Vibrational Spectroscopic Investigations, Electronic Properties, Molecular Structure and Quantum Mechanical Study of an Antifolate Drug: Pyrimethamine

Abstract

The computational modelling supported by experimental results can explain the molecular structure, vibrational assignments, reactive sites and several structural properties. In this context, the spectroscopic (FT-IR, FT-Raman and NMR) analysis, electronic properties (HOMO and LUMO energies) and molecular structure of pyrimethamine (Pyr) were investigated by density functional theory (DFT) method associated with three levels of theory viz., B3LYP, MN15 and wB97XD with 6-311++G(d,p) and def2TZVPP as basis sets, respectively in the Gaussian 16 programs. The 1 H and 13 C NMR chemical shifts were calculated with a gauge-independent atomic orbital (GIAO) approach by also applying the same levels of theory and basis sets. All experimental results were compared with theoretical data. Although the results revealed high degrees of correlation between the theoretical and experimental values for spectroscopic properties using the three methods. Furthermore, the atomic and natural charges, energy band gap and chemical reactivity were determined, while the frontier molecular orbital (FMO) and molecular electrostatic potential (MEP) surfaces were plotted to explain the reactive nature of the title molecule.

Spectroscopic properties (FT-IR, NMR and UV) and DFT studies of amodiaquine

“…In this work, the = C–H stretching vibrations of the AQ ring appear in the IR spectrum at 3000 cm −1 while simulated ones at 3107, 3103, 3100, 3071, 3066, 3046 and 3032 cm −1 . Because of the confusion (sometimes strongly) with various C C ring vibrations, many bands in the 1600-1000 cm −1 are involved in-plane C-Η bending vibrations [ 45 , 46 ]. The C–H in plane bending vibrations of phenyl rings were observed at ∼1055 cm −1 (FTIR spectrum), while the calculated values appeared at 1485, 1224, 1219, 1148, 1138 and 1085 cm −1 .…”

Dehydration-Triggered Afterglow Transition in a Mellitate-Based Coordination Polymer

“…The constructed geometries were optimized using Gaussian 09 packages 35 at the B3LYP/6-31G(d) 36 level. Considering the weak interaction in the structure, DFT-D3 dispersion correction is used in the calculation.…”