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

Abstract

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 presented here from characterization via high-resolution electrospray ionization mass spectrometry on an Orbitrap instrument confirm 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 the (130, 50), recently determined to have a truncated-decahedral structure, and a (137, 56) component 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.

New Evidence of the Bidentate Binding Mode in 3-MBA Protected Gold Clusters: Analysis of Aqueous 13&ndash;18 kDa Gold-Thiolate Clusters by HPLC-ESI-MS Reveals Special Compositions Au<em>_n</em>(3-MBA)<em>_p</em>, (<em>n</em> = 48 &ndash; 67, <em>p</em> = 26-30)

“…The compositions arrived at by these procedures (68, 32) and (144, ~40) are respectively distinctly and strikingly different from those determined previously for aliphatic ligands, (67,35) and (144, 60), or for the more directly relevant water-soluble aromatic pMBA ligand (146, 57). [The Figure 6 presents these compositions in graphical format.…”

MicroED Structure of Au146(p-MBA)57 at Subatomic Resolution Reveals a Twinned FCC Cluster

“…The gold nanoclusters were produced by two-phase method with some modifications (23,25,31,32). Stock solution of para-mercaptobenzoic acid (p-MBA) at 100 mM was prepared in 300 mM NaOH by vigorous stirring for at least 3 h or overnight and pulsed sonication.…”

“…We previously reported a detailed electrospray ionization mass spectrometric (ESI-MS) analysis of the cluster sample without ammonium acetate coprecipitation (25). In that analysis, the dominant species was reported as (144,60) while stressing the presence of other "hidden" components, including intact (130,50), and ESI fragmentation products of (137,56), (102,44), and (180,66).…”

Atomic-level separation of thiolate-protected metal clusters

“…82 In this way, it is possible to isolate SR-protected metal clusters composed of various ligands and metal elements with atomic precision using PAGE. [83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100][101] By conducting research on a series of separated clusters, much knowledge has been obtained on the chemical composition and stability, electronic/geometrical structure, and physical properties of various SR-protected metal clusters.…”