Deprotonated purine dissociation: experiments, computations, and astrobiological implications.

Area of Science:

• Astrobiology and Astrochemistry
• Physical Chemistry and Molecular Dynamics

Background:

• Astrobiology investigates the abiotic synthesis of biomolecules, crucial for understanding life's origins.
• Organic anions detected in the interstellar medium (ISM) suggest their potential role in prebiotic chemistry.
• Understanding molecular dissociation pathways provides insights into synthesis routes.

Purpose of the Study:

• To experimentally and computationally investigate the dissociation mechanisms of deprotonated adenine and guanine.
• To elucidate potential anionic precursor roles in the formation of purines in extraterrestrial environments.
• To determine the acidity of abundant fragment ions.

Main Methods:

• Collision-induced dissociation (CID) experiments using an ion trap mass spectrometer to measure product branching fractions.
• Tandem mass spectrometry (MS(n)) to analyze sequential fragmentation patterns.
• Theoretical calculations at the B3LYP/6-311++G(d,p) level to delineate dissociation mechanisms and energy landscapes.

Main Results:

• Deprotonated guanine primarily dissociates via deammoniation (97%), with minor losses of other small molecules.
• Deprotonated adenine predominantly fragments through loss of HCN/HNC (90%), with minor carbodiimide/cyanamide loss (10%).
• All observed neutral fragments have been detected in the ISM, supporting the potential for nucleobase formation in space.

Conclusions:

• The dissociation pathways of deprotonated adenine and guanine provide evidence for their potential formation in the interstellar medium.
• This research highlights the significance of anionic species in astrochemical pathways leading to prebiotic molecules.
• Experimental and theoretical data support the role of these anions as precursors to biologically relevant purines.