Search results for "Distribution constant"
showing 7 items of 17 documents
Effect of ionization and the nature of the mobile phase in quantitative structure-retention relationship studies.
2005
Abstract The octanol–water distribution constant, commonly called partition coefficient, Po/w, is a parameter often retained as a measure of the hydrophobicity of a molecule. log Po/w, for a given molecule, can be conveniently evaluated constructing correlation lines between standard retention factor logarithms (log k) in reversed-phase liquid chromatography (RPLC) and standard log Po/w values. Many compounds of pharmaceutical interest can be quite hydrophobic and have, simultaneously, basic nitrogen atoms or acidic sulfur containing groups in their structure. This renders them ionizable. The hydrophobicity of the molecular drug form (Po/w value) is completely different from its ionic form …
Heat capacities, volumes and solubilities of pentanol in aqueous surfactant solutions
1989
Apparent molar heat capacities and volumes of pentanol (PentOH) 0.05m in dodecyltrimethylammonium chloride (DTAC), dodecyldimethylammonium chloride (DDAC) and dodecylamine hydrochloride (DAC) micellar solutions were measured at 25°C. They were assumed to approach the standard infinite dilution values and rationalized by means of previously reported equations. The distribution constant between the aqueous and the micellar phase and heat capacity and volume of pentanol in both phases were thus derived. The results show that the presence of methyl groups on the surfactant head group does not appreciably influence the apparent molar volume and heat capacity of pentanol in micellar phase and the…
Standard partial molar volumes of alcohols in aqueous dodecyltrimethylammonium bromide solutions
1990
Density measurements of water-dodecyltrimethylammonium bromide (DTAB)-alcohol ternary systems as a function of alcohol and surfactant concentrations were carried out at 25°C. The alcohols were propanol (PrOH), 2-propanol (2-PrOH) and hexanol (HexOH). The apparent molar volume Vϕ,R of alcohols have been calculated and the standard (infinite dilution) partial molar volumes of alcohols V R at each surfactant concentration were obtained by means of a least squares fit of Vϕ,R vs. the alcohol concentration. The V R vs. surfactant concentration curves have been rationalized in terms of the partial molar volume of alcohol in the aqueous V f and the micellar V b phases and the distribution constant…
Calorimetric study on the solubilization of some primary alcohols by reversed AOT micelles
1989
A calorimetric method to evaluate, at the same time, the distribution constant and the standard enthalpy of transfer of a solute partitioned between organic phase and reversed micelles is proposed. The method was applied to the partition of methanol, 1-propanol and 1-pentanol between n-heptane and AOT reversed micelles containing water at 25°C. The results show that the distribution constant decreases as the alcohol alkyl chain length increases and that the solubilization site can change as the water content of reversed AOT micelles increases. In particular, at sufficiently high water content, methanol seems to be preferably solubilized in the aqueous pseudophase whereas 1-pentanol prefers …
Enthalpies of Mixing of Some Primary Hydrogenated and Fluorinated Alcohols and Sodium Dodecanoate Aqueous Solutions
1993
Abstract The enthalpies of transfer from water to the surfactant solutions ΔH(W → W + S) of some hydrogenated and fiuorinated alkanols and of sodium dodecanoate NaL were determined. In the premicellar region the measurements were carried out as functions of both the additive and the surfactant concentrations in order to evaluate the interaction parameters between the additive and the surfactant molecules. It is shown that in this region, pair, triplet, and quadruplet interaction parameters between unlike solute molecules contribute to ΔH(W → W + S). Within the large uncertainty with which these parameters are determined because of the very narrow surfactant and alcohol concentration interva…
Heat capacities, volumes and solubilities of pentanol in aqueous alkyltrimethylammonium bromides
1988
Apparent molar heat capacities and volumes of pentanol, 0.05m in decyl-, tetradecyl- and hexadecyltrimethylammonium bromides micellar solutions, were measured at 25°C. They were assumed to approach the standard infinite dilution values and rationalized by means of previously reported equations following which the distribution constant between the aqueous and the micellar phase, heat capacity, and volume of pentanol in both phases are simultaneously derived. The present results show that the volume of the micellar core does not seem to have a significant effect on the apparent molar volume and heat capacity of pentanol in the micellar phase and on the free energy of transfer of pentanol from…
Heat capacities of butanol and pentanol in aqueous dodecyltrimethylammonium bromide solutions
1987
Heat capacities of the ternary systems water-dodecyltrimethylammonium bromide (DTAB)-butanol and water-DTAB-pentanol were measured at 25°C. The standard partial molar heat capacities of pentanol in micellar solutions show a maximum at about 0.35 mol-kg−1 DTAB that has been attributed to a micellar structural transition. This maximum tends to vanish by increasing the alcohol concentration and by decreasing the alcohol alkyl chain length; in the case of butanol it was not detected. The behavior of the standard partial molar heat capacities of alcohols in micellar solutions in the region above the cmc and below the structural transition was explained using a previously reported mass-action mod…