Retention of substituted coumarins using immobilized artificial membrane (IAM) chromatography: A comparative study with n-octanol partitioning and reversed-phase HPLC and TLC

The chromatographic indices log kwIAM have been determined by HPLC on an immobilized artificial membrane column for a set of coumarin derivatives. The investigated compounds contain substituted amidoximes, or substituted heterocycles directly attached to the coumarinic skeleton. The log kwIAM values were compared to previously reported data of octanol-water partition coefficients and extrapolated capacity factors determined by reversed phase HPLC and TLC. The log kwIAM values of the investigated compounds were found to be comparable with the corresponding log P values, although they constitute a lower lipophilicity scale due to the reduced hydrophobic environment of the IAM stationary phase. These features were exemplified in their interrelationship with a slope close to unity and a large negative intercept. In contrast their comparison with the corresponding HPLC and RP-TLC capacity factors revealed differences in the retention mechanism reflected in slopes lower than unity, which were postulated to be due to secondary interactions under the reversed phase chromatographic conditions. However, conformational effects in the molecular structures of the coumarin derivatives were found to have a similar impact in their affinity for the IAM and octadecyl silane stationary phases, while they did not affect their octanol-water partitioning.