Thermodynamics of sulfate anion binding by macrocyclic polyammonium receptors

The interaction of SO42- with polyammonium cations derived from fourteen po lyamines (5 polyazacycloalkanes, 2 polyazacyclophanes, 3 phenanthrolinacycl ophanes, 2 dibenzenacyclophanes and 2 acyclic polyamines) in aqueous soluti on has been studied by means of potentiometric and microcalorimetric techni ques. Only 1:1 receptor-anion complexes have been found in solution. Comple xed species of considerable stability are formed, although the two acyclic polyamines (dimethylpentaethylenehexaamine and dimethylhexaethyleneheptaami ne) and the smallest phenanthrolinacyclophane do not interact with the anio n. The complexation reactions are endothermic, or almost athermic, and prom oted by invariably favourable entropic contributions, indicating that these pairing processes are mostly determined by the desolvation of the interact ing species that occurs upon charge neutralisation. The results are compare d with those previously obtained for phosphate binding.