Binding properties and molecular mechanics calculations of p-tert-butylhexahomotrioxacalix[3]arene tri(diethyl)amide with alkali, alkaline earth, transition and heavy metal cations

The binding of alkali, alkaline earth, transition (Mn2 +, Fe2 +, CO2 +, Ni2 +, Cu2 + and Zn2 +) and heavy metal (Ag+, Cd2 + Hg2 + and Pb2 +) cations by cone p-tert-butylhexahomotrioxacalix[3]arene tri(diethyl)amide (1b) has been assessed by extraction studies of metal picrates from water to dichloromethane and proton NMR titration experiments. Molecular modelling techniques were also employed to complement the NMR data. The results are compared to those obtained with the dihomooxacalix[4]arene (2b) and calix[4]arene (3b) derivative analogues. Triamide 1b displays a high extracting ability towards Na+, Ba2 +, Ni2 +, CO2 +, Ag+ and mainly Pb2 + (80% E). However, these values are lower than those obtained with tetraamides 2b and 3b, presumably due to the higher conformational flexibility of 1b. H-1 NMR titrations indicate the formation of 1 : 1 complexes between 1b and all the cations studied, and also that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms