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Sample records for dft theoretical studies

  1. Theoretical and practical aspects of chemical functionalization of carbon nanofibers (CNFs): DFT calculations and adsorption study.

    PubMed

    Rokhina, Ekaterina V; Lahtinen, Manu; Makarova, Katerina; Jegatheesan, Veeriah; Virkutyte, Jurate

    2012-06-01

    The nitric acid-functionalized commercial carbon nanofibers (CNFs) were comprehensively studied by instrumental (XRD, BET, SEM, TGA) and theoretical (DFT calculations) methods. The detailed surface study revealed the variation in the characteristics of functionalized CNFs, such as a decreased (up to 34%) surface area and impacted structural, electronic and chemical properties. The effects of functional groups were studied by comparison with pristine nanofibers. The results showed that the C-C bond lengths of the modified CNFs varied significantly. Chemical functionalization altered the frontier orbitals of the pristine material, and therefore altered the nature of their interactions with other substances. Moreover, the pristine and modified CNFs were tested for the removal of phenol from aqueous solutions. It was observed that surface modification tuned the adsorption capacity of carbon nanofibers (up to 0.35 mmol g(-1)), whereas original fibers did not demonstrate any adsorption capacity of phenol. PMID:22209137

  2. An experimental Raman and theoretical DFT study on the self-association of acrylonitrile.

    PubMed

    Alía, Jose M; Edwards, Howell G M; Fawcett, W Ronald; Smagala, Thomas G

    2007-02-01

    The liquid structure of acrylonitrile (propenenitrile) has been investigated using Raman spectroscopy and density functional theory (DFT) ab initio calculations with the 6-311++G** basis set. Two different and complementary experimental approaches were undertaken: FT-Raman spectra of 13 acrylonitrile solutions in carbon tetrachloride (concentration range=0.25-12.0 mol.L-1) were studied in detail including principal component analysis (PCA) of the CN stretching band. Furthermore, dispersive Raman spectra of neat acrylonitrile were obtained at eight different temperatures from 238 up to 343 K. The complex and asymmetric acrylonitrile Raman CN stretching band can be decomposed into two components attributed to monomeric and self-associated forms. Ab initio results fully support this assignment and suggest that the self-associated complex is a nonplanar trimer held together by dipole-dipole interactions. At ambient temperature, the composition of acrylonitrile can be expressed as a mixture of 25% monomers and 75% trimers. Close to the boiling point, trimers still represent 65% of the liquid composition. The corresponding enthalpy of association was estimated to be -22+/-2 kJ.mol-1. PMID:17266219

  3. Theoretical DFT study on spectroscopic signature and molecular dynamics of neurotransmitter and effect of hydrogen removal

    NASA Astrophysics Data System (ADS)

    Mukherjee, V.; Singh, N. P.; Yadav, R. A.

    2013-04-01

    Vibrational spectroscopic study has been made for the serotonin molecule and its deprotonated form. The Infrared and Raman spectra in optimum geometry of these two molecules are calculated using density functional theorem and the normal modes are assigned using potential energy distributions (PEDs) which are calculated using normal coordinate analysis method. The vibrational frequencies of these two molecules are reported and a comparison has been made. The effect of removal of the hydrogen atom from the serotonin molecule upon its geometry and vibrational frequencies are studied. Electronic structures of these two molecules are also studied using natural bond orbital (NBO) analysis. Theoretical Raman spectrum of serotonin at different exciting laser frequencies and at different temperatures are obtained and the results are discussed. Present study reveals that some wrong assignments had been made for serotonin molecule in earlier study.

  4. A DFT theoretical study of heats of formation and detonation properties of nitrogen-rich explosives.

    PubMed

    Jaidann, Mounir; Roy, Sandra; Abou-Rachid, Hakima; Lussier, Louis-Simon

    2010-04-15

    We present density-functional theory predictions and analysis of some properties of synthesized high-nitrogen compounds 3,6-diazido-1,2,4,5-tetrazine (DiAT) and N-oxides of 3,3'-azo-bis(6-amino-1,2,4,5-tetrazine) (DAATO) together with 3,6-di(hydrazino)-1,2,4,5-tetrazine (DHT) and 3,3'-azo-bis(6-amino-1,2,4,5-tetrazine) (DAAT) for which experimental data are available. In this work the reference molecules DHT and DAAT have been studied in order to validate the theoretical approach and facilitate further progress developments for the molecules of interest such as DiAT and DAATO. Geometries of all compounds have been optimized employing the B3LYP density-functional method in conjunction with 6-311++G(3d,3p) basis sets. The energy content of the molecules in the gas phase is evaluated by calculating standard enthalpies of formation, using isodesmic reaction paths. We also include estimates of the condensed-phase heats of formation and heats of sublimation in the framework of the Politzer approach. The obtained results show that DiAT compound has the highest heat of formation (231 kcal/mol) in comparison with those of DHT, DAAT and DAATO molecules. The detonation velocity and pressure have also been estimated for these molecules using the Stine method. PMID:19945785

  5. PBE-DFT theoretical study of organic photovoltaic materials based on thiophene with 1D and 2D periodic boundary conditions

    NASA Astrophysics Data System (ADS)

    Saïl, K.; Bassou, G.; Gafour, M. H.; Miloua, F.

    2015-12-01

    Conjugated organic systems such as thiophene are interesting topics in the field of organic solar cells. We theoretically investigate π-conjugated polymers constituted by n units ( n = 1-11) based on the thiophene (Tn) molecule. The computations of the geometries and electronic structures of these compounds are performed using the density functional theory (DFT) at the 6-31 G( d, p) level of theory and the Perdew-Burke-Eenzerhof (PBE) formulation of the generalized gradient approximation with periodic boundary conditions (PBCs) in one (1D) and two (2D) dimensions. Moreover, the electronic properties (HOCO, LUCO, E gap, V oc, and V bi) are determined from 1D and 2D PBC to understand the effect of the number of rings in polythiophene. The absorption properties—excitation energies ( E ex), the maximal absorption wavelength (λmax), oscillator strengths, and light harvesting—efficiency are studied using the time-dependent DFT method. Our studies show that changing the number of thiophene units can effectively modulate the electronic and optical properties. On the other hand, our work demonstrates the efficiency of theoretical calculation in the PBCs.

  6. PBE–DFT theoretical study of organic photovoltaic materials based on thiophene with 1D and 2D periodic boundary conditions

    SciTech Connect

    Saïl, K. Bassou, G.; Gafour, M. H.; Miloua, F.

    2015-12-15

    Conjugated organic systems such as thiophene are interesting topics in the field of organic solar cells. We theoretically investigate π-conjugated polymers constituted by n units (n = 1–11) based on the thiophene (Tn) molecule. The computations of the geometries and electronic structures of these compounds are performed using the density functional theory (DFT) at the 6–31 G(d, p) level of theory and the Perdew–Burke–Eenzerhof (PBE) formulation of the generalized gradient approximation with periodic boundary conditions (PBCs) in one (1D) and two (2D) dimensions. Moreover, the electronic properties (HOCO, LUCO, E{sub gap}, V{sub oc}, and V{sub bi}) are determined from 1D and 2D PBC to understand the effect of the number of rings in polythiophene. The absorption properties—excitation energies (E{sub ex}), the maximal absorption wavelength (λ{sub max}), oscillator strengths, and light harvesting—efficiency are studied using the time-dependent DFT method. Our studies show that changing the number of thiophene units can effectively modulate the electronic and optical properties. On the other hand, our work demonstrates the efficiency of theoretical calculation in the PBCs.

  7. Experimental (FTIR, Raman, UV-visible and PL) and theoretical (DFT and TDDFT) studies on bis(8-hydroxyquinolinium) tetrachlorocobaltate(II) compound

    NASA Astrophysics Data System (ADS)

    Chaouachi, Soumaya; Elleuch, Slim; Hamdi, Besma; Zouari, Ridha

    2016-12-01

    The purpose of this paper is to present the chemical preparation, crystal structure, vibrational study and optical features for new organic-inorganic compound [C9H8NO]2CoCl4 abbreviated [8-HQ]2CoCl4. The structural study by X-ray diffraction prove that this compound crystallize in a monoclinic unit-cell with space group C2/c (point group 2/m = C2h). It is built of tetrahedra [CoCl4]2- anions and (C9H8NO)+ cations in the 1/2 ratio. The crystal structure is stabilized by network three-dimensional of Nsbnd H⋯Cl, Nsbnd H⋯O, Osbnd H⋯Cl, Csbnd H⋯Cl hydrogen bonds, and offset π-π stacking interactions. Also, the Hirshfeld Surface projections and Fingerprint plots were elucidated the relative contribution of the type, nature and explore the H⋯Cl, C⋯H, C⋯C, C⋯N, H⋯O intermolecular contacts in the crystal in a visual manner. Furthermore, vibrational analysis of the structural groups in the compound was carried out by both Fourier transforms infrared (FT-IR) and Raman spectra. The spectral data are complemented by good information at the region characteristic of metal-ligand, which evidences coordination through the compound. The optical properties of the crystal were studied by using optical absorption UV-visible and photoluminescence (PL) spectroscopy studies. Theoretical calculations were performed using density functional theory (DFT) at (DFT/B3LYP/LanL2DZ) level in the aim of aiding in studying structural, vibrational and optical properties of the investigated compound. Good relationship consistency is found between the experimental and theoretical studies. Inspection of the optical properties has lead to confirm the exhibition of a green photoluminescence and the occurrence of charge transfer phenomenon in this material.

  8. Theoretical DFT and matrix isolation FTIR studies of 2-(1,2,4-triazolyl)phenol isomers

    NASA Astrophysics Data System (ADS)

    Pagacz-Kostrzewa, Magdalena; Sałdyka, Magdalena; Wierzejewska, Maria; Khomenko, Dmytro M.; Doroschuk, Roman O.

    2016-07-01

    The structure, isomerization pathways and vibrational spectra of the important heterocyclic 2-(1,2,4-triazolyl)phenol molecule were investigated by DFT calculations and matrix isolation FTIR spectroscopy. Among forty-five minima located on PES three isomers with intramolecular hydrogen bond Osbnd H⋯N, 2-TRP1, 1-TRP1 and 1-TRP2, are the most stable forms with the calculated abundance of 83.4%, 10.3% and 6.0%, respectively. The presented FTIR results allow identification and characterization of these species. Several hydrogen bond parameters such as OH bond distance, νOH wavenumber shift and occupancy of the antibonding σ∗(OH) orbital were found to be linearly related with the estimated interaction energy.

  9. Experimental (X-ray, FT-IR and UV-vis spectra) and theoretical methods (DFT study) of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol

    NASA Astrophysics Data System (ADS)

    Demircioğlu, Zeynep; Albayrak, Çiğdem; Büyükgüngör, Orhan

    2014-07-01

    A suitable single crystal of (E)-3-methoxy-2-[(p-tolylimino)methyl]phenol, formulated as C15H15N1O2, reveals that the structure is adopted to its E configuration about the azomethine Cdbnd N double bond. The compound adopts a enol-imine tautomeric form with a strong intramolecular Osbnd H⋯N hydrogen bond. The single crystal X-ray diffraction analysis at 296 K crystallizes in the monoclinic space group P21/c with a = 13.4791(11) Å, b = 6.8251(3) Å, c = 18.3561(15) Å, α = 90°, β = 129.296(5)°, γ = 90° and Z = 4. Comprehensive theoretical and experimental structural studies on the molecule have been carried out by FT-IR and UV-vis spectrometry. Optimized molecular structure and harmonic vibrational frequencies have been investigated by DFT/B3LYP method with 6-31G(d,p) basis set. Stability of the molecule, hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed by using natural bond orbital (NBO) analysis. Electronic structures were discussed by TD-DFT method and the relocation of the electron density were determined. The energetic behavior of the title compound has been examined in solvent media using polarizable continuum model (PCM). Molecular electrostatic potential (MEP), Mulliken population method and natural population analysis (NPA) have been studied. Nonlinear optical (NLO) properties were also investigated. In addition, frontier molecular orbitals analysis have been performed from the optimized geometry. An ionization potential (I), electron affinity (A), electrophilicity index (ω), chemical potential (μ), electronegativity (χ), hardness (η), and softness (S), have been investigated.

  10. Ion interactions with a new ditopic naphthalimide-based receptor: a photophysical, NMR and theoretical (DFT) study.

    PubMed

    Mohan, Vaisakh; Nijamudheen, A; Das, Sudhir Kumar; Sahu, Prabhat K; Kar, Usha Pallabi; Rahaman, Abdur; Sarkar, Moloy

    2012-12-01

    A new multi-component chemosensor system comprising a naphthalimide moiety as fluorophore is designed and developed to investigate receptor-analyte binding interactions in the presence of metal and non-metal ions. A dimethylamino moiety is utilized as receptor for metal ions and a thiourea receptor, having acidic protons, for binding anions. The system is characterized by conventional analytical methods. The absorption and fluorescence spectra of the system consist of a broad band typical for an intramolecular charge transfer (ICT). The effects of various metal-ion additives on the spectral behavior of the present sensor system are examined in acetonitrile. It is found that among the metal ions studied, alkali/alkaline earth-metal ions and transition-metal ions modulate the absorption and fluorescence spectra of the system. As an additional feature, the anion signaling behavior of the system in acetonitrile is studied. A decrease in fluorescence efficiency of the system is observed upon addition of fluoride and acetate anions. Fluorescence quenching is most effective in the case of fluoride ions. This is attributed to the enhancement of the photoinduced electron transfer from the anion receptor to the fluorophore moiety. Hydrogen-bond interactions between the acidic NH protons of the thiourea moiety and the F(-) anions are primarily attributed to the fluoride-selective signaling behavior. Interestingly, a negative cooperativity for the binding event is observed when the interactions of the system are studied in the presence of both Zn(2+) and F(-) ions. NMR spectroscopy and theoretical calculations are also carried out to better understand the receptor-analyte binding. PMID:23007900

  11. Structural characterization, solvent effects on nuclear magnetic shielding tensors, experimental and theoretical DFT studies on the vibrational and NMR spectra of 3-(acrylamido)phenylboronic acid

    NASA Astrophysics Data System (ADS)

    Alver, Özgür; Kaya, Mehmet Fatih; Dikmen, Gökhan

    2015-12-01

    Structural elucidation of 3-(acrylamido)phenylboronic acid (C9H10BNO3) was carried out with 1H, 13C and HETCOR NMR techniques. Solvent effects on nuclear magnetic shielding tensors were examined with deuterated dimethyl sulfoxide, acetone, methanol and water solvents. The correct order of appearance of carbon and hydrogen atoms on NMR scale from highest magnetic field region to the lowest one were investigated using different types of theoretical levels and the details of the levels were presented in this study. Stable structural conformers and vibrational band analysis of the title molecule (C9H10BNO3) were studied both experimental and theoretical viewpoints using FT-IR, Raman spectroscopic methods and density functional theory (DFT). FT-IR and Raman spectra were obtained in the region of 4000-400 cm-1, and 3700-10 cm-1, respectively. Becke-3-Lee-Yang-Parr (B3LYP) hybrid density functional theory method with 6-31++G(d, p) basis set was included in the search for optimized structures and vibrational wavenumbers. Experimental and theoretical results show that after application of a suitable scaling factor density functional B3LYP method resulted in acceptable results for predicting vibrational wavenumbers except OH and NH stretching modes which is most likely arising from increasing unharmonicity in the high wave number region and possible intra and inter molecular interaction at OH edges those of which are not fully taken into consideration in theoretical processes. To make a more quantitative vibrational assignments, potential energy distribution (PED) values were calculated using VEDA 4 (Vibrational Energy Distribution Analysis) program.

  12. Analyte interactions with a new ditopic dansylamide-nitrobenzoxadiazole dyad: a combined photophysical, NMR, and theoretical (DFT) study.

    PubMed

    Bhoi, Abhas Kumar; Das, Sudhir Kumar; Majhi, Debashis; Sahu, Prabhat Kumar; Nijamudheen, A; N, Anoop; Rahaman, Abdur; Sarkar, Moloy

    2014-08-21

    due to transition-metal ion binding. Theoretical (density functional theory) studies are also performed for the better understanding of the receptor-analyte interaction. Interestingly, negative cooperativity in binding is observed when the interaction of this system is studied in the presence of both Zn(2+) and F(-). Fluorescence microscopy studies also revealed that the newly developed fluorescent sensor system can be employed as an imaging probe in live cells. PMID:25116958

  13. Molecular structure of tetraaqua adenosine 5'-triphosphate aluminium(III) complex: A study involving Raman spectroscopy, theoretical DFT and potentiometry

    NASA Astrophysics Data System (ADS)

    Tenório, Thaís; Silva, Andréa M.; Ramos, Joanna Maria; Buarque, Camilla D.; Felcman, Judith

    2013-03-01

    The Alzheimer's disease is one of the most common neurodegenerative diseases that affect elderly population, due to the formation of β-amyloid protein aggregate and several symptoms, especially progressive cognitive decline. The result is a decrease in capture of glucose by cells leading to obliteration, meddling in the Krebs cycle, the principal biochemical route to the energy production leading to a decline in the levels of adenosine 5'-triphosphate. Aluminium(III) is connected to Alzheimer's and its ion provides raise fluidity of the plasma membrane, decrease cell viability and aggregation of amyloid plaques. Studies reveal that AlATP complex promotes the formation of reactive fibrils of β-amyloid protein and independent amyloidogenic peptides, suggesting the action of the complex as a chaperone in the role pathogenic process. In this research, one of complexes formed by Al(III) and adenosine 5'-triphosphate in aqueous solution is analyzed by potentiometry, Raman spectroscopy and ab initio calculations. The value of the log KAlATP found was 9.21 ± 0.01 and adenosine 5'-triphosphate should act as a bidentate ligand in the complex. Raman spectroscopy and potentiometry indicate that donor atoms are the oxygen of the phosphate β and the oxygen of the phosphate γ, the terminal phosphates. Computational calculations using Density Functional Theory, with hybrid functions B3LYP and 6-311++G(d,p) basis set regarding water solvent effects, have confirmed the results. Frontier molecular orbitals, electrostatic potential contour surface, electrostatic potential mapped and Mulliken charges of the title molecule were also investigated.

  14. Theoretical and Electrochemical Study of the Quinone-Benzoic Acid Adduct Linked by Hydrogen Bonds DFT Study of Electronic Structure and Geometry of Neutral and Anionic Silver Clusters

    SciTech Connect

    Matulis, Vitaly E.; Ivashkevich, Oleg A.; Gurin, Valerij

    2003-12-15

    A comparative analysis of bond lengths vertical detachment energies (VDE), excitation energies of neutral clusters with geometry of anions and vertical ionization potentials of neutral clusters calculated within density functional theory (DFT) using different functionals with both effective core potential (ECP) and all-electron basis sets for silver clusters Ag n, have been carried out. DFT methods provide a good agreement between calculated and experimental data of some characteristics. The accurate prediction of all characteristics simultaneously can be achieved with all-electron DZVP basis set only. A new functional has been developed. It provides results close to experimental data using the moderate basis set. For anionic clusters Ag2?10-, the difference between calculations with this functional and experimental values of VDE and for the most stable isomers does not exceed 0.1 eV. Based on both total energy calculations and comparison of experimental and calculated photoelectron spectra, the structural assignment of clusters Ag7-, Ag9- and Ag10- has been made. The electronic structure and geometrical characteristics of the low-lying isomers has been studied.

  15. Theoretical study of zeatin - A plant hormone and potential drug for neural diseases - On the basis of DFT, MP2 and target docking

    NASA Astrophysics Data System (ADS)

    Liu, Xueping; Bereźniak, Tomasz; Panek, Jarosław Jan; Jezierska-Mazzarello, Aneta

    2013-02-01

    Zeatin, a cytokinin of the adenine family, originally isolated from Zea mays L., exhibits also bioeffects towards human cells: it is a potent acetylcholinesterase inhibitor and can potentially inhibit amyloid β-protein formation. The role of zeatin in neural disease treatment is yet to be established. This computational study describes a hierarchy of interactions between zeatin and a receptor, a protein from the nodulin family. DFT in hybrid and dispersion-corrected form as well as MP2 approaches were used to derive interaction energies. Docking procedure was employed to investigate the role of selected interaction for anchoring the ligand.

  16. Synthesis, spectroscopic characterization and crystallographic behavior of a biologically relevant novel indole-fused heterocyclic compound - Experimental and theoretical (DFT) studies

    NASA Astrophysics Data System (ADS)

    Sharma, Sakshi; Brahmachari, Goutam; Banerjee, Bubun; Nurjamal, Khondekar; Kumar, Abhishek; Srivastava, Ambrish Kumar; Misra, Neeraj; Pandey, Sarvesh Kumar; Rajnikant; Gupta, Vivek K.

    2016-08-01

    The present communication deals with the eco-friendly synthesis, spectral properties and X-ray crystal structure of an indole derivative - Ethyl 2'-amino-3'-cyano-6'-methyl-5-nitro-2-oxospiro [indoline-3,4'-pyran]-5'-carboxylate. The title compound was synthesized in 87% yield. The crystal structure of the molecule is stabilized by intermolecular Nsbnd H … N, Nsbnd H … O and Csbnd H … π interactions. The molecule is organized in the crystal lattice forming sheet like structure. To interpret the experimental data, ab initio computations of the vibrational frequencies were carried out using the Gaussian 09 program followed by the full optimizations done using Density Functional Theory (DFT) at B3LYP/6-31 + G(d,p) level. The combined use of experiments and computations allowed a firm assignment of the majority of observed bands for the compound. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) with frontier orbital gap were presented. The electronic and charge transfer properties have been explained on the basis of highest occupied molecular orbitals (HOMOs), lowest unoccupied molecular orbitals (LUMOs) and density of states (DOS). From the optimized geometry of the molecule, molecular electrostatic potential (MEP) distribution, frontier molecular orbitals (FMOs) of the title compound have been calculated in the ground state theoretically. The theoretical results showed good agreement with the experimental values. First hyperpolarizability values have been calculated to describe the nonlinear optical (NLO) property of the synthesized compound.

  17. Perfluorination of tetracene: effects on the optical gap and electron-acceptor properties. An electrochemical, theoretical DFT, and Raman spectroscopic study

    NASA Astrophysics Data System (ADS)

    Ponce Ortiz, Rocío; Malavé Osuna, Reyes; Ruiz Delgado, Mari Carmen; Casado, Juan; Hernández, Víctor; López Navarrete, Juan Teodomiro; Sakamoto, Youichi; Suzuki, Toshiyasu

    2006-04-01

    We report the synthesis and characterization of perfluorinated tetracene; a material with potential applications in organic electronics. The electrochemical behaviour of the compound is analyzed by differential pulse voltammetry, and compared with that of tetracene. The structure of perfluorotetracene is planar as observed for pentacene. We also report a comparative Raman spectroscopic study of tetracene and perfluorotetracene in relation to their π-conjugational properties. Density functional theory (DFT) calculations have been also performed, at the B3LYP/6-31G** level, to assess information regarding the topologies and energies of the frontier molecular orbitals (MOs) around the gap, and about the vibrational normal modes associated with the Raman features selectively enhanced by the π-conjugation.

  18. Vibrations and reorientations of NH3 molecules in [Mn(NH3)6](ClO4)2 studied by infrared spectroscopy and theoretical (DFT) calculations.

    PubMed

    Hetmańczyk, Joanna; Hetmańczyk, Łukasz; Migdał-Mikuli, Anna; Mikuli, Edward

    2015-02-01

    The vibrational and reorientational motions of NH3 ligands and ClO4(-) anions were investigated by Fourier transform middle-infrared spectroscopy (FT-IR) in the high- and low-temperature phases of [Mn(NH3)6](ClO4)2. The temperature dependencies of full width at half maximum (FWHM) of the infrared bands at: 591 and 3385cm(-1), associated with: ρr(NH3) and νas(N-H) modes, respectively, indicate that there exist fast (correlation times τR≈10(-12)-10(-13)s) reorientational motions of NH3 ligands, with a mean values of activation energies: 7.8 and 4.5kJmol(-1), in the phase I and II, respectively. These reorientational motions of NH3 ligands are only slightly disturbed in the phase transition region and do not significantly contribute to the phase transition mechanism. Fourier transform far-infrared and middle-infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TC(c)=137.6K (on cooling), which suggested lowering of the crystal structure symmetry. Infrared spectra of [Mn(NH3)6](ClO4)2 were recorded and interpreted by comparison with respective theoretical spectra calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on H, N, Cl, O atoms) for the isolated equilibrium two models (Model 1 - separate isolated [Mn(NH3)6](2+) cation and ClO4(-) anion and Model 2 - [Mn(NH3)6(ClO4)2] complex system). Calculated optical spectra show a good agreement with the experimental infrared spectra (FT-FIR and FT-MIR) for the both models. PMID:25459713

  19. Vibrations and reorientations of NH3 molecules in [Mn(NH3)6](ClO4)2 studied by infrared spectroscopy and theoretical (DFT) calculations

    NASA Astrophysics Data System (ADS)

    Hetmańczyk, Joanna; Hetmańczyk, Łukasz; Migdał-Mikuli, Anna; Mikuli, Edward

    2015-02-01

    The vibrational and reorientational motions of NH3 ligands and ClO4- anions were investigated by Fourier transform middle-infrared spectroscopy (FT-IR) in the high- and low-temperature phases of [Mn(NH3)6](ClO4)2. The temperature dependencies of full width at half maximum (FWHM) of the infrared bands at: 591 and 3385 cm-1, associated with: ρr(NH3) and νas(N-H) modes, respectively, indicate that there exist fast (correlation times τR ≈ 10-12-10-13 s) reorientational motions of NH3 ligands, with a mean values of activation energies: 7.8 and 4.5 kJ mol-1, in the phase I and II, respectively. These reorientational motions of NH3 ligands are only slightly disturbed in the phase transition region and do not significantly contribute to the phase transition mechanism. Fourier transform far-infrared and middle-infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TCc = 137.6 K (on cooling), which suggested lowering of the crystal structure symmetry. Infrared spectra of [Mn(NH3)6](ClO4)2 were recorded and interpreted by comparison with respective theoretical spectra calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311 + G(d,p) basis set (on H, N, Cl, O atoms) for the isolated equilibrium two models (Model 1 - separate isolated [Mn(NH3)6]2+ cation and ClO4- anion and Model 2 - [Mn(NH3)6(ClO4)2] complex system). Calculated optical spectra show a good agreement with the experimental infrared spectra (FT-FIR and FT-MIR) for the both models.

  20. Theoretical assessment of the selective fluorescence quenching of 1-amino-8-naphthol-3,6-disulfonic acid (H-Acid) complexes with Zn(2+), Cd(2+), and Hg(2+): A DFT and TD-DFT study.

    PubMed

    Zarabadi-Poor, Pezhman; Barroso-Flores, Joaquín

    2014-12-26

    Density functional theory (DFT) and time-dependent (TD)-DFT calculations at the PBE0/6-31++G** aug-cc-PVDZ (along with corresponding ECP for metal ions) level of theory were carried out to investigate the differences in structure, bonding, and fluorescence behavior of 1-amino-8-naphthol-3,6-disulfonic acid (H-acid) (1) when coordinated to Zn(2+) (2), Cd(2+) (3), and Hg(2+) (4) in a simulated continuous aqueous media (PCM). Ground and excited state calculations were performed on all compounds in order to gain insight on their bonding properties, as well as on their photochemical behavior, since we previously reported that complexation of Hg(2+) quenches the fluorescence properties of ligand (1), while at the same time exhibits a different coordination pattern than the two other remaining complexes. Changes in the excited states' radiative lifetime upon coordination to different metals account for this selective quenching. PMID:25479191

  1. Photoinduced interaction studies on N-(2-methylthiophenyl)-2-hydroxy-1-naphthadiamine with TiO2 nanoparticles: A combined experimental and theoretical (DFT and spectroscopic) approach

    NASA Astrophysics Data System (ADS)

    Pushpam, S.; Gayathri, S.; Ramakrishnan, V.

    2014-12-01

    Schiff base derivative synthesized by the reaction of 2-(methylthio) aniline and 2-hydroxy-1-naphthaldehyde exhibits keto-amine tautomerism in methanol solvent. The fluorescence quenching of N-(2-methyl thiophenyl)-2-hydroxy-1-naphthadiamine (NMTHN) by TiO2 nanoparticles in methanol has been studied. The excitation and emission peaks have been observed at 439 and 509 nm respectively. The apparent association constant has been deduced from the absorption spectral changes of NMTHN-TiO2 nanoparticles using Bensi-Hildebrand equation. The number of binding sites and the binding constant have been calculated from the relevant fluorescence data. Quenching of fluorescence of NMTHN by TiO2 could be due to a dynamic mode. Density Functional Theory (DFT) calculations also have been performed to study the charge distribution of NMTHN-TiO2 both in ground and excited states. The HOMO-LUMO analysis of NMTHN-TiO2 in the ground state has been made.

  2. Theoretical study of adsorption of amino acids on graphene and BN sheet in gas and aqueous phase with empirical DFT dispersion correction.

    PubMed

    Singla, Preeti; Riyaz, Mohd; Singhal, Sonal; Goel, Neetu

    2016-02-21

    Understanding interactions of biomolecules with nanomaterials at the molecular level is crucial to design new materials for practical use. In the present study, adsorption of three distinct types of amino acids, namely, valine, arginine and aspartic acid, over the surface of structurally analogous but chemically different graphene and BN nanosheets has been explored within the formalism of DFT. The explicit dispersion correction incorporated in the computational methodology improves the accuracy of the results by accounting for long range van der Waals interactions and is essential for agreement with experimental values. The real biological environment has been mimicked by re-optimizing all the model structures in an aqueous medium. The study provides ample evidence in terms of adsorption energy, solvation energy, separation distance and charge analysis to conclude that both the nano-surfaces adsorb the amino acids with release of energy and there are no bonded interactions between the two. The polarity of the BN nanosheet provides it an edge over the graphene surface to have more affinity towards amino acids. PMID:26863069

  3. DFT CONFORMATIONAL STUDIES OF ALPHA-MALTOTRIOSE

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recent DFT optimization studies on alpha-maltose improved our understanding of the preferred conformations of alpha-maltose and the present study extends these studies to alpha-maltotriose with three alpha-D-glucopyranose residues linked by two alpha-[1-4] bridges, denoted herein as DP-3's. Combina...

  4. DFT STUDIES OF DP-3 AMYLOSE FRAGMENTS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study extends our work on mono- and disaccharides to structures with three glucose residues by two alpha-[1-4] bridges, denoted herein as DP-3's. DFT optimization studies of DP-3 fragments have been carried out at the B3LYP/6-311++G** level of theory. Different hydroxymethyl conformations (gg...

  5. Microwave Assistant Synthesis, Antifungal Activity and DFT Theoretical Study of Some Novel 1,2,4-Triazole Derivatives Containing Pyridine Moiety

    PubMed Central

    Sun, Guo-Xiang; Yang, Ming-Yan; Shi, Yan-Xia; Sun, Zhao-Hui; Liu, Xing-Hai; Wu, Hong-Ke; Li, Bao-Ju; Zhang, Yong-Gang

    2014-01-01

    In order to investigate the biological activity of novel 1,2,4-triazole compounds, seventeen novel 1,2,4-triazole derivatives containing pyridine moiety were synthesized under microwave assistant condition by multi-step reactions. The structures were characterized by 1H NMR, MS and elemental analyses. The target compounds were evaluated for their fungicidal activities against Stemphylium lycopersici (Enjoji) Yamamoto, Fusarium oxysporum. sp. cucumebrium, and Botrytis cinerea in vivo, and the results indicated that some of the title compounds displayed excellent fungicidal activities. Theoretical calculation of the title compound was carried out with B3LYP/6-31G (d,p). The full geometry optimization was carried out using 6-31G (d,p) basis set, and the frontier orbital energy, atomic net charges were discussed, and the structure-activity relationship was also studied. PMID:24815069

  6. A theoretical DFT-based and experimental study of the transmetalation step in Au/Pd-mediated cross-coupling reactions.

    PubMed

    Hansmann, Max M; Pernpointner, Markus; Döpp, René; Hashmi, A Stephen K

    2013-11-01

    In this work a combined theoretical and experimental investigation of the cross-coupling reaction involving two metallic reaction centers, namely gold and palladium, is described. One metal center (Au) hereby is rather inert towards change in its oxidation state, whereas Pd undergoes oxidative insertion and reductive elimination steps. Detailed mechanistic and energetic studies of each individual step, with the focus on the key transmetalation step are presented and compared for different substrates and ligands on the catalytic Pd center. Different aryl halides (Cl, Br, I) and aryl triflates were investigated. Hereby the nature of the counteranion X turned out to be crucial. In the case of X=Cl and L=PMe3 the oxidative addition is rate-determining, whereas in the case of X=I the transmetalation step becomes rate-determining in the Au/Pd-cross-coupling mechanism. A variety of Au-Pd transmetalation reaction scenarios are discussed in detail, favoring a transition state with short intermetallic Au-Pd contacts. Furthermore, without a halide counteranion the transmetalation from gold(I) to palladium(II) is highly endothermic, which confirms our experimental findings that the coupling does not occur with aryl triflates and similar weakly coordinating counteranions--a conclusion that is essential in designing new Au-Pd catalytic cycles. In combination with experimental work, this corrects a previous report in the literature claiming a successful coupling potentially catalytic in both metals with weakly coordinating counteranions. PMID:24115258

  7. DFT theoretical and FT-IR spectroscopic investigations of the plasticity of clay minerals dispersions

    NASA Astrophysics Data System (ADS)

    Kasprzhitskii, A.; Lazorenko, G.; Yavna, V.; Daniel, Ph.

