Two dimensional correlation analysis of Fourier transform ion cyclotron resonance mass spectra of dissolved organic matter: a new graphical analysis of trends

Novel insights into the relationship between the functional groups and photoactivity of biochar-derived dissolved organic matter

Due to the production of a large amount of biochar, highly photoactive biochar-derived dissolved organic matter (BDOM) from different sources is released into surface water. This study investigated the molecular composition of BDOM (sludge, bamboo and stalk BDOM) using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and used tetracycline (TC) as model pollutant to investigate the relationship between molecular composition and BDOM photoactivity, specifically focusing on reactive oxygen species (ROS) production. The results indicate that the fluorescence signal intensity of humic acid-like and aromatic proteins in the plant-derived BDOM are significantly higher than that derived from sewage sludge. FT-ICR MS results also showed that plant-derived BDOM contained more CHO molecular formula. Photodegradation experiments of TC mediated by various BDOM analogues demonstrated the photoactivity is highly correlated with the components and functional groups. The electrochemical experiments and density functional theory (DFT) calculations further verified that the aromatic moiety, sulfydryl group and amino group of BDOM affected the electronic supply and energy transfer. Higher electron and energy transfer favor the reaction of BDOM with the ground state oxygen to generate ROS, thus promoting photodegradation of TC. This study provides a new basis for better assessing the ecological risks of BDOM.

Molecular-level insights into the heterogeneous variations and dynamic formation mechanism of leached dissolved organic matter during the photoaging of polystyrene microplastics

Microplastics (MPs) and their derivatives have received worldwide attention owing to their adverse effects on ecosystems. However, molecular diversity and dynamic formation of dissolved organic matter (DOM) during the photoaging of MPs remain unclear. Herein, we explored a molecular‒level formation mechanism for polystyrene MP (MPPS)‒derived DOM (PSDOM) during the photoaging of MPs to explain the evolution, heterogeneity, and sequential response of molecules to irradiation. Two‒dimensional correlation spectroscopy was applied to correlate the variations of PSDOM molecules detected by Fourier transform-ion cyclotron resonance mass spectrometry with those of MPPS functional groups detected by Fourier transform infrared spectroscopy. Irradiation‒induced PSDOM contained the most highly unsaturated structures with oxygen, but showed fewer aromatic structures than natural aquatic DOM. Photochemical transformations occurred between saturated‒reduced and oxidized molecules during PSDOM leaching, with the low‒oxidized and high‒oxidized molecules undergoing considerable changes in the normal carbon oxidation state and molecular number, respectively. The primary sequential response of PSDOM molecules to increasing irradiation time [low‒oxidized/high‒weight (450 Collapse

Key Words

• Dynamic formation
• Fluorescence properties
• Heterogeneous correlations
• Leaching responses
• Molecular parameters
• Unique molecules

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MESH Headings

• Microplastics
• Polystyrenes
• Plastics
• Dissolved Organic Matter
• Ecosystem
• Skin Aging

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Affiliation(s)

Fanhao Song State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China
Tingting Li State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; School of Environment, Tsinghua University, Beijing 100084, China
Jin Hur Department of Environment and Energy, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul, 05006, South Korea
Quan Shi State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China
Fengchang Wu State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China.
Wei He Ministry of Education Key Laboratory of Groundwater Circulation and Environmental Evolution, China University of Geosciences (Beijing), Beijing 100083, China
Di Shi State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China
Chen He State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, China
Lingfeng Zhou State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China
Mingqi Ruan State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China
Yuhan Cao State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China

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Temperature-Dependent Molecular Evolution of Biochar-Derived Dissolved Black Carbon and Its Interaction Mechanism with Polyvinyl Chloride Microplastics

