Title

Chemical-Structural Properties of Tetracycline Derivatives. 7. Evidence for the Coexistence of the Zwitterionic and Nonionized forms of the Free Base in Solution

Document Type

Article

Publication Date

2-1-1979

Abstract

Circular dichroism spectra have been measured for oxytetracycline free base dissolved in an ethanol/water solvent system over a wide range of composition. The spectra demonstrate a solvent-dependent equilibrium between the zwitterionic form and the nonionized form. The zwitterion clearly predominates in water-rich solutions, whereas the nonionized form becomes the species of preference when the ethanol content exceeds ca. 85% (v/v). This dependence upon the thermodynamic environment supports the concept that the nonionized form of the free base is the important lipid-soluble tetracycline species and suggests, in the context of the known three-dimensional structure of biologically active and nonactive tetacycline derivatives, that the conformational-structural adaptability of tetracycline free bases is a significant factor in their broad spectrum antibacterial action. © 1979, American Chemical Society. All rights reserved.

Publication Name

Journal of the American Chemical Society

Volume Number

101

First Page

7655

Last Page

7657

Issue Number

26

DOI

10.1021/ja00520a003

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