Thermodynamic study of the retention behaviour of selected macrocycles using reversed-phase high-performance thin-layer chromatography plates and methanol-water mobile phases

摘要

The influence of temperature and mobile-phase composition on retention of α-, β-, and γ-cyclodextrins and two macrocyclic antibiotics (rifamycin B and rifampicin) has been examined by reversed-phase thin-layer chromatography, using wide-range (0-100%) binary mixtures of methanol-water. Retardation fact9rs (R_F) of the solute molecules were measured at different temperatures from 5 to 60°C. Temperature changes of the chromatographic conditions produce significant differences in migration of the investigated macrocyclic compounds. Generally, the plots of the rate mobility factor (R_M) versus the reciprocal of the absolute temperature are linear. The ranges of mobile-phase composition in which R_F values are equal to unity were wider at higher temperatures. From linear Van't Hoff plots thermodynamic parameters such as the change of enthalpy (△H°) and the change of entropy (△S") were estimated. In each case the sign of the calculated parameters is negative. However, the magnitudes of △H° and △S° indicate significant thermodynamic differences between two groups of solutes, one of which includes α- and γ-cyclodextrins and the other macrocyclic antibiotics and β-cyclodextrin.