Variation in morphology of gold nanoparticles synthesized by the spontaneous reduction of aqueous chloroaurate ions by alkylated tyrosine at a liquid-liquid and air-water interface

We demonstrate the formation of gold nanocrystals of different morphologies using alkylated tyrosine (AT) as a reducing agent at a liquid-liquid and air-water interface. The reduction of aqueous chloroaurate ions occurs in a single step wherein the AT molecule plays the multifunctional role of a phase transfer, reducing and capping agent. Gold nanoparticles formed at the air-water interface are very thin, flat sheet or ribbon-like nanostructures, which are highly oriented in the (111) direction. On the other hand, reduction of aqueous chloroaurate ions at a liquid-liquid interface by AT molecules present in the organic phase yielded nanoparticles having predominantly spherical morphology but with no specific crystallographic orientation. The difference in morphology of the nanoparticles may be due to the different orientational and translational degrees of freedom of the AT molecules and gold ions at these two interfaces. The AT-capped gold nanoparticles were characterized by UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and nuclear magnetic resonance spectroscopy (¹H NMR), while the LB films of flat gold sheets were also studied by X-ray photoemission spectroscopy (XPS).