Foto: Waterdance
Dance of water molecules;© RUB

In the virtual laboratory, scientists headed by Professor Dominik Marx and Professor Martina Havenith-Newen found evidence for a mechanism that allows dissolved biomolecules to influence water molecules at distances extending to several molecule diameters.
The interfaces between biomolecules and water play a crucial role.

At frequencies which correspond to infrared light, vibrational motions within single molecules can be observed. “At lower frequencies, in the Terahertz range, which is situated between the frequencies of the infrared light and microwave radiation in the electromagnetic spectrum, far more complex motions take place involving motions of whole water molecules relative to each other”, explains Havenith-Newen. “In particular, these motions involve closing and breaking of the three dimensional hydrogen bond network of water, which interconnects water molecules and is responsible for the unique properties of water.”

Observations of this kind have become feasible only lately with the development of advanced laser light sources. Studies performed at the RUB lead to the discovery of an unexpectedly long ranged influence of biologically relevant solutes, such as sugars and proteins, on the motions of water, the so-called “Terahertz-dance” of water. In the vicinity of the molecule, water motion is highly ordered: “While water molecules usually behave like disco dancers, in the proximity of biomolecules they perform a minuet”, says Havenith-Newen. However, until now a detailed explanation of this unexpected phenomenon was not available.

The use of newly developed analysis methods yielded a precise description of the THz vibrations in water as a correlated motion of many water molecules: a sort of motion of water droplets within the water. “Therefore we have uncovered ‘the choreography of pure water’ at low frequencies”, says Professor Marx.

If another substance, such as a protein, is dissolved in water, it “perturbs” this choreography at its interface. “The correlated motions of water molecules at THz frequencies exhibit entirely new characteristics, which are significantly different from the well-known infrared vibrations of the chemical bonds within a molecule”, explains Professor Marx. This is in stark contrast to the choreography of the THz dance of water: Here, many water molecules, connected only indirectly via hydrogen bonds, move together in a concerted motion in space and time. It is the change of this correlation, evoked by the biomolecule-water interface, which is detected by THz spectroscopy and used for technological applications.; Source: Ruhr-Universität Bochum