Anomalous volume change of gramicidin A in ethanol solutions

Gramicidin A (GA) in absolute ethanol (AE) at concentrations (c), below 0.01 g/100 ml, failed to sediment but sedimented normally in ethanol-water mixtures (EWM). The apparent partial specific volume, φ, increased on decreasing c in AE but no increase was observed in EWM, where it remained around φ=0.83. These results indicate that GA solutions consist of an equilibrium system containing species differing in volume. This behavior may help to explain the biological mechanism of action of GA.