[Acid-base properties of gramicidin C]

The acid and basic properties of gramicidin S, a polypeptide antibiotic were studied. Calculation of the protonization constants with the Schwarzenbach method showed that the capacity of the antibiotic amino groups for protonization depended on both the solvent nature and the gramicidin S concentration. No such phenomena were observed in the study on the acid and basic properties of N,N -dimethyldiaminogramicidin. This confirmed the possible effect of the association of the gramicidin S molecules on the protolytic properties of the antibiotic.