Detailed Investigation of the Spectroscopic Features of Nicardipine Hydrochloride Using Experimental and Quantum Chemical Methods

Abstract Context The structural and spectroscopic properties of drug groups can be determined using spectroscopic techniques and quantum chemical calculations. In this study, the structural and spectroscopic properties of Nicardipine, a potent calcium channel blocker belonging to the dihydropyridine drug group, were investigated. For this purpose, FT-IR, Raman, NMR and UV-Vis spectra of nicardipine hydrochloride were recorded. The ground state geometry optimisation performed under vacuum conditions showed excellent agreement with X-ray diffraction (XRD) data, with root-mean-square deviations of bond lengths and bond angles calculated as 0.017 Å and 2.2°, respectively. Vibrational spectrum analysis revealed all characteristic modes, and theoretical B3LYP predictions largely agreed with experimental data. NMR spectra recorded in chloroform solvent confirmed the molecular structure of Nicardipine. A comparison with previously reported data revealed significant differences in the proton NMR results, while the carbon NMR data showed consistency. The GIAO method, commonly used for NMR spectrum prediction, yielded results within an acceptable error range despite minor inconsistencies arising from differences between experimental and computational conditions. In the UV-Vis spectrum of Nicardipine HCl, an absorption peak corresponding to π-π* excitation was observed at 238 nm. Method The geometric optimisations and vibration spectra of the nicardipine drug molecule were performed using the Gaussian 09 programme with the B3LYP functional and the 6-311 + + G(d,p) basis set. Visualisations were performed using the GaussView 5.0 interface programme. NMR spectra were recorded in chloroform solvent using the GIAO method. Molecular electrostatic potential (MEP) maps and Mulliken atomic charges were analysed to gain deeper insight into the electronic properties.