title: Protonated serine octamer cluster: structure elucidation by gas-phase H/D exchange reactions.
abstract: The H/D exchange kinetics of the protonated serine octamer was investigated by both flow-tube and FT-ICR experiments. The exchange was observed to be bimodal in agreement with previous observations. Quantitative analysis of the experimental results led to site-specific H/D exchange rate constants on the basis of which the structures of both ion populations were deduced. We observe the two separate conformers exchanging 33 hydrogens each-in an independent manner and at different rates. This result was achieved through a probabilistic algorithm that groups together equivalent hydrogen atoms having equal rate constants. The slower exchanging population A is assigned an all-zwitterionic structure. Its faster exchanging counterpart B is assigned an all-neutral structure. Population A was found to be more stable toward collision-induced activation than population B. All of these findings are consistent with previous experimental results, thus comprising a self-consistent picture of the protonated serine octamer and its gas-phase properties.
authors.affiliation: Department of Physical Chemistry and The Farkas Center for Light Induced Processes, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
authors.forename: Ulf
authors.initials: U
authors.lastname: Mazurek
authors.forename: Orit
authors.initials: O
authors.lastname: Geller
authors.forename: Chava
authors.initials: C
authors.lastname: Lifshitz
authors.forename: Melinda A
authors.initials: MA
authors.lastname: McFarland
authors.forename: Alan G
authors.initials: AG
authors.lastname: Marshall
authors.forename: Bryan G
authors.initials: BG
authors.lastname: Reuben