¹⁴N NQR Spectra of two Benzodiazepines: Diazepam and Lorazepam

The ¹⁴N nuclear quadrupole resonance (NQR) spectra of two common benzodiazepines, Diazepam and Lorazepam, have been recorded using cross relaxation double resonance. Benzodiazepines are characterized by a fused diazepine and benzene ring and act as central nervous system depressants or tranquilizers. Each compound has two distinct nitrogen atoms in their molecular structure. Both nitrogen atoms of diazepam have similar asymmetry parameters. However, the imine nitrogen of diazepam has a slightly higher quadrupole coupling constant (χ) than its tertiary amide nitrogen. The ¹⁴N NQR signals of lorazepam suggests that there is more than one form present in the solid. The imine nitrogen shows similar frequencies and NQR parameters to that of diazepam. However, the frequencies assigned to the secondary amide nitrogen result in a lower χ and a relatively higher asymmetry parameter (η) than the amide nitrogen of diazepam. This has been attributed to hydrogen bonding of the amide proton in lorazepam. Ab-initio and DFT calculations have been performed to support the assignments.