Hydration of l-tyrosine in aqueous medium. An experimental and theoretical study by mixed quantum mechanical/molecular mechanics methods

Quantum mechanical/molecular mechanics (QM/MM) calculations were carried out in order to study the theoretical structures of l-tyrosine in both gas phase and in aqueous solution and observe the changes that occur on the structural and vibrational properties in two phases. Therefore, the molecule was characterized by infrared and Raman spectroscopy in solid phase and aqueous solution. Optimized geometries and relative stabilities for the zwitterion l-tyrosine derivatives have been calculated taking into account the solvent effects by using the self-consistent reaction field (SCRF) theory. For a complete assignment of the IR and Raman spectra of l-tyrosine in solid and aqueous solution phases, density functional theory (DFT) calculations were combined with Pulay's scaled quantum mechanical force field (SQMFF) methodology in order to fit the theoretical wavenumber values to the experimental ones. A good agreement between theoretical and available experimental results is found.