Abstract
L-Glutamic acid crystallizes at ambient pressure in two different
polymorphic forms, the alpha- and beta-forms. In this work the
vibrational properties of the alpha-form are investigated by Raman
spectroscopy under high pressure. A single crystal of alpha-L-glutamic
acid, immersed in paraffin oil, was submitted to pressures up to 7.5 GPa
using a diamond anvil cell. The analysis of the Raman spectra of the
crystal shows that alpha-L-glutamic acid presents two phase transitions,
one between 1.9 and 2.3 GPa and another one between 3.3 and 3.7 GPa,
both characterized by modifications in the low-wavenumber spectral
region. Additionally, an impressive increase of the band linewidth is
observed for pressures between 5.6 and 6.0 GPa. Such increase suggests
that disorder is induced by pressure, and these changes can be directly
associated with the solidification of paraffin oil. A discussion on the
reversibility and possible mechanisms governing the phase transitions is
also provided. (C) 2016 Elsevier B.V. All rights reserved.
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