Biochar-derived dissolved black carbon (DBC) molecules are dependent on the BC formation temperature and affect the fate of emerging contaminants in waters, such as polyvinyl chloride microplastic (MP_PVC). However, the temperature-dependent evolution and MP_PVC-interaction of DBC molecules remain unclear. Herein, we propose a novel DBC-MP_PVC interaction mechanism by systematically interpreting heterogeneous correlations, sequential responses, and synergistic relationships of thousands of molecules and their linking functional groups. Two-dimensional correlation spectroscopy was proposed to combine Fourier transform-ion cyclotron resonance mass spectrometry and spectroscopic datasets. Increased temperature caused diverse DBC molecules and fluorophores, accompanied by molecular transformation from saturation/reduction to unsaturation/oxidation with high carbon oxidation states, especially for molecules with acidic functional groups. The temperature response of DBC molecules detected via negative-/positive-ion electrospray ionization sequentially occurred in unsaturated hydrocarbons → lignin-like → condensed aromatic → lipid-/aliphatic-/peptide-like → tannin-like → carbohydrate-like molecules. DBC molecular changes induced by temperature and MP_PVC interaction were closely coordinated, with lignin-like molecules contributing the most to the interaction. Functional groups in DBC molecules with m/z < 500 showed a sequential MP_PVC-interaction response of phenol/aromatic ether C-O, alkene C═C/amide C═O → polysaccharides C-O → alcohol/ether/carbohydrate C-O groups. These findings help to elucidate the critical role of DBCs in MP environmental behaviors.

Machine-learning assisted molecular formula assignment to high-resolution mass spectrometry data of dissolved organic matter

High-resolution mass spectrometry (HRMS) provides molecular compositional information of dissolved organic matter (DOM) through isotopic assignment from the molecular mass. However, due to the inevitable deviation of molecular mass measurement and the limitation of resolving power, multiple possible solutions frequently occur for a given molecular mass. Lowering the mass deviation threshold and adding assignment restriction rules are often applied to exclude the incorrect solutions, which generally involves time-consuming manual post-processing of mass data. To improve the result accuracy in an automated manner, we developed a molecular formula assignment algorithm based on machine-learning technology. The method integrated a logistic regression model using manually corrected isotopic composition and the peak features of HRMS data (m/z, signal-to-noise ratio, isotope type, and number, etc.) as training data. The developed model can evaluate the correctness of a candidate formula for the given mass peak based on the peak features. The method was verified by various DOM samples FT-ICR MS data (direct infusion negative mode electrospray), achieving a ∼90% accuracy (compared to the traditional approach) for formula assignment. The method was applied to a series of NOM samples and showed a significant improvement in formula assignment compared with the mass matching method.

Extracellular polymeric substances mediate defect generation and phytotoxicity of single-layer MoS2

Two-dimensional transition metal dichalcogenide (TMDC) nanomaterials have attracted tremendous research interest in various fields, but the effects of eco-corona formation on the transformation mechanisms and ecological risk of TMDCs remain largely unknown. The effect of eco-corona formation on TMDC reactivity was explored using extracellular polymeric substances (EPS) as the eco-corona constituents and single-layer molybdenum disulfide (SLMoS₂) as the model TMDC. We found that EPS promoted lattice distortion and the formation of defects (sulfur vacancies and pores) on SLMoS₂ after it was aged (precoated) with EPS under simulated visible-light irradiation. In addition, the EPS-corona induced higher free radical (especially hyperoxide radical) photogeneration by SLMoS₂. Furthermore, compared to pristine SLMoS₂, SLMoS₂-EPS exhibited stronger developmental inhibition, oxidative stress, membrane damage, photosynthetic toxicity and metabolic perturbation effects on Chlorella vulgaris. However, the endocytosis pathway (especially macropinocytosis) of SLMoS₂ entry into C. vulgaris was inhibited by EPS. Metabolic and transcriptomic analyses revealed that the enhanced toxicity of SLMoS₂-EPS was associated with the downregulation of fatty acid metabolism and transcription related to photosynthesis, respectively. The present work provides mechanistic insights into the roles of the EPS-corona on the environmental transformation and phytotoxicity of TMDCs, which benefit environmental safety assessments and sustainable applications of engineered nanomaterials.

Marine dissolved organic matter: a vast and unexplored molecular space

Abstract

Marine dissolved organic matter (DOM) comprises a vast and unexplored molecular space. Most of it resided in the oceans for thousands of years. It is among the most diverse molecular mixtures known, consisting of millions of individual compounds. More than 1 Eg of this material exists on the planet. As such, it comprises a formidable source of natural products promising significant potential for new biotechnological purposes. Great emphasis has been placed on understanding the role of DOM in biogeochemical cycles and climate attenuation, its lifespan, interaction with microorganisms, as well as its molecular composition. Yet, probing DOM bioactivities is in its infancy, largely because it is technically challenging due to the chemical complexity of the material. It is of considerable interest to develop technologies capable to better discern DOM bioactivities. Modern screening technologies are opening new avenues allowing accelerated identification of bioactivities for small molecules from natural products. These methods diminish a priori the need for laborious chemical fractionation. We examine here the application of untargeted metabolomics and multiplexed high-throughput molecular-phenotypic screening techniques that are providing first insights on previously undetectable DOM bioactivities.

