Synthesis of carboxylated styrene polymer for internal calibration of Fourier transform ion cyclotron resonance mass-spectrometry of humic substances

Impact of ozone treatment on dissolved organic matter in land-based recirculating aquaculture systems studied by Fourier transform ion cyclotron resonance mass spectrometry

In land-based recirculating aquaculture systems (RAS), the accumulation of dissolved organic matter (DOM) can have detrimental effects on water quality impacting the system performance, microbial community, and consequently fish health and welfare. Ozone is used in the RAS water treatment process to improve water quality and remove DOM. However, little is known about the molecular composition of DOM in RAS and its transformation when exposed to ozone. In this study, we performed a detailed molecular characterization of DOM in RAS and explored its transformation induced by ozonation of RAS waters. Ultra-high resolution (UHR) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) was used to characterize the DOM matrix of RAS waters (pump-sump and tanks) and to evaluate its transformation by ozonation. The analysis of DOM extracted from makeup water and feed samples allowed for the determination of DOM sources in RAS prior to ozonation. The CHO and unsaturated group of compounds were the most abundant class found in water samples. On the contrary, the DOM from feed samples was unique and consisted mainly of CHO, CHON and unsaturated group of compounds. After the ozonation of RAS waters, humic-like and unsaturated compounds [positive oxygen subtracted double bond equivalent per carbon (DBE-O)/C)] were decomposed, particularly the CHO-DOM that contained fewer -CH₂- features. Fulvic-like compounds and several hundred saturated compounds [negative (DBE-O)/C)] were formed post ozonation, particularly the CHON and CHONS group of compounds that were associated with fish diets, makeup waters and transformation products from the ozonation of the RAS waters. This study showed that the high accuracy of the ultra-high resolution FTICR MS can be applied to characterize and monitor the changes of DOM at a molecular level in RAS waters. To our knowledge, this is the first study where FTICR MS was incorporated for the characterization of DOM and its sources in RAS.

Antiviral activity of natural humic substances and shilajit materials against HIV-1: Relation to structure

Natural products, such as humic substances (HS) and shilajit, are known to possess antiviral activity. Humic-like components are often called as carriers of biological activity of shilajit. The goal of this study was to evaluate anti-HIV activity of well characterized HS isolated from coal, peat, and peloids, and compare it to that of water-soluble organic matter (OM) isolated from different samples of Shilajit. The set of humic materials included 16 samples of different fractional composition: humic acid (HA), hymatomelanic acid (HMA), fulvic acid (FA). The set of shilajit OM included 19 samples of different geographic origin and level of alteration. The HIV-1 p24 antigen assay and cell viability test were used for assessment of antiviral activity. The HIV-1 Bru strain was used to infect CEM-SS cells. The obtained EC50 values varied from 0.37 to 1.4 mg L^-1 for the humic materials, and from 14 to 142 mg L^-1 for the shilajit OM. Hence, all humic materials used in this study outcompeted largely the shilajit materials with respect to anti-HIV activity: For the humic materials, the structure-activity relationships revealed strong correlation between the EC50 values and the content of aromatic carbon indicating the most important role of aromatic structures. For shilajit OM, the reverse relationship was obtained indicating the different mechanism of shilajit activity. The FTICRMS molecular assignments were used for ChEMBL data mining in search of the active humic molecules. As potential carriers of antiviral activity were identified aromatic structures with alkyl substituents, terpenoids, N-containing analogs of typical flavonoids, and aza-podophyllotoxins. The conclusion was made that the typical humic materials and Shilajit differ greatly in molecular composition, and the humic materials have substantial preferences as a natural source of antiviral agents as compared to shilajit.

Fourier transform ion cyclotron resonance mass spectrometry for the analysis of molecular composition and batch-to-batch consistency of plant-derived polyphenolic ligands developed for biomedical application

Complex plant-derived polyphenols are promising for biomedical application. Their high complexity prevents the use of conventional pharmacopoeia techniques to perform quality control. The goal of this study was to apply ultra-high-resolution mass spectrometry to evaluate the batch-to-batch consistency of the molecular composition of a polyphenolic ligand using appropriate statistical metrics.

METHODS

Polyphenols were obtained by hydrolyzed-lignin oxidation. Manufacturing was performed under a range of reaction conditions: heating cycles, oxygen flows, purification. Direct-injection Fourier transform ion cyclotron resonance mass spectrometry (DI FTICR-MS) was applied to analyze reaction products. For pairwise comparison Jaccard and Tanimoto similarities calculations were proposed. In addition, principal component analysis (PCA) was applied for sample grouping based on the molecular class contributions.

RESULTS

FTICR-MS analysis revealed moderate Jaccard similarity of products synthesized under the same conditions, which shared about 50% of the formulae calculated in each sample. The intensity-based Tanimoto index indicated high similarity of major components distribution of samples synthesized under standard conditions, while products obtained with variations in synthetic conditions were significantly different. PCA of molecular class contributions showed similar grouping with a high cumulative score.

