Chemistry at the rim: Differentiation of isomeric open-cage fullerenes by MALDI-LIFT and ESI-MS/MS.

Graphical abstract Differentation of open-cage fullerene isomers by dissociation of sodiated monomers (using LIFT) and dimers (using CID) reveals multiple interaction motives. Highlights • Ion formation of open-cage fullerenes (OCFs) by DCTB- / pencil lead- MALDI and ESI. • MS2 spectra of the molecular ions of isomeric OCFs are indistinguishable. • MS2 spectra of sodiated and potassiated OCFs differentiate between isomers. • Metal coordination to the heteroatoms at the cage orifice causes differentiation. • Relative sodium ion affinities are obtained by the kinetic method. Abstract Isomeric open-cage fullerenes (OCFs) are studied by MALDI-LIFT. The two types of isomers feature different connectivities of the heteroatoms at the rim of the orifice to the fullerene cage. The molecular ions (radical cations, M+.) are generated by electron transfer MALDI, using DCTB as the matrix. The resulting LIFT spectra are indistinguishable. The alternative use of pencil lead is found inferior as a matrix but proves an exceptionally facile method of creating sodium and potassium adducts. The fragmentation of these metallated OCFs reveals different fragmentation pathways allowing the differentiation of the OCF isomers. This is evidently caused by the different interactions of the metal cation with the heteroatoms at the rim of the orifice. Additionally, the influence of the functionalization and isomer structure on the sodium ion affinity (SIA) is analysed by the kinetic method investigating the dissociations of sodium-bound hetero-dimers in electrospray ionization/ collision-induced dissociation (ESI-CID) experiments. [ABSTRACT FROM AUTHOR]