Ultrahigh-resolution Fourier Transform Ion Cyclotron Research Articles

Comprehensive Metabolomic Analysis of Human Heart Tissue Enabled by Parallel Metabolite Extraction and High-Resolution Mass Spectrometry.

The heart contracts incessantly and requires a constant supply of energy, utilizing numerous metabolic substrates, such as fatty acids, carbohydrates, lipids, and amino acids, to supply its high energy demands. Therefore, a comprehensive analysis of various metabolites is urgently needed for understanding cardiac metabolism; however, complete metabolome analyses remain challenging due to the broad range of metabolite polarities, which makes extraction and detection difficult. Herein, we implemented parallel metabolite extractions and high-resolution mass spectrometry (MS)-based methods to obtain a comprehensive analysis of the human heart metabolome. To capture the diverse range of metabolite polarities, we first performed six parallel liquid-liquid extractions (three monophasic, two biphasic, and one triphasic) of healthy human donor heart tissue. Next, we utilized two complementary MS platforms for metabolite detection: direct-infusion ultrahigh-resolution Fourier-transform ion cyclotron resonance (DI-FTICR) and high-resolution liquid chromatography quadrupole time-of-flight tandem MS (LC-Q-TOF-MS/MS). Using DI-FTICR MS, 9644 metabolic features were detected where 7156 were assigned a molecular formula and 1107 were annotated by accurate mass assignment. Using LC-Q-TOF-MS/MS, 21,428 metabolic features were detected where 285 metabolites were identified based on fragmentation matching against publicly available libraries. Collectively, 1340 heart metabolites were identified in this study, which span a wide range of polarities including polar (benzenoids, carbohydrates, and nucleosides) as well as nonpolar (phosphatidylcholines, acylcarnitines, and fatty acids) compounds. The results from this study will provide critical knowledge regarding the selection of appropriate extraction and MS detection methods for the analysis of the diverse classes of human heart metabolites.

Unambiguous molecular characterization of solid electrolyte interphase species on graphite negative electrodes

Performances of lithium-ion batteries (LIBs) are closely related to the control of solid-electrolyte interface (SEI) stability. To decrease the capacity losses linked to the build-up of this interface or potentially reverse such losses, electrolyte formulations have been continuously optimized over years to evaluate how they affect SEI. However, direct molecular characterization of the diverse interphases remains extremely challenging. Herein, we report the molecular imaging of SEI components formed on graphite electrodes by laser desorption ionization (LDI) coupled to ultrahigh-resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS). By exploiting the surface analysis offered by LDI combined with the molecular formula attributions provided by the FT-ICR MS, it is possible to unambiguously identify/exclude suspected molecules in the SEI such as lithium ethylene dicarbonate and lithium ethylene mono carbonate. Moreover, thousands of unknown species were observed, which could be exploited for further understanding of the surface composition. We believe this methodology to be a critical advance for the design of high-performance LiBs.

Interpreting pH-Dependent Differential UV/VIS Absorbance Spectra to Characterize Carboxylic and Phenolic Chromophores in Natural Organic Matter

Natural organic matter (NOM) is critical for the biogeochemical cycles of energy and many elements in terrestrial and aquatic ecosystems, and protonation-active functional groups in NOM molecules, notably carboxylic and phenolic groups often mediate these critical environmental functions. Molecular heterogeneity, polydispersity and dynamic behavior of NOM complicate achieving an unambiguous description of its molecular properties and reactivity. This study demonstrates that differential ultraviolet-visible (UV/VIS) absorbance spectra (DAS) of NOM acquired at varying pH values exhibit several distinct features associated with the deprotonation of NOM molecules, independent of the environmental provenance of NOM (e.g., surface water, seawater, sediment, and wastewater). The protonation-active functionalities that contribute to the Gaussian distribution bands present in the DAS were identified here by comparing characteristic properties of the bands with the stoichiometries of NOM molecules ascertained by Ultrahigh-Resolution Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). The protonation-active individual chromophores universally present in NOM molecules were identified by a genetic molecular network analysis. The observed DAS features were closely modeled via superimposing DAS spectra of 51 individual protonation-active chromophores. Molecular orbital theory was applied to further interpret the deprotonation of these chromophores, their molecular structure, electron distribution, and electron transitions measured using DAS. The high sensitivity and easy implementation of the DAS approach allows using it as a powerful tool to quantify the molecular properties and reactivity of NOM at environmental concentrations.

