Evidence for π-π electron donor-acceptor interactions between π-donor aromatic compounds and π-acceptor sites in soil organic matter through pH effects on sorption

Dongqiang Zhu, Seunghun Hyun, Joseph J. Pignatello, Linda S. Lee

Research output: Contribution to journalArticle

186 Citations (Scopus)

Abstract

Elucidation of molecular-level interactions controlling the sorption of organic compounds in soils is of major theoretical and practical interest. Sorption of π-electron donor compounds, pentamethylbenzene (PMB), naphthalene (NAPH), and phenanthrene (PHEN), in a number of soils was found to increase with decreasing pH in the range of approximately pH 2.5-7. This behavior could not be attributed to pH-dependent alteration of the hydrophobic character of humic substances, π-H-bonding, interaction with mineral surfaces, interaction with black carbons, solute coplanarity, or pH effects on solute activity coefficient. No significant effect of pH was observed for non-π-donor hydrophobic compounds, whether planar or not: trans-1,2-dichlorocyclohexane (DCCH), hexachloro-1,3-butadiene (HCBD), 1,2,4-trichlorobenzene (TCB), 2,2′,5,5′-tetrachlorobiphenyl, and 3,3′.4,4′- tetrachlorobiphenyl. The opposite pH effect was observed for 2-nonanol and 2-nonanone, which are non-π-donors, but capable of H-bonding. Also, no pH-dependent sorption was observed between the π-donor PHEN and alumina, a model inorganic surface. We propose that the π-donor solutes interact with π-acceptor sites in soil organic matter (SOM), including aromatic rings with multiple carboxyl groups, aromatic amines, or heteroaromatic amines. The π-acceptor ability of such aromatic moieties would increase with protonation, π-π Interactions between PMB, NAPH, and PHEN, and model SOM acceptors, 1,3,5-benzenetricarboxylic acid (BTA), 1,4,5,8-naphthalenetetracarboxylic acid (NTA), and pyridine (PY) in methanol and methanol-water, were verified by the appearance of pH-dependent upfield 1H NMR chemical shifts induced by ring current effects. UV/vis spectra showed pH-dependent charge-transfer bands for various donors with NTA. No NMR shifts or charge-transfer bands were found for nondonor compounds paired with the model acceptors.

Original languageEnglish
Pages (from-to)4361-4368
Number of pages8
JournalEnvironmental Science and Technology
Volume38
Issue number16
DOIs
Publication statusPublished - 2004 Aug 15
Externally publishedYes

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pH effects
Aromatic compounds
Biological materials
soil organic matter
Sorption
Soil
phenanthrene
sorption
Electrons
Soils
solute
electron
Naphthalene
naphthalene
Amines
Methanol
nuclear magnetic resonance
methanol
Acids
Charge transfer

ASJC Scopus subject areas

  • Environmental Science(all)
  • Environmental Chemistry
  • Environmental Engineering

Cite this

Evidence for π-π electron donor-acceptor interactions between π-donor aromatic compounds and π-acceptor sites in soil organic matter through pH effects on sorption. / Zhu, Dongqiang; Hyun, Seunghun; Pignatello, Joseph J.; Lee, Linda S.

In: Environmental Science and Technology, Vol. 38, No. 16, 15.08.2004, p. 4361-4368.

Research output: Contribution to journalArticle

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abstract = "Elucidation of molecular-level interactions controlling the sorption of organic compounds in soils is of major theoretical and practical interest. Sorption of π-electron donor compounds, pentamethylbenzene (PMB), naphthalene (NAPH), and phenanthrene (PHEN), in a number of soils was found to increase with decreasing pH in the range of approximately pH 2.5-7. This behavior could not be attributed to pH-dependent alteration of the hydrophobic character of humic substances, π-H-bonding, interaction with mineral surfaces, interaction with black carbons, solute coplanarity, or pH effects on solute activity coefficient. No significant effect of pH was observed for non-π-donor hydrophobic compounds, whether planar or not: trans-1,2-dichlorocyclohexane (DCCH), hexachloro-1,3-butadiene (HCBD), 1,2,4-trichlorobenzene (TCB), 2,2′,5,5′-tetrachlorobiphenyl, and 3,3′.4,4′- tetrachlorobiphenyl. The opposite pH effect was observed for 2-nonanol and 2-nonanone, which are non-π-donors, but capable of H-bonding. Also, no pH-dependent sorption was observed between the π-donor PHEN and alumina, a model inorganic surface. We propose that the π-donor solutes interact with π-acceptor sites in soil organic matter (SOM), including aromatic rings with multiple carboxyl groups, aromatic amines, or heteroaromatic amines. The π-acceptor ability of such aromatic moieties would increase with protonation, π-π Interactions between PMB, NAPH, and PHEN, and model SOM acceptors, 1,3,5-benzenetricarboxylic acid (BTA), 1,4,5,8-naphthalenetetracarboxylic acid (NTA), and pyridine (PY) in methanol and methanol-water, were verified by the appearance of pH-dependent upfield 1H NMR chemical shifts induced by ring current effects. UV/vis spectra showed pH-dependent charge-transfer bands for various donors with NTA. No NMR shifts or charge-transfer bands were found for nondonor compounds paired with the model acceptors.",
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AB - Elucidation of molecular-level interactions controlling the sorption of organic compounds in soils is of major theoretical and practical interest. Sorption of π-electron donor compounds, pentamethylbenzene (PMB), naphthalene (NAPH), and phenanthrene (PHEN), in a number of soils was found to increase with decreasing pH in the range of approximately pH 2.5-7. This behavior could not be attributed to pH-dependent alteration of the hydrophobic character of humic substances, π-H-bonding, interaction with mineral surfaces, interaction with black carbons, solute coplanarity, or pH effects on solute activity coefficient. No significant effect of pH was observed for non-π-donor hydrophobic compounds, whether planar or not: trans-1,2-dichlorocyclohexane (DCCH), hexachloro-1,3-butadiene (HCBD), 1,2,4-trichlorobenzene (TCB), 2,2′,5,5′-tetrachlorobiphenyl, and 3,3′.4,4′- tetrachlorobiphenyl. The opposite pH effect was observed for 2-nonanol and 2-nonanone, which are non-π-donors, but capable of H-bonding. Also, no pH-dependent sorption was observed between the π-donor PHEN and alumina, a model inorganic surface. We propose that the π-donor solutes interact with π-acceptor sites in soil organic matter (SOM), including aromatic rings with multiple carboxyl groups, aromatic amines, or heteroaromatic amines. The π-acceptor ability of such aromatic moieties would increase with protonation, π-π Interactions between PMB, NAPH, and PHEN, and model SOM acceptors, 1,3,5-benzenetricarboxylic acid (BTA), 1,4,5,8-naphthalenetetracarboxylic acid (NTA), and pyridine (PY) in methanol and methanol-water, were verified by the appearance of pH-dependent upfield 1H NMR chemical shifts induced by ring current effects. UV/vis spectra showed pH-dependent charge-transfer bands for various donors with NTA. No NMR shifts or charge-transfer bands were found for nondonor compounds paired with the model acceptors.

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