Self-Assembly Behavior of Amino Acids on Au (111) Surfaces: A Molecular Dynamics Study

The emerging amino acid nanostructures provide a new type of smart biomaterial for biomedical applications. However, the lack of mechanistic understanding of their temperature-dependent self-assembly on inert solid surfaces limits the rational design of the desired nanostructures. Herein, we report different monolayer patterns of valine, leucine, and isoleucine molecules on a Au surface and uncover the influence of temperature on their self-assembly behavior. The randomly distributed amino acid molecules self-assemble into long-range periodic ordered monolayer assembly structures at a temperature of 600 K, which exhibit a characteristic periodic molecular arrangement but not the strict crystallographic features of 2D crystals. Temperature controls the kinetic accessibility and molecular diffusion, enabling the balance between intermolecular interactions and thermal motion to yield ordered assemblies at 600 K. l-Valine molecules on an inert Au (111) confinement surface exhibit the coexistence of two different motif arrangements: the antiparallel and parallel structures, whereas l-leucine and l-isoleucine molecules show only the antiparallel structure. The noncovalent interaction, which competes with the thermal motion of molecules, is closely associated with the formation of periodic dipole moment distributions and periodic molecular structures, thereby giving rise to the highly ordered monolayer structure of amino acid molecules.