Protein hydration in living cells probed by Fourier transform infrared (FT-IR) spectroscopic imaging

An application of disrelation mapping to Fourier transform infrared (FT-IR) spectroscopic imaging datasets is provided to reveal different H-bonded water species within a mammalian cell. 2D correlation analysis revealed a disrelation peak at (3420 cm^-1, 3220 cm^-1), showing the existence of a specific water band at around 3220 cm^-1 whose variation of absorbance did not follow the trend of water molecules with a well-coordinated H-bonding network. Disrelation maps constructed with disrelation intensities between (3420 cm^-1, 3220 cm^-1) and (3420 cm^-1, 1540 cm^-1) reveal that the disruption of the water network occurs around the interfacial regions between the cell and media, indicating the disintegration of the H-bonding network of bulk water due to the entrapment of water by the protein inside the cell. This hydration effect also becomes apparent around the area adjacent to the cellular nucleus, reflecting the fact that protein synthesis mainly occurs in this region. These results clearly show the presence of different molecular states of water inside living cells, which are not readily identified by conventional analysis methods.