Thermodynamic studies of complexation and enantiorecognition processes of monoterpenoids by α- and β-cyclodextrin in gas chromatography

Gas–liquid chromatography was applied in thermodynamic investigations of processes of complexation and enantioseparation by α- and β-cyclodextrins of chiral monoterpenoids. The distribution constants, stability constants and thermodynamic parameters enthalpy, entropy and free energy of the complexation processes were determined. It has been found that enantioseparation of monoterpenes by α- and β-cyclodextrins is the result of formation of 1:2 stoichiometric complexes. When 1:1 stoichiometric complexes are formed, enantioselectivity is not observed. All investigated processes of complexation are enthalpy-driven regardless of the stoichiometry of the formed complexes. −ΔH, −TΔS and −ΔG of complexation process have higher values for bicyclic than for monocyclic monoterpenoids as well as for α-CD than for β-CD. The first or second step of complexation may be responsible for enantioselectivity.