Synthetic fentanyls evaluation and characterization by infrared spectroscopy employing in silico methods

Non-pharmaceutical fentanyls (NPFs) are synthetic substances analogous to fentanyl that have not been approved for medical use. Their clandestine synthesis involves chemical modification of an existing drug, which may cause unpredictable pharmacological effects. New structures are emerging rapidly, and there is a lack of information for characterization. It makes their chemical identification difficult. In this scenario, in silico methods have become an alternative to study these systems. Here, we have applied factorial design to decide the best conditions to perform quantum calculations to obtain the infrared spectra of 46 seized NPFs. A multivariate classification was used to establish the main spectral characteristics of these substances. Similarities between theoretical and experimental spectra were determined through vibrational frequencies comparison, Kullback-Leibler divergence, and SIMCA evaluation. The in silico methods provided valuable information about illegal substances and proved helpful in predict the spectroscopic properties of new fentanyl analogous drugs.