Low-frequency Vibrational Spectroscopy of \gamma-Aminobutyric Acid Derivatives: GABA Hydrochloride and \beta-Phenyl-GABA Hydrochloride

The anti-anxiety drug \beta-phenyl-\gamma-aminobutyric acid (\beta-phenyl-GABA) has poorly characterized solid-state properties, despite its close similarity to the well-known neurotransmitter \gamma - aminobutyric acid (GABA). Here, the hydrochloride salts of both molecules are studied since drug formulations are often enhanced with crystallized salt variants to alter solubility. The packing arrangement of \beta-phenyl-GABA·HCI yields low-frequency spectra indicative of the unique intermolecular potential energy surface created from the forces holding the crystalline solid together. Clear differences can be seen between the terahertz spectra of GABA·HCI and \beta-phenyl-GABA·HCI with solid-state density functional theory simulations providing insight into the specific intermolecular forces that dominate this spectral region.