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    Detailed investigation of the spectroscopic features of nicardipine hydrochloride using experimental and quantum chemical methods
    (Springer, 2025) Can, Sumeyra; Cinar, Mehmet; Baris, Ozlem
    ContextThe 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 optimization 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 & Aring; and 2.2 degrees, 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 gauge-invariant atomic orbital (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 pi-pi* excitation was observed at 238 nm.MethodThe geometric optimizations and vibration spectra of the nicardipine drug molecule were performed using the Gaussian 09 program with the B3LYP functional and the 6-311 + + G(d,p) basis set. Visualizations were performed using the GaussView 5.0 interface program. NMR spectra were recorded in chloroform solvent using the GIAO method. Molecular electrostatic potential (MEP) maps and Mulliken atomic charges were analyzed to gain deeper insight into the electronic properties.
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    Diltiazem and Verapamil: Combined experimental and computational approaches to structural and spectroscopic characterization
    (Elsevier, 2024) Cinar, Mehmet; Can, Sumeyra; Baris, Ozlem; Demirci, Cigdem Elif
    Diltiazem and Verapamil are two important drug molecules in a separate group of Calcium Channel Blockers. The purpose of this work is to determine and compare the structural and spectroscopic properties of these two molecules using a number of experimental techniques and quantum chemical calculations. Compounds were characterized spectroscopically using FT-IR, Raman, NMR (1H, 13C, and DEPT), and UV-vis methods. Further-more, the Density Functional Theory (DFT) method, Becke's three-parameter hybrid functional (B3LYP), and the 6-311++G(d,p) basis set were used to determine the ground state geometric structures of molecules, and the spectroscopic properties of the obtained optimum structures were investigated computationally. The optimization studies performed under vacuum circumstances and for the isolated molecules were found to be very close to the experimental results. In fact, r.m.s. values were discovered for Diltiazem and Verapamil with bond lengths of 0.013 and 0.024, and bond angles of 1 degrees and 2 degrees, respectively. The vibration characteristics of the compounds were discovered using the collected FT-IR and Raman spectra, and significant vibrational modes were assigned. After scaling, it was revealed that the quantum chemical data was congruent with the experimental ones, and that the characteristic vibrational modes were appropriately predicted. DFT calculations effectively determine molecules' structures due to internal consistency, despite being slightly distant from experimental data. Theoretical values for carbon and hydrogen atoms are better in agreement with observed values when scaling with 0.92 and 0.90. From the UV-vis spectra, Diltiazem HCl absorbance peaks were found at 207 and 237 nm, whereas Verapamil HCl absorbance peaks were identified at 203, 229, and 278 nm. When the theoretical calculations and experimental findings were compared, the anticipated absorption peaks were found to have shifted nearer the visible area. Furthermore, Hirshfeld surfaces and Molecular Electrostatic Potential surfaces were obtained and analyzed in order to better understand the electronic characteristics. The TDOS and PDOS (total and partial density of state) spectra were also studied. Finally, using the HOMO and LUMO energy values, the critical chemical parameters were evaluated, and it was discovered that both molecules had positive electron affinity and electro-negativity values, indicating that they will accept electrons when the electron-nucleus attraction exceeds the electron-electron repulsion.
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    Molecular structure, spectral characteristics, and nonlinear optical properties of labetalol: an experimental and computational investigation
    (Springer, 2026) Cinar, Mehmet; Can, Sumeyra
    Labetalol is an antihypertensive agent that possesses both alpha- and beta-adrenergic blocking properties. This characteristic allows for its clinical use in both chronic hypertension and hypertensive emergencies. In this study, the FT-IR, FT-Raman, 1 H, 13 C, and DEPT-135 NMR spectra of labetalol hydrochloride (Labetalol HCl) were recorded and examined. Furthermore, the pharmacologically active (R, R) stereoisomer of labetalol was theoretically investigated using the B3LYP functional and the 6-311++G(d, p) basis set. The theoretically determined ground-state geometry of the molecule showed excellent agreement with experimental data reported in the literature. Using the obtained optimized structure, the vibrational spectra of the molecule were simulated, and the vibrational modes were assigned by evaluating them together with the experimental data. Nuclear Magnetic Resonance (NMR) analysis of the molecule was performed considering experimentally recorded values and calculations for gas phase, DMSO, and chloroform solvent environments, and the chemical shift values for each H and C atom were determined. Using Time-Dependent Density Functional Theory (TD-DFT) and Solvation Model based on Density (SMD) approaches, the UV-Vis spectra of the molecule were obtained in the gas phase and in four different solvent environments (ethanol, methanol, DMSO, and water). To better understand the electronic properties of the molecule, Frontier Molecular Orbitals (FMO), Molecular Electrostatic Potential Surface (MEPS), Hirshfeld surface analysis, Mulliken and Hirshfeld charge distributions, and Density States (DoS) analyses were performed. In addition, the non-linear optical (NLO) properties of the molecule were theoretically calculated, and the results showed that the molecule could be a promising NLO candidate.