Molecular insights into the pH-dependent adsorption and removal of ionizable antibiotic oxytetracycline by adsorbent cyclodextrin polymers

PLoS One. 2014 Jan 21;9(1):e86228. doi: 10.1371/journal.pone.0086228. eCollection 2014.

Abstract

Effects of pH on adsorption and removal efficiency of ionizable organic compounds (IOCs) by environmental adsorbents are an area of debate, because of its dual mediation towards adsorbents and adsorbate. Here, we probe the pH-dependent adsorption of ionizable antibiotic oxytetracycline (comprising OTCH2 (+), OTCH(±), OTC(-), and OTC(2-)) onto cyclodextrin polymers (CDPs) with the nature of molecular recognition and pH inertness. OTCH(±) commonly has high adsorption affinity, OTC(-) exhibits moderate affinity, and the other two species have negligible affinity. These species are evidenced to selectively interact with structural units (e.g., CD cavity, pore channel, and network) of the polymers and thus immobilized onto the adsorbents to different extents. The differences in adsorption affinity and mechanisms of the species account for the pH-dependent adsorption of OTC. The mathematical equations are derived from the multiple linear regression (MLR) analysis of quantitatively relating adsorption affinity of OTC at varying pH to adsorbent properties. A combination of the MLR analysis for OTC and molecular recognition of adsorption of the species illustrates the nature of the pH-dependent adsorption of OTC. Based on this finding, γ-HP-CDP is chosen to adsorb and remove OTC at pH 5.0 and 7.0, showing high removal efficiency and strong resistance to the interference of coexisting components.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adsorption
  • Anti-Bacterial Agents / chemistry*
  • Cellulose / chemistry*
  • Cyclodextrins / chemistry*
  • Hydrogen-Ion Concentration
  • Oxytetracycline / chemistry*

Substances

  • Anti-Bacterial Agents
  • Cyclodextrins
  • cyclodextrin polymer
  • Cellulose
  • Oxytetracycline

Grants and funding

This study was supported by the National Basic Research Program of China (No. 2013CB430403, http://www.most.gov.cn), the National Natural Science Foundation of China (Nos. 41171382, 21077020, and 21137001, http://www.nsfc.gov.cn), and the Program for New Century Excellent Talents in University (No. NCET-11-0047, http://www.dost.moe.edu.cn). We thank the Key Laboratory for Ecological Environmental in Coastal Areas, State Oceanic Administration (No. 201105, www.nmemc.gov.cn) for the support to X Cai. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.