    2016-04-01

    Plasticity is the most important property of dispersions of clay minerals that determine the character of participation of these systems in many natural and technological processes. We report on the results of studies of hydration mechanism in typical clay minerals making part of natural dispersions of sedimentation masses by means of IR spectroscopy and theoretical density functional theory (DFT) methods. X-ray diffraction analysis of clay minerals of Millerovo mineral deposit (Russian Federation) is carried out. Regularities and peculiarities of interaction of water molecules with kaolinite basal planes (001) and (00 1 bar) are analyzed. The role of water in the formation of plasticity of clay minerals dispersions is revealed. The modes of water molecules placement and their state and structure in the system "clay mineral-water" is defined. Phase transition processes of clay minerals dispersion into plastic and liquid state and their influence on spectral characteristics of the systems are investigated. The interpretation of clay minerals phase transitions into plastic and fluid state based on the results of DFT simulation is given. The relation is established between specific variation of spectral characteristics and phase transitions of clay minerals dispersions into plastic and liquid state.

  8. Ab-initio DFT FP-LAPW GGA and LDA TB-mBJ and SO theoretical study of structural and elastic properties of Zinc-Blende crystal phase GaAs1-xBix alloys

    NASA Astrophysics Data System (ADS)

    Menezla, S.; Kadri, A.; Zitouni, K.; Djelal, A.; Djermouni, M.; Hallouche, A.; Zaoui, A.

    2015-12-01

    We present an ab-initio theoretical study of structural and elastic properties of GaAs1-xBix alloys in the Zinc-Blende (ZB) phase. We use a recent version of Wien2k package code based on Density Functional Theory (DFT) Full Potential and Linearized Augmented Plane Waves (FP-LAPW) method including recent Tran-Blaha modified Becke-Johnson correction of the exchange potential (TB-mBJ) and the spin-orbit interaction (SO). The calculations are performed within the Local Density Approximation (LDA) as well as the Generalized Gradient Approximation (GGA). We study first the structural properties of GaAs1-xBix alloys by solving Murnaghan equation of state. Our results show that the ZB phase is the lowest equilibrium crystal structure of GaAs1-xBix in the whole alloy composition range, in agreement with previous theoretical predictions. The variations versus Bi contents of the ZB GaAs1-xBix lattice constant a0, bulk modulus B0 and its pressure derivative B0‧ are also found very close to other theoretical and experimental data, but with much smaller bowing effects indicating a better resolution thanks to TB-mBJ correction. The variations of B0 versus the reverse equilibrium volume of the unit cell (1/V0) are found to be described by the simple linear empirical expression B0 = -0.21068 + 0.16695/V0 which is close to the theoretical prediction for III-V semiconductors with, however, somewhat lower linear coefficients values, suggesting a more metallic behavior. In a second part of this work, we use Birch-Murnaghan approach to study the elastic properties of GaAs1-xBix alloys. The elastic stiffness coefficients, C11, C12 and C44, and their variations versus alloy composition were determined for ZB GaAs1-xBix alloy. Their values in GaAs and GaBi binary compounds are found in very good agreement with available experimental and/or theoretical data. Their variations in GaAs1-xBix alloy show a monotonic decrease with increasing Bi contents, indicating a softening behavior as is

  9. Structure, IR and Raman spectra of phosphotrihydrazide studied by DFT

    NASA Astrophysics Data System (ADS)

    Furer, V. L.; Vandyukov, A. E.; Majoral, J. P.; Caminade, A. M.; Kovalenko, V. I.

    2016-09-01

    The FTIR and FT Raman measurements of the phosphotrihydrazide (S)P[N(Me)-NH2]3 have been performed. This compound is a zero generation dendrimer G0 with terminal amine groups. Structural optimization and normal mode analysis were obtained for G0 by the density functional theory (DFT). Optimized geometric bond length and angles obtained by DFT show good agreement with experiment. The amine terminal groups are characterized by the well-defined bands at 3321, 3238, 1614 cm- 1 in the experimental IR spectrum and by bands at 3327, 3241 cm- 1 in the Raman spectrum of G0. The experimental frequencies of asymmetric and symmetric NH2 stretching vibrations of amine group are lower than theoretical values due to intramolecular Nsbnd H ⋯ S hydrogen bond. This hydrogen bond is also responsible for higher experimental infrared intensity of these bands as compared with theoretical values. Relying on DFT calculations a complete vibrational assignment is proposed for the studied dendrimer.

  10. Structure, IR and Raman spectra of phosphotrihydrazide studied by DFT.

    PubMed

    Furer, V L; Vandyukov, A E; Majoral, J P; Caminade, A M; Kovalenko, V I

    2016-09-01

    The FTIR and FT Raman measurements of the phosphotrihydrazide (S)P[N(Me)-NH2]3 have been performed. This compound is a zero generation dendrimer G0 with terminal amine groups. Structural optimization and normal mode analysis were obtained for G0 by the density functional theory (DFT). Optimized geometric bond length and angles obtained by DFT show good agreement with experiment. The amine terminal groups are characterized by the well-defined bands at 3321, 3238, 1614cm(-1) in the experimental IR spectrum and by bands at 3327, 3241cm(-1) in the Raman spectrum of G0. The experimental frequencies of asymmetric and symmetric NH2 stretching vibrations of amine group are lower than theoretical values due to intramolecular NH⋯S hydrogen bond. This hydrogen bond is also responsible for higher experimental infrared intensity of these bands as compared with theoretical values. Relying on DFT calculations a complete vibrational assignment is proposed for the studied dendrimer. PMID:27179692

  11. IR, Raman, SERS and DFT study of amoxicillin

    NASA Astrophysics Data System (ADS)

    Bebu, Andreea; Szabó, László; Leopold, Nicolae; Berindean, Cătălin; David, Leontin

    2011-05-01

    In this work a joint experimental and theoretical study on amoxicillin is reported. The molecular vibrations of amoxicillin were investigated by FTIR, FT-Raman and SERS spectroscopies. In parallel, quantum chemical calculations based on density functional theory (DFT) were used to determine the geometrical, energetic and vibrational characteristics of the molecule with particular emphasis put on the interaction and adsorption geometry of the molecule to the silver colloidal surface. The SERS spectrum of amoxicillin was recorded using a 532 nm laser line and hydroxylamine reduced silver colloid as SERS substrate. FTIR, FT-Raman and SERS spectra of amoxicillin were assigned based on DFT calculations with the hybrid B3LYP exchange-correlation functional, coupled with the standard 6-31G(d) basis set. The calculated molecular electrostatic potential (MEP) was used in conjunction with SERS data to predict the adsorption geometry of the molecule on the silver surface.

  12. A comparative study of experimental and theoretical results of conformations of oxovanadium(IV) complexes with 4-acyl pyrazolone ligands using DFT method.

    PubMed

    Parihar, Sanjay; Gupta, Sanjeev K; Jadeja, R N; Jha, Prafulla K

    2014-07-15

    The optimized structures and electronic properties of the oxovanadium(IV) complexes containing 4-acyl pyrazolone ligands were calculated using density functional theory. The total energies of both the complexes were calculated e.g. syn and anti conformation of complex 1 and complex 2 with and without solvent. The calculated total energy for syn conformation was -10.162 keV, while total energy for anti conformation was -10.155 keV. Similarly, the calculated total energy for complex 2 with solvent was obtained -10.793 keV, while total energy for complex 2 without solvent was -10.158 keV. The total energy calculation shows that syn conformation is more stable in complex 1, while complex 2 is more stable in twisted geometry with solvent. In order to investigate the electronic properties of ligands and complexes, quantum chemical parameters, such as the highest occupied molecular orbital energy (HOMO), the lowest unoccupied molecular orbital energy (LUMO), and energy gap were calculated. The theoretically calculated data of the complexes are in good agreement with the data obtained by the single-crystal X-ray diffraction analysis. PMID:24682060

  13. A comparative study of experimental and theoretical results of conformations of oxovanadium(IV) complexes with 4-acyl pyrazolone ligands using DFT method

    NASA Astrophysics Data System (ADS)

    Parihar, Sanjay; Gupta, Sanjeev K.; Jadeja, R. N.; Jha, Prafulla K.

    2014-07-01

    The optimized structures and electronic properties of the oxovanadium(IV) complexes containing 4-acyl pyrazolone ligands were calculated using density functional theory. The total energies of both the complexes were calculated e.g. syn and anti conformation of complex 1 and complex 2 with and without solvent. The calculated total energy for syn conformation was -10.162 keV, while total energy for anti conformation was -10.155 keV. Similarly, the calculated total energy for complex 2 with solvent was obtained -10.793 keV, while total energy for complex 2 without solvent was -10.158 keV. The total energy calculation shows that syn conformation is more stable in complex 1, while complex 2 is more stable in twisted geometry with solvent. In order to investigate the electronic properties of ligands and complexes, quantum chemical parameters, such as the highest occupied molecular orbital energy (HOMO), the lowest unoccupied molecular orbital energy (LUMO), and energy gap were calculated. The theoretically calculated data of the complexes are in good agreement with the data obtained by the single-crystal X-ray diffraction analysis.

  14. Direct and remarkably efficient conversion of methane into acetic acid catalyzed by amavadine and related vanadium complexes. A synthetic and a theoretical DFT mechanistic study.

    PubMed

    Kirillova, Marina V; Kuznetsov, Maxim L; Reis, Patrícia M; da Silva, José A L; da Silva, João J R Fraústo; Pombeiro, Armando J L

    2007-08-29

    Vanadium(IV or V) complexes with N,O- or O,O-ligands, i.e., [VO{N(CH2CH2O)3}], Ca[V(HIDPA)2] (synthetic amavadine), Ca[V(HIDA)2], or [Bu4N]2[V(HIDA)2] [HIDPA, HIDA = basic form of 2,2'-(hydroxyimino)dipropionic or -diacetic acid, respectively], [VO(CF3SO3)2], Ba[VO(nta)(H2O)]2 (nta = nitrilotriacetate), [VO(ada)(H2O)] (ada = N-2-acetamidoiminodiacetate), [VO(Hheida)(H2O)] (Hheida = 2-hydroxyethyliminodiacetate), [VO(bicine)] [bicine = basic form of N,N-bis(2-hydroxyethyl)glycine], and [VO(dipic)(OCH2CH3)] (dipic = pyridine-2,6-dicarboxylate), are catalyst precursors for the efficient single-pot conversion of methane into acetic acid, in trifluoroacetic acid (TFA) under moderate conditions, using peroxodisulfate as oxidant. Effects on the yields and TONs of various factors are reported. TFA acts as a carbonylating agent and CO is an inhibitor for some systems, although for others there is an optimum CO pressure. The most effective catalysts (as amavadine) bear triethanolaminate or (hydroxyimino)dicarboxylates and lead, in a single batch, to CH3COOH yields > 50% (based on CH4) or remarkably high TONs up to 5.6 x 103. The catalyst can remain active upon multiple recycling of its solution. Carboxylation proceeds via free radical mechanisms (CH3* can be trapped by CBrCl3), and theoretical calculations disclose a particularly favorable process involving the sequential formation of CH3*, CH3CO*, and CH3COO* which, upon H-abstraction (from TFA or CH4), yields acetic acid. The CH3COO* radical is formed by oxygenation of CH3CO* by a peroxo-V complex via a V{eta1-OOC(O)CH3} intermediate. Less favorable processes involve the oxidation of CH3CO* by the protonated (hydroperoxo) form of that peroxo-V complex or by peroxodisulfate. The calculations also indicate that (i) peroxodisulfate behaves as a source of sulfate radicals which are methane H-abstractors, as a peroxidative and oxidizing agent for vanadium, and as an oxidizing and coupling agent for CH3CO* and that (ii) TFA is

  15. Experimental (XAS STEM TPR and XPS) and Theoretical (DFT) Characterization of Supported Rhenium Catalysts

    SciTech Connect

    S Bare; S Kelly; F Vila; D Boldingh; E Karapetrova; J Kas; G Mickelson; F Modica; N Yang; J Rehr

    2011-12-31

    A high surface area supported Re-based catalyst, fundamental to heterogeneous catalysis, is studied in the oxidic and reduced states using a combination of experimental (XAFS, STEM, TPR, and XPS) and theoretical (DFT and X-ray spectroscopy simulations) approaches. In the calcined dried catalyst, the Re species is present as an isolated trioxo(oxoaluminate) Re(VII) species. The temperature at which the Re undergoes reduction is a function of the hydrogen partial pressure and temperature ramp rate, but the maximum rate of reduction occurs in the range 300-400 C. Following reduction at 500 or 700 C in dry hydrogen, the Re is present as a mixture of species: unreduced trioxo(oxoaluminate) Re(VII) species, Re nanoclusters, and isolated Re atoms. By using a multifaceted approach, it is apparent that the majority species is an isolated Re adatom bound to the alumina support. DFT calculations identify several likely adsorption sites for these Re adatoms on the [110] surface of {gamma}-Al{sub 2}O{sub 3}. The final extended X-ray absorption fine structure (EXAFS) model taking into account these three species is used to identify the dominant adsorption site for Re on the alumina surface. FEFF8 X-ray absorption near-edge spectroscopy (XANES) calculations of unsupported and alumina-supported Re nanoclusters provide interpretation of the shape and edge position of the Re L{sub 3}-edge XANES after reduction. The presence of moisture during reduction stronly affects the mobility of the Re on the alumina leading to agglomeration. Subsequent air exposure of a reduced catalyst readily reoxidizes the reduced Re. The power of using a combination of analysis tools provides insight into the behavior of dispersed Re on supported alumina under oxidizing and reducing conditions relevant to heterogeneous catalysis.

  16. Molecular orbital studies (hardness, chemical potential and electrophilicity), vibrational investigation and theoretical NBO analysis of 4-4'-(1H-1,2,4-triazol-1-yl methylene) dibenzonitrile based on abinitio and DFT methods.

    PubMed

    Sheela, N R; Muthu, S; Sampathkrishnan, S

    2014-01-01

    The Fourier transform infrared (FTIR) and FT Raman (FTR) of 4-4'-(1H-1, 2, 4-triazol-1-yl methylene) dibenzonitrile (4-HTMDBN) have been recorded and analyzed. The equilibrium geometry harmonic vibrational frequencies have been investigated with the help of standard HF and DFT methods with 6-31G(d,p) as basis set. The assignments of the vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). Theoretical simulations of the FTIR and FTR spectra of the title compound have been calculated. The (1)H and (13)C Nuclear Magnetic Resonance (NMR) chemical shifts of the molecule were calculated by the Gauge including atomic orbital (GIAO) method. The stability of the molecule has been analyzed using natural bond orbital (NBO) analysis. The linear polarizability (α) and the first order hyperpolarizability (β) values of the investigated molecule have been computed using HF/DFT/6-31G(d,p) methods on the finite field approach. UV-Vis spectrum of the compound is recorded and the electronic properties such as HOMO and LUMO energies, are performed. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity (χ), electrophilicity index (ω), hardness (η) and chemical potential (ρ) are all correlated with the HOMO and LUMO energies with their molecular properties. Mulliken population analysis on atomic charges, molecular electrostatic potential maps (MEP) and thermodynamical properties of title compound at different temperature have been calculated. PMID:24184626

  17. Synthesis of 4-((1E, 6E)-7-(4-hydroxy-3-methoxyphenyl)-3, 5-dioxohepta-1, 6-dienyl)-2-methoxyphenyl 4-fluorobenzoate, a novel monoester derivative of curcumin, its experimental and theoretical (DFT) studies

    NASA Astrophysics Data System (ADS)

    Srivastava, Sangeeta; Gupta, Preeti; Amandeep; Singh, Ranvijay Pratap

    2016-04-01

    Curcumin (1), isolated as a major component from the chloroform extract of Curcuma longa was converted to its ester derivative 4-((1E, 6E)-7-(4-hydroxy-3-methoxyphenyl)-3,5-dioxohepta-1,6-dienyl)-2-methoxyphenyl 4-fluorobenzoate (2). The compound has been characterized with the help of 1H, 13C NMR, UV, IR and mass spectrometry. The molecular geometry of synthesized compound was calculated in ground state by Density functional theory (DFT/B3LYP) using 6-31G (d,p) basis set. 1H and 13C NMR chemical shifts were calculated in ground state by using Gauge-Including Atomic Orbital (GIAO) approach and these values were correlated with experimental observations. The electronic properties such as HOMO and LUMO energies were calculated using time dependent Density Functional Theory (TD-DFT). Stability of the molecule as a result of hyper conjugative interactions and electron delocalization were analysed using Natural bond orbital (NBO) analysis. Intramolecular interactions were analysed by AIM (Atom in molecule) approach. Global reactivity descriptors were calculated to study the reactive site within molecule. The vibrational wavenumbers were calculated using DFT method and assigned with the help of potential energy distribution (PED). First hyperpolarizability values have been calculated to describe the nonlinear optical (NLO) property of the synthesized compounds. Molecular electrostatic potential (MEP) analysis has also been carried out.

  18. Theoretical simulations on the antioxidant mechanism of naturally occurring flavonoid: A DFT approach

    NASA Astrophysics Data System (ADS)

    Praveena, R.; Sadasivam, K.

    2016-05-01

    Synthetic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are found to be toxic, hence non-carcinogenic naturally occurring radical scavengers especially flavonoids have gained considerable importance in the past two decades. In the present investigation, the radical scavenging activity of C-glycosyl flavonoids is evaluated using theoretical approach which could broaden its scope in therapeutic applications. Gas and solvent phase studies of structural and molecular characteristics of C-glycosyl flavonoid, isovitexin is investigated through hydrogen atom transfer mechanism (HAT), Electron transfer-proton transfer (ET-PT) and Sequential proton loss electron transfer (SPLET) by Density functional theory (DFT) using hybrid parameters. The computed values of the adiabatic ionization potential, electron affinity, hardness, softness, electronegativity and electrophilic index indicate that isovitexin possess good radical scavenging activity. The behavior of different -OH groups in polyphenolic compounds is assessed by considering electronic effects of the neighbouring groups and the overall geometry of molecule which in turn helps in analyzing the antioxidant capacity of the polyphenolic molecule. The studies indicate that the H-atom abstraction from 4'-OH site is preferred during the radical scavenging process. From Mulliken spin density analysis and FMOs, B-ring is found to be more delocalized center and capable of electron donation. Comparison of antioxidant activity of vitexin and isovitexin leads to the conclusion that isovitexin acts as a better radical scavenger. This is an evidence for the importance of position of glucose unit in the flavonoid.

  19. DFT Studies of SN2 Dechlorination of Polychlorinated Biphenyls.

    PubMed

    Krzemińska, Agnieszka; Paneth, Piotr

    2016-06-21

    Nucleophilic dechlorination of all 209 PCBs congeners by ethylene glycol anion has been studied theoretically at the DFT level. The obtained Gibbs free energies of activation are in the range 7-22 kcal/mol. The reaction Gibbs free energies indicate that all reactions are virtually irreversible. Due to geometric constrains these reactions undergo rather untypical attack with attacking oxygen atom being nearly perpendicular to the attacked C-Cl bond. The most prone to substitution are chlorine atoms that occupy ortho- (2, 2', 6, 6') positions. These results provide extensive information on the PEG/KOH dependent PCBs degradation. They can also be used in further developments of reaction class transition state theory (RC-TST) for description of complex reactive systems encountered for example in combustion processes. PMID:27244043

  20. Comparative vibrational analysis of 1,2-Dinitro benzene and 1-Fluoro-3-nitro benzene: A combined experimental (FT-IR and FT-Raman) and theoretical study (DFT/B3LYP/B3PW91)

    NASA Astrophysics Data System (ADS)

    Mahadevan, D.; Periandy, S.; Ramalingam, S.

    2011-12-01

    In this work, the comparative analysis is made on the structure and vibrational spectra of 1,2-Dinitro benzene (1,2-DNB) and 1-Fluoro-3-nitro benzene (1-F-3-NB) molecules. The FT-IR and FT-Raman experimental spectra of the molecules have been recorded using Bruker IFS 66 V spectrometer in the range of 4000-100 cm -1. Making use of the recorded data, the complete vibrational assignments are made and analyses of the observed fundamental bands of molecules are carried out. The experimental determinations of vibrational frequencies are compared with those obtained theoretically from ab-initio Hartree-fock (HF) and DFT (B3LYP and B3PW91) methods with 6-31++G (d, p) and 6-311++G (d, p) basis sets. The differences between the observed and scaled wave number values of most of the fundamentals of the molecules are very small in B3LYP than HF. The geometries and normal modes of vibrations obtained from ab-initio HF and B3LYP/B3PW91 calculations are compared with the experimentally observed data. Comparison of the simulated spectra of the molecules provides important information regarding the difference and similarity of the vibrational characteristics between the molecules. The impact of substitutions on the structures between the molecules is also investigated.

  1. Inelastic and elastic neutron scattering studies of the vibrational and reorientational dynamics, crystal structure and solid-solid phase transition in [Mn(OS(CH3)2)6](ClO4)2 supported by theoretical (DFT) calculations

    NASA Astrophysics Data System (ADS)

    Szostak, Elżbieta; Hetmańczyk, Joanna; Migdał-Mikuli, Anna

    2015-06-01

    The vibrational and reorientational dynamics of CH3 groups from (CH3)2SO ligands in the high- and low-temperature phases of [Mn(OS(CH3)2)6](ClO4)2 were investigated by quasielastic and inelastic incoherent neutron scattering (QENS and IINS) methods. The results show that above the phase transition temperature (detected earlier by differential scanning calorimetry (DSC) at TC5c = 222.9 K on cooling and at TC5h = 225.4 K on heating) the CH3 groups perform fast (τR ≈ 10-12-10-13 s) reorientational motions. These motions start to slow down below TC5c Neutron powder diffraction (NPD) measurements, performed simultaneously with QENS and IINS, indicated that this phase transition is associated with a change of the crystal structure, too. Theoretical infrared absorption, Raman and inelastic incoherent neutron scattering spectra were calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on C, H, S, O atoms) for the isolated equilibrium model (isolated [Mn(DMSO)6]2+ cation and ClO4- anion). Calculated spectra show a good agreement with the experimental spectra (FT-IR, RS and IINS). The comparison of the results obtained by these complementary methods was made.

  2. Inelastic and elastic neutron scattering studies of the vibrational and reorientational dynamics, crystal structure and solid-solid phase transition in [Mn(OS(CH₃)₂)₆](ClO₄)₂ supported by theoretical (DFT) calculations.

    PubMed

    Szostak, Elżbieta; Hetmańczyk, Joanna; Migdał-Mikuli, Anna

    2015-06-15

    The vibrational and reorientational dynamics of CH3 groups from (CH3)2SO ligands in the high- and low-temperature phases of [Mn(OS(CH3)2)6](ClO4)2 were investigated by quasielastic and inelastic incoherent neutron scattering (QENS and IINS) methods. The results show that above the phase transition temperature (detected earlier by differential scanning calorimetry (DSC) at TC5(c)=222.9K on cooling and at TC5(h)=225.4K on heating) the CH3 groups perform fast (τR≈10(-12)-10(-13)s) reorientational motions. These motions start to slow down below TC5(c) Neutron powder diffraction (NPD) measurements, performed simultaneously with QENS and IINS, indicated that this phase transition is associated with a change of the crystal structure, too. Theoretical infrared absorption, Raman and inelastic incoherent neutron scattering spectra were calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on C, H, S, O atoms) for the isolated equilibrium model (isolated [Mn(DMSO)6](2+) cation and ClO4(-) anion). Calculated spectra show a good agreement with the experimental spectra (FT-IR, RS and IINS). The comparison of the results obtained by these complementary methods was made. PMID:25795611

  3. Structural, vibrational and nuclear magnetic resonance investigations of 4-bromoisoquinoline by experimental and theoretical DFT methods

    NASA Astrophysics Data System (ADS)

    Arjunan, V.; Thillai Govindaraja, S.; Jayapraksh, A.; Mohan, S.

    2013-04-01

    Quantum chemical calculations of energy, structural parameters and vibrational wavenumbers of 4-bromoisoquinoline (4BIQ) were carried out by using B3LYP method using 6-311++G**, cc-pVTZ and LANL2DZ basis sets. The optimised geometrical parameters obtained by DFT calculations are in good agreement with electron diffraction data. Interpretations of the experimental FTIR and FT-Raman spectra have been reported with the aid of the theoretical wavenumbers. The differences between the observed and scaled wavenumber values of most of the fundamentals are very small. The thermodynamic parameters have also been computed. Electronic properties of the molecule were discussed through the molecular electrostatic potential surface, HOMO-LUMO energy gap and NBO analysis. To provide precise assignments of 1H and 13C NMR spectra, isotropic shielding and chemical shifts were calculated with the Gauge-Invariant Atomic Orbital (GIAO) method.

  4. DFT/PCM theoretical study of the conversion of methyl 4-O-methyl-α-d-galactopyranoside 6-sulfate and its 2-sulfated derivative into their 3,6-anhydro counterparts.

    PubMed

    Cosenza, Vanina A; Navarro, Diego A; Stortz, Carlos A

    2016-05-13

    Modeling of the conversion of methyl 4-O-methyl-α-d-galactopyranoside 6-sulfate (2) and 2,6-disulfate (1) into methyl 3,6-anhydro-4-O-methyl-α-d-galactopyranoside (4) and its 2-sulfate (3), respectively (Scheme 1) has been carried out using DFT at the M06-2X/6-311 + G(d,p)//M06-2X/6-31 + G(d,p) level with the polarizable continuum model (PCM) in water. The three steps necessary for the alkaline transformation of 6-sulfated (and 2,6-disulfated) galactose units into 3,6-anhydro derivatives were evaluated. The final substitution step appears to be the rate limiting, involving an activation energy of ca. 23 kcal/mol. The other two steps (deprotonation and chair inversion) combined involve lower activation energies (9-12 kcal/mol). Comparison of the thermodynamics and kinetics of the reactions suggest that if the deprotonation step precedes the chair inversion, the reaction should be faster for both compounds. No major differences in reaction rate can be theoretically predicted to be caused by the presence of sulfate on O-2, although one experimental result suggested that O-2 sulfation should increase the reaction rate. The conformational pathways are complex, given the large number of rotamers available for each compound, and the way that some of these rotamers combine into some of the pathways. In any case, the conformation (O)S2 appears as a common intermediate for the chair inversion processes. PMID:27043470

  5. 3-Iodobenzaldehyde: XRD, FT-IR, Raman and DFT studies.

    PubMed

    Kumar, Chandraju Sadolalu Chidan; Parlak, Cemal; Tursun, Mahir; Fun, Hoong-Kun; Rhyman, Lydia; Ramasami, Ponnadurai; Alswaidan, Ibrahim A; Keşan, Gürkan; Chandraju, Siddegowda; Quah, Ching Kheng

    2015-06-15

    The structure of 3-iodobenzaldehyde (3IB) was characterized by FT-IR, Raman and single-crystal X-ray diffraction techniques. The conformational isomers, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of 3IB were examined using density functional theory (DFT) method, with the Becke-3-Lee-Yang-Parr (B3LYP) functional and the 6-311+G(3df,p) basis set for all atoms except for iodine. The LANL2DZ effective core basis set was used for iodine. Potential energy distribution (PED) analysis of normal modes was performed to identify characteristic frequencies. 3IB crystallizes in monoclinic space group P21/c with the O-trans form. There is a good agreement between the theoretically predicted structural parameters, and vibrational frequencies and those obtained experimentally. In order to understand halogen effect, 3-halogenobenzaldehyde [XC6H4CHO; X=F, Cl and Br] was also studied theoretically. The free energy difference between the isomers is small but the rotational barrier is about 8kcal/mol. An atypical behavior of fluorine affecting conformational preference is observed. PMID:25767992

  6. 3-Iodobenzaldehyde: XRD, FT-IR, Raman and DFT studies

    NASA Astrophysics Data System (ADS)

    Kumar, Chandraju Sadolalu Chidan; Parlak, Cemal; Tursun, Mahir; Fun, Hoong-Kun; Rhyman, Lydia; Ramasami, Ponnadurai; Alswaidan, Ibrahim A.; Keşan, Gürkan; Chandraju, Siddegowda; Quah, Ching Kheng

    2015-06-01

    The structure of 3-iodobenzaldehyde (3IB) was characterized by FT-IR, Raman and single-crystal X-ray diffraction techniques. The conformational isomers, optimized geometric parameters, normal mode frequencies and corresponding vibrational assignments of 3IB were examined using density functional theory (DFT) method, with the Becke-3-Lee-Yang-Parr (B3LYP) functional and the 6-311+G(3df,p) basis set for all atoms except for iodine. The LANL2DZ effective core basis set was used for iodine. Potential energy distribution (PED) analysis of normal modes was performed to identify characteristic frequencies. 3IB crystallizes in monoclinic space group P21/c with the O-trans form. There is a good agreement between the theoretically predicted structural parameters, and vibrational frequencies and those obtained experimentally. In order to understand halogen effect, 3-halogenobenzaldehyde [XC6H4CHO; X = F, Cl and Br] was also studied theoretically. The free energy difference between the isomers is small but the rotational barrier is about 8 kcal/mol. An atypical behavior of fluorine affecting conformational preference is observed.

  7. Theoretical study for high-energy-density compounds derived from cyclophosphazene. IV. DFT studies on 1,1-diamino-3,3,5,5,7,7-hexaazidocyclotetraphosphazene and its isomers.

    PubMed

    Zhang, Jianguo; Zheng, Huihui; Zhang, Tonglai; Wu, Man

    2009-01-01

    In the present study, a theoretical study of 1,1-diaminohexaazidocyclotetraphophazene (DAHA) and its isomers has been performed, using quantum computational density functional theory (B3LYP and B3PW91 methods) with 6-31G* and 6-31G** basis sets implemented in Gaussian 03 program suite. Molecular structure and bonding, vibrational frequencies, Milliken population analysis, and natural bond orbit (NBO) have been studied. The heats of formation from atomization energies have also been calculated based on the optimized geometry. The obtained heats of formation data are compared with their homologous cyclophosphazene in order to demonstrate the accuracy of the methods, which indicate that the studied compounds might be potentially used as high energetic materials. In addition, the relative stability of five isomers have been deduced based on the total energy and the gap of frontier orbital energies. PMID:19756156

  8. Detection of electronically equivalent tautomers of adenine base: DFT study

    SciTech Connect

    Siddiqui, Shamoon Ahmad; Bouarissa, Nadir; Rasheed, Tabish; Al-Assiri, M.S.; Al-Hajry, A.

    2014-03-01

    Graphical abstract: - Highlights: • DFT calculations have been performed on adenine and its rare tautomer Cu{sup 2+} complexes. • Interaction of A-Cu{sup 2+} and rA-Cu{sup 2+} complexes with AlN modified fullerene (C{sub 60}) have been studied briefly. • It is found that AlN modified C{sub 60} could be used as a nanoscale sensor to detect these two A-Cu{sup 2+} and rA-Cu{sup 2+} complexes. - Abstract: In the present study, quantum chemical calculations were carried out to investigate the electronic structures and stabilities of adenine and its rare tautomer along with their Cu{sup 2+} complexes. Density Functional Theory (B3LYP method) was used in all calculations. The two Cu{sup 2+} complexes of adenine have almost similar energies and electronic structures; hence, their chemical differentiation is very difficult. For this purpose, interactions of these complexes with AlN modified fullerene (C{sub 60}) have been studied. Theoretical investigations reveal that AlN-doped C{sub 60} may serve as a potentially viable nanoscale sensor for detection of the two Cu{sup 2+} complexes of adenine.

  9. A DFT Approach to the Mechanistic Study of Hydrozone Hydrolysis.

    PubMed

    Yildiz, Ibrahim

    2016-05-26

    Hydrazone chemistry is widely utilized in biomedical field as a means of bioconjugation protocol, especially in drug delivery field due to pH labile nature of this linkage. In the light of kinetics studies, the generally accepted mechanism for the hydrolysis of hydrazones involves two main steps, namely, nucleophilic addition of water molecule to the hydrazone molecule to form carbinolamine intermediate and subsequent decomposition of this intermediate into the hydrazine and aldehyde/ketone moieties. Hydrolysis of hydrazones is catalyzed in the acidic environments and is thought to proceed through several proton transfer steps. To the best of our knowledge, in the literature no detailed theoretical study has been reported related to the mechanism of hydrolysis. In this study, we evaluated the proposed mechanism with DFT calculations with M06-2X functional at the 6-311+g(d,p) level including conductor-like polarizable continuum model solvation model. We also analyzed possible proton transfer pathways and assessed energetics of each step. PMID:27136330

  10. Why use DFT methods in the study of carbohydrates?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The recent advances in density functional theory (DFT) and computer technology allow us to study systems with more than 100 atoms routinely. This makes it feasible to study large carbohydrate molecules via quantum mechanical methods, whereas in the past, studies of carbohydrates were restricted to ...

  11. SERS and DFT study of crystal violet

    NASA Astrophysics Data System (ADS)

    Meng, Wei; Hu, Fang; Zhang, Ling-Yan; Jiang, Xiao-Hong; Lu, Lu-De; Wang, Xin

    2013-03-01

    Six silver colloids were prepared by the reduction of silver nitrate with different amounts of sodium citrate. The obtained silver colloids were characterised by UV-vis spectroscopy, transmission electron microscopy and zeta potential measurements. The surface-enhanced Raman scattering (SERS) activities of these silver colloids were investigated using crystal violet (CV) as a SERS probe. Based on density functional theory (DFT) calculations at the level of B3LYP, the Raman spectra and the optimised geometry of CV were analysed. The results show that the sodium citrate content strongly influences the sizes, zeta potentials and SERS activities of the silver colloids. As the sodium citrate content increases in the preparation of silver colloids, the mean diameters of the silver nanoparticles decrease. The most intense SERS of CV on the silver colloids is obtained when 3 mL of 1% sodium citrate is used. CV has D3 point group symmetry, and the Raman vibrational modes belong to A1 or E irreducible representations. The non-totally symmetric vibrational modes E are selectively enhanced in the SERS of CV through a Herzberg-Teller vibronic coupling mechanism, indicating a considerable charge transfer between CV and the silver nanoparticles.