Comprehensive Characterization of Endogenous Phospholamban Proteoforms Enabled by Photocleavable Surfactant and Top-down Proteomics.

Top-down mass spectrometry (MS)-based proteomics has become a powerful tool for analyzing intact proteins and their associated post-translational modifications (PTMs). In particular, membrane proteins play critical roles in cellular functions and represent the largest class of drug targets. However, the top-down MS characterization of endogenous membrane proteins remains challenging, mainly due to their intrinsic hydrophobicity and low abundance. Phospholamban (PLN) is a regulatory membrane protein located in the sarcoplasmic reticulum and is essential for regulating cardiac muscle contraction. PLN has diverse combinatorial PTMs, and their dynamic regulation has significant influence on cardiac contractility and disease. Herein, we have developed a rapid and robust top-down proteomics method enabled by a photocleavable anionic surfactant, Azo, for the extraction and comprehensive characterization of endogenous PLN from cardiac tissue. We employed a two-pronged top-down MS approach using an online reversed-phase liquid chromatography tandem MS method on a quadrupole time-of-flight MS and a direct infusion method via an ultrahigh-resolution Fourier-transform ion cyclotron resonance MS. We have comprehensively characterized the sequence and combinatorial PTMs of endogenous human cardiac PLN. We have shown the site-specific localization of phosphorylation to Ser16 and Thr17 by MS/MS for the first time and the localization of S-palmitoylation to Cys36. Moreover, we applied our method to characterize PLN in disease and reported the significant reduction of PLN phosphorylation in human failing hearts with ischemic cardiomyopathy. Taken together, we have developed a streamlined top-down targeted proteomics method for comprehensive characterization of combinatorial PTMs in PLN toward better understanding the role of PLN in cardiac contractility.

Linking the source, molecular composition, and reactivity of dissolved organic matter in major rivers across the pearl river delta

Dissolved organic matter (DOM) constitutes a substantial portion of the global carbon cycle and serves as the largest reservoir of reactive carbon on Earth. Studying DOM's sources, molecular compositions, and reactivity is central to understanding the fate and environmental effects of organic carbon, yet, links between DOM composition and reactivity remain to be established. In this study, stable carbon isotopic composition and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) were combined with degradation experiments to comprehensively study DOM's properties in the major rivers across the Pearl River Delta (PRD) in South China. The increasing δ13C-DOC along the Pearl River at the PRD suggests that terrestrial DOM from upstream was gradually diluted by local processes. Although affected by different interaction patterns of multiple sources, a major component of DOM, enriched in CHO and lignins, is molecularly indistinguishable in different rivers (molecular Bray-Curtis dissimilarity of 15%–31%). The photo-degradation removed 34% (PDOC%) of initial DOM within 14 days, twice that by biodegradation (BDOC%). In contrast to earlier research, the distinctive integration of molecular characterization with DOM degradation kinetics indicates that both regional (common shared molecules) and local (partial shared and unique molecules) derived DOM play a collective role in governing the bio-degradation kinetics of DOM, while the photo-degradation kinetics of DOM are barely correlated to molecular composition. The thorough investigation of DOM molecular composition and its correlation with bulk DOM properties in the PRD region, though requiring further investigation into its mechanisms, offers valuable insights into the role of riverine DOM in coastal hypoxia and the global carbon cycle.

Spectral Quality Assessment Strategy Based on the 13C-Isotopic Pattern for the Fourier Transform Ion Cyclotron Resonance Mass Spectra of Dissolved Organic Matter.

The interpretation of data and optimization spectral acquisition of dissolved organic matter (DOM) by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) have been challenging due to the varied instrument performances among laboratories and the complex chemical characteristics of DOM. However, a universal spectral optimization strategy for FT-ICR MS spectra is still unavailable. The results of this study showed that the number, intensity, and resolving power of all assigned peaks increased with the ion accumulation time (IAT) and DOM concentrations within a reasonable range. The space-charge effect induced by the excess ions in the ICR cell can deteriorate the data quality of the FT-ICR MS spectra, which could be inspected by examining the mass errors and intensity deviation of the monoisotopic and 13C-isotopic peaks based on the 13C-isotopic pattern. The maximum absolute mass error and 13C-isotopic pattern-based intensity deviation are two critical criteria for inspecting the space-charge effect, which was suggested to be 2.0 ppm and 20%, respectively. Therefore, a novel strategy based on the 13C-isotopic pattern has been proposed in this study to optimize the FT-ICR MS spectra of DOM based on their wide occurrence of monoisotopic and 13C-isotopic signals. This optimization strategy has laid the fundamentals for the method development of FT-ICR MS and could be extended to different FT-ICR MS instruments and various organic complex mixtures.

