Does the Abiotic Formation of Oligopeptides on TiO2 Nanoparticles Require Special Catalytic Sites? Apparently Not

<div>Preprint version of the paper:</div><div>Does the Abiotic Formation of Oligopeptides on TiO2Nanoparticles Require Special Catalytic Sites? Apparently Not</div><div>by:</div><div>Marco Fabbiani, Marco Pazzi, Marco Vincenti, Gloria Tabacchi, Ettore Fois, Gianmario Martra<br></div><div><br></div><div>Published on 1st August 2018 in:</div><div><a href="https://www.ingentaconnect.com/content/asp/jnn">Journal of Nanoscience and Nanotechnology</a>, 2018, 18, 5854-5857<br></div><div><br></div>The oligomerization of non-activated amino acids catalyzed by nanostrucrured mineral oxide surfaces holds promises as a sustainable route for the industrial production of polypeptides. To analyze the influence of the surface type on the catalytic process, we performed, via a mild Chemical Vapor Deposition approach, the oligomerization of Glycine on two samples of TiO2 nanoparticles characterized by different relative amounts of defective surface terminations. Based on infrared spectroscopy and mass spectrometry data, we show herein that the formation of peptide bonds on titania nanoparticles does not require highly energetic surface terminations, but can occur also on the most abundant and thermodynamically most stable {101} facets of nanosized anatase

How Does Silica Catalyze the Amide Bond Formation under Dry Conditions? Role of Specific Surface Silanol Pairs

The mechanism of the amide bond formation between nonactivated carboxylic acids and amines catalyzed by the surface of amorphous silica under dry conditions is elucidated by combining spectroscopic measurements and quantum chemical simulations. The results suggest a plausible explanation of the catalytic role of silica in the reaction. Both experiment and theory identify very weakly interacting SiOH surface group pairs (ca. 5 Å apart) as key specific sites for simultaneously hosting, in the proper orientation, ionic and canonical pairs of the reactants. An atomistic interpretation of the experiments indicates that this coexistence is crucial for the occurrence of the reaction, since the components of the canonical pair are those undergoing the amidation reaction while the ionic pair directly participates in the final dehydration step. Transition state theory based on quantum mechanical free energy potential energy shows the silica-catalyzed amide formation as being relatively fast. The work also points out that the presence of the specific SiOH group pairs is not exclusive of the adopted silica sample, as they can also be present in natural forms of silica, for instance as hydroxylation defects on α-quartz, so that they could exhibit similar catalytic activity toward the amide bond formation

Emergence of Order in Origin-of-Life Scenarios on Mineral Surfaces: Polyglycine Chains on Silica

The polymerization of amino acids (AAs) to peptides on oxide surfaces has attracted interest owing to its high importance in biotechnology, prebiotic chemistry, and origin of life theories. However, its mechanism is still poorly understood. We tried to elucidate the reactivity of glycine (Gly) from the vapor phase on the surface of amorphous silica under controlled atmosphere at 160 °C. Infrared (IR) spectroscopy reveals that Gly functionalizes the silica surface through the formation of ester species, which represent, together with the weakly interacting silanols, crucial elements for monomers activation and polymerization. Once activated, β-turns start to form as initiators for the growth of long linear polypeptides (poly-Gly) chains, which elongate into ordered structures containing both β-sheet and helical conformations. The work also points to the role of water vapor in the formation of further self-assembled β-sheet structures that are highly resistant to hydrolysis