S. Muthu

Quantum mechanical, spectroscopic and docking studies of 2-Amino-3-bromo-5-nitropyridine by Density Functional Method

Experimental and theoretical investigations on the molecular structure, electronic and vibrational characteristics of 2-Amino-3-bromo-5-nitropyridine are presented. The vibrational frequencies were obtained by DFT/B3LYP calculations employing 6-311++G (d, p) basis set. This was compared with experimental FT-IR and FT-Raman spectral data. Simulated FT-IR (4000-400cm-1) and FT-Raman spectra (4000-100cm-1) showed good agreement with the observed spectra. The molecular equilibrium geometry of the title compound was fully optimized. Quantum chemical calculations of the equilibrium geometry and the complete vibrational assignments of wavenumbers using potential energy distribution (PED) were calculated with scaled quantum mechanics. HOMO-LUMO energies, energy gap (ΔE), electronegativity (χ), chemical potential (μ), global hardness (η), softness (S) and the Fukui function were calculated for the title molecule. The title compound has a low softness value (0.239) and the calculated value of electrophilicity index (5.905) describes the biological activity. The stability and charge delocalization of the title molecule were studied by Natural Bond Orbital (NBO) analysis, Non-Linear Optical (NLO) behaviour in terms of first order hyperpolarizability, dipole moment and anisotropy of polarizability and Molecular Electrostatic Potential (MEP) were accounted. The computed values of μ, α and β for the title molecule are 1.851 Debye, 1.723×10-23esu and 7.428×10-30esu respectively. The high β value and non-zero value of μ indicate that the title compound might be a good candidate for NLO material. Thermodynamic properties of the title molecule were studied for different temperatures thereby revealing the correlations between heat capacity (C), entropy (S) and enthalpy changes (H) with temperatures. Docking studies of the title compound were scrutinized to predict the preferred binding orientation, affinity and activity of the given compound. The title compound was docked into the active site of the protein 5FCT which belongs to the class of proteins exhibiting the property as a Dihydrofolate synthase inhibitor. A minimum binding energy of -5.9kcal/mol and intermolecular energy of -6.5kcal/mol is seen in the interaction.

Quantum mechanical and spectroscopic (FT-IR, FT-Raman) study, NBO analysis, HOMO-LUMO, first order hyperpolarizability and molecular docking study of methyl[(3R)-3-(2-methylphenoxy)-3-phenylpropyl]amine by density functional method

Quantum chemical techniques such as density functional theory (DFT) have become a powerful tool in the investigation of the molecular structure and vibrational spectrum and are finding increasing use in application related to biological systems. The Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) techniques are employed to characterize the title compound. The vibrational frequencies were obtained by DFT/B3LYP calculations with 6-31G(d,p) and 6-311++G(d,p) as basis sets. The geometry of the title compound was optimized. The vibrational assignments and the calculation of Potential Energy Distribution (PED) were carried out using the Vibrational Energy Distribution Analysis (VEDA) software. Molecular electrostatic potential was calculated for the title compound to predict the reactive sites for electrophilic and nucleophilic attack. In addition, the first-order hyperpolarizability, HOMO and LUMO energies, Fukui function and NBO were computed. The thermodynamic properties of the title compound were calculated at different temperatures, revealing the correlations between heat capacity (C), entropy (S) and enthalpy changes (H) with temperatures. Molecular docking studies were also conducted as part of this study. The paper further explains the experimental results which are in line with the theoretical calculations and provide optimistic evidence through molecular docking that the title compound can act as a good antidepressant. It also provides sufficient justification for the title compound to be selected as a good candidate for further studies related to NLO properties.

Spectroscopic profiling (FT-IR, FT-Raman, NMR and UV-Vis), autoxidation mechanism (H-BDE) and molecular docking investigation of 3-(4-chlorophenyl)-N,N-dimethyl-3-pyridin-2-ylpropan-1-amine by DFT/TD-DFT and molecular dynamics: A potential SSRI drug

