Complexation of some amino acids and peptides by p-sulfonatocalix[4] arene and hexasodium p-sulfonatocalix[6] arene in aqueous solution

The stability constants (log K), the reaction enthalpy (DeltaH) and entropy (DeltaS) of the complexes formed between some amino acids (glycine, L-alanine, L-valine, L-leucine, L-phenylalanine, L-tryptophan, L-threonine, and L-lysine) and peptides (glycyl-glycine, glycyl-L-alanine, glycyl-L-leucine, glycyl-L-phenylalanine, L-leucyl-glycine, L-leucyl-L-alanine, glycyl-L-valine, L-leucyl-glycyl-glycine, and glycyl-glycyl-glycine) with p-sulfonatocalix[4] arene and hexasodium p-sulfonatocalix[ 6] arene in aqueous solutions by means of calorimetric titration have been investigated. The reported results demonstrate that the amino acids and peptides under study form complexes with both p-sulfonatocalix[ 4] arene and hexasodium p-sulfonatocalix[6] arene. In the case of the amino acids and peptides the complexation with water-soluble calixarenes in aqueous solution is favored by enthalpic contributions and disfavored by entropic contributions. However, no influence of the ring size of the calixarenes upon the complexation is observed. By comparison with the reaction of the sodium salt of phenol-4-sulfonic acid with amino acids a macrocyclic effect in case of the calixarenes is possible.