PMID: 11393970Jun 8, 2001Paper

New structural information on a humic acid from two-dimensional 1H-13C correlation solid-state nuclear magnetic resonance

Environmental Science & Technology
J D MaoKlaus Schmidt-Rohr

Abstract

New information on the chemical structure of a peat humic acid has been obtained using a series of two-dimensional 1H-13C heteronuclear correlation solid-state NMR (HETCOR) experiments with different contact times and with spectral editing by dipolar dephasing and 13C transverse relaxation filtering. Carbon-bonded methyl groups (C-CH3) are found to be near both aliphatic and O-alkyl but not aromatic groups. The spectra prove that most OCH3 groups are connected directly with the aromatic rings, as is typical in lignin. As a result, about one-third of the aromatic C-O groups is not phenolic C-OH but C-OCH3. Both protonated and unprotonated anomeric O-C-O carbons are identified in the one- and two-dimensional spectra. COO groups are found predominantly in OCHn-COO environments, but some are also bonded to aromatic rings and aliphatic groups. All models of humic acids in the literature lack at least some of the features observed here. Compositional heterogeneity was studied by introducing 1H spin diffusion into the HETCOR experiment. Comparison with data for a synthetic polymer, polycarbonate, indicates that the separation between O-alkyl and aromatic groups in the humic acid is less than 1.5 nm. However, transverse 13C relaxation ...Continue Reading

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Citations

May 26, 2004·Solid State Nuclear Magnetic Resonance·J-D Mao, K Schmidt-Rohr
Oct 20, 2012·Environmental Science & Technology·Charisma LattaoJoseph J Pignatello
Sep 6, 2012·Environmental Science & Technology·James G LongstaffeAndré J Simpson
Nov 29, 2005·Chemosphere·Chongshan LiangCongqiang Liu
Jun 25, 2008·Journal of Environmental Quality·Charisma LattaoRobert L Cook
Oct 25, 2017·The Analyst·Jun Kikuchi, Shunji Yamada
Feb 7, 2018·Progress in Nuclear Magnetic Resonance Spectroscopy·Jun KikuchiYasuhiro Date
Mar 15, 2011·Progress in Nuclear Magnetic Resonance Spectroscopy·André J SimpsonMyrna J Simpson
Jan 25, 2018·Environmental Science & Technology·Xiaoyan CaoKlaus Schmidt-Rohr

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