Structural Insight into ESI+-Generated Ions of Oxazolochlorin Derivatives Using Cryogenic Infrared Ion Spectroscopy

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Organic Chemistry

Background:

• Oxazolochlorins are synthetic porphyrinoids with unique oxazoline rings.
• Electrospray ionization mass spectrometry (ESI-MS) is used to analyze these compounds.
• Understanding the structure of ions formed during ESI-MS is crucial for characterization.

Purpose of the Study:

• To investigate the structural characterization of oxazolochlorin ions formed by ESI-MS.
• To demonstrate the utility of cryogenic ion vibrational spectroscopy (CIVS) for analyzing these ions.
• To explore the influence of protonation sites, isomers, and metal ions on ion structure.

Main Methods:

• Electrospray ionization mass spectrometry (ESI-MS) for ion generation.
• Cryogenic ion vibrational spectroscopy (CIVS) for structural analysis.
• Density-functional theory (DFT) calculations for spectral interpretation.

Main Results:

• CIVS successfully distinguished between different protonation sites and constitutional isomers of oxazolochlorins.
• The technique provided information about alkoxy side chains on protonated oxazolochlorins.
• The influence of Ni2+ and Ag2+ metal ions on vibrational spectra was elucidated, confirming their coordination and impact on macrocycle structure.

Conclusions:

• Cryogenic infrared ion spectroscopy is a powerful tool for detailed structural elucidation of oxazolochlorin ions generated via ESI.
• This study provides a proof of concept for applying CIVS to porphyrinoid ions, expanding structural understanding under ESI conditions.