Interfacial charge transfer complex formation between silver nanoparticles and aromatic amino acids.

Area of Science:

• Physical Chemistry
• Materials Science
• Nanotechnology

Background:

• Silver nanoparticles (Ag NPs) exhibit unique optical properties crucial for various applications.
• Understanding surface interactions is key to controlling nanoparticle behavior and stability.
• Aromatic amino acids like tryptophan and histidine are biologically relevant molecules with potential for nanoparticle functionalization.

Purpose of the Study:

• To investigate the optical properties of silver nanoparticles modified with tryptophan and histidine.
• To elucidate the electronic charge redistribution upon chemisorption of these amino acids onto silver surfaces.
• To explore the formation of interfacial charge transfer complexes and their impact on Ag NP oxidation.

Main Methods:

• Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations using a cluster model.
• Theoretical determination of electronic charge redistribution.
• Experimental spectroscopic measurements to validate theoretical findings.

Main Results:

• Theoretical data indicate the formation of an interfacial charge transfer (ICT) complex between silver and the amino acid ligands.
• Partial oxidation of surface silver atoms and increased electron density in ligand molecules were observed.
• Experimental results show a new visible absorption band and significantly faster oxidation of surface-modified Ag NPs in air.

Conclusions:

• The study reports, for the first time, the formation of an ICT complex between noble metal nanoparticles and aromatic amino acids.
• Surface modification with tryptophan and histidine alters the electronic structure and optical properties of Ag NPs.
• The findings provide insights into the stability and reactivity of functionalized silver nanoparticles.