CONCLUSIONS

FTICR-MS provides robust metrics for the examination of batch-to-batch consistency of synthetic polyphenol materials. This approach can be proposed for the analysis of reference samples and for development of complementary methods for quality control of medicinal agents based on various biologically active matrices.

Photoreactivity of humic-like polyphenol material under irradiation with different wavelengths explored by FTICR MS and deuteromethylation

The goal of this study was to establish reactivity of lignin-derived synthetic polyphenolic material under irradiation by ultraviolet (254 nm) and visible (460 and 525 nm) light in order to deeper examine relationships between the optical properties of this complex mixture and its individual constituents. In all photoirradiation experiments, blue shift of the fluorescence spectrum was observed. We aimed at understanding whether these changes could be explained on the basis of the chromophore interactions hypothesis, which implies destruction of electron-acceptor pairs via free radical transformations to be responsible for the alteration of optical properties. For this, changes in molecular composition were explored by Fourier transform ion cyclotron resonance mass spectrometry. Irradiation with UV resulted in a pronounced oxidation of polyphenols, which was manifested in the van Krevelen diagram by the formation of components with higher O/C ratio. At the same time, irradiation by visible light had led to the appearance of more condensed molecules depleted of oxygen. Consideration of changes in relative contribution of 500 most abundant components in polyphenol materials revealed higher transformation yields under UV light as compared to the visible light. Further studies using deuteromethylation followed by Fourier transform ion cyclotron resonance mass spectrometry enabled to enumerate the number of carboxylic groups in individual components of the parent polyphenol material. It was shown that at all wavelengths irradiation mainly impacted carboxylic-rich unsaturated and aromatic compounds, which can be considered as strong electron-acceptors. We suggest that their transformation is responsible for the blue shift of fluorescence spectrum, thus emphasizing the role of chromophore interaction mechanism of the optical properties formation.

Optical Properties of Soil Dissolved Organic Matter Are Related to Acidic Functions of Its Components as Revealed by Fractionation, Selective Deuteromethylation, and Ultrahigh Resolution Mass Spectrometry

The goal of this study was to establish a relationship between the optical properties of soil dissolved organic matter (DOM) and acidic functions carried out by its individual constituents. We obtained 12 fractions of DOM samples using sequential solid phase extraction on nonionic sorbent at steadily lowered pH values: 7, 5, 3, 2, which correspond to low bounds of pK_a values of phenols, aliphatic, and aromatic carboxylic acids, and ketoacids. The structural studies were conducted with the use of NMR and selective deuteromethylation of isolated fractions coupled to ultrahigh resolution mass spectrometry. First, a gradual shift of molecular compositions was observed from reduced components to aromatic oxidized compounds isolated at pH 7 and 2, respectively. Changes in molecular compositions were accompanied by a red shift of fluorescence spectra. Further application of deuteromethylation enabled us to distinguish DOM constituents with different amounts of carboxylic groups. Moreover, identification of structural isomers in a single DOM sample was achieved. Statistical analysis revealed that red shift of fluorescence is facilitated by the increase of a contribution of aromatic poly(carboxylic acid)s with high conjugation lengths. Additionally, analysis of the labeled fractionated permafrost thaw DOM directly showed carboxyl-rich alicyclic molecules, while the same components from lower-latitude DOM were assigned to lignin-like species.

Structural investigation of coal humic substances by selective isotopic exchange and high-resolution mass spectrometry

Here, we report the application of a selective liquid-phase hydrogen/deuterium exchange (HDX) coupled to ultra-high resolution FTICR MS for structural investigations of individual constituents of humic substances (HS) isolated from three coal samples of different geographical origin. Selectivity was achieved by conducting reactions in DCl or NaOD solutions for catalyzing HDX in aromatic ring and side-chain positions with enhanced C-H acidity, respectively. FTICR MS analysis showed a significant overlap of molecular compositions in the HS samples under study, with 2000 common formulae. Using HDX, we demonstrated that the determined common formulae are presented by different structural isomers. We found that aromatic compounds varied both in the substitution pattern and the number of aromatic protons. Depending on the sample, lignin components with the same molecular formulae were composed of coumaryl, coniferyl or sinapyl moieties. Enumeration of HDX series for the 800 most abundant compounds showed that the results of HDX agreed well with the model structures suggested for humic components occupying a van Krevelen plot. In addition, we explored chemical transformations, which could connect individual constituents of coal HS. These transformations included hydrolysis of a guaiacyl moiety and reduction of a catechol unit, which corresponds to the conversion of a coniferyl fragment into a coumaryl unit. The obtained results were supportive of the hypothesis of the reducing humification pathway suggested for lignin transformation in the environment. The conclusion was made that the molecular ensemble of coal HS is composed of individual constituents produced at different humification stages.

