Dissociation of Valine Cluster Cations

Area of Science:

• Mass spectrometry
• Physical chemistry
• Computational chemistry

Background:

• Protonated cluster cations (M_nH⁺) are unexpectedly dominant for aliphatic amino acids.
• Gas-phase dissociation typically involves loss of the carboxylic group (45 Da).

Purpose of the Study:

• Elucidate the formation pathways of M_nH⁺ cations from amino acid clusters.
• Investigate the dissociation dynamics of valine cluster cations (M_n⁺) and their protonated forms (M_nH⁺).

Main Methods:

• Collision-induced dissociation experiments.
• Ab initio calculations.
• Cluster ion assembly within Helium droplets.

Main Results:

• Successfully prepared and studied valine cluster cations (M_n⁺) using Helium droplet isolation.
• Observed dissociation of M_n⁺ into M_n-1H⁺ and [M_n-COOH]⁺.
• Found M_n-1H⁺ formation becomes dominant with increased internal energy.

Conclusions:

• The high abundance of protonated amino acid clusters is explained by the M_n-1H⁺ formation pathway.
• M_n-1H⁺ ions predominantly fragment via monomer loss, reinforcing their prevalence in mass spectra.