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

Abstract

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.

Formula Assignment Algorithm for Deuterium-Labeled Ultrahigh-Resolution Mass Spectrometry: Implications of the Formation Mechanism of Halogenated Disinfection Byproducts

“…The number of labile D linearly increased with increasing average values of O number and O/C ratios for D-SRNOM molecules (R 2 =0.944 and 0.968, respectively, Figure S10). This result further supported the hypothesis that carboxyl and hydroxyl functional groups were the predominant contributors of labile H (or D) for SRNOM [16][17][18] . Furthermore, Figure S10A revealed the presence of O-containing function groups irrelevant to labile H (such as the carbonyl or ether group) 13 for D-SRNOM molecules with number of labile D being no more than seven.…”

“…Since its first application to NOM study 6 , FTICR-MS has been widely adopted to characterize the complexity of NOM in the last two decades through the development of automated molecular formula assignment methods such as the inhouse code from Kujawinski and Behn 7 , MassCal 8 , Formularity software 9 , MFAssignR 10 , ICBM-OCEAN 11 , and the TRFu code 12 . Moreover, FTICR-MS with stable isotope labeling has initiated the new possibilities of quantifying the number of labile H and O and structural information such as ether O atoms, carboxyl and hydroxyl functional groups in individual molecules of NOM 1,[13][14][15] , further refining compound aromaticity 16 , and relation of NOM molecular structures with optical property 17 . However, data interpretation of stable isotope-labeled UHR-MS spectra remains challenging, and only a few methods have been developed to address the formula assignment for stable isotope-labeled UHR-MS spectra.…”

Application of ESI FT-ICR MS to Study Kraft Lignin Modification by the Exoenzymes of the White Rot Basidiomycete Fungus TrametesHirsutaLE-BIN 072

“…For lignin degradation experiment, the 200 mL of GP medium was supplied with the 2 g/l of alkali lignin (Sigma-Aldrich, USA). The submerged cultivation was performed 8th Scientific and Practical Conference on Brunswick Innova 44 (Eppendorf Inc., USA) rotary shaker at 180 RPM in the dark at 26-28 ∘ C Preparation of lignin samples and (-)ESI FT-ICR MS was performed as described in [12]. Preparation of exoproteomic samples, 2D gel electrophoresis and MALDI-TOF/TOFMSwas performed as described in [13].…”

Solid-Phase Extraction of Aquatic Organic Matter: Loading-Dependent Chemical Fractionation and Self-Assembly

“…Chromophoric DOM (CDOM), the optically active fraction of bulk DOM, also plays an important role in biogeochemical cycles. − Optical spectroscopy (absorbance and fluorescence) has been widely used to characterize the properties and dynamics of CDOM in the original matrix because of its relative ease of use and high sensitivity. − Fluorescence excitation–emission matrices evaluated with parallel factor analysis (EEM-PARAFAC) is an effective tool for tracking and characterizing the source, distribution, composition, and turnover of fluorescent DOM (FDOM). − Moreover, targeted analysis of specific DOM compounds (such as amino acids) or untargeted analysis (such as polarity assessment) using, for example, reversed-phase high-performance liquid chromatography (RP-HPLC) is also applied to chemically characterize DOM. , …”