Gold nanomolecules have a distinct number of gold atoms and thiolate ligands, Aux(SR)y. They are less than 2nm in size, highly monodisperse, and exhibit molecular-like properties. Gold-thiolate nanomolecules also have unique spectroscopic, electrochemical, and chiral properties. These properties make them useful in applications such as, catalysis, bio-sensing, drug delivery, and cancer therapy. Within the field, it is well known that the ligand induces changes within the nanostructure, which induces changes in the unique properties of the material. Here we demonstrate this ligand dictation and the first interconversion between two nanomolecules: Au36(SPhX)24, (where X = -H or -tBu) and Au30(S-tBu)18. The conversion is achieved through a thermochemical etching process, with HSPhX on Au30(S-tBu)18 which converts the nanomolecule to Au36(SPhX)24. Furthermore, this conversion is reversible from Au36(SPhX)24 to Au30(S-tBu)18 with tert-butyl thiol (HS-tBu) under the same conditions. The interconversion of the two nanomolecules is especially interesting because the nanomolecules entirely different staple arrangements. Furthermore, Au36(SPhX)24 and Au30(S-tBu)18, have a Au28 and Au20 core, respectively. Theoretical studies further revealed that the difference between Au30(S-tBu)18 and Au36(SPhH)24 resides in the different fragmentation energy of the two species, and that Au30(S-tBu)18 appears to be slightly more stable than Au36(SPhH)24 in terms of atomization energy of the Au cluster and the ligand/ligand interactions. Experimental evidence for this reversible conversion is provided using matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), nano-electrospray ionization mass spectrometry (nESI-MS), and UV−vis−NIR spectroscopy. This discovery leads to crucial insight into the inherent nature of ligand dictation on the composition and atomic structure of gold−thiolate nanomolecules as well as their influence in controlling the total nanostructure.

Core size interconversions of gold nanomolecules: Au30(S-tBu)18 and Au36(SPhX)24

255th National Meeting (2018)

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