Key points

• Marine DOM is a vast, unexplored biotechnological resource.

• Untargeted bioscreening approaches are emerging for natural product screening.

• Perspectives for developing bioscreening platforms for marine DOM are discussed.

Insight into transformation of dissolved organic matter in the Heilongjiang River

Heilongjiang is a "browning" river that receives substantial terrestrial organic matter, where reactivity of dissolved organic matter (DOM) may have important effect on ecosystem function and carbon biogeochemical cycle. However, little is known about microbial transformations of different DOM components, which could provide valuable insight into biogeochemical reactivity of DOM. In this study, bioavailability experiments were conducted for 55 days to determine changes of different DOM components by microbial transformations. Labile matter (C1) was detected only in initial DOM, and tryptophan-like substances (C4) were observed from day 5 onwards. Thus, three individual components were identified at each sampling time of the bioavailability experiment. The increase of F_max in DOM components revealed that microbial humic-like substances (C2), terrestrial humic-like substances (C3), and C4 were produced by microbial transformation, especially in the spring samples. Further, two-dimensional correlation spectroscopy (2D-COS) indicated that shorter wavelength tryptophan-like and microbial humic-like substances can be degraded by microbes or transformed into longer wavelength complex substances. Relatively simple microbial humic-like substances were preferentially produced compared to complex terrestrial humic-like substances. The results make sense to understand the biogeochemical cycling and environmental effects of DOM in the Heilongjiang River.

Using network analysis to discern compositional patterns in ultrahigh-resolution mass spectrometry data of dissolved organic matter

RATIONALE

Marine dissolved organic matter (DOM) has long been recognized as a large and dynamic component of the global carbon cycle. Yet, DOM is chemically varied and complex and these attributes present challenges to researchers interested in addressing questions about the role of DOM in global biogeochemical cycles.

METHODS

Organic matter extracts from seawater were analyzed by direct infusion with electrospray ionization into a Fourier transform ion cyclotron resonance mass spectrometer. Network analysis was used to quantify the number of chemical transformations between mass-to-charge values in each sample. The network of chemical transformations was calculated using the MetaNetter plug-in within Cytoscape. The chemical transformations serve as markers for the shared structural characteristics of compounds within complex DOM.

RESULTS

Network analysis revealed that transformations involving selected sulfur-containing moieties and isomers of amino acids were more prevalent in the deep sea than in the surface ocean. Common chemical transformations were not significantly different between the deep sea and surface ocean. Network analysis complements existing computational tools used to analyze ultrahigh-resolution mass spectrometry data.

CONCLUSIONS

This combination of ultrahigh-resolution mass spectrometry with novel computational tools has identified new potential building blocks of organic compounds in the deep sea, including the unexpected importance of dissolved organic sulfur components. The method described here can be readily applied by researchers to analyze heterogeneous and complex DOM. Copyright © 2016 John Wiley & Sons, Ltd.

Adsorption Behavior of Extracellular Polymeric Substances on Graphene Materials Explored by Fluorescence Spectroscopy and Two-Dimensional Fourier Transform Infrared Correlation Spectroscopy

Adsorption isotherms of extracellular polymeric substances (EPS) on graphene oxide (GO) and reduced GO (rGO) were studied using fluorescence excitation-emission matrix-parallel factor analysis (EEM-PARAFAC) and two-dimensional correlation spectroscopy (2D-COS) combined with Fourier transform infrared spectroscopy (FTIR). Chemical reduction of GO resulted in a greater extent of carbon adsorption with a higher degree of isotherm nonlinearity, suggesting that heterogeneous adsorption sites were additionally created by GO reduction. Two protein-like and two humic-like components were identified from EPS by EEM-PARAFAC. Adsorption of protein-like components was greater than that of humic-like components, and the preferential adsorption was more pronounced for GO versus rGO. Adsorption of protein-like components was more governed by site-limiting mechanisms than humic-like components as shown by the higher isotherm nonlinearity. 2D-COS provided further information on the adsorption of secondary protein structures. Adsorption of the EPS structures related to amide I and aromatic C-C bands was greater for rGO versus GO. Protein structures of EPS were more favorable for adsorption in the order of α-helix → amide II → β-sheet structures with increasing site limitation. Our results revealed successful applicability of EEM-PARAFAC and 2D-COS in examining the adsorption behavior of heterogeneous biological materials on graphene materials.

