Excited-State Dynamics of Protonated
Aromatic Amino Acids
9
Claude Dedonder, Ge ´raldine Fe ´raud, and Christophe Jouvet
Abstract
The electronic spectroscopy and the electronic excited state dynamics of the
three protonated aromatic amino acids (PAAAs) phenylalanine (Phe), tyrosine
(Tyr) and tryptophan (Trp) are presented in this chapter. Ab-initio calculations
combined with various experimental techniques such as coincidence
experiments, pump-probe spectroscopy and photo-fragmentation of cold trapped
ions have been implemented to work out the complex photophysical processes
involved in these AAs. The results include photo-fragmentation spectra, excitedstate lifetimes, full fragmentation patterns at fixed excitation energies and
specific fragmentation channels as a function of the excitation energy. Fragmentation patterns depending on the electronic excited state are detailed.
9.1
Introduction
There are three aromatic amino acids: phenylalanine (Phe) with benzene as the
aromatic chromophore, tyrosine (Tyr) for which phenol is the aromatic moiety, and
tryptophan (Trp) for which it is indole (Fig. 9.1). These are responsible for the
absorption of UV light by proteins. The oscillator strength of the electronic transition in Trp is one order of magnitude larger than that of Tyr and two orders of
magnitude larger than the Phe transition [1–3]. Thus, Trp is the amino acid mostly
responsible for the optical properties of proteins in the UV-B (315–260 nm) spectral
region. Trp has an emission band centre that strongly depends on the local environment, and this property is used to follow the folding/unfolding processes in
proteins; Trp residues that are buried in the hydrophobic core of proteins can
have spectra shifted by tens of nm compared to Trp on the surface of the protein
C. Dedonder (*) • G. Fe ´raud • C. Jouvet
Laboratoire de Physique des Interactions Ioniques et Mole ´culaires, CNRS UMR 7345,
Aix Marseille Universite ´. Centre de Saint-Je ´ro ˆme, 13397 Marseille Cedex 20, France
e-mail: Christophe.jouvet@univ-amu.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_9,
# Springer-Verlag Berlin Heidelberg 2013
155
Aromatic Amino Acids
9
Claude Dedonder, Ge ´raldine Fe ´raud, and Christophe Jouvet
Abstract
The electronic spectroscopy and the electronic excited state dynamics of the
three protonated aromatic amino acids (PAAAs) phenylalanine (Phe), tyrosine
(Tyr) and tryptophan (Trp) are presented in this chapter. Ab-initio calculations
combined with various experimental techniques such as coincidence
experiments, pump-probe spectroscopy and photo-fragmentation of cold trapped
ions have been implemented to work out the complex photophysical processes
involved in these AAs. The results include photo-fragmentation spectra, excitedstate lifetimes, full fragmentation patterns at fixed excitation energies and
specific fragmentation channels as a function of the excitation energy. Fragmentation patterns depending on the electronic excited state are detailed.
9.1
Introduction
There are three aromatic amino acids: phenylalanine (Phe) with benzene as the
aromatic chromophore, tyrosine (Tyr) for which phenol is the aromatic moiety, and
tryptophan (Trp) for which it is indole (Fig. 9.1). These are responsible for the
absorption of UV light by proteins. The oscillator strength of the electronic transition in Trp is one order of magnitude larger than that of Tyr and two orders of
magnitude larger than the Phe transition [1–3]. Thus, Trp is the amino acid mostly
responsible for the optical properties of proteins in the UV-B (315–260 nm) spectral
region. Trp has an emission band centre that strongly depends on the local environment, and this property is used to follow the folding/unfolding processes in
proteins; Trp residues that are buried in the hydrophobic core of proteins can
have spectra shifted by tens of nm compared to Trp on the surface of the protein
C. Dedonder (*) • G. Fe ´raud • C. Jouvet
Laboratoire de Physique des Interactions Ioniques et Mole ´culaires, CNRS UMR 7345,
Aix Marseille Universite ´. Centre de Saint-Je ´ro ˆme, 13397 Marseille Cedex 20, France
e-mail: Christophe.jouvet@univ-amu.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_9,
# Springer-Verlag Berlin Heidelberg 2013
155