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Abstract  

The influence of H2O–EtOH and H2O–Acetone mixed solvents at various compositions on the thermodynamics of complex formation reaction between crown ether 18-crown-6 (18C6) and glycine (Gly) was studied. The standard thermodynamic parameters of the complex [Gly18C6] (log K°, Δr H°, Δr S°) were calculated from thermochemical data at 298.15 K obtained by titration calorimetry. The complex stability and its formation enthalpy increase with increasing the non aqueous component concentration in both mixed solvents. The thermodynamic data were discussed on the basis of the solvation thermodynamic approach and the solvation contributions of the reagents and of the complex to the complex stability were analyzed.

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reason, both the methods require the presence of an organic ligand able to strongly bind the heavy metal for its selective recovery. Therefore, the determination of the thermodynamic parameters of complex formation with Cd(II) in water or organic

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Abstract  

The interaction between erythritol and 4-hexylresorcinol during heating was investigated by thermal analysis, powder X-ray diffractometry and infrared spectroscopy. A phase diagram was constructed by measuring the thermal behaviour of various resolidified physical mixtures of erythritol and 4-hexylresorcinol. The phase diagram revealed complex formation between erythritol and 4-hexylresorcinol with incongruent melting at 84C; the stoichiometry was a molar raio of 1:2 erythritol:4-hexylresorcinol. The complex gave diffraction peaks at 2θ=5.6 and 11.2 in the X-ray powder diffraction pattern. In the infrared spectrum, a new peak due to the complex was observed at 3504 cm–1. The complex prepared by grinding and evaporation had the same molecular arrangement as the complex prepared by sealed heating.

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. Therefore, the CdEdta 2− complex is coordinately unsaturated, resulting in mixed complex formation of the type CdEdtaL. Earlier, the thermodynamic studies of CdEdtaEn formation have been carried out [ 2 ]. The author proposed the possible monodentate

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Abstract  

The complex formation of Ag+ with polyether 18-crown-6 (18C6) and their solvation have been studied using calorimetric and potentiometric methods in H2O-EtOH solvents in wide range of ethanol concentration. The standard enthalpies of dissolution AgNO3, AgClO4 and 18C6 in aqueous-ethanol solvents are obtained. The stability of a complex [Ag18C6]+ grows with increasing the EtOH content a solvent. Using the method based on the thermodynamic characteristics of solvation of metal-ion, ligand and complex-ion the interpretation of the results has been given.

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Abstract  

The complexation of urea and some guanidinium derivatives by the ligands 15-crown-5, 18-crown-6, benzo-18-crown-6 and diaza-18-crown-6 in methanol has been studied by means of calorimetric titrations. The complex formation is mainly favored by entropic contributions. The number of solvent molecules released during the complex formation is responsible for the stability of the complexes formed.

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Abstract  

Calorimetry, densimetry, 1H NMR and UV–vis spectroscopy were used to characterize inclusion complex formation of hydroxypropylated α- and β-cyclodextrins with meta- and para-aminobenzoic acids in aqueous solutions at 298.15 K. Formation of more stable inclusion complexes between para-aminobenzoic acid and cyclodextrins was observed. The binding of aminobenzoic acids with hydroxypropyl-α-cyclodextrin was found to be enthalpy-governed owing to the prevalence of van der Waals interactions and possible H-binding. Complex formation of hydroxypropyl-β-cyclodextrin with both acids is mainly entropy driven. The increased entropy contribution observed in this case is determined by dehydration of solutes occurring during the revealed deeper insertion of aminobenzoic acids into the cavity of hydroxypropyl-β-cyclodextrin. By comparing complex formation of aminobenzoic acids with native and substituted cyclodextrins it was found that the availability of hydroxypropyl groups slightly influenced the thermodynamic parameters and did not change the binding mode or driving forces of interaction.

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Abstract  

The inclusion complex formation of riboflavin (RF) with hydroxypropyl-β-cyclodextrin (HP-β-CD) in water was investigated by 1H NMR, UV-vis spectroscopy, and solubility methods. A 1:1 stoichiometry and thermodynamic parameters of complex formation (K, Δc G 0, Δc H 0, and Δc S 0) were determined. Complexation was characterized by negative enthalpy and entropy changes due to prevalence of van der Waals interactions and hydrogen bonding between polar groups of the solutes. A partial insertion of RF into macrocyclic cavity was revealed on the basis of 1H NMR data and molecular mechanics calculation. Location of benzene ring of RF molecule inside the hydrophobic cavity of HP-β-CD results in an increase of aqueous solubility of the former.

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Abstract  

The mixed-ligand complex formation in the system Cu2+−Edta4−−(CH2)6(NH2)2 (L), where L is hexamethylenediamine has been calorimetrically, pH-potentiometrically and spectrophotometrically studied in aqueous solution at 298.15 K and the ionic strength of I = 0.5 (KNO3). The thermodynamic parameters of formation of the CuEdtaL2−, CuEdtaHL (CuEdta)2L4− and (CuEdta)2En4− complexes have been determined. The most probable coordination mode for the complexone and the ancillary ligand in the mixed-ligand complexes was discussed.

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Abstract  

Titrations of Pu(IV) with HNO3 in a series of aqueous HClO4 solutions ranging in ionic strength from 2 to 19 molal were followed using visible and near-infrared absorption spectrophotometry. The Pu 5f-5f spectra in the visible and near IR range change with complex formation. At each ionic strength, a series of spectra were obtained by varying nitrate concentration. Each series was deconvoluted into spectra of Pu4+ (aq), Pu(NO3)3− and Pu(NO3)2 2+ complexes, and simultaneously their formation constants were determined. When corrected for the incomplete dissociation of nitric acid, the ionic strength dependence of each formation constant can be described by two parameters, β0 and Δε using the formulae of specific ion interaction theory.

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