pK(a) Values and activation parameters for ring inversion of 25,27-diamino-5,11,17,23-tetra-t-butylcalix[4]arene-26,28-diol were estimated. It was found that in the OH groups of this compound the "super-acidic" proton, observed for conventional calix[4]arene-25,26,27,28-tetrols, no longer exists and ring inversion occurs more easily.