Abstract
The octanol-water partition coefficient (Po/w), or the octanol-water distribution coefficient (Do/w) for ionized compounds, is a key parameter in the drug development process. In a previous work, this parameter was estimated through the retention factor measurements in a sodium dodecyl sulfate (SDS) - microemulsion electrokinetic chromatography (MEEKC) system for acidic compounds. Nonetheless, when ionized basic compounds were analyzed, undesirable ion pairs were formed with the anionic surfactant and avoided a good estimation of log Do/w. For this reason, an alternative MEEKC system based on a cationic surfactant has been evaluated to estimate Po/w or Do/w of neutral compounds and ionized bases. To this end, it has been characterized through the solvation parameter model (SPM) and compared to the octanol-water partition system. Results pointed out that both systems show a similar partition behavior. Hence, the log Po/w of a set of neutral compounds has been successfully correlated against the logarithm of the retention factor (log k) determined in this MEEKC system. Then, the log Do/w of 6 model bases have been estimated at different pH values and they have been compared to data from the literature, determined by the reference shake-flask and potentiometric methods. Good agreement has been observed between the literature and the estimated values when the base is neutral or partially ionized (up to 99% of ionization).
Highlights
Chromatographic systems based on different techniques such as high performance liquid chromatography (HPLC) and electrokinetic chromatography (EKC) have been widely used to determine biopartitioning properties [1,2,3,4,5,6]
The aim of the present study is to evaluate the applicability of microemulsion electrokinetic chromatography (MEEKC) measurements to estimate the log Po/w and log Do/w of ionized basic compounds, which are positively charged in their ionized form
The TTAB-MEEKC system has been characterized through the solvation parameter model (SPM) in order to later evaluate its similarity with the octanol-water partition system
Summary
Chromatographic systems based on different techniques such as high performance liquid chromatography (HPLC) and electrokinetic chromatography (EKC) have been widely used to determine biopartitioning properties [1,2,3,4,5,6]. In these systems, the compounds experience a partition between an aqueous phase and a stationary phase, for HPLC systems, or a pseudoestationary phase, for EKC systems, similar to the partition that compounds experience in a biological system. The direct method to determine this parameter is the shake-flask method It is a tedious procedure and it is not fully automated. The estimation of Po/w through high-throughput systems such as chromatographic ones is of great interest
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