Formation of complexes between PAMAM-NH2 G4 dendrimer and l-α-tryptophan and l-α-tyrosine in water

•PAMAM G4 dendrimer coordinates about 25 molecules of tryptophan.•PAMAM G4 dendrimer coordinates about 24 molecules of tyrosine.•Binding constant between PAMAM G4 and tryptophan equals about 130.•Solubility, dialysis, 1H NMR, NOESY and CD confirm the investigated interactions.

Interactions between electromagnetic radiation and the side substituents of aromatic amino acids are widely used in the biochemical studies on proteins and their interactions with ligand molecules. That is why the aim of our study was to characterize the formation of complexes between PAMAM-NH2 G4 dendrimer and l-α-tryptophan and l-α-tyrosine in water. The number of l-α-tryptophan and l-α-tyrosine molecules attached to the macromolecule of PAMAM-NH2 G4 dendrimer and the formation constants of the supramolecular complexes formed have been determined. The macromolecule of PAMAM-NH2 G4 can reversibly attach about 25 l-α-tryptophan molecules with equilibrium constant K equal to 130 ± 30 and 24 ± 6 l-α-tyrosine molecules. This characterization was deduced on the basis of the solubility measurements of the amino acids in aqueous dendrimer solutions, the 1H NMR and 2D-NOESY measurements of the dendrimer solutions with the amino acids, the equilibrium dialysis and the circular dichroism measurements of the dendrimer aqueous solutions with l-α-tryptophan. Our date confirmed the interactions of l-α-tryptophan and l-α-tyrosine with the dendrimer in aqueous solution and indicated a reversible character of the formed complexes.

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