Effects of micellar structure on solubilization ofn-octane andn-octanol

Influence of Hydrophobic and Hydrophilic Chain Length of CiEj Surfactants on the Solubilization of Active Pharmaceutical Ingredients

Up to 90% of all newly developed active pharmaceutical ingredients (APIs) are poorly water soluble, most likely also showing a low oral bioavailability. In order to increase the aqueous solubility of these APIs, surfactants are promising excipients to increase both solubility and consequently bioavailability (e.g., in lipid- and surfactant-based drug delivery systems). In this work, we investigated the influence of hydrophobic and hydrophilic chain lengths of C_iE_j surfactants (C₈E₆, C₁₀E₆, and C₁₀E₈) toward the solubilization of fenofibrate, naproxen, and lidocaine. Furthermore, we investigated the partitioning of these APIs between the surfactant aggregates and the surrounding aqueous bulk phase. For all APIs considered, we determined the locus of API solubilization as well as the individual aggregation numbers (N_agg) of surfactants and API molecules in an API/surfactant aggregate. We further determined the hydrodynamic radius (R_h) of the API/surfactant aggregates in the absence and presence of the APIs. The size of the API/surfactant aggregates (N_agg, R_h) passes through a minimum upon lidocaine solubilization; it gradually increases upon naproxen solubilization and is almost constant upon fenofibrate solubilization. The results give valuable insights into the solubilization mechanisms of APIs in the C_iE_j surfactant aggregates. Our results reveal that fenofibrate is solely solubilized in the hydrophobic core of the C_iE_j surfactant aggregates, as only the hydrophobic chain length of the surfactant influences its solubilization. Naproxen is solubilized in the palisade layer of the surfactant aggregates, as both the hydrophobic and hydrophilic chain lengths are decisive for its solubilization. Lidocaine is mainly solubilized in the rather hydrophilic corona region of the surfactant aggregates, as the hydrophilic chain length of the surfactant governs its solubilization. The results further reveal that the hydrophilic/lipophilic balance is not an appropriate measure to estimate the solubilization capacity of surfactant aggregates.

Solubilization of Aldehydes and Amines in Aqueous CiEj Surfactant Aggregates: Solubilization Capacity and Aggregate Properties

Hydroformylation of olefins to aldehydes and subsequent reductive amination of aldehydes to amines takes place in an aqueous system using a water-soluble catalyst. It is limited to short-chain molecules due to an insufficient solubility of long-chain molecules in water. A promising approach to increase the solubility of long-chain aldehydes and amines is the addition of surfactants to the aqueous phase. In this work, we thus determined the solubilization capacity (SC) of different nonionic C_iE_j surfactants (C₈E₆, C₁₀E₆, and C₁₀E₈) toward long-chain aldehydes and amines. We used static and dynamic light scattering techniques to investigate the influence of both the surfactant and solute molecular structures on the SC as well as on the aggregation number (N_agg) and hydrodynamic radius (R_h) of mixed aggregates. Our data reveals that an optimum ratio of hydrophobic to hydrophilic chain length of C_iE_j surfactants exists where the SC toward long-chain aldehydes and amines possesses a maximum. Further, the size of the aggregates (N_agg, R_h) passes through a minimum upon amine solubilization, while upon aldehyde solubilization, the aggregate size increases gradually. The results shown in this work give valuable insights to the solubilization of aldehydes and n-amines into nonionic C_iE_j surfactants and facilitate the search of suitable surfactants for hydroformylation and reductive amination as "green" solvents based on the detailed knowledge about the aggregate structure.

Effect of Temperature on the Mixed Micellar Tetradecyltrimethylammonium Bromide-Butanol System

The TTAB-butanol system has been studied over a temperature range of 15 to 35 degreesC and at butanol concentrations up to 0.3 mol/kg. The CMC vs temperature curves have a smooth minimum whose location is not markedly influenced by alcohol presence. The molar fraction of butanol in the micelles and the entropy of micellization have been calculated using a theoretical treatment of critical micelle concentration data based on excess thermodynamic quantities. The heat capacity of micellization has been obtained and compared with results predicted by a recent thermodynamical theory which describes a universal behavior exhibited by ionic surfactants. Both the entropy and the enthalpy of micellization increase with alcohol concentration. The butanol molar fraction in micelles enables us to estimate the standard free energy of solubilization, which is found to decrease with temperature. It is important to emphasize the chance of predicting the value of these interesting thermodynamic quantities without the need for measuring them. The degree of micelle ionization has also been evaluated using two different methods, and no significant differences have been observed. Copyright 1997 Academic Press.