title: Supramolecular aggregates in vacuum: positively monocharged sodium alkanesulfonate clusters.
abstract: The formation and structural features of positively monocharged aggregates of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and sodium methane--(MetS), butane--(ButS) and octane--(OctS) sulfonate molecules in gas phase have been investigated by electrospray ionization mass spectrometry, energy resolved mass spectrometry and density functional theory (DFT) calculations. The experimental results show that the center-of-mass collision energy required to dissociate 50% of these monocharged aggregates scantly depends on the length of the alkyl chain as well as on the aggregation number. This, together with the large predominance of monocharged species in the mass spectra, was rationalized in terms of an aggregation pattern mainly driven by the counter ions and head groups electrostatic interactions while minor effects were attributed to the steric hindrance caused by the size of the surfactant head group and alkyl chain. DFT calculations show that the most favoured structural arrangement of these aggregates is always characterized by an internal polar core constituted by the sodium counter ions and surfactant head groups surrounded by an external layer composed by the surfactant alkyl chains.
authors.affiliation: Dipartimento di Chimica e Tecnologie Farmaceutiche, Università di Palermo, Via Archirafi 32, I-90123 Palermo, Italy.
authors.forename: David
authors.initials: D
authors.lastname: Bongiorno
authors.forename: Leopoldo
authors.initials: L
authors.lastname: Ceraulo
authors.forename: Gianluca
authors.initials: G
authors.lastname: Giorgi
authors.forename: Serena
authors.initials: S
authors.lastname: Indelicato
authors.forename: Angela
authors.initials: A
authors.lastname: Ruggirello
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Turco Liveri
mesh_terms: D000476:Alkanesulfonates / Q000737:chemistry*; D011789:Quantum Theory; D012964:Sodium / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry; D014618:Vacuum
chemical_list: D000476:Alkanesulfonates; D012964:Sodium