Calorimetric investigation of guanidinium-carboxylate interactions

Isothermal titration calorimetry was utilized to study the association between a series of guanidinium derivatives and tetrabutylammonium acetate. This technique provides a measure of association strength, stoichiometry of binding, as well as thermodynamic parameters of association from a single experiment. Guanidinium derivatives which can form bidentate linear hydrogen bonds with acetate show significant, exothermic binding in DMSO (Ka = 5600 M-1; Delta H = -3.6 kcal/mol), while derivatives which lack this bidentate linear hydrogen bonding interaction result in complexes where association is weaker (Ka approximate to 100 M-1) and enthalpically neutral or endothermic. Additionally calorimetry permits the complete assessment of the multiple binding equilibria when derivatives complex two equivalents of guest. (C) 1999 Elsevier Science Ltd. All rights reserved.