nn1012447_si_001.pdf (951.13 kB)
Ion Mobility Mass Spectrometry of Au25(SCH2CH2Ph)18 Nanoclusters
journal contributionposted on 2010-08-24, 00:00 authored by Laurence A. Angel, Lance T. Majors, Asantha C. Dharmaratne, Amala Dass
Ion mobility mass spectrometry (IM-MS) can separate ions based on their size, shape, and charge as well as mass-to-charge ratios. Here, we report experimental IM-MS and IM-MS/MS data of the Au25(SCH2CH2Ph)18− nanocluster. The IM-MS of Au25(SCH2CH2Ph)18− exhibits a narrow, symmetric drift time distribution that indicates the presence of only one structure. The IM-MS/MS readily distinguishes between the fragmentation of the outer protecting layer, made from six [−SR−Au−SR−Au−SR−] “staples’ where R = CH2CH2Ph, and the Au13 core. The fragmentation of the staples is characterized by the predominant loss of Au4(SR)4 from the cluster and the formation of eight distinct bands. The consecutive eight bands contain an increasing variety of AulSmRn− product ions due to the incremental fragmentation of the outer layer of Au21X14−, where X = S or SCH2CH2Ph. The mobility of species in each individual band shows that the lower mass species exhibit greater collision cross sections, facilitating the identification of the AulSmRn− products. Below the bands, in the region 1200−2800 m/z, product ions relating to the fragmentation of the Au13 core can be observed. In the low mass 50−1200 m/z region, fragment ions such as Au(SR)2−, Au2(SR)3−, Au3(SR)4−, and Au4(SR)5− are also observed, corresponding to the large fragments Au25-x(SR)18-(x+1). The study shows that most of the dominant large fragments are of the general type Au21X14∓, and Au17X10∓ with electron counts of 8 and 6 in negative and positive mode, respectively. This suggests that geometric factors may outweigh electronic factors in the selection of Au25(SR)18 structure.