Mechanistic aspects of the stereospecific interaction for aminoindanol with a crown ether column

Investigations into the mechanistic aspects of the stereospecific interaction of the four optical isomers of aminoindanol on a silica based crown ether column were performed. The nature and concentration of the mobile phase's counteranion affected the hydrophobic interaction but had little effect on the inclusion interaction. Minimal changes in the separation factor of the enantiomers were observed in the pH range of 1-5.2, but a minimum in the capacity factor was observed at pH 3.75. Van't Hoff plots indicated a high entropy and a positive enthalpy at pH 5.2, while a lower entropy and a negative enthalpy were observed at and below pH 3.75. Hill plots indicated that there were more active binding sites at pH 3.0 as compared to pH 1.0 and that the binding ratio of aminoindanol to active sites was also greater. Apparently at higher pH values, as the silica becomes deprotonated, there is an additional electrostatic interaction between the protonated aminoindanol and the deprotonated silica sites.