Two-Color IRMPD Applied to Conformationally Complex Ions: Probing Cold Ion Structure and Hot Ion Unfolding

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Physical Chemistry

Background:

• One-color infrared multiphoton dissociation (IRMPD) spectroscopy can suffer from spectral distortions caused by nonlinear absorption.
• Complex peptide ions often exist as mixtures of conformers, making spectral analysis challenging.

Purpose of the Study:

• To apply and evaluate a two-color infrared multiphoton dissociation (2C-IRMPD) technique for analyzing conformationally complex peptide ions.
• To demonstrate the control over internal energy and spectral output offered by the 2C-IRMPD method.
• To investigate the potential for resolving single conformers and studying conformational unfolding in peptide ions.

Main Methods:

• Utilized a 2C-IRMPD scheme with two independently tunable infrared laser sources.
• Varied experimental parameters including trap temperature, laser time delays and fluences, and laser wavelength scanning.
• Recorded near-infrared action spectra for both cations and anions across a temperature range of 10–300 K.

Main Results:

• Successfully recorded near-linear action spectra of peptide ions, mitigating nonlinear absorption distortions.
• Identified conditions for obtaining IR spectra of single conformers within a mixture.
• Demonstrated the ability to probe conformational unfolding by manipulating ion internal energy.

Conclusions:

• The 2C-IRMPD technique provides enhanced control over spectral acquisition for complex peptide ions.
• This method is valuable for detailed conformational analysis, including distinguishing conformers and studying dynamic structural changes.
• The study highlights the advantages and limitations of 2C-IRMPD for conformationally complex systems using Leu-enkephalin and YGPAA ions as models.