What controls au nanoparticle dispersity during growth?

Nanoparticles are critical in diverse nanotechnological areas. Their physical and chemical properties are essentially determined by their size, shape, and dispersity, but the underlying mechanisms that determine these are generally poorly understood. Herein, we focus on the electronic structure and solvation properties of the Au-thiolate capping agents (Au(n)MBA(n)) used in the synthesis of gold nanoparticles and whose accepted function is to stump growth. By DFT calculations we show that they exhibit "magic" number, electronic configuration, and stability for n = 4 and 8. By Molecular Dynamics simulations, we learn that in water-methanol solution the dominant species is the Au(4)MBA(4) complex, in a conformation stabilized by hydrogen bonds. We argue that the solvent has a multifunctional role: the water acts via hydrogen bonding as a "molecular locker" stabilizing particular conformers, while the methanol prevents polymeric growth of the Au(n)MBA(n) complexes. A plausible growth mechanism conducive to the formation of monodisperse gold nanoparticles is proposed.