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 nanoparticle surfaces was monitored by four main experimental techniques, thermogravimetric analysis/differential thermal analysis (TGA/DTA), XPS, infrared spectroscopy (IR), and mass spectrometry. Glycine polymerizes by peptide bond formation in the 180–190 °C temperature range, which is somewhat higher than on previously studied oxides such as silica or alumina, giving mostly short linear peptides. At slightly higher temperatures, under an inert gas, the iron oxyhydroxides act as stoichiometric 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 the growth of prebiotic complexity, the redox reactivity of the supports limits the temperature stability range of the oligopeptides. Glycine was adsorbed on iron oxide nanoparticles, and peptide condensation was carried out by thermal activation. This activation allows the formation of small linear peptides. Infrared spectroscopy has enlightened the specific intramolecular structuration of the formed peptides on the particles.