), bonding and antibonding orbital's second-order perturbation energy (E(2)). The calculated EHOMO and ELUMO energies of the title molecule can be used to explain the charge transfer in the molecule and to calculate the global properties; the chemical hardness (η), softness(S), global electrophilicity index (w), and electronegativity (χ). The NLO parameters: static dipole moment (µ), polarizability (α), anisotropy polarizability (Δα), first-order hyperpolarizability (βtot) and third-order hyperpolarizability ⟨γ⟩), of the studied molecule have been calculated at the same level of theory.The Molecular Electrostatic Potential (MEP) and ElectroStatic Potential (ESP) for the title molecule were investigated and analyzed. Also, the electronic absorption spectra were discussed by time-dependent density functional theory (TD-DFT) calculations in ethanol and water solvents. From the experimental conductance measurements, the association thermodynamic parameters (KA, ∆GA, ∆HA, and ∆SA) and complex formation thermodynamic parameters (Kf, ∆Gf, ∆Hf, and ∆Sf) of nano-CuSO4 in presence of 18-crown-6 as a ligand in 10% ethanol-waterer solvents at different temperatures (298.15, 303.15, 308.15 and 313.15K) were applied and calculated.

Theoretical Study of 1,4-Dioxane in Aqueous Solution and Its Experimental Interaction with Nano-CuSO4

The electronic structure, Non-Linear Optical (NLO) properties and Natural Bonding Orbital (NBO) analysis of 1,4-dioxane were investigated using the theoretical study of Density Functional Theory (DFT) calculations at the B3LYP/6-311G (d,p) level of theory. The optimized structure is nonlinear as indicated from the dihedral angles. Natural bonding orbital analysis has been analyzed in terms of the hybridization of each atom, natural charges (Core, Valence and Rydberg), bonding and antibonding orbital's second order perturbation energy (E(2)). The calculated EHOMO and ELUMO energies of the title molecule can be used to explain the charge transfer in the molecule and to calculate the global properties; the chemical hardness (η), softness (S) and electronegativity (χ). The NLO parameters: static dipole moment (µ), polarizability (α), anisotropy polarizability (Δα) and first order hyperpolarizability (βtot) of the studied molecule have been calculated at the same level of theory. The Molecular Electrostatic Potential (MEP) and Electro Static Potential (ESP) for 1,4-dioxane were investigated and analyzed. Also, the electronic absorption spectra were discussed by Time-Dependent Density Functional Theory (TD-DFT) calculations for 1,4-dioxane in 10% ethanol/water. From the experimental conductance measurements, the association thermodynamic parameters (KA, ∆GA, ∆HA and ∆SA) and complex formation thermodynamic parameters (Kf, ∆Gf, ∆Hf and ∆Sf) of nano-CuSO4 in the presence of 1,4-dioxane as a ligand in 10% ethanol-water at different temperatures (298.15, 303.15, 308.15 and 313.15 oK) were applied and calculated.

Effect of calcon carboxylic acid on association process of vanadyl sulfate in water‐N, N‐dimethyl formamide mixed solvents

Abstract The complexation reaction between calcon carboxylic acid (CCA) and vanadyl sulfate was studied in water and mixed water‐N, N‐dimethyl formamide mixed solvents (DMF–H 2 O) using conductometric measurements. The experimental data are already analyzed with the use of Fuoss–Shedlovsky technique in absence and presence of CCA. The ion-pair association (K A ), and also the standard thermodynamic parameters for association (∆G o A , ∆H o A and ∆S o A ) were estimated and compared in absence and presence of CCA. The main difference between Gibbs free energy of association in the presence and the case of absence of CCA indicate the value of free enthalpy of complexation (∆G° complexing ). Walden product (Λ 0 η 0 ), hydrodynamic radii (R H ) and the energy of activation (E a. ) were also calculated. This work provides the suggested structure of the complex based on elemental analyses and spectral study (IR) which provide the thermodynamic results with useful discussion. CCA act as binegative tetradentate coordination.

