Phase-transition of hydrophobic dipeptide l-phenylalanyl-l-alanine under high pressure via Raman spectroscopy

The study conducted on l-Phenylalanyl-l-Alanine (C₁₂H₁₆N₂O₃) dehydrated crystals under high-pressure conditions up to 7.0 GPa using Raman spectroscopy revealed significant modifications in both lattice and internal modes. Particularly, alterations were observed in modes associated with carbonyl and NH₂ functionalities around 1600 cm^-1. The Raman spectra exhibited distinct changes in modes related to torsions and stretching of the ring, suggesting a potential conformational change in specific pressure intervals: 2.6-3.0 GPa, and 5.0-5.1 GPa. Furthermore, notable changes between 0.4 and 1.0 GPa hinted at a structural transformation in the crystal. Additionally, Scanning Electron Microscopy-Field Emission Gun (SEM-FEG) was employed to elucidate the crystal pattern of Phe-Ala·2H₂O. The ambient study, incorporating calculations, infrared, and Raman spectroscopy, contributed to a comprehensive understanding of vibrational mode assignments. This research sheds light on the behavior of l-Phenylalanyl-l-Alanine dehydrated crystals under varying pressure conditions, offering valuable insights for medicinal and pharmacological applications.