Photochemical selectivity in guanine-cytosine base-pair structures

Area of Science:

• Astrobiology
• Photochemistry
• Molecular Biophysics

Background:

• Prebiotic chemistry occurred before Earth's oxygen-rich atmosphere, under intense UV radiation.
• The UV photochemical stability of biomolecule building blocks may have influenced their selection.
• Understanding UV effects on base-pairing is crucial for origins of life research.

Purpose of the Study:

• To investigate the role of UV irradiation in the stability of guanine-cytosine (G-C) base pairs.
• To determine if specific base-pairing structures offer photochemical stability under prebiotic conditions.
• To explore the potential selective pressures of UV radiation on early life's molecular components.

Main Methods:

• Studied guanine (G) and cytosine (C) base pairs without the RNA backbone.
• Utilized IR-UV hole-burning spectroscopy to distinguish base-pair structures.
• Employed high-level correlated ab initio calculations for structural analysis.

Main Results:

• The Watson-Crick (WC) G-C base pair structure exhibited broad UV absorption.
• Other G-C base pair structures and other base pairs showed different UV absorption profiles.
• The WC structure's broad absorption is attributed to rapid internal conversion.

Conclusions:

• The Watson-Crick G-C base pair arrangement is uniquely photochemically stable under UV irradiation.
• This stability may have been a significant factor in the selection of G-C base pairs in early life.
• Photochemical stability likely played a role in determining the chemical makeup of critical biomolecules.