T. N. Rekha

Vibrational spectroscopic, molecular docking and density functional theory studies on 2-acetylamino-5-bromo-6-methylpyridine

Conformational and molecular docking analysis of 2-acetylamino-5-bromo-6-methylpyridine molecule was carried out and the vibrational spectral analysis was also carried out using experimental and theoretical methods. The calculated and experimentally observed vibrational frequencies of the molecule were assigned and compared. The pyridine ring CH stretching and CH3 stretching vibrational modes were shifted towards higher wavenumber (blue shift). The C=O stretching vibrational frequency was shifted towards lower wavenumber (red shift). Ultraviolet-visible spectrum of the molecule simulated theoretically was further validated experimentally. Molecular reactivity and stability were investigated using the frontier molecular orbital analysis and the related quantum chemical molecular properties. Natural bond orbital analysis and the structure activity relations were also studied to confirm the bioactivity of the molecule. Anticancer activity was examined based on molecular docking analysis and it has been identified that the AABMP molecule can act as a good inhibitor against lung cancer.

Conformational, vibrational spectroscopic, nonlinear optical activity, and structure–activity studies on 2-hydroxy-3,5-dinitropyridine: Combined experimental and density functional theory approach

ABSTRACT The conformational analysis was carried out to predict the most stable, optimized structure of 2-hydroxy-3,5-dinitropyridine among various conformers. The most stable, optimized structure of the molecule was predicted by the density functional theory (DFT) using the B3LYP method with the cc-pVQZ basis set. The vibrational frequencies, natural atomic charge distribution, and thermodynamic properties were calculated. The molecular electrostatic potential surface and contour map were simulated. The experimental and theoretical vibrational frequencies were assigned on the basis of potential energy distribution calculation. The density of states (DOS) spectrum was simulated. The frontier molecular orbital analysis was carried out. The natural bond orbital (NBO) analysis was performed to evaluate the donor–acceptor interactions in the molecule. The structure–activity descriptors were determined by Fukui functions and local reactivity descriptor calculations. The nonlinear optical (NLO) activity of the molecule was studied. The second harmonic generation test confirms the NLO activity of the title molecule.

Structural and spectroscopic study of adsorption of anthracene on silver

Adsorption of anthracene on silver is investigated based on the density functional theory and the surface-enhanced Raman spectroscopy (SERS). Variations in bond and dihedral angles of the optimised geometry of anthracene indicate distortions in the hexagonal structure of the ring nearer to the silver cluster and deviations in the co-planarity of carbon atoms. Natural bond orbital analysis confirms intramolecular charge transfers from π(C–C) to π*(C–C) and π(C–C) to σ*(Ag–Ag) orbitals. Higher polarisation resulting from charge transfers on adsorption accounts for Raman enhancements of selective vibrational modes and band shifts. Surface plasmon resonance peak of silver nanoparticles after the adsorption of anthracene observed around 399 nm compares well with the theoretically simulated UV–vis spectrum derived using the time-dependent density functional theory. Theoretical and experimental SERS correlate well, confirming the process of adsorption, the tilted orientation of anthracene on the silver surface and the adsorption mechanism reported. Localisation of the electron density together with a reduced band gap after the adsorption on silver suggests its utility in the design of electro-active organic molecular devices.

Surface enhanced Raman spectroscopic studies on aspirin : An experimental and theoretical approach

Surface enhanced Raman scattering (SERS) studies on aspirin molecule adsorbed on silver nanoparticles (AgNPs) were investigated by experimental and density functional theory approach. The AgNPs were synthesized by the solution-combustion method and characterized by the X-ray diffraction and high resolution-transmission electron microscopy techniques. The averaged particle size of synthesized AgNPs was calculated as ∼55 nm. The normal Raman spectrum (nRs) and SERS spectrum of the aspirin were recorded. The molecular structure of the aspirin and aspirin adsorbed on silver cluster were optimized by the DFT/ B3PW91 method with LanL2DZ basis set. The vibrational frequencies were calculated and assigned on the basis of potential energy distribution calculation. The calculated nRs and SERS frequencies were correlated well with the observed frequencies. The flat-on orientation was predicted from the nRs and SERS spectra, when the aspirin adsorbed on the AgNPs. Hence, the present studies lead to the understanding ...

Vibrational spectroscopic, structural and nonlinear optical activity studies on 2-amino-3-chloro-5-trifluoromethyl pyridine: A DFT approach

The conformational analysis was carried out for 2-amino-3-chloro-5-trifluoromethylpyridine using potential energy surface (PES) scan and the most stable optimized conformer was predicted. The theoretical vibrational frequencies were calculated for the optimized geometry using DFT/B3LYP cc-pVQZ basis set by Gaussian 09 Program. The vibrational frequencies were assigned on the basis of potential energy distribution calculation using VEDA 4.0 program package. The Mulliken atomic charge values were calculated. In the Frontier molecular orbitals analysis, the molecular reactivity, kinetic stability, intermolecular charge transfer studies and the calculation of ionization energy, electron affinity, global hardness, chemical potential, electrophilicity index and softness of the molecule were carried out. The nonlinear optical (NLO) activity was studied and the first order hyperpolarizability value was computed, which was 3.48 times greater than the urea. The natural bond orbital analysis was also performed to co...