Molecular weight of dissolved organic matter determines its interactions with microbes and its assembly processes in soils

Dissolved organic matter (DOM) is involved in numerous biogeochemical processes, and its molecular weight affects many of these processes through its bioavailability and sorptive capacity. However, it remains unknown to what extent the molecular weight of DOM mediates its dynamics, for example, influencing its role in DOM-microbe interactions and the processes determining the compositional assembly of DOM. To address this issue, ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and high-throughput sequencing were applied to investigate how the molecular weight of DOM was associated with its dynamics in two typical agricultural soils with different fertility. Our results showed that low-molecular-weight DOM had lower biological stability and a higher transformation potential. Analysis of the DOM-microbe co-occurrence network showed that low-molecular-weight DOM displayed tighter interactions with a diversity of microbes, while high-molecular-weight DOM interacted with only a few microbes. Ecological null models revealed that the compositional assembly of low-molecular-weight DOM, but not high-molecular-weight DOM, was more controlled by deterministic processes. Taken together, our results demonstrate the fundamental role the molecular weight of DOM plays in determining biological stability, transformation potential, interactions with microbes, and assembly mechanisms of DOM in agricultural soils. This work provides the foundation for general principles explaining complex dynamics of DOM in natural ecosystems, highlighting that using theories and concepts in metacommunity ecology, such as community diversity and assembly mechanisms, may open a new avenue to understand DOM dynamics from a macro perspective.

Effects of burn severity on organic nitrogen and carbon chemistry in high-elevation forest soils

Fire frequency and severity have increased in recent decades in the western United States, with direct implications for the quantity and composition of soil organic matter (SOM). While the effects of wildfire on soil carbon (C) and inorganic nitrogen (N) have been well studied, little is known about its impacts on soil organic N. Since organic N is the most abundant form of soil N in conifer forests and dominant source of plant N facilitated by symbiotic mycorrhizae and mineralization, better understanding of post-fire organic N chemistry will help address a critical gap in our understanding of fire effects on SOM. Here, we characterized changes to organic N chemistry across fire severity gradients resulting from two wildfires that burned lodgepole pine (Pinus contorta) forest along the Colorado/Wyoming border, USA. One representative gradient was selected for high-resolution analysis based on results from bulk data (total C and N, and pH). Mineral soils were collected from two depths in low, moderate, and high severity burned areas and adjacent, unburned locations one year following the Ryan and Badger Creek fires. Nuclear magnetic resonance spectroscopy and 21 tesla ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry analysis showed that N content and aromaticity of water-extractable SOM (0–5 ​cm depth) increased with burn severity, while minimal changes to 5–10 ​cm depth were observed. Heterocyclic N species are generally higher in toxicity compared to their non-nitrogenated counterparts, which prompted soil toxicity measurements. Complementary Microtox® analysis revealed a positive relationship between increased fire severity and increased soil toxicity to Aliivibrio fischeri (microbial test species). These findings add to our molecular-level understanding of organic C and N responses to wildfire severity, with likely implications for nutrient cycling, forest recovery and water quality following severe wildfire.

Ultramarathon induces metabolite changes associated with the pathophysiology of cardiovascular diseases- in silico and in vivo analysis

