Femtosecond studies of tryptophan solvation: correlation function and water dynamics at lipid surfaces

We report here a complete study of solvation dynamics of tryptophan in bulk water with femtosecond resolution and present an accurate method for the construction of its solvation correlation function. The water dynamics was observed in one hundred picosecond (∼108 ps) at lipid–water interfaces while in buffer and salt/buffer solutions it becomes faster in tens of picoseconds (∼7–20 ps). These water motions are being elucidated on the femtosecond to subnanosecond (or longer) time scale for their different biological functions, such as global structural stability of membranes through well-ordered interfacial water structures and efficient recognition of molecules (and ions) by membrane proteins through ultrafast water displacement.