title: Solid-solid phase transitions in DL-norvaline studied by differential scanning calorimetry and Raman spectroscopy.
abstract: The structural modifications of the amino acid DL-Norvaline have been studied using differential scanning calorimetry (DSC) and Raman spectroscopy. DSC results showed that this amino acid undergoes two solid-solid phase transitions at -116.9 and -76.1 degrees C in the temperature range -130 to +300 degrees C. Raman spectroscopy was applied to complement DSC results. The combination of the two methodologies point out that the observed phase transitions correspond to an increment of disordering in the aliphatic side chain of amino acid, an augmentation of the rotational motion of the amino group and a decrease of the strength of the intramolecular hydrogen bonding of the initial dimers at low temperatures. The observed phase transitions of DL-norvaline are compared with those found in DL-norleucine.
authors.affiliation: Chemistry Department, Laboratory of Physical Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis, Athens 157 71, Greece. pchatzig@chem.uoa.gr
authors.forename: Petros
authors.initials: P
authors.lastname: Chatzigeorgiou
authors.forename: Nikos
authors.initials: N
authors.lastname: Papakonstantopoulos
authors.forename: Nikolitsa
authors.initials: N
authors.lastname: Tagaroulia
authors.forename: Evangelos
authors.initials: E
authors.lastname: Pollatos
authors.forename: Pantelis
authors.initials: P
authors.lastname: Xynogalas
authors.forename: Kyriakos
authors.initials: K
authors.lastname: Viras
mesh_terms: D002152:Calorimetry, Differential Scanning; D008958:Models, Molecular; D008968:Molecular Conformation; D009646:Norleucine / Q000737:chemistry; D013059:Spectrum Analysis, Raman; D013696:Temperature; D014633:Valine / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D009646:Norleucine; C005313:norvaline; D014633:Valine