Synthesis and characterization of hydrophobic, organically-soluble gold nanocrystals functionalized with primary amines

We report on the synthesis and characterization of 25-70 Angstrom diameter amine-capped gold nanocrystals. In particular, we show how these particles can be prepared by a simple procedure and confirm the particle composition (including the identity of the amine surface passivant) through several materials characterization techniques that include infrared spectroscopy, nuclear magnetic resonance spectroscopy, ultraviolet-visible spectroscopy, mass spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction analysis, differential scanning calorimetry, thermogravimetric analysis, and elemental analysis. All physical characterizations are consistent with a charge-neutral amine/gold surface interaction described by a weak covalent bond. The stability of the particles appears to be largely kinetic, rather than thermodynamic, in nature. Comparison of these nanocrystals to amines adsorbed onto bulk Au surfaces indicates that the stability of the nanocrystal/amine system is a finite-size effect.