Dissolved organic matter in Lake Superior: insights into the effects of extraction methods on chemical composition

Dissolved organic matter (DOM) in aquatic systems plays many biogeochemical roles, acting as a sunscreen, a food source, a trace metal chelator, and a photosensitizer. The efficiency of DOM in these roles is, in part, a function of its composition, which is difficult to determine due to its heterogeneity and the difficulty in isolating representative portions for subsequent molecular level analyses. In this study, the performance of two major types of solid phase extraction (SPE) resins (C18 vs. polymeric SDVB) in disk format (C18 disk vs. SDB-XC disk) was studied using DOM from Lake Superior, the earth's largest lake by area. The performance of the two SPE disks and their influences on the molecular chemical composition of the extracted retentates were studied with UV-vis spectrometry and negative-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). We found that SDB-XC disks outperformed C18 disks in the isolation of DOM in terms of both higher recovery and less fractionation relative to the initial DOM composition. Extracts of the same samples obtained with the different resins shared 70% of molecular formulae. Compounds exclusive to the SDB-XC extractions exhibited similar compound distributions to those of the shared formulae but were enriched in N, P, and S and more aromatic. The C18 exclusive compounds had somewhat higher H/C ratios and contained a large proportion of compounds with oxygen and nitrogen (CHON). Cluster analysis and principle component analysis confirmed that sample location was the main driver of the composition of extracted samples but showed some fractionation of the samples based upon the type of resin.

Chromatographic methods for the isolation, separation and characterisation of dissolved organic matter

This review presents an overview of the separation techniques applied to the complex challenge of dissolved organic matter characterisation. The review discusses methods for isolation of dissolved organic matter from natural waters, and the range of separation techniques used to further fractionate this complex material. The review covers both liquid and gas chromatographic techniques, in their various modes, and electrophoretic based approaches. For each, the challenges that the separation and fractionation of such an immensely complex sample poses is critically reviewed.

Innovative methods in soil phosphorus research: A review

Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development. This review provides an overview of advanced state-of-the-art methods currently used in soil P research. These involve bulk and spatially resolved spectroscopic and spectrometric P speciation methods (1 and 2D NMR, IR, Raman, Q-TOF MS/MS, high resolution-MS, NanoSIMS, XRF, XPS, (µ)XAS) as well as methods for assessing soil P reactions (sorption isotherms, quantum-chemical modeling, microbial biomass P, enzymes activity, DGT, ³³P isotopic exchange, ¹⁸O isotope ratios). Required experimental set-ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.

Photochemical alterations of natural and anthropogenic dissolved organic nitrogen in the York River

In the following study, we addressed the effects of photoirradiation on the turnover of dissolved organic nitrogen (DON) from both natural and anthropogenic sources at the molecular level. Analysis of long-term photoirradiated samples via Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) identified both the photolabile and the photoproduced DON from both natural and anthropogenic sources. Although photoproduction of DON was prominent with natural dissolved organic matter (DOM) sources, even in a low nitrogen environment, the anthropogenic source shows a shift from photobleaching to photohumification denoted by an increase in the average molecular weight (MW) and the double bound equivalent (DBE) after 25 days of a continuous exposure to UV light, implying condensation of low MW molecules (LMW) to form high MW (HMW) molecules. Furthermore, the sharp increase in N/C molar ratio, in the anthropogenic source, substantiates the photoinduced dissolved inorganic nitrogen (DIN) incorporation hypothesis. Hence, our findings suggest that anthropogenic input will drive substantial variation in riverine DOM and, thus, estuarine optics and photochemistry and bioavailability. Furthermore, we validate that photochemistry is one of the main processes that shapes the DON quality in aquatic systems regardless of its original source.