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Science Centre (NCN) and Internal source of Medical University of Warsaw. Introduction Regular physical exercise is analogous to improved cardiovascular health and increased longevity. However, if in excess it can act as a double edged sword. Acute bouts of extreme physical activity trigger complex molecular responses reflected by changes in inflammatory markers and metabolic pathways that are believed to yield detrimental effects on the cardiovascular system (CVS)[1]. Purpose We aimed to assess the effects of high-intensity and long-lasting exercise prototype (100km run) on the metabolomic changes in a unique population of high-level long-term ultra-marathon runners. Methods Plasma samples were collected from ultramarathon runners (n=22) with 2-time points: before and after the run (Completion (100 km) or exhaustion (52 - 91 km, median 74 km)). For untargeted metabolomic analysis we used ultra-high resolution Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry with an electrospray ion source in direct injection. Mass spectra were analyzed by T-Rex2D algorithm in the MetaboScape5.0. Identified compounds were ontologically analyzed using MetaboAnalystR. MetscapeCytoscape plugin was used for metabolite-gene interaction analysis and gene lists were obtained from Biomart and DisGeNet. Results Mann-Whitney test (FDR<0.05) identified 1601 up and 1030 downregulated metabolites with a at least 2 fold of difference after high-intensity run. Enrichment analysis showed that the top pathways affected by analyzed metabolites were the TCA cycle (FDR=0.0442), metabolism of; Sphingolipids (p=0.00774), Glyoxylate and dicarboxylate (p=0.0249) and Butanoate (p=0.0352). Top disease phenotypes associated with differentially regulated metabolites were critical illness (major trauma, severe septic shock, or cardiogenic shock) (p=0.00154) and multiple CVS-related diseases (Fig1). Top after the run up-regulated metabolites identified in the study included heart failure associated acetylcarnitines[2] CAR(14:2) (log2FC=11.57; AUC=0.97), Dodecanoylcarnitine (2.00;0.960), 9-Decenoylcarnitine (1.78;0.95), CAR(DC8:0) (14.99;0.94), but also 2-Carboxy-5,7-dimethyl-4-octanolide (8.04;0.98), Methylmalonic acid (9.33;0.96) and cardiotoxic Cyclophosphamide (16.29;0.940)[3]. Top down-regulated metabolites after the run included potentially cardio-protective Gamma Glutamylglutamic acid (log2FC=-1.81; AUC=0.85), Fructose 1,6-bisphosphate (-2.42;0.88)[4], Oleamide (-1.82;0.86) and gamma-Glutamylglycine (-7.98;0.85). Interaction network analysis focused on genes associated with CVS identified atherosclerosis/ obesity-related Phospholipase A2 Group IB (PLA2G1B) as potentially the most affected gene by analyzed metabolites (Fig2). Conclusion Results show a twofold post run increase in metabolites that are both potential markers for acute exercise and that are strongly associated with CV diseases. This calls for consideration of the detrimental effects of excessive exercise and implementation of monitoring in amateur athletes.

Analysis of Volatile and Nonvolatile Constituents in Gin by Direct-Infusion Ultrahigh-Resolution ESI/APPI FT-ICR Mass Spectrometry

Gin is one of the most consumed distilled alcoholic spirits worldwide, with more than 400 million liters sold every year. It is most often produced through redistillation of agricultural ethanol in the presence of botanicals, most notably juniper berries, which give gin its characteristic flavor. Due to its natural ingredients, gin is a complex mixture of hundreds of volatile and nonvolatile chemical constituents. In this work, ultrahigh-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry was used for the compositional analysis of 16 commercially produced gins. Two complementary ionization methods, namely, electrospray ionization (ESI) and atmospheric-pressure photoionization (APPI), were employed to cover a wider compositional space. Each gin provided unique chemical fingerprints by ESI and APPI, which allowed semiquantitative analysis of 135 tentatively identified compounds, including terpene hydrocarbons, terpenoids, phenolics, fatty acids, aldehydes, and esters. Most of these compounds have not been previously reported in gins. While chemical fingerprints were rather similar between most products, some products contained unique compounds due to their special natural ingredients or the production methods applied. For instance, a barrel-matured gin contained a high content of syringaldehyde and sinapaldehyde, which are typical phenolic aldehydes originated from oak wood. In addition, the relative abundance of vanillin, vanillic acid, gallic acid, coniferyl aldehyde, and syringaldehyde was clearly higher than in the other gin samples. Ultrahigh-resolution FT-ICR MS serves as a powerful tool for direct chemical fingerprinting of gin or any other distilled spirit, which can be used for rapid product quality screening, product optimization, or possible counterfeit product discovery.

