Thermodynamic Study of Enantioseparation of Arylpropionic Acids with a Chiralcel OJ‐H Stationary Phase

Abstract

Enantioseparation data of ketoprofen, fenoprofen, and ibuprofen have been obtained and thermodynamically analyzed. The Chiralcel OJ column was used for chiral separation. The mobile phases were 100/0, 95/5, and 90/10 v/v% hexane/2‐propanol mixtures with 0.5% acetic acid. The capacity factors of the solutes were measured at 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C. The thermodynamic properties of solute transfer from the mobile to the stationary phase were critically analyzed in comparison with the thermodynamic properties obtained by the Chirex 3001 phase in methanol/water eluents. The well‐known enthalpic–entropic compensation is clearly valid for the systems studied in this research. The solute–Chiralcel OJ interactions of R‐ and S‐ibuprofen were found weaker than those of R‐ and S‐fenoprofen and ketoprofen, since ibuprofen is much less polar than others and subject to much weaker interactions with the stationary phase. Careful interpretation of the data revealed that the solute–Chiralcel OJ interaction is stronger than the solute–Chirex 3001 interaction. It is likely that the supramolecular structure of the Chiralcel OJ phase with chiral cavities provides more versatile functional and steric environments, to give stronger interactions and better chiral recognition and discrimination. There appeared extrema in the plots of ΔH ⁰ and ΔS ⁰ against eluent composition obtained in the Chiralcel OJ system. Adsorption of 2‐propanol to multiple sites with different priorities and different steric environments seems to cause such a phenomenon.

Keywords:

• Thermodynamic properties
• enantioseparation
• arylpropionic acids
• chiralcel OJ phase

Acknowledgment

This work was supported by the Korea Research Foundation grant (KRF‐2003‐015‐C00417).