Environmental Photochemistry of Tylosin:  Efficient, Reversible Photoisomerization to a Less-Active Isomer, Followed by Photolysis

Jeffrey J. Werner,† Mahati Chintapalli,‡ Rachel A. Lundeen,§ Kristine H. Wammer,§ William A. Arnold,*†‡ and Kristopher McNeill*†#
Water Resources Science Program, University of Minnesota, 1985 Buford Avenue, St. Paul, Minnesota 55108, Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive SE, Minneapolis, Minnesota 55455, Department of Chemistry, University of Saint Thomas, 2115 Summit Avenue, St. Paul, Minnesota 55105, and Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455
J. Agric. Food Chem., 2007, 55 (17), pp 7062–7068
DOI: 10.1021/jf070101h
Publication Date (Web): July 26, 2007
Copyright © 2007 American Chemical Society
†

 Water Resources Science Program, University of Minnesota.

,
‡

 Department of Civil Engineering, University of Minnesota.

,
§

 Department of Chemistry, University of St. Thomas.

,
*

 To whom correspondence should be addressed. E-mail:  arnol032@umn.edu. Phone:  612-625-8582 (W. A. Arnold). E-mail:  mcneill@chem.umn.edu. Phone:  612-625-0781 (K. McNeill).

,
#

 Department of Chemistry, University of Minnesota.

Abstract

The environmental photochemical kinetics of tylosin, a common veterinary macrolide antibiotic and growth promoter, were investigated under simulated sunlight. An efficient, reversible photoisomerization was characterized using kinetic, mass spectrometry, and proton nuclear magnetic resonance data. The photoisomerization was confirmed to occur by a rotation about the distal alkene of the ketodiene functionality. Concurrent forward (quantum yield = 0.39 ± 0.09) and back (quantum yield = 0.32 ± 0.08) reactions lead to a photochemical equilibrium near a tylosin/photoisomer ratio of 50:50, completed in less than 2 min under a spectrum equivalent to noontime, summer sunlight. The activity of the isomer for the inhibition of Escherichia coli DH5α growth was observed to be less than that of tylosin. On a longer time scale than that of isomerization, the isomer mixture undergoes photolysis with a quantum yield of (1.4 ± 0.3) × 10-3. The observed quantum yields and UV−vis absorbance data allow for the prediction of the photochemical behavior of tylosin in most environmental systems. Indirect photosensitization was not a significant loss process in solutions of Suwannee River fulvic acid with concentrations from 1 to 20 mg L-1.

Keywords: Tylosin; environmental fate; photolysis; quantum yield; antibiotic activity

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History

  • Published In Issue August 22, 2007
  • Received for review January 12, 2007. Revised manuscript received June 14, 2007. Accepted June 15, 2007.

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