When the Surface Matters: Prebiotic Peptide-Bond Formation on the TiO

Area of Science:

• Computational Chemistry
• Surface Science
• Astrobiology
• Materials Science

Background:

• Peptide-bond formation is fundamental to life's origins and industrial amide synthesis.
• Understanding catalytic mechanisms on mineral surfaces is key to prebiotic chemistry.
• Titanium dioxide (TiO2) anatase is a relevant mineral surface for catalytic studies.

Purpose of the Study:

• To investigate the mechanism of peptide-bond formation between two glycine molecules on a TiO2 anatase surface.
• To compare the catalytic efficiency of the TiO2 surface with the gas-phase reaction.
• To elucidate the role of surface sites and co-present molecules in the reaction mechanism.

Main Methods:

• Periodic Density Functional Theory (DFT) simulations using PBE-D2* and PBE0-D2* functionals.
• Investigation of reaction pathways, energy barriers, and thermodynamic stability.
• Comparison of gas-phase and surface-catalyzed reaction mechanisms.

Main Results:

• The TiO2 anatase surface facilitates peptide-bond formation through a stepwise mechanism, unlike the concerted gas-phase reaction.
• Surface Lewis and Brønsted sites lower the free energy barrier by ~6 kcal/mol.
• Water and glycine molecules act as proton-transfer assistants, further reducing the kinetic barrier.
• The anatase surface acts as a dehydration agent by strongly anchoring released water molecules, leading to favorable thermodynamics.

Conclusions:

• The TiO2 anatase surface significantly catalyzes peptide-bond formation, relevant for both prebiotic chemistry and industrial applications.
• The surface mechanism involves distinct steps compared to the gas-phase reaction, with Lewis/Brønsted sites playing a crucial role.
• The findings align with experimental observations of polyglycine formation on TiO2 surfaces under dry conditions, supporting prebiotic scenarios involving wet-dry cycles.