Competitive Radical Migrations and Ribose Ring Cleavage in Adenosine and 2'-Deoxyadenosine Cation Radicals

Area of Science:

• Physical Chemistry
• Chemical Kinetics
• Mass Spectrometry

Background:

• Adenosine cation radicals are important in biological systems and chemical reactions.
• Understanding radical reaction mechanisms is crucial for various scientific disciplines.
• Previous studies have explored radical fragmentation but lacked detailed kinetic insights.

Purpose of the Study:

• To elucidate the mechanism and kinetics of intramolecular hydrogen transfer in adenosine cation radicals.
• To investigate the subsequent ribose ring cleavage pathways.
• To compare the reactivity of adenosine and 2'-deoxyadenosine cation radicals.

Main Methods:

• Generation of adenosine cation radicals via collision-induced dissociation (CID).
• Characterization using tandem mass spectrometry and UV-vis photodissociation action spectroscopy.
• Kinetic analysis employing deuterium labeling and computational methods (RRKM, TST, DFT).

Main Results:

• Intramolecular hydrogen transfer primarily involves the 3'-H position, with minor contributions from 5'-H and 2'-H.
• Hydrogen transfer is the rate-determining step, preceding rapid ribose ring cleavage.
• 2'-deoxyadenosine cation radicals exhibit lower transition state energies for hydrogen transfer and ring cleavage compared to adenosine.

Conclusions:

• The study provides a detailed kinetic model for hydrogen transfer and fragmentation in adenosine cation radicals.
• The findings highlight the significant role of the ribose moiety in radical stabilization and reaction pathways.
• Computational and experimental data offer valuable insights into the fundamental chemistry of nucleoside radicals.