Temperature and pressure effects on conformational equilibria of alanine dipeptide in aqueous solution

We investigated the temperature and pressure effects on conformational equilibria of N-acetyl-L-alanine-Nʹmethylamide (AAlaMA) in aqueous solution by Raman spectroscopy. Scattering intensities in the skeletal stretching mode of AAlaMA in aqueous solution were decomposed into some component bands by the spectra analysis. Our results indicate that each component band for AAlaMA adopts not only the PII and (alpha)R conformations but also the C7eq conformation. From temperature and pressure dependencies of the band intensities, we determined the enthalpy differences and the volume differences between the conformers. The C7eq conformer is enthalpically most stable due to the intramolecular hydrogen bond. The partial molar volume of the C7eq conformer is the smallest through the solvent-exclusion effect rather than the solute-solvent electrostatic interaction effect.