10.1039/C39900000116
The research investigates the interaction between the macrobicyclic ligand cryptand 222 and various amino acids in methanol. The study aims to provide the first thermodynamic data on the formation of 1:1 complexes between cryptand 222 and amino acids, including glycine, DL-alanine, DL-phenylalanine, DL-serine, DL-proline, and DL-tryptophan, at 298.15 K. Using titration calorimetry and potentiometric titration, the researchers determined the stability constants (log Ks), Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) of these complexation reactions. The results indicate that the amino group of the amino acids is the primary active site for interaction with cryptand 222, and the stability of the complexes is influenced by steric factors from substituent groups on the α-carbon of the amino acids. The study concludes that complexation is enthalpically and entropically favored for most amino acids, except glycine. Additionally, computer modeling suggests that the interaction occurs through hydrogen bonds and electrostatic interactions between the amino group and the oxygen atoms of cryptand 222. The findings have implications for understanding the transport of amino acids across cell membranes, enhancing their solubility in organic solvents, and developing methods for their separation.
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