Structural and vibrational spectral analysis of polymorphs of anhydrous Acyclovir Using terahertz and Raman spectroscopy

Acyclovir (ACV), a prototypical antiviral drug, exhibits distinct physicochemical properties due to its polymorphism. In this study, two stable anhydrous forms of ACV were prepared at room temperature through high-temperature dehydration and recrystallization from methanol solution, respectively. Our objective was to delve into the differences in internal structure and vibrational modes between these two forms. Terahertz (THz) spectroscopy, combined with Raman spectroscopy, served as the primary characterization techniques. Additionally, gas-phase and multiple solid-state quantum chemical software packages based on density functional theory (DFT) were utilized for simulations to assist in interpreting experimental spectral data, evaluating the accuracy of different simulation methods for spectral prediction, and achieving amore comprehensive and accurate assignment of vibrational modes. These studies not only provide important insights into the THz and Raman spectroscopic characteristics of ACV but also offer novel ideas and methodologies for the spectroscopy study of related drug molecules.