Pushing the Limit of Infrared Multiphoton Dissociation to Megadalton-Size DNA Ions

Abstract

We report the use of infrared multiphoton dissociation (IRMPD) for the determination of relative activation energies for unimolecular dissociation of megadalton DNA ions. Single ions with masses in the megadalton range were stored in an electrostatic ion trap for a few tens of milliseconds and the image current generated by the roundtrips of ions in the trap was recorded. While being trapped, single ions were irradiated by a CO2 laser and fragmented, owing to multiphoton IR activation. The analysis of the single-ion image current during the heating period allows us to measure changes in the charge of the trapped ion. We estimated the activation energy associated with the dissociation of megadalton-size DNA ions in the frame of an Arrhenius-like model by analyzing a large set of individual ions in order to construct a frequency histogram of the dissociation rates for a collection of ions.

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“…83–86 The high IRMPD efficiency of oligodeoxynucleotides was recognized 20 years ago in a study comparing dissociation of oligodeoxynucleotides and proteins in an FTICR instrument. 40 IRMPD mass spectra of deprotonated oligodeoxynucleotides exhibit a great array of sequence ions, such as ( a – B ) and w ions for oligodeoxyribonucleotides which arise from cleavage of the 3′-C-O bond after initial base loss (Figure 3) and internal fragment ions (denoted by Bx:By in which the Bx and By indicate the positions of the nucleobases that are incorporated in the internal products), and c- and y -type ions for oligoribonucleotides.…”

Single‐molecule mass spectrometry

“…A similar ion trap has been used by Antoine and co‐workers to do tandem MS. They studied infrared multiphoton dissociation of MDa‐range DNA (Doussineau et al, , , ) and PEG (Antoine et al, ) ions. A single‐pass charge detector tube preceded the trap and was used to trigger a trapping event for an ion with the appropriate mass and charge.…”

“…The inset shows an expanded view of the signal between 8 and 10 ms. Adapted fromDoussineau et al (2012a).…”

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“…The image charge waveform also yields the particle time-of-flight (TOF) and velocity through the pickup providing the mass-to-charge ratio for fixed energy particles [15]. This method has been used in accelerator experiments since at least 1960 [9], and with the increasing interest in studies of massive biomolecules, cells and nanoparticles it has seen more recent applications in mass spectrometry measurements [16][17][18][19][20][21][22][23][24], with the state of the art recently described by Keifer and Jarrold [25]. In our own laboratory, we make use of a variant of this approach, applying a charge-pickup electrode in an electrostatic fast-ion beam trap to monitor the ion density oscillating in the trap and carry out Fourier-transform (FT) mass spectrometry on ensembles of molecular ions [26,27].…”