Stability of the crystal structure of L‐valine under high pressure

Abstract

Raman scattering measurements were carried out on a single crystal of L‐valine with the pressure increasing from the ambient value to 6.9 GPa. Sudden changes in intensity of the bands were observed in the higher energy spectral range at ∼3 GPa and ∼5.3 GPa. Discontinuities observed in the wave number vs. pressure plots occurred in the complete spectrum at those same pressures, suggesting changes in the crystal structure. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Raman spectroscopy and inelastic neutron scattering study of crystalline L-valine

“…Finally, the mode assigned as rocking of CO 2 [ρ(CO 2 )] at ∼540 cm −1 is practically not affected by increasing temperature. Such a fact is different from what is observed at the low temperature [26] and the highpressure [28] measurements where a splitting of the mode is very clear. The splitting could be understood as a break of degeneracy, as mentioned above, due to the phase transition undergone by the crystal.…”

“…Figure 4 shows the Raman spectra of L-valine crystal in the spectral range (40-700) cm −1 at several temperatures from 295 to 423 K. We remember that a phase transition observed in L-valine crystal at high-pressure measurements was supported mainly by modifications of the Raman spectra in the region of the lattice modes [28]. By inspecting the inset of figure 4 it is possible to observe in detail the Raman spectra of Lvaline in this low frequency spectral region.…”

“…Low temperature studies of L-valine indicate one phase transition [26] at ∼120 K, while DSC-investigations show no evidence for a phase transition on both forms of valine between 233 and 423 K [27]. On the other hand, while L-valine undergoes two phase transitions [28] at ∼3.0 and ∼5.0 GPa, even if a substantial reduction in the intensity of the N-HO librational mode is observed at ∼3.0 GPa [29], DL-valine seems to be stable at least up to 7.9 GP. In summary, such findings can certainly be interpreted in terms of changes in the hydrogen bonding interaction.…”

Hydrogen‐bonding interactions in fully deuterated α‐glycine at high pressures

“…Raman [30] 3 --DL-Valine Raman [19] 3 Subtle change (reversible) -L-Cysteine Raman [17,33] X-ray [18] 1.1, 3 (Raman) Structural Change in orientation and type of hydrogen bonding of sulfhydryl groups (Raman) 1.8 GPa (X-ray)…”

Luminescent properties of tris(2,2′‐bipyridine) dichloro ruthenium(II) hexahydrate under high pressure

“…The essential effect of pressure is to reduce the intermolecular distances firstly, which leading to modifications in lattice constants of crystalline solids as well as to the changes in atomic positions within a crystallographic cell, then reduce the inner molecular distance (bond length) and finally break the chemical bonds to form new materials. High pressure technology is then a powerful tool for the research of molecular crystals not only for producing new phases but also for providing a better understanding of their chemical and physical properties [10,11]. In situ high pressure fluorescence spectrum can be employed to study the changes of molecular orbital level with variation of emission intensity, it can also provide evidence for the mechanism of pressure-induced phase transition and characterize the state of molecular electronic level and validate the related theory of electrons and/or molecules interactions.…”