Spectroscopic profiling in terms of FT-IR, FT-Raman, UV-vis and NMR in addition to reactivity study by density functional theory (DFT) and molecular dynamics (MD) simulations of 3-(4-chlorophenyl)-N,N-dimethyl-3-pyridin-2-ylpropan-1-amine (C16H19ClN2) have been discussed. In order to assign principal vibrational numbers, the Potential energy distribution (PED) analysis has been executed. Frontier molecular orbitals (FMOs) analysis in addition to the stabilization energy and natural hybrid orbital analysis has been done. Local reactivity properties of this compound have been addressed through molecular electrostatic potential (MEP) and average local ionization energy (ALIE) surfaces. The bond dissociation energy for hydrogen abstraction (H-BDE) and chemical bonding analysis in terms of electron localization function gave details regarding the Pauli exchange repulsion effect in the electrons of the molecule. Molecular dynamics simulation has been performed in order to understand reactivity of title molecule with water. Molecular docking study was executed to evaluate the potential of the title molecule to bind with 5-HT1 A serotonin receptor and thus can be a lead compound for developing new SSRI (Selective serotonin reuptake inhibitor) drug. Aside from molecular docking, drug likeness parameters have been also considered and by QSAR modeling the comparison of physiochemical parameters of commercially available SSRI drugs and title molecule is carried out.

Spectroscopic (FT-IR, FT-Raman) investigation, topology (ESP, ELF, LOL) analyses, charge transfer excitation and molecular docking (dengue, HCV) studies on ribavirin

Abstract Ribavirin, a triazole derivative has a wide application in the medical field as an antiviral drug. In the present work, a quantum chemical approach was followed to study the vibrational modes and the reactivity. Experimental techniques of FT-IR, FT-Raman were used to study the vibrational spectrum. A complete vibrational analysis was carried out and assignments of the fundamental modes were proposed. Molecular electrostatic potential, frontier molecular orbitals, electronic localization function and fukui functions were analyzed by using wavefunction analyser, Multiwfn 3.4.1 to study the chemical reactivity. Band gap energy of the title molecule is found to be 6.01 eV, as calculated from the HOMO-LUMO energies. The intermolecular charge transfer within the molecule was confirmed from the charge transfer interactions. Molecular docking studies were carried out to study the biological activity of the compound. Viral target proteins such as Dengue and Hepatitis C were chosen and the respective docking parameters were calculated.

Comprehensive spectroscopic (FT-IR, FT-Raman, 1H and 13C NMR) identification and computational studies on 1-acetyl-1H-indole-2,3-dione

Abstract Fourier transform infrared (FT-IR) and FT-Raman spectra of 1-acetyl-1H-indole-2,3-dione (N-acetylisatin) were recorded in the solid phase and analyzed. The molecular geometry, vibrational frequencies, infrared intensities, Raman activities and atomic charges were calculated using density functional theory (DFT/B3LYP) calculations with a standard 6-311++G(d,p) basis set. The fundamental vibrational modes of N-acetylisatin were analyzed and fully assigned with the aid of the recorded FT-IR and FT-Raman spectra. The simulated FT-IR and FT-Raman spectra showed good agreement with the experimental spectra. The stability of the molecule, arising from hyper-conjugative interactions and charge delocalization, was analyzed using natural bond orbital (NBO) analysis. The dipole moment (µ), polarization (α) and hyperpolarization (β) values of N-acetylisatin were also computed. The potential energy distribution (PED) was computed for the assignment of unambiguous vibrational fundamental modes. The HOMO and LUMO energy gap illustrated the chemical activity of N-acetylisatin. The energy and oscillator strength were calculated by DFT. Gauge–including atomic orbital NMR (1H and 13C) chemical shift calculations were performed and compared with the experimental values. Thermodynamic properties (heat capacity, entropy and enthalpy) of the compound at different temperatures were also calculated.

Quantum Computational and Molecular docking studies of 2-{2-[(2,6-dichlorophenyl)amino]phenyl}acetic acid based on density functional theory

In this study, FT-Raman and FTIR spectroscopy have been applied to the vibrational characterization of diclofenac (DCF). The vibrational analysis was aided by DFT calculation based on B3LYP/6-31G(d,p) basis set. The optimized geometries, IR and Raman intensities and harmonic vibrational frequencies were computed. The complete vibrational assignments were performed based on potential energy distribution (PED). The correlation between entropy, enthalpy and Heat capacity at different temperatures has been studied. In addition, the first-order hyperpolarisability, NBO, HOMO and LUMO energies, Fukui function and molecular electrostatic potential were computed. Molecular docking studies suggest that the title compound exhibit anti-inflammatory activity.