Article,
High-pressure Raman spectra and DFT calculations of L-tyrosine hydrochloride crystal
PHYSICA B-CONDENSED MATTER, (2018)
DOI: 10.1016/j.physb.2017.11.090
Abstract
High-pressure Raman spectra of L-tyrosine hydrochloride crystal were
obtained from 1.0 atm to 7.0 GPa in the 90-1800 cm(-1) spectral region.
At atmospheric pressure, the Raman spectrum was obtained in the 50-3200
cm(-1) spectral range and the assignment of the normal modes based on
density functional theory calculations was provided. We found good
correspondence between the calculated and the observed intramolecular
geometry parameters. This confirms the correct assignment of the normal
modes, since it was crucial to understand the meaning of the changes
observed in particular Raman active modes. Here we show that bands
associated with internal modes undergo slight modifications during
compression. However, an inversion of the relative intensity of bands
around 125 cm(-1) as well as a change of slope d omega/dP from 1.0 to
1.5 GPa was understood as a conformational change involving a torsion of
the L-tyrosine molecule. As a consequence, it is possible to conclude
that the crystal remained in the same monoclinic structure in the 1
atm-7.0 GPa interval, although conformational change of the molecule was
verified. A comparison of our results with other selected studies
provided insights about the role of the amino acid side chain on the
arrangement of hydrogen bonds. Finally, when the pressure was released
back to 1 atm, the Raman spectrum was recovered and no hysteresis was
observed.
