Molecular Recognition of Ferrioxamine B by Host-Guest Complex Formation with Lasalocid A in Chloroform

Journal Article (Journal Article)

The polyether carboxylic acid antibiotic lasalocid A was employed as an ionophore in the extraction of ferrioxamine B (FeHDFB from H O to CHC1 at aqueous pH 3 and pH 9. Lasalocid can selectively recognize and extract FeHDFB in the presence of the cations Mg , Na , and Li through formation of a neutral second-sphere complex composed of the anionic form of lasalocid and the cationic FeHDFB . The extraction constant for the following reaction was determined to be log K = -3.9 ±0.1: FeHDFB + HLas = (FeHDFB,Las) + H (K ). While lasalocid is highly effective as an anionic ionophore, it does not act as a neutral ionophore even at low pH, despite its ability to assume pseudo-crown conformations. The extraction constant for the iron-free ligand H DFB was determined to be log K = -4.4 ± 0.2, similar in magnitude to the constant for the complex, suggesting that the salicylate group of lasalocid does not enter the inner coordination sphere of the iron center. Lasalocid is selective for FeHDFB by 1-3 orders of magnitude over alkali metal ions. Lasalocid is 300 times as effective as a lariat, ether (benzo-18-crown-6 with a 12-atom carboxylic acid side chain) in the extraction of FeHDFB from H O to CHCl at pH 9. Since both the lariat ether and the lasalocid have easily ionizable protons to provide charge neutralization, the superiority of lasalocid is attributed to its open chain structure, which permits a stronger interaction between the backbone oxygens and the hydrogen atoms of the siderophore's pendant ammonium group. + + 2+ + + + + + + + + 2 3 ex aq org org aq ex 4 ex 2 3

Full Text

Duke Authors

Cited Authors

  • Caldwell, CD; Crumbliss, AL

Published Date

  • January 1, 1998

Published In

Volume / Issue

  • 37 / 8

Start / End Page

  • 1906 - 1912

International Standard Serial Number (ISSN)

  • 0020-1669

Digital Object Identifier (DOI)

  • 10.1021/ic971038o

Citation Source

  • Scopus