  12. The solvatochromic, spectral, and geometrical properties of nifenazone: a DFT/TD-DFT and experimental study.

    PubMed

    Bani-Yaseen, Abdulilah Dawoud; Al-Balawi, Mona

    2014-08-01

    The solvatochromic, spectral, and geometrical properties of nifenazone (NIF), a pyrazole-nicotinamide drug, were experimentally and computationally investigated in several neat solvents and in hydro-organic binary systems such as water-acetonitrile and water-dioxane systems. The bathochromic spectral shift observed in NIF absorption spectra when reducing the polarity of the solvent was correlated with the orientation polarizability (Δf). Unlike aprotic solvents, a satisfactory correlation between λ(max) and Δf was determined (linear correlation of regression coefficient, R, equal to 0.93) for polar protic solvents. In addition, the medium-dependent spectral properties were correlated with the Kamlet-Taft solvatochromic parameters (α, β, and π*) by applying a multiple linear regression analysis (MLRA). The results obtained from this analysis were then employed to establish MLRA relationships for NIF in order to estimate the spectral shift in different solvents, which in turn exhibited excellent correlation (R > 0.99) with the experimental values of ν(max). Density functional theory (DFT) and time-dependent DFT theory calculations coupled with the integral equation formalism-polarizable continuum model (IEF-PCM) were performed to investigate the solvent-dependent spectral and geometrical properties of NIF. The calculations showed good and poor agreements with the experimental results using the CAM-B3LYP and B3LYP functionals, respectively. Experimental and theoretical results confirmed that the chemical properties of NIF are strongly dependent on the polarity of the chosen medium and its hydrogen bonding capability. This in turn supports the hypothesis of the delocalization of the electron density within the pyrazole ring of NIF. PMID:24954054

  13. IR, Raman, SERS and DFT study of paroxetine

    NASA Astrophysics Data System (ADS)

    Cozar, I. B.; Szabó, L.; Mare, D.; Leopold, N.; David, L.; Chiş, V.

    2011-05-01

    Structural investigations by different vibrational spectroscopic methods (FTIR, Raman and SERS), as well as density functional theory (DFT) calculations were performed on paroxetine (IUPAC name: (3S,4R)-3-[(1,3-benzodioxol-5-yloxy)methyl]-4-(4-fluorophenyl)piperidine. After the identification of the lowest energy conformer of the investigated molecule, the FTIR, FT-Raman and SERS spectra were assigned on the basis of DFT calculations at B3LYP/6-31G(d) level of theory. The very good correlation found between experimental and theoretical data is a clear evidence for a reliable assignment of the vibrational bands. The molecular electrostatic potential was calculated and used for the prediction of preferred adsorption sites of the paroxetine molecule on the silver nanoparticles surface. Based on SERS spectra analysis it is shown that the molecule is adsorbed on the silver surface through the benzodioxol ring, in a tilted orientation.

  14. Is It Fe(III)-Oxyl Radical That Abstracts Hydrogen in the C-H Activation of TauD? A Theoretical Study Based on the DFT Potential Energy Surfaces.

    PubMed

    Mai, Binh Khanh; Kim, Yongho

    2016-04-18

    Taurine:α-ketoglutarate dioxygenase (TauD) is one of the most important enzymes in the α-ketoglutarate dioxygenase family, which are involved in many important biochemical processes. TauD converts taurine into amino acetaldehyde and sulfite at its nonheme iron center, and a large H/D kinetic isotope effect (KIE) has been found in the hydrogen atom transfer (HAT) of taurine suggesting a large tunneling effect. Recently, highly electrophilic Fe(III)-oxyl radicals have been proposed as a key species for HAT in the catalytic mechanism of C–H activation, which might be prepared prior to the actual HAT. In order to investigate this hypothesis and large tunneling effect, DFT potential energy surfaces along the intrinsic reaction path were generated. The predicted rate constants and H/D KIEs using variational transition-state theory including multidimensional tunneling, based on these potential surfaces, have excellent agreement with experimental data. This study revealed that the reactive processes of C–H activation consisted of two distinguishable parts: (1) the substrate approaching the Fe(IV)-oxo center without C–H bond cleavage, which triggers the catalytic process by inducing metal-to-ligand charge transfer to form the Fe(III)-oxyl species, and (2) the actual HAT from the substrate to the Fe(III)-oxyl species. Most of the activation energy was used in the first part, and the actual HAT required only a small amount of energy to overcome the TS with a very large tunneling effect. The donor–acceptor interaction between σC–H and σ*Fe–O orbitals reduced the activation energy significantly to make C–H activation feasible. PMID:27031914

  15. Electronic Absorption Spectra of Tetrapyrrole-Based Pigments via TD-DFT: A Reduced Orbital Space Study.

    PubMed

    Shrestha, Kushal; Virgil, Kyle A; Jakubikova, Elena

    2016-07-28

    Tetrapyrrole-based pigments play a crucial role in photosynthesis as principal light absorbers in light-harvesting chemical systems. As such, accurate theoretical descriptions of the electronic absorption spectra of these pigments will aid in the proper description and understanding of the overall photophysics of photosynthesis. In this work, time-dependent density functional theory (TD-DFT) at the CAM-B3LYP/6-31G* level of theory is employed to produce the theoretical absorption spectra of several tetrapyrrole-based pigments. However, the application of TD-DFT to large systems with several hundreds of atoms can become computationally prohibitive. Therefore, in this study, TD-DFT calculations with reduced orbital spaces (ROSs) that exclude portions of occupied and virtual orbitals are pursued as a viable, computationally cost-effective alternative to conventional TD-DFT calculations. The effects of reducing orbital space size on theoretical spectra are qualitatively and quantitatively described, and both conventional and ROS results are benchmarked against experimental absorption spectra of various tetrapyrrole-based pigments. The orbital reduction approach is also applied to a large natural pigment assembly that comprises the principal light-absorbing component of the reaction center in purple bacteria. Overall, we find that TD-DFT calculations with proper and judicious orbital space reductions can adequately reproduce conventional, full orbital space, TD-DFT results of all pigments studied in this work. PMID:27392135

  16. Structure and absorption of Co(III) azo complex dyes based on pyrrolinone esters: DFT and TD DFT study

    NASA Astrophysics Data System (ADS)

    Luňák, Stanislav; Aysha, Tarek; Lyčka, Antonín; Machalický, Oldřich; Hrdina, Radim

    2014-07-01

    The relation between structure and absorption of three symmetrical 2:1 octahedral Co(III) azo complexes was studied. Quantum chemical calculations based on density functional theory (DFT) relate well with E-azo configuration of ligands with coordinated nitrogen atoms coming solely from phenolic residues. DFT calculations estimate the mer stereoisomer as remarkably preferred with respect to any fac arrangement. Time dependent DFT calculations using B3LYP and CAM-B3LYP functionals were successfully used to interpret the absorption spectra in a visible range.

  17. Vibrational spectroscopic studies and DFT calculations of 4-aminoantipyrine

    NASA Astrophysics Data System (ADS)

    Swaminathan, J.; Ramalingam, M.; Sethuraman, V.; Sundaraganesan, N.; Sebastian, S.

    2009-08-01

    The pyrazole derivative, 4-aminoantipyrine (4AAP), used as an intermediate for the synthesis of pharmaceuticals especially antipyretic and analgesic drugs has been analyzed experimentally and theoretically for its vibrational frequencies. The FTIR and FT Raman spectra of the title compound have been compared with the theoretically computed frequencies invoking the standard 6-311g(d,p) and cc-pVDZ basis sets at DFT level of theory (B3LYP). The harmonic vibrational frequencies at B3LYP/cc-pVDZ after appropriate scaling method seem to coincide satisfactorily with the experimental observations rather than B3LYP/6-311g(d,p) results. The theoretical spectrograms for FT-IR and FT-Raman spectra of 4AAP have been also constructed and compared with the experimental spectra. Additionally, thermodynamic data have also been calculated and discussed.

  18. Theoretical studies of molecular processes

    NASA Astrophysics Data System (ADS)

    Cui, Qiang

    1997-09-01

    The current thesis concerns with theoretical studies of molecular processes and consists of two parts. The first part includes theoretical studies of dynamics of unimolecular and bimolecular reactions, in particular those involving non-adiabatic processes. In chapter 2 and 3, we have presented our studies of detailed mechanisms for the photodissociation of C2H2 and C2H, and the ion-molecule reactions of C2H2+ + CH4 or NH3, respectively. In chapter 4, we have presented our study that extends TST to non-adiabatic reactions, and an application of the theory of the spin-forbidden reaction of CH(2/Pi)+N2. In chapter 5, we have included our analyses on the photodissociation of triplet ketene, where an extensive seam has been found all along the reaction coordinate. Finally, in Chapter 6, we have presented our study on the photodissociation of O3/sp-, which includes qualitative electronic structure calculations and construction of global potential energy functions for coupled electronic states. The second part of the thesis deals with theoretical studies of organometallic reactions, metal clusters, and gas-surface interactions. With theoretical calculations, one can study the reactivities of transition metal compounds systematically, which allows one to understand the key parameters that control the reactivities of those compounds. In chapter 2, we have presented our implementation of analytical hessian for effective core potential, which makes normal mode analysis possible for large organometallic systems and has proven to be very useful in the study of systems containing transition metals. In chapter 3-5, we have included our studies on the detailed mechanisms of several interesting reactions including platinum/palladium(0) catalyzed diboration and thioboration reactions of acetylene and olefin, and H- H/C-H bond activation on small metal clusters Pt/Pdn(n = 1[-]3). For truly large systems such as surfaces or proteins, full quantum mechanical treatments are

  19. [IR and Raman spectra studies of Rotundine based on DFT].

    PubMed

    Li, Jun-Ping; Zhou, Guang-Ming; Zhang, Li-Jun; Cheng, Hong-Mei; Qin, Hong-Ying

    2014-11-01

    Infrared spectroscopy (IR), the normal Raman spectroscopy (NRS) and the surface enhanced Raman spectroscopy (SERS) in new Ag/Cu nanomaterial of Rotundine were studied in the present paper. The IR and the NRS of Rotundine were calculated by the density functional theory (DFT) using B3LYP/6-311+G(d, p), then the spectral intensity graph of Rotundine were given. The vibrational peaks were assigned comprehensively by the visualization software of Gauss view 5. 0. Rotundine has obvious infrared and Raman vibrational peak in the wave number range of 3 300-2500 and 1 800-600 cm(-1). SnCl2 and PVP was used as capping agent for the silver nanoparticles in SERS of Rotundine. Finally, by using the method of cyclic immersion well dispersed silver nanoparticles was obtained and achieved good enhancement effect. This molecule acquired strong selective enhancement vibration peak, In the wave number ranges of 1 500-1 400 and 1 000-700 cm(-1) the enhancement effect is most obvious. After analyzed, the methylene of this molecule is adsorbed on the silver nanoparticles surface and the angle between the benzene ring and the silver substrate is close to 90 degrees. The theoretically calculated spectra of Rotundine are consistent with the obtained experimental spectra. There are some differences may be due to the interaction forces between molecules and so on. The visualization software displayed the structure characteristics and molecular group vibration of this molecular visually and provided important basis for assigning the vibrational peaks. Rotundine is an important traditional Chinese medicine agent contained in many kinds of sedative drugs. The study provides a strong basis for the rapid, feature and trace identification of Rotundine and also supplies important reference for the biological role of central inhibition of analgesic drugs. PMID:25752044

  20. Charge transfer properties of pentacene adsorbed on silver: DFT study

    SciTech Connect

    N, Rekha T.; Rajkumar, Beulah J. M.

    2015-06-24

    Charge transfer properties of pentacene adsorbed on silver is investigated using DFT methods. Optimized geometry of pentacene after adsorption on silver indicates distortion in hexagonal structure of the ring close to the silver cluster and deviations in co-planarity of carbon atoms due to the variations in bond angles and dihedral angles. Theoretically simulated absorption spectrum has a symmetric surface plasmon resonance peak around 486nm corresponding to the transfer of charge from HOMO-2 to LUMO. Theoretical SERS confirms the process of adsorption, tilted orientation of pentacene on silver surface and the charge transfers reported. Localization of electron density arising from redistribution of electrostatic potential together with a reduced bandgap of pentacene after adsorption on silver suggests its utility in the design of electro active organic semiconducting devices.

  1. DFT/TD-DFT study of solvent effect as well the substituents influence on the different features of TPP derivatives for PDT application

    NASA Astrophysics Data System (ADS)

    Dulski, Mateusz; Kempa, Marta; Kozub, Patrycja; Wójcik, Justyna; Rojkiewicz, Marcin; Kuś, Piotr; Szurko, Agnieszka; Ratuszna, Alicja; Wrzalik, Roman

    2013-03-01

    Spectral characteristics study of meso-tetraphenylporphyrin derivatives (TPP1 and TPP2) used as photosensitizers for utilization in photodynamic therapy (PDT) has been performed by density functional theory (DFT) and time dependent DFT (TD-DFT) calculations at B3LYP/6-31G(d) level of theory using PCM solvation model. The geometrical parameters of porphyrins have been studied for ground and excited-state geometry to deduce the influence of various substituents as well as solvent effect on the deformation of porphyrin ring. Two theoretical approaches - linear response (LR) and external iteration (EI) - have been performed to replicate absorption and fluorescence emission spectra. Experimental and theoretical investigations have shown that EI method reproduces the absorption energies very well for both singlet-singlet and triplet-triplet transitions, whereas the LR approach is more coherent with experimental fluorescence emission spectra. Spectral features and HOMO-LUMO band gap analysis have shown that TPP1 can be more useful in PDT. Calculations have revealed that two the highest occupied and two the lowest unoccupied molecular orbitals are responsible for the Q-band absorption and are located mainly on the porphyrin ring. In order to verify the substituent effect on the activity of tested compounds in their ground and excited states, the molecular electrostatic potential surfaces have been analyzed.

  2. Conformational studies of cellulosic fragments by DFT

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The study of cellulosic fragments by DFTr is a continuation of our efforts to produce quality structural data that will be valuable to those working in the field of cellulose structure and enzymatic degradation. Using a reduced basis set and density functional DFTr (B3LYP), optimization of cellulosi...

  3. Physicochemical studies of chemosensor imidazole derivatives: DFT based ESIPT process

    NASA Astrophysics Data System (ADS)

    Jayabharathi, Jayaraman; Thanikachalam, Venugopal; Jayamoorthy, Karunamoorthy

    2012-04-01

    A series of substituted imidazoles have been synthesized in very good yield under a solvent free condition using molecular iodine as the catalyst. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazole has been studied using emission spectroscopy. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the imidazole derivatives have been performed and discussed. DFT analysis about HOMO, HOMO-1, LUMO and LUMO+1 has been carried out and discussed. The energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state that is shown by PES calculation. The molecular electrostatic potential surface (MEP) has also been employed to show the higher electron density at N(3) nitrogen. Fluorescence enhancement has been found in the presence of transition metal ions and this may result from the suppression of radiationless transitions from the n-π* state in the chemosensors.

  4. DFT study of Al doped armchair SWCNTs

    NASA Astrophysics Data System (ADS)

    Dhiman, Shobhna; Rani, Anita; Kumar, Ranjan; Dharamvir, Keya

    2016-05-01

    Electronic properties of endohedrally doped armchair single-walled carbon nanotubes (SWCNTs) with a chain of six Al atoms have been studied using ab-initio density functional theory. We investigate the binding energy/atom, ionization potential, electron Affinity and Homo-Lumo gap of doped armchair SWNTs from (4,4) to (6,6) with two ends open. BE/dopant atom and ionization potential is maximum for (6, 6) doped armchair carbon nanotube; suggest that it is more stable than (4, 4) and (5, 5) doped tubes. HOMO - LUMO gap of Al doped arm chair carbon nanotubes decreases linearly with the increase in diameter of the tube. This shows that confinement induce a strong effect on electronic properties of doped tubes. These combined systems can be used for future nano electronics. The ab-initio calculations were performed with SIESTA code using generalized gradient approximation (GGA).

  5. Experimental and DFT computational studies of L-alanine cadmium chloride crystals

    NASA Astrophysics Data System (ADS)

    Ignatius, I. Cicili; Dheivamalar, S.; Kirubavathi, K.; Selvaraju, K.

    2016-05-01

    In this work, we report the combined experimental and theoretical study on molecular structure and vibrational spectra of nonlinear optical crystal L-alanine cadmium chloride (LACC). The single X-ray diffraction studies have revealed that the compound crystallizes in monoclinic system C2 space group with cell parameters a = 16.270, b = 7.358, c = 7.887 and Z = 4. FTIR and Raman spectra of the nonlinear optical materials LACC have been recorded and analyzed. The optimized geometric bond length and bond angles are obtained with the help of density functional theory (DFT) (B3LYP) calculation. The optimized geometric bond lengths and bond angles obtained by using DFT show good agreement with the experimental data. Using the natural bond orbital analysis the electronic effect and hydrogen bonding were confirmed. The HOMO-LUMO energy gap and the first order hyperpolarizability were calculated and it supports the nonlinear optical activity of LACC crystal.

  6. Molecular structures of 2-arylaminomethyl-1H-benzimidazole: Spectral, electrochemical, DFT and biological studies

    NASA Astrophysics Data System (ADS)

    Abdel Ghani, Nour T.; Mansour, Ahmed M.

    2012-06-01

    In the present work, structural studies on (1H-benzimidazol-2-ylmethyl)-N-(4-chloro-phenyl)-amine (L1) and (1H-benzimidazol-2-ylmethyl)-N-(4-iodo-phenyl)-amine (L2) have been done extensively by a variety of physico-chemical techniques. Optimized geometrical structures, harmonic vibrational frequencies, natural bonding orbital (NBO) analysis, and Frontier molecular orbitals (FMO) were obtained by DFT/B3LYP method. TD-DFT calculations help to assign the electronic transitions. The polarizable continuum model (PCM) fails to describe the experimental chemical shift associated with the NH protons as calculated by applying Gauge-invariant atomic orbital (GIAO) method, but a very good correlation between the theoretical and experimental values was achieved by taking into account the specific solute-solvent interactions. DFT calculations showed a good agreement between the theoretical and observed results. These compounds exhibited a high biological activity through the inhibition of the metabolic growth of the investigated bacteria.

  7. Electronic structure and mesoscopic simulations of nonylphenol ethoxylate surfactants. a combined DFT and DPD study.

    PubMed

    Valencia, Diego; Aburto, Jorge; García-Cruz, Isidoro

    2013-01-01

    The aim of this work was to gain insight into the effect of ethylene oxide (EO) chains on the properties of a series of nonylphenol ethoxylate (NPE) surfactants. We performed a theoretical study of NPE surfactants by means of density functional theory (DFT) and dissipative particle dynamics (DPD). Both approximations were used separately to obtain different properties. Four NPEs were selected for this purpose (EO = 4, 7, 11 and 15 length chains). DFT methods provided some electronic properties that are related to the EO units. One of them is the solvation Gibbs energy, which exhibited a linear trend with EO chain length. DPD calculations allow us to observe the dynamic behavior in water of the NPE surfactants. We propose a coarse-grained model which properly simulates the mesophases of each surfactant. This model can be used in other NPEs applications. PMID:23966071

  8. Dissociation curves of diatomic molecules: A DC-DFT study

    SciTech Connect

    Sim, Eunji; Kim, Min-Cheol; Burke, Kieron

    2015-12-31

    We investigate dissociation of diatomic molecules using standard density functional theory (DFT) and density-corrected density functional theory (DC-DFT) compared with CCSD(T) results as reference. The results show the difference between the HOMO values of dissociated atomic species often can be used as an indicator whether DFT would predict the correct dissociation limit. DFT predicts incorrect dissociation limits and charge distribution in molecules or molecular ions when the fragments have large HOMO differences, while DC-DFT and CCSD(T) do not. The criteria for large HOMO difference is about 2 ∼ 4 eV.

  9. Raman spectroscopic study of the Chromobacterium violaceum pigment violacein using multiwavelength excitation and DFT calculations.

    PubMed

    Jehlička, Jan; Edwards, Howell G M; Němec, Ivan; Oren, Aharon

    2015-12-01

    Violacein is a bisindole pigment occurring as a biosynthetic product of Chromobacterium violaceum and Janthinobacterium lividum. It has some structural similarities to the cyanobacterial UV-protective pigment scytonemin, which has been the subject of comprehensive spectroscopic and structural studies. A detailed experimental Raman spectroscopic study with visible and near-infrared excitation of violacein produced by C. violaceum has been undertaken and supported using theoretical DFT calculations. Raman spectra with 514 and 785 nm excitation of cultivated cells as well as extracts and Gaussian (B3LYP/6-311++G(d,p)) calculations with proposed molecular vibrational assignments are reported here. PMID:26151435

  10. Adsorption of silver dimer on graphene - A DFT study

    SciTech Connect

    Kaur, Gagandeep; Gupta, Shuchi; Rani, Pooja; Dharamvir, Keya

    2014-04-24

    We performed a systematic density functional theory (DFT) study of the adsorption of silver dimer (Ag{sub 2}) on graphene using SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms) package, in the generalized gradient approximation (GGA). The adsorption energy, geometry, and charge transfer of Ag2-graphene system are calculated. The minimum energy configuration for a silver dimer is parallel to the graphene sheet with its two atoms directly above the centre of carbon-carbon bond. The negligible charge transfer between the dimer and the surface is also indicative of a weak bond. The methodology demonstrated in this paper may be applied to larger silver clusters on graphene sheet.

  11. Hydrogen molecule on lithium adsorbed graphene: A DFT study

    NASA Astrophysics Data System (ADS)

    Kaur, Gagandeep; Gupta, Shuchi; Gaganpreet, Dharamvir, Keya

    2016-05-01

    Electronic structure calculations for the adsorption of molecular hydrogen on lithium (Li) decorated and pristine graphene have been studied systematically using SIESTA code [1] within the framework of the first-principle DFT under the Perdew-Burke-Ernzerhof (PBE) form of the generalized gradient approximation (GGA)[2], including spin polarization. The energy of adsorption of hydrogen molecule on graphene is always enhanced by the presence of co-adsorbed lithium. The most efficient adsorption configuration is when H2 is lying parallel to lithium adsorbed graphene which is in contrast to its adsorption on pristine graphene (PG) where it prefers perpendicular orientation.

  12. Thiosaccharine disulfide: Synthesis, crystal structure, spectroscopic characterization and theoretical study

    NASA Astrophysics Data System (ADS)

    Ferullo, Ricardo M.; Granados, Alejandro; Lanterna, Anabel; Güida, Jorge A.; Piro, Oscar E.; Castellano, Eduardo E.; Dennehy, Mariana

    2013-01-01

    The title compound, (thiosaccharine disulfide), bis[1,1'dioxide-2,3-dihidro-1,2-benzoisothiazol]disulfide, (tsac)2 has been synthesized and fully characterized by UV-Visible, IR, Raman, 1H and 13C NMR spectroscopy elemental analysis and structural X-ray crystallography. A DFT theoretical study has been performed and good agreement between experimental and theoretical values of structural parameters and vibration frequencies have been achieved.

  13. Computational study of AuSin (n=1-9) nanoalloy clusters invoking DFT based descriptors

    NASA Astrophysics Data System (ADS)

    Ranjan, Prabhat; Kumar, Ajay; Chakraborty, Tanmoy

    2016-04-01

    Nanoalloy clusters formed between Au and Si are topics of great interest today from both scientific and technological point of view. Due to its remarkable catalytic, electronic, mechanical and magnetic properties Au-Si nanoalloy clusters have extensive applications in the field of microelectronics, catalysis, biomedicine, and jewelry industry. Density Functional Theory (DFT) is a new paradigm of quantum mechanics, which is very much popular to study the electronic properties of materials. Conceptual DFT based descriptors have been invoked to correlate the experimental properties of nanoalloy clusters. In this venture, we have systematically investigated AuSin (n=1-9) nanoalloy clusters in the theoretical frame of the B3LYP exchange correlation. The experimental properties of AuSin (n=1-9) nanoalloy clusters are correlated in terms of DFT based descriptors viz. HOMO-LUMO gap, Electronegativity (χ), Global Hardness (η), Global Softness (S) and Electrophilicity Index (ω). The calculated HOMO-LUMO gap exhibits interesting odd-even alteration behaviour, indicating that even numbered clusters possess higher stability as compare to their neighbour odd numbered clusters. This study also reflects a very well agreement between experimental bond length and computed data.

  14. DFT studies on the structural and vibrational properties of polyenes.

    PubMed

    Kupka, Teobald; Buczek, Aneta; Broda, Małgorzata A; Stachów, Michał; Tarnowski, Przemysław

    2016-05-01

    Detailed density functional theory (DFT) calculations on the structure and harmonic frequencies of model all-trans and all-cis polyenes were undertaken. For the first time, we report on the convergence of selected B3LYP/6-311++G** and BLYP/6-311++G** calculated structural parameters resulting from a systematic increase in polyene size (chains containing 2 to 14 C = C units). The limiting values of the structural parameters for very long chains were estimated using simple three-parameter empirical formulae. BLYP/6-311++G** calculated ν(C = C) and ν(C-C) frequencies for all-trans and all-cis polyenes containing up to 14 carbon-carbon double bonds were used to estimate these values for very long chains. Correction of raw, unscaled vibrational data was performed by comparing theoretical and experimental wavenumbers for polyenes chains containing 3 to 12 conjugated C = C units with both ends substituted by tert-butyl groups. The corrected ν(C = C) and ν(C-C) wavenumbers for all-trans molecules were used to estimate the presence of 9 - 12 C = C units in all-trans polyene pigment in red coral. Graphical abstract Detailed density functional theory (DFT) calculations on the structure and harmonic frequencies of model all-trans and all-cis polyenes were undertaken. For the first time, we report on the convergence of selected B3LYP/6-311++G** and BLYP/6-311++G** calculated structural parameters resulting from a systematic increase in polyene size (chains containing 2 to 14 C=C units). The limiting values of the structural parameters for very long chains were estimated using simple three-parameter empirical formulae. PMID:27048200

  15. Adsorption of CGA on colloidal silver particles: DFT and SERS study

    NASA Astrophysics Data System (ADS)

    Biswas, Nandita; Kapoor, Sudhir; Mahal, Harbir S.; Mukherjee, Tulsi

    2007-08-01

    Raman and surface-enhanced Raman scattering (SERS) of chlorogenic acid (CGA) have been investigated. CGA is an important plant metabolite with anti-viral and anti-bacterial properties and thus, it is useful to study its surface adsorption characteristics. The experimental Raman data is supported with DFT calculations using B3LYP functional with 6-31G ∗ and LANL2DZ basis set. This is the first report on the vibrational analysis of CGA and its silver complex. From the SERS spectra as well as theoretical calculations, it has been inferred that the molecule is chemisorbed to the silver surface through the oxygen atoms of the carboxylate group.

  16. Iodine adsorption on Ni(111): STM and DFT study

    NASA Astrophysics Data System (ADS)

    Komarov, N. S.; Pavlova, T. V.; Andryushechkin, B. V.

    2016-09-01

    Iodine adsorption on the Ni(111) surface has been studied in ultra-high vacuum conditions with scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and density functional theory (DFT) calculations. At the first stage of adsorption, iodine was found to form a simple commensurate (√{ 3 } ×√{ 3 }) R 30∘ structure at the coverage of 0.33 ML. According to DFT calculations, all iodine atoms in the (√{ 3 } ×√{ 3 }) R 30∘ structure occupy fcc hollow sites. Increase of the coverage in the range of (0.333 ML <θ < 0.364 ML) results in the uniaxial compression of the iodine lattice and the formation of the high-order commensurate structure (11 ×√{ 3 } R 30∘). The mechanism of compression involves the formation and the development of the striped super-heavy domain wall network. Further iodine dosing gives rise to nucleation and growth of flat 2D islands of surface nickel iodide. Atomic resolution STM images of iodide islands, in addition to atomic modulation, exhibit clear visible moiré-like superstructures with a period about 26 Å. The origin of the moiré-patterns was explained by the incommensurability of lattices of the surface nickel iodide and underlying Ni(111).

  17. Insights on selenium and tellurium diaryldichalcogenides: A benchmark DFT study.

    PubMed

    Zaccaria, Francesco; Wolters, Lando P; Fonseca Guerra, Célia; Orian, Laura

    2016-07-01

    Selenium based diaryl dichalcogenides are compounds that are receiving attention in organic synthesis as eco-friendly oxidation agents as well as in pharmaceutical chemistry, where, together with tellurium-based derivatives, are appealing drugs mainly for their antioxidant properties. A benchmark study to establish optimal density functional theory (DFT) methods for the description of their molecular and electronic structure as well as for their energetics is presented here. Structural features, such as the orientation of the phenyl rings, as well as energetic aspects, i.e., the chalcogen-chalcogen bond strength, are discussed, with the aim of applying the novel insights to quantum mechanics-based investigations of their reactivity and to facilitate drug design. © 2016 Wiley Periodicals, Inc. PMID:27093091

  18. Spectroscopic Raman characterization of rutherfordine: a combined DFT and experimental study.

    PubMed

    Bonales, L J; Colmenero, F; Cobos, J; Timón, V

    2016-06-28

    A rutherfordine mineral was studied by means of Raman spectroscopy combined with first principle calculations based on the density functional theory (DFT) method. The pseudopotential of a uranium atom was generated and its performance was evaluated for a series of uranium-containing minerals. The structure of rutherfordine was determined for two symmetries (Pmmn and Imm2) and the resulting lattice parameters, bond lengths, bond angles, and X-ray powder diffractogram were found to be in very good agreement with experimental values. The Raman spectrum was experimentally determined in the range 0-1700 cm(-1) and calculated using density functional perturbation theory. The non-scaled theoretical wavenumbers also agreed with the experimental values, and therefore a detailed interpretation of the theoretical spectra allowed us to assign the Raman bands found in the experimental spectrum. PMID:27271869

  19. Vibrational spectra and non linear optical proprieties of L-histidine oxalate: DFT studies.

    PubMed

    Ben Ahmed, A; Elleuch, N; Feki, H; Abid, Y; Minot, C

    2011-08-01

    This paper presents the results of our calculations on the geometric parameters, vibrational spectra and hyperpolarizability of a nonlinear optical material L-histidine oxalate. Due to the lack of sufficiently precise information on geometric structure in literature, theoretical calculations were preceded by re-determination of the crystal X-ray structure. Single crystal of L-histidine oxalate has been growing by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in the non-Centro symmetric space group P2(1)2(1)2(1) of orthorhombic system. The FT-IR and Raman spectra of L-histidine oxalate were recorded and analyzed. The vibrational wave numbers were examined theoretical with the aid of Gaussian98 package of programs using the DFT//B3LYP/6-31G(d) level of theory. The data obtained from vibrational wave number calculations are used to assign vibrational bands obtained in IR and Raman spectroscopy of the studied compound. The geometrical parameters of the title compound are in agreement with the values of similar structures. To investigate microscopic second order non-linear optical NLO behaviour of the examined complex, the electric dipole μ(tot), the polarizability α(tot) and the hyperpolarizability β(tot) were computed using DFT//B3LYP/6-31G(d) method. According to our calculation, the title compound exhibits non-zero β(tot) value revealing microscopic second order NLO behaviour. PMID:21530379

  20. Vibrational spectra and non linear optical proprieties of L-histidine oxalate: DFT studies

    NASA Astrophysics Data System (ADS)

    Ahmed, A. Ben; Elleuch, N.; Feki, H.; Abid, Y.; Minot, C.

    2011-08-01

    This paper presents the results of our calculations on the geometric parameters, vibrational spectra and hyperpolarizability of a nonlinear optical material L-histidine oxalate. Due to the lack of sufficiently precise information on geometric structure in literature, theoretical calculations were preceded by re-determination of the crystal X-ray structure. Single crystal of L-histidine oxalate has been growing by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in the non-Centro symmetric space group P2 12 12 1 of orthorhombic system. The FT-IR and Raman spectra of L-histidine oxalate were recorded and analyzed. The vibrational wave numbers were examined theoretical with the aid of Gaussian98 package of programs using the DFT//B3LYP/6-31G(d) level of theory. The data obtained from vibrational wave number calculations are used to assign vibrational bands obtained in IR and Raman spectroscopy of the studied compound. The geometrical parameters of the title compound are in agreement with the values of similar structures. To investigate microscopic second order non-linear optical NLO behaviour of the examined complex, the electric dipole μtot, the polarizability αtot and the hyperpolarizability βtot were computed using DFT//B3LYP/6-31G(d) method. According to our calculation, the title compound exhibits non-zero βtot value revealing microscopic second order NLO behaviour.

