Interaction of the Macrolide Antimicrobial Clarithromycin with Dissolved Humic Acid
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- 作者：Samuel D. Sibley ; Joel A. Pedersen
- 刊名：Environmental Science & Technology
- 出版年：2008
- 出版时间：January 15, 2008
- 年：2008
- 卷：42
- 期：2
- 页码：422 - 428
- 全文大小：182K
- 年卷期：v.42,no.2(January 15, 2008)
- ISSN：1520-5851
文摘
The association of the cationic macrolide antimicrobial clarithromycin (CLA) with dissolved Elliot soil humic acid (ESHA) was investigated as a function of solution chemistry. CLA–ESHA association was strongly pH-dependent, reaching a maximum near pH 6.5, and was modeled successfully using FITEQL as a 1:1 complexation reaction between CLA+ and discreet deprotonated acidic functional groups with pKa values of 4 and 6. Approximate order of magnitude increases in ionic strength produced ~10-fold decreases in CLA+–ESHA association. Coefficients for CLA+–ESHA association were significantly smaller in the presence of K+ vs Na+. Sorption data were well-fit by the Freundlich model; the Freundlich exponent was <1, suggesting CLA+ interacted with sites having a range of binding energies. Sorption appeared largely reversible; little sorption–desorption hysteresis was observed. The affinities of erythromycin and CLA+ for ESHA association sites were indistinguishable, suggesting interaction with specific sorption sites. Comparison of experimentally determined CLA–ESHA association coefficients with those predicted from single-parameter linear free energy relationships based on log Kow suggested limited contribution of hydrophobic interactions to CLA–ESHA association at environmentally relevant pH values. CLA–ESHA association constants were similar in magnitude (103.9-104.6) to those of many nonpolar organic contaminants, and macroscopic binding data were consistent with cation exchange dominating CLA+-ESHA association.