The smallest cucurbituril analogue with high affinity for Ag.

A new host, Me8TD[4], was prepared for the first time from propanediurea-formaldehyde condensation in the presence of CaCl2 as the template and it is the smallest cucurbituril analogue reported so far. Measurements of the thermodynamic quantities (log K, ΔH, and ΔS values) of the interactions of Me8TD[4] with a series of cations by isothermal titration calorimetry indicated that Me8TD[4] binds selectively towards Ag+ with a high binding constant, K ∼ 1.3 × 106 M-1.