Theoretical calculations of solvation 12-Crown-4 (12CN4) in aqueous solution and its experimental interaction with nano CuSO4

Theoretical study of the electronic structure, and nonlinear optical properties (NLO) analysis of 12-crown-4were done using Density Functional Theory (DFT) evaluations at the B3LYP/6-311G (d,p) level of theory. The optimized structure is nonlinear compound as indicated from the dihedral angles were presented. The calculated EHOMO and ELUMO energies of 12-Crown-4 (12CN4) can be used to explain the charge transfer in 12-Crown-4 (12CN4) and to calculated the global properties; the chemical hardness (η), softness (S) and electronegativity (χ). The NLO parameters: static dipole moment (µ), polarizability (α), anisotropy polarizability (Δα) and first order hyperpolarizability (βtot) of the 12-Crown-4 (12CN4) have been calculated at the same level of theory.The molecular electrostatic potential (MEP) and electrostatic potential (ESP) for the title molecule were investigated and analyzed. Also the electronic absorption spectra were measured in ethanol and water solvents and the assignment of the observed bands has been discussed by time-dependent density functional theory (TD-DFT) calculations. The correspondences between calculated and experimental transitions energies are satisfactory. From the experimental conductance measurements, the association thermodynamic parameters (KA, ∆GA, ∆HA and ∆SA) and complex formation thermodynamic parameters (Kf, ∆Gf, ∆Hf and ∆Sf) for nano-CuSO4 in presence of 12-crown-4 (12CN4) as chelating agent in 10% ethanol – water solvents at different temperatures (298.15, 303.15, 308.15 and 313.15K) were applied and calculated.

The effect of temperature on association constants and conductivities of ferrous chloride and ferric chloride in DMF-water mixtures

Conductance measurements at five different temperatures varying from 288.15 to 328.15 K were performed for ferrous chloride (FeCl 2 ) and ferric chloride (FeCl 3 ) in 20-80 wt % in N , N -dimethylformamide (DMF)-water mixture. To analyze conductivity data, density and viscosity values of the DMF-water mixtures have been determined experimentally at the same temperatures. The conductivity data has been analyzed using the Kraus-Bray and Shedlovsky models. The limiting equivalent conductance values, the association constants ( K A ), thermodynamic parameters of association (Gibbs energy, enthalpy and entropy changes) for FeCl 2 and FeCl 3 were calculated and discussed depending on temperature and the composition of solvent mixture.

Effect of t-octylphenoxylpolyethoxyethanol (TX-100) on the dilute aqueous solution phase diagrams, surface activity and micellization behavior of non-ionic silicone surfactants (SS) in aqueous media

Dilute aqueous solution phase diagrams, surface tension, dynamic light scattering (DLS) and dilute solution viscosity measurements have been made in aqueous solutions of nonionic silicone surfactants (SS) in presence of t-octylphenoxylpolyethoxyethanol (TX-100). Critical micelle concentration, thermodynamic parameters of association, interfacial characteristics such as pC20, surface excess, Γmax , area per adsorbed molecule, a1s along with the size and shape and intrinsic viscosities of the associates have been determined and discussed to ascertain the effect of TX-100 as an additive in SS aqueous solutions. The importance of hydrophobic/hydrophilic (hp/hl) ratio of the SS rather than their molecular architecture and molar mass on their overall interaction with TX-100 micelles has been reflected in the above parameters for the mixture solutions. It was observed that the mixed species in SS aqueous solutions in TX-100 are more hydrophilic in nature and the overall association process in the mixture solutions is entropy driven. TX-100 addition to SS micellar solutions induces the dissociation of SS micelles. As compared to the room temperature, the mixed micelles at elevated temperatures were large in size suggesting that the ellipsoidal micelles in mixed state grow along their major axis that is typically characteristic of the micelles of the individual nonionic SS or TX-100 surfactants at temperatures close to the turbid point.

