Hydrolysis of Chloramphenicol Catalyzed by Clay Minerals under Nonaqueous Conditions

Abstract

Soil contamination with antibiotics has raised great environmental concerns, while the abiotic degradation of antibiotics on drought soil particles has been largely ignored. In this study, we examined the transformation of chloramphenicol (CAP) on phyllosilicates under nonaqueous conditions. A significant hydrolysis of CAP mediated by kaolinite occurred under moderate relative humidities (RH: 33–76%) with the half-lives of 10–20 days. By contrast, incubation with montmorillonite did not result in detectable degradation of CAP. Infrared and Raman spectroscopies together with density functional theory calculations suggested that the surface-catalyzed CAP hydrolysis was mainly attributed to the basal plane hydroxyl groups of kaolinite, which formed hydrogen-bond interactions with the carbonyl of CAP such that the hydrolysis activation energy of CAP was greatly reduced. Neither the Brønsted nor the Lewis acidity was the determinant for the hydrolysis reaction. The surface moisture content played an essential role in CAP hydrolysis. Specifically, water facilitated the mass transfer of CAP over the low-RH range, whereas excessive water competed for the reactive hydroxyl sites. These results highlight an important but long-overlooked abiotic transformation pathway for antibiotics in field soil, where the soil moisture is low and the microbial activity is suppressed.

Iron Minerals Mediated Interfacial Hydrolysis of Chloramphenicol Antibiotic under Limited Moisture Conditions

“…As natural soil is usually not fully water-saturated (with water content from 2 to 60%), , the reactions of organic contaminants under limited moisture conditions might be completely different from those occurring in aqueous solution. ,, Prior studies demonstrated that the hydrolysis of organophosphorus pesticides catalyzed by phyllosilicates was highly moisture-dependent, and the reactions were greatly enhanced under dry conditions with water content <10%. − Similarly, the low moisture also accelerated the hydrolysis of NO 2 and carbonyl sulfide and other compounds by surface hydroxyl groups on atmospheric mineral dusts. − In addition, our recent research found that the drought-surface of kaolinite and montmorillonite significantly catalyzed the hydrolysis of chloramphenicol (CAP) antibiotic via forming surface hydrogen bonds or inducing surface Brønsted/Lewis acidities. , Further investigation showed that limited surface water could facilitate CAP to diffuse into the reactive sites on a clay surface, while excessive water molecules would compete for surface reactive sites. , …”

“…33−35 In addition, our recent research found that the drought-surface of kaolinite and montmorillonite significantly catalyzed the hydrolysis of chloramphenicol (CAP) antibiotic via forming surface hydrogen bonds or inducing surface Brønsted/Lewis acidities. 36,37 Further investigation showed that limited surface water could facilitate CAP to diffuse into the reactive sites on a clay surface, while excessive water molecules would compete for surface reactive sites. 36,37 In this study, we hypothesize that different iron minerals would impose different interaction modes to antibiotics with respect to surface moisture, thus inducing varied hydrolytic performance.…”

“…36,37 Further investigation showed that limited surface water could facilitate CAP to diffuse into the reactive sites on a clay surface, while excessive water molecules would compete for surface reactive sites. 36,37 In this study, we hypothesize that different iron minerals would impose different interaction modes to antibiotics with respect to surface moisture, thus inducing varied hydrolytic performance. Therefore, four iron minerals, including hematite, maghemite, goethite, and siderite were selected to investigate the nonaqueous surface-catalyzed hydrolysis of CAP, which is a widely used antibiotic with substantial detection in soils.…”

Facet effect of hematite on the hydrolysis of phthalate esters under ambient humidity conditions

“…PAEs are hydrolysable, however, at slow hydrolysis rates with the hydrolysis half-lives ( t 1/2 ) even up to several years under neutral pH conditions 9 . In our previous studies, we found that chloramphenicol antibiotic could be rapidly hydrolyzed by clay minerals and iron oxides under limited surface moisture conditions, attributing to the strong Brønsted-/Lewis-acidities of the dry mineral surface 10 – 12 . By contrast, under water-oversaturated conditions, the surface reactions were completely suppressed due to the shielding effect of surface water layers 10 – 12 .…”

“…In our previous studies, we found that chloramphenicol antibiotic could be rapidly hydrolyzed by clay minerals and iron oxides under limited surface moisture conditions, attributing to the strong Brønsted-/Lewis-acidities of the dry mineral surface 10 – 12 . By contrast, under water-oversaturated conditions, the surface reactions were completely suppressed due to the shielding effect of surface water layers 10 – 12 . Therefore, moisture plays an important role on surface-mediated reactions.…”