Neutron Scattering And Raman Spectra Studies Of The Interaction Between Water And Amino Acids

Water is the key element for life on earth. Despite its simple formula water is by no means a simple compound. Its unique properties make it so important for the function of every organism. Neutron Scattering is an ideal technique for studying hydrogenous compounds, thus during the last 20 years it has become very useful for the study of water. The aim of this research was to study the interaction of water with different biomolecules on the molecular level using that technique. Bands appearing in the neutron scattering spectrum (predominated by H motion) in the low energy transfers region are mainly due to hydrogen bonding between water and amino acids, or between water molecules. Inelastic neutron scattering can be employed as a vibrational spectroscopy method that provides information in the same energy ranges as Raman spectroscopy. However, Raman has better resolution in the high-energy transfer (in C-H, O-H, N-H bending and stretching) regions. Combining Raman is complemented so that we can extend the comparison of the vibrational spectrum. This study has proved that the water molecules that come into immediate contact with the biomolecules have a different dynamical behaviour to the bulk ones.The vibrational dynamics of water around some typical amino acids (i.e. glycine, alanine, serine, cysteine and proline) was investigated by using inelastic neutron scattering (INS) and Raman spectroscopy. The study clearly show that for some of the amino acids, such as glycine, the presence of water hardly changes the main features, illustrated the hydrophobic nature of these amino acids, however the water spectra are perturbed considerably from bulk water. For others, such as serine, the main features (versus the dry sample) have been altered considerably, new sharp peaks appeared in the INS spectrum and the hydrogen bonding between water and serine extraordinary disturbed the structure of amino acids molecules. The hydrogen bonding related to inter-molecule interaction can be analyzed from INS spectra in detail. The change of molecular vibrations can be complemented by Raman spectroscopy. Deep studies of a series of amino acids make us understand the interaction mechanism between amino acids and aqueous solution.