Molecular orientation and intermolecular interaction in alanine on Cu(001)

Area of Science:

• Surface Science
• Physical Chemistry
• Materials Science

Background:

• Understanding molecular adsorption on metal surfaces is crucial for catalysis and materials design.
• Alanine, an amino acid, serves as a fundamental building block in biological systems and can exhibit chirality.

Purpose of the Study:

• To elucidate the molecular orientation and surface structure of L-alanine and racemic alanine on a Copper(001) surface.
• To investigate the role of intermolecular interactions in self-assembly and domain formation.

Main Methods:

• Reflection Absorption Infrared Spectroscopy (RAIRS) for vibrational mode identification.
• Low-Energy Electron Diffraction (LEED) for structural analysis.
• Scanning Tunneling Microscopy (STM) for submolecular resolution imaging.

Main Results:

• Alanine adsorbs in an anionic form, bonding to copper via carboxylate and amino groups, with the methyl group oriented upwards.
• Hydrogen bonds between amino and carboxylate groups drive the formation of ordered adlayers with c(2 x 4) periodicity.
• Racemic alanine mixtures segregate into homochiral domains, forming distinct boundaries along specific crystallographic directions.

Conclusions:

• The study reveals detailed adsorption configurations and self-assembly mechanisms of alanine on Cu(001).
• Chiral segregation in racemic mixtures is driven by intermolecular hydrogen bonding, leading to domain formation.
• STM imaging provides submolecular insights into the hydrogen-bonding networks stabilizing these chiral domains.