  1. Theoretical investigation of lead vapor adsorption on kaolinite surfaces with DFT calculations.

    PubMed

    Wang, Xinye; Huang, Yaji; Pan, Zhigang; Wang, Yongxing; Liu, Changqi

    2015-09-15

    Kaolinite can be used as the in-furnace sorbent/additive to adsorb lead (Pb) vapor at high temperature. In this paper, the adsorptions of Pb atom, PbO molecule and PbCl2 molecule on kaolinie surfaces were investigated by density functional theory (DFT) calculation. Si surface is inert to Pb vapor adsorption while Al surfaces with dehydroxylation are active for the unsaturated Al atoms and the O atoms losing H atoms. The adsorption energy of PbO is much higher than that of Pb atom and PbCl2. Considering the energy barriers, it is easy for PbO and PbCl2 to adsorb on Al surfaces but difficult to escape. The high energy barriers of de-HCl process cause the difficulties of PbCl2 to form PbO·Al2O3·2SiO2 with kaolinite. Considering the inertia of Si atoms and the activity of Al atoms after dehydroxylation, calcination, acid/alkali treatment and some other treatment aiming at amorphous silica producing and Al activity enhancement can be used as the modification measures to improve the performance of kaolinite as the in-furnace metal capture sorbent. PMID:25880048

  2. DFT and DMFT: Implementations and applications to the study of correlated materials

    NASA Astrophysics Data System (ADS)

    Ylvisaker, Erik Ryan

    While DFT-LDA has enjoyed great success in describing many ground-state properties of solids, there is an ever increasing list of materials which are not described even qualitatively correct in DFT-LDA. Here I describe some applications of DFT and dynamical mean field theory. This dissertation is divided into two parts. Part I describes the theoretical background of DFT and DMFT, and the simplest extension to DFT to study correlated materials, LDA+U, is examined in detail. We find that the behavior of LDA+U can differ quite strongly between AMF and FLL, the two commonly used double-counting functionals. AMF has a strong energetic penalty for magnetic states, which roughly cancels the exchange splitting found in LSDA. In Part I, I also describe in detail the implementation of LDA+DMFT in the publicly available code FFLO. Part II focuses on applications. I describe the application of LDA to LiNbO2, where Wannier functions and effective tight-binding Hamiltonians are constructed for LiNbO2. We found that second neighbor hopping t2 is the largest, but the first neighbor hopping depends strongly on the Nb-O distance, so that with small variations of 0 position t1 varies by an order of magnitude. I also describe in part II the application of LDA in density functional perturbation theory (DFPT) to calculate phonons for Al, Na and diamond to compute melting curves using the Lindemann criteria. The resulting Tm( P) curves agree rather well with experiment in most conditions for these materials, including reproducing the drop of 300 K of T m in bcc-Na. Detailed calculations in LDA+DMFT using Hubbard I and QMC impurity solvers are used to describe the valence transition in Yb. The agreement with experimental XAES and RIXS measurements of nf is rather good, and even the highly approximate Hubbard I impurity solver gives reasonably good results. Finally, I discuss the application of LDA+U to molecular orbitals in RbO2 to examine the possibility of orbital ordering in the O pi

  3. HCOOH decomposition on Pt(111): A DFT study

    NASA Astrophysics Data System (ADS)

    Scaranto, Jessica; Mavrikakis, Manos

    2016-06-01

    Formic acid (HCOOH) decomposition on transition metal surfaces is important for hydrogen production and for its electro-oxidation in direct HCOOH fuel cells. HCOOH can decompose through dehydrogenation leading to formation of CO2 and H2 or dehydration leading to CO and H2O; because CO can poison metal surfaces, dehydrogenation is typically the desirable decomposition path. Here we report a mechanistic analysis of HCOOH decomposition on Pt(111), obtained from a plane wave density functional theory (DFT-PW91) study. We analyzed the dehydrogenation mechanism by considering the two possible pathways involving the formate (HCOO) or the carboxyl (COOH) intermediate. We also considered several possible dehydration paths leading to CO formation. We studied HCOO and COOH decomposition both on the clean surface and in the presence of other relevant co-adsorbates. The results suggest that COOH formation is energetically more difficult than HCOO formation. In contrast, COOH dehydrogenation is easier than HCOO decomposition. We found that CO2 is the main product through both pathways and that CO is produced mainly through the dehydroxylation of the COOH intermediate.

  4. Palladium dimers adsorbed on graphene: A DFT study

    SciTech Connect

    Kaur, Gagandeep; Gupta, Shuchi; Dharamvir, Keya

    2015-05-15

    The 2D structure of graphene shows a great promise for enhanced catalytic activity when adsorbed with palladium. We performed a systematic density functional theory (DFT) study of the adsorption of palladium dimer (Pd{sub 2}) on graphene using SIESTA package, in the generalized gradient approximation (GGA). The adsorption energy, geometry, and charge transfer of Pd{sub 2}-graphene system are calculated. Both horizontal and vertical orientations of Pd{sub 2} on graphene are studied. Our calculations revealed that the minimum energy configuration for Pd dimer is parallel to the graphene sheet with its two atoms occupying centre of adjacent hexagonal rings of graphene sheet. Magnetic moment is induced for Pd dimer adsorbed on graphene in vertical orientation while horizontal orientation of Pd dimer on graphene do not exhibit magnetism. Insignificant energy differences among adsorption sites means that dimer mobility on the graphene sheet is high. There is imperceptible distortion of graphene sheet perpendicular to its plane. However, some lateral displacements are seen.

  5. A DFT study of IRMOF-3 catalysed Knoevenagel condensation.

    PubMed

    Cortese, Remedios; Duca, Dario

    2011-09-21

    It has been recently reported that IRMOF-3 [Gascon et al., J. Catal, 2009, 261, 75] may behave as a basic catalyst, active in the Knoevenagel condensation. In particular, it has been shown that the basicity of aniline-like amino moieties is enhanced, along with the catalytic activity, when incorporated into MOF structures. The computational study here was aimed at finding possible atomistic explanations of the increased basicity and catalytic activity of the IRMOF-3 embedded aniline groups, experimentally claimed. It was, moreover, aimed at guessing a reaction mechanism for the IRMOF-3 catalysed Knoevenagel condensation of benzaldehyde and ethyl-cyanoacetate. Within the DFT framework we have studied structure and basicity properties of IRMOF-3 and we have analysed the energetics of the catalytic cycle as well as of possible deactivation paths, including it. The increased basicity of IRMOF-3 over other amminic catalysts has been explained via the formation of protonated conjugate derivatives, involving hydrogen-bonds and originating quasi-planar 6-term rings. Several plausible reaction steps have been moreover taken into account and a mechanism for the Knoevenagel condensation, including catalyst deactivation, has been proposed for aniline molecules and embedded aniline moieties. This allowed us to suggest that the increased IRMOF-3 activity, as a basic catalyst, should be mostly related to its water adsorption ability, preserving the properties of the catalytically active amino moieties. PMID:21814670

  6. Vibrational and structural study of onopordopicrin based on the FTIR spectrum and DFT calculations.

    PubMed

    Chain, Fernando E; Romano, Elida; Leyton, Patricio; Paipa, Carolina; Catalán, César A N; Fortuna, Mario; Brandán, Silvia Antonia

    2015-11-01

    In the present work, the structural and vibrational properties of the sesquiterpene lactone onopordopicrin (OP) were studied by using infrared spectroscopy and density functional theory (DFT) calculations together with the 6-31G(∗) basis set. The harmonic vibrational wavenumbers for the optimized geometry were calculated at the same level of theory. The complete assignment of the observed bands in the infrared spectrum was performed by combining the DFT calculations with Pulay's scaled quantum mechanical force field (SQMFF) methodology. The comparison between the theoretical and experimental infrared spectrum demonstrated good agreement. Then, the results were used to predict the Raman spectrum. Additionally, the structural properties of OP, such as atomic charges, bond orders, molecular electrostatic potentials, characteristics of electronic delocalization and topological properties of the electronic charge density were evaluated by natural bond orbital (NBO), atoms in molecules (AIM) and frontier orbitals studies. The calculated energy band gap and the chemical potential (μ), electronegativity (χ), global hardness (η), global softness (S) and global electrophilicity index (ω) descriptors predicted for OP low reactivity, higher stability and lower electrophilicity index as compared with the sesquiterpene lactone cnicin containing similar rings. PMID:26057092

  7. Vibrational spectroscopic analysis of aluminum phthalocyanine chloride. experimental and DFT study

    NASA Astrophysics Data System (ADS)

    Soliman, I. M.; El-Nahass, M. M.; Eid, Kh. M.; Ammar, H. Y.

    2016-06-01

    In this work, we report a combined experimental and theoretical study of aluminum phthalocyanine chloride (AlPcCl). The FT-IR and Raman spectra of AlPcCl were recorded and analyzed. The density functional theory (DFT) computations have been performed at B3LYP/6-31g and B3LYP/6-311g to derive equilibrium geometry, vibrational wavenumbers, intensity and NLO properties. All the observed vibrational bands have been discussed and assigned to normal mode or to combinations on the basis of our DFT calculations as a primary source of attribution and also by comparison with the previous results for similar compounds. The natural bond orbital (NBO) calculations were performed to study the atomic charge distribution of the investigated compound. The calculated results showed that dipole moment of the investigated compound was 4.68 Debye and HOMO-LUMO energy gap was 2.14 eV. The lowering of frontier orbital gap appears to be the cause of its enhanced charge transfer interaction.

  8. SERS and DFT study of p-hydroxybenzoic acid adsorbed on colloidal silver particles.

    PubMed

    Chen, Y; Chen, S J; Li, S; Wei, J J

    2015-01-01

    In this study, normal Raman spectra of p—hydroxybenzoic acid (PHBA) powder and its surface—enhanced Raman scattering (SERS) spectra in silver colloidal solutions were measured under near infrared excitation conditions. In theoretical calculation, two models of PHBA adsorbed on the surfaces of silver nanoparticles were established. The Raman frequencies of these two models using density functional theory (DFT) method were calculated, and compared with the experimental results. It was found that the calculated Raman frequencies were in good agreement with experimental values, which indicates that there are two enhanced mechanism physical (electromagnetic, EM) enhancement and chemical (charge—transfer, CT) enhancement, in silver colloidal solutions regarding SERS effect. Furthermore, from high—quality SERS spectrum of PHBA obtained in silver colloids, we inferred that PHBA molecules in silver colloids adsorb onto the metal surfaces through carboxyl at a perpendicular orientation. The combination of SERS spectra and DFT calculation is thus useful for studies of the adsorption—orientation of a molecule on a metal colloid. PMID:26475382

  9. Using DFT Methods to Study Activators in Optical Materials

    DOE PAGESBeta

    Du, Mao-Hua

    2015-08-17

    Density functional theory (DFT) calculations of various activators (ranging from transition metal ions, rare-earth ions, ns2 ions, to self-trapped and dopant-bound excitons) in phosphors and scintillators are reviewed. As a single-particle ground-state theory, DFT calculations cannot reproduce the experimentally observed optical spectra, which involve transitions between multi-electronic states. However, DFT calculations can generally provide sufficiently accurate structural relaxation and distinguish different hybridization strengths between an activator and its ligands in different host compounds. This is important because the activator-ligand interaction often governs the trends in luminescence properties in phosphors and scintillators, and can be used to search for new materials.more » DFT calculations of the electronic structure of the host compound and the positions of the activator levels relative to the host band edges in scintillators are also important for finding optimal host-activator combinations for high light yields and fast scintillation response. Mn4+ activated red phosphors, scintillators activated by Ce3+, Eu2+, Tl+, and excitons are shown as examples of using DFT calculations in phosphor and scintillator research.« less

  10. Using DFT Methods to Study Activators in Optical Materials

    SciTech Connect

    Du, Mao-Hua

    2015-08-17

    Density functional theory (DFT) calculations of various activators (ranging from transition metal ions, rare-earth ions, ns2 ions, to self-trapped and dopant-bound excitons) in phosphors and scintillators are reviewed. As a single-particle ground-state theory, DFT calculations cannot reproduce the experimentally observed optical spectra, which involve transitions between multi-electronic states. However, DFT calculations can generally provide sufficiently accurate structural relaxation and distinguish different hybridization strengths between an activator and its ligands in different host compounds. This is important because the activator-ligand interaction often governs the trends in luminescence properties in phosphors and scintillators, and can be used to search for new materials. DFT calculations of the electronic structure of the host compound and the positions of the activator levels relative to the host band edges in scintillators are also important for finding optimal host-activator combinations for high light yields and fast scintillation response. Mn4+ activated red phosphors, scintillators activated by Ce3+, Eu2+, Tl+, and excitons are shown as examples of using DFT calculations in phosphor and scintillator research.

  11. DFT calculation and vibrational spectroscopic studies of 2-(tert-butoxycarbonyl (Boc) -amino)-5-bromopyridine

    NASA Astrophysics Data System (ADS)

    Premkumar, S.; Jawahar, A.; Mathavan, T.; Kumara Dhas, M.; Sathe, V. G.; Milton Franklin Benial, A.

    2014-08-01

    The molecular structure of 2-(tert-butoxycarbonyl (Boc) -amino)-5-bromopyridine (BABP) was optimized by the DFT/B3LYP method with 6-311G (d,p), 6-311++G (d,p) and cc-pVTZ basis sets using the Gaussian 09 program. The most stable optimized structure of the molecule was predicted by the DFT/B3LYP method with cc-pVTZ basis set. The vibrational frequencies, Mulliken atomic charge distribution, frontier molecular orbitals and thermodynamical parameters were calculated. These calculations were done at the ground state energy level of BABP without applying any constraint on the potential energy surface. The vibrational spectra were experimentally recorded using Fourier Transform-Infrared (FT-IR) and micro-Raman spectrometer. The computed vibrational frequencies were scaled by scale factors to yield a good agreement with observed experimental vibrational frequencies. The complete theoretically calculated and experimentally observed vibrational frequencies were assigned on the basis of Potential Energy Distribution (PED) calculation using the VEDA 4.0 program. The vibrational modes assignments were performed by using the animation option of GaussView 05 graphical interface for Gaussian program. The Mulliken atomic charge distribution was calculated for BABP molecule. The molecular reactivity and stability of BABP were also studied by frontier molecular orbitals (FMOs) analysis.

  12. Band structure tunability in MoS2 under interlayer compression: A DFT and GW study

    NASA Astrophysics Data System (ADS)

    Espejo, C.; Rangel, T.; Romero, A. H.; Gonze, X.; Rignanese, G.-M.

    2013-06-01

    The electronic band structures of MoS2 monolayer and 2H1 bulk polytype are studied within density-functional theory (DFT) and many-body perturbation theory (GW approximation). Interlayer van der Waals (vdW) interactions, responsible for bulk binding, are calculated with the postprocessing Wannier functions method. From both fat bands and Wannier functions analysis, it is shown that the transition from a direct band gap in the monolayer to an indirect band gap in bilayer or bulk systems is triggered by medium- to short-range electronic interactions between adjacent layers, which arise at the equilibrium interlayer distance determined by the balance between vdW attraction and exchange repulsion. The semiconductor-to-semimetal (S-SM) transition is found from both theoretical methods: around c=10.7 Å and c=9.9 Å for DFT and GW, respectively. A metallic transition is also observed for the interlayer distance c=9.7 Å. Dirac conelike band structures and linear bands near Fermi level are found for shorter c lattice parameter values. The VdW correction to total energy was used to estimate the pressure at which S-SM transition takes place from a fitting to a model equation of state.

  13. DFT study of Rb-TFA structure after high-pressure action

    NASA Astrophysics Data System (ADS)

    Scholtzová, Eva

    2011-12-01

    The pressure-induced A-B phase transition of synthetic Rb-tetra-ferri-annite (Rb-TFA) mica was studied theoretically by means of Density Functional Theory (DFT) method. The calculations show that Rb-TFA keeps a Franzini A-type structure up to at least 5.39 GPa of pressure, whereas at higher pressure, it transforms to a Franzini B-type structure. The negative value of the tetrahedral rotation angle α = -4.68° has appeared at 5.56 GPa of calculated pressure. This result is in a relatively good agreement with experimentally estimated phase transition area in the range of 3.36-3.84 GPa. The energy difference between the A and B structures is very small (ΔE = 8 kJ/mol). The detailed analysis of the optimized structural data shows minimal changes in the structure of Rb-TFA after the pressure-induced phase transition.

  14. A DFT Study of Pyrrole-Isoxazole Derivatives as Chemosensors for Fluoride Anion

    PubMed Central

    Jin, Ruifa; Sun, Weidong; Tang, Shanshan

    2012-01-01

    The interactions between chemosensors, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (AIC) derivatives, and different anions (F− Cl−, Br−, AcO−, and H2PO4−) have been theoretically investigated using DFT approaches. It turned out that the unique selectivity of AIC derivatives for F− is ascribed to their ability of deprotonating the host sensors. Frontier molecular orbital (FMO) analyses have shown that the vertical electronic transitions of absorption and emission for the sensing signals are characterized as intramolecular charge transfer (ICT). The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for fluoride chemosensors both in UV-vis and fluorescence spectra except for derivative with benzo[d]thieno[3,2-b]thiophene fragment that can serve as ratiometric fluorescent fluoride chemosensor only. PMID:23109833

  15. DFT-D studies of single porphyrin molecule on doped boron silicon surfaces.

    PubMed

    Boukari, Khaoula; Sonnet, Philippe; Duverger, Eric

    2012-12-01

    We present a theoretical study in the framework of density functional calculations, taking into account the van der Waals interactions (DFT-D) of isolated Cu-5,10,15,20-tetrakis(3,5-di-tert-butyl-phenyl) porphyrin (Cu-TBPP) molecules in a C2v conformation adsorbed on a Si(111)√3x√3R30°-boron surface [denoted Si(111)-B]. With this approach, we investigate interactions between perfect or boron-defect Si(111)-B substrates and the Cu-TBPP molecule as well as the consequences of demetallation of Cu-TBPP. For each model, we determine the structural equilibrium, the spatial charge-density distribution and the electronic properties of the ground state. We conclude that there is potential for Si adatom capture by a porphyrin without strong modification of the porphyrin response, as seen from simulated scanning tunneling microscopy (STM) images. PMID:23055297

  16. DFT Study of Oxygen Dissociation in Molten Carbonate.

    PubMed

    Lei, Xueling; Haines, Kahla; Huang, Kevin; Qin, Changyong

    2015-08-20

    Using density functional theory method, we have studied the oxygen dissociation in alkali molten carbonate at the B3LYP/6-31G(d) level. The calculated energies were then verified by MP4 and CCSD(T). A four-formula cluster (M2CO3)4, M = Li, Na, and K was used to describe the molten carbonate. It was found that the adsorption of oxygen to molten carbonate is of a chemical type and leads to the formation of CO5(2-) in MC, which was confirmed for the first time by DFT calculations. The energy barrier for its dissociation is calculated to be 197.9, 116.7, and 170.3 kJ/mol in the (M2CO3)4 cluster, M = Li, Na, and K, respectively. If the reaction of O2 + 2CO3(2-) → 2CO4(2-) is approximated as a one-step reaction, the activation energy is estimated to be 96.2, 15.1, and 68.6 kJ/mol, respectively. The reaction rate is first order to the pressure of oxygen. Surprisingly, the reaction of oxygen dissociation has the lowest energy barrier in sodium carbonate, which is consistent with the recent experimental findings. It is very clear that the molten carbonate salt has directly participated in the ORR process and plays an important role as a catalyst in the cathode of SOFCs. The oxygen reduction has been facilitated by MC and enhanced cell performance has been observed. PMID:26219024

  17. Molecular structure and charge transfer contributions to nonlinear optical property of 2-Methyl-4-nitroaniline: A DFT study

    NASA Astrophysics Data System (ADS)

    Jasmine, G. Femina; Amalanathan, M.; Roy, S. Dawn Dharma

    2016-05-01

    The Charge transfer contributions to the second-order nonlinear optical properties of 2-Methyl-4-nitroaniline have been performed by means of DFT computation. The vibrational contribution studies of 2-Methyl-4-nitroaniline have also been performed using FTIR, FT-Raman analysis. More support on the experimental findings were added from the quantum chemical studies performed with DFT (B3LYP) method using 6-311++G(d,p)basis sets. Natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction. The HOMO and LUMO analysis reveals the possibility of charge transfer within the molecule. The first order hyperpolarizability (α0) and related properties (β,α0 and Δα) of 2-Methyl-4-nitroaniline were calculated. In addition, molecular electrostatic potential (MEP), charge analysis also were investigated using theoretical calculations.

  18. Understanding natural semiquinone radicals--multifrequency EPR and relativistic DFT studies of the structure of Hg(II) complexes.

    PubMed

    Witwicki, Maciej; Jerzykiewicz, Maria; Ozarowski, Andrzej

    2015-01-01

    Multifrequency EPR spectroscopy and DFT calculations were used to investigate Hg(II) complexes with semiquinone radical ligands formed in a direct reaction between the metal ions and tannic acid (a polyphenol closely related to tannins). Because of the intricate structure of tannic acid a vast array of substituted phenolic compounds were tested to find a structural model mimicking its ability to react with Hg(II) ions. The components of the g matrix (the g tensor) determined from the high field (208 GHz) EPR spectra of the Hg(II) complexes with the radical ligands derived from tannic acid and from the model compounds were analogous, indicating a similar coordination mode in all the studied Hg(II) complexes. Since catechol (1,2-dihydroxybenzene) was the simplest compound undergoing the reaction with Hg(II) it was selected for DFT studies which were aimed at providing an insight into the structural properties of the investigated complexes. Various coordination numbers and different conformations and protonation states of the ligands were included in the theoretical analyses. g Matrices were computed for all the DFT optimized geometries. A good agreement between the theoretical and experimental values was observed only for the model with the Hg(II) ion tetracoordinated by two ligands, one of the ligands being monoprotonated with the unpaired electron mainly localized on it. PMID:25108678

  19. Theoretical analysis of an all-photonic multifunctional molecular logic device: Using TD-DFT//DFT to assess photochromic activity of multimeric photochrome

    NASA Astrophysics Data System (ADS)

    Belfon, Kellon A. A.; Gough, Jonathan D.

    2013-10-01

    The structures and properties of a single-molecule photochromic switch consisting of 3 photochromic moieties is investigated. Using time-dependent density functional theory (TD-DFT) we calculated the λmax within ± 30 nm (± 0.18 eV) and produced spectra that were similar. The charge-transfer (CT) character of the molecular orbitals (MO) was assessed via the overlap between the occupied and virtual orbitals (Λ diagnostic) and did not suffer from CT failure. The MOs were consistent with photochemically productive photochromes. The MO and their contribution to different excited states paralleled both the observed activity and observed inactivity of the photochrome.

  20. Temperature dependent Raman and DFT study of creatine.

    PubMed

    Gangopadhyay, Debraj; Sharma, Poornima; Singh, Ranjan K

    2015-01-01

    Temperature dependent Raman spectra of creatine powder have been recorded in the temperature range 420-100K at regular intervals and different clusters of creatine have been optimized using density functional theory (DFT) in order to determine the effect of temperature on the hydrogen bonded network in the crystal structure of creatine. Vibrational assignments of all the 48 normal modes of the zwitterionic form of creatine have been done in terms of potential energy distribution obtained from DFT calculations. Precise analysis gives information about thermal motion and intermolecular interactions with respect to temperature in the crystal lattice. Formation of higher hydrogen bonded aggregates on cooling can be visualized from the spectra through clear signature of phase transition between 200K and 180K. PMID:26010702

  1. DFT Study of Optical Properties of Pt-based Complexes

    NASA Astrophysics Data System (ADS)

    Oprea, Corneliu I.; Dumbravǎ, Anca; Moscalu, Florin; Nicolaides, Atnanassios; Gîrţu, Mihai A.

    2010-01-01

    We report Density Functional Theory (DFT) calculations providing the geometrical and electronic structures, as well as the vibrational and optical properties of the homologous series of Pt-pyramidalized olefin complexes (CH2)n-(C8H10)Pt(PH3)2, where n = 0, 1, and 2, in their neutral and oxidized states. All complexes were geometry optimized for the singlet ground state in vacuum using DFT methods with B3LYP exchange-correlation functional and the Effective Core Potential LANL2DZ basis set, within the frame of Gaussian03 quantum chemistry package. We find the coordination geometry of Pt to be distorted square planar, with dihedral angles ranging from 0°, for n = 0 and 1, which have C2V symmetry to 3.4°, for n = 2 with C2 symmetry. The Mulliken charge analysis allows a discussion of the oxidation state of the Pt ion. Electronic transitions were calculated at the same level of theory by means of Time Dependant-DFT. For n = 2 the electronic absorption bands are located in the UV region of the spectrum, the transitions being assigned to metal to ligand charge transfers. The relevance of these Pt-based compounds as possible pigments for dye-sensitized solar cells is discussed.

  2. Charged vanadium-benzene multidecker clusters: DFT and quantum Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Tokár, K.; Derian, R.; Mitas, L.; Štich, I.

    2016-02-01

    Using explicitly correlated fixed-node quantum Monte Carlo and density functional theory (DFT) methods, we study electronic properties, ground-state multiplets, ionization potentials, electron affinities, and low-energy fragmentation channels of charged half-sandwich and multidecker vanadium-benzene systems with up to 3 vanadium atoms, including both anions and cations. It is shown that, particularly in anions, electronic correlations play a crucial role; these effects are not systematically captured with any commonly used DFT functionals such as gradient corrected, hybrids, and range-separated hybrids. On the other hand, tightly bound cations can be described qualitatively by DFT. A comparison of DFT and quantum Monte Carlo provides an in-depth understanding of the electronic structure and properties of these correlated systems. The calculations also serve as a benchmark study of 3d molecular anions that require a balanced many-body description of correlations at both short- and long-range distances.

  3. Charged vanadium-benzene multidecker clusters: DFT and quantum Monte Carlo study.

    PubMed

    Tokár, K; Derian, R; Mitas, L; Štich, I

    2016-02-14

    Using explicitly correlated fixed-node quantum Monte Carlo and density functional theory (DFT) methods, we study electronic properties, ground-state multiplets, ionization potentials, electron affinities, and low-energy fragmentation channels of charged half-sandwich and multidecker vanadium-benzene systems with up to 3 vanadium atoms, including both anions and cations. It is shown that, particularly in anions, electronic correlations play a crucial role; these effects are not systematically captured with any commonly used DFT functionals such as gradient corrected, hybrids, and range-separated hybrids. On the other hand, tightly bound cations can be described qualitatively by DFT. A comparison of DFT and quantum Monte Carlo provides an in-depth understanding of the electronic structure and properties of these correlated systems. The calculations also serve as a benchmark study of 3d molecular anions that require a balanced many-body description of correlations at both short- and long-range distances. PMID:26874484

  4. DFT studies of CNT-functionalized uracil-acetate hybrids

    NASA Astrophysics Data System (ADS)

    Mirzaei, Mahmoud; Gulseren, Oguz

    2015-09-01

    Calculations based on density functional theory (DFT) have been performed to investigate the stabilities and properties of hybrid structures consisting of a molecular carbon nanotube (CNT) and uracil acetate (UA) counterparts. The investigated models have been relaxed to minimum energy structures and then various physical properties and nuclear magnetic resonance (NMR) properties have been evaluated. The results indicated the effects of functionalized CNT on the properties of hybrids through comparing the results of hybrids and individual structures. The oxygen atoms of uracil counterparts have been seen as the detection points of properties for the CNT-UA hybrids.

  5. DFT studies and vibrational spectra of isoquinoline and 8-hydroxyquinoline

    NASA Astrophysics Data System (ADS)

    Krishnakumar, V.; Ramasamy, R.

    2005-02-01

    The geometry, frequency and intensity of the vibrational bands of isoquinoline (IQ) and 8-hydroxyquinoline (8-HQ) were obtained by the density functional theory (DFT) calculations with the B3LYP functional and 6-31 G* basis set. The vibrational spectral data obtained from the solid phase mid and far FT-IR and FT-Raman spectra of IQ and 8-HQ are assigned based on the results of the normal coordinate calculations. The observed and the calculated spectra are found to be in good agreement.

  6. Properties of the Oxidized Cu(110) Surface: The DFT study

    NASA Astrophysics Data System (ADS)

    Olenga, Antoine; Fazleev, N. G.

    2012-10-01

    The study of adsorption of oxygen on transition metal surfaces is important for the understanding of oxidation, heterogeneous catalysis, and metal corrosion. In this work we have studied from first principles the changes of electronic properties of the Cu(110) surface due to oxygen adsorption. Especially, we have focused on studies of changes in the work function, electronic density, interlayer spacing, density of states and band structure with oxygen coverage. Calculations of electronic properties from first principles have been also performed for the (110) and surface of Cu2O to use for comparison. The first-principles calculations in this work have been performed on the basis of the Density Functional Theory and using DMOl3 code. The obtained theoretical results have been compared with available experimental data.

  7. Photophysics of octabutoxy phthalocyaninato-Ni(II) in toluene: ultrafast experiments and DFT/TDDFT studies.

    PubMed

    Gunaratne, Tissa C; Gusev, Alexey V; Peng, Xinzhan; Rosa, Angela; Ricciardi, Giampaolo; Baerends, Evert Jan; Rizzoli, Corrado; Kenney, Malcolm E; Rodgers, Michael A J

    2005-03-17

    Reported herein is a combination of experimental and DFT/TDDFT theoretical investigations of the ground and excited states of 1,4,8,11,15,18,22,25-Octabutoxyphthalocyaninato-nickel(II), NiPc(BuO)(8), and the dynamics of its deactivation after excitation into the S(1)(pi,pi) state in toluene solution. According to X-ray crystallographic analysis NiPc(BuO)(8) has a highly saddled structure in the solid state. However, DFT studies suggest that in solution the complex is likely to flap from one D(2)(d)-saddled conformation to the opposite one through a D(4)(h)-planar structure. The spectral and kinetic changes for the complex in toluene are understood in terms of the 730 nm excitation light generating a primarily excited S(1) (pi,pi) state that transforms initially into a vibrationally hot (3)(d(z)2,d(x)2(-)(y)2) state. Cooling to the zeroth state is complete after ca. 8 ps. The cold (d,d) state converted to its daughter state, the (3)LMCT (pi,d(x)2(-)(y)2), which itself decays to the ground state with a lifetime of 640 ps. The proposed deactivation mechanism applies to the D(2)(d)-saddled and the D(4)(h)-planar structure as well. The results presented here for NiPc(BuO)(8) suggest that in nickel phthalocyanines the (1,3)LMCT (pi,d(x)2(-)(y)2) states may provide effective routes for radiationless deactivation of the (1,3)(pi,pi) states. PMID:16838978

  8. Crystal structure, spectroscopy, DFT studies and thermal characterization of Cobalt(II) complex with 2-protonated aminopyridinium cation as ligand

    NASA Astrophysics Data System (ADS)

    Mhadhbi, Noureddine; Saïd, Salem; Elleuch, Slim; Naïli, Houcine

    2016-03-01

    Single crystals of a new organic-inorganic hybrid compound (2-HAMP)2[CoBr4], (2-HAMP = 2-protonated aminopyridinium cation) was synthesized and characterized by X-Ray diffraction at room temperature, DTA-TG measurement, FT-IR and FT-Raman spectroscopies and optical absorption. Its crystal structure is a packing of alternated organic and inorganic layers parallel to (a, b) plane. The different components are connected by a network of N/C-H⋯Br hydrogen bonds and halogen⋯halogen interactions. These hydrogen bonds give notable vibrational effects. Theoretical calculations were performed using density functional theory (DFT) for studying the molecular structure, vibrational spectra and optical properties of the investigated molecule in the ground state. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental UV-Visible spectrum. The results show good consistent with the experiment and confirm the contribution of metal orbital to the HOMO-LUMO boundary. Thermal analysis studies indicate the presence of three phase transitions at 68, 125 and 172 °C, which are confirmed by X-ray powder diffraction as a function of temperature.

  9. Synthesis, structural, spectral characterization, DFT analysis and antimicrobial studies of aquabis(L-ornithine)copper(II) picrate

    NASA Astrophysics Data System (ADS)

    Kumar, Rakesh; Obrai, Sangeeta; Sharma, Aparna; Kaur Jassal, Amanpreet; Hundal, Maninder Singh; Mitra, Joyee

    2014-10-01

    The present work consists of synthesis, spectroscopic, DFT studies and crystal structure investigation of complex [Cu(L-orn)2(H2O)](PIC)2 (where L-orn = L-ornithine, PIC = picrate anion). The molecular structure of complex was determined by X-ray crystallography and refined by three-dimensional least squares techniques. Copper atom is five coordinate and two molecules of L-ornithine are coordinating with it through their carboxylate oxygens and amine nitrogens whereas the fifth site is occupied by water molecule. Both of the picrate anions are present outside the coordination sphere of metal ion resulting in formation of charge-separated type complex. EPR spectrum suggests about the distorted square-pyramidal geometry of the complex and is confirmed by X-ray crystallography. The optimized structure of the present complex has been studied using the DFT/B3LYP/6-31G*(d,p)/LANL2DZ level of theory. The vibrational assignments and HOMO-LUMO were theoretically examined by means of the hybrid DFT method. Also the antimicrobial properties of the title complex have been explored in the present work.

  10. Assessment of TD-DFT and LF-DFT for study of d − d transitions in first row transition metal hexaaqua complexes

    SciTech Connect

    Vlahović, Filip; Perić, Marko; Zlatar, Matija; Gruden-Pavlović, Maja

    2015-06-07

    Herein, we present the systematic, comparative computational study of the d − d transitions in a series of first row transition metal hexaaqua complexes, [M(H{sub 2}O){sub 6}]{sup n+} (M{sup 2+/3+} = V {sup 2+/3+}, Cr{sup 2+/3+}, Mn{sup 2+/3+}, Fe{sup 2+/3+}, Co{sup 2+/3+}, Ni{sup 2+}) by the means of Time-dependent Density Functional Theory (TD-DFT) and Ligand Field Density Functional Theory (LF-DFT). Influence of various exchange-correlation (XC) approximations have been studied, and results have been compared to the experimental transition energies, as well as, to the previous high-level ab initio calculations. TD-DFT gives satisfactory results in the cases of d{sup 2}, d{sup 4}, and low-spin d{sup 6} complexes, but fails in the cases when transitions depend only on the ligand field splitting, and for states with strong character of double excitation. LF-DFT, as a non-empirical approach to the ligand field theory, takes into account in a balanced way both dynamic and non-dynamic correlation effects and hence accurately describes the multiplets of transition metal complexes, even in difficult cases such as sextet-quartet splitting in d{sup 5} complexes. Use of the XC functionals designed for the accurate description of the spin-state splitting, e.g., OPBE, OPBE0, or SSB-D, is found to be crucial for proper prediction of the spin-forbidden excitations by LF-DFT. It is shown that LF-DFT is a valuable alternative to both TD-DFT and ab initio methods.

