Through the combination of indoor simulations and field sampling,the studio of Professor Wang Yawei at the School of Environment, Hangzhou Institute for Advanced Study, UCAS (hereinafter referred to as HIAS), analyzed the role of Maillard chemistry in the formation of secondary atmospheric brown carbon (BrC) and its potential contribution to the chemical diversity of atmospheric aerosols with Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). The research paper entitled "Unexpected molecular diversity of brown carbon formed by Maillard-like reactions in aqueous aerosols" was published online in Chemical Science (Chem. Sci., 2022, DOI: 10.1039/D2SC02857C).
The Maillard reaction, also known as the "non-enzymatic browning reaction", was proposed by French chemist L.C. Maillard in 1912. It is a classic reaction in food chemistry. Many delicacies in our daily life, such as barbecued meat, toast, French fries, and braised meat, are products of the Maillard reaction. Recent studies have shown that this reaction can produce delicious food on the table and brown aerosols (brown carbon) in the atmosphere. The amines and carbonyl compounds ubiquitously present in the atmosphere are important precursors of the Maillard reaction. However, due to the extremely complex process of the Maillard reaction, the academic community's understanding of the role and mechanism of Maillard chemistry in the formation of secondary BrC was limited. The advantages of the ultra-high mass resolution FT-ICR MS in analyzing complex organic mixtures offer new opportunities to analyze the molecular composition of the products of Maillard chemical reactions in the atmosphere.
Figure 1 Analysis of Optical Properties and Chemical Composition of Secondary BrC
The studio simulated a series of Maillard reactions between carbonyl and amine compounds in the laboratory. Multiple kinds ofoptical spectroscopy,1H nuclear magnetic resonance (NMR), and FT-ICR MS were employed to comprehensively characterize the light-absorbing characteristics, functional group structures and molecular composition of the products generated from different precursors. The findings indicate that both the light-absorbing and molecular characteristics of secondary BrC are highly related to the structures of their precursors.Dicarbonyl compounds have better light absorption ability than monocarbonyl compounds, and organic amines have better light absorption ability than the products ofinorganic ammonia reactions. Based on the spectra and molecular characteristics of several products and FT-ICR MS/MS analysis, nitrogen heterocycles are the main light-absorbing component in the Maillard reaction products. Overall, more than 14,000 molecularformulae have been detected through simple precursor simulations. This indicates the molecular diversity of the Maillard reaction products and the larger contribution of carbonyl precursors to such molecular diversity. Meanwhile, 35%-64% of the molecular products detected in the simulated reactions have been also detected in real atmospheric PM2.5 samples, indicating that Maillard chemistry has a potentially important contribution to atmospheric organic aerosol molecules.As the first analysis of the molecular diversity of secondary BrC formed by the Maillard reaction, this research offers a new idea to further understand the formation and chemical diversity mechanism of atmospheric secondary organic aerosols.
The first author of this paper is Tang Shanshan, a postdoctoral fellow from the School of Environment, HIAS, and the corresponding authors are professor Wang Yawei and Lv Jitao, an associate research fellow from the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences.The research was supported by the National Natural Science Foundation of China and the China Postdoctoral Science Foundation.
Source | School of Environment
Typesetter | Wang Zhe
Executive Editor | Wang Xia