Urban particulate water-soluble organic matter in winter: Size-resolved molecular characterization, role of the S-containing compounds on haze formation

Water-soluble organic matter (WSOM), as a group of ubiquitous components in atmospheric PM, plays a crucial role in global climate change and carbon cycle. In this study, the size-resolved molecular characterization of WSOM in the range of 0.010–18 μm PM was studied to gain insights into their formation processes. The CHO, CHNO, CHOS, CHNOS compounds were identified by the ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry in ESI source mode. A bimodal pattern of the PM mass concentrations was found in the accumulation and coarse mode. The increasing mass concentration of PM was mainly attributed to the growth of large-size PM with the occurrence of haze. Both Aiken-mode (70.5–75.6 %) and coarse-mode (81.7–87.9 %) particles were proven the main carriers of the CHO compounds, the majority of which were indicated to be the saturated fatty acids and their oxidized derivatives. The S-containing (CHOS and CHNOS) compounds in accumulation-mode (71.5–80.9 %) increased significantly in hazy days, where organosulfates (C11H20O6S, C12H22O7S) and nitrooxy-organosulfates (C9H19NO8S, C9H17NO8S) were confirmed in majority. The S-containing compounds in accumulation-mode particle with high oxygen content (6–8 oxygen atoms), unsaturation degree (DBE < 4), and reactivity could facilitate the particle agglomeration and accelerate the haze formation.

Impact of biogenic secondary organic aerosol (SOA) loading on the molecular composition of wintertime PM2.5 in urban Tianjin: an insight from Fourier transform ion cyclotron resonance mass spectrometry

Abstract. Biomass burning is one of the key sources of urban aerosols in the North China Plain, especially during winter, when the impact of secondary organic aerosols (SOAs) formed from biogenic volatile organic compounds (BVOCs) is generally considered to be minor. However, little is known about the influence of biogenic SOA loading on the molecular composition of wintertime organic aerosols. Here, we investigated the water-soluble organic compounds in fine particulate matter (PM2.5) from urban Tianjin by ultrahigh-resolution Fourier transform ion cyclotron resonanc mass spectrometry (FT-ICR MS). Our results show that most of the CHO and CHON compounds are derived from biomass burning which are poor in oxygen and contain aromatic rings that probably contribute to light-absorbing brown carbon (BrC) chromophores. Under moderate to high SOA-loading conditions, the nocturnal chemistry is more efficient than photooxidation to generate secondary CHO and CHON compounds with high oxygen content. Under low SOA loading, secondary CHO and CHON compounds with low oxygen content are mainly formed by photochemistry. Secondary CHO compounds are mainly derived from oxidation of monoterpenes. However, nocturnal chemistry may be more productive to sesquiterpene-derived CHON compounds. In contrast, the number- and intensity-weight of S-containing groups (CHOS and CHONS) increased significantly with the increase of biogenic SOA loading, which agrees with the fact that a majority of the S-containing groups are identified as organosulfates (OSs) and nitrooxy–organosulfates (nitrooxy–OSs) that are derived from the oxidation of BVOCs. Terpenes may be potential major contributors to organosulfates and nitrooxy–organosulfates. While the nocturnal chemistry is more beneficial to the formation of organosulfates and nitrooxy–organosulfates under low SOA loading. The SOA loading is an important factor that is associated with the oxidation degree, nitrate group content and chemodiversity of nitrooxy-organosulfates. Furthermore, our study suggests that the hydrolysis of nitrooxy-organosulfates is a possible pathway for the formation of organosulfates.

Description of Dissolved Organic Matter Transformational Networks at the Molecular Level.

Dissolved Organic Matter (DOM) is an important component of the global carbon cycle. Unscrambling the structural footprint of DOM is key to understand its biogeochemical transformations at the mechanistic level. Although numerous studies have improved our knowledge of DOM chemical makeup, its three-dimensional picture remains largely unrevealed. In this work, we compare four solid phase extracted (SPE) DOM samples from three different freshwater ecosystems using high resolution mobility and ultrahigh-resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FT-ICR MS/MS). Structural families were identified based on neutral losses at the level of nominal mass using continuous accumulation of selected ions-collision induced dissociation (CASI-CID)FT-ICR MS/MS. Comparison of the structural families indicated dissimilarities in the structural footprint of this sample set. The structural family representation using Cytoscape software revealed characteristic clustering patterns among the DOM samples, thus confirming clear differences at the structural level (Only 10% is common across the four samples.). The analysis at the level of neutral loss-based functionalities suggests that hydration and carboxylation are ubiquitous transformational processes across the three ecosystems. In contrast, transformation mechanisms involving methoxy moieties may be constrained in estuarine systems due to extensive upstream lignin biodegradation. The inclusion of the isomeric content (mobility measurements at the level of chemical formula) in the structural family description suggests that additional transformation pathways and/or source variations are possible and account for the dissimilarities observed. While the structural character of more and diverse types of DOM samples needs to be assessed and added to this database, the results presented here demonstrate that Graph-DOM is a powerful tool capable of providing novel information on the DOM chemical footprint, based on structural interconnections of precursor molecules generated by fragmentation pathways and collisional cross sections.

