Do Water Molecules Always Stabilize Resonances? Microhydration Effects on Thymine Shape Resonances

Area of Science:

• Computational chemistry
• Theoretical chemistry
• Quantum chemistry

Background:

• Thymine is a fundamental nucleobase.
• Understanding nucleobase interactions in aqueous environments is crucial for molecular biology and chemistry.
• Resonance states play a key role in the electronic properties and reactivity of molecules.

Purpose of the Study:

• To investigate the impact of microhydration on the low-lying π* shape resonances of thymine.
• To quantify changes in resonance positions and lifetimes upon hydration.
• To elucidate the underlying mechanisms responsible for hydration effects on thymine resonances.

Main Methods:

• Utilized the Resonance via Padé approach.
• Employed the EA-EOM-DLPNO-CCSD computational method.
• Benchmarked calculations against projected CAP-EA-EOM-CCSD and compared with experimental data.

Main Results:

• Observed systematic stabilization and increased lifetimes for the 1π* and 2π* resonances upon hydration.
• The 3π* resonance exhibited more complex behavior.
• Resonance lifetimes increased significantly, e.g., from 39 fs to 110 fs for the lowest resonance in a trimer cluster.
• Identified contributions from hydrogen bonding, electrostatic interactions, geometric distortion, and basis set effects.

Conclusions:

• Microhydration leads to genuine physical stabilization of thymine resonance states.
• Resonance stabilization is sensitive to local hydrogen-bonding arrangements and microsolvation geometry.
• A subtle interplay between geometry, basis set effects, and intermolecular interactions governs resonance stabilization in microhydrated nucleobases.