Abstract
The influence of temperature and mobile-phase composition on retention of α-, ß-, 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 factors ( 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 ( ΔH°) and the change of entropy ( ΔS°) were estimated. In each case the sign of the calculated parameters is negative. However, the magnitudes of ΔH° and ΔS° indicate significant thermodynamic differences between two groups of solutes, one of which includes α- and γ-cyclodextrins and the other macrocyclic antibiotics and ß-cyclodextrin.
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