Effect of pressure on crystalline L - and DL -serine: revisited by a combined single-crystal X-ray diffraction at a laboratory source and polarized Raman spectroscopy study (original) (raw)
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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.
Acta Crystallographica Section B Structural Science, 2005
The crystal structure of l-serine has been determined at room temperature at pressures between 0.3 and 4.8 GPa. The structure of this phase (hereafter termed l-serine-I), which consists of the molecules in their zwitterionic tautomer, is orthorhombic, space group P2 1 2 1 2 1 . The least compressible cell dimension (c), corresponds to chains of head-to-tail NHÁ Á Ácarboxylate hydrogen bonds. The most compressible direction is along b, and the pressure-induced distortion in this direction takes the form of closing up voids in the middle of Rtype hydrogen-bonded ring motifs. This occurs by a change in the geometry of hydrogen-bonded chains connecting the hydroxyl groups of the ÐCH 2 OH side chains. These hydrogen bonds are the longest conventional hydrogen bonds in the system at ambient pressure, having an OÁ Á ÁO separation of 2.918 (4) A Ê and an OÁ Á ÁOÁ Á ÁO angle of 148.5 (2) ; at 4.8 GPa these parameters are 2.781 (11) and 158.5 (7) . Elsewhere in the structure one NHÁ Á ÁO interaction reaches an NÁ Á ÁO separation of 2.691 (13) A Ê at 4.8 GPa. This is amongst the shortest of this type of interaction to have been observed in an amino acid crystal structure. Above 4.8 GPa the structure undergoes a single-crystal-to-single-crystal phase transition to a hitherto uncharacterized polymorph, which we designate lserine-II. The OHÁ Á ÁOH hydrogen-bonded chains of l-serine-I are replaced in l-serine-II by shorter OHÁ Á Ácarboxyl interactions, which have an OÁ Á ÁO separation of 2.62 (2) A Ê . This phase transition occurs via a change from a gauche to an anti conformation of the OH group, and a change in the NC CO torsion angle from À178.1 (2) at 4.8 GPa to À156.3 (10) at 5.4 GPa. Thus, the same topology appears in both crystal forms, which explains why it occurs from one single-crystal form to another. The transition to l-serine-II is also characterized by the closing-up of voids which occur in the centres of other R-type motifs elsewhere in the structure. There is a marked increase in CHÁ Á ÁO hydrogen bonding in both phases relative to l-serine-I at ambient pressure.
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.
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 Physics: Conference Series, 2008
The contribution summarizes the results of recent studies of phase transitions induced by high pressure in a number of molecular organic crystals, such as polymorphs of paracetamol, chlorpropamide, polymorphs of glycine, L-and DL-serine, β-alanine. The main attention is paid to the following topics: (1) Reversible / irreversible transformations; (2) Different behavior of single crystals / powders; (3) The role of pressure-transmitting liquid; (4) The role of the kinetic factors: phase transitions on decompression, or after a long storage at a selected pressure; (5) Isosymmetric phase transitions; (6) The role of the changes in the hydrogen bond networks / intramolecular conformational changes in the phase transitions; (7) Superstructures / nanostructures formed as a result of pressure-induced phase transitions.
High-pressure Raman spectra of deuterated L-alanine crystal
Journal of Raman Spectroscopy, 2009
Raman spectra of deuterated L-alanine have been obtained at high pressure conditions. A phase transition at ~ 1.5 GPa associated with the splitting of some internal modes and increase of the wavenumber of the external modes was observed. Similarly to the hydrogenated L-alanine crystal, this first transition was related to a symmetry change.
β-Alanine under pressure: towards understanding the nature of phase transitions
CrystEngComm, 2015
We report the unusual behavior of β-alanine under pressure. Depending on the protocol with which pressure was increased, the crystals of β-alanine I after transition to phase II either transformed into monoclinic phase V at approximately 6 GPa or remained orthorhombic at least up to 8 GPa in phase II with a molecular packing very similar to that of phase I.