Production and Characterization of Hydrothermal Extracts of the Needles from Four Conifer Tree Species: Scots Pine, Norway Spruce, Common Juniper, and European Larch.

Coniferous trees are the most dominant trees in Finland with a great economic value for pulp, paper, and timber making. Thus, their utilization also results in large quantities of residues, especially bark and needles. Tree needles are a rich source of bioactive compounds, which have a considerable utilization potential in different pharmaceutical or techno-chemical applications. In this study, hydrothermal extraction (HTE) of the needles from four conifer tree species, namely, Scots pine, Norway spruce, common juniper, and European larch, was performed. Besides water, ethanol was also used as a solvent to enhance extraction efficiency and selectivity. All of the HTE experiments were conducted with a customized high-pressure reactor operated at 120 °C and 5 bar. The obtained needle extracts were then analyzed using a direct-infusion ultrahigh-resolution Fourier transform ion cyclotron (FT-ICR) mass spectrometry. The FT-ICR analysis of water and ethanol extracts allowed identification of over 200 secondary plant metabolites, including monosaccharides, organic acids, terpenoids, a variety of phenolic compounds, and nitrogen alkaloids. The use of ethanol as the extraction solvent considerably enhanced the recovery of lipids, especially terpenoids, some polyphenols, and other unsaturated hydrocarbon species.

Optical and molecular diversity of dissolved organic matter in sediments of the Daning and Shennong tributaries of the Three Gorges Reservoir

Introduction: Damming significantly modifies the function of natural river networks and influences sediment dynamics with a reservoir’s operation. The dissolved organic matter (DOM) in reservoir sediments severely affects carbon flow from land to sea. However, the properties of DOM (e.g., quantity and quality) in reservoir sediments and their relationship with carbon cycling remain unclear as complex reservoir construction interrupts the environmental processes.Methods: This study characterizes the optical and molecular properties of sediment water-extractable organic matter (WEOM) in the Daning and Shennong tributaries of the world’s largest reservoir—the Three Gorges Reservoir (TGR)—by applying optical techniques and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS).Results and Discussion: We first assessed the link between light-absorbing components and the individual molecules in WEOM, which were significantly different than DOM in water and indicated that there might be an intrinsic variation between DOM in sediment and in water. Then, with the unique optical–molecular property linkage assessed, multiple sources (autochthonous and terrestrial) were identified, and a declining trend of terrestrial and recalcitrant WEOM was revealed from the tributaries upstream to downstream. Finally, through covariance analysis of the properties between WEOM and sediment particles, we demonstrated that the WEOM dynamic was most likely regulated by hydrologic sorting-induced particle size and mineral composition variations of sediment. Moreover, assessment between lability and WEOM molecular properties suggested that the WEOM dynamic likely contributes to carbon burial in the reservoir. This study emphasizes the influence of dam construction on organic matter accumulation and riverine carbon cycling.

Characterization of modified methylaluminoxane by ion mobility spectrometry mass spectrometry and ultra-high resolution Fourier-transform ion cyclotron resonance mass spectrometry

High resolution mass spectrometry and ion mobility spectrometry with paraffin inert ASAP provide valuable information on the structure of modified methylaluminoxane (MMAO).

Deciphering the Fingerprint of Dissolved Organic Matter in the Soil Amended with Biodegradable and Conventional Microplastics Based on Optical and Molecular Signatures.

Biodegradable polymers are promoted as promising alternatives for conventional non-degradable plastics, but they may also negatively impact soil ecosystems. Here, we estimated the effects of biodegradable (polylactide (PLA) and polybutylene succinate (PBS)) and non-biodegradable (polyethylene (PE) and polystyrene (PS)) microplastics at a concentration of 1% (w/w) on dissolved organic matter (DOM) in two soil types, a black soil (BS) and a yellow soil (YS), by using fluorescence excitation-emission matrix spectroscopy and ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). PBS significantly increased the contents of soil dissolved organic carbon (DOC) and the relative intensities of protein-like components. The turnover rates of soil DOM were statistically higher in PBS treatments (0.106 and 0.196, p < 0.001) than those in other microplastic groups. The FT-ICR-MS results indicated that more labile-active DOM molecules were preferentially obtained in biodegradable microplastic treatments, which may be attributed to the polymer degradation. The conventional microplastics showed no significant effects on the optical characteristics but changed the molecular compositions of the soil DOM. More labile DOM molecules were observed in BS samples treated with PE compared to the control, while the conventional microplastics decreased the DOM lability in YS soil. The distinct priming effects of plastic-leached DOM may trigger the DOM changes in different soils. This study provided important information for further understanding the impact of microplastics on soil carbon processes.

