Reaction of Amino Acids, Di- and Tripeptides with the Environmental Oxidant NO3.: A Laser Flash Photolysis and Computational Study

• Published in: Chemistry, an Asian journal Vol. 11; no. 22; pp. 3188 - 3195
• Main Authors: Nathanael, Joses G., Hancock, Amber N., Wille, Uta
• Format: Journal Article
• Language: English
• Published: Weinheim Blackwell Publishing Ltd 22.11.2016; Wiley Subscription Services, Inc
• Subjects: Chemistry; density functional calculations; kinetics; nitrate radical; oxidative damage; peptides; reaction mechanisms
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201600994

Absolute rate coefficients for the reaction between the important environmental free radical oxidant NO3. and a series of N‐ and C‐protected amino acids, di‐ and tripeptides were determined using 355 nm laser flash photolysis of cerium(IV) ammonium nitrate in the presence of the respective substrates in acetonitrile at 298±1 K. Through combination with computational studies it was revealed that the reaction with acyclic aliphatic amino acids proceeds through hydrogen ion from the α‐carbon, which is associated with a rate coefficient of about 1.8×106 m−1 s−1 per able hydrogen atom. The considerably faster reaction with phenylalanine [k=(1.1±0.1)×107 m−1 s−1] is indicative for a mechanism involving electron transfer. An unprecedented amplification of the rate coefficient by a factor of 7–20 was found with di‐ and tripeptides that contain more than one phenylalanine residue. This suggests a synergistic effect between two aromatic rings in close vicinity, which makes such peptide sequences highly vulnerable to oxidative damage by this major environmental pollutant. Unexpected synergism: Kinetic studies revealed an unprecedented amplification of the reactivity of di‐ and tripeptides with two phenylalanine residues in close vicinity towards nitrate radicals, NO3.. This suggests that such peptide sequences are highly prone to oxidative damage by this important environmental radical oxidant.