Enantioselective retention mechanisms of dipeptides on antibiotic-based chiral stationary phases. II. Effect of the methanol content in the mobile phase

• Published in: Journal of Chromatography A 2020-08, Vol.1626, p.461371, Article 461371
• Main Authors: Asnin, Leonid D., Kopchenova, Margarita V., Vozisov, Stepan E., Klochkova, Mariya A., Klimova, Yana A.
• Format: Article
• Language: English
• Subjects: Chiral chromatography; Dipeptides; Macrocyclic antibiotics; Retention mechanisms; Ristocetin A
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2020.461371

•Retention of dipeptides on Chirobiotic R was studied with methanol-water eluents.•Lipophilicity of dipeptide determines how retention depends on eluent composition.•Solvation in the bulk liquid and on the surface is important for retention.•Solvation on the surface and solvent displacement influence enantioselectivity.•Adsorption of methanol-water mixtures on Chirobiotic R was studied. Effect of mobile phase (water-methanol) composition on the enantioseparation of dipeptides on the chiral stationary phase Chirobiotic R was investigated using Ala-Ala, Leu-Leu, Gly-Leu, and Leu-Gly as case studies. The lipophilicity of dipeptides was found to be an essential factor in the dependence of their retention on the methanol percentage, the retention factor of lipophobic dipeptides increasing monotonously and that of lipophilic dipeptides changing according to an asymmetric U-shaped trajectory as methanol concentration increases. The behavior of enantioselectivity as a function of the methanol content also depends on the lipophilicity of dipeptide. For lipophilic Leu-Leu, the dependence has a dome-like shape, and for more lipophobic dipeptides, Ala-Ala and Gly-Leu, it is an increasing function of the methanol concentration. The importance of solvation equilibria in the bulk liquid and on the surface of the stationary phase for the total retention is discussed from the thermodynamic point of view. Special consideration is given to the adsorption of the water-methanol mixture on the surface of the Chirobiotic R stationary phase.