AEI 52 |
| Tetracycline is transformed by covalently bonding to oligomers of natural organic matter constituent through oxidative cross coupling reactions mediated by extracellular oxidoreductases. Appearance of new peaks in 1D [1H] and new cross-peaks in 2D [13C, 1H] HSQC nuclear magnetic resonance spectroscopy (NMR) was followed by confirmation of reaction products in solution using ion trap mass spectrometry with positive electrospray ionization ((+)ESI-IT-MS), which provide evidence of horseradish peroxidase (HRP) mediated cross coupling of tetracycline with syringic oligomers. Incubation of tetracycline with Elliot soil humic acid and Waskish peat fulvic acid in presence of HRP for a period of 10 days showed appearance of new cross peaks in 2D [13C, 1H] HSQC and high molecular weight ion peaks in fast atom bombardment mass spectrometry (FAB-MS). This indicates a change in the chemical environment due to a fraction of tetracycline molecules being incorporated into soil humus via covalent linkage. The 1H and 13C spin-lattice relaxation times (T1) for aromatic protons and carbons of tetracycline were found to decrease with increasing additions of Elliot soil humic acid. Decreasing T1 values, significant change in the chemical shifts of hydroxyl and amide functionalities due to hydrogen bonding, lack of significant chemical shift change of aromatic and aliphatic protons due to hydrophobic interactions, and an increase in signal line broadening observed in 1H-1D NMR indicate non-covalent nature of interactions between tetracycline and humus. Our results indicate that initially the adsorption of tetracycline into soil occurs via non-covalent interactions. Longer the adsorbed tetracycline residues remain sequestered in soil could result in their slow chemical incorporation into humus via covalent bonding. Because phenolic diketone moiety is the principal active center in tetracycline group of antibiotics, involvement of the phenolic oxygen attached to the tetracycline aromatic ring in covalent bonding with humic substances can diminish its mobility, bioavailability, and bioactivity. |
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Academic Employment Initiative
8:00 PM-10:00 PM, Monday, August 20, 2007 BCEC -- Exhibit Hall - B2, Sci-Mix
Academic Employment Initiative |