Conformational difference in cation complexes of tetranactin in solution

✍ Scribed by Masaharu Ueno; Yoshimasa Kyogoku

• Publisher: Wiley (John Wiley & Sons)
• Year: 1979
• Tongue: English
• Weight: 532 KB
• Volume: 18
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1979.360181102

✦ Synopsis

Abstract

The conformational changes and binding behavior of tetranactin on complexation with sodium, potassium, rubidium, cesium, and ammonium ions were investigated by the measurements of proton magnetic resonance, ir, and Raman spectra. It has been clearly shown that alkali cations coordinate to the oxygen atoms of both the carbonyl group and the tetra‐hydrofuran ring, but the ammonium ion coordinates only to the oxygen atom of the tetrahydrofuran. Among the alkali cations the potassium ion most strongly coordinates to the tetrahydrofuran oxygen atoms. The complexation with larger cations induces an expansion of the cavity of the macrocyclic ring of tetranactin and smaller cations contract the cavity. The evidence is revealed by the coupling constants of the methylene protons and the frequency separation between the carbonyl stretching vibrations of the ir‐ and Raman‐active modes. The conformations of the cation complexes in the solid are maintained in solution but that of the cation free form is not.