Studies on the effect of ethanol on the solvation behaviour of thiamine hydrochloride in water

The specific conductance of Thiamine hydrochloride in water and water-ethanol mixtures was measured at different temperatures 283, 293, 303 and 313 K. Kraus-Bray and Shedlovsky models of conductivity were used for analyzing conductance data. The limiting molar conductance, association constant Ka, energy of activation of the rate process Ea, and related thermodynamic parameters have been determined. Based on viscosity of the solvent, Walden product and Stokes molecular radius were also been determined. Born model of ion solvation was proved. Standard thermodynamic parameters of association (Ga, Ha and Sa) were calculated and discussed. The results show the decrease in limiting molar conductance and increase in Ka with decrease in relative permittivity. Such computed values have been used to discuss the solvation behaviour of Thiamine hydrochloride in water-ethanol mixtures.

Thermodynamic parameters for the binding process of the OH− ion with the dissipative structures. Calorimetric and conductometric titrations

Conductometric and calorimetric titrations of Extremely Diluted Solutions (EDS) were performed by adding HCl or NaOH solutions. The aim of this study is to obtain further confirmation of the hypothesized presence, in the EDS, of molecular aggregates of water molecules. The measurements on the EDS evidenced some relevant differences compared to those on solutions with just water as solvent. The conductivity and the pH caused by adding the titrant, namely NaOH or HCl, were markedly different to those of the control solutions. We suppose that the preparation procedure of the EDS could produce non-equilibrium changes in the supramolecular structure of water. The experimental results were interpreted by considering the interactions that can take place between the OH− or H3O+ and the hypothesized molecular aggregates of water molecules i.e. dissipative structures. A comparison was made about the nature of the driving force that leads to the formation of the complexes between the two ions deriving from probes and the molecular aggregates of water molecules (dissipative structures). In this study, we have determined the thermodynamic parameters of association between molecular aggregates of water molecules (dissipative structures) in the EDS and OH− or H3O+ probe ions. The experimental results were interpreted by considering a favorable interaction between the H3O+ and OH− ions and the dissipative structures, due, probably, to steric hindrance and chemical affinity with the aggregates.

Effect of ethanol on the solvation behaviour of BiI 3 in acetonitrile, methanol and DMF as a function of temperature

This paper reports the results of the investigations carried out on the effect of added ethanol on the conductance behaviour of bismuth tri-iodide in acetonitrile, methanol and dimethylformamide at 288, 298, 308 and 318 K. From the experimental molar conductance value, the limiting molar conductance was determined for all the cases using the Shedlovsky model of conductivity. The limiting molar conductance was found to decrease continuously with the increase in the amount of ethanol either to CH 3CN, CH 3OH or DMF. In pure solvents, conductance varied in the order of CH 3CN>CH 3OH>DMF>C 2H 5OH. Association constant was determined in the three solvent systems. Results predicted the endothermic behaviour of the process in most of the cases. Energy of activation of the conducting rate process and thermodynamic parameters of association were calculated and reported. Walden product and corrected Stokes molecular radius were also computed. The solvation number of the species was calculated in the case of pure solvents and the value indicated the existence of solvent shared or separated ion pair in the system.

A comparison of biological and calorimetric analyses of multivalent glycodendrimer ligands for concanavalin A

The cluster glycoside effect — the observation that multivalent glycosides bind to their polyvalent protein receptors with apparent affinities greater than those that can be rationalized solely on the basis of valency — is by now a well established phenomenon. As part of a continuing effort to provide a molecular basis for the cluster glycoside effect, we report here the synthesis of two series of mannosylated dendritic ligands and their performance in a range of competitive and non-competitive binding assays, including hemeagglutination inhibition (HIA), enzyme-linked lectin assays (ELLA) and isothermal titration microcalorimetry (ITC). The first series of ligands contained a semi-rigid glycylglycine spacer and showed no significant performance enhancement in any binding studies. The second series of ligands contained a flexible tetraethylene glycol spacer; these ligands showed marked enhancements at tetravalent and hexavalent levels in both HIA (IC 50=3 and<0.8 μM, respectively) and ITC (K A=6.2×10 4 and 1.5×10 6 M −1, respectively) studies. In all cases, the thermodynamic parameters of association are consistent with non-specific aggregation rather than enhanced lectin–ligand affinity. This conclusion is reinforced by the lack of enhancements in ligand activity observed in ELLA studies.

