High-pressure Raman spectra of deuterated L-alanine crystal (original) (raw)
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High-pressure Raman study of l-alanine crystal
Solid State Communications, 2000
Pressure-dependent Raman scattering studies in the range 0.0-32 kbar were carried out in L-alanine in order to investigate its external mode phonon spectra in relation to the phase transitions in the crystal. A careful analysis of the spectra shows that the low-energy Raman modes exhibit variation both in frequency and in intensity and between 26 and 28 kbar it is observed a splitting of a external mode, indicating that the D 2 normal phase undergoes a transition. Pressure coefficients for external modes are also given.
High-pressure Raman spectra of racemate dl-alanine crystals
Vibrational Spectroscopy, 2010
Raman spectroscopy investigations of dl-alanine crystal under high pressures have been carried out up to 18.0 GPa. For instance, around 1.0 GPa and between 1.7 and 2.3 GPa changes in the Raman profile were observed and associated to conformational changes of the molecules in the unit cell or to a phase transition accompanied to slight conformational change of the molecule through CH and CH 3 groups. Moreover, between 6.0 and 7.3 GPa, the appearance of a new low energy lattice modes and to the splitting of a band assigned to the stretching vibration of the CCH 3 moiety were related to a second phase transition. Finally, changes in lattice modes, red shift of the band associated to CCH 3 stretching and increasing of line-width of the band associated to the wagging of CO 2 , between 11.6 and 13.2 GPa, are ascribed to a third phase transition. On release of pressure the original phase was obtained again.
High-pressure Raman spectra of L-isoleucine crystals
Solid State Communications, 2009
Raman spectroscopy investigations of L-isoleucine crystals under high pressures have been carried out up to 7.3 GPa. From this study it was possible to observe modifications on bands associated to both rocking vibrations of r(NH + 3 ) and r(CO − 2 ) as well as to lattice modes at about 2.3 and 5.0 GPa. These modifications were correlated to either conformational change of molecules or to a solid-solid phase transition undergone by the crystals involving the hydrogen bonds that maintain the molecules held in the unit cell. A comparison with a few results on other amino acid crystals is also given.
Journal of Raman Spectroscopy, 2011
The properties of the crystalline L-alanine have been attracting attention for a very long time, and there is much controversy in the results already reported. One of the most interesting problems is that of the localization of vibrational energy and the micro-transitions (named 'breathers' by Barthes et al. . ]. In the present study, we have addressed this problem once again, having measured the high-resolution polarized Raman spectra in the temperature range from 4 to 300 K. The wavenumber, bandwidth and intensity of all the modes polarized along the c-axis (the axis of the head-to-tail chains of zwitterion in the structure) show discontinuities at 30-50, 100-120 and 180-220 K. We interpret the observed anomalies of spectral characteristics in terms of micro-conformational transitions accompanied by the rearrangement of the hydrogen-bond network and relate them to previously published work.
Acta Crystallographica Section B Structural Science, 2012
Information on the effect of pressure on hydrogen bonds, which could be derived from single-crystal X-ray diffraction at a laboratory source and polarized Raman spectroscopy, has been compared. l-Serine and dl-serine were selected for this case study. The role of hydrogen bonds in pressure-induced phase transitions in the first system and in the structural stability of the second one are discussed. Non-monotonic distortion of selected hydrogen bonds in the pressure range below $ 1-2 GPa, a change in the compression mechanism at $ 2-3 GPa, and the evidence of formation of bifurcated N-HÁ Á ÁO hydrogen bonds in dl-serine at $ 3-4 GPa are considered. research papers Acta Cryst. (2012). B68, 275-286 Zakharov et al. Effect of pressure on serine 285
Chemical Physics Letters, 2006
A series of extended reversible phase transitions at ∼0.1, 1.5, 2.0, and ∼5 GPa was observed for the first time in the crystals of DL-cysteine by Raman spectroscopy. These are the first examples of the phase transitions induced by increasing pressure in the racemic crystal of an amino acid. In the crystals of the orthorhombic L-cysteine, a sequence of reversible structural changes in the pressure range between 1.1 and 3 GPa could be observed by Raman spectroscopy, instead of a single sharp phase transition at 1.9 GPa reported previously in (Moggach, et al. Acta Crystallogr. 2006, B62, 296-309). The role of the movements of the side-CH 2 SH groups and of the changes in the hydrogen-bonding type in DL-and L-cysteine during the phase transitions with increasing pressure is discussed and compared with that on cooling down to 3 K.
Vibrational analysis of crystalline tri‐L‐alanine
Biopolymers, 1991
We have found that tri-L-alanine (Alas) can crystallize in a parallel-chain @ structure in addition to the previously known antiparallel-chain @ structure. Although the chain conformations in each structure are essentially similar, the ir and Raman spectra are distinctively different. We have calculated the normal modes of each structure, and can account in significant detail for these differences. This demonstrates the essential validity of our empirically refined force fields, as well as showing that deeper insights into polypeptide and protein structure can be achieved through the rigorous analyses of normal mode calculations.
Low-temperature Raman spectra of racemate DL-Alanine crystals
Journal of Raman Spectroscopy, 2009
Raman spectra of DL-alanine crystals were investigated in the 50 -3200 cm -1 spectral region for temperatures ranging from 15 to 295 K. The crystalline structure of DLalanine represents a rare example of an amino acid racemate crystallizing in a noncentrosymmetric space group. From this study we have observed changes in the wavenumber of modes associated both to rocking of CO 2 and to skeletal vibrations. On the other hand, neither change in the modes associated to CH or CH 3 vibrations nor substantial modifications of the lattice modes of the crystal were observed. Such result indicates slight changes of the CO 2 group orientation without observation of a solidsolid phase transition in DL-alanine crystal. keywords: Amino acid; hydrogen bond; low temperature * e-mail: tarso@fisica.ufc.br, FAX: 55-85-4008 9450, Phone: 55-85-4008 9925
Pressure-induced phase transitions in L-leucine crystal
Journal of Raman Spectroscopy, 2009
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.