title: Electrospray ion mobility mass spectrometry of positively and negatively charged (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide aggregates.
abstract: BACKGROUND
  Self-assembling processes of surfactants in the gas phase constitute a developing research field of interest since they allow information to be gained on the peculiar structural organization of these aggregates, on their ability to incorporate from small molecules up to proteins and on their possible use as carriers of drugs in the gas phase or as cleaning agents and exotic reaction media.
  
  
  METHODS
  The mass spectra of charged aggregates of the chiral surfactant (1R,2S)-dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB) in the gas phase have been recorded using a Synapt G2-Si mass spectrometer in the positive and negative ion mode. For comparison purposes, the mass spectra of sodium bis(2-ethylhexyl)sulfosuccinate and sodium octane sulfonate aggregates have also been recorded under the same experimental conditions. The collisional cross sections of positively and negatively charged DMEB aggregates were obtained through an appropriate calibration of the measured drift times.
  
  
  RESULTS
  For all the surfactants investigated, it has been found that there is a lowest and a highest limit of the aggregation number at each charge state: no aggregates are found outside this range. Moreover, the occurrence at each aggregation number and extra charge of a unique value of drift time points toward aggregates whose conformations do not show discernible shape change in the experiment time scale. The analysis of the collisional cross sections emphasizes that the DMEB aggregates are nearly spherical clusters somewhat affected by the charge state and constituted by interlaced polar and apolar domains.
  
  
  CONCLUSIONS
  The analysis of all the experimental findings indicates that in the gas phase DMEB forms supramolecular aggregates characterized by an internal organization whose stability is triggered by the charge state. The comparison of the behavior of DMEB aggregates with that of sodium bis(2-ethylhexyl)sulfosuccinate and sodium octane sulfonate aggregates allows us to highlight the effects on the aggregate organization in gas phase due to nature of the head group and alkyl chain steric hindrance.
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, Via Archirafi 32, I-90123, Palermo, Italy.
authors.forename: Serena
authors.initials: S
authors.lastname: Indelicato
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, Via Archirafi 32, I-90123, Palermo, Italy.
authors.forename: David
authors.initials: D
authors.lastname: Bongiorno
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, Via Archirafi 32, I-90123, Palermo, Italy.
authors.forename: Leopoldo
authors.initials: L
authors.lastname: Ceraulo
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, Via Archirafi 32, I-90123, Palermo, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Calabrese
authors.affiliation: Dipartimento di Fisica e Chimica, Università degli Studi di Palermo, Viale delle Scienze, Ed. 17, I-90128, Palermo, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Piazzese
authors.affiliation: Dipartimento di Chimica e Tecnologie Chimiche, Università della Calabria, Via P. Bucci Cubo 12/C, I-87036, Arcavacata di Rende, (CS)-Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Napoli
authors.affiliation: Dipartimento di Chimica e Tecnologie Chimiche, Università della Calabria, Via P. Bucci Cubo 12/C, I-87036, Arcavacata di Rende, (CS)-Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Mazzotti
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, Via Archirafi 32, I-90123, Palermo, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Avellone
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, Via Archirafi 32, I-90123, Palermo, Italy.
authors.forename: Vita
authors.initials: V
authors.lastname: Di Stefano
authors.affiliation: Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, Via Archirafi 32, I-90123, Palermo, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Turco Liveri