FT-IR spectroscopic study on conformational equilibria of [Leu]5-enkephalin in DMSO and 2H2O solutions

The solvent effect on the conformational equilibria of [Leu]5-enkephalin was investigated using FT-IR spectroscopy. FT-IR spectra of the amide I region of [Leu]5-enkephalin were decomposed into several component bands using a curve fitting method. Infrared bands of the β-turn, 310-helix, and the extended conformers were observed in deuterium oxide (2H2O) solution, while the band of the 310-helix was not observed in dimethylsulfoxide (DMSO). From the temperature dependence of the relative integrated intensity ratio, we determined the enthalpy differences between the conformers (the β-turn, 310-helix, and extended conformers). The enthalpy level is the β-turn