Search Results

You are looking at 1 - 10 of 223 items for :

  • "complex formation" x
  • Refine by Access: All Content x
Clear All

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.

Restricted access

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.

Restricted access

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.

Restricted access

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

Restricted access

. 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

Restricted access

Abstract  

The formation of crystalline inclusion complex of triamterene with β-cyclodextrin (β-CD) was studied, evaluating the thermal behaviour and dispersion state of this drug in different types of binary systems. Spray-drying and co-grinding (oscillating mill) mixtures of triameterene with β-CD were prepared in 1∶1 molar ratio. The changes of crystalline properties of original (untreated) triamterene, β-CD, and composites obtained by co-grinding and spray-drying were investigated in comparison with those produced in simple physical mixtures. The thermal behaviour of the different samples was investigated using DTA. X-ray diffraction was applied as a complementary technique. The results have been explained by formation of amorphous drug particles on spray-drying samples and co-grinding or alternatively by means of a solid dispersion formation or a combination of these two. A contamination effect by grinding media was also observed as increasing grinding time.

Restricted access

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.

Restricted access

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.

Restricted access

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.

Restricted access