Ion Mobility Mass Spectrometry of Au25(SCH2CH2Ph)18 Nanoclusters

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 Au-25(SCH2CH2Ph)(18)(-) nanocluster. The IM-MS of Au-25(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 Au-13 core. The fragmentation of the staples is characterized by the predominant loss of Au-4(SR)(4) from the cluster and the formation of eight distinct bands. The consecutive eight bands contain an increasing variety of AuISmRn- 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 AuISmRn- products. Below the bands, in the region 1200-2800 m/z, product ions relating to the fragmentation of the Au-13 core can be observed. In the low mass 50-1200 m/z region, fragment ions such as Au(SR)(2)(-), Au-2(SR)(3)(-), Au-3(SR)(4)(-), and Au-4(SR)(s)(-)(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 Au-25(SR)(18) structure.