Calorimetric investigation of guanidinium-carboxylate interactions

Isothermal titration calorimetry was utilized to study the association between a series of guanidinium derivatives and tetrabutylammonium acetate. This technique provides a measure of association strength, stoichiometry of binding, as well as thermodynamic parameters of association from a single experiment. Guanidinium derivatives which can form bidentate linear hydrogen bonds with acetate show significant, exothermic binding in DMSO (Ka = 5600 M −1; ΔH = −3.6 kcal/mol), while derivatives which lack this bidentate linear hydrogen bonding interaction result in complexes where association is weaker (Ka ≈ 100 M −1) and enthalpically neutral or endothermic. Additionally calorimetry permits the complete assessment of the multiple binding equilibria when derivatives complex two equivalents of guest.

IR spectroscopic study of molecular associates of mesogenic cyanophenyls

Molecular association greathy affects the physicochemical properties of mesogenic cyanophenyls, which are currently widely used as molecular materials for optoelectronics. This paper reports on a polythermal IR spectroscopic study of molecular association for mesogenic alkyl/alkoxycyanobiphenyls and their hydrated and heteroaromatic analogs in nonpolar solutions, low-temperature inert matrices, and molecular condensate layers in the temperature ranges of 5–10 and 80–330 K. Correlation of the thermodynamic parameters of association with molecular structure of cyanophenyls is established.

Electrochemical and thermodynamic studies of the ion-pair formation of chloropentamminecobalt(III) ion in ethyl alcohol-water media containing different dicarboxylate ligands

The ion-pair dissociation constants, K D, of the ion-pair formed between chloropentamminecobalt(III) ion (CpX 2+) and a variety of dicarboxylate ligands, have been determined from EMF measurements of a cell composed of glass and calomel electrodes. Measurements were made in water and in aqueous binary mixtures of ethyl alcohol, over a wide range of solvent composition (0–60 wt% ethyl alcohol), at six different temperatures (ranging from 30 to 55°C at intervals of 5°C). The thermodynamic parameters of association Δ G ass 0, Δ H ass 0 and Δ S ass 0 have been calculated and discussed. Δ H ass 0–Δ S ass 0, Δ S ass 0–Δ S 1(or 2) 0, Δ G ass 0– G 1(or 2) 0 and Δ H ass 0–Δ H 1(or 2) 0 correlations among different solvent media and different dicarboxylate ligands were examined (where 1 and 2 denote the first and the second dissociation reactions of the studied dicarboxylic acids). The p K D value has been correlated with the dielectric constant of the medium according to Born's equation.

Roles of Hydrogen Bonding Residues in the Interaction between the α and β Subunits in the Tryptophan Synthase Complex: Asn-104 OF THE α SUBUNIT IS ESPECIALLY IMPORTANT

The interaction of the alpha subunit with the beta2 subunit of tryptophan synthase is known to be necessary for the activation of each subunit and for the catalytic efficiency of the alpha2beta2 complex. To elucidate the roles of hydrogen bonds in the interaction site between the alpha and beta subunits for subunit association, eight mutant alpha subunits at five hydrogen bonding residues (N104D, N104A, N108D, N108A, E134A, E135A, N157D, and N157A) were constructed, and the thermodynamic parameters of association with the beta subunit were obtained using a titration calorimeter. The N104D and N104A mutations remarkably decreased the stimulation activities, the association constants, and the association enthalpies. Although the association constant and the stimulation activities of E134A were reduced in the absence of salt, the change in the association enthalpy was relatively small, and the addition of salt could repair its defects. The substitutions at positions 135 and 157 did not affect the stimulation activity and decreased the Gibbs energy of association corresponding to the defect in 1 mol of hydrogen bond. The present results suggest that the alpha subunit which has a mutation at position 104 cannot fold into an intact conformation upon complex formation, resulting in reduced stimulation activities. The hydrogen bond with Asn-104, which is a conserved residue among 16 microorganisms, was especially important for alpha/beta interaction and mutual activation.

