Chapter 8
Ultrafast Ionization and Fragmentation:
From Small Molecules to Proteomic Analysis
Marcos Dantus and Christine L. Kalcic
Abstract Proteomic analysis offers great diagnostic relevance, because unlike
DNA, different cells in an organism express different proteins. In fact, the cellular proteome can vary as a function of time or in response to stimuli. Beyond amino
acid sequence, protein function depends on chemical modifications known as posttranslational modifications (PTMs) that serve as “switches” and “signals” that activate or inhibit vital functions. Despite advances in mass spectrometry, which have
led to the development of fully automated protein sequencing instruments, the mapping of PTMs remains a challenge. The interaction of intense near-infrared femtosecond laser pulses with isolated molecules or ions leads to the creation of radicalion species through an ultrafast process known as tunnel ionization. The resulting
unstable ions fragment according to predictable dissociation pathways. Progress analyzing and controlling the fundamental processes taking place during photoionization and fragmentation of small polyatomic molecules has led to the development of
femtosecond laser-induced ionization/dissociation (fs-LID) for proteomic analysis.
Fs-LID has been proven effective for the mapping of phosphorylation sites as well
as other PTMs along the peptide backbone. The fundamental steps involved in fsLID, which permits cleavage of strong bonds while leaving chemically labile bonds
intact, are discussed. Numerous examples are given to illustrate this exciting new
ion activation method, and potential applications are identified.
8.1 Ultrafast Field Ionization and Its Application to Analytical
Chemistry
The utility of ultrafast photoionization in analytical chemistry stems from the mechanism by which energy is deposited into the population of molecules or ions being studied. While IR laser excitation is comparable to a slow-heating method, and
UV laser excitation relies on resonant photon absorption, the femtosecond laser can
cause ultrafast electron loss (oxidation) through a process known as tunnel ionM. Dantus (B) · C.L. Kalcic
Michigan State University, East Lansing, MI, USA
e-mail: dantus@msu.edu
R. de Nalda, L. Bañares (eds.), Ultrafast Phenomena in Molecular Sciences,
Springer Series in Chemical Physics 107, DOI 10.1007/978-3-319-02051-8_8,
© Springer International Publishing Switzerland 2014
171
Ultrafast Ionization and Fragmentation:
From Small Molecules to Proteomic Analysis
Marcos Dantus and Christine L. Kalcic
Abstract Proteomic analysis offers great diagnostic relevance, because unlike
DNA, different cells in an organism express different proteins. In fact, the cellular proteome can vary as a function of time or in response to stimuli. Beyond amino
acid sequence, protein function depends on chemical modifications known as posttranslational modifications (PTMs) that serve as “switches” and “signals” that activate or inhibit vital functions. Despite advances in mass spectrometry, which have
led to the development of fully automated protein sequencing instruments, the mapping of PTMs remains a challenge. The interaction of intense near-infrared femtosecond laser pulses with isolated molecules or ions leads to the creation of radicalion species through an ultrafast process known as tunnel ionization. The resulting
unstable ions fragment according to predictable dissociation pathways. Progress analyzing and controlling the fundamental processes taking place during photoionization and fragmentation of small polyatomic molecules has led to the development of
femtosecond laser-induced ionization/dissociation (fs-LID) for proteomic analysis.
Fs-LID has been proven effective for the mapping of phosphorylation sites as well
as other PTMs along the peptide backbone. The fundamental steps involved in fsLID, which permits cleavage of strong bonds while leaving chemically labile bonds
intact, are discussed. Numerous examples are given to illustrate this exciting new
ion activation method, and potential applications are identified.
8.1 Ultrafast Field Ionization and Its Application to Analytical
Chemistry
The utility of ultrafast photoionization in analytical chemistry stems from the mechanism by which energy is deposited into the population of molecules or ions being studied. While IR laser excitation is comparable to a slow-heating method, and
UV laser excitation relies on resonant photon absorption, the femtosecond laser can
cause ultrafast electron loss (oxidation) through a process known as tunnel ionM. Dantus (B) · C.L. Kalcic
Michigan State University, East Lansing, MI, USA
e-mail: dantus@msu.edu
R. de Nalda, L. Bañares (eds.), Ultrafast Phenomena in Molecular Sciences,
Springer Series in Chemical Physics 107, DOI 10.1007/978-3-319-02051-8_8,
© Springer International Publishing Switzerland 2014
171