A size-dependent transition from molecule-like to plasmonic behaviour is demonstrated in the case of water soluble Au:SG nanomolecules. This was achieved using PAGE separation of smaller and larger nanomolecules, resulting in an unprecedented 26 bands, in a wide-range from 10's to 1000's of Au-atoms. PAGE separation of larger plasmonic nanomolecules is demonstrated for the first time. High resolution ESI-MS, with isotopic resolution, of smaller nanoparticles is reported, including the first time report of Au43(SG)26. This report will aid in the fundamental understanding of size-dependent properties of nanomolecules. The synthetic procedure employs a green approach with non-toxic chemicals and processes. The water solubility, non-toxicity and biocompatibility will lead to applications in biomedicine.