title: Low-temperature polymorphic phase transition in a crystalline tripeptide L-Ala-L-Pro-Gly·H2O revealed by adiabatic calorimetry.
abstract: We demonstrate application of precise adiabatic vacuum calorimetry to observation of phase transition in the tripeptide L-alanyl-L-prolyl-glycine monohydrate (APG) from 6 to 320 K and report the standard thermodynamic properties of the tripeptide in the entire range. Thus, the heat capacity of APG was measured by adiabatic vacuum calorimetry in the above temperature range. The tripeptide exhibits a reversible first-order solid-to-solid phase transition characterized by strong thermal hysteresis. We report the standard thermodynamic characteristics of this transition and show that differential scanning calorimetry can reliably characterize the observed phase transition with <5 mg of the sample. Additionally, the standard entropy of formation from the elemental substances and the standard entropy of hypothetical reaction of synthesis from the amino acids at 298.15 K were calculated for the studied tripeptide.
authors.affiliation: Lobachevsky State University of Nizhny Novgorod , Gagarin Pr. 23/5, Nizhny Novgorod 603950, Russia.
authors.forename: Alexey V
authors.initials: AV
authors.lastname: Markin
authors.forename: Evgeny
authors.initials: E
authors.lastname: Markhasin
authors.forename: Semen S
authors.initials: SS
authors.lastname: Sologubov
authors.forename: Qing Zhe
authors.initials: QZ
authors.lastname: Ni
authors.forename: Natalia N
authors.initials: NN
authors.lastname: Smirnova
authors.forename: Robert G
authors.initials: RG
authors.lastname: Griffin
mesh_terms: D000595:Amino Acid Sequence; D002152:Calorimetry, Differential Scanning; D003080:Cold Temperature; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*; D044367:Phase Transition; D013816:Thermodynamics
chemical_list: D009842:Oligopeptides