title: Electrospray mass spectrometry study of tiopronin monolayer-protected gold nanoclusters.
abstract: Electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS) and gel permeation chromatography (GPC) were used to study the synthesis of a series of tiopronin monolayer-protected gold nanoclusters (MPCs) and to monitor their postsynthesis peptide ligand place-exchange reactions. All mass spectra identified the presence of cyclic gold(I)-thiolates with a strong preference for tetrameric species. During the synthesis of pre-monolayer-protected nanoclusters (pre-MPCs), esterified gold(I)-thiolate tetramers were initially observed in minor abundance (with respect to disulfide bridged tiopronin species) before dramatically increasing in abundance and precipitating from solution. After conversion of pre-MPCs to MPCs, ESI-TOF mass spectra demonstrated an overall predominance of tetrameric species with conversion from ester-terminated end groups to carboxyl-terminated end groups. Further modifications were performed through postsynthesis ligand place-exchange reactions to validate the existence of the tetramers. This work suggests that monolayer protection is accomplished by cyclized gold(I)-thiolate tetramers on the gold core surface, and/or that gold(I)-thiolates are a basic building block within the nanoparticles.
authors.affiliation: Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, USA. a.gies@vanderbilt.edu
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Gies
authors.forename: David M
authors.initials: DM
authors.lastname: Hercules
authors.forename: Aren E
authors.initials: AE
authors.lastname: Gerdon
authors.forename: David E
authors.initials: DE
authors.lastname: Cliffel
mesh_terms: D002850:Chromatography, Gel / Q000379:methods; D006046:Gold / Q000737:chemistry*; D008024:Ligands; D049329:Nanostructures / Q000737:chemistry*; D036103:Nanotechnology; D009942:Organometallic Compounds / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013499:Surface Properties; D008625:Tiopronin / Q000737:chemistry*
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D013438:Sulfhydryl Compounds; D006046:Gold; D008625:Tiopronin