THE COMPLEXATION OF AMINO-ALCOHOLS AND AMINO-ACIDS BY THE CROWN-ETHER18C6 AND THE CRYPTAND-(222) IN METHANOL

The complex formation between certain amino alcohols and amino acids a nd the crown ether (18-crown-6) and the cryptand (222) in methanol was studied by calorimetric titrations. In the case of the amino alcohols , no influence of the number of methylene groups upon the complex form ation with both ligands is observed. After protonation of one amino al cohol, the value of the reaction enthalpy with 18-crown-6 is doubled. In comparison with amino alcohols, amino acids form more stable comple xes with both ligands. However, favorable enthalpic changes during the complex formation are compensated for by unfavorable entropic contrib utions. The amino groups of the amino acids are already protonated. Ev en in methanol as solvent, the amino acids examined exist in their zwi tterionic form. (C) 1998 Elsevier Science B.V.