Structure of tyrocidine micelles in isotropic aqueous solution.

Aqueous solutions of tyrocidine B, iodoacetyltyrocidine B, and diiodotyrocidine B in 40% H2O:60% ethanol (w/w) were investigated by analytical ultracentrifugation, light scattering, and small-angle X-ray scattering techniques. A reasonable hydrodynamic description of the aggregates of molecular weight 28,600 is a rod with a length of 170 A and a diameter of 30 A; this description is consistent with the X-ray scattering data. Over a broad range of concentrations, inelastic light scattering measurements and small-angle X-ray scattering experiments provide the same hydrodynamic values (e.g., Stokes radii and frictional ratios). The positions of the iodines were resolved and found at a radius (R) of 16 A. So, the iodine-iodine distance across the cross section is 34 A, indicating that labeled tyrocidine B is not affected during the aggregational process.