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Energetics of Dissociation of Peptide Radical Cations


EMSL Project ID
14395

Abstract

Our intended studies will utilize time- and energy-resolved SID, combined with an RRKM-based modeling approach, to determine the energetics of dissociation of medium-size molecular radical
cationic oligopeptides, such as angiotensin III(RVYIHPF) and its derivatives ; or YGGFLK•+ and its
derivatives. Our recent success at forming a wide variety of radical cations of oligopeptides should
greatly expand the scope of investigations of molecular radical cations of oligopeptides.1 The ability to
form peptide radical cations in the gas phase raises a question about their stability relative to those of
the corresponding protonated species and smaller organic radical cations. Are the energetics of
dissociation of these species similar to the dissociation energetics of smaller radical cations? Does
conformational flexibility of these molecules have an effect on their gas phase stability? It is known that
the bond dissociation energy for organic radical cations is in the range 2.5–6 eV,2 while dissociation of
protonated peptides requires only 0.8–2 eV.3 This relative ease of dissociation of protonated peptides
has been attributed to the presence of a proton that migrates along the backbone of the peptide and
weakens the peptide bond in its vicinity—the “mobile proton model”.4 Studies of M•+ and [M + H]•2+
can help to bridge the gap between small organic cations and protonated peptide ions and facilitate an
understanding of the factors that govern bond strengths in ionic systems. This M•+ and [M +
H]•2+species have a large number of vibrational degrees of freedom, which results in a slow dissociation
that is ideally suited for kinetic studies on the timescale of our FT-ICR SID MS. An ion of almost
identical molecular weight—protonated angiotensin III(RVYIHPF)—has been studied extensively and
validated using the proposed methodologies.
For the upcoming program in the Pacific Northwest National Laboratory’s Summer Research
Institute in Interfacial and Condensed Phase Chemical Physics, we will conduct experiments on
molecular radical cationic oligopeptides using aforementioned method. The advantages provided by SID
include very fast ion activation, which eliminates possible discrimination against higher-energy
dissociation pathways, and efficient “amplification” of small changes in the dissociation parameters.4 We
will use this approach to address the question of stability of gas phase peptide radical cations. We will
use a combination of experimental and computational approaches to conduct the first studies on the
energetics of the dissociation of selected peptide radical cations and dications and compare these
results with the dissociation energetics of their corresponding protonated species.Collision energyresolved
studies provide important information on the appearance energies of different product ions and
on the amount of energy required for dissociation of the precursor ions. Another dimension is added to
SID experiments by conducting kinetic studies through varying the delay between the ion–surface
collision and the analysis of the resulting products.8 Although studies of time- and energy-resolved
spectra have been conducted so far for only a limited number of large ions, they have demonstrated a
great potential for allowing the detailed elucidation of fragmentation energetics and mechanisms.

Project Details

Start Date
2006-03-14
End Date
2007-06-04
Status
Closed

Team

Principal Investigator

Ivan Chu
Institution
The University of Hong Kong

Team Members

Ngor Wai Lam
Institution
The University of Hong Kong

Zhibo Yang
Institution
University of Colorado at Boulder

Jean Futrell
Institution
Pacific Northwest National Laboratory

Julia Laskin
Institution
Purdue University

Related Publications

J. Laskin, J. H. Futrell and I. K. Chu. “Is Dissociation of Peptide Radical Cations an Ergodic Process?”, J. Am. Chem. Soc. (Communication), 129, 9598-9599 (2007).
J. Laskin, Z. Yang, Corey Lam, and I. K. Chu “Charge-Remote Fragmentation of Odd-Electron Peptide Ions”, Anal. Chem., 79, 6607-6614 (2007)
Laskin J, Z Yang, and IK Chu. 2008. "Energetics and Dynamics of Electron Transfer and Proton Transfer in Dissociation of Metal III (salen)-Peptide Complexes in the Gas Phase." Journal of the American Chemical Society 130(10):3218-3230. doi:10.1021/ja077690s
Z. Yang, C. Lam, I. K. Chu, J. Laskin “The Effect of the Secondary Structure on Dissociation of Peptide Radical Cations: Fragmentation of Angiotensin III and Its Analogues”, J. Phys. Chem. B, 112, 12468-12478 (2008)