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. 2015 Feb 5;119(5):1787-92.
doi: 10.1021/jp508710g. Epub 2015 Jan 27.

Low-temperature polymorphic phase transition in a crystalline tripeptide L-Ala-L-Pro-Gly·H2O revealed by adiabatic calorimetry

Alexey V Markin  1 , Evgeny Markhasin, Semen S Sologubov, Qing Zhe Ni, Natalia N Smirnova, Robert G Griffin
Affiliations

Low-temperature polymorphic phase transition in a crystalline tripeptide L-Ala-L-Pro-Gly·H2O revealed by adiabatic calorimetry

Alexey V Markin et al. J Phys Chem B. .

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.

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Figures

Figure 1
Figure 1
Temperature dependence of the molar heat capacity Cp,m of l-Ala-l-Pro-Gly·H2O. Pink line corresponds to a metastable state.
Figure 2
Figure 2
Photographs showing a supercooled single crystal of APG fracturing due to a polymorphic phase transition.
Figure 3
Figure 3
DSC traces for two samples of APG (10.6 mg, top; 4.7 mg, bottom) showing the phase-transition region.
See this image and copyright information in PMC

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