High-pressure Raman study of taurine crystal

et al. 2005

J. Raman Spectrosc.

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Single crystals of L-valine, C 5 H 11 O 2 N, have been studied by Raman spectroscopy at temperatures from 17 to 300 K over the spectral range 20-3300 cm −1 . A tentative assignment of the bands is given. Careful analysis of the Raman spectra suggests that a series of changes in the low-wavenumber region may be associated with a phase transition undergone by the material, and this possibility is discussed.

Section: Resultsmentioning

confidence: 99%

Raman scattering ofL-valine crystals

et al. 2005

J. Raman Spectrosc.

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“…Moreover, the best way to decide about the occurrence or not of a structural modification is through the observation of the external modes of the crystal. 9 The strong temperature dependence of linewidth of the (NH 2 ) bands can be associated with the reduction of the 4 However, the N-H bond length, which is about 0.78Å, is appreciably shorter. 4 This arrangement can favor anharmonicity and/or orientational motion in the (NH 2 ) vibration at high temperatures and, as a consequence, an increase in the linewidth.…”

Section: Resultsmentioning

confidence: 99%

“…However, the Raman scattering experiment, through the observation of changes in the low-wavenumber region (<170 cm 1 ), has been found to be a sensitive probe of phase transitions in amino acid crystals. 8,9,11,15 Figure 4 shows the Raman spectra of LAHCL in the x zz x scattering geometry ( < 135 cm 1 ) taken at four different temperatures. Figure 4(a) shows the Raman spectra between 130 and 170 cm 1 .…”

Section: Resultsmentioning

confidence: 99%

Temperature‐dependent Raman study of L‐arginine hydrochloride monohydrate single crystal

Sasaki

et al. 2002

J Raman Spectroscopy

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Polarized Raman spectra of L-arginine hydrochloride monohydrate single crystal were studied at temperatures ranging from 295 to 10 K. The behavior of the linewidth, wavenumber and intensity of several bands is discussed and related to some particular vibrational modes associated with hydrogen bonds or even to other vibrations, such as CN, CCC, CCN and CH vibrations. The disappearance of some bands in the lattice vibrational region was associated with a phase transition undergone by the crystal between 100 and 110 K.

“…[13] Other amino acid crystals that undergo structural phase transitions are L-threonine, at ∼2.1 GPa, [14] and taurine, at ∼0.7 GPa and possibly another at 5.2 GPa. [15] DL-Valine crystal was also investigated through Raman spectroscopy and, although no clear change of structure was observed, a particular pressure dependence of N-H· · ·O librational modes suggested modifications in the nature of hydrogen-bond interactions at about 3 GPa. [16] Recently, studies on vibrational and structural changes of L-serine, DL-serine, L-cysteine, and Lmethionine under high-pressure conditions have been reported by several authors.…”

Section: Introductionmentioning

confidence: 96%

Pressure‐induced phase transitions in L‐leucine crystal

Filho

Melo

et al. 2008

J Raman Spectroscopy

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Raman spectra of a crystal of L-leucine, an essential amino acid, were obtained for pressures between 0 and 6 GPa. The results show anomalies at three pressure values, one between 0 and 0.46 GPa, another between 0.8 and 1.46 GPa, and a third at P ∼ 3.6 GPa. The first two anomalies are characterized by the disappearance of lattice modes (which can indicate occurrence of phase transitions), the appearance of several internal modes, or the splitting of modes of high wavenumbers. The changes of internal modes are related to CH and CH 3 unit motions as well as hydrogen bonds, as can be inferred from the behavior of bands associated with CO 2 − moieties. The third anomaly is a discrete change of the slopes of the wavenumber versus pressure plots for most modes observed. Further, decompression to ambient pressure generates the original Raman spectrum, showing that the pressure-induced anomalies undergone by L-leucine crystals are reversible.