Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 50, Issue 4, Pages 1663-1669Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.5b02859
Keywords
-
Categories
Funding
- Sedimentary Geology and Paleobiology Program of the National Science Foundation [EAR-1226323]
- Directorate For Geosciences
- Division Of Earth Sciences [1226323] Funding Source: National Science Foundation
Ask authors/readers for more resources
A lignite humic acid (HA) was separated from inorganic and non-HA impurities (i.e., aluminosilicates, metals) and fractionated by a combination of dialysis and XAD-8 resin. Fractionation revealed a more homogeneous structure of lignite HA. New and more specific structural information on the main lignite HA fraction is obtained by solid-state nuclear magnetic resonance (NMR) spectroscopy. Quantitative C-13 multiple cross-polarization (multiCP) NMR indicated oxidized phenyl propane structures derived from lignin. MultiCP experiments, conducted on potassium HA salts titrated to pH 10 and pH 12, revealed shifts consistent with carboxylate and phenolate formation, but structural changes associated with enolate formation from aromatic beta keto acids were not detected. Two-dimensional H-1-C-13 heteronuclear correlation (2D HETCOR) NMR indicated aryl-aliphatic ketones, aliphatic and aromatic carboxyl groups, phenol, and methoxy phenyl ethers. Acidic protons from carboxyl groups in both the lignite HA fraction and a synthetic HA-like polycondensate were found to be hydrogen-bonded with electron-rich aromatic rings. Our results coupled with published infrared spectra provide evidence for the preferential hydrogen bonding of acidic hydrogens with electron-rich aromatic rings rather than adjacent carbonyl groups. These hydrogen-bonding interactions likely result from stereochemical arrangements in primary structures and folding.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available