Self-assembly and intra-cluster reactions of erbium and ytterbium bis(2-ethylhexyl)sulfosuccinates in the gas phase.

Abstract

The study of surfactant organization in vacuum allows surfactant-surfactant interaction to be unveiled in the absence of surrounding solvent molecules. Knowledge on their chemical-physical properties may also lead to the definition of more efficient gas-phase carriers, air-cleaning agents and nanoreactors. In addition, the presence of lanthanide-group ions adds unique photochemical properties to surfactants. The structural features, stability and fragmentation patterns of charged aggregates formed by lanthanide-functionalized surfactants, ytterbium and erbium bis(2-ethylhexyl)sulfosuccinate ((AOT)3Yb and (AOT)3Er), have been investigated by electrospray ionization mass spectrometry (ESI-MS), tandem mass spectrometry (ESI-MS/MS) and energy-resolved mass spectrometry (ER-MS). The experimental data indicate that the self-assembling of (AOT)3Yb and (AOT)3Er in the gas phase leads to the formation of a wide range of singly charged aggregates differing in their aggregation number, relative abundance and stability. In addition to specific effects on aggregate organization due to the presence of lanthanide ions, ER-MS experiments show rearrangements and in-cage reactions activated by collision, eventually including alkyl chain intra-cluster migration. Analysis of the experimental findings suggests that the observed chemical transformations occur within an organized supramolecular assembly rather than in a random association of components. The fragmentation pathways leading to the neutral loss of a fragment of nominal mass 534 Da, assigned as C28 H54 O7 S, from some positively charged aggregates has been rationalized.