Low-Temperature Polymorphic Phase Transition in a Crystalline Tripeptide L-Ala-L-Pro-Gly·H2O Revealed by Adiabatic Calorimetry

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.National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-003151)National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-001960)National Institute of Biomedical Imaging and Bioengineering (U.S.) (EB-002026

Effect of ball-milling on the formation of betulin and betulin diacetate composites with polyethylene glycol

Betulin and betulin diacetate (BDA) composites with polyethylene glycol (PEG) were obtained by ball-milling. In case of betulin - PEG mixtures, there was almost complete amorphization under ball-milling. On the contrary, there were no significant changes in the intensity of the reflections in the powder X-ray diffraction patterns for ball-milled mixtures of BDA with PEG. Dissolution of BDA in PEG melts formed at the contacts of particles under collisions with milling bodies leading to crystallization of the drug was suggested. An opportunity to dissolve BDA crystals in PEG melt followed by their crystallization was proven by DSC and hot stage optical microscopic observatio

Crystal structure of 4-benzylcarbamoyl-1-methylpyridin-1-ium iodide: an efficient multimodal antiviral drug

In the title compound, [MeC5H4NCONHCH2C6H5]I or C14H15N2O+·I−, a cation and an anion form an ionic pair linked by a strong N—H...I hydrogen bond. In the crystal, ionic pairs linked by weak C—H...I hydrogen bonds form infinite ribbons along the crystallographic a axis. Polymorphism screening varying crystallization solvents (water, acetone 90%–water, ethanol 90%–water, 2-propanol 90%–water, DMF, DMSO, methanol, acetonitrile) and conditions (solution temperature, heating and cooling protocols) did not reveal any other polymorphs than the one reported in this work