Antamanide. Relaxation Study of Conformational Equilibria

Abstract

Ultrasonic absorption of antamanide in different solvents was measured in the frequency range of 0.5–100 MHz. Three relaxation effects could be resolved, each occurring at a given frequency which remains unchanged for the different solvents. The slowest effect disappears upon Na + ‐complex formation. It is ascribed to a conformational transition of the peptide backbone. Rate constants of this effect are in the range of 10 6 s −1 . The two other relaxation effects may be caused by rotational isomerism of amino‐acid side chains. The solvent dependence of the structural conformations is discussed.