Application of molecular sieve technique in solubilization studies of benzoic acid in solutions of cetomacrogol 1000

Equilibrium dialysis of barbituric acids up to high concentrations of aqueous sodium alkylsulfonate solutions

The partition coefficient K of four barbituric acids has been determined by the equilibrium dialysis method in aqueous solutions of sodium alkylsulfonate at 25 degrees C. The results obtained from dilute solutions to 0.3 M surfactant concentration are compared with solubility data for the same systems. The K values as deduced from Langmuir or Freundlich isotherms decrease with increasing surfactant concentration. The detergent used was an impure commercial product of known composition, which could be considered as a mixed surfactant. The change of partition coefficient with surfactant concentration as obtained from equilibrium dialysis experiments has been interpreted by assuming a continuous change of micelle composition.

Effects of surfactants on the aqueous stability and solubility of beta-lactam antibiotics

Studies were undertaken to elucidate the interaction between beta-lactam antibiotics and surfactant micelles and to examine the effects of surfactants on their aqueous stability and solubility. The apparent binding constant of the micelle-antibiotic complex was determined as a function of the solution pH at 37 degrees and mu = 0.15 by the dynamic dialysis method and hydrolysis study. In the interaction with nonionic and anionic micelles of polyoxyethylene-23-lauryl ether (I) and sodium lauryl sulfate (II), large differences were noted in the binding constants between the undissociated and ionized species of penicillins. However, the cationic surfactants, cetyltrimethylammonium bromide (III), showed no significant difference in the binding constants for both species. Acid degradation of penicillins was protected in micellar solutions of I and III but was facilitated in micelles of II. The surfactants exerted no influence on the neutral degradation of the antibiotics used. The solubilization of penicillin V acid by micelles of I was studied at pH 2.0 and 35 degrees. The solubility increased threefold in the presence of 10 mM I.

Effect of a second solubilizate on the partition coefficient of drugs in micellar solution and their permeation rate across an artificial membrane

The distribution of a solubilizate between micelles and the aqueous phase does not obey a simple partition law when a second solubilizate species is present. Alterations of the apparent partition coefficient cannot be explained in terms of a simple displacement mechanism, following the interaction of both solubilizates with the same site of the micelle. A non linear increase in solubilizate association to micelles following an increase in surfactant concentration is observed in the presence of a second solubilizate. A depression in the cloud point temperature follows the addition of a second species and is such that cannot be interpreted as a simple additive effect. Alteration of the apparent partition coefficient in a miscellar solution has an effect on the permeation rate of the solubilizate across an artificial membrane. Biopharmaceutical implications are discussed.

Interaction of substituted benzoic acids with polysorbate 20 micelles

Equilibrium solubilities of a series of substituted benzoic acids in different concentrations of polysorbate 20 at controlled pH were measured. The maintenance of pH was achieved using a pH-stat assembly. A linear relationship was found between the amount of benzoic acid solubilized and surfactant concentration. As solubilizate polarity increased, the amount solubilized also increased. Solubility data were analyzed, and the interaction between solubilizate molecules and micelles was calculated in terms of partition coefficients of ionized and unionized molecules between aqueous and micellar phases. A linear relationship between pi values (log partition coefficients) of functional groups and aqueous-micellar partition coefficient was found.

Interaction of preservatives with cetomacrogol

The interaction of a number of commonly used preservatives (benzoic acid, p-hydroxybenzoic acid, methyl p-hydroxybenzoate, propyl p-hydroxybenzoate and chloroxylenol with the non-ionic surfactant cetomacrogol was examined and a comparison made of various methods of expressing this interaction. It is suggested that the Scatchard equation is the most satisfactory equation for describing the binding data. Binding parameters determined from a Scatchard plot in the concentration range of free preservative appropriate for antimicrobial activity can be used to calculate the total concentration of preservative required in the surfactant system.