  11. Oxygen adsorption on single layer graphyne: a DFT study.

    PubMed

    Kang, Baotao; Liu, Hongguang; Lee, Jin Yong

    2014-01-21

    Graphyne is a rising two-dimensional (2D) carbon allotrope with excellent electronic properties. In this paper, theoretical calculations were performed to study the corresponding electronic properties of the oxygenated graphyne. Atomic oxygen when bound to the carbon atom of graphyne forms a stable oxide, with a much larger binding energy compared to that on graphene. Owing to the oxygen adsorption, the α- and β-graphyne change from a zero-band-gap material to a semiconductor as indicated in the band structure calculations. Moreover, spin splitting was observed from the band structure of the oxygenated γ-graphyne. These electronic properties are tunable by altering the oxygen coverage through changing the supercell size. Our results based on the first-principles calculations imply that oxygenation is a promising method to functionalize graphyne to achieve designated properties. PMID:24281199

  12. Synthesis and antibacterial activity of sulfonamides. SAR and DFT studies

    NASA Astrophysics Data System (ADS)

    Boufas, Wahida; Dupont, Nathalie; Berredjem, Malika; Berrezag, Kamel; Becheker, Imène; Berredjem, Hajira; Aouf, Nour-Eddine

    2014-09-01

    A series of substituted sulfonamide derivatives were synthesized from chlorosulfonyl isocyanate (CSI) in tree steps (carbamoylation, sulfamoylation and deprotection). Antibacterial activity in vitro of some newly formed compounds investigated against clinical strains Gram-positive and Gram-negative: Escherichia coli and Staphylococcus aureus applying the method of dilution and minimal inhibition concentration (MIC) methods. These compounds have significant bacteriostatic activity with totalities of bacterial strains used. DFT calculations with B3LYP/6-31G(d) level have been used to analyze the electronic and geometric characteristics deduced for the stable structure of three compounds presenting conjugation between a nitrogen atom N through its lone pair and an aromatic ring next to it. The principal quantum chemical descriptors have been correlated with the antibacterial activity.

  13. Copper-ceria interaction: A combined photoemission and DFT study

    NASA Astrophysics Data System (ADS)

    Szabová, Lucie; Skála, Tomáš; Matolínová, Iva; Fabris, Stefano; Farnesi Camellone, Matteo; Matolín, Vladimír

    2013-02-01

    Stoichiometric and partially reduced ceria films were deposited on preoxidized Ru(0 0 0 1) crystal by Ce evaporation in oxygen atmosphere of different pressures at 700 K. Copper-ceria interaction was investigated by deposition of metalic copper on both types of substrate. The samples were characterized by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) of core states and resonant photoelectron spectroscopy (RPES) of the valence bands. Copper adsorption on stoichiometric ceria caused reduction of CeO2, while on the oxygen-defficient ceria it partially reoxidized the substrate. This is in agreement with DFT+U calculations of copper adsorption on stoichiometric and defective ceria surfaces.

  14. DFT study of linear and nonlinear optical properties of donor-acceptor substituted stilbenes, azobenzenes and benzilideneanilines.

    PubMed

    Krawczyk, Przemysław

    2010-04-01

    A theoretical analysis of the linear and nonlinear optical properties of six push-pull pi-conjugated molecules with stilbene, azobenzene and benzilideneaniline as a backbone is presented. The photophysical properties of the investigated systems were determined by using response functions combined with density functional theory (DFT). Several different exchange-correlation potentials were applied in order to determine parameters describing the one- and two-photon spectra of the studied molecules. In particular, the recently proposed Coulomb-attenuated model (CAM-B3LYP) was used to describe charge-transfer (CT) excited states. In order to compare theoretical predictions with available experimental data, calculations with inclusion of solvent effects were performed. The BLYP and the CAM-B3LYP functionals were found to yield values of two-photon absorption (TPA) probabilities closer to experimental values than the B3LYP functional or the HF wavefunction. Moreover, molecular static hyperpolarisabilities were determined using both DFT and second-order Møller-Plesset perturbation (MP2) theory. Likewise, the CAM-B3LYP functional was found to outperform other applied exchange-correlation potentials in determining first hyperpolarisability (beta). Moreover, it was confirmed on a purely theoretical basis that the presence of a -C=C- bridge between the phenyl rings leads to a much larger nonlinear optical response in comparison with a -N=N- bridge. PMID:19957196

  15. Determination of Structural and Vibrational Properties of 5-QUINOLINECARBOXALDEHYDE Using Experimental Ft-Ir Ft-Raman Techniques and Theoretical HF and DFT Methods

    NASA Astrophysics Data System (ADS)

    Kumru, Mustafa; Kocademir, Mustafa; Bardakci, Tayyibe

    2013-06-01

    Quinoline derivatives have been used in several pharmaceuticals. They have vital roles in regulating the functions of DNA and cancerous cells. It's necessary to determine the structures and spectroscopic properties of quinoline derivates. In this study, the FT-IR (including mid and far regions) and FT-Raman spectra of 5-quinolinecarboxaldehyde have been investigated. Hartree-Fock (HF) and density functional B3LYP calculations have also been employed with the 6-311++G(d,p) basis set for investigating the structural and spectroscopic properties of the cis and trans conformers of 5-quinolinecarboxaldehyde. Experimental and theoretical results have been compared and the results are in good agreement with each other. Keywords: 5-quinolinecarboxaldehyde; Vibrational Spectroscopy; FT-IR spectra; FT-Raman spectra; Vibrational Modes; HF; DFT [1] V. Kucuk, A. Altun, M. Kumru, Spectrochim. Acta Part A 85(2012)92-98 [2] M. Kumru, V. Kucuk, T. Bardakci, Spectrochim. Acta Part A 90(2012)28-34 [3] M. Kumru, V. Kucuk, M. Kocademir, Spectrochim. Acta Part A, 96 (2012) 242-251 We thank the Turkish Scientific and Technical Research Council (TUBITAK) for their financial support through National Postdoctoral Research Scholarship Programme and Scientific Research Fund of Fatih University under the project number P50011001 G (1457).

  16. First principles DFT study of dye-sensitized CdS quantum dots

    SciTech Connect

    Jain, Kalpna; Singh, Kh. S.; Kishor, Shyam; Josefesson, Ida; Odelius, Michael; Ramaniah, Lavanya M.

    2014-04-24

    Dye-sensitized quantum dots (QDs) are considered promising candidates for dye-sensitized solar cells. In order to maximize their efficiency, detailed theoretical studies are important. Here, we report a first principles density functional theory (DFT) investigation of experimentally realized dye - sensitized QD / ligand systems, viz., Cd{sub 16}S{sub 16}, capped with acetate molecules and a coumarin dye. The hybrid B3LYP functional and a 6−311+G(d,p)/LANL2dz basis set are used to study the geometric, energetic and electronic properties of these clusters. There is significant structural rearrangement in all the clusters studied - on the surface for the bare QD, and in the positions of the acetate / dye ligands for the ligated QDs. The density of states (DOS) of the bare QD shows states in the band gap, which disappear on surface passivation with the acetate molecules. Interestingly, in the dye-sensitised QD, the HOMO is found to be localized mainly on the dye molecule, while the LUMO is on the QD, as required for photo-induced electron injection from the dye to the QD.

  17. Dimerization of Indanedioneketene to Spiro-oextanone: A Theoretical Study

    SciTech Connect

    Bakalbassis, Evangelos G; Malamidou-Xenikaki, Elizabeth; Spyroudis, Spyros; Xantheas, Sotiris S

    2010-08-20

    Indanedioneketene, a compound resulting from the thermal degradation of the phenyliodonium ylide of lawsone, dimerises quantitatively to a spiro-oxetanone derivative, a key compound for further transformations. A theoretical DFT study of this unusual for α-oxoketenes [2+2] cyclization reaction both in the gas phase and in dichloromethane solution, provides support for a) a single-step, transitionstate (involving a four-membered cyclic ring) charge controlled, concerted mechanism, and b) a [4+2] cyclization reaction, not observed but studied theoretically in this study. A parallel study of an open chain α,α'-dioxoketene dimerization explains the difference in the stability and reactivity observed experimentally between the cyclic and open chain products.

  18. Investigation of ground state charge transfer complex between paracetamol and p-chloranil through DFT and UV-visible studies

    NASA Astrophysics Data System (ADS)

    Shukla, Madhulata; Srivastava, Nitin; Saha, Satyen

    2012-08-01

    The present report deals with the theoretical investigation on ground state structure and charge transfer (CT) transitions in paracetamol (PA)/p-chloranil (CA) complex using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) method. It is found that Cdbnd O bond length of p-chloranil increases on complexation with paracetamol along with considerable amount of charge transfer from PA to CA. TD-DFT calculations have been performed to analyse the observed UV-visible spectrum of PA-CA charge transferred complex. Interestingly, in addition to expected CT transition, a weak symmetry relieved π-π* transition in the chloranil is also observed.

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

    NASA Astrophysics Data System (ADS)

    Asath, R. Mohamed; Premkumar, S.; Rekha, T. N.; Jawahar, A.; Mathavan, T.; Benial, A. Milton Franklin

    2016-05-01

    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 performed to confirm the NLO activity of the molecule. Hence, the ANA molecule is a promising candidate for the NLO materials.

  20. DFT study of cisplatin@carbon nanohorns complexes.

    PubMed

    De Souza, Leonardo A; Nogueira, Camila A S; Lopes, Juliana F; Dos Santos, Hélio F; De Almeida, Wagner B

    2013-12-01

    This paper reports a quantum chemical investigation of the inclusion complex formation between a carbon nanohorn structure and cisplatin molecule, using the density functional theory (DFT) with the B3LYP functional and 6-31G(d,p)/LanL2DZ standard basis sets. The inclusion of the drug in host molecules such as carbon nanohorns (CNHs), aims to reduce the toxicity and enhance the effectiveness of cisplatin. In this work we carried out a search for minimum energy structures on the potential energy surface (PES) for CNH-cisplatin interaction, and then calculated the stabilization energy, charge distribution and NMR spectra, which can be of great aid for the experimental identification of the inclusion compound. Our results indicate that the CNH and cisplatin can indeed form stable inclusion complex, with the calculated (1)H NMR and (15)N NMR chemical shifts for cisplatin atoms revealing very substantial changes due to complex formation (~20ppm) that can be easily experimentally observed, which is helpful to the spectra assignment and the inclusion compound structural elucidation. PMID:24091348

  1. Protonation of sodium ionophore III: Extraction and DFT study

    NASA Astrophysics Data System (ADS)

    Makrlík, Emanuel; Kvíčala, Jaroslav; Vaňura, Petr

    2014-08-01

    On the basis of extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium H3O+(aq) + 1ṡNa+(nb) ⇆ 1ṡH3O+(nb) + Na+(aq) occurring in the two-phase water-nitrobenzene system (1 = sodium ionophore III; aq = aqueous phase, nb = nitrobenzene phase) was determined as log Kex (H3O+, 1ṡNa+) = 0.0 ± 0.1. Further, the stability constant of the 1ṡH3O+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb (1ṡH3O+) = 6.4 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1ṡH3O+ was derived. In the resulting complex, the "central" cation H3O+ is bound by two linear hydrogen bonds and one bifurcated hydrogen bond to the corresponding four oxygens of the parent ligand 1. The interaction energy of the considered 1ṡH3O+ complex was found to be -556.6 kJ/mol, confirming also the formation of this cationic species.

  2. DFT study of glycosyl group reactivity in quercetin derivatives

    NASA Astrophysics Data System (ADS)

    Jeevitha, D.; Sadasivam, K.; Praveena, R.; Jayaprakasam, R.

    2016-09-01

    Density functional theory (DFT) is used to compute relevant electronic properties with the purpose of generating precise information which facilitates the best activity given by the positions of glycosyl group attached at all 3 different rings of quercetin such as Q3G (C- ring), Q7G (A-ring) and Q3‧G (B-ring). Computed values of the OH BDE, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP), Density of states (DOS,PDOS,OPDOS) and electronic properties such as electron affinity (EA), ionization potential (IP), softness (S), hardness (η), electronegativity (χ) and electrophilic index (ω) indicate that the title compounds possess good radical scavenging activity. Charge delocalization and intramolecular hydrogen bonds are characterized using natural bond orbital (NBO) analysis. NBO accurately differentiate the weak and strong intramolecular hydrogen bond of quercetin-O-glycoside compounds. Results available from the computational investigation have proved that A-ring glycoside of quercetin is capable of donating electrons and acts as a good anti-oxidant than B-ring glycoside and C-ring glycoside of quercetin.

  3. DFT and ab initio quantum chemical studies on p-cyanobenzoic acid

    NASA Astrophysics Data System (ADS)

    Arjunan, V.; Rani, T.; Varalakshmy, L.; Mohan, S.; Tedlamelekot, F.

    2011-05-01

    The Fourier transform infrared (FTIR) and FT-Raman spectra of p-cyanobenzoic acid (CBA) have been recorded in the range 4000-400 and 4000-100 cm -1, respectively. The complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT-Raman data. The vibrational frequencies determined experimentally were compared with theoretical wavenumbers obtained from ab initio HF and DFT-B3LYP gradient calculations employing 6-31G**, 6-311++G** and cc-pVTZ basis sets for the optimised geometry of the compound. The geometry and normal modes of vibration obtained from the HF and DFT methods are in good agreement with the experimental data. The normal coordinate analysis was also carried out with ab initio force fields utilising Wilson's FG matrix method. The interactions of cyano and carboxylic acid groups with the skeletal vibrational modes were investigated.

  4. Structural and spectroscopic characterization of a thiosemicarbazidatodioxouranium(VI) complex: a combined experimental and DFT study.

    PubMed

    Şahin, Musa; Özdemir, Namık; Bal-Demirci, Tülay; Ülküseven, Bahri; Dinçer, Muharrem; Soylu, Mustafa Serkan

    2015-01-25

    The title thiosemicarbazidatodioxouranium(VI) compound was synthesized and characterized by FT-IR, NMR and UV-vis spectroscopies. Solid-state structure of the compound was confirmed by X-ray crystallography. Besides, the molecular geometry, vibrational frequencies and gauge-independent atomic orbital (GIAO) (1)H and (13)C NMR chemical shift values of the compound in the ground state have been calculated using the density functional theory (DFT/B3LYP) method with the 6-311++G(d,p) basis set for the C, H, Cl, N, O, S atoms and SDD pseudo-potential for the U atom, and compared with the experimental data. Using the TD-DFT method, electronic absorption spectra of the compound have been predicted at same level. As a result, a good agreement is obtained between the experimental and theoretical ones. PMID:25168237

  5. Theoretical studies of combustion dynamics

    SciTech Connect

    Bowman, J.M.

    1993-12-01

    The basic objectives of this research program are to develop and apply theoretical techniques to fundamental dynamical processes of importance in gas-phase combustion. There are two major areas currently supported by this grant. One is reactive scattering of diatom-diatom systems, and the other is the dynamics of complex formation and decay based on L{sup 2} methods. In all of these studies, the authors focus on systems that are of interest experimentally, and for which potential energy surfaces based, at least in part, on ab initio calculations are available.

  6. Hydrogen adsorption in ZIF-7: A DFT and ab-initio molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Dixit, Mudit; Major, Dan Thomas; Pal, Sourav

    2016-05-01

    Primary H2 adsorption sites in a zeolitic imidazolate framework, ZIF-7, are identified using ab-initio density functional theory (DFT) based molecular dynamics annealing simulations. The simulations suggest several low energy adsorption sites. The effect of light transition metal decoration on hydrogen storage properties was studied. Our ab-intio DFT calculations illustrate that decorating the ZIF with Sc increases both the number of H2 molecules, as well as the H2 binding energy. The binding energy (∼25 kJ/mol per H2) at 8H2 loading in the pore, suggests that Sc-ZIFs can be potential candidates for hydrogen storage.

  7. SERS and DFT study of copper surfaces coated with corrosion inhibitor.

    PubMed

    Muniz-Miranda, Maurizio; Muniz-Miranda, Francesco; Caporali, Stefano

    2014-01-01

    Azole derivatives are common inhibitors of copper corrosion due to the chemical adsorption occurring on the metal surface that gives rise to a protective film. In particular, 1,2,4-triazole performs comparable to benzotriazole, which is much more widely used, but is by no means an environmentally friendly agent. In this study, we have analyzed the adsorption of 1,2,4-triazole on copper by taking advantage of the surface-enhanced Raman scattering (SERS) effect, which highlights the vibrational features of organic ligand monolayers adhering to rough surfaces of some metals such as gold, silver and copper. To ensure the necessary SERS activation, a roughening procedure was implemented on the copper substrates, resulting in nanoscale surface structures, as evidenced by microscopic investigation. To obtain sufficient information on the molecule-metal interaction and the formation of an anticorrosive thin film, the SERS spectra were interpreted with the aid of theoretical calculations based on the density functional theory (DFT) approach. PMID:25671144

  8. SERS and DFT study of copper surfaces coated with corrosion inhibitor

    PubMed Central

    Muniz-Miranda, Francesco; Caporali, Stefano

    2014-01-01

    Summary Azole derivatives are common inhibitors of copper corrosion due to the chemical adsorption occurring on the metal surface that gives rise to a protective film. In particular, 1,2,4-triazole performs comparable to benzotriazole, which is much more widely used, but is by no means an environmentally friendly agent. In this study, we have analyzed the adsorption of 1,2,4-triazole on copper by taking advantage of the surface-enhanced Raman scattering (SERS) effect, which highlights the vibrational features of organic ligand monolayers adhering to rough surfaces of some metals such as gold, silver and copper. To ensure the necessary SERS activation, a roughening procedure was implemented on the copper substrates, resulting in nanoscale surface structures, as evidenced by microscopic investigation. To obtain sufficient information on the molecule–metal interaction and the formation of an anticorrosive thin film, the SERS spectra were interpreted with the aid of theoretical calculations based on the density functional theory (DFT) approach. PMID:25671144

  9. Spectroscopic, thermal analysis and DFT computational studies of salen-type Schiff base complexes

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Hossein Pasha; Hadi, Jabbar S.; Abdulnabi, Zuhair A.; Bolandnazar, Zeinab

    2014-01-01

    A new series of metal(II) complexes of Co(II), Ni(II), Cu(II), Zn(II), and Pb(II) have been synthesized from a salen-type Schiff base ligand derived from o-vanillin and 4-methyl-1,2-phenylenediamine and characterized by elemental analysis, spectral (IR, UV-Vis, 1H NMR, 13C NMR and EI-mass), molar conductance measurements and thermal analysis techniques. Coats-Redfern method has been utilized to calculate the kinetic and thermodynamic parameters of the metal complexes. The molecular geometry, Mulliken atomic charges of the studied compounds were investigated theoretically by performing density functional theory (DFT) to access reliable results to the experimental values. The theoretical 13C chemical shift results of the studied compounds have been calculated at the B3LYP, PBEPBE and PW91PW91 methods and standard 6-311+G(d,p) basis set starting from optimized geometry. The comparison of the results indicates that B3LYP/6-311+G(d,p) yields good agreement with the observed chemical shifts. The measured low molar conductance values in DMF indicate that the metal complexes are non-electrolytes. The spectral and thermal analysis reveals that all complexes have octahedral geometry except Cu(II) complex which can attain the square planner arrangement. The presence of lattice and coordinated water molecules are indicated by thermograms of the complexes. The thermogravimetric (TG/DTG) analyses confirm high stability for all complexes followed by thermal decomposition in different steps.

  10. Spectroscopic studies on 9H-carbazole-9-(4-phenyl) boronic acid pinacol ester by DFT method

    NASA Astrophysics Data System (ADS)

    Sas, E. B.; Kurt, M.; Can, M.; Horzum, N.; Atac, A.

    2016-08-01

    9H-Carbazole-9-(4-phenyl) boronic acid pinacol ester (9-CPBAPE) molecule was investigated by FT-IR, Raman, UV-vis, 1H and 13C NMR spectra. FT-IR, FT-Raman and dispersive Raman spectra were recorded in the solid phase. 1H, 13C NMR and UV-vis spectra were recorded in dimethyl sulfoxide (DMSO) solution. The results of theoretical calculations for the spectra of the title molecule were compared with the experimental spectra. The highest occupied molecular orbital (HOMO) the lowest unoccupied molecular orbital (LUMO) and molecular electrostatic potential (MEP) analyses were performed. The theoretical calculations for the molecular structure and spectroscopic studies were performed with DFT (B3LYP) and 6-311G (d,p) basis set calculations using the Gaussian 09 program. The total (TDOS), partial (PDOS) density of state and overlap population density of state (OPDOS) diagrams analyses were performed using GaussSum 2.2 program.

  11. Ru L[subscript 2,3] XANES theoretical simulation with DFT: A test of the core-hole treatment

    SciTech Connect

    Alperovich, Igor; Moonshiram, Dooshaye; Soldatov, Alexander; Pushkar, Yulia

    2012-10-09

    Density functional theory (DFT)-based relativistic calculations were performed to model the Ru L-edge X-ray absorption near edge structure (XANES) spectra of the hexaammineruthenium complex [Ru(NH{sub 3}){sub 6}]{sup 3+} and 'blue dimer' water oxidation catalyst, cis,cis- [(bpy){sub 2}(H{sub 2}O)Ru{sup III}ORu{sup III}(OH{sub 2})(bpy){sub 2}]{sup 4+} (bpy is 2,2-bipyridine). Two computational approaches were compared: simulations without the core-hole and by modeling of the core-hole within the Z+1 approximation. Good agreement between calculated and experimental XANES spectra is achieved without including the core-hole. Simulations with algorithms beyond the Z+1 approximation were only possible in a framework of the scalar relativistic treatment. Time-dependent DFT (TD-DFT) was used to compute the Ru L-edge spectrum for [Ru(NH{sub 3}){sub 6}]{sup 3+} model compound. Three different core-hole treatments were compared in a real-space full multiple scattering XANES modeling within the Green function formalism (implemented in the FEFF9.5 package) for the [Ru(Mebimpy)(bpm)(H{sub 2}O)]{sup 2+} complex. The latter approaches worked well in cases where spin-orbit treatment of relativistic effects is not required.

  12. Theoretical Studies on Cluster Compounds

    NASA Astrophysics Data System (ADS)

    Lin, Zhenyang

    Available from UMI in association with The British Library. Requires signed TDF. The Thesis describes some theoretical studies on ligated and bare clusters. Chapter 1 gives a review of the two theoretical models, Tensor Surface Harmonic Theory (TSH) and Jellium Model, accounting for the electronic structures of ligated and bare clusters. The Polyhedral Skeletal Electron Pair Theory (PSEPT), which correlates the structures and electron counts (total number of valence electrons) of main group and transition metal ligated clusters, is briefly described. A structural jellium model is developed in Chapter 2 which accounts for the electronic structures of clusters using a crystal-field perturbation. The zero-order potential we derive is of central-field form, depends on the geometry of the cluster, and has a well-defined relationship to the full nuclear-electron potential. Qualitative arguments suggest that this potential produces different energy level orderings for clusters with a nucleus with large positive charge at the centre of the cluster. Analysis of the effects of the non-spherical perturbation on the spherical jellium shell structures leads to the conclusion that for a cluster with a closed shell electronic structure a high symmetry arrangement which is approximately or precisely close packed will be preferred. It also provides a basis for rationalising those structures of clusters with incomplete shell electronic configurations. In Chapter 3, the geometric conclusions derived in the structural jellium model are developed in more detail. The group theoretical consequences of the Tensor Surface Harmonic Theory are developed in Chapter 4 for (ML_2) _{rm n}, (ML_4) _{rm n} and (ML_5 ) _{rm n} clusters where either the xz and yz or x^2 -y^2 and xy components to L_sp{rm d}{pi } and L_sp{rm d} {delta} do not contribute equally to the bonding. The closed shell requirements for such clusters are defined and the orbital symmetry constraints pertaining to the

  13. Putting DFT to the Test: A First-Principles Study of Electronic, Magnetic, and Optical Properties of Co3O4

    NASA Astrophysics Data System (ADS)

    Singh, Vijay; Kosa, Monica; Majhi, Koushik; Major, Dan Thomas; Arie Zaban Collaboration, Prof.

    First-principles density functional theory (DFT) and a many-body Green's function method have been employed to elucidate the electronic, magnetic, and photonic properties of a spinel compound, Co3O4. Co3O4 is believed to be a strongly correlated material, where the on-site Coulomb interaction (U) on Co d orbitals is presumably important, although this view has recently been contested. The suggested optical band gap for this material ranges from 0.8 to 2.0 eV, depending on the type of experiments and theoretical treatment. Thus, the correlated nature of the Co d orbitals in Co3O4 and the extent of the band gap are still under debate, raising questions regarding the ability of DFT to correctly treat the electronic structure in this material. To resolve the above controversies, we have employed a range of theoretical methods, including pure DFT, DFT +U, and a range-separated exchange-correlation functional (HSE06) as well as many-body Green's function theory (i.e., the GW method). We compare the electronic structure and band gap of Co3O4 with available photoemission spectroscopy and optical band gap data and confirm a direct band gap of ca. 0.8 eV. Furthermore, we have also studied the optical properties of Co3O4 by calculating the imaginary part of the dielectric function (Im(ε)) , facilitating direct comparison with the measured optical absorption spectra.

  14. Theoretical studies of molecular collisions

    NASA Technical Reports Server (NTRS)

    Kouri, Donald J.

    1991-01-01

    The following subject areas are covered: (1) total integral reactive cross sections and vibrationally resolved reaction probabilities for F + H2 = HF + H; (2) a theoretical study of inelastic O + N2 collisions; (3) body frame close coupling wave packet approach to gas phase atom-rigit rotor inelastic collisions; (4) wave packet study of gas phase atom-rigit motor scattering; (5) the application of optical potentials for reactive scattering; (6) time dependent, three dimensional body frame quantal wave packet treatment of the H + H2 exchange reaction; (7) a time dependent wave packet approach to atom-diatom reactive collision probabilities; (8) time dependent wave packet for the complete determination of s-matrix elements for reactive molecular collisions in three dimensions; (9) a comparison of three time dependent wave packet methods for calculating electron-atom elastic scattering cross sections; and (10) a numerically exact full wave packet approach to molecule-surface scattering.

  15. DFT study of zigzag (n, 0) single-walled carbon nanotubes: (13)C NMR chemical shifts.

    PubMed

    Kupka, Teobald; Stachów, Michal; Stobiński, Leszek; Kaminský, Jakub

    2016-06-01

    (13)C NMR chemical shifts of selected finite-size models of pristine zigzag single walled carbon nanotubes (SWCNTs) with a diameter of ∼0.4-0.8nm and length up to 2.2nm were studied theoretically. Results for finite SWCNTs models containing 1, 4 and 10 adjacent bamboo-type units were compared with data obtained for infinite tubes in order to estimate the reliability of small finite models in predicting magnetic properties of real-size nanotubes and to assess their tube-length dependence. SWCNTs were fully optimized using unrestricted density functional theory (DFT-UB3LYP/6-31G*). Cyclacenes, as the shortest models of open-ended zigzag SWCNTs, with systematically varying diameter were calculated as well. GIAO NMR calculations on the SWCNT and cyclacene models were performed using the BHandH density functional combined with relatively small STO-3Gmag basis set, developed by Leszczyński and coworkers for accurate description of magnetic properties. Regular changes of carbon (13)C chemical shifts along the tube axis of real size (6, 0) and (9, 0) zigzag carbon nanotubes were shown. The (13)C NMR shifts according to increasing diameter calculated for zigzag (n, 0, n=5-10) cyclacenes followed the trends observed for zigzag (n, 0) SWCNTs. The results for 4-units long SWCNTs match reasonably well with the data obtained for infinite zigzag (n, 0) SWCNTs, especially to those with bigger diameter (n=8-15). The presence of rim hydrogens obviously affects theoretical (13)C chemical shieldings and shifts in cyclacenes and thus cyclacenes can provide only approximate estimation of (13)C NMR parameters of real-size SWCNTs. The NMR properties predicted for the longest 10-units long models of SWCNTs reliably correspond to results obtained for infinite nanotubes. They were thus able to accurately predict also recently reported experimental chemical shift of chiral (6, 5) SWCNT. PMID:27155813

  16. A Theoretical Study on Seasonality

    PubMed Central

    Schmal, Christoph; Myung, Jihwan; Herzel, Hanspeter; Bordyugov, Grigory

    2015-01-01

    In addition to being endogenous, a circadian system must be able to communicate with the outside world and align its rhythmicity to the environment. As a result of such alignment, external Zeitgebers can entrain the circadian system. Entrainment expresses itself in coinciding periods of the circadian oscillator and the Zeitgeber and a stationary phase difference between them. The range of period mismatches between the circadian system and the Zeitgeber that Zeitgeber can overcome to entrain the oscillator is called an entrainment range. The width of the entrainment range usually increases with increasing Zeitgeber strength, resulting in a wedge-like Arnold tongue. This classical view of entrainment does not account for the effects of photoperiod on entrainment. Zeitgebers with extremely small or large photoperiods are intuitively closer to constant environments than equinoctial Zeitgebers and hence are expected to produce a narrower entrainment range. In this paper, we present theoretical results on entrainment under different photoperiods. We find that in the photoperiod-detuning parameter plane, the entrainment zone is shaped in the form of a skewed onion. The bottom and upper points of the onion are given by the free-running periods in DD and LL, respectively. The widest entrainment range is found near photoperiods of 50%. Within the onion, we calculated the entrainment phase that varies over a range of 12 h. The results of our theoretical study explain the experimentally observed behavior of the entrainment phase in dependence on the photoperiod. PMID:25999912

  17. Vibrational spectroscopic investigations, ab initio and DFT studies on 7-bromo-5-chloro-8-hydroxyquinoline.

    PubMed

    Arjunan, V; Mohan, S; Ravindran, P; Mythili, C V

    2009-05-01

    The Fourier transform infrared (FTIR) and FT-Raman spectra of 7-bromo-5-chloro-8-hydroxyquinoline (BCHQ) have been measured in the range 4000-400 and 4000-100cm(-1), respectively. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT-Raman data. The geometry was optimised without any symmetry constrains using the DFT/B3LYP and HF methods with 6-31G** basis set. The vibrational frequencies which were determined experimentally are compared with those obtained theoretically from ab initio HF and density functional theory (DFT) gradient calculations employing the HF/6-31G** and B3LYP/6-31G** methods for the optimised geometry of the compound. The structural parameters and normal modes of vibration obtained from HF and DFT methods are in good agreement with the experimental data. Normal coordinate analysis was also carried out with ab initio force fields utilising Wilson's FG matrix method. PMID:19112045

  18. Vibrational spectroscopic investigations, ab initio and DFT studies on 7-bromo-5-chloro-8-hydroxyquinoline

    NASA Astrophysics Data System (ADS)

    Arjunan, V.; Mohan, S.; Ravindran, P.; Mythili, C. V.

    2009-05-01

    The Fourier transform infrared (FTIR) and FT-Raman spectra of 7-bromo-5-chloro-8-hydroxyquinoline (BCHQ) have been measured in the range 4000-400 and 4000-100 cm -1, respectively. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FTIR and FT-Raman data. The geometry was optimised without any symmetry constrains using the DFT/B3LYP and HF methods with 6-31G** basis set. The vibrational frequencies which were determined experimentally are compared with those obtained theoretically from ab initio HF and density functional theory (DFT) gradient calculations employing the HF/6-31G** and B3LYP/6-31G** methods for the optimised geometry of the compound. The structural parameters and normal modes of vibration obtained from HF and DFT methods are in good agreement with the experimental data. Normal coordinate analysis was also carried out with ab initio force fields utilising Wilson's FG matrix method.

  19. Experimental (FT-IR and FT-Raman), electronic structure and DFT studies on 1-methoxynaphthalene

    NASA Astrophysics Data System (ADS)

    Govindarajan, M.; Ganasan, K.; Periandy, S.; Karabacak, M.

    2011-08-01

    In this work, FT-IR and FT-Raman spectra of 1-methoxynapthalene (C 11H 10O) have been reported in the regions 4000-400 cm -1 and 3500-100 cm -1, respectively. Density functional method (DFT) has been used to calculate the optimized geometrical parameters, atomic charges, vibrational wavenumbers and intensity of the vibrational bands. The vibrational frequencies have been calculated and scaled values are compared with experimental FT-IR and FT-Raman spectra. The structure optimizations and normal coordinate force field calculations are based on density functional theory (DFT) method with B3LYP/3-21G, B3LYP/6-31G, B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p) basis sets. The complete vibrational assignments of wavenumbers are made on the basis of potential energy distribution (PED). The optimized geometric parameters are compared with experimental values of naphthoic acid. The results of the calculation shows excellent agreement between experimental and calculated frequencies in B3LYP/6-311++G(d,p) basis set. The effects due to the substitutions of methyl group and carbon-oxygen bond are also investigated. A study on the electronic properties, such as excitation energies and wavelengths, were performed by time-dependent DFT (TD-DFT) approach. HOMO and LUMO energies are calculated that these energies show charge transfer occurs within the molecule.

