Identifying Cytosine-Specific Isomers via High-Accuracy Single Photon Ionization

Area of Science:

• Biophysical Chemistry
• Computational Chemistry
• Molecular Spectroscopy

Background:

• Biological molecules like DNA bases and proteins exist as numerous tautomers and isomers with similar energies.
• Experimental identification of a specific tautomer is difficult due to these energetic similarities.

Purpose of the Study:

• To experimentally determine the adiabatic ionization energies (AIEs) of specific gas-phase cytosine tautomers.
• To showcase a methodology for characterizing complex mixtures of tautomers in biological molecules.

Main Methods:

• Utilized vacuum ultraviolet (VUV) synchrotron-based experiments on a molecular beam.
• Employed state-of-the-art ab initio computational methods, including explicitly correlated approaches.
• Analyzed experimental spectra to resolve contributions from individual neutral cytosine tautomers.

Main Results:

• Successfully identified and characterized five neutral cytosine tautomers in the gas phase.
• Experimentally determined the adiabatic ionization energies (AIEs) for these tautomers with high accuracy (0.003 eV).
• Spectra showed well-resolved bands corresponding to distinct tautomeric contributions prior to ionization.

Conclusions:

• This study provides the first experimental AIEs for specific cytosine tautomers.
• The combined experimental and computational approach is effective for studying complex tautomeric systems.
• The methodology can be applied to other biological molecules with dense isomeric and tautomeric forms.