Faraday’s legendary ‘Molecules of Gold’ have stimulated intense interest (over 165 years) but have only recently begun to yield their secrets to modern methods of chemical analysis. Here(in), we demonstrate how striking charging patterns emerge directly from native electrospray of large, gold-rich molecules that were generated by reduction of various (8) small gold(I)thiolate complexes [-RS-Au(I)-SR-], followed by extensive thermochemical processing to enrich the most robust forms. In each case (R), electrospray ionization of a picomolar solution yields a characteristic series of intense, highly resolved peaks at related (m/z)-ratios, that can be used to deduce charges {z e+} and hence a distinct molecular mass, {MR}. A plot of {MR} versus thiolate-mass {mR} yields a straight line with slope 60.0 (the ligand count) and an intercept of 28,364-Da, the mass of 144 Au-atoms. i.e., a unique molecular composition {197Au144(SR)60}. This formula agrees with the unique chiral-icosahedral structure-model, c@12@42@60@(30,60), the Pd145(CO)60-structure, that features a massively-compact globular Au114-core (~1.6-nm) and an intrinsically chiral (I) outer shell (~2.0-nm) with 60- fold site equivalence, denoted by Martin et al. as ‘virus-like’ on the basis of its resemblance of icosahedral-virus capsids. The charging patterns are interpreted within this model as characteristic of the R-group class. The mass-fraction of the isotopically-pure 197Au144 ranges from a high 88.6% (R = C2H5) down to ~60% (PEGylated and quaternized R-groups). The remarkable set of features discussed herein suggests that these ubiquitous, robust, virus-like molecules-of-gold may serve an important function as widely available high-performance standards. The author is grateful to his students and colleagues for their original contributions to the results and for discussion of the interpretations presented herein.

Unified interpretation of Faraday's legendary Molecules-of-Gold as viruslike clusters of metal atoms: Native electrospray analysis of isostructural emergent-metallic phases encapsulated by thiolate ligand shells

ACS Spring 2022

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