Fragmentation of Neutral Amino Acids and Small Peptides by Intense, Femtosecond Laser Pulses
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High power femtosecond laser pulses have unique properties that could lead to their application as ionization or activation sources in mass spectrometry. By concentrating many photons into pulse lengths approaching the timescales associated with atomic motion, very strong electric field strengths are generated, which can efficiently ionize and fragment molecules without the need for resonant absorption. However, the complex interaction between these pulses and biomolecular species is not well understood. To address this issue, we have studied the interaction of intense, femtosecond pulses with a number of amino acids and small peptides. Unlike previous studies, we have used neutral forms of these molecular targets, which allowed us to investigate dissociation of radical cations without the spectra being complicated by the action of mobile protons. We found fragmentation was dominated by fast, radical-initiated dissociation close to the charge site generated by the initial ionization or from subsequent ultrafast migration of this charge. Fragments with lower yields, which are useful for structural determinations, were also observed and attributed to radical migration caused by hydrogen atom transfer within the molecule.
Key wordsIon activation Non-statistical dissociation Femtosecond laser induced dissociation Femtosecond laser ionization Radical induced dissociation Charge migration Peptide sequencing Time of flight
The authors acknowledge support for this work by the Leverhulme Trust, STFC through access to the Artemis Laser Facility, and EPSRC through the STFC Laser Loan Pool. C.R.C. acknowledges support from EPSRC through the Postdoctoral Fellowship Programme (grant number EP/H027319/1). L.B. and M.J.D. acknowledge the support of the Department of Employment and Learning, Northern Ireland. T.J.K. and J.T.C. acknowledge support from Science Foundation Ireland. The authors also acknowledge the technical assistance provided by Phil Rice at the Artemis Laser Facility.
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