title: Unimolecular chemistry of doubly protonated zwitterionic clusters.
abstract: Electrospray ionization and tandem mass spectrometry experiments have been used to study the fragmentation and electron-ion interactions of doubly charged zwitterionic clusters, [M(15) + 2H](2+) (where M = Glycine Betaine (GB), (CH(3))(3)N(+)CH(2)CO(2)(-), and Dimethylsulfonioacetate (DMSA), (CH(3))(2)S(+)CH(2)CO(2)(-)) which are close to the stability limit, i.e., the Coulomb repulsion of the charge within the cluster competes with attractive forces. The intercluster chemistry was studied using collision-induced dissociation (CID) and electron-induced dissociation (EID) in which the energy of the electrons has been varied from >0 to 30 eV. Experimental results suggest that the zwitterionic binding energy in the clusters follow the order GB > DMSA, which is consistent with theoretical calculations that highlight that the lower dipole moment of DMSA leads to a binding energy of DMSA that is 0.86 times smaller than that for GB. Multiply protonated clusters of both GB and DMSA dissociate through Coulomb explosion, which is in competition with neutral evaporation for DMSA. Electronic excitation of the cluster under EID conditions at higher electron energies >12 eV can lead to new intercluster reactions associated with bond cleavages where differences between the sulfur and nitrogen betaines are minor.
authors.affiliation: ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, School of Chemistry and Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Victoria, Australia.
authors.forename: Ellie Jung-Hwa
authors.initials: EJ
authors.lastname: Yoo
authors.forename: Linda
authors.initials: L
authors.lastname: Feketeová
authors.forename: George N
authors.initials: GN
authors.lastname: Khairallah
authors.forename: Richard A J
authors.initials: RA
authors.lastname: O'Hair
mesh_terms: D001622:Betaine / Q000737:chemistry*; D015394:Molecular Structure; D011522:Protons; D011789:Quantum Theory; D021241:Spectrometry, Mass, Electrospray Ionization; D013452:Sulfonium Compounds / Q000737:chemistry*
chemical_list: D011522:Protons; D013452:Sulfonium Compounds; D001622:Betaine; C121105:dimethylsulfonioacetate