UV–Visible Absorption Spectroscopy
of Protein Ions
8
Rodolphe Antoine and Philippe Dugourd
Abstract
Optical spectroscopy has contributed enormously to our knowledge of the
structure and dynamics of atoms and molecules and is now emerging as a
cornerstone of the gas-phase methods available for investigating biomolecular
ions. This chapter focuses on the UV and visible spectroscopy of peptide and
protein ions stored in ion traps. First, we discuss experimental set-ups, deexcitation mechanisms following photo-excitation in electronically excited
states and principles of action spectroscopy. Then, we report action spectra for
different classes of gas-phase peptides and proteins. The optical activity of
proteins in the near UV is directly related to the electronic structure and optical
absorption of aromatic amino acids (Trp, Phe and Tyr). Some proteins also show
absorption in the visible range due to the presence of a prosthetic group.
Influence of protein charge state, formation of radical aromatic amino acids
and solvation on proteins’ visible and UV spectra is discussed.
8.1
Introduction
UV–Vis excitation entails the electronic excitation of a molecular species. The
resulting spectra reflect the density of vibronic states and, depending on the type of
excitation, UV–Vis excitation can probe, for example, charge-transfer mechanisms,
the excitation of delocalised electrons and even ionisation processes. The first UV
spectrum of a gas-phase amino acid was reported in 1985 by Levy and co-workers
[1], using a cold molecular beam, and was rapidly followed by spectra for small
neutral peptides [2]. Peptides display strong absorption bands in the vacuum
ultraviolet (VUV) associated in particular with backbone peptide bond excitation.
R. Antoine (*) • P. Dugourd
Institut Lumie `re Matie `re, UMR5306 Universite ´ Lyon 1-CNRS Universite ´ de Lyon, 69622
Villeurbanne Cedex, France
e-mail: rodolphe.antoine@univ-lyon1.fr; philippe.dugourd@univ-lyon1.fr
S. Brøndsted Nielsen and J.A. Wyer (eds.), Photophysics of Ionic Biochromophores,
Physical Chemistry in Action, DOI 10.1007/978-3-642-40190-9_8,
# Springer-Verlag Berlin Heidelberg 2013
141
of Protein Ions
8
Rodolphe Antoine and Philippe Dugourd
Abstract
Optical spectroscopy has contributed enormously to our knowledge of the
structure and dynamics of atoms and molecules and is now emerging as a
cornerstone of the gas-phase methods available for investigating biomolecular
ions. This chapter focuses on the UV and visible spectroscopy of peptide and
protein ions stored in ion traps. First, we discuss experimental set-ups, deexcitation mechanisms following photo-excitation in electronically excited
states and principles of action spectroscopy. Then, we report action spectra for
different classes of gas-phase peptides and proteins. The optical activity of
proteins in the near UV is directly related to the electronic structure and optical
absorption of aromatic amino acids (Trp, Phe and Tyr). Some proteins also show
absorption in the visible range due to the presence of a prosthetic group.
Influence of protein charge state, formation of radical aromatic amino acids
and solvation on proteins’ visible and UV spectra is discussed.
8.1
Introduction
UV–Vis excitation entails the electronic excitation of a molecular species. The
resulting spectra reflect the density of vibronic states and, depending on the type of
excitation, UV–Vis excitation can probe, for example, charge-transfer mechanisms,
the excitation of delocalised electrons and even ionisation processes. The first UV
spectrum of a gas-phase amino acid was reported in 1985 by Levy and co-workers
[1], using a cold molecular beam, and was rapidly followed by spectra for small
neutral peptides [2]. Peptides display strong absorption bands in the vacuum
ultraviolet (VUV) associated in particular with backbone peptide bond excitation.
R. Antoine (*) • P. Dugourd
Institut Lumie `re Matie `re, UMR5306 Universite ´ Lyon 1-CNRS Universite ´ de Lyon, 69622
Villeurbanne Cedex, France
e-mail: rodolphe.antoine@univ-lyon1.fr; philippe.dugourd@univ-lyon1.fr
S. Brøndsted Nielsen and J.A. Wyer (eds.), Photophysics of Ionic Biochromophores,
Physical Chemistry in Action, DOI 10.1007/978-3-642-40190-9_8,
# Springer-Verlag Berlin Heidelberg 2013
141