  20. Interaction of selected gases with zinc phthalocyanine thin films: theoretical and experimental studies

    NASA Astrophysics Data System (ADS)

    Šebera, Jakub; Fitl, Přemysl; Vlček, Jan; Vrňata, Martin; Fendrych, František; Kopeček, Jaromír; Kratochvílová, Irena

    2013-10-01

    In this work we studied both theoretically and experimentally interactions between zinc phthalocyanine (ZnPc) and selected gases (Ar, He, N2, O2, H2, NO2). Specifically, we focused on electrical conductivity as important macroscopical physical parameter reflecting ZnPc/gas complexes interaction states. To interpret the measured data and determine the main parameters that influence the resistivity/charge transport ability of ZnPc in a specific gas atmosphere, the density functional theory (DFT) has been used. Combining experimental results and DFT modeling we were able to characterize states/parameters influencing charge transport conditions from new and comprehensive perspectives.

  1. DFT STUDY REVISES INTERSTITIAL CONFIGURATIONS IN HCP Zr

    SciTech Connect

    Samolyuk, German D; Golubov, Stanislav I; Osetskiy, Yury N; Stoller, Roger E

    2012-06-01

    Analysis of experimental result on microstructure evolution in irradiated Zr and alloys has demonstrated that available knowledge on self-interstitial defects in Zr is in contradiction. We therefore have initiated an extensive theoretical and modeling program to clarify this issue. In this report we present first ab initio calculations results of single SIA configurations in Zr. We demonstrate importance of simulations cell size, applied exchange-correlation functional and simulated c/a ratio. The results obtained demonstrate clearly that the most stable configurations are in basal plane and provide some evidences for enhanced interstitial transport along basal planes. The results obtained will be used in generation a new interatomic potential for Zr to be used in large-scale atomistic modeling of mechanisms relevant for radiation-induced microstructure evolution.

  2. Crystal structure, vibrational studies, optical properties and DFT calculations of 2-amino-5-diethyl-aminopentanium tetrachlorocadmate (II).

    PubMed

    Baklouti, Yosra; chaari, Najla; Feki, Habib; Chniba-Boudjada, Nassira; Zouari, Fatma

    2015-02-01

    Single crystals of a new organic-inorganic compound (C9H24N2) CdCl4 were grown by the slow evaporation technique and characterized by X-ray diffraction, infrared absorption Raman spectroscopy scattering, optical absorption, differential scanning calorimetry (DSC) analysis and dielectric measurements. The title compound belongs to the orthorhombic space group Pbca with the following unit cell parameters: a=11.397(7), b=13.843(4), c=22.678(5)Å and Z=8. In crystal structure, the tetrachlorocadmate anion is connected to organic cations through N-H⋯Cl hydrogen bonds. Theoretical calculations were performed using density functional theory (DFT) with the B3LYP/LanL2DZ level of theory for studying the molecular structure and vibrational spectra of the title compound. Good consistency is found between the calculated results and the experimental structure, IR, and Raman spectra. The detailed interpretation of the vibrational modes was carried out on the basis on our DFT calculations as primary source of assignment and by comparison with spectroscopic studies of similar compounds. The optical properties were investigated by optical absorption and show three bands at 300, 329 and 513 nm. PMID:25311521

  3. DFT modeling, UV-Vis and IR spectroscopic study of acetylacetone-modified zirconia sol-gel materials.

    PubMed

    Georgieva, Ivelina; Danchova, Nina; Gutzov, Stoyan; Trendafilova, Natasha

    2012-06-01

    Theoretical and spectroscopic studies of a series of monomeric and dimeric complexes formed through the modification of a zirconium butoxide precursor with acetylacetone and subsequent hydrolysis and/or condensation have been performed by applying DFT/B3LYP/6-31++G(d) and highly accurate RI-ADC(2) methods as well as IR and UV-Vis transmittance and diffuse reflectance spectroscopies. Based on DFT model calculations and simulated and experimental UV-Vis and IR spectra of all the studied structures, the most probable building units of the Zr(IV)-AcAc gel were predicted: the dimeric double hydroxo-bridged complex Zr(2)(AcAc)(2)(OH)(4)(OH)(2br) 9 and the monooxo-bridged complex Zr(2)(AcAc)(2)(OH)(4)O(br)·2H(2)O 12. In both structures, the two AcAc ligands are coordinated to one Zr atom. It was shown that building units 9 and 12 determine the photophysical and vibrational properties of the gel material. The observed UV-Vis and IR spectra of Zr(IV)-AcAc gel were interpreted and a relation between the spectroscopic and structural data was derived. The observed UV-Vis bands at 315 nm and 298/288 nm were assigned to partial ligand-metal transitions and to intra-/inter-AcAc ligand transitions, respectively. PMID:21989960

  4. A DFT study on dihydropyrazine annulated linear polyacenes: aromaticity, stability and HOMO-LUMO energy modulation.

    PubMed

    Rakhi, Ramachandran; Suresh, Cherumuttathu H

    2016-09-21

    Linear polyacenes (LPAs) beyond pentacene are highly unstable and their application potential in the optoelectronics field is very limited. On the basis of theoretical studies at the M06L/6-311++G(d,p) level of DFT, we show that annulating dihydropyrazine units to LPA cores can yield large LPA mimics. This strategy enhances the aromaticity of the LPA core and also provides a way to modulate the HOMO-LUMO energy gap by choosing an appropriate LPA core and extending dihydropyrazine annulation. The study is conducted for LPA mimics containing up to six dihydropyrazine units annulated to benzene (pB1-pB6), naphthalene (pN1-pN6), anthracene (pA1-pA6) and tetracene (pT1-pT6) cores. The longest of them pT6 contains 34 linearly connected six-membered rings. The dehydrogenation energy (Edh) of the N-heterocycles of the LPA mimics showed endothermic character and indicated their higher stability than dehydrogenated N-heteroacenes. The total Edh (ΣEdh) is proportional to the increase in the number of heterocycles and the increase in the size of the LPA core. The aromaticity of individual rings of all the LPA mimics is assessed on the basis of the harmonic oscillator model of aromaticity (HOMA) and nucleus independent chemical shift (NICS) parameters. Both parameters showed strong linear correlation with ΣEdh, confirming the geometric, magnetic and energetic criteria of aromaticity. The electronic features of the LPA mimics assessed by analysing molecular electrostatic potential topography and molecular orbitals have shown that the LPA cores retain the reactivity of the parent LPA. Furthermore, significant mixing of the N-lone pairs of the heterocycle with carbon π-orbitals improves aromaticity and decreases the HOMO-LUMO energy gap. PMID:27546099

  5. DFT studies on vibrational spectra, HOMO-LUMO, NBO and thermodynamic function analysis of cyanuric fluoride

    NASA Astrophysics Data System (ADS)

    Prabhaharan, M.; Prabakaran, A. R.; Gunasekaran, S.; Srinivasan, S.

    2015-02-01

    In this work, the theoretical vibrational spectral characteristics of cyanuric fluoride (C3N3F3) have been investigated and compared with existing experimental results. The density functional theoretical (DFT) computations were performed at the B3LYP level with the basis sets 6-31G(d,p) and 6-311++G(d,p) levels to derive the optimized geometry, vibrational wavenumbers with IR intensities of cyanuric fluoride. In addition, the molecular orbital calculations such as Natural Bond Orbitals (NBOs), HOMO-LUMO energy gap and Mapped molecular Electrostatic Potential (MEP) surfaces were also performed with the same level of DFT. Electronic stability of the compound arising from hyper conjugative interactions and charge delocalization were also investigated based on the natural bond orbital (NBO) analysis. Effective stabilization energy E(2) connected with the interactions of the π and the lone pair of electrons was determined by the NBO analysis. Mulliken population analysis on atomic charges is also calculated. The thermodynamic properties of the cyanuric fluoride at different temperatures have also been calculated for the range of temperature 50-1000 K.

  6. Antiplasmodial Drugs in the Gas Phase: A CID and DFT Study of Quinolon-4( 1H)-Imine Derivatives

    NASA Astrophysics Data System (ADS)

    Amorim Madeira, Paulo J.; Sitoe, Ana Raquel Fernandes; Gonçalves, Daniel; Rodrigues, Tiago; Guedes, Rita C.; Lopes, Francisca; Moreira, Rui; Bronze, M. Rosário

    2014-09-01

    The gas-phase behavior of 12 quinolon-4( 1H)-imine derivatives with antiplasmodial activity was investigated using electrospray ionization tandem mass spectrometry together with collision induced dissociation and density functional theory (DFT) calculations. The most probable protonation site was predicted by calculating the proton affinity (PA) values for each possible protonation site and it was found to be the imine nitrogen for all compounds under study. Fragmentation pathways of the protonated molecules were proposed and the assignment of product ion structures was performed taking into account theoretical calculations. The nature of the quinoline substituent was found to influence the gas-phase behavior of the compounds under study. The data acquired allowed to bracket the proton affinity of the quinolin-4-imine scaffold, which can be a useful starting point to choose appropriate references for determining PA values of this scaffold.

  7. Detailed structural study of β-artemether: Density functional theory (DFT) calculations of Infrared, Raman spectroscopy, and vibrational circular dichroism

    NASA Astrophysics Data System (ADS)

    Wang, Zhiqiang; Chen, Jianchao; Li, Linwei; Zhou, Zhixu; Geng, Yiding; Sun, Tiemin

    2015-10-01

    In this study, the experimental and theoretical studies on the structure of β-artemether are presented. The optimized molecular structure, Mulliken atomic charges, vibrational spectra (IR, Raman and vibrational circular dichroism), and molecular electrostatic potential have been calculated by density functional theory (DFT) using B3LYP method with the 6-311++G (2d, p) basis set. Reliable vibrational assignments for Artemether have been made on the basis of potential energy distribution (PED). The vibrational circular dichroism (VCD) has been explored by ab initio calculations, and then was used to compare with the experimental VCD. The consistence between them confirmed the absolute configuration of Artemether. In addition, HOMO-LUMO of the title compound as well as thermo-dynamical parameters has illustrated the stability of β-artemether.

  8. Study of structure-activity relationship of enantiomeric, protonated and deprotonated forms of warfarin via vibrational spectroscopy and DFT calculations

    NASA Astrophysics Data System (ADS)

    Mishra, Alok; Srivastava, Sunil Kumar; Swati, D.

    2013-09-01

    The structure-activity relationship of the anticoagulant drug warfarin were studied by studying two enantiomeric forms (S-form and R-form) of warfarin and its protonated as well as deprotonated structures in aqueous media using density functional theory (DFT). Theoretically computed Raman and IR spectra of all the computed structures were compared and their specific vibrational spectroscopic signatures were discussed. The percentage contributions of individual normal modes of warfarin, which provides direct evidence of the different molecular activity due to change in relative atomic position of atoms in molecule, were investigated through potential energy distribution (PED). The optimized energy and molecular electrostatic potential (MEP) maps show that the S-form of the drug molecules warfarin is energetically more stable than R-form and provides higher docking opportunity for the molecular binding with the receptors in the bio-systems.

  9. Potential routes to carbon inclusion in apatite minerals: a DFT study

    NASA Astrophysics Data System (ADS)

    Rabone, J. A. L.; de Leeuw, N. H.

    2007-09-01

    We have conducted a computational study to investigate a number of possible routes for the incorporation of carbon into apatites. Using density functional theory (DFT) we have calculated geometry optimised structures for fluor- and hydroxy-apatites with and without various substitutions. We have studied several different carbonate substitutions, pure carbonate and pure formate apatites, neutral carbon atoms occupying interstices, and carbon dioxide and acetylene absorbed in oxyapatite.

  10. Methanol adsorption on magnesium oxide surface with defects: a DFT study

    NASA Astrophysics Data System (ADS)

    Branda, M. M.; Ferullo, R. M.; Belelli, P. G.; Castellani, N. J.

    2003-03-01

    The methanol adsorption on several defects of the magnesium oxide surface were studied. Structural and electronic study with geometrical optimization and natural bond orbital (NBO) analysis were performed using a density functional theory (DFT) method. Oxygen and magnesium with different coordination numbers have very different reactivity in this surface producing dissociated and non-dissociated species. These results are in agreement with infrared spectroscopy observations where CH 3OH, OCH 3 and OH species were found in defective MgO surfaces.

  11. A Comprehensive Study of Copper Guanidine Quinoline Complexes: Predicting the Activity of Catalysts in ATRP with DFT.

    PubMed

    Rösener, Thomas; Bienemann, Olga; Sigl, Kerstin; Schopp, Nora; Schnitter, Fabian; Flörke, Ulrich; Hoffmann, Alexander; Döring, Artjom; Kuckling, Dirk; Herres-Pawlis, Sonja

    2016-09-12

    Copper complexes of the hybrid guanidine ligands 1,3-dimethyl-N-(quinolin-8-yl)-imidazolidin-2-imine (DMEGqu) and 1,1,3,3-tetramethyl-2-(quinolin-8-yl)-guanidine (TMGqu) have been studied comprehensively with regard to their structural and electrochemical properties and their activity in atom transfer radical polymerization (ATRP). A simple analysis of the molecular structures of the complexes gives no indication about their activity in ATRP; however, with the help of DFT and NBO analysis the influence of particular coordinating donors on the electrochemical properties could be fully elucidated. With an adequate DFT methodology and newly applied theoretical isodesmic reactions it was possible to predict the relative position of the redox potentials of copper complexes containing DMEGqu and TMGqu ligands. In addition, predictions could be made as to whether the complexes of DMEGqu or TMGqu are more active in ATRP. Four new Cu(I) complexes were tested in standard ATRP reactions and kinetically investigated both in bulk and in solution. It could be proven that complexes featuring DMEGqu possess a lower redox potential and are more active in ATRP, although the tetramethylguanidine moiety represents the stronger donor. PMID:27505859

  12. TDDFT study of UV-vis spectra of permethrin, cypermethrin and their beta-cyclodextrin inclusion complexes: A comparison of dispersion correction DFT (DFT-D3) and DFT

    NASA Astrophysics Data System (ADS)

    Chen, Feifei; Wang, Yujiao; Xie, Xiaomei; Chen, Meng; Li, Wei

    2014-07-01

    A comparative study of DFT and DFT-D3 has been carried out on the UV-vis absorption of permethrin, cypermethrin and their β-cyclodextrin inclusion complexes. The TDDFT method with PCM (or COSMO) model was adopted and B3LYP, BLYP and BLYP-D3 functionals were selected. Comparing the simulated spectra with experimental one, we can notice that pure BLYP functional can better reproduce the UV-vis spectra than hybrid B3LYP, but empirical dispersion corrections BLYP-D3 has better performance than BLYP. BLYP-D3 calculations reveal that the main absorption bands of permethrin and cypermethrin arise from the π → π* transition, after encapsulated by β-CD to form inclusion complexes, the host-guest intermolecular charge transfer (ICT) makes the main absorption bands to be changed significantly in wavelength and intensity.

  13. Chemical, spectroscopic characterization, DFT studies and antibacterial activities in vitro of a new gold(I) complex with rimantadine.

    PubMed

    Sucena, Suelen F; Paiva, Raphael E F; Abbehausen, Camilla; Mattos, Ives B; Lancellotti, Marcelo; Formiga, André L B; Corbi, Pedro P

    2012-04-01

    A novel gold(I) complex with rimantadine (RTD) was obtained and structurally characterized by a set of chemical and spectroscopic analysis. 1H, 13C and 15N nuclear magnetic resonance (NMR) and infrared (IR) spectroscopic measurements suggest coordination of the ligand to Au(I) through the N atom of the ethanamine group. Theoretical (DFT) calculations confirmed the IR assignments and permit proposing an optimized geometry for the complex. The gold(I)-rimantadine complex (Au-RTD) is soluble in methanol, ethanol, dimethylsulfoxide, acetone and acetonitrile. The preliminary kinetic studies based on UV-vis spectroscopic measurements indicate the stability of the compound in solution. Antibacterial activities of the complex were evaluated by an antibiogram assay. The Au-RTD complex showed an effective in vitro antibacterial activity against the Pseudomonas aeruginosa, Escherichia coli (Gram-negative), and Staphylococcus aureus (Gram-positive) bacterial strains. PMID:22257715

  14. A Combined Theoretical and Experimental Study for Silver Electroplating

    PubMed Central

    Liu, Anmin; Ren, Xuefeng; An, Maozhong; Zhang, Jinqiu; Yang, Peixia; Wang, Bo; Zhu, Yongming; Wang, Chong

    2014-01-01

    A novel method combined theoretical and experimental study for environmental friendly silver electroplating was introduced. Quantum chemical calculations and molecular dynamic (MD) simulations were employed for predicting the behaviour and function of the complexing agents. Electronic properties, orbital information, and single point energies of the 5,5-dimethylhydantoin (DMH), nicotinic acid (NA), as well as their silver(I)-complexes were provided by quantum chemical calculations based on density functional theory (DFT). Adsorption behaviors of the agents on copper and silver surfaces were investigated using MD simulations. Basing on the data of quantum chemical calculations and MD simulations, we believed that DMH and NA could be the promising complexing agents for silver electroplating. The experimental results, including of electrochemical measurement and silver electroplating, further confirmed the above prediction. This efficient and versatile method thus opens a new window to study or design complexing agents for generalized metal electroplating and will vigorously promote the level of this research region. PMID:24452389

  15. DFT and post-DFT studies of metallic MXY3-type compounds for low temperature TE applications

    NASA Astrophysics Data System (ADS)

    Bilal, M.; Saifullah; Ahmad, Iftikhar; Jalali-Asadabadi, S.; Ahmad, Rashid; Shafiq, M.

    2016-10-01

    In this paper, thermoelectric properties of carbon and nitrogen based twenty metallic antiperovskites MXY3 (M=Al, Ga, Ir, Mg, Pd, Pt, Rh; X=C, N; Y=Mn, Ni, Sc, Ti, Cr, Fe) using ab-initio density functional theory and post-DFT Boltzmann's techniques are investigated. The electronic properties of these compounds are also discussed. We find high values of Seebeck coefficient and small values of electronic thermal conductivity for AlCTi3, AlNSc3, AlCNi3, AlNTi3, GaCCr3 and MgCNi3 between -0.25 and 0.25 eV chemical potential. These results show high dimensionless figure of merit in metallic materials and therefore, we predict these materials can be potential candidates for low temperature thermoelectric applications.

  16. Study of electronic effects in a catalytic diode: DFT calculations and MEIRAS experiments

    NASA Astrophysics Data System (ADS)

    Deshlahra, Prashant

    The role of electron transfer between metal catalyst and its oxide support in modifying the binding of the molecules adsorbed on the catalyst surface is investigated using Pt/TiO2 catalytic diode as a novel model catalyst system. The effect of electron transfer is interpreted and demonstrated as that of creating an electric field at the metal-support interface. The effect of such electric fields is studied by using Density Functional Theory (DFT) calculations to simulate adsorption of different molecules under a uniform external electric field. Experimentally, the charge transfer at metal support junction and the resulting electric field is controlled by applying an external bias voltage to the catalytic diode. The effect of controlling the charge transfer on CO molecules used as probe adsorbates is studied using a multilayer enhanced reflection adsorption spectroscopy (MEIRAS) technique developed in this work. DFT calculations show that the sensitivity of adsorption energy of a molecule on a metal surface to the external electric field depends on its dipole moment and polarizability. The dipole moment varies significantly from one molecule to another, and changes with the surface adsorbate coverage due to the electrostatic interaction from neighboring adsorbates on the surface. Vibrational frequency of molecules shifting linearly with external electric field is shown to be a key experimental observable useful in the study of these effects. MEIRAS is a new form of the Fourier Transform Infrared (FTIR) spectroscopy performed in reflection mode, in which, the multilayer structure of the sample and its interaction with the incident infrared causes a large enhancement in the sensitivity. The mechanism of sensitivity enhancement is elucidated through experimental measurement of wavelength dependent reflectance of multilayer structures and theoretical optical analysis of infrared reflection on such structures. An experimental setup is developed for MEIRAS measurements

  17. Vibrational spectroscopy and theoretical studies on 2,4-dinitrophenylhydrazine

    NASA Astrophysics Data System (ADS)

    Chiş, V.; Filip, S.; Miclăuş, V.; Pîrnău, A.; Tănăselia, C.; Almăşan, V.; Vasilescu, M.

    2005-06-01

    In this work, we will report a combined experimental and theoretical study on molecular and vibrational structure of 2,4-dinitrophenylhydrazine. FT-IR, FT-IR/ATR and Raman spectra of normal and deuterated DNPH have been recorded and analyzed in order to get new insights into molecular structure and properties of this molecule, with particular emphasize on its intra- and intermolecular hydrogen bonds (HB's). For computational purposes we used density functional theory (DFT) methods, with B3LYP and BLYP exchange-correlation functionals, in conjunction with 6-31G(d) basis set. All experimental vibrational bands have been discussed and assigned to normal modes on the basis of DFT calculations and isotopic shifts and by comparison to other dinitro- substituted compounds [V. Chiş, Chem. Phys., 300 (2004) 1]. To aid in mode assignments, we based on the direct comparison between experimental and calculated spectra by considering both the frequency sequence and the intensity pattern of the experimental and computed vibrational bands. It is also shown that semiempirical AM1 method predicts geometrical parameters and vibrational frequencies related to the HB in a pleasant agreement with experiment, being surprisingly accurate from this perspective.

  18. Unravelling the structure of protic ionic liquids with theoretical and experimental methods: ethyl-, propyl- and butylammonium nitrate explored by Raman spectroscopy and DFT calculations.

    PubMed

    Bodo, E; Mangialardo, S; Ramondo, F; Ceccacci, F; Postorino, P

    2012-11-29

    We present an analysis of gas-phase structures of small clusters of n-alkylammonium nitrates (ethyl, propyl, and butyl) together with vibrational Raman spectroscopy of their respective liquid phases. The assignment and interpretation of the resonant frequencies have been performed by comparison with high-quality ab initio (DFT) computations. The theoretical spectra are in excellent agreement with the measured ones and allow the interpretation and assignment of almost all the spectral features. A careful analysis of the vibrational frequencies and of the electronic structure of the compounds has provided additional information on various structural features and on the rather complex hydrogen bonding network that exists in such compounds. A geometric structure of the short-range local arrangement in the bulk phases is also proposed. PMID:22973943

  19. FT-Raman, FT-IR spectroscopic and DFT studies of hexaphenoxycyclotriphosphazene

    NASA Astrophysics Data System (ADS)

    Furer, V. L.; Vandyukov, A. E.; Padie, C.; Majoral, J. P.; Caminade, A. M.; Kovalenko, V. I.

    2016-07-01

    The FTIR and FT Raman measurements of zero Gc0‧ -H and first Gc1‧ -H generations of phosphorus dendrimer built from cyclotriphosphazene core with phenoxy and deuterophenoxy terminal groups have been performed. In order to evaluate how much the frequencies, shift when changing the electronics of the system the FTIR and FT Raman spectra of phosphorus‒containing dendron with five terminal oxybenzaldehyde and one ester function Gci‧ have been also studied. Structural optimization and normal mode analysis were obtained for Gc0‧ -H and Gc0‧ -D by the density functional theory (DFT). It is discovered that dendrimer molecule exists in a stable conformation with six phenoxy terminal groups spaced above and below the flat cyclotriphosphazene core. Optimized geometric bond length and angles obtained by DFT show good agreement with a previously-published X-ray study. The phenoxy terminal groups are characterized by the well-defined line at 993 cm-1 in the experimental Raman spectrum of Gc0‧ -H and by line at 960 cm-1 in the Raman spectrum of Gc0‧ -D. Relying on DFT calculations a complete vibrational assignment is proposed for the studied dendrimers. The frequencies and relative intensity of the bands at 1589, 1487 cm-1 in the IR spectra show marked difference in dependence of the substituents on the aromatic ring.

  20. Interaction of Boron Clusters with Oxygen: a DFT Study

    NASA Astrophysics Data System (ADS)

    Salavitabar, Kamron; Boggavarapu, Kiran; Kandalam, Anil

    A controlled combustion involving aluminum nanoparticles has often been the focus of studies in the field of solid fuel propellants. However very little focus has been given to the study of boron nanoparticles in controlled combustion. In contrast to aluminum nanoclusters, boron nanoclusters (Bn) are known to exhibit a planar geometries even at the size of n = 19 - 20, and thus offer a greater surface area for interaction with oxygen. Earlier experimental studies have shown that boron nanoclusters exhibit different reactivity with oxygen depending on their size and charge. In this poster, we present our recent density functional theory based results, focusing on the reactivity patterns of neutral and negatively charged B5 cluster with On, where n = 1 - 5; and B6 cluster with On (n = 1 - 2). The effect of charge on the reactivity of boron cluster, variation in the stability of product clusters, i e., neutral and negatively charged B5On (n = 1 - 5) and B6On (n = 1 - 2) are also examined. Financial Support from West Chester University Foundation under FaStR grant is acknowledged.

  1. a Comprehensive DFT Study of Zinc Oxide in Different Phases

    NASA Astrophysics Data System (ADS)

    Ul Haq, Bakhtiar; Afaq, A.; Ahmed, R.; Naseem, S.

    2012-06-01

    A density functional study for structural and electronic properties of Zinc Oxide (ZnO), in wurtzite, rock salt and zinc-blende phases has been performed using full potential-linearized augmented plane wave/linearized augmented plane wave plus local ideal orbital (FP-LAPW/L(APW+lo) approach as realized in WIEN2k code. To approximate exchange correlation energy and corresponding potential, a special GGA parameterized by Wu-Cohen has been implemented. Our results of lattice constants, bulk moduli as well as for internal parameter with GGA-WC are found to be more reliable. This study reveals that value of internal parameter decreases with increasing volume whereas computed electronic band structure confirms the direct band gap behavior of ZnO in B4 and B3 phases while indirect band gap behavior in B1 phase. Moreover, two fold degeneracy at the maxima of valence band for B4 and B1 phases whereas three fold for B3 is observed. A detailed comparison with experimental and other first principles studies is also made.

  2. DFT and TD-DFT study on geometries, electronic structures and electronic absorption of some metal free dye sensitizers for dye sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Mohr, T.; Aroulmoji, V.; Ravindran, R. Samson; Müller, M.; Ranjitha, S.; Rajarajan, G.; Anbarasan, P. M.

    2015-01-01

    The geometries, electronic structures, polarizabilities and hyperpolarizabilities of 2-hydroxynaphthalene-1,4-dione (henna1), 3-(5-((1E)-2-(1,4-dihydro-1,4-dioxonaphthalen-3-yloxy) vinyl) thiophen-2-yl)-2-isocyanoacrylic acid (henna2) and anthocyanin dye sensitizers were studied based on density functional theory (DFT) using the hybrid functional B3LYP. The Ultraviolet-Visible (UV-Vis) spectrum was investigated by using a hybrid method which combines the properties and dynamics of many-body in the presence of time-dependent (TD) potentials, i.e. TDSCF-DFT (B3LYP). Features of the electronic absorption spectrum in the visible and near-UV regions were plotted and assigned based on TD-DFT calculations. Due to the absorption, bands of the metal-organic compound are n → π* present. The calculated results suggest that the three lowest energy excited states of the investigated dye sensitizers are due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer is owing to an electron injection process from excited dye to the semiconductor's conduction band. The role of linking the henna1 dye with a carboxylic acid via a thiophene bridge was analyzed. The results are that using a stronger π-conjugate bridge as well as a strong donator and acceptor group enhances the efficiency.

  3. Conformations and Conformational Processes of Hexahydrobenzazocines by NMR and DFT Studies.

    PubMed

    Musielak, Bogdan; Holak, Tad A; Rys, Barbara

    2015-09-18

    Conformational processes that occur in hexahydrobenzazocines have been studied with the (1)H and (13)C dynamic nuclear magnetic resonance (DNMR) spectroscopy. The coalescence effects are assigned to two different conformational processes: the ring-inversion of the ground-state conformations and the interconversion between two different conformers. The barriers for these processes are in the range of 42-52 and 42-43 kJ mol(-1), respectively. Molecular modeling on the density functional theory (DFT) level and the gauge invariant atomic orbitals (GIAO)-DFT calculations of isotropic shieldings and coupling constants for the set of low-energy conformations were compared with the experimental NMR data. The ground-state of all compounds in solution is the boat-chair (BC) conformation. The BC form adopts two different conformations because the nitrogen atom can be in the boat or chair parts of the BC structure. These two conformers are engaged in the interconversion process. PMID:26317238

  4. A DFT study on the interaction between adsorbed silver on C₆₀ and disulfide bond.

    PubMed

    Azizi, Khaled; Sohrabinia, Ali

    2012-09-01

    Adsorption of a silver atom on the surface of Buckyball (C₆₀) was investigated using density functional theory (DFT). The Ag atom tends to occupy the bridge site over C--C bond in pentagon-hexagon ring junction with the binding energy of -38.33 kcal mol⁻¹. The capability of destroying S--S bond by both a single silver atom and the silver atom adsorbed on C₆₀ was also investigated by DFT calculations using dimethyl disulfide as the molecular model. The results of the natural bond orbital (NBO) and population analysis indicate that the cleavage of the S--S bond effectively occurs by the silver atom adsorbed on C₆₀. Since denaturation of disulfide bonds of envelope glycoprotein (gp) 120 is a key step in the prevention of the spread of HIV-1, the development of the proposed study is promised to HIV-1 research field. PMID:23085174

  5. Comparative DFT study of crystalline ammonium perchlorate and ammonium dinitramide.

    PubMed

    Zhu, Weihua; Wei, Tao; Zhu, Wei; Xiao, Heming

    2008-05-22

    The electronic structure, vibrational properties, absorption spectra, and thermodynamic properties of crystalline ammonium perchlorate (AP) and ammonium dinitramide (ADN) have been comparatively studied using density functional theory in the local density approximation. The results shows that the p states for the two solids play a very important role in their chemical reaction. From the low frequency to high frequency region, ADN has more motion modes for the vibrational frequencies than AP. The absorption spectra of AP and ADN display a few, strong bands in the fundamental absorption region. The thermodynamic properties show that ADN is easier to decompose than AP as the temperature increases. PMID:18396853

  6. Cooperativity in bifurcated lithium-bonded complexes: A DFT study

    NASA Astrophysics Data System (ADS)

    Solimannejad, Mohammad; Rezaie, Forough; Esrafili, Mehdi D.

    2016-07-01

    Density functional theory calculations at the B3LYP/6-311++G(d,p) level are performed to analyze intermolecular interactions in complexes connected via bifurcated lithium bonds. Linear (LiN(CHO)2)2-7 clusters are chosen as a model system in the present study. Stabilization energies for these clusters are in the range of -42.59 to -334.05 kcal mol-1. Cooperativity effects based on energy and dipole moment are computed for these clusters. The contraction of Li⋯O binding distances along with an increase in the magnitude of stabilization energies with the cluster size can be regarded as a signature of cooperative effects in these systems.

  7. X-ray, kinetics and DFT studies of photochromic substituted benzothiazolinic spiropyrans.

    PubMed

    Kumar, Satish; Velasco, Kriya; McCurdy, Alison

    2010-04-01

    Photochromic molecules have the potential to find utility in a wide variety of applications including photoswitchable binding and optical memory. This work explores the relationship between photochromism and structural parameters such as particular bond lengths for this class of compounds for which very few crystal structures have been published. Photochemical kinetics, Density Functional Theory (DFT) and X-ray crystallography were used to study the benzothiazolinic spiropyran 3-methyl-6-nitro-3'-methylspiro-[2H-l-benzopyran-2,2'-benzothiazoline]. A second benzothiazolinic spiropyran 3-methyl-8-methoxy-6-nitro-3'-methylspiro-[2H-l-benzopyran-2,2'-benzothiazoline] was synthesized and subjected to photochemical and computational studies. Selected structural and photochemical data for these, related benzothiazolinic spirooxazines and spiropyrans, and related thiazolidinic spiropyrans are compared. Both benzothiazolinic spiropyrans exhibit photochromic properties that are influenced by substituents, solvent, and temperature. The crystallographic C(spiro)-O bond distance of 3-methyl-6-nitro-3'-methylspiro-[2H-l-benzopyran-2,2'-benzothiazoline] that has been shown to correlate with photochromic properties is 1.458 A. The crystallographic C(spiro)-O bond distance matches that of the structure generated by DFT calculations exactly. The effect of substituents on calculated bond lengths and photochemical parameters was determined. For this class of compounds, both X-ray geometry and DFT optimized geometry may be used to predict photochromism, but not degree of photocolorability. PMID:20383273

  8. X-ray, kinetics and DFT studies of photochromic substituted benzothiazolinic spiropyrans

    NASA Astrophysics Data System (ADS)

    Kumar, Satish; Velasco, Kriya; McCurdy, Alison

    2010-04-01

    Photochromic molecules have the potential to find utility in a wide variety of applications including photoswitchable binding and optical memory. This work explores the relationship between photochromism and structural parameters such as particular bond lengths for this class of compounds for which very few crystal structures have been published. Photochemical kinetics, Density Functional Theory (DFT) and X-ray crystallography were used to study the benzothiazolinic spiropyran 3-methyl-6-nitro-3'-methylspiro-[2H-l-benzopyran-2,2'-benzothiazoline]. A second benzothiazolinic spiropyran 3-methyl-8-methoxy-6-nitro-3'-methylspiro-[2H-l-benzopyran-2,2'-benzothiazoline] was synthesized and subjected to photochemical and computational studies. Selected structural and photochemical data for these, related benzothiazolinic spirooxazines and spiropyrans, and related thiazolidinic spiropyrans are compared. Both benzothiazolinic spiropyrans exhibit photochromic properties that are influenced by substituents, solvent, and temperature. The crystallographic C spiro-O bond distance of 3-methyl-6-nitro-3'-methylspiro-[2H-l-benzopyran-2,2'-benzothiazoline] that has been shown to correlate with photochromic properties is 1.458 Å. The crystallographic C spiro-O bond distance matches that of the structure generated by DFT calculations exactly. The effect of substituents on calculated bond lengths and photochemical parameters was determined. For this class of compounds, both X-ray geometry and DFT optimized geometry may be used to predict photochromism, but not degree of photocolorability.

