Investigation of conformational equilibrium and proton affinity of Thiacalix[4] arenas and their complexes with cations : research report

Abstract

The p-tert-butylsulfonylcalix[4]arene and sulfonycalix[4]arene conformers have been obtained by AM1 geometry optimizations. The structural cavities of p-tert-butylsulfonylcalix[4]arene and sulfonylcalix[4]arene conformers of which phenol groups are bridged by sulfonyl sulfur have been compared to the calix[4]arene and thiacalix[4]arene. The conformational energies of p-tert-butylsulfonylcalix[4]arene have been compared with the energies of sulfonylcalix[4]arene, calix[4]arene and thiacalix[4]arene. The most stable conformer of sulfonylcalix[4]arene and p-tert-butylsulfonylcalix[4]arene are 1,2-alternate and 0011-AAAA 1,2-alternate conformers, respectively. Two different types of hydrogen bond presented in the sulfonyl calix[4]arene cone and partial cone conformers and p-tert-butylsulfonylcalix[4]arene cone conformer have been found. Ab initio energies of the AM1 optimized structures of sulfonylcalix[4]arene and p-tert-butylsulfonylcalix[4]arene conformers and their complexes with zinc(II) have been computed at HF/6-31G* and B3LYP/6-31G* theoretical levels. The optimized structure of complex species of p-tert-butylsulfonylcalix[4]arene with zinc(II) is in good agreement with recent x-ray geometry data.