New approach for studying slow fragmentation kinetics in FT-ICR: Surface-induced dissociation combined with resonant ejection

Abstract

A B S T R A C TWe introduce a new approach for studying the kinetics of large ion fragmentation in the gas phase by coupling surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer with resonant ejection of selected fragment ions using a relatively short (5 ms) ejection pulse. The approach is demonstrated for singly protonated angiotensin III ions excited by collisions with a self-assembled monolayer of alkylthiol on gold (HSAM). The overall decomposition rate and rate constants of individual reaction channels are controlled by varying the kinetic energy of the precursor ion in a range of 65-95 eV. The kinetics of peptide fragmentation are probed by varying the delay time between ion activation by collision and short (5 ms) resonant ejection of selected fragment ions at a constant total reaction time of 150 ms. RRKM modeling indicates that the shape of the kinetics plots is strongly affected by the shape and position of the energy deposition function (EDF) describing the internal energy distribution of the ion following ion-surface collision. Modeling of the kinetics data provides detailed information on the shape of the EDF and energy and entropy effects of individual reaction channels.

Effect of basic residue on the kinetics of peptide fragmentation examined using surface-induced dissociation combined with resonant ejection

“…Resonant ejection was performed by applying an excitation pulse of t 1 ms duration at the resonant frequency of a fragment ion of interest to the two excitation plates of the ICR cell 6 ring electrode. [42] In this study, SID spectra were acquired at 15 delay times between ion trapping and resonant ejection given by equation (1): (1) with the shortest delay time placing the ejection pulse right before ion trapping and the longest delay time of 179 ms. This allowed access to both fast and slow fragmentation pathways.…”

“…[18,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] Another approach for studying the kinetics of large ion fragmentation combines SID in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) with resonant ejection of selected fragment ions at a variable delay time. [42] In this approach, fragment ions at a particular m/z formed before the ejection pulse is applied are removed from the spectrum, while ions at the same m/z formed after the ejection pulse are detected in the spectrum. In addition, product ions formed through sequential fragmentation of the ejected fragment are affected by the ejection pulse, while all other fragments remain unperturbed.…”

“…RRKM modeling enables determination of both the dissociation parameters of the individual fragmentation channels and the shape of the EDF from the time-resolved resonant ejection SID data. [42] In this study, time-resolved resonant ejection SID experiments are used to examine the effect of basic residue on the fragmentation kinetics of protonated peptides.…”

“…However, the shapes of the kinetics plots vary widely for different fragment ions. In this study, the experimental conditions were optimized for characterizing the kinetics of both fast and slow fragmentation pathways by applying a substantially shorter ejection pulse, 1 ms in duration, compared with the 5 ms ejection pulse used in a previous study[42] and extending the range of short delay times at which the ejection pulse is applied. Under these conditions, good quality kinetics plots could be obtained for fast fragmentation pathways, including the formation of the b5 +H 2 O ion (panel b), b 2 ion (panel e), and b 1 ion (panel f), for which the fragmentation kinetics are complete after a 1-5 ms reaction delay.…”

Surface-Induced Dissociation: A Unique Tool for Studying Energetics and Kinetics of the Gas-Phase Fragmentation of Large Ions

“…SID in FT-ICR-MS provides several advantages for studying energy and entropy effects in the dissociation of large ions 19 influenced by the presence of a kinetic shift. 41 These include the efficient collection of scattered ions in a strong magnetic field, a long and variable delay time between the ion-surface collision and the analysis that facilitates time-resolved SID studies, 40 and resonant ejection of selected fragment ions, recently used for studying the kinetics and mechanisms of peptide fragmentation in the gas phase on a timescale of >1 ms. 42 Furthermore, it has been demonstrated that small changes in dissociation parameters are efficiently amplified in FT-ICR-MS SID experiments. 19 This "amplification" originates from differences in kinetic shifts that are substantial for slow fragmentation pathways and from partial conversion of the projectile ion's kinetic energy into the vibrational excitation.…”