  9. DFT studies of the phenol adsorption on boron nitride sheets.

    PubMed

    Hernández, Jose Mario Galicia; Cocoletzi, Gregorio Hernández; Anota, Ernesto Chigo

    2012-01-01

    We perform first principles total energy calculations to investigate the atomic structures of the adsorption of phenol (C(6)H(5)OH) on hexagonal boron nitride (BN) sheets. Calculations are done within the density functional theory as implemented in the DMOL code. Electron-ion interactions are modeled according to the local-spin-density-approximation (LSDA) method with the Perdew-Wang parametrization. Our studies take into account the hexagonal h-BN sheets and the modified by defects d-BN sheets. The d-BN sheets are composed of one hexagon, three pentagons and three heptagons. Five different atomic structures are investigated: parallel to the sheet, perpendicular to the sheet at the B site, perpendicular to the sheet at the N site, perpendicular to the central hexagon and perpendicular to the B-N bond (bridge site). To determine the structural stability we apply the criteria of minimum energy and vibration frequency. After the structural relaxation phenol molecules adsorb on both h-BN and d-BN sheets. Results of the binding energies indicate that phenol is chemisorbed. The polarity of the system increases as a consequence of the defects presence which induces transformation from an ionic to covalent bonding. The elastic properties on the BN structure present similar behavior to those reported in the literature for graphene. PMID:21523546

  10. Why thiocolchicine does not undergo photochemical isomerization: A theoretical study

    NASA Astrophysics Data System (ADS)

    Cacelli, Ivo; D'Auria, Maurizio; Villani, Vincenzo

    2008-06-01

    The reasons why colchicine undergoes photochemical cyclization to give lumicolchicine, whereas thiocolchicine does not, are investigated by theoretical methods. The relative stability of the reagent and of the products is computed at DFT level of theory and indicates that such a photochemical reaction is energetically possible. The photochemical reaction path of thiocolchicine is studied within the relaxed energy scan, at MC-SCF level of theory. The results are again rather similar to those of colchicine. Finally, the spin-orbit coupling between S 1 and T 1 has been computed and are two order of magnitude greater than those of colchicine, that makes plausible that spin-orbit is the main reason of the observed reaction quenching.

  11. Conformational isomerism of pyridoxal. Infrared matrix isolation and theoretical studies

    NASA Astrophysics Data System (ADS)

    Kwiatek, Anna; Mielke, Zofia

    2015-01-01

    A combined matrix isolation FTIR and theoretical DFT/B3LYP/6-311++G(2p,2d) study of pyridoxal was performed. The calculations resulted in five stable PLHB conformers stabilized by intramolecular Osbnd H⋯O bonding between phenolic OH and carbonyl Cdbnd O groups and another thirteen conformers in which OH or/and aldehyde groups are rotated by 180° around CO or/and CC bonds leading, respectively, to formation of PLO, PLA and PLOA conformers. The analysis of the spectra of the as-deposited matrix indicated that two most stable PLHB1 and PLHB2 conformers with intramolecular hydrogen bond are present in the matrix. The exposure of the PL/Ar matrix to mercury lamp radiation (λ > 345 nm) induced conformational change of PLHB isomers to PLOA ones.

  12. Experimental and theoretical study on THz spectrum artesunate

    NASA Astrophysics Data System (ADS)

    Zhang, Ai-Bing; Kong, Ling-Gao; Wang, Shi-Jin; Li, Lei; Zheng, Xiang-Zhi

    2008-10-01

    Artesunate is a very effective drug to treat malaria. They are studied experimentally by Terahertz (THz) time-domain spectroscopy (THz-TDS), and the characteristic absorption spectra are obtained in the range of 0.2 to 2.6 THz. The vibrational frequencies are calculated using the density functional theory (DFT). Theoretical results show that 0.71, 1.94 and 2.46 THz are significant agreement with the experimental results in 0.87, 1.82 and 2.46THz, and identification of vibrational modes are given. The calculated results further confirm that the characteristic frequencies come from the collective vibrational modes. The results suggest that the use of the THz-TDS technique can be an effective way to inspect for Chinese medicine.

  13. Conformational isomerism of pyridoxal. Infrared matrix isolation and theoretical studies.

    PubMed

    Kwiatek, Anna; Mielke, Zofia

    2015-01-25

    A combined matrix isolation FTIR and theoretical DFT/B3LYP/6-311++G(2p,2d) study of pyridoxal was performed. The calculations resulted in five stable PLHB conformers stabilized by intramolecular O-H⋯O bonding between phenolic OH and carbonyl C=O groups and another thirteen conformers in which OH or/and aldehyde groups are rotated by 180° around CO or/and CC bonds leading, respectively, to formation of PLO, PLA and PLOA conformers. The analysis of the spectra of the as-deposited matrix indicated that two most stable PLHB1 and PLHB2 conformers with intramolecular hydrogen bond are present in the matrix. The exposure of the PL/Ar matrix to mercury lamp radiation (λ>345 nm) induced conformational change of PLHB isomers to PLOA ones. PMID:25173527

  14. Vibrational study, molecular properties and first-order molecular hyperpolarizability of Methyl 2-amino 5-bromobenzoate using DFT method

    NASA Astrophysics Data System (ADS)

    Saxena, Avinay; Agrawal, Megha; Gupta, Archana

    2015-08-01

    The molecular structure of Methyl 2-amino 5-bromobenzoate (M2A5B) was investigated by density functional theory employing Becke's three parameter hybrid exchange functional with Lee-Yang-Parr (B3LYP) co-relational functional involving 6-311++G(d,p) basis set. Harmonic vibrational wavenumber calculation along with the normal mode analysis has been carried out in order to obtain a complete description of molecular dynamics. A detailed interpretation of the Infrared and Raman spectra of M2A5B have been reported. Complete vibrational assignments of the vibrational modes have been done on the basis of the potential energy distribution (PED) in terms of internal coordinates. The scaled vibrational wavenumbers corrected by a recommended set of scaling factors were compared with the experimental results and a fairly good agreement was obtained. The molecular electrostatic potential mapped onto total density surface has been obtained. A study on the electronic properties, such as absorption wavelength, excitation energy and frontier molecular orbitals energy, was performed by time dependent DFT (TD-DFT) approach. Additionally, major contribution from molecular orbitals to the electronic transition was investigated theoretically. The stability of the molecule arising from hyper conjugative interactions and accompanying charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The theoretical 1H and 13C NMR chemical shifts have been calculated by GIAO method and compared with experimentally measured ones. The polarizability and first order hyperpolarizability of the title molecule were calculated and interpreted. The energy gap between frontier orbitals has been used along with electric moments and first order hyperpolarizability, to understand the non linear optical (NLO) activity of the molecule. The prominent vibrational modes contributing to the NLO activity have been identified and examined from the concurrent IR and Raman activity. Thermodynamic

  15. Uranyl extraction by N,N-dialkylamide ligands studied using static and dynamic DFT simulations.

    PubMed

    Sieffert, Nicolas; Wipff, Georges

    2015-02-14

    We report DFT static and dynamic studies on uranyl complexes [UO(2)(NO(3))x(H(2)O)(y)L(z)](2-x) involved in the uranyl extraction from water to an "oil" phase (hexane) by an amide ligand L (N,N-dimethylacetamide). Static DFT results "in solution" (continuum SMD models for water and hexane) predict that the stepwise formation of [UO(2)(NO(3))(2)L(2)] from the UO(2)(H(2)O)(5)(2+) species is energetically favourable, and allow us to compare cis/trans isomers of penta- and hexa-coordinated complexes and key intermediates in the two solvents. DFT-MD simulations of [UO(2)(NO(3))(2)L(2)], [UO(2)(NO(3))(2)(H(2)O)L(2)], and [UO(2)(NO(3))(H(2)O)L(2)](+) species in explicit solvent environments (water, hexane, or the water/hexane interface) represented at the MM or full-DFT level reveal a versatile solvent dependent binding mode of nitrates, also evidenced by metadynamics simulations. In water and at the interface, the latter exchange from bi- to monodentate, via in plane rotational motions in some cases. Remarkably, structures of complexes at the interface are more "water-like" than gas phase- or hexane-like. Thus, the order of U-O(NO(3))/U-O(L) bond distances observed in the gas phase (U-O(nit) < U-OL) is inverted at the interface and in water. Overall, the results are consistent with the experimental observation of uranyl extraction from nitric acid solutions by amide analogues (bearing "fatty" substituents), and allow us to propose possible extraction mechanisms, involving complexation of L "right at the interface". They also point to the importance of the solvent environment and the dynamics on the structure and stability of the complexes. PMID:25412447

  16. Gas Phase Elimination Kinetics of Methyl Mandelate: Experimental and DFT Studies

    NASA Astrophysics Data System (ADS)

    Rotinov, Alexandra; Escalante, Luz; Ramirez, Beatriz; Pereira, Desiree; Córdova, Tania; Chuchani, Gabriel

    2009-10-01

    The gas phase elimination kinetics of racemic methyl mandelate was determined in a static system, and yielded on decomposition benzaldehyde, methanol, and carbon monoxide. The reaction was homogeneous, unimolecular, and follows a first-order law in the temperature range 379.5-440 °C and pressure range of 21.5-71.1 Torr. The variation of the rate coefficient with temperature is expressed by the following Arrhenius equation: log k1 = (12.70 ± 0.14) - (206.5 ± 1.9) kJ/mol (2.303RT)-1. The theoretical estimations of the kinetics and thermodynamics parameters were carried out using DFT methods B3LYP, B3PW91, MPW1PW91, and PBEPBE. Calculation results are in reasonably good agreement with the experimental energy and enthalpy values when using the PBEPBE DFT functional. However, regarding the entropy of activation, the MPW1PW91 functional is more adequate to describe the reaction. These calculations imply a molecular concerted nonsynchronous mechanism involving a two-step process, where the formation of the unstable α-lactone intermediate is the rate-determining factor. The lactone intermediate rapidly decarbonylates to produce benzaldehyde and carbon monoxide. The transition state is late in the reaction coordinate, resembling the lactone configuration.

  17. 13C CPMAS NMR studies and DFT calculations of triterpene xylosides isolated from Actaea racemosa

    NASA Astrophysics Data System (ADS)

    Jamróz, Marta K.; Paradowska, Katarzyna; Gliński, Jan A.; Wawer, Iwona

    2011-05-01

    13C CPMAS NMR spectra of four triterpene glycosides: cimigenol xyloside ( 1), 26-deoxyactein ( 2), cimicifugoside H-1 ( 3) and 24-acethylhydroshengmanol xyloside ( 4) were recorded and analyzed to characterize their solid-state structure. Experimental data were supported by theoretical calculations of NMR shielding constants with the GIAO/6-31G**-su1 approach. A number of methods for the conformational search and a number of functionals for the DFT calculations were applied to ( 1). The best method was proven to be MMFF or MMFFAQ for the conformational search and the PBE1PBE functional for the DFT calculations. Extra calculations simulating C16 dbnd O⋯HOH hydrogen bond yield the isotropic shielding closer to the experimental solid-state value. For all the compounds CP kinetics parameters were calculated using either the I-S or the I-I*-S model. The analysis of CP kinetics data for methyl groups revealed differences in the T2 time constant for two methyl groups (C29 and C30) linked at C4.

  18. Synthesis, crystal structure, spectral analysis and DFT computational studies on a novel isoindoline derivative

    NASA Astrophysics Data System (ADS)

    Evecen, Meryem; Duru, Gülcan; Tanak, Hasan; Ağar, Ayşen Alaman

    2016-08-01

    The isoindoline compound, 2-(3-chloro-4-(4-chlorophenoxy)phenyl)isoindoline-1,3-dione, has been synthesized and characterized by FT-IR, UV-Vis and X-ray single-crystal determination. The compound crystallizes in the monoclinic space group P21/c with a = 20.441 (3) Å, b = 4.0258 (4) Å, c = 23.836 (2) Å, β = 121.918 (7)° and Z = 4. The molecular structure and vibrational frequencies in the ground state were calculated using the density functional theory method (B3LYP) with 6-311++G(d,p) basis set. The results obtained from the optimization and vibrational analyses are agree with the experimental results. Using the TD-DFT method, electronic absorption spectra have been calculated, and they are compatible with the experimental ones. The electric dipole moment (μ), polarizability (α) and the first hyperpolarizability (β) values of the compound were calculated theoretically. The first hyperpolarizability of the molecule shows that the compound can be a good candidate of nonlinear optical material. In addition, DFT calculations of the compound, atomic charges, molecular electrostatic potential and thermodynamic properties were also performed at B3LYP/6-311++G(d,p) level of theory.

  19. The crystal structure of sulfamethoxazole, interaction with DNA, DFT calculation, and molecular docking studies

    NASA Astrophysics Data System (ADS)

    Das, Dipankar; Sahu, Nilima; Roy, Suman; Dutta, Paramita; Mondal, Sudipa; Torres, Elena L.; Sinha, Chittaranjan

    2015-02-01

    Sulfamethoxazole (SMX) [4-amino-N-(5-methyl-1,2-oxazol-3-yl)benzenesulfonamide] is structurally established by single crystal X-ray diffraction measurement. The crystal packing shows H-bonded 2D polymer through N(7)sbnd H(7A)---O(2), N(7)sbnd H(7B)---O(3), N(1)sbnd H(1)---N(2), C(5)sbnd H(5)---O(3)sbnd S(1) and N(7)sbnd (H7A)---O(2)sbnd S(1). Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) computations of optimized structure of SMX determine the electronic structure and has explained the electronic spectral transitions. The interaction of SMX with CT-DNA has been studied by absorption spectroscopy and the binding constant (Kb) is 4.37 × 104 M-1. The in silico test of SMX with DHPS from Escherichia coli and Streptococcus pneumoniae helps to understand drug metabolism and accounts the drug-molecule interactions. The molecular docking of SMX-DNA also helps to predict the interaction feature.

  20. Electronic spectroscopy of HRe(CO) 5: a CASSCF/CASPT2 and TD-DFT study

    NASA Astrophysics Data System (ADS)

    Bossert, J.; Ben Amor, N.; Strich, A.; Daniel, C.

    2001-07-01

    The low-lying excited states of HRe(CO) 5 have been calculated at the CASSCF/CASPT2 and TD-DFT level of theory using relativistic effective core potentials (ECP) or ab initio model potentials (AIMP). The theoretical absorption spectrum is compared to the experimental one. Despite the similarity between the experimental absorption spectra of HMn(CO) 5 and HRe(CO) 5 in the UV/visible energy domain it is shown that the assignment differs significantly between the two molecules. The low-lying excited states of HRe(CO) 5 correspond to 5d→π *CO excitations whereas the spectrum of HMn(CO) 5 consists mainly of 3d→3d and 3d→ σ*Mn-H excitations. If the CASPT2 and TD-DFT results are quite comparable for the lowest excited states, the upper part assignment is more problematic with the TD-DFT method.

  1. Electronic structures of hydrogen functionalized carbon nanotube: Density functional theory (DFT) study

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto; Iyama, Tetsuji; Kawabata, Hiroshi

    2016-05-01

    Electronic structures and formation mechanism of hydrogen functionalized carbon nanotube (CNT) have been investigated by means of density functional theory (DFT) method. The mechanism of hydrogen addition reaction to the CNT surface was also investigated. Pure and boron-nitrogen (BN) substituted CNT (denoted by CNT and BN-CNT, respectively) were examined as the carbon nanotubes. It was found that the additions of hydrogen atom to B (boron atom) and C (carbon atom) sites of BN-CNT proceed without activation barrier, whereas the hydrogenation of N (nitrogen atom) site needs the activation energy. The electronic states of hydrogen functionalized CNT and BN-CNT were discussed on the basis of theoretical results.

  2. Low frequency collective vibrational spectra of zwitterionic glycine studied by DFT

    NASA Astrophysics Data System (ADS)

    Ma, Shi Hua; Chen, Hua; Cui, Yi Ping

    2012-12-01

    Fourier transform infrared spectrometer and THz-TDS were used to obtain the experimental spectrum of glycine below 600 cm-1, and theoretical results of one or more zwitterionic glycine were calculated by DFT at the basis set of b31yp 6- 31+g(d,p) level based on Gaussian 03 software package in FIR region. There is more reasonable qualitative agreement between the calculated data of crystalline and observed line positions. Detailed assignments of the observed vibrational frequencies are discussed and the origins of some frequencies are analyzed by contrast. The low frequency collective mode of zwitterionic glycine is affected greatly by the intermolecular interaction and hydrogen-bonding effects and their vibrational modes are collective motion.

  3. Structural studies of PCU-hydrazones: NMR spectroscopy, X-ray diffractions, and DFT calculations

    NASA Astrophysics Data System (ADS)

    Veljković, Jelena; Šekutor, Marina; Molčanov, Krešimir; Lo, Rabindranath; Ganguly, Bishwajit; Mlinarić-Majerski, Kata

    2011-06-01

    In this article we present a detailed structural investigation for the configurational isomers of PCU-hydrazones. The structural characterization of these hydrazones was performed using NMR spectroscopy, X-ray diffraction analysis and theoretical calculations. The single crystal X-ray structures of PCU-hydrazones 6B and 6C have been solved and used to conclusively confirm the characterization obtained via NMR spectra of a particular isomer. Nuclear magnetic shielding values calculated for 6A-C using DFT calculations were correlated with the experimentally determined chemical shifts. The computed results were found to be in good agreement with the observed 13C NMR values. The computed NMR results helped to ascertain the isomers of PCU-hydrazones 4A-C.

  4. Studies in theoretical particle physics

    NASA Astrophysics Data System (ADS)

    Kaplan, D. B.

    1991-07-01

    This proposal focuses on research on three distinct areas of particle physics: (1) Nonperturbative QCD. I tend to continue work on analytic modelling of nonperturbative effects in the strong interactions. I have been investigating the theoretical connection between the nonrelativistic quark model and QCD. The primary motivation has been to understand the experimental observation of nonzero matrix elements involving current strange quarks in ordinary matter, which in the quark model has no strange quark component. This has led to my present work on understanding constituent (quark model) quarks as collective excitations of QCD degrees of freedom. (2) Weak Scale Baryogenesis. A continuation of work on baryogenesis in the early universe from weak interactions. In particular, an investigation of baryogenesis occurring during the weak phase transition through anomalous baryon violating processes in the standard model of weak interactions. (3) Flavor and Compositeness. Further investigation of a new mechanism that I recently discovered for dynamical mass generation for fermions, which naturally leads to a family hierarchy structure. A discussion of recent past work is found in the next section, followed by an outline of the proposed research. A recent publication from each of these three areas is attached to this proposal.

  5. Studies in theoretical particle physics

    SciTech Connect

    Kaplan, D.B.

    1991-07-01

    This proposal focuses on research on three distinct areas of particle physics: (1) Nonperturbative QCD. I tend to continue work on analytic modelling of nonperturbative effects in the strong interactions. I have been investigating the theoretical connection between the nonrelativistic quark model and QCD. The primary motivation has been to understand the experimental observation of nonzero matrix elements involving current strange quarks in ordinary matter -- which in the quark model has no strange quark component. This has led to my present work on understanding constituent (quark model) quarks as collective excitations of QCD degrees of freedom. (2) Weak Scale Baryogenesis. A continuation of work on baryogenesis in the early universe from weak interactions. In particular, an investigation of baryogenesis occurring during the weak phase transition through anomalous baryon violating processes in the standard model of weak interactions. (3) Flavor and Compositeness. Further investigation of a new mechanism that I recently discovered for dynamical mass generation for fermions, which naturally leads to a family hierarchy structure. A discussion of recent past work is found in the next section, followed by an outline of the proposed research. A recent publication from each of these three areas is attached to this proposal.

  6. First principle calculation of physical properties of barium based chalcogenides BaM4S7 (M = Ga, Al); a DFT, DFT-D and hybrid functional HSE06 study

    NASA Astrophysics Data System (ADS)

    Benghia, Ali; Dahame, Tahar; Bentria, Bachir

    2016-04-01

    The electronic structure, elastic and optical properties have been calculated for the novel nonlinear optical (NLO) crystals BaQ4S7 (Q = Ga, Al) using plane wave pseudo-potential density functional theory (DFT) method as implemented in CASTEP and ABINIT codes. In this study we used both hybrid HSE06 and DFT-D functionals with GGA approximation. These NLO compounds, which belong to the mm2 point group, are particularly interesting because of their transparency in the mid-infrared region and wide energy band gap. We present results for electronic structure, elastic tensor coefficients, refractive indices and second order nonlinear optical susceptibilities. The calculated energy band gap and frequency dependent refractive indices as well as the NLO coefficients of BaGa4S7 are in good agreement with the experimental values. With no reported theoretical or experimental energy band gap and optical properties of BaAl4S7, we present for the first time its electronic structure and above mentioned optical coefficients. This compound has higher direct band gap with 3.74 eV, better optical birefringence and second-order NLO coefficients than most NLO compounds. The second-order NLO coefficients for BaAl4S7 have been calculated as d31 = 3.15 pm/V, d31 = 2.20 pm/V, d33 = -6.31 pm/V.

  7. Collector attachment to lead-activated sphalerite - Experiments and DFT study on pH and solvent effects

    NASA Astrophysics Data System (ADS)

    Sarvaramini, A.; Larachi, F.; Hart, B.

    2016-03-01

    The interactions of diisobutyl dithiophosphinate with bare (un-activated) and lead-activated sphalerite were studied both experimentally and through DFT simulations. Sphalerite activated by lead in acidic and alkaline conditions showed considerably greater affinity for diisobutyl dithiophosphinate adsorption than bare sphalerite. Experimental observations supported by DFT simulations concur in that attachment of the solvated collector to the activated sphalerite surface is through adsorbed lead cations or lead hydroxides where as for the bare sphalerite, the collector was most stable in its solvated state and not as an adsorbed specie. Accounting for solvation effects by including a swarm of water molecules in DFT simulations was necessary to infer plausible surface interactions between collector, solvent, and bare or lead-activated sphalerite. The experimental data and DFT simulations indicate, affinity of the collector toward surface-adsorbed lead species was predicted to form stable covalent bonds between collector sulfur atoms and lead.

  8. Putting DFT to the test: a first-principles study of electronic, magnetic, and optical properties of Co3O4.

    PubMed

    Singh, Vijay; Kosa, Monica; Majhi, Koushik; Major, Dan Thomas

    2015-01-13

    First-principles density functional theory (DFT) and a many-body Green's function method have been employed to elucidate the electronic, magnetic, and photonic properties of a spinel compound, Co3O4. Co3O4 is an antiferromagnetic semiconductor composed of cobalt ions in the Co(2+) and Co(3+) oxidation states. Co3O4 is believed to be a strongly correlated material, where the on-site Coulomb interaction (U) on Co d orbitals is presumably important, although this view has recently been contested. The suggested optical band gap for this material ranges from 0.8 to 2.0 eV, depending on the type of experiments and theoretical treatment. Thus, the correlated nature of the Co d orbitals in Co3O4 and the extent of the band gap are still under debate, raising questions regarding the ability of DFT to correctly treat the electronic structure in this material. To resolve the above controversies, we have employed a range of theoretical methods, including pure DFT, DFT+U, and a range-separated exchange-correlation functional (HSE06) as well as many-body Green's function theory (i.e., the GW method). We compare the electronic structure and band gap of Co3O4 with available photoemission spectroscopy and optical band gap data and confirm a direct band gap of ca. 0.8 eV. Furthermore, we have also studied the optical properties of Co3O4 by calculating the imaginary part of the dielectric function (Im(ε)), facilitating direct comparison with the measured optical absorption spectra. Finally, we have calculated the nearest-neighbor interaction (J1) between Co(2+) ions to understand the complex magnetic structure of Co3O4. PMID:26574204

  9. Theoretical Study of Sulphur Interaction with Ceria

    SciTech Connect

    Baranek, Ph.; Gauthier, L.; Marrony, M.

    2007-12-26

    Sulphur-containing molecules are responsible for the poisoning of catalysts used in many chemical processes such as fuel processing for hydrogen production and for fuel cells. An option which would constitute a breakthrough in this field would be to develop sulphur tolerant catalysts. Ceria (CeO{sub 2}) is an important ceramic material exploited in a wide range of applications such as solid oxide fuel cells. Then it is important to understand its surface catalytic properties. The adsorption of S, H{sub 2}S and other S-containing compounds on different surfaces of ceria are investigated at the ab initio quantum mechanical level, by using the periodic CRYSTAL06 code. In this extended abstract, we focus on the S adsorption on the stoichiometric (111), (110) and (100) surfaces of ceria. The equilibrium lattice parameters of CeO{sub 2}, surface stabilities, and S adsorption energies have been evaluated. The calculations have been performed at the Hartree-Fock (HF), density functional theory (DFT) and hybrid levels. A good agreement between calculated, and, other theoretical and experimental various properties has been found with hybrid approximations. The role of f orbitals of Ce is commented.

  10. Theoretical Study of Sulphur Interaction with Ceria

    NASA Astrophysics Data System (ADS)

    Baranek, Ph.; Gauthier, L.; Marrony, M.

    2007-12-01

    Sulphur-containing molecules are responsible for the poisoning of catalysts used in many chemical processes such as fuel processing for hydrogen production and for fuel cells. An option which would constitute a breakthrough in this field would be to develop sulphur tolerant catalysts. Ceria (CeO2) is an important ceramic material exploited in a wide range of applications such as solid oxide fuel cells. Then it is important to understand its surface catalytic properties. The adsorption of S, H2S and other S-containing compounds on different surfaces of ceria are investigated at the ab initio quantum mechanical level, by using the periodic CRYSTAL06 code. In this extended abstract, we focus on the S adsorption on the stoichiometric (111), (110) and (100) surfaces of ceria. The equilibrium lattice parameters of CeO2, surface stabilities, and S adsorption energies have been evaluated. The calculations have been performed at the Hartree-Fock (HF), density functional theory (DFT) and hybrid levels. A good agreement between calculated, and, other theoretical and experimental various properties has been found with hybrid approximations. The role of f orbitals of Ce is commented.

  11. A combined experimental and theoretical quantum chemical studies on 4-morpholinecarboxaldehyde

    NASA Astrophysics Data System (ADS)

    Arjunan, V.; Rani, T.; Santhanalakshmi, K.; Mohan, S.

    2011-09-01

    Extensive spectroscopic investigations have been carried out by recording the Fourier transform infrared (FTIR) and FT-Raman spectra and carrying out the theoretical quantum chemical studies on 4-morpholinecarboxaldehyde (4MC). From the ab initio and DFT analysis using HF, B3LYP and B3PW91 methods with 6-31G(d,p) and 6-311G++(d,p) basis sets the energies, structural, thermodynamical and vibrational characteristics of the compound were determined. The energy difference between the chair equatorial and chair axial conformers of 4MC have been calculated by density functional theory (DFT) method. The optimised geometrical parameters, theoretical wavenumbers and thermodynamic properties of the molecule were compared with the experimental values. The effect of carbonyl group on the characteristic frequencies of the morpholine ring has been analysed. The mixing of the fundamental modes with the help of potential energy distribution (PED) through normal co-ordinate analysis has been discussed.

  12. Theoretical study on icosahedral water clusters

    NASA Astrophysics Data System (ADS)

    Loboda, Oleksandr; Goncharuk, Vladyslav

    2010-01-01

    Here we present a structural study of different gas hydrates using the B3LYP hybrid DFT exchange-correlation functional. A new concept for viewing the icosahedral cluster as an expansion of dodecahedral subclusters is introduced. The investigated structures consist of 280 water molecules. Structural and orientational features of various guest molecules occupying the central cavity of the clusters are established. It was found that water as the guest molecule has the highest stabilization energy in studied clusters. The conformational changes in dimer and trimer water molecules upon incorporation into hydrate cavity are discussed. The influence of second- and third-order solvent shells is illustrated on example of icosahedral water cluster derivatives.

  13. Molecular structure, vibrational spectra and quantum chemical MP2/DFT studies toward the rational design of hydroxyurea imprinted polymer

    NASA Astrophysics Data System (ADS)

    Prasad, Bhim Bali; Rai, Garima

    2013-03-01

    In this study, both experimental and theoretical vibrational spectra of template (hydroxyurea, HU), monomer (N-(4,6-bisacryloyl amino-[1,3,5] triazine-2-yl-)-acryl amide, TAT), and HU-TAT complexes were compared and these were respectively found to be in good agreement. Binding energies of HU, when complexed with different monomers, were computed using second order Moller Plesset theory (MP2) at 6-311++G(d,p) level both in the gas as well as solution phases. HU is an antineoplastic agent extensively being used in the treatment of polycythaemia Vera and thrombocythemia. It is also used to reduce the frequency of painful attacks in sickle cell anemia. It has antiretroviral property in disease like AIDS. All spectral characterizations were made using Density Functional Theory (DFT) at B3LYP employing 6-31+g(2d, 2p) basis set. The theoretical values for 13C and 1H NMR chemical shifts were found to be in accordance with the corresponding experimental values. Of all different monomers studied for the synthesis of molecularly imprinted polymer (MIP) systems, the monomer TAT (2 mol) was typically found to have a best binding score requisite for complexation with HU (1 mol) at the ground state.

  14. Identification of structural and spectral features of synthesized cyano-stilbene dye derivatives: a comparative experimental and DFT study.

    PubMed

    Karabacak, M; Asiri, A M; Al-Youbi, A O; Qusti, A H; Cinar, M

    2014-01-01

    The synthesized three dye derivatives of cyano-stilbene monomer were identified by experimental spectroscopic techniques and density functional approach. The optimized geometrical structure, vibrational and electronic transitions along with the nonlinear optical (NLO) properties of those compounds were presented in this study. The vibrational spectra of investigated compounds were recorded in solid state with FT-IR and FT-Raman spectrometry in the range of 4000-400 cm(-1) and 3600-50 cm(-1), respectively. The theoretical ground state equilibrium conformations and vibrational wavenumbers were carried out by using density functional method with 6-311G(d,p) basis set. Assignments of the fundamental vibrational modes were examined on the basis of the measured data and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanical (SQM) method. The UV absorption spectra of monomers were observed in the range of 200-600 nm in chloroform, acetonitrile and toluene, and time dependent DFT method was used to obtain the electronic properties. The linear polarizability and first hyperpolarizability of the studied molecules indicates that the title compounds can be used as a good nonlinear optical material. A detailed description of spectroscopic behaviors of compounds was given based on the comparison of experimental measurements and theoretical computations. PMID:24177881

  15. Expedient synthesis of novel pregnane-NSAIDs prodrugs, XRD, stereochemistry of their C-20 derivatives by circular dichroism, conformational analysis, their DFT and TD-DFT studies

    NASA Astrophysics Data System (ADS)

    Singh, Ranvijay Pratap; Sharma, Sonia; Kant, Rajni; Amandeep; Singh, Praveer; Sethi, Arun

    2016-02-01

    Four novel pregnane-NSAIDs prodrugs 3β-(2-(6-methoxynaphthalene-2yl) propionoxy)-16α-methoxy-pregn-5-ene-20-one (3), 16α-methoxy-pregn-5-ene-20-one-3yl-2(4-iso butyl phenyl) propanoate (4), 3β-(2-(6-methoxynaphthalene-2yl) propionoxy) 20-hydroxy-16α-methoxy-pregn-5-ene (5) and 20-hydroxy-16α-methoxy-pregn-5-ene-20-one-3yl-2(4-iso butyl phenyl) propanoate (6) have been synthesized. They were analyzed experimentally by spectroscopic techniques like 1H, 13C NMR, FT-IR, UV-visible spectroscopy, mass spectrometry and correlated by theoretical calculations. The structure and conformations of 3 was established by single crystal X-ray diffraction, which crystallized in orthorhombic form having P212121 space group. Absolute configuration of C-20 hydroxy derivatives 5 and 6 was established by circular dichroism (CD) analysis. Conformational analysis of 5 was carried out to determine the most stable conformation. The electronic properties, such as frontier orbitals, band gap energies, oscillator strength and wavelength have been calculated using time dependent density functional theory (TD-DFT). The vibrational wavenumbers have been calculated using DFT method and assigned with the help of potential energy distribution (PED). Global and local reactivity descriptors have been computed to predict reactivity and reactive sites in the molecule. First hyperpolarizability (β0) of synthesized compounds has been computed to evaluate non-linear optical (NLO) response. Molecular electrostatic potential (MEP) for synthesized compounds have also been determined to check their electrophilic or nucleophilic reactivity as well as reaction path.

  16. A combined experimental and theoretical (DFT and AIM) studies on synthesis, molecular structure, spectroscopic properties and multiple interactions analysis in a novel ethyl-4-[2-(thiocarbamoyl)hydrazinylidene]-3,5-dimethyl-1H-pyrrole-2-carboxylate and its dimer.

