Complexation of p-Sulphonato-calix[6]arene by Glycine, Glycyl-glycine, and Glycyl-glycyl-glycine in Aqueous Solution

摘要

The complexing ability of p-sulphonato-calix[6]arene towards glycine, glycylglycine, and glycyl-glycyl-glycine has been evaluated at pH = 1.8 and 7.9 using UV–Vis spectrophotometry. At these pHs the guest molecules are in their cationic and zwitterionic forms, respectively. The results showed that the host is capable of complexing with the guests in 1:1 guest-to-host ratios. Formation constants of the systems have been determined at different temperatures (20 ± 0.1 to 40 ± 0.1 ℃). Considering the formation constant values, the binding selectivity of the host towards the guests is in the order glycyl-glycyl-glycine>glycyl-glycine>glycine. The thermodynamic parameters have been evaluated and are interpreted in terms of the importance of the various interactions responsible for the complexation. A roughly linear relationship between ΔH° and TΔS°has been observed for the studied systems and is discussed.