Raman spectroscopy of ?-aminobutyric acid under high pressure

γ-Aminobutyric acid is a gamma-amino acid playing a fundamental role in the balance between neuronal excitation and inhibition in the mammalian central nervous system, being involved in several neuronal disorders. In this study, the monoclinic phase of γ-aminobutyric acid was investigated through Raman spectroscopy in the spectral range from 30 to 1700 cm-1 for pressure between 1 atm and 7.1 GPa. A series of phase transitions at ~0.1, 2.0 and 4.0 GPa was observed during the compression cycle. The modifications in the Raman spectra were interpreted mainly regarding the conformational changes of the molecules in the unit cell. In the phase transition at 4.0 GPa, modifications in the modes associated with both torsion and rocking of NH3+ were interpreted as a change in the hydrogen-bond network, beyond the conformational change itself. An analysis of sample integrity after the experiment aid to compare the degree of the conformational changes with those observed in phase transitions studied in some α-amino acid crystals.