The electrical conductivities of aqueous solutions of quinic acid and its sodium salt were measured from 293.15 to 328.15 K in steps of 5 K. The molar conductivities of the sodium salt were treated ...by the Lee–Wheaton equation, in the form of Pethybridge and Taba, and the Kohlrausch equations. The limiting molar conductivities of the quinate anion were estimated, as well as the corresponding ionic association constants and standard thermodynamic functions of the ionic association reaction. The hydrodynamic radius of the quinate anion was calculated from the Walden rule and compared with the van der Waals radius. The dissociation constant of quinic acid was evaluated from the known value of the limiting molar conductivity of quinic acid using the conductivity equation of Pethybridge and Taba. The standard thermodynamic functions of the dissociation process, i.e., the Gibbs energy, enthalpy, entropy and heat capacity, were obtained using the non-empirical procedure given by Clarke and Glew. The standard thermodynamic functions of dissociation of quinic acid are discussed in terms of solute–solvent interactions and stabilization of the quinate anion due to hydrogen bonding of the α-hydroxyl group to the carboxyl group.
In the course of a study on artificial sweeteners, new crystal structures of cyclamic acid, sodium cyclamate, potassium cyclamate, ammonium cyclamate, rubidium cyclamate and tetra‐n‐propylammonium ...cyclamate have been determined. Cyclamic acid exists in its zwitterionic form in the crystalline state. The zwitterions are connected through hydrogen bonds of the N—H...O type to form two‐dimensional sheets. The sodium, potassium, ammonium and rubidium cyclamates are isostructural, with the cyclamate moieties linked through hydrogen bonds into linear chains. Taking into account the connectivity through cations, two‐dimensional layers with a hydrophobic surface are constructed. In tetra(n‐propyl)ammonium cyclamate the large, non‐coordinating cation apparently prevents the formation of chains and thereby facilitates the centrosymmetric head‐to‐head discrete dimeric arrangement of the cyclamate moieties.
From commercially available pectin, (OBIPEKTIN AG), pectic acid was isolated by alkaline catalysed hydrolysis and physicochemically characterized. The conductivities of aqueous solutions of ...tetramethyl-, tetraethyl-, tetra-
n-propyl- and tetra-
n-butyl pectate were determined. The concentration dependence of the conductivity as well as the conductometric titration of the investigated systems exhibited typical polyelectrolyte behaviour. The mobility of the polyelectrolyte solute was found to be influenced by the nature of the counterion. The calculated values of the molar conductivity deduced on the basis of the Manning limiting law were found to be lower than the experimental ones. The fraction of free counterions was evaluated and found to depend on the concentration and on the nature of the counterion.
The viscosities of aqueous solutions of some poly(ethylene glycol)s (PEG) with nominal molecular weights ranging from 300 to 35 000 g mol
−1 were determined up to a concentration of 0.3 g cm
−3 at ...298.15 K. From these data the intrinsic viscosity and the viscosity average molecular weight of the solute were calculated. The viscosity coefficients
B were evaluated and hence the partial molar Gibbs free energy of activation of viscous flow of solute at infinite dilution was calculated and interpreted in terms of the relative effects of solute on the ground and transition state solvent. The hydration numbers were determined and compared with available values in the literature.
Cholesterol complexes with tri-
n
-butyl phosphate, tri-
n
-octylamine,
N
,
N
-dimethylacetamide, and cyclohexanone in benzene and toluene solutions were studied using conventional IR spectroscopy. ...The spectra were recorded in the region of fundamental OH stretching (3,700–3,100 cm
−1
) at 298 K. The experimental spectra were resolved into bands corresponding to the cholesterol monomer and particular oligomeric and complex species. The formation constants of complexes were determined from the-least squares plots of the linearized expressions of Bjerrum’s formation function. The stoichiometry of complexes was also identified in this way. The identification of the particular resolved bands was performed from their location, and from the dependence of their intensity on the cholesterol monomer and free base concentration.
Graphical Abstract
The hydrogen bonding interactions of moderately associated cholesterol with tri-
n-butylphosphate, tri-
n-octylamine and cyclohexanone in dilute solutions of tetrachloromethane, 1,2-dichloroethane ...and trichloromethane were studied by conventional IR spectroscopy. Information on the stoichiometry of the complexes formed was derived from least squares plots of the linearized expressions of Bjerrum's degree of system formation. The formation constants of the complexes were also determined in this way. The spectra recorded in the O
H region from 3100 to 3700
cm
−1 were resolved in to the bands of the cholesterol species and the complexes formed. The complexes responsible for the observed bands were recognized from the dependence of their intensity on cholesterol monomer and free base concentration and from their frequency locations. The presence of the complexes B···HO(R) and B···HO(R)···HO(R) with tri-
n-butylphosphate and tri-
n-octylamine was established in all of the solutions and also for the system cholesterol
+
cyclohexanone in 1,2-dichloroethane. On the other hand, for cholesterol bonding to cyclohexanone in tetrachloromethane, the model considering complexes with 3:1 and 1:1 stoichiometry seemed the most appropriate.
Tetraalkylammonium salts of cyclohexylsulfamic acid were used as model systems to study the ion-pairing process of hydrophobic ions.
The electric conductivities of aqueous solutions of tetramethyl-, ...tetraethyl-, tetrapropyl-, tetrabutyl- and tetrapentylammonium salts of cyclohexylsulfamic acid were measured from 278.15
K to 303.15
K (in steps of 5
K) in the concentration range ∼
0.2
∙
10
−
3
<
c (mol
dm
−
3
)
<
∼
6
∙
10
−
3
. Evaluation of the limiting molar conductivity
Λ
∞
and the association constant
K
A was based on the low concentration chemical model of electrolyte solutions, that includes short-range forces. From the temperature dependence of the limiting molar conductivities Eyring's enthalpy of activation of charge transport was estimated. The standard Gibbs free energy, enthalpy and entropy of the ion-pairing process were calculated from the temperature dependence of the ion-association constants. It was found that in the investigated systems the ion association can be interpreted as strongly enthalpy driven process that does not include any important release of water molecules from the hydration shells of ions. The non-Coulombic contribution to the Gibbs free energy was evident and favours the association process.
