DFT Meets Wave-Function Composite Methods for Characterizing Cytosine Tautomers in the Gas Phase

Area of Science:

• Computational Chemistry
• Biomolecular Modeling
• Spectroscopy

Background:

• Accurate computation of biomolecule properties is crucial for understanding biological processes.
• Tautomeric equilibria present a significant challenge in theoretical chemistry.
• Gas-phase studies provide a fundamental baseline for molecular behavior.

Purpose of the Study:

• To improve and validate a computational strategy for accurate gas-phase structural and spectroscopic properties of biomolecule building blocks.
• To apply the refined method to the complex problem of cytosine tautomers.
• To provide an unbiased interpretation of experimental spectroscopic data.

Main Methods:

• Utilized the cc-pVTZ-F12 basis set for Density Functional Theory (DFT) and Coupled Cluster with Singles and Doubles and perturbative Triples (CCSD(T))-F12 computations.
• Included core-valence correlation in geometry optimizations using double-hybrid functionals.
• Employed the cc-pVQZ-F12 basis set for complete basis set extrapolation at the Møller–Plesset perturbation theory (MP2)-F12 level.

Main Results:

• Achieved remarkable agreement between computed and experimental rotational and vibrational spectroscopic parameters for cytosine tautomers.
• Successfully interpreted spectroscopic data in terms of structural and thermochemical features.
• Demonstrated the accuracy of the composite method for gas-phase molecular analysis.

Conclusions:

• The improved composite method provides accurate and cost-effective computational results without empirical parameters.
• This validated strategy is suitable for precise investigations of other essential biomolecular building blocks.
• The study offers reliable insights into the tautomeric equilibria of biologically relevant molecules.