Infrared spectrum, NBO, HOMO-LUMO, MEP and molecular docking studies (2E)-3-(3-nitrophenyl)-1-[4-piperidin-1-yl]prop-2-en-1-one

Effects of Au6 and Au20 Adsorption Sites of Cyromazine-Au Complexes by Raman Spectroscopy and Density Functional Theory

Cyromazine, when used as an insect growth regulator and low-toxicity insecticide, may degrade into melamine and pose a potential threat to the environment and soil health, which has thus attracted extensive research on eliminating such a harmful effect. In this paper, density functional theory (DFT)/LC-BLYP/6-311G(d,p) is used to optimize the geometric structure and analyze the vibration of cyromazine. The DFT/LC-BLYP/def2-SVP is used for the cyromazine-Au complex optimization and vibration analysis. The molecular electrostatic potential (MEP), frontier molecular orbitals (FMOs), vibration frequency, electrophilicity-based charge transfer (ECT) descriptor, binding energy (BE), polarizability, normal Raman spectroscopy (NRS), and surface-enhanced Raman spectroscopy (SERS) of cyromazine adsorbing on Au6 and Au20 are calculated. The study of the chemical enhancement mechanism of SERS of cyromazine at different adsorption sites of Au6 or Au20 confirms the existence of a charge transfer between cyclopromazine and Au6 and Au20, which can adsorb and form stable cyromazine-Au complexes. The results show that N2, H13, and N4 are the adsorption sites of Au6 and Au20. The Raman spectra of the cyromazine-Au complex can be selectively enhanced with a factor up to 9.07. Compared with those of cyromazine-Au6, the Raman spectra of cyromazine-Au20 are enhanced more significantly.

Theoretical Investigation of para Amino-Dichloro Chalcone Isomers. Part II: A DFT Structure-Stability Study of the FMO and NLO Properties

The density functional theory (DFT) method using the functional hybrid (B3LYP) and 6-311G(d,p) basis set was utilized for the geometry optimization with dispersion correction, procedure (GO + DC), for the E and Z chalcone isomers -1-(4-aminophenyl)- 3-(i,j-dichlorophenyl)prop-2-en-1-one, where (i) and (j) represent the positions of the two chlorine atoms [(2,3), (2,4),(2,5),(2,6),(3,4), and (3,5)] abbreviated (i,j)-chalcone, and 4-(x,y-dichloro-8aH-chromen-2-yl)aniline, where (x = 5,6 and y = 6,7,8,8a) abbreviated (x,y)-chromen isomers. The calculations revealed that E chalcones are the most stable and the 4-(x,y-dichloro-8aH-chromen-2-yl) aniline isomers are the least stable. The (3,5) chalcones were the most stable in both E and Z chalcone series. However, the 4-(5,8a-dichloro-8aH-chromen-2-yl) aniline is the most stable in the series. The isomer stability order is the same as in Part 1, in which the geometry optimization calculation was followed by the dispersion correction single point energy calculation (GO/SPDC) procedure. The procedures (GO + DC) and (GO/SPDC) were used to calculate energies of the highest occupied molecular orbital (HOMO) and lowest-unoccupied molecular orbital (LUMO) and related properties. The order of the HOMO-LUMO energy gap (ΔE _gap) was chromens <E chalcones <Z chalcones. The lowest ΔE _gap was calculated for the (6,8)-chromen, while the highest energy gap was calculated for the Z (2,6)-chalcone, the least planar isomer. Among the E chalcones, the (2,6)-has the highest E _HOMO, E _LUMO, ΔE _gap, hardness, and electronic chemical potential while possessing the lowest Mulliken electronegativity, electrophilicity index, ionization potential, and electron affinity. The (3,5)-isomer behaved oppositely. The Z chalcones have higher ΔE _gap than E chalcones but follow the same trend as the E series with regard to the E _HOMO. Among the chromens, the (5,8a)-chromen has the highest ΔE _gap, electron affinity, Mulliken electronegativity, hardness, and electrophilicity index but has the lowest E _HOMO and E _LUMO, and electronic chemical potential. (5,6)-Chromen was found to have the highest E _LUMO, electronic chemical potential, and lowest electron affinity. The highest E _HOMO is acquired by (6,8)-chromen; however, it has the lowest hardness value. The chromen isomers possessed the highest first-order hyperpolarizability due to being more planar and having longer π-conjugation than the other isomers. In contrast, the Z chalcones had the lowest hyperpolarizability. The HOMO and LUMO surfaces revealed intramolecular charge transfer in the E and Z chalcones and chromens. Calculations of the molecular electrostatic potential showed that oxygen was the most negative. The HOMOs, LUMOs, and related properties mentioned above calculated according to the (GO + DC) and (GO/SPDC) procedures are in complete numerical agreement.

