Chemical transformations of peptide containing fine particles: oxidative processing, accretion reactions and implications to the atmospheric fate of cell-derived materials in organic aerosol

Abstract

The atmospheric processing by ozone of peptide-containing mixed particles was investigated as proxies for biogenic and sea spray primary organic aerosol. Reactions were performed in a flow reactor and particle composition was monitored by photoelectron resonance capture ionization aerosol mass spectrometry. Mixed particles containing dipeptides in a saturated organic matrix of stearic and palmitic acids showed no reaction under ozonolysis at exposure levels of 2.5 × 10−4 atm s O3. However reactions of mixed particles of a dipeptide (Leu-Leu) in an unsaturated matrix (oleic acid) under the same conditions resulted in a rapid loss of the peptide ion signal, as well as the carrier matrix, and appearance of a number of ion signals corresponding to secondary products. High molecular weight imides and amides have been identified corresponding to possible reactions of ozonolysis products and reactive intermediates (i.e. aldehydes, stabilized Criegee intermediates). Additionally, tautomerisation of the imides to enamines in the particle phase is postulated, with ozonolysis of the enamine followed by regioselective decomposition of the primary ozonide to form an amide whereby the peptide incorporates an aldehydic group at the N-terminus. The same general reactivity pattern was observed for mixed particles of diglycine and oleic acid. This behavior was not observed in solution phase experiments, where the tautomerisation favors the more stable imine form, indicating that particulate phase reactions of this nature may be dependent on the specific particle physical properties. The implications of this chemistry with respect the atmospheric aging of cell-derived organic aerosol are discussed.