Kinetic ion thermometers for electron transfer dissociation

Area of Science:

• Mass spectrometry
• Chemical kinetics
• Physical chemistry

Background:

• Peptide cation-radicals are crucial in proteomics.
• Electron transfer dissociation (ETD) is a key fragmentation technique.
• Understanding internal energy in gas-phase ions is vital for accurate analysis.

Purpose of the Study:

• To utilize z-type peptide fragment ions as kinetic thermometers.
• To quantify the internal energy of peptide cation-radicals generated by ETD.
• To investigate energy partitioning during ion dissociation.

Main Methods:

• Time-resolved kinetic measurements using a linear ion trap mass spectrometer.
• Kinetic modeling incorporating collisional cooling and product neutralization.
• Application of RRKM theory to convert dissociation rate constants to internal energies.

Main Results:

• Spontaneous dissociation of z2 ions (z2(Leu-Lys), z2(Leu-Arg)) by loss of C3H7 was observed.
• Internal energy of fragment ions decreased with increasing precursor peptide ion size.
• Experimentally determined excitation energies were lower than theoretically predicted.

Conclusions:

• Z-type ions serve as effective kinetic thermometers for gas-phase ions.
• Vibrational energy partitioning is consistent with ergodic behavior.
• A discrepancy exists between experimental and theoretical excitation energies, suggesting energy loss mechanisms warrant further investigation.