Complex Mixture Analysis of Emerging Contaminants Generated from Coal Tar- and Petroleum-Derived Pavement Sealants: Molecular Compositions and Correlations with Toxicity Revealed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Pavement sealants are of environmental concern because of their complex petroleum-based chemistry and potential toxicity. Specifically, coal tar-derived sealants contain high concentrations of toxic/carcinogenic polycyclic aromatic hydrocarbons (PAHs) that, when weathered, can be transferred into the surrounding environment. Previous studies have demonstrated the effects of coal tar sealants on PAH concentration in nearby waterways and their harmful effects in aquatic ecosystems. Here, we investigate and compare the molecular composition of two different pavement sealants, petroleum asphalt- and coal tar-derived, and their photoproducts, by positive-ion (+) atmospheric pressure photoionization (APPI) and negative-ion (-) electrospray ionization (ESI) coupled with ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry to address species (high-boiling and/or high oxygen content) that lie outside the analytical window of other techniques due to ultra-high molecular complexity. In addition, we evaluate the toxicity of the water-soluble photoproducts by use of Microtox bioassay. The results demonstrate that the coal tar sealant contains higher amounts of PAHs and produces abundant water-soluble compounds, relative to unweathered materials, with a high abundance of PAH-like molecules of high toxicity. By comparison, the asphalt sealant produces fewer toxic water-soluble species, with molecular compositions that are consistent with natural dissolved organic matter. These results capture the mass, chemical diversity, toxicity, and source/photoproduct relationship of these compositionally complex emerging contaminants from the built environment.

Using Potential Molecular Transformation To Understand the Molecular Trade-Offs in Soil Dissolved Organic Matter

Understanding the chemical composition and molecular transformation in soil dissolved organic matter (DOM) is important to the global carbon cycle. To address this issue, ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was applied to investigate DOM molecules in 36 paddy soils collected from subtropical China. All the detected 7576 unique molecules were divided into seven compound groups, and nine trade-off relationships between different compound groups were revealed based on principal component analysis and Pearson's correlation. An optimized method was developed to evaluate all potential molecular transformations in DOM samples. The concept of thermodynamics was introduced to evaluate the identified molecular transformations and classify them as thermodynamically favorable (TFP) and thermodynamically limited (TLP) processes. Here, we first tried to understand the molecular trade-offs by using the potential molecular transformations. All the nine trade-offs could be explained by molecular transformations. Six trade-offs had bases of biochemical reactions, and the trade-off-related direct transformations could explain the content variations of carbohydrate-like, condensed aromatic-like, tannin-like, and lignin-like compounds in TLP. More reasonable explanations existed in the TLP rather than TFP, which demonstrated the critical role of external energy in the molecular transformation of soil DOM.

Oxygen availability driven trends in DOM molecular composition and reactivity in a seasonally stratified fjord

Ocean deoxygenation could potentially trigger substantial changes in the composition and reactivity of dissolved organic matter (DOM) pool, which plays an important role in the global carbon cycle. To evaluate links between DOM dynamics and oxygen availability, we investigated the DOM composition under varying levels of oxygen in a seasonally hypoxic fjord through a monthly time-series over two years. We used ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to characterize DOM on a molecular level. We find a clear trend both in diversity and molecular composition of the DOM along the oxygen gradient. As oxygen decreased, the chemodiversity was significantly increased, along with accumulation of relatively high-molecular-weight, reduced and unsaturated compounds enriched with carboxyl-group structures, which were also thermodynamically less favorable to biodegradation. Our results suggested that oxygen depletion selectively protected otherwise bioavailable compounds from decomposition and may promote the accumulation of a larger recalcitrant DOM pool in the global ocean, which could provide negative feedback to the ocean carbon sequestration and climate change.