Separation of Benzoic and Unconjugated Acidic Components of Leonardite Humic Material Using Sequential Solid-Phase Extraction at Different pH Values as Revealed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Correlation Nuclear Magnetic Resonance Spectroscopy

Here, we report on sequential solid-phase extraction of leonardite hymatomelanic acid (CHM) on a non-ionic sorbent at four steadily lowered pH values: 7, 5, 3, and 2, yielding fractions with different acidic properties. Using nuclear magnetic resonance (NMR) spectroscopy and ultrahigh-resolution mass spectrometry, we revealed a gradual shift of dominating scaffolds in the fractions of CHM from reduced saturated to oxidized aromatic compounds. An increase on the average aromaticity of the CHM fractions was accompanied by a red shift in fluorescence spectra. These results were supported by heteronuclear single quantum coherence and heteronuclear multiple bond correlation NMR experiments. We have demonstrated that the CHM fraction isolated at pH 5 was dominated by aliphatic carboxyl carriers, while the pH 3 fraction was dominated by aromatic carboxyl acids. The developed fractionation technique will enable deeper insight on structure-property relationships and the design of the humic-based materials with tailored reactive properties.

The Structural Arrangement and Relative Abundance of Aliphatic Units May Effect Long-Wave Absorbance of Natural Organic Matter as Revealed by 1H NMR Spectroscopy

The objective of this study was to shed light on structural features which underlay intensity of long wave absorbance of natural organic matter (NOM) using ¹H NMR spectroscopy. For this purpose, a set of the NOM samples was assembled from arctic and nonarctic sampling sites (the Kolyma river basin and Moscow region, respectively). It was to ensure a substantial difference in the humification degree of the isolated organic matter-the biogeochemical proxy of the long-wave absorbance of NOM. The assembled NOM set was analyzed using solution-state ¹H NMR spectroscopy. The distribution of both backbone and exchangeable protons was determined using acquisition of spectra in three different solvents. The substantially higher contribution of nonfunctionalized aliphatic moieties CHn (e.g., materials derived from linear terpenoids, MDLT) in the arctic NOM samples was revealed as compared to the nonarctic ones. The latter were characterized with the higher content of CHα protons adjacent to electron-withdrawing groups which belong to carboxyl rich alicyclic moieties (CRAMs) or to aromatic constituents of NOM. We have calculated a ratio of CHn to CHα protons as a structural descriptor which showed significant inverse correlation to intensity of long wave absorbance assessed with a use of E₄/ E₆ ratio and the slope of absorption spectrum. The steric hindrance of aromatic chromophoric groups of the NOM ensemble by bulky nonfunctionalized aliphatic moieties (e.g., MDLT) was set as a hypothesis for explanation of this phenomenon. The bulky aliphatics might increase a distance between the interacting groups resulting in inhibition of electronic (e.g., charge-transfer) interactions in the NOM ensemble. The obtained relationships were further explored using Fourier transform mass spectrometry as complementary technique to ¹H NMR spectroscopy. The data obtained on correlation of molecular composition of NOM with ¹H NMR data and optical properties were very supportive of our hypothesis that capabilities of NOM ensemble of charge transfer interactions can be dependent on structural arrangement and relative abundance of nonabsorbing aliphatic moieties.

Novel water-soluble lignin derivative BP-Cx-1: identification of components and screening of potential targets in silico and in vitro

Identification of molecular targets and mechanism of action is always a challenge, in particular – for natural compounds due to inherent chemical complexity. BP-Cx-1 is a water-soluble modification of hydrolyzed lignin used as the platform for a portfolio of innovative pharmacological products aimed for therapy and supportive care of oncological patients. The present study describes a new approach, which combines in vitro screening of potential molecular targets for BP-Cx-1 using Diversity Profile - P9 panel by Eurofins Cerep (France) with a search of possible active components in silico in ChEMBL - manually curated chemical database of bioactive molecules with drug-like properties. The results of diversity assay demonstrate that BP-Cx-1 has multiple biological effects on neurotransmitters receptors, ligand-gated ion channels and transporters. Of particular importance is that the major part of identified molecular targets are involved in modulation of inflammation and immune response and might be related to tumorigenesis. Characterization of molecular composition of BP-Cx-1 with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and subsequent identification of possible active components by searching for molecular matches in silico in ChEMBL indicated polyphenolic components, nominally, flavonoids, sapogenins, phenanthrenes, as the major carriers of biological activity of BP-Cx-1. In vitro and in silico target screening yielded overlapping lists of proteins: adenosine receptors, dopamine receptor DRD4, glucocorticoid receptor, serotonin receptor 5-HT1, prostaglandin receptors, muscarinic cholinergic receptor, GABAA receptor. The pleiotropic molecular activities of polyphenolic components are beneficial in treatment of multifactorial disorders such as diseases associated with chronic inflammation and cancer.