Thermodynamics of macrocyclic compounds I. Inclusion complexes of α- and β-cyclodextrins with some nonelectrolytes in water

The equilibrium constants for the association of a series of α,ω-alkanediols (S) with α- and β-cyclodextrins (CD) in water were estimated spectrophotometrically by the competitive binding effects of the diols on the association of CD with methyl orange. Effects of methanol, ionic strength and temperature on these interactions were also investigated to gain further knowledge on the mechanism of the inclusion process. Moreover, the thermodynamic parameters for association were derived and discussed. The linear correlation between the association constants and the partition coefficient of the diols in a diethyl ether-water system and the constant increment in Gibbs free energy per CH 2 group for the transfer of α,ω-alkanediols from the aqueous phase to the cyclodextrin cavity suggest that the binding mechanism is of a hydrophobic nature. Furthermore, the size of the cavity of cyclodextrins plays an important role in the association process. The α-CD cavity was found to have a greater affinity for the diols than the β-CD, whereas the reverse is the case for methyl orange.

Spectral study of association of nitroamines

This paper reports on the study of the thermodynamic parameters of association carried out by a spectral investigation of CC14 solutions of nitroamines, whose proton-donor capacity in the H bond has already been investigated. Here the series of nitroamines is somewhat shortened since, because of the low solubility of some of the nitroamines in CC14, a measurable concentration of the associated form could not be obtained.

Investigations of the autoassociation of phenol by the NMR method

1. The chemical shift of the OH group of the phenol monomer was determined. 2. In phenolinert solvent systems a monomer-trimer equilibrium is observed, with the exception of low concentrations of phenol (~0.03 mole fraction). 3. The chemical shift of the signal of the OH group of the phenol trimer depends on the temperature. 4. The solvent CCl4 is not entirely inert. 5. The constants and thermodynamic parameters of association in systems of phenol and in inert solvent were determined. 6. In all the systems studied the enthalpy remains constant, while the entropy varies from system to system.

Polymerization of ethylene oxide by alkali metal-naphthalene complexes in tetrahydrofuran

The kinetics of ethylene oxide polymerization in THF, with Na, K and Cs-naphthalene complexes as initiators, have been studied in detail. Polymerization is first order with respect to monomer without chain termination or transfer. The complicated dependence of the polymerization rate on active centre concentration is due to strong association. Rate constants of the propagation and thermodynamic parameters of association have been determined from this dependence. Contact type ion pairs are shown to be the active propagating species. Their activity increases and association ability decreases from Na + to Cs +. Solvation of the active species plays the decisive part in this process.

Thyroxine-Protein Interactions: IV. THERMODYNAMIC VALUES FOR THE ASSOCIATION OF THYROXINE WITH HUMAN SERUM ALBUMIN

Abstract The effect of temperature on the binding of l-thyroxine to human serum albumin and to albumin defatted by the method of Goodman has been studied by equilibrium dialysis. The albumin was first freed of other contaminating thyroxine-binding proteins by zone electrophoresis on a preparative Porath cellulose column. Albumin, both native and defatted, shows only a small temperature dependence of binding. At 30° and 37° (pH 7.4), the constants that best fit the binding data for native albumin are n1 = 0.85 ± 0.15, k'1 = 1.41 x 106 m-1 ± 0.2, n2 = 5 or 6, k'2 = 0.095 x 106 m-1 or 0.067 x 106 m-1. At 6° the constants for native albumin are n1 = 1, k'1 = 1.6 x 106 m-1, n2 = 6, k'2 = 0.05 x 106 m-1. For defatted albumin the primary binding constants at 30° are n1 = 1, k'1 = 1.4 x106m-1. At 6° the primary binding constants for defatted albumin are n1 = 1, k'1 = 1.6 x 106 m-1. The thermodynamic parameters for association at the primary binding site are (a) for native albumin, ΔF° = -8.40 kcal per mole (30°, n1 = 1), ΔH° = -2.02 kcal per mole, ΔS° = +21 e.u.; (b) for defatted albumin, ΔF° = -8.51 kcal per mole (30°), ΔH° = -0.94 kcal per mole, ΔS° = +25 e.u. Chloride ions inhibit thyroxine binding to albumin. At 30° and pH 7.4, thyroxine binding to albumin is reduced by 50% in the presence of 0.1 m NaCl.