Research Article

Vibrational Spectroscopic Analysis and Laser Irradiation Effect on Pharmaceutical Compounds: An Integrated Experimental and Density Functional Theory Approach

Abstract

Knowledge of structural integrity of pharmaceutical compounds at energetic stress is essential to drug safety and efficacy. The paper describes a detailed experiment on the molecular stability of active pharmaceutical ingredients under constant wave laser light, which is performed with the help of a unified system of vibrational spectroscopy and quantum mechanical simulations. The vibrational landscape of the target compound was mapped using high-resolution Raman scattering and Fourier Transform Infrared spectroscopy and a solid theoretical basis of spectral assignment was presented using Density Functional Theory at a B3LYP/6-311++G(d,p) level. The geometry at the ground-state was determined with great accuracy by correlation of experimental mode measurements and calculated potential energy distributions. Dose dependent spectral changes with effects of exposure to 532 nm laser excitation included the destruction of the aromatic ring breathing mode at 1000 cm−1 and the appearance of a specific redshift in the carbonyl stretching vibration. These spectral changes indicate that the mechanism is important in the disruption of intermolecular hydrogen networks and local photochemical disordering as opposed to direct thermal decomposition. Latent statistical analysis of the spectral data showed that the Principal Component Analysis was useful in separating native and irradiated samples on the basis of variation in individual vibrational bands. The results prove that experimental spectroscopy fingerprints coupled with theoretical modeling provide a robust methodology of non-destructive monitoring of the photodegradation profiles of sensitive pharmaceutical materials.