THE FORMATION OF CUCURBITURIL COMPLEXES WITH AMINO-ACIDS AND AMINO-ALCOHOLS IN AQUEOUS FORMIC-ACID STUDIED BY CALORIMETRIC TITRATIONS

The complex formation between cucurbituril and some amino acids and am ino alcohols was studied by means of calorimetric titrations in aqueou s formic acid (50% v/v). In the case of amino acids no influence of th e number of methylene groups upon the stability constants could be obs erved. The complex formation is favoured by enthalpic and entropic con tributions. During complex formation water molecules bound to carboxyl ic groups are set free. The situation changes completely in the case o f amino alcohols. Reaction enthalpies and entropies are influenced by the number of methylene groups. The amino alcohol with three methylene groups forms the most stable complex. With increasing number of methy lene groups the stability of the complexes formed decreases. For this decrease only entropic factors are responsible. (C) 1998 Elsevier Scie nce B.V.