Determination of distribution constants of antioxidants by electrokinetic chromatography

Abstract

Liposome electrokinetic chromatography and micellar electrokinetic chromatography were used for studying the lipophilic properties of natural antioxidants, specifically phenolic acids and flavonoids. The employed negatively charged liposomes were composed of mixtures of 1-palmitoyl-2-oleyl-sn-glycerophosphatidylcholine and 1-palmitoyl-2-oleoyl-sn-phosphatidylserine or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol. In micellar electrokinetic chromatography, sodium dodecyl sulphate micelles were used as the pseudostationary phase. The retention factors of the studied compounds were determined at pH 7.4. The corresponding distribution constants were calculated from the experimentally determined retention factors and the phase ratios of the liposome dispersions and the micellar system. The distribution constants between the aqueous phase and the liposomes or micelles were compared with octanol/water partition or distribution constants of the studied compounds, which were predicted using the ACD/Labs Percepta Platform—PhysChem Module. Our results indicate that the correlations between the distribution constants of the two tested liposome systems were much stronger than those between the liposome/micellar systems. The correlations between the n-octanol phase and the liposome phases were similar to that between n-octanol and the micellar phase. Our data shows that electrokinetic chromatography is an efficient method for determining partition coefficients of compounds, but the type of pseudostationary phase has a clear impact on the values.

Keywords:

• antioxidants
• distribution constants
• electrokinetic chromatography
• liposome
• retention factors

Public Interest Statement

Lipophilicity is a property of a compound, which is related to its solubility between water and an organic (lipid) phase. Lipophilic compounds often display high volumes of distribution and are therefore distributed amongst many different tissues and organs. The most common surrogate for lipophilicity is the octanol/water partition coefficient. Here, we used micellar electrokinetic chromatography (MEKC) and liposome electrokinetic chromatography (LEKC) for studying the lipophilic properties of natural antioxidants. By measuring the interactions between the compounds and the micelles or liposomes, we were able to determine the corresponding distribution constants of the compounds. Such values are of great importance for people in the field of pharma and medical science, because compounds’ lipophilicity is one of the most important properties determining the distribution of compounds in the body.

Competing Interests

The authors declare no competing interest.

Additional information

Notes on contributors

Jana Váňová

Susanne K. Wiedmer is university lecturer at the Department of Chemistry at the University of Helsinki (Finland). Susanne Wiedmer’s group has expertise in chromatographic and capillary electromigration (CE) techniques, field flow fractionation (AF4) and in biosensing methods. Much focus has been on liposomes and on liposome-analyte interactions using various modes of CE, on studying interactions between biomembrane-imitating surfaces and analytes (by CE, nanoplasmonic sensing and quartz crystal microbalance), as well as on characterising lipid vesicles and particles (by CE and AF4). Recently, emphasis has been on the determination of distribution constants of analytes using liposomes of synthetic lipids or lipids extracted from biological samples. Ionic liquids have been another research target in the group, and focus has been on the determination of the toxicity of novel synthesised ionic liquids. Liposomes, cells and zebrafish models have been used for that purpose.