Nature of biological water: a femtosecond study.

The quasi-bound biological or structured water molecules in a protein play a key role in many biological processes. The dynamics of the biological water has been studied by femtosecond spectroscopy and large-scale computer simulations. Solvation dynamics of biological water displays an almost bulk-water like ultrafast component (approximately 1 ps) and a surprising slow component at the 100-1000 ps time scale. In this article, we discuss several examples of the ultraslow component, its possible origin and implications in biology. We show that the ultrafast (approximately 1 ps) component arises from an extended hydrogen bond network while the ultraslow component originates from binding of a water molecule to a biological macromolecule.