Konformationsanalyse und Kinetik der Konformationsänderungen von membranaktiven Antibiotika

Abstract

Molecular properties of the membrane active antibiotics enniatin B, valinomycin and gramicidin A were investigated in various solvents. The conformational rearrangements of these antibiotics have been studied as a function of solvent polarity by spectroscopic techniques and ultrasonic absorption measurements. The results of these experiments provide information about conformational equilibria, about the number of populated conformers, and the kinetics of their interconversions. Enniatin B shows conformational changes which can be explained by reorientation of the polar groups in the molecule induced by specific interactions between polar solvent molecules with the ester and amide groups of the depsipeptide. The conformational rearrangements of valinomycin are due to a step-wise opening of a structure stabilized by intramolecular hydrogen bonds. These conformational transitions give rise to relatively rapid relaxation processes in the frequency range of 10 to 100 MHz and also to slower conformational processes around 1 MHz rate constants of about 10⁷s^-1.