Complexation of Fe(III)/Catechols in atmospheric aqueous phase and the consequent cytotoxicity assessment in human bronchial epithelial cells (BEAS-2B)

https://doi.org/10.1016/j.ecoenv.2020.110898Get rights and content

Highlights

  • Catechols/Fe(III) mixtures formed the complexes.

  • The phenolic-NO2 group enhanced the stability of complexes.

  • Chemical composition and cytotoxicity of these mixtures were investigated.

  • The reaction mechanism was proposed.

Abstract

Recent research has shown that the complexation of metals-organics plays an important role in atmospheric particulate matter, whose health effects should be taken into account. This work investigates the interactions between catechols (CAs), i.e., 4-nitrocatechol (4NC) and 4-methylcatechol (4MC), and transition metals (i.e., Fe) in the aqueous phase dark reaction. The formation of Fe/CAs complexes and secondary organics products are analyzed by UV–Vis spectroscopy, stopped-flow spectroscopy, high-resolution mass spectrometry and Raman spectroscopy, while the insoluble particulate matter formed from the CAs/Fe mixtures are characterized by the FTIR, X-ray photoelectron spectroscopy (XPS) and thermogravimetric-quadrupole-mass spectrometry (TG-Q-MS). On the basis of the density functional theory (DFT) calculation and experimental results, the possible formation pathways for the complexes of Fe(III) with 4NC (a proxy for organics) are proposed. The Fe/CAs complexes and organics products perhaps have significant sources of light absorption which play an important role in influencing the intensity of atmospheric radiation and particulate phase photochemistry. Besides, the cytotoxicity is tested as a function of concentrations for CAs/Fe mixtures in BEAS-2B cells. Our results show that CAs/Fe mixtures have strong association with cytotoxicity, indicating the mixtures have potential influence to human health.

Introduction

Biomass burning (BB) has long been regarded as an important source of air pollution, which has significant impacts on global and regional air quality, public health and climate (Chen et al., 2017). The inorganic and organic compounds emitted from BB that are important component of atmospheric particulate matter (Li et al., 2017), while BB emitted directly or formed indirectly significant amounts of organic compounds which are important precursors of secondary organic aerosol (SOA) (e.g., phenols, polycyclic aromatic hydrocarbon) (Yu et al., 2014). Phenolic compounds have high concentrations are obtained in the plumes of BB (Guieu et al., 2005; Ito, 2015; Wang et al., 2017), and amounts of previous studies have indicated that phenols and nitrophenols play an important role in the chemistry process of atmosphere (Finewax et al., 2018; Kroflic et al., 2015; Laskin et al., 2015; Lin et al., 2017; Vidovic et al., 2018).

In addition, the transition metals (e.g., Fe, Cu, Mn) are the important component of particulate matter in atmosphere, which can take part in the chemical process of inorganic and organics, affecting the formation of SOA (Al-Abadleh, 2015; Deguillaume et al., 2005; Herrmann et al., 2015). Iron is the most abundant transition metal in the atmospheric aqueous phase, and iron mainly exists in the form of reduced ferrous iron (Fe(II)) or oxidized ferric iron (Fe(III)) in atmospheric aqueous phase (Deguillaume et al., 2005; Herrmann et al., 2015; Ito, 2015). Recent work has pointed out that the interactions between metals and organics are important and complicated, which can form the metals-organics complexation in the atmospheric particulate matter (Lin et al., 2020; Wei et al., 2019). However, a handful of work has reported the interactions of phenols-metals in the atmospheric aqueous phase (Lavi et al., 2017; Slikboer et al., 2015). Slikboer (Slikboer et al., 2015) demonstrated that dark redox reactions involving iron and phenolic compounds lead to the formation of complex polymeric products, that strongly absorb visible light. So far, the effects of secondary products formed from the interactions between metals-organics on the biosphere are unknow, and the toxicity toward living organisms (including humans) has not been assessed. Recent reports indicate that a synergistic effect between metals and organic compounds in atmospheric particulate matter, which can generate reactive oxygen species (ROS) and cause inflammation (Lin et al., 2020; Lyu et al., 2018; Ovrevik et al., 2015), further leading to the cardiopulmonary illnesses (Cao et al., 2012).

In this work, we investigate the interactions of Fe(III) with CAs (i.e., 4NC, 4MC) in dark. 4NC and 4MC are proxies for phenolic compounds which were emitted from BB, and the precursor of SOA (Desyaterik et al., 2013), while that are also the products from the phenols in the atmospheric photochemical reaction (Finewax et al., 2018; Pillar and Guzman, 2017). With a series of analytical instruments, we conducted the comprehensive of tests to evaluate how the interaction between CAs and Fe(III) affects the chemical and toxicological properties of aerosol. Besides, we proposed the possible reaction mechdnanism for the products (i.e., the complexes, quinones and oligomers) in the CAs/Fe mixtures.

Section snippets

Chemicals

All chemicals were used as received. More details (e.g., sources, purity) are presented in the Supplementary Materials (SM).

Mixtures experiment

All dark reaction experiments were carried out in beakers, wrapped in aluminum foil to avoid the light. The dark reaction of CAs (0.02 mmol) with ferric chloride (0.04 mmol) were in 100 mL of aqueous solution for 120 min at room temperature (25 ± 2 °C), which named as CAs/Fe mixtures (i.e., 4NC/Fe mixture, 4MC/Fe mixture). We note that reagents concentration (0.2 mmol/L)

UV–vis spectra

In Fig. 1a and b, UV–Vis spectra are plotted as a function of pH for 1:2 CAs/Fe mixtures after 2 h in dark reaction. CAs/Fe mixtures show the obvious absorption in the visible light region at pH of 2.0 or 3.0, however, the CAs/Fe mixtures present no absorption in this region at pH of 4.0 or 5.0. This result shows that the absorption in the visible region is strongly dependent on pH value. Besides, the absorption spectra at a function of pH for the CAs or Fe solution are shown in Figs. S1a, b, c

Conclusions

This work investigates chemistry and cytotoxicity induced by catechols (i.e., 4NC, 4MC) and Fe(III) interactions in aqueous phase dark reaction. In the terms of 4NC/Fe mixture and 4MC/Fe mixture, similar results are in the formation of secondary organic products, i.e., quinones (important redox-active organics in the atmosphere), oligomers (significant source of BrC), and small organic acids (important components in the atmosphere). In the case of the Fe/CAs complexes formation. It is ranked

CRediT authorship contribution statement

Zhonghong Zhu: Investigation, Methodology, Writing - original draft. Jin Zhang: Methodology, Investigation. Guochun Lv: Formal analysis. Christian George: Writing - review & editing. Hartmut Herrmann: Writing - review & editing. Hongbo Fu: Writing - review & editing. Dan Li: Resources. Liwu Zhang: Resources. Xiaomin Sun: Resources. Hao Sun: Methodology. Xiaohong Guan: Resources. Qing Li: Writing - review & editing. Wenbo Dong: Resources. Xiang Li: Writing - review & editing. Xinke Wang: Writing

Declaration of competing interest

The authors declare that they have no conflict of interest.

Acknowledgments

This work was funded by National Natural Science Foundation of China (No. 91843301, 91743202, 21527814) and Marie Skłodowska-Curie Actions (690958-MARSU-RISE-2015). Zhonghong Zhu acknowledges a scholarship fund from the China Scholarship Council (File 201706100091) for participation in this research. The high-resolution mass spectrometry research described in this paper was performed at Waters Technology Co., Ltd. (Shanghai), and thanks very much for the technical support.

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