title: Photodissociation of protonated tryptophan and alteration of dissociation pathways by complexation with crown ether.
abstract: The behavior of protonated tryptophan (TrpH(+)) and its complex with 18-crown-6-ether (CE) after photoexcitation has been explored based on measurements of dissociation lifetimes, fragmentation channels, and absorption spectra using an electrostatic ion storage ring. A recent implementation of pulsed power supplies for the ring elements with microsecond response times allows us to identify the daughter ion fragment masses and to disentangle fragmentation that occurs from excited states immediately after photoexcitation from that occurring on a longer time scale of several microseconds to milliseconds. We find that attachment of crown ether significantly alters the dissociation channels since it renders the pisigma(*)(NH(3)) state inaccessible and hence prevents the N-H bond breakage which is an important fragmentation channel of TrpH(+). As a result, on a long time scale (>10 micros), photoexcited TrpH(+)(CE) decays exponentially whereas TrpH(+) displays a power-law decay. The only ions remaining in the latter case are Trp(+) radical cations with a broad internal energy distribution caused by the departing hydrogen. Large changes in the fragment branching ratios as functions of excitation wavelength between 210 and 290 nm were found for both TrpH(+) and TrpH(+)(CE).
authors.affiliation: Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C, Denmark. kumesh@phys.au.dk
authors.forename: Umesh
authors.initials: U
authors.lastname: Kadhane
authors.forename: Jens Ulrik
authors.initials: JU
authors.lastname: Andersen
authors.forename: Anneli
authors.initials: A
authors.lastname: Ehlerding
authors.forename: Preben
authors.initials: P
authors.lastname: Hvelplund
authors.forename: Maj-Britt S
authors.initials: MB
authors.lastname: Kirketerp
authors.forename: Morten Køcks
authors.initials: MK
authors.lastname: Lykkegaard
authors.forename: Steen Brøndsted
authors.initials: SB
authors.lastname: Nielsen
authors.forename: Subhasis
authors.initials: S
authors.lastname: Panja
authors.forename: Jean Ann
authors.initials: JA
authors.lastname: Wyer
authors.forename: Henning
authors.initials: H
authors.lastname: Zettergren
mesh_terms: D000042:Absorption; D043844:Crown Ethers / Q000737:chemistry*; D004579:Electron Transport; D007211:Indoles / Q000737:chemistry; D007700:Kinetics; D013058:Mass Spectrometry; D010782:Photolysis; D011522:Protons; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D013997:Time Factors; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D043844:Crown Ethers; D007211:Indoles; D011522:Protons; D000644:Quaternary Ammonium Compounds; C030374:indole; D014364:Tryptophan