relaxation channels were observed for cations [28, 29]. After photoexcitation,
direct dissociation in the excited state competes with internal conversion to the
electronic ground state and with radiative de-excitation. Control of the fragmentation pathways by photon activation would open new perspectives from the
fundamental as well as analytical viewpoint. This could possibly be achieved
through wavelength tuning [30]. A more general control of the dynamics will
certainly involve optimal control, using shaped femtoseconds laser pulses [31] to
drive the chosen process.
All the results discussed in this chapter rely on the electronic excitation of
natural protein chromophores to the first excited states (ππ* or charge-transfer
type of excitations). Other electronic excitations can be explored by increasing
the energy of the photons. In the vacuum ultra-violet range, excitation of
peptides and proteins arises from ππ
* , nπ, . . . excitations of different functional
groups as well as photoionisation processes (see Chap. 11 by Schlatho ¨lter and
Hoekstra) [10, 32, 33]. Another approach for exploring different types of
excitations is to modify the optical properties of proteins. Proteins can be tagged
with covalently or non-covalently bound chromophores, in particular to allow
excitations in the near-UV or visible range. We have shown one example for
cytochrome c with visible excitation of the prosthetic heme group. Tagging
specific amino acids with dyes has also been used in the literature [34–36].
In parallel to these spectroscopic investigations, UV and visible lasers can be
used to create new reactive intermediates that can be stored and manipulated in
ion traps [37]. Electron photodetachment, which was the main focus of this
chapter, leads to the formation of radical anions [38, 39]. The isolation of the
oxidised radical anions and subsequent fragmentation initiated by collisioninduced dissociation (Activated-EPD) [9] leads to high sequence coverages.
This new technique is complementary to electron detachment dissociation
(EDD) and reverse-electron transfer dissociation (ETD) for peptide and protein
polyanions [40, 41].
References
1. Rizzo, T.R., Park, Y.D., Peteanu, L., Levy, D.H.: Electronic spectrum of the amino acid
tryptophan cooled in a supersonic molecular beam. J. Chem. Phys. 83, 4819–4820 (1985)
2. Cable, J.R., Tubergen, M.J., Levy, D.H.: Electronic spectroscopy of small tryptophan peptides
in supersonic molecular beams. J. Am. Chem. Soc. 110, 7349–7355 (1988)
3. Creighton, T.E.: Proteins: Structures and Molecular Properties, 2nd edn. W. H. Freeman,
New York (1992)
4. Rizzo, T.R., Stearns, J.A., Boyarkin, O.V.: Spectroscopic studies of cold, gas-phase biomolecular ions. Int. Rev. Phys. Chem. 28, 481–515 (2009)
5. Nielsen, S.B., Lapierre, A., Andersen, J.U., Pedersen, U.V., Tomita, S., Andersen, L.H.:
Absorption spectrum of the green fluorescent protein chromophore anion in vacuo. Phys.
Rev. Lett. 87, 228102 (2001)
6. Nielsen, I.B., Boye-Peronne, S., El Ghazaly, M.O.A., Kristensen, M.B., Nielsen, S.B.,
Andersen, L.H.: Absorption spectra of photoactive yellow protein chromophores in vacuum.
Biophys. J. 89, 2597–2604 (2005)
8 UV–Visible Absorption Spectroscopy of Protein Ions
151
direct dissociation in the excited state competes with internal conversion to the
electronic ground state and with radiative de-excitation. Control of the fragmentation pathways by photon activation would open new perspectives from the
fundamental as well as analytical viewpoint. This could possibly be achieved
through wavelength tuning [30]. A more general control of the dynamics will
certainly involve optimal control, using shaped femtoseconds laser pulses [31] to
drive the chosen process.
All the results discussed in this chapter rely on the electronic excitation of
natural protein chromophores to the first excited states (ππ* or charge-transfer
type of excitations). Other electronic excitations can be explored by increasing
the energy of the photons. In the vacuum ultra-violet range, excitation of
peptides and proteins arises from ππ
* , nπ, . . . excitations of different functional
groups as well as photoionisation processes (see Chap. 11 by Schlatho ¨lter and
Hoekstra) [10, 32, 33]. Another approach for exploring different types of
excitations is to modify the optical properties of proteins. Proteins can be tagged
with covalently or non-covalently bound chromophores, in particular to allow
excitations in the near-UV or visible range. We have shown one example for
cytochrome c with visible excitation of the prosthetic heme group. Tagging
specific amino acids with dyes has also been used in the literature [34–36].
In parallel to these spectroscopic investigations, UV and visible lasers can be
used to create new reactive intermediates that can be stored and manipulated in
ion traps [37]. Electron photodetachment, which was the main focus of this
chapter, leads to the formation of radical anions [38, 39]. The isolation of the
oxidised radical anions and subsequent fragmentation initiated by collisioninduced dissociation (Activated-EPD) [9] leads to high sequence coverages.
This new technique is complementary to electron detachment dissociation
(EDD) and reverse-electron transfer dissociation (ETD) for peptide and protein
polyanions [40, 41].
References
1. Rizzo, T.R., Park, Y.D., Peteanu, L., Levy, D.H.: Electronic spectrum of the amino acid
tryptophan cooled in a supersonic molecular beam. J. Chem. Phys. 83, 4819–4820 (1985)
2. Cable, J.R., Tubergen, M.J., Levy, D.H.: Electronic spectroscopy of small tryptophan peptides
in supersonic molecular beams. J. Am. Chem. Soc. 110, 7349–7355 (1988)
3. Creighton, T.E.: Proteins: Structures and Molecular Properties, 2nd edn. W. H. Freeman,
New York (1992)
4. Rizzo, T.R., Stearns, J.A., Boyarkin, O.V.: Spectroscopic studies of cold, gas-phase biomolecular ions. Int. Rev. Phys. Chem. 28, 481–515 (2009)
5. Nielsen, S.B., Lapierre, A., Andersen, J.U., Pedersen, U.V., Tomita, S., Andersen, L.H.:
Absorption spectrum of the green fluorescent protein chromophore anion in vacuo. Phys.
Rev. Lett. 87, 228102 (2001)
6. Nielsen, I.B., Boye-Peronne, S., El Ghazaly, M.O.A., Kristensen, M.B., Nielsen, S.B.,
Andersen, L.H.: Absorption spectra of photoactive yellow protein chromophores in vacuum.
Biophys. J. 89, 2597–2604 (2005)
8 UV–Visible Absorption Spectroscopy of Protein Ions
151