Vibrational circular dichroism of gramicidin D in organic solvents

Abstract

The vibrational circular dichroism (VCD) and absorption spectra of gramicidin D in different organic solvents are presented in the amide I and II regions. The absorption and VCD spectra suggest that gramicidin structures are similar in dioxane and chloroform. However, the structures adopted by gramicidin in chloroform are due to the trace amount of protective ethanol present in chloroform solvent. In the absence of this protective ethanol, gramicidin appears to aggregate in chloroform. The gramicidin structures appear to be similar in propanol and ethanol, but the composition of these structures appear to be different from those in dioxane and chloroform. In methanol-d₄, a different composition of structures, including monomers, appears to be present. The structures in dimethyl-d₆-sulfoxide and 2,2,2-trifluoroethanol are entirely different from those in all other solvents. © 1999 John Wiley & Sons, Inc. Biospectroscopy 5: 276–283, 1999