Infrared spectroscopic studies of major cellular components. Part I: The effect of hydration on the spectra of proteins

The infrared absorption spectra of two sample proteins as dry, lyophilized powders in KBr pellets, as hydrated proteins in KBr pellets, as hydrated or dehydrated films, and in solution phase are reported. We find an enormous increase in the absorption intensities of the amide I and amide II vibrations between the dry and the hydrated phases. This intensity enhancement was observed for hydration hy both H2O and D2O. Furthermore, we observe significant changes in the amide I/amide II intensity ratios when comparing solution spectra acquired in transmission and attenuated total reflection (ATR) modes. Observed intensity changes between dry and hydrated protein samples were interpreted in terms of variations in the dielectric constant of the immediate surroundings of the peptide linkages.