| Abstract: | A small fraction of carboxylic acid functional groups in humic substances are exceptionally acidic with pKa values as low as 0.5. A review of acid-group theory eliminated most models and explanations for these exceptionally acidic carboxyl groups. These acidic carboxyl groups in Suwannee River fulvic acid were enriched by a 2-stage fractionation process and the fractions were characterized by elemental, molecular-weight, and titrimetric analyses, and by infrared and 13C- and 1H-nuclear magnetic resonance spectrometry. An average structural model of the most acidic fraction derived from the characterization data indicated a high density of carboxyl groups clustered on oxygen-heterocycle alicyclic rings. Intramolecular H-bonding between adjacent carboxyl groups in these ring structures enhanced stabilization of the carboxylate anion which results in low pKa1 values. The standard, tetrahydrofuran tetracarboxylic acid, was shown to have similar acidity characteristics to the highly acidic fulvic acid fraction. The end products of 3 known diagenetic pathways for the formation of humic substances were shown to result in carboxyl groups clustered on oxygen-heterocycle alicyclic rings. |
| Genre: | Article |
| ProdID: | 70025964 |
| Citation Author: | Leenheer, J. A.; Wershaw, R. L.; Brown, G. K.; Reddy, M. M. |
| Citation Contributing Office: | |
| Citation Datum: | |
| Citation Day: | |
| Citation Edition: | |
| Citation Editor: | |
| Citation End Page: | 482 |
| Citation Issue: | 3 |
| Citation Keywords: | |
| Citation Language: | English |
| Citation Larger Work Title: | Applied Geochemistry |
| Citation LatN: | |
| Citation LatS: | |
| Citation LonE: | |
| Citation LonW: | |
| Citation Month: | |
| Citation No Pagination: | |
| Citation Number Of Pages: | 12 |
| Citation Online Only Flag: | |
| Citation Phsyical Description: | |
| Citation Projection: | |
| Citation Public Comments: | |
| Citation Publisher: | |
| Citation Series: | |
| Citation Series Code: | |
| Citation Series Number: | |
| Citation Search Results Text: | Characterization and diagenesis of strong-acid carboxyl groups in humic substances; 2003; Article; Journal; Applied Geochemistry; Leenheer, J. A.; Wershaw, R. L.; Brown, G. K.; Reddy, M. M. |
| Citation Start Page: | 471 |
| Citation Volume: | 18 |
| Citation Year: | 2003 |
| Type: | citation/reference |
| Text: | Characterization and diagenesis of strong-acid carboxyl groups in humic substances; 2003; Article; Journal; Applied Geochemistry; Leenheer, J. A.; Wershaw, R. L.; Brown, G. K.; Reddy, M. M. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1016/S0883-2927(02)00100-2 |
| Date Other: | Wed, 1 Jan 2003 00:00 -0600 |
| Publisher: | |
