High temperature Raman spectra of L-leucine crystals

Abstract

Single crystal samples of L-leucine, C 6 H 13 NO 2 , a fundamental aliphatic amino acid of the human body, have been studied by Raman spectroscopy at temperatures from 300 to 430 K over the spectral range from 50 to 3100 cm −1 . A tentative assignment of all bands is given. For high temperatures, several modifications on the Raman spectra were observed at about 353 K, giving evidence that the L-leucine crystal undergoes a structural phase transition. An interpretation for this phase transition in terms of group theory analysis is given.

Comparative vibrational spectra of pilosine and epiisopilosine crystals

“…For organic crystals the region about 3000 cm −1 , in general, contains the bands originated from CH, CH 2 , CH 3 , and NH vibrations [17,18]. For some materials this region condenses very important informations, being a tool to understand conformation of the molecules in the unit cell or even interactions such hydrogen bonds.…”

Neutron Scattering

“…A previous research demonstrated the occurrence of a phase transition in L-leucine at ~ 353 K possibly maintaining the crystal with a monoclinic structure [22]. ) presents a red shift down to 190 K and below this, presents a blue shift; also, the intensity increases on cooling.…”

“…Such a vibrational aspect can be translated to the structural language if one assumes that the room temperature monoclinic structure C 2 change to a monoclinic C s structure [22]. In other words, from the point of view of the spectroscopic scrutiny the C 2 → C s phase transition is a viable path.…”

Vibrational spectra of pilocarpine hydrochloride crystals

“…However, all bands are well resolved, allowing for their identification as listed in Table 4. For organic crystals the region about 3000 cm −1 , in general, contains the bands originated from C-H, CH 2 , CH 3 , and N-H vibrations [21,22]. For some materials this region condenses very important informations, being a tool to understand conformation of the molecules in the unit cell or even interactions such as hydrogen bonds.…”