Ultrafast Spectroscopy research activities

Water interacting with lipid membranes, polypeptides and poly sugars

The conformation of proteins and membranes is largely determined by their interaction with water. However, vice versa these biopolymers have a profound effect on the dynamics and structure of the nearby water layers. Recently, we studied the dynamics and structure of water molecules hydrating lipid membranes and proteins. We observed that water molecules hydrating membranes show much slower reorientation dynamics than water molecules in bulk liquid water. In the future we will study the dynamics and structure of water molecules hydrating photo-active proteins. In particular, we will investigate how the hydration of water changes upon the triggering of a conformational change of the protein. To this purpose we will use a three-pulse optical excitation and infrared probing technique, as illustrated in the figure.

Schematic picture of the three-pulse visible-mid-infrared pump-pump-probe setup. Variation of the delay Tau1 enables the selection of a particular stage of the photocycle. Variation of the delay Tau2 (at a certain Tau1) enables the measurement of the translational and orientational dynamics of the water molecules at that stage.

Another future direction is the study of the effects of co-solutes like salts and sugars on the properties of proteins and polysaccharides in aqueous solution. It is well known that ions and sugars have a profound effect on the spatial conformation of biomolecular systems, but the molecular mechanisms underlying these effects are poorly understood. Ions can affect the conformation by binding directly to the protein, thereby exerting strong local electric fields, or by changing the structure and dynamics of the solvating water. It is also possible that a combination of these effects is at play. This latter project will be carried out in a cooperation with Danone and Unilever (within the Nanonext program).