Iron(III) Oxide Nanoparticles as Catalysts for the Formation of Linear Glycine Peptides

We have studied the behavior upon thermal activation of glycine adsorbed on three well-characterized Fe3+ oxide nanoparticle phases, maghemite, hematite and akaganeite. The behavior of the adsorbed molecules and of the nanoparticles surfaces were followed by four main experimental techniques, TGA-DTA, XPS, vibrational spectroscopy (IR), and mass spectrometry. Glycine polymerizes by peptide bond formation in the 180-190 °C temperature range, i.e. somewhat higher than on previously studied oxides such as silica or alumina, giving mostly short linear peptides. At slightly higher temperatures, under inert atmosphere, the iron oxyhydroxides act as stoechiometric oxidants and cause oxidative degradation of the peptides formed in the previous step, while they are reduced to FeO; under air, dioxygen causes reoxidation of the nanoparticle surfaces so that the overall effect is a catalytic oxidation by O2. While the direct formation of linear peptides may be beneficial to prebiotic complexity growth, the redox reactivity of the supports limits the temperature stability ranged of the oligopeptides