title: Tandem mass spectrometry of thiolate-protected Au nanoparticles Na(x)Au25(SC2H4Ph)(18-y)(S(C2H4O)5CH3)(y).
abstract: We report the first collision-induced dissociation tandem mass spectrometry (CID MS/MS) of a thiolate-protected Au nanoparticle that has a crystallographically determined structure. CID spectra assert that dissociation pathways for the mixed monolayer Na(x)Au(25)(SC(2)H(4)Ph)(18-y)(S(C(2)H(4)O)(5)CH(3))(y) centrally involve the semi-ring Au(2)L(3) coordination (L = some combination of the two thiolate ligands) that constitutes the nanoparticle's protecting structure. The data additionally confirm charge state assignments in the mass spectra. Prominent among the fragments is [Na(2)AuL(2)](1+), one precursor of which is identified as another nanoparticle fragment in the higher m/z region. Another detected fragment, [Na(2)Au(2)L(3)](1+), represents a mass loss equivalent to an entire semi-ring, whereas others suggest involvement (fragmentation/rearrangement) of multiple semi-rings, e.g., [NaAu(3)L(3)](1+) and [NaAu(4)L(4)](1+). The detailed dissociation/rearrangement mechanisms of these species are not established, but they are observed in other mass spectrometry experiments, including those under non-CID conditions, namely, electrospray ionization mass spectrometry (ESI-MS) with both time-of-flight (TOF) and FT-ICR analyzers. The latter, previously unreported results show that even soft ionization sources can result in Au nanoparticle fragmentation, including that yielding Au(4)L(4) in ESI-TOF of a much larger thiolate-protected Au(144) nanoparticle under non-CID conditions.
authors.affiliation: Kenan Laboratories of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
authors.forename: Christina A
authors.initials: CA
authors.lastname: Fields-Zinna
authors.forename: Jason S
authors.initials: JS
authors.lastname: Sampson
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Crowe
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Tracy
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Parker
authors.forename: Alexander M
authors.initials: AM
authors.lastname: deNey
authors.forename: David C
authors.initials: DC
authors.lastname: Muddiman
authors.forename: Royce W
authors.initials: RW
authors.lastname: Murray
mesh_terms: D018360:Crystallography, X-Ray; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D053719:Tandem Mass Spectrometry
chemical_list: D013438:Sulfhydryl Compounds; D006046:Gold