Guest-host chemistry of p-sulfonatocalix[6]arene and nizatidine

This work investigates the guest-host chemistry in water of p-sulfonatocalix[6]arene and a number of guests related to the amino acids arginine and lysine. Two questions are particularly important: what are the interactions that drive guest-host binding and what is the role of the solvent. The answers to these questions are investigated with isothermal titration calorimetry (lTC), which gives K, ?H, and ?S, and pressure perturbation calorimetry (PPC), which allows the calculation of the thermal coefficient of expansion ? and relating it to a molecule's structure-breaking or structure-making properties. The ITC data suggests that hydrogen bonding and charge-charge interactions are the dominant factors in the formation of guest-host complexes, while PPC showed that the host and all the guests are structure-breakers. Computational investigation of the structure of the guest-host complex suggests that the preferred orientation of the guest is when its guanidinium group points towards the phenolic oxygens of the host and its amino group forms hydrogen bonds with the host 's sulfonato groups. Quantitative structure activity relationship (QSAR) studies suggested that the solvent contribution includes a significant entropy component. In addition to this guest-host system, the binding of nizatidine to a number of guests related to pyridoxine was investigated by ITC and high performance liquid chromatography (HPLC). Contradictory to previous findings, no binding between nizatidine and any of its potential guests was observed.