# Unraveling the Role of the Multifunctional Groups in the Adsorption of l‑Cysteine on Rutile TiO2(110)

## TL;DR

This study explores how l-cysteine interacts with a titanium dioxide surface, revealing new insights into molecular configurations and bonding.

## Contribution

The study is the first to highlight the thiol group's role in cysteine adsorption on TiO2 and dimer formation.

## Key findings

- Three distinct adsorption geometries were identified, including two bidentate bridging modes and a thiolate group interaction.
- Cysteine molecules form dimers stabilized by disulfide bonds at low coverage while remaining zwitterionic.
- The thiol group plays a key role in both direct surface binding and dimer formation on TiO2.

## Abstract

Understanding the interaction between biomolecules and
oxide surfaces
is essential for advancing technologies in photocatalysis, virus inactivation,
and self-cleaning materials. This study investigates the adsorption
behavior of l-cysteine on the rutile TiO2(110)
surface using a combined experimental and theoretical approach. By
employing X-ray photoelectron spectroscopy (XPS), Fourier-transform
infrared reflection absorption spectroscopy (FT-IRRAS), scanning tunneling
microscopy (STM), and density functional theory (DFT) calculations,
we elucidate the molecular configurations and bonding mechanisms involved
in the interaction of cysteine with the TiO2 surface. The
results reveal three distinct adsorption geometries: two bidentate
bridging modes involving the carboxylate group and amino group and
a configuration involving the interaction of the thiolate group with
titanium atoms. Additionally, cysteine molecules form dimers stabilized
by disulfide bonds even at low coverage while maintaining a zwitterionic
state. Our study highlights, for the first time, the key role of the
thiol group in cysteine adsorption on TiO2, both for surface
direct binding and dimer formation. These findings provide new insights
into the fundamental principles of biomolecule–semiconductor
interactions with important implications for surface-functionalized
materials in catalysis and sensing.