DOI: 10.5061/dryad.jsxksn0hr
title: 13C NMR data for the five dissolved organic matter

description: Dissolved organic matter (DOM) is one of the most complex, dynamic, and
 abundant sources of organic carbon, but its chemical reactivity remains
 uncertain. Greater insights into DOM structural features could facilitate
 understanding its synthesis, turnover, and processing in the global carbon
 cycle. Here we use complementary multiplicity-edited 13C NMR
 spectra to quantify key substructures assembling the carbon skeletons of
 DOM from four main Amazon rivers and two mid-size Swedish boreal lakes. We
 find that one type of reaction mechanism, oxidative dearomatization (ODA),
 widely used in organic synthesic chemistry to create natural product
 scaffolds, is likely a key driver for generating structural
 diversity during processing of DOM that are rich in suitable polyphenolic
 precursor molecules. Our data suggest a high abundance of tetrahedral
 quaternary carbons bound to one oxygen and three carbon atoms (OCqC3
 units). These units are rare in common biomolecules but could be readily
 produced by ODA of lignin and tannin derived polyphenols. Tautomerization
 of (poly)phenols by ODA creates non-planar cyclohexadienones which are
 subject to immediate and parallel cycloadditions. This combination amounts
 to a proliferation of structural diversity of DOM compounds from early
 stages of DOM processing, with an increase in oxygenated aliphatic
 structures. Overall, we propose that ODA is a key reaction mechanism for
 complexity acceleration in the processing of DOM molecules, creation of
 novel oxygenated aliphatic molecules, and that it could be prevalent in
 nature.
description: These files comprise <sup>13</sup>C NMR section
 integrals for the five DOM, divided into buckets of 0.1 ppm width, and
 ranging from d<sub>C</sub> = 0 – 235 ppm. The total integral
 of these <sup>13</sup>C NMR spectra is area normalized to
 C<sub>all</sub> = 100% for all five DOM, and to
 CH<sub>0123</sub> according to its proportions. The
 <sup>13</sup>C NMR section integral from
 d<sub>C</sub> = 47 - 51 ppm is set to zero for all five
 <sup>13</sup>C NMR spectra of DOM, because of interference
 from the solvent <sup>12</sup>CD<sub>3</sub>OD,
 which resonates at d<sub>C</sub> = 49.0 ppm.
description: # 13C NMR data for the five dissolved organic matter
 Five *.pdf files with the
 13C NMR data for the five dissolved organic matter investigated. N-DOM
 (DOM in the Negro River), S-DOM (DOM in the Solimões River), A-DOM (DOM in
 the Amazonas River), T-DOM (DOM in the Tapajós River), B-DOM (DOM in the
 boreal lakes). ## Description of the data and file structure These files
 comprise 13C NMR section integrals for the five DOM, divided into buckets
 of 0.1 ppm width, and ranging from δC = 0 – 235 ppm. The total integral of
 these 13C NMR spectra is area normalized to Call = 100% for all five DOM,
 and to CH0123 according to its proportions. The 13C NMR section integral
 from δC = 47 - 51 ppm is set to zero for all five 13C NMR spectra of DOM,
 because of interference from the solvent 12CD3OD, which resonates at δC =
 49.0 ppm. ## Methods Overview A Bruker Avance III spectrometer and TopSpin
 3.6/PL6 software were used to acquire 13C nuclear magnetic resonance (NMR)
 spectra of re-dissolved DOM (10-40 mg solid SPE-DOM in typically 75-135 µL
 CD3OD (99.95 % 2H; 13C-depleted 12CD3OD, Aldrich, Steinheim, Germany).
 Briefly, the re-dissolved DOM were transferred to 2.5-3.0 mm Bruker Match
 tubes and sealed. A cryogenic classical geometry 5 mm z-gradient 13C, 1H
 probe (B0 = 11.7 T) was used for acquisition of 13C NMR spectra.
 Transmitter pulses were at ~10 µs for 1H and 13C, and calibrated
 90/180-degree pulses were employed for each sample. We used inverse-gated
 1H decoupling for 13C NMR spectra to eliminate nOe effects (nuclear
 Overhauser effects), and (acquisition-time adjusted) linear combinations
 of the 13C DEPT-45, -135 and -90 NMR spectra (1JCH: 150 Hz) to compute the
 individual traces of CH (13C DEPT-90 NMR spectrum), CH2 (13C DEPT-45 minus
 13C DEPT-135) and CH3 ([13C DEPT-45 plus 13C DEPT-135] minus 13C DEPT-90).
 We corrected the 13C DEPT-90 NMR spectrum by subtracting an appropriate
 amount (commonly ~2-3%) of the 13C DEPT-45 NMR spectrum to attenuate
 leakage of CH3 and CH2 into the 13C DEPT-90 NMR spectrum (methine carbon
 (CH) in DOM does not show appreciable 13C NMR resonances at δC &lt; 20
 ppm) that arises from the unavoidable variance in 1JCH of DOM. Then we
 determined the relative contributions of the individual spectra (CH3, CH2,
 CH1) to the sum CH123 as observed in 13C DEPT-45 NMR spectra with
 recognition of the individual transfer amplitudes which were as follows
 (CH3 = 1.06; CH2 = 1.0; CH = 0.707). The proportions of quaternary carbon
 atoms Cq in DOM were computed from comparison of 13C DEPT-45, 13C QUAT,
 and single pulse 13C NMR spectra. 13C NMR overlay figures were computed
 using the Bruker AMIX software (version 3.9.4) from area normalized
 spectra with 0.1 ppm buckets and 100% total NMR integral area from δC:
 0-235 ppm, with exclusion of the solvent 12CD3OD, which resonates at δC =
 49.0 ppm.