Structural properties of double-stranded helical poly (gamma-benzyl-D-L-glutamate) in solution. Comparison with some solution properties of linear gramicidin.

The double-stranded helical conformations of alternating PBD-LG found in the solid state have been studied in infrared, circular dichroism, and NMR techniques in solution in methylene chloride, chloroform dioxane, and collidine. The infrared and CD properties of the solutions, transconformations between single- and double-stranded helices and transconformations within the family of double helices, support the hypothesis that the conformation in solution is the same as that found after evaporation of the solvent, namely the pi pi DL 7.2, pI pI DL 9.0, and pi pi DL 10.8 helices, depending on the solvent. An attempt to identify the conformation of linear gramicidin is made on the basis of the CD spectra and the infrared frequencies conformation relationship established for PBD-LG. However, owing to the great number of different conformations observed for the antibiotic, no firm conclusion can yet be drawn, except for the probable existence of the double antiparallel helical structure.