The chemical adsorption effect of surface enhanced Raman spectroscopy of nitrobenzene and aniline using the density functional theory

Nitrobenzene and Aniline are representatives of the nitro or amino compounds of benzene, mainly used in the manufacture of dyes, spices, medicines, and so on. Extensive use of Nitrobenzene and Aniline may cause pesticide residue pollution and have carcinogenic effects on organisms. In this paper, the Nitrobenzene and Aniline single molecules and their complexes with gold nanoparticles are studied theoretically by Raman spectroscopy, the surface-enhanced Raman spectroscopy (SERS) and the density functional theory (DFT) simulations. Selective binding of gold nanoparticles (AuNPs) to the analyte was used to study the molecular electrostatic potential (MEP), frontier molecular orbital (FMO) and the Raman activity spectra of Nitrobenzene and Aniline, as well as the Raman activity spectrum of the complexes. The most electronegative sites of Nitrobenzene and Aniline are found in the MEP and the hypothesis that these sites might be the adsorption sites of Nitrobenzene/Aniline molecules at the gold surface. At the same time, the MEP of the Nitrobenzene/Aniline complexes also prove the existence of the charge transfer effect between Nitrobenzene/Aniline and Au. The FMO energy gap of Nitrobenzene/Aniline is 0.18983 eV and 0.18953 eV, respectively, and which, after adding the Au₃ clusters, change to 0.03376 eV and 0.0797 eV, respectively, indicating that the Nitrobenzene/Aniline-Au₃ complexes have stronger chemical activities and are more prone to the charge transfer effects. The electrophilic indices of Nitrobenzene (0.17921 eV) and Aniline (0.05635 eV) are calculated and analyzed, as well as that of Nitrobenzene/Aniline-Au₃ complexes after adding the Au₃ atomic clusters, 0.80819 eV and 0.19819 eV, respectively. The obvious increasing trend in the electrophilic indices of the Nitrobenzene/Aniline-Au₃ complexes indicate their stronger biological activities and more prone to chemical reactions. The chemisorption of Nitrobenzene/Aniline and gold nanoparticles complexes is studied by the SERS, and the Raman formation of the complexes at different binding sites of Nitrobenzene/Aniline and Nitrobenzene/Aniline-Au₃ is well explained by the surface selection rule. The reason for the selective enhancement of the spectral peaks presented in the Raman activity spectrum is calculated, and the enhancement factor of the chemical enhancement due to the charge transfer effect is calculated as well. The reason for the peak offset in the SERS spectrum to the conventional Raman spectrum is explained.

Spectroscopic investigation, vibrational assignments, HOMO-LUMO, NBO, MEP analysis and molecular docking studies of oxoaporphine alkaloid liriodenine

A combined experimental and theoretical DFT study of the structural, vibrational and electronic properties of liriodenine is presented using B3LYP function with 6-311G (2d, p) basis set. The theoretical geometry optimization data were compared with the X-ray data for a similar structure in the associated literature, showing similar values. In addition, natural bond orbitals (NBOs), HOMO-LUMO energy gap, mapped molecular Electrostatic Potential (MEP) surface calculation, first and second order hyperpolarizabilities were also performed with the same calculation level. Theoretical UV spectrum agreed well with the measured experimental data, with transitions assigned. The molecular electrostatic potential map shows opposite potentials regions that forms hydrogen bonds that stabilize the dimeric form, which were confirmed by the close values related to the CO bond stretching between the dimeric form and the experimental IR spectra (1654cm^-1 for the experimental, 1700cm^-1 for the dimer form). Calculated HOMO/LUMO gaps shows the excitation energy for Liriodenine, justifying its stability and kinetics reaction. Molecular docking studies with Candida albicans dihydrofolate reductase (DHFR) and Candida albicans secreted aspartic protease (SAP) showed binding free energies values of -8.5 and -8.3kcal/mol, suggesting good affinity between the liriodenine and the target macromolecules.