Thermal Method for Prediction of Host Selectivity to Guest Isomers

Differential scanning calorimetric analysis was employed to determine the thermal property of the inclusion compounds; the purpose of performing the analysis was to elucidate the possibility of its use as a tool for predicting host selectivity to a given isomer mixture. From the analysis, it was observed that the energy of guanidinium 4,4′-biphenyldisulfonate (G2BPDS·(p-xylene)) is the highest among all inclusion compounds, whereas that of G2BPDS·(m-xylene) is the lowest among them. The result agrees with the selective preference of the G2BPDS host in a previous experiment. Similarly, the guest release onset temperature of the G2BPDS inclusion compounds also decreased in the order G2BPDS·(p-xylene) > G2BPDS·(o-xylene) > G2BPDS·(m-xylene). In the case of guanidinium 2,6-naphthalenedisulfonate (G2NDS) inclusion compounds, both the energy and the guest release onset temperature of G2NDS·(p-xylene) were higher than those of G2NDS·3(o-xylene). In fact, the structure of G2NDS·(p-xylene) was stabilized to a great extent by the CH···O interaction between the host and guest as compared to the G2NDS·3(o-xylene) structure. Consequently, from the good agreement between the thermal property of inclusion compounds and host selectivity, it was noted that the differential scanning calorimetric study of inclusion compounds can be performed to predict the host selectivity prior to the competition experiment.