Impairment of a model peptide by oxidative stress: Thermodynamic stabilities of asparagine diamide Cα-radical foldamers

Electron structure calculations on N-acetyl asparagine N-methylamide were performed to identify the global minimum from which radicals were formed after H-abstraction by the OH radical. It was found that the radical generated by breaking the C–H bond of the α-carbon was thermodynamically the most stable one in the gas- and aqueous phases. The extended (βL and βD) backbone conformations are the most stable, but syn–syn or inverse γ-turn (γL) and γ-turn (γD) have substantial stability too. The highest energy conformers are the degenerate εL and εD foldamers. Clearly, the most stable β foldamer is the most likely intermediate for racemization.