Hidden Components in Aqueous ‘Gold-144’ Fractionated by PAGE: High Resolution Orbitrap ESI-MS Identifies the Gold-102 and Higher All-Aromatic Au-pMBA Cluster Compounds

摘要

Experimental and theoretical evidence reveals the resilience and stability of the larger aqueous gold clusters protected with p-mercaptobenzoic acid ligands (pMBA) of composition Aun(pMBA)p or (n,p). The Au144(pMBA)60, (144,60), or Gold-144 aqueous gold cluster is considered special because of its high symmetry, abundance, and icosahedral structure as well as its many potential uses in material and biological sciences. Yet to this date, direct confirmation of its precise composition and total structure remains elusive. Results described here from characterization via high-resolution electrospray ionization mass spectrometry on an Orbitrap instrument show Au102(pMBA)44 at isotopic resolution. Further, what usually appears as a single band for (144,60) in electrophoresis (PAGE) is shown to also contain (130,50), recently determined to have a truncated decahedral structure, and (137,56) in addition to the dominant (144,60) compound of chiral icosahedral structure. This finding is significant in that it reveals the existence of structures never before observed in all-aromatic water soluble species while pointing out the path toward elucidation of the thermodynamic control of protected gold nanocrystal formation.