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United States Department of Agriculture

Agricultural Research Service

Title: Characterization of tannin-metal complexes by UV-visible spectrophotometry

item Liu, Ruiqiang
item Tindall, Steven
item Gonzalez, Javier
item Halvorson, Jonathan
item Hagerman, Ann

Submitted to: American Chemical Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/30/2010
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Tannins enter soils by plant decay and rain throughfall, but little is known of their effects on soils. Tannins may influence bioavailability and toxicity of metals by forming complexes and by mediating redox reactions. We evaluated the affinity and stoichiometry of Al(III) for a gallotannin, pentagalloyl glucose and an ellagitannin, oenothein B, using spectrophotometric titration and Job's method. The 280 nm absorbance band of the phenolics was shifted to 330 nm upon addition of Al(III) at pH 6 or pH 4 but absorbance was much weaker at the lower pH Al(III) formed 2:1 complexes with apparent formation constants (Kf) of 1011 M-2 with both tannins at pH 6, and 1:1 complexes, Kf 105 M-1, at pH 4. The characterization of reactions between metals and well characterized tannins will lead to better understandings of the role tannins may play in plant nutrient cycling, detoxification of heavy metals, and water quality.

Last Modified: 07/26/2017
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