Melanin Polymerization Held in Check: A Composite of Dihydroxyphenylalanine with Zeolite Beta

The potential use of l-3,4-dihydroxyphenylalanine (l-DOPA) amino acid in the treatment of Parkinson’s disease is hindered by an oxidative polymerization under air that might be at least partially circumvented by the immobilization on an inorganic matrix. This study reports on the preparation of dihydroxyphenylalanine (DOPA)–zeolite beta composites. The materials obtained from the oxidative reactions of DOPA in aqueous solution in the presence of the zeolitic matrix are characterized by a combination of different spectroscopic techniques including Raman, infrared, ultraviolet–visible, and NMR, and by periodic density functional theory calculations in order to understand the mode of interaction between the biomolecules and the inorganic matrix. The set of experimental data unambiguously proves that the oxidation of DOPA is slowed in acidic medium and that a dimerization occurs in the pores of the inorganic lattice. The states of DOPA and its cyclized forms (dopachrome and leucodopachrome) are determined. The results of the study can be used to control the immobilization of amino acids on porous matrices.