The functioning of biomolecules depends on the conformational shape they adopt, their charge state and their interactions with the surrounding environment, which includes water, other biomolecules and metal ions. Laser-based gas phase spectroscopic techniques, with the aid of computational chemistry, are now providing information about conformation and intermolecular interactions in rich and exquisite detail. In the example shown here, conformation of the neurotransmitter side chain is seen to change as water is added one molecule at a time.
Intramolecular hydrogen bonding within the neurotransmitter side chain is disrupted by insertion of a single water molecule. The onset of a 3D network of hydrogen bonding occurs with four water molecules bound to the neurotransmitter side chain. (Macleod et al, 2003) Quantum chemical calculations play an ever increasing role in chemistry research as they can make an important contribution to a wide range of problems.
In the context of the experimental program described here, theoretical calculations are crucial in the assignment and interpretation of spectral data. A range of structures are computed, corresponding to different molecular conformers, dimers or complexes in which water molecules are attached to the host molecule in various ways. The calculated properties of each one may then be compared to experiment to determine which ones are actually observed and to aid the interpretation of spectral trends.