DFT and SERS Study of Adsorption of 1,4-Dimethoxy-2-nitro-3-methylanthracene-9,10-dione onto Silver Nanoparticles

Surface-enhanced Raman scattering (or spectroscopy), commonly known as SERS, has been employed to investigate the adsorption mechanism and orientation of 1,4-dimethoxy-2-nitro-3-methylanthracene-9,10-dione (DMNMAD) molecule onto silver. Silver nanoparticles (Ag NPs) were synthesized based on a solution combustion method using citric acid as a fuel. Scanning electron microscopy and transition electron microscopy studies confirm the crystalline nature and morphology of the synthesized silver nanoparticles. Theoretical normal Raman spectra (nRs) and SERS spectra of the DMNMAD molecule, simulated based on DFT/B3PW91 level of theory were validated experimentally. Experimental and theoretical vibrational modes correlate well, confirming the reliable assignments of the vibrational bands. Enhancement of C=O stretching and C–H in-plane vibrational modes in the SERS spectrum indicates the ‘stand-on’ orientation of the molecule on the silver nanoparticles after adsorption. The frontier molecular orbitals confirm the charge transfers between the molecule and silver nanoparticles following the process of adsorption. As anthraquinone derivatives have been recently used as potent anti-tumour drugs, the adsorption studies reported in the current investigation can pave way to the potential application of DMNMAD in drug delivery.

Substitution effects on nonlinear optical activity of (X-methylphenyl)-5-nitro-6-amino-3-pyridinecarboxmide (X=2,3,4,5,6): A DFT approach

The substitution effects on the first order hyperpolarizability value of (X-methylphenyl)-5-nitro-6-amino-3-pyridinecarboxmide (X-MPNAPC),{X=2,3,4,5,6}molecule was calculated with the aid of density functional theory calculations. The optimized molecular structure of urea and (X-methylphenyl)-5-nitro-6-amino-3-pyridinecarboxmide (X-MPNAPC), {X=2,3,4,5,6} were predicted by the DFT/B3LYP method with cc-pVTZ basis set. The higher first order hyperpolarizability values were obtained for all molecules compared with the urea, which confirm that the higher nonlinear optical activity of the molecules. The frontier molecular orbitals (FMOs) analysis was carried out and their related molecular properties were calculated. The higher first order hyperpolarizability value was obtained for 4-MPNAPC molecule compared with other molecules, which indicates that the lower energy gap and extended π-conjugated bridge between the donor and acceptor group leads to the higher NLO activity of the molecule. Hence, this present in...

Vibrational spectroscopic, structural and nonlinear optical activity studies on 6-aminonicotinamide: A DFT approach

The conformational analysis was carried out for 6-aminonicotinamide (ANA) using potential energy surface scan method and the most stable optimized conformer was predicted. The theoretical vibrational frequencies were calculated for the optimized geometry using DFT/B3LYP cc-pVQZ basis set by Gaussian 09 Program. The vibrational frequencies were assigned on the basis of potential energy distribution calculation using VEDA 4.0 program. The Mulliken atomic charge values were calculated. In the Frontier molecular orbitals analysis, the molecular reactivity, kinetic stability, intermolecular charge transfer studies and the related molecular properties were calculated. The ultraviolet-visible spectrum was simulated for both in the gas phase and liquid phase (ethanol) and the л to л* electronic transition was predicted. The nonlinear optical (NLO) activity was studied by means of the first order hyperpolarizability value, which was 8.61 times greater than the urea and the natural bond orbital analysis was also pe...

Molecular docking studies of (X-methylphenyl)-5-nitro-6-amino-3-pyridinecarboxmide (X=2,3,4,5,6) as potential inhibitors for Alzheimer’s disease

An insilico and density functional theory (DFT) calculations were carried out for (X-methylphenyl)-5-nitro-6-amino-3-pyridinecarboxmide (X-MPNAPC),{X=2,3,4,5,6} to evaluate the potential inhibitors for Alzheimer’s disease. The molecular structure of 2-MPNAPC, 3-MPNAPC, 4-MPNAPC, 5-MPNAPC and 6-MPNAPC molecules was optimized by the DFT/B3LYP method with cc-pVTZ basis set using the Gaussian 09 program. The inhibitory nature of the molecules against enzyme acetylcholinesterase (AChE) catalyzes was evaluated by molecular docking studies. The molecular docking parameters such as binding energy, inhibition constant and intermolecular energy were calculated by the AutoDock 4.0 software. The higher binding energy, intermolecular energy and lower inhibition constant values suggested that the 2-MPNAPC molecule has higher inhibitory nature against the AChE catalyzes, which confirm that the 2-MPNAPC molecule is a potential inhibitor for the Alzheimer’s disease. The molecular reactivity was also studied by the frontier molecular orbitals analysis.An insilico and density functional theory (DFT) calculations were carried out for (X-methylphenyl)-5-nitro-6-amino-3-pyridinecarboxmide (X-MPNAPC),{X=2,3,4,5,6} to evaluate the potential inhibitors for Alzheimer’s disease. The molecular structure of 2-MPNAPC, 3-MPNAPC, 4-MPNAPC, 5-MPNAPC and 6-MPNAPC molecules was optimized by the DFT/B3LYP method with cc-pVTZ basis set using the Gaussian 09 program. The inhibitory nature of the molecules against enzyme acetylcholinesterase (AChE) catalyzes was evaluated by molecular docking studies. The molecular docking parameters such as binding energy, inhibition constant and intermolecular energy were calculated by the AutoDock 4.0 software. The higher binding energy, intermolecular energy and lower inhibition constant values suggested that the 2-MPNAPC molecule has higher inhibitory nature against the AChE catalyzes, which confirm that the 2-MPNAPC molecule is a potential inhibitor for the Alzheimer’s disease. The molecular reactivity was also studied by the frontie...