    PubMed

    Singh, R N; Kumar, Amit; Tiwari, R K; Rawat, Poonam

    2013-08-01

    In the present work, ethyl-4-[2-(thiocarbamoyl)hydrazinylidene]-3,5-dimethyl-1H-pyrrole-2-carboxylate (3) has been synthesized and characterized by (1)H NMR, UV-Vis, FT-IR and Mass spectroscopy. The formation of the compound and its properties have also been evaluated by quantum chemical calculations using DFT, B3LYP functional and 6-31G(d,p) as basis set. The calculated thermodynamic parameters show that the formation of 3 is an exothermic and spontaneous reaction at room temperature. (1)H NMR chemical shifts are calculated using gauge including atomic orbitals (GIAO) approach in DMSO-d6 as solvent. Time dependent density functional theory (TD-DFT) is used to calculate the energy (E), oscillator strength (f) and wavelength absorption maxima (λ(max)) of various electronic transitions and their nature within the molecule. NBO analysis is carried out to investigate the charge transfer or charge delocalization in various intra- and intermolecular interactions of molecular system. The vibrational analysis indicates the formation of dimer in the solid state by intermolecular heteronuclear hydrogen bonding (NH···O). Topological parameters at bond critical points (BCP) are calculated to analyze the strength and nature of various types of intra and intermolecular interactions in dimer by Bader's 'Atoms in molecules' AIM theory in detail. The binding energy of intermolecular multiple interactions is calculated to be 15.54 kcal/mol, using AIM calculation. The local reactivity descriptors such as Fukui functions (f(k)(+),f(k)(-)), local softnesses (s(k)(+),s(k)(-)) and electrophilicity indices (ω(k)(+),ω(k)(-)) analyses are performed to determine the reactive sites within molecule. PMID:23666353

  17. Crystallographic, experimental (FT-IR and FT-RS) and theoretical (DFT) investigation, UV-Vis, MEP, HOMO-LUMO and NBO/NLMO of (E)-1-[1-(4-Chlorophenyl)ethylidene]thiosemicarbazide

    NASA Astrophysics Data System (ADS)

    Saravanan, R. R.; Seshadri, S.; Gunasekaran, S.; Mendoza-Meroño, R.; Garcia-Granda, S.

    2014-03-01

    Crystallographic, experimental (FT-IR and FT-RS) and theoretical density function theory (DFT) and UV-Vis spectra of (E)-1-[1-(4-Chlorophenyl)ethylidene]thiosemicarbazide) (ECET) are investigated. The optimized geometry of the compound was calculated from the DFT-B3LYP gradient calculations employing 6-31G (d,p) basis set and calculated vibrational frequencies are evaluated via comparison with experimental values. Molecular stability has been analyzed using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analysis and the limits of the molecular electrostatic potential observed. The calculated HOMO and LUMO energies show the charge transfer occurs within the molecule.

  18. Spin state transition in the active center of the hemoglobin molecule: DFT + DMFT study

    NASA Astrophysics Data System (ADS)

    Novoselov, D.; Korotin, Dm. M.; Anisimov, V. I.

    2016-05-01

    An ab initio study of electronic and spin configurations of the iron ion in the active center of the human hemoglobin molecule is presented. With a combination of the Density Functional Theory (DFT) method and the Dynamical Mean Field Theory (DMFT) approach, the spin state transition description in the iron ion during the oxidation process is significantly improved in comparison with previous attempts. It was found that the origin of the iron ion local moment behavior both for the high-spin and for the low-spin states in the hemoglobin molecule is caused by the presence of a mixture of several atomic states with comparable statistical probability.

  19. Natural carotenoids as nanomaterial precursors for molecular photovoltaics: a computational DFT study.

    PubMed

    Ruiz-Anchondo, Teresita; Flores-Holguín, Norma; Glossman-Mitnik, Daniel

    2010-07-01

    In this work several natural carotenoids were studied as potential nanomaterial precursors for molecular photovoltaics. M05-2X/6-31+G(d,p) level of theory calculations were used to obtain their molecular structures, as well as to predict the infrared (IR) and ultraviolet (UV-Vis) spectra, the dipole moment and polarizability, the pKa, and the chemical reactivity parameters (electronegativity, hardness, electrophilicity and Fukui functions) that arise from Conceptual DFT. The calculated values were compared with the available experimental data for these molecules and discussed in terms of their usefulness in describing photovoltaic properties. PMID:20657373

  20. Electrochemical oxidation stability of anions for modern battery electrolytes: a CBS and DFT study.

    PubMed

    Jónsson, Erlendur; Johansson, Patrik

    2015-02-01

    The electrochemical stability vs. oxidation is a crucial property of anions in order to be suitable as components in lithium-ion batteries. Here the applicability of a number of computational approaches and methods to assess this property, employing a wide selection of DFT functionals, has been studied using the CCSD(T)/CBS method as the reference. In all, the vertical anion oxidation potential, ΔEv, is a fair way to calculate the stability vs. oxidation, however, a functional of at least hybrid quality is recommended. In addition, the chemical hardness, η, is identified as a novel approach to calculate the stability vs. oxidation. PMID:25557392

  1. Effects of Local Protein Environment on the Binding of Diatomic Molecules to Heme in Myoglobins. DFT and Dispersion-Corrected DFT Studies

    PubMed Central

    Liao, Meng-Sheng; Huang, Ming-Ju; Watts, John D.

    2013-01-01

    The heme-AB binding energies (AB = CO, O2) in a wild-type myoglobin (Mb) and two mutants (H64L, V68N) of Mb have been investigated in detail with both DFT and dispersioncorrected DFT methods, where H64L and V68N represent two different, opposite situations. Several dispersion correction approaches were tested in the calculations. The effects of the local protein environment were accounted for by including the five nearest surrounding residues in the calculated systems. The specific role of histidine-64 in the distal pocket was examined in more detail in this study than in other studies in the literature. Although the present calculated results do not change the previous conclusion that the hydrogen bonding by the distal histidine-64 residue plays a major role in the O2/CO discrimination by Mb, more details about the interaction between the protein environment and the bound ligand have been revealed in this study by comparing the binding energies of AB to a porphyrin and the various myoglobins. The changes in the experimental binding energies from one system to another are well reproduced by the calculations. Without constraints on the residues in geometry optimization, the dispersion correction is necessary, since it improves the calculated structures and energetic results significantly. PMID:23661270

  2. Synthesis, spectroscopic characterizations, crystal structures and DFT studies of nalidixic acid carbonyl hydrazones derivatives

    NASA Astrophysics Data System (ADS)

    Bergamini, F. R. G.; Ribeiro, M. A.; Lancellotti, M.; Machado, D.; Miranda, P. C. M. L.; Cuin, A.; Formiga, A. L. B.; Corbi, P. P.

    2016-09-01

    This article describes the synthesis and characterization of the 1-ethyl-7-methyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carbohydrazide (hzd) and six carbonyl hydrazones derivatives of the nalidixic with 1H-pyrrol-2-ylmethylidene (hpyrr), 1H-imidazol-2-ylmethylidene (h2imi), pyridin-2-ylmethylidene (h2py), pyridin-3-ylmethylidene (h3py), pyridin-4-ylmethylidene(h4py) and (2-hydroxyphenyl)methylidene (hsali). The carbonyl hydrazones were characterized by elemental and ESI-QTOF-MS analyses, IR and detailed NMR spectroscopic measurements. The 2D NMR experiments allowed the unambiguous assignment of the hydrogen, carbon and nitrogen atoms, which have not been reported for nalidixic acid carbonyl hydrazone derivatives so far. Crystal structures of hzd and the new carbonyl hydrazones h2imi, hpyrr and h3py were determined by X-ray diffraction studies. Although the synthesis of hzd was reported decades ago, the hzd crystal structure have not been reported yet. Geometric optimizations of all the characterized structures were performed with the aid of DFT studies. Despite the fact that the hydrazones with 2-pyridine carboxylic acid (h2py) and salicyl aldehyde (hsali) were already reported by literature, a detailed spectroscopic study followed by DFT studies are also reported for such compounds in this manuscript. Antimicrobial studies of the compounds are also presented.

  3. Inclusion complexes of cypermethrin and permethrin with monochlorotriazinyl-beta-cyclodextrin: A combined spectroscopy, TG/DSC and DFT study

    NASA Astrophysics Data System (ADS)

    Yao, Qi; You, Bin; Zhou, Shuli; Chen, Meng; Wang, Yujiao; Li, Wei

    2014-01-01

    The suitable size hydrophobic cavity and monochlorotriazinyl group as a reactive anchor make MCT-β-CD to be widely used in fabric finishing. In this paper, the inclusion complexes of monochlorotriazinyl-beta-cyclodextrin (MCT-β-CD) with cypermethrin (CYPERM) and permethrin (PERM) are synthesized and analyzed by TG/DSC, FT-IR and Raman spectroscopy. TG/DSC reveals that the decomposed temperatures of inclusion complexes are lower by 25-30 °C than that of physical mixtures. DFT calculations in conjunction with FT-IR and Raman spectral analyses are used to study the structures of MCT-β-CD and their inclusion complexes. Four isomers of trisubstituted MCT-β-CD are designed and DFT calculations reveal that 1,3,5-trisubstituted MCT-β-CD has the lowest energy and can be considered as main component of MCT-β-CD. The ground-state geometries, vibrational wavenumbers, IR and Raman intensities of MCT-β-CD and their inclusion complexes were calculated at B3LYP/6-31G (d) level of theory. Upon examining the optimized geometry of inclusion complex, we find that the CYPERM and PERM are inserted into the toroid of MCT-β-CD from the larger opening. The band at 1646 cm-1 in IR and at 1668 cm-1 in Raman spectrum reveals that monochloroazinyl group of MCT-β-CD exists in ketone form but not in anion form. The noticeable IR and Raman shift of phenyl reveals that these two benzene rings of CYPERM and PERM stays inside the cavity of MCT-β-CD and has weak interaction with MCT-β-CD. This spectroscopy conclusion is consistent with theoretical predicted structure.

  4. DFT-D study of 14N nuclear quadrupolar interactions in tetra-n-alkyl ammonium halide crystals.

    PubMed

    Dib, Eddy; Alonso, Bruno; Mineva, Tzonka

    2014-05-15

    The density functional theory-based method with periodic boundary conditions and addition of a pair-wised empirical correction for the London dispersion energy (DFT-D) was used to study the NMR quadrupolar interaction (coupling constant CQ and asymmetry parameter ηQ) of (14)N nuclei in a homologous series of tetra-n-alkylammonium halides (C(x)H(2x+1))4N(+)X(-) (x = 1-4), (X = Br, I). These (14)N quadrupolar properties are particularly challenging for the DFT-D computations because of their very high sensitivity to tiny geometrical changes, being negligible for other spectral property calculations as, for example, NMR (14)N chemical shift. In addition, the polarization effect of the halide anions in the considered crystal mesophases combines with interactions of van der Waals type between cations and anions. Comparing experimental and theoretical results, the performance of PBE-D functional is preferred over that of B3LYP-D. The results demonstrated a good transferability of the empirical parameters in the London dispersion formula for crystals with two or more carbons per alkyl group in the cations, whereas the empirical corrections in the tetramethylammonium halides appeared to be inappropriate for the quadrupolar interaction calculation. This is attributed to the enhanced cation-anion attraction, which causes a strong polarization at the nitrogen site. Our results demonstrated that the (14)N CQ and ηQ are predominantly affected by the molecular structures of the cations, adapted to the symmetry of the anion arrangements. The long-range polarization effect of the surrounding anions at the target nitrogen site becomes more important for cells with lower spatial symmetry. PMID:24758512

  5. Interrogating the strength of the bond between salt and water: a combined DFT and MP2 study

    NASA Astrophysics Data System (ADS)

    Li, Bo; Michaelides, Angelos; Scheffler, Matthias

    2007-03-01

    The interaction of water with salt (NaCl) is of widespread importance and of considerable general interest. Although numerous theoretical studies have been reported [1], none has provided a convincingly reliable estimate of the strength of the bond between water and a flat NaCl surface, such as NaCl(001). Moreover, the computed adsorption energies predicted by DFT vary from 0.2-0.7 eV/H2O depending on the choice of exchange-correlation functional [2]. Here, we address this issue through an extensive series of periodic Hartree-Fock and post-Hartree Fock [Møller-Plesset perturbation (MP2) and coupled cluster (CCSD(T))] calculations. Periodic Hartree-Fock calculations have been performed for H2O molecules adsorbed on NaCl slabs, and by evaluating the local dependence of the correlation contribution to the adsorption energy with respect to cluster size, we obtain accurate MP2 and CCSD(T) estimates of the H2O adsorption energy on NaCl(001). Our computed adsorption energy, which is around 0.6 eV/H2O, comes close to the experimental value [3] and is at the upper end of the range predicted by DFT. [1] A. Verdaguer, G. M. Sacha, H. Bluhm, and M. Salmeron, Chem. Rev. 106, 1478 (2006). [2] B. Li, A. Michaelides, and M. Scheffler, in preparation. [3] L. W. Bruch, A. Glebov, J. P. Toennies, and H. Weiss, J. Chem. Phys. 103, 5109 (1995).

  6. Theoretical study of the adsorption of histidine amino acid on graphene

    NASA Astrophysics Data System (ADS)

    Rodríguez, S. J.; Makinistian, L.; Albanesi, E.

    2016-04-01

    Previous studies have demonstrated how the interactions between biomolecules and graphene play a crucial role in the characterization and functionalization of biosensors. In this paper we present a theoretical study of the adsorption of histidine on graphene using density functional theory (DFT). In order to evaluate the relevance of including the carboxyl (-COOH) and amino (-NH2) groups in the calculations, we considered i) the histidine complete (i.e., with its carboxyl and its amino groups included), and ii) the histidine’s imidazole ring alone. We calculated the density of states for the two systems before and after adsorption. Furthermore, we compared the results of three approximations of the exchange and correlation interactions: local density (LDA), the generalized gradients by Perdew, Burke and Ernzerhof (GGA-PBE), and one including van der Waals forces (DFT-D2). We found that the adsorption energy calculated by DFT-D2 is higher than the other two: Eads-DFT-D2 >E ads-LDA >E ads-GGA . We report the existence of charge transfer from graphene to the molecule when the adsorption occurs; this charge transfer turns up to be greater for the complete histidine than for the imidazole ring alone. Our results revealed that including the carboxyl and amino groups generates a shift in the states of imidazole ring towards EF .

  7. Theoretical studies of interstellar processes

    NASA Technical Reports Server (NTRS)

    Guberman, Steven L.

    1995-01-01

    We have been studying the dissociative recombination (DR) of HeH(+) with an electron with the goal of calculating accurate cross sections and rate coefficients to allow for the accurate modelling of the abundance of HeH(+) in planetary nebulae and supernova envelopes. A unique feature of the HeH potential curves is that none of the neutral states cross the ion curve. This required a new approach to the calculation of DR cross sections and rate coefficients that had not yet appeared in the literature. Because of the lack of a potential curve crossing, the initial electron capture occurs by Born-Oppenheimer breakdown, i.e. by the interaction of the motion of the incoming electron with the nuclear motion. This same mechanism also drives DR in H3(+) and the methods developed and described below for HeH(+) DR will be used for the future calculation of H3(+) DR.

  8. A combined experimental and DFT study of a novel unsymmetrical azine 2-(4-methoxybenzylidene)-1-(1-(4-isobutylphenyl) ethylidene) hydrazine

    NASA Astrophysics Data System (ADS)

    Vijaya, P.; Sankaran, K. R.

    2015-03-01

    A novel unsymmetrical azine 2-(4-methoxybenzylidene)-1-(1-(4-isobutylphenyl) ethylidene) hydrazine (UA) was prepared and characterized by IR, 1H and 13C NMR spectral studies. A 2D - potential energy scan (PES) of p-isobutylacetophenone (IBAP) was the portal to the conformational analysis of UA by density functional theory (DFT) methods using 6-31G(d,p) basis set by Gaussian 03 program. The theoretical IR frequencies were found to be in good agreement with the experimental values. The IR frequencies of UA were analyzed by means of Potential energy Distribution (PED %) calculation using Vibrational Energy Distribution Analysis (VEDA 4) program. The experimental NMR chemical shift values of UA were compared with the theoretical values obtained by DFT method. Nonlinear optical behavior of the unsymmetrical azine is also examined by the theoretically predicted values of dipole moment (μ), polarizability (α0) and first hyperpolarizability (βtot). Stability of the UA molecule has been analyzed using NBO analysis. The electrochemistry of UA studied experimentally by cyclic voltammetry is complemented by the computational analysis of the anionic form of the molecule UA. The determination of various global and local reactivity descriptors in the context of chemical reactivity is also performed and the electrophilicity at the vital atomic sites in UA is revealed. Bader's Atoms in molecules (AIM) theory of UA indicated the presence of intramolecular hydrogen bonding in the molecule. The molecular electrostatic potential (MEP) and HOMO-LUMO orbital analysis are also performed for the molecule UA.

  9. Study on the structure and vibrational spectra of efavirenz conformers using DFT: Comparison to experimental data

    NASA Astrophysics Data System (ADS)

    Mishra, Soni; Tandon, Poonam; Ayala, A. P.

    2012-03-01

    Efavirenz, (S)-6-chloro-4-(cyclopropylethynyl)-1,4-dihydro-4-(trifluoromethyl)-2H-3,1-benzoxazin-2-one, is an anti HIV agent belonging to the class of the non-nucleoside inhibitors of the HIV-1 virus reverse transcriptase. A systematic quantum chemical study of the possible conformations, their relative stabilities and vibrational spectra of efavirenz has been reported. Structural and spectral characteristics of efavirenz have been studied by vibrational spectroscopy and quantum chemical methods. Density functional theory (DFT) calculations for potential energy curve, optimized geometries and vibrational spectra have been carried out using 6-311++G(d,p) basis sets and B3LYP functionals. Based on these results, we have discussed the correlation between the vibrational modes and the crystalline structure of the most stable form of efavirenz. A complete analysis of the experimental infrared and Raman spectra has been reported on the basis of wavenumber of the vibrational bands and potential energy distribution. The infrared and the Raman spectra of the molecule based on DFT calculations show reasonable agreement with the experimental results. The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule.

  10. Electronic Structure of Fullerene Acceptors in Organic Bulk-Heterojunctions. A Combined EPR and DFT Study

    SciTech Connect

    Mardis, Kristy L.; Webb, J.; Holloway, Tarita; Niklas, Jens; Poluektov, Oleg G.

    2015-11-16

    Organic photovoltaic (OPV) devices are a promising alternative energy source. Attempts to improve their performance have focused on the optimization of electron-donating polymers, while electron-accepting fullerenes have received less attention. Here, we report an electronic structure study of the widely used soluble fullerene derivatives PC61BM and PC71BM in their singly reduced state, that are generated in the polymer:fullerene blends upon light-induced charge separation. Density functional theory (DFT) calculations characterize the electronic structures of the fullerene radical anions through spin density distributions and magnetic resonance parameters. The good agreement of the calculated magnetic resonance parameters with those determined experimentally by advanced electron paramagnetic resonance (EPR) allows the validation of the DFT calculations. Thus, for the first time, the complete set of magnetic resonance parameters including directions of the principal g-tensor axes were determined. For both molecules, no spin density is present on the PCBM side chain, and the axis of the largest g-value lies along the PCBM molecular axis. While the spin density distribution is largely uniform for PC61BM, it is not evenly distributed for PC71BM.

  11. Electronic Structure of Fullerene Acceptors in Organic Bulk-Heterojunctions: A Combined EPR and DFT Study.

    PubMed

    Mardis, Kristy L; Webb, Jeremy N; Holloway, Tarita; Niklas, Jens; Poluektov, Oleg G

    2015-12-01

    Organic photovoltaic (OPV) devices are a promising alternative energy source. Attempts to improve their performance have focused on the optimization of electron-donating polymers, while electron-accepting fullerenes have received less attention. Here, we report an electronic structure study of the widely used soluble fullerene derivatives PC61BM and PC71BM in their singly reduced state, that are generated in the polymer:fullerene blends upon light-induced charge separation. Density functional theory (DFT) calculations characterize the electronic structures of the fullerene radical anions through spin density distributions and magnetic resonance parameters. The good agreement of the calculated magnetic resonance parameters with those determined experimentally by advanced electron paramagnetic resonance (EPR) allows the validation of the DFT calculations. Thus, for the first time, the complete set of magnetic resonance parameters including directions of the principal g-tensor axes were determined. For both molecules, no spin density is present on the PCBM side chain, and the axis of the largest g-value lies along the PCBM molecular axis. While the spin density distribution is largely uniform for PC61BM, it is not evenly distributed for PC71BM. PMID:26569578

  12. A DFT study of a new class of gold nanocluster-photochrome multi-functional switches.

    PubMed

    Fihey, Arnaud; Maurel, François; Perrier, Aurélie

    2014-12-21

    With the help of a computational scheme combining molecular dynamics, DFT and TD-DFT methods, the conformational, electronic and optical properties of a new class of hybrid compounds where a photochromic molecule belonging to the dithienylethene family (DTE) is covalently linked to a Au25 nanocluster (gold nanocluster or GNC) are investigated. We compare two types of hybrid GNC-DTE systems where the aromatic linker between the metallic and the DTE moieties is either a phenyl or a thiophene ring. By examining the perturbation of the DTE electronic structure after grafting upon the GNC, we show that the hybrid system with a phenyl linker should preserve its photochromic activity. For the latter system, we have then studied the possible energy and electron transfer between the GNC and the DTE units. The energy transfer between the two moieties can be a priori discarded while a uni-directional electron transfer should take place from the GNC to the excited DTE. We show that this transfer can be controlled by switching the state of the molecule. PMID:25363237

  13. Electronic properties of transition metal atoms on Cu2 N/Cu(100): a DFT comparative study

    NASA Astrophysics Data System (ADS)

    Ferron, Alejandro; Lado, José; Fernández-Rossier, Joaquín

    2015-03-01

    We study the electronic and magnetic properties of individual transition metal atoms (Ti, V, Cr, Mn, Fe, Co and Ni) deposited on a Cu2N /Cu(100) surface by means of spin-polarized density functional theory (DFT) calculations. We focus our work on a comparative study of the various quantities, such as magnetic moment, orbital occupation, structural properties, hybridization with the substrate and spin polarization of the substrate, paying attention to the trends as the transition metal is changed. In this work we try to go beyond existing theoretical works by providing a comprehensive and comparative study of the electronic, magnetic and structural properties of these seven atoms including also Ni, for which there are no published calculations to the best of our knowledge. In the case of Mn, Fe and Co, we connect our results with the existing scanning tunneling microscope experiments. A.F. acknowledges funding from the European Union's Seventh Framework Programme for research, technological development and demonstration, under the PEOPLE programme, Marie Curie COFUND Actions, grant agreement number 600375 and CONICET.

  14. Analysis on linear and nonlinear optical properties of two Bisphenols with DFT approach: A comparative study

    NASA Astrophysics Data System (ADS)

    Vijayalakshmi, S.; Kalyanaraman, S.

    2015-04-01

    Density functional theory (DFT) method with B3LYP functional has been employed for the polarizability (α) and first order hyperpolarizability (β) calculations of two Bisphenols (4,4‧ thiodiphenol and 4,4‧ sulfonyldiphenol). Correlation between the dipole moment, polarizability and charge distribution is analyzed extensively. The calculated octupolar over dipolar contribution ratio parameter ρ from the hyperpolarizability components gives rise to macroscopic second harmonic generation (SHG) phenomenon identifying with the dipole nature of 4,4‧ thiodiphenol and the tendency towards the octupole nature of 4,4‧ sulfonyldiphenol molecule. Discussions on the geometrical structures of both Bisphenol molecules have been extended based on the comparison of optimized gas phase with solid state geometrical parameters to explain the high coplanarity in 4,4‧ sulfonyldiphenol molecule which leads to the extended π-conjugation. Theoretically predicted large value of SHG in 4,4‧ sulfonyldiphenol and zero value in case of 4,4‧ thiodiphenol are confirmed with Kurtz-Perry Powder technique.

  15. Crystal structure, vibrational studies, optical properties and DFT calculation of bis 2-aminobenzothiazolium tetrachloridocuprate.

    PubMed

    Kessentini, A; Belhouchet, M; Abid, Y; Minot, C; Mhiri, T

    2014-03-25

    The zero dimensional organic-inorganic hybrid compound (C7H7N2S)2CuCl4 was synthesized and characterized by X-ray diffraction, infrared absorption, Raman spectroscopy scattering and optical transmission measurements. The title compound crystallizes in the monoclinic system with P21/c space group. The unit cell parameters are a=7.060 (5) Å, b=9.748 (5) Å, c=14.037 (5) Å, β=98.520 (5)° and Z=2. The copper (II) ion has square planar coordination environment and the structure is built up from isolated [CuCl4](2)(-) anion surrounded by organic cations connected together via N-H⋯Cl hydrogen bonding. Room temperature IR and Raman spectra of the title compound were recorded and analyzed. The theoretical geometrical parameters in the ground state have been investigated by density functional theory (DFT) with the B3LYP/LanL2DZ level of theory. The organic-inorganic hybrid crystal thin film can be easily prepared by spin-coating method from the ethanol solution of the (C7H7N2S)2CuCl4 compound and it showed characteristic absorptions of Cu-Cl based layered perovskite centered at 288 and 400 nm. PMID:24326264

  16. Surface mediated chiral interactions between cyclodextrins and propranolol enantiomers: a SERS and DFT study.

    PubMed

    Stiufiuc, Rares; Iacovita, Cristian; Stiufiuc, Gabriela; Bodoki, Ede; Chis, Vasile; Lucaciu, Constantin M

    2015-01-14

    The nanoparticles mediated enantioselective recognition of propranolol enantiomers through native cyclodextrin complexation has been investigated by using surface-enhanced Raman spectroscopy (SERS). The highly efficient chiral recognition mechanism is based on a synergistic interaction between spherical noble metal nanoparticles, propranolol enantiomers and native cyclodextrins (CDs). Amongst the native cyclodextrins, β-CD has the highest chiral recognition ability for propranolol enantiomers, due to its specific shape and cavity size, thus producing the largest difference between the recorded SERS spectra of the two hosted enantiomers. The molecular interaction mechanism responsible for enantioselectivity was furthermore proven by quantum chemical calculations based on density functional theory (DFT). The theoretical calculations and experimental SER spectra allowed the assignment of functional moieties involved in the chiral recognition mechanism. The most important factors governing the highly efficient chiral probing by SERS are the fundamentally different mechanism of interaction between the R- and S-enantiomers and β-CD and the strength of interaction between the nanoparticle surface and the two propranolol-CD complexes. The role of metallic nanoparticles in the enantioselective recognition process has been experimentally evaluated by using silver and gold nanoparticles as SERS substrates, given their ability to interact differently with the complexes. The viability of this new method for chiral discrimination has been demonstrated for both substrates and could open new avenues for these kinds of applications. PMID:25420457

  17. Vibrational spectroscopic study and NBO analysis on tranexamic acid using DFT method

    NASA Astrophysics Data System (ADS)

    Muthu, S.; Prabhakaran, A.

    2014-08-01

    In this work, we reported the vibrational spectra of tranexamic acid (TA) by experimental and quantum chemical calculation. The solid phase FT-Raman and FT-IR spectra of the title compound were recorded in the region 4000 cm-1 to 100 cm-1 and 4000 cm-1 to 400 cm-1 respectively. The molecular geometry, harmonic vibrational frequencies and bonding features of TA in the ground state have been calculated by using density functional theory (DFT) B3LYP method with standard 6-31G(d,p) basis set. The scaled theoretical wavenumber showed very good agreement with the experimental values. The vibrational assignments were performed on the basis of the potential energy distribution (PED) of the vibrational modes. Stability of the molecule, arising from hyperconjugative interactions and charge delocalization, has been analyzed using Natural Bond Orbital (NBO) analysis. The results show that ED in the σ* and π* antibonding orbitals and second order delocalization energies E(2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. The electrostatic potential mapped onto an isodensity surface has been obtained. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The thermodynamic properties (heat capacity, entropy, and enthalpy) of the title compound at different temperatures were calculated in gas phase.

  18. Chalcogen analogues of nicotine lactam studied by NMR, FTIR, DFT and X-ray methods

    NASA Astrophysics Data System (ADS)

    Jasiewicz, Beata; Malczewska-Jaskóła, Karolina; Kowalczyk, Iwona; Warżajtis, Beata; Rychlewska, Urszula

    2014-07-01

    The selenoanalogue of nicotine has been synthesized and characterized by spectroscopic and X-ray diffraction methods. The crystals of selenonicotine are isomorphic with the thionicotine homologue and consist of molecules engaged in columnar π⋯π stacking interactions between antiparallely arranged pyridine moieties. These interactions, absent in other crystals containing nicotine fragments, seem to be induced by the presence of a lactam group. The molecular structures in the vacuum of the oxo-, thio- and selenonicotine homologues have been calculated by the DFT method and compared with the available X-ray data. The delocalized structure of thionicotine is stabilized by intramolecular Csbnd H⋯S hydrogen bond, which becomes weaker in the partial zwitterionic resonance structure of selenonicotine in favor of multiple Csbnd H⋯Se intermolecular hydrogen-bonds. The calculated data allow a complete assignment of vibration modes in the solid state FTIR spectra. The 1H and 13C NMR chemical shifts were calculated by the GIAO method with B3LYP/6-311G(3df) level. A comparison between experimental and calculated theoretical results indicates that the density functional B3LYP method provided satisfactory results for predicting FTIR, 1H, 13C NMR spectra properties.

  19. DFT study of 1-butyl-3-methylimidazolium salicylate: a third-generation ionic liquid.

    PubMed

    Armaković, Stevan; Armaković, Sanja J; Vraneš, Milan; Tot, Aleksandar; Gadžurić, Slobodan

    2015-09-01

    A detailed theoretical investigation of the third-generation ionic liquid (IL) 1-butyl-3-methylimidazolium salicylate ([BMIM][Sal]), performed within the framework of density functional theory (DFT), is presented in this paper. The B3LYP-D3, M06-2X, and M06-2X-D3 functionals were used to obtain the equilibrium geometries of the two ions [BMIM](+) and [Sal](-). It is shown that the equilibrium ion geometries obtained with the dispersion-corrected B3LYP functional are very close to the ion geometries obtained with the M06-2X and M06-2X-D3 functionals. Global reactivity was assessed using molecular orbital theory and quantum molecular descriptors. Molecular electrostatic potential (MEP) surfaces and average local ionization energy (ALIE) surfaces were created in order to elucidate the charge distribution and reactivity of the investigated IL. Ion-pair binding energies were calculated with all three functionals, and the results confirmed the presence of a strong electrostatic interaction between the ions, while further insight into the interactions between the two ions was obtained by analyzing noncovalent interactions based on the reduced density gradient (RDG) surface, which revealed a total of nine interactions between the ions. Finally, the aromaticity of each ion was investigated by calculating the nucleus-independent chemical shift (NICS) parameter, which indicated that significant changes in the charge delocalization on each ion occur when the two ions interact. PMID:26318199

  20. Exploring the interaction between lithium ion and defective graphene surface using dispersion corrected DFT studies

    SciTech Connect

    Vijayakumar, M.; Hu, Jian Z.

    2013-10-15

    To analyze the lithium ion interaction with realistic graphene surfaces, we carried out dispersion corrected DFT-D3 studies on graphene with common point defects and chemisorbed oxygen containing functional groups along with defect free graphene surface. Our study reveals that, the interaction between lithium ion (Li+) and graphene is mainly through the delocalized π electron of pure graphene layer. However, the oxygen containing functional groups pose high adsorption energy for lithium ion due to the Li-O ionic bond formation. Similarly, the point defect groups interact with lithium ion through possible carbon dangling bonds and/or cation-π type interactions. Overall these defect sites render a preferential site for lithium ions compared with pure graphene layer. Based on these findings, the role of graphene surface defects in lithium battery performance were discussed.

  1. C2-Symmetric ferrocenyl bisthiazoles: synthesis, photophysical, electrochemical and DFT studies.

    PubMed

    Maragani, Ramesh; Gautam, Prabhat; Mobin, Shaikh M; Misra, Rajneesh

    2016-03-21

    A series of donor-acceptor ferrocenyl substituted bisthiazoles 3-8 were designed and synthesized by the Pd-catalyzed Suzuki, Heck, and Sonogashira cross-coupling reactions. Their photophysical, electrochemical and computational studies reveal strong donor-acceptor interactions. The photonic and electrochemical studies show that the ferrocenyl bisthiazoles with vinyl linkage ferrocenyl-bisthiazole 4, show better electronic communication compared to rest of the ferrocenyl bisthiazoles. The time dependent density functional theory (TD-DFT) calculation at B3LYP on the ferrocenyl substituted bisthiazoles 3-5 was performed, in which the ferrocenyl-bisthiazole 4 shows strong donor-acceptor interactions compared to the Fc-bisthiazoles 3 and 5. The thermal stability of the ferrocenyl substituted bisthiazoles 3-8 is reported, in which Fc-bisthiazole 8 shows high thermal stability. The single crystal structures of ferrocenyl-bisthiazoles 3 and 5 are reported. PMID:26866584

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

    NASA Astrophysics Data System (ADS)

    Asath, R. Mohamed; Premkumar, S.; Rekha, T. N.; Jawahar, A.; Mathavan, T.; Benial, A. Milton Franklin

    2016-05-01

    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 confirm the NLO activity of the molecule. Hence, the ACTP molecule is a promising candidate for NLO materials.

  3. Synthesis, characterization and DFT studies of diethyl 4-hydroxy-6-nitro-4H-chromene-2,3-dicarboxylate

    NASA Astrophysics Data System (ADS)

    Dinparast, Leila; Valizadeh, Hassan; Vessally, Esmail; Bahadori, Mir Babak

    2016-02-01

    In the present study, diethyl 4-hydroxy-6-nitro-4H-chromene-2,3-dicarboxylate (DHNC) was synthesized and characterized using FT-IR, 1H and 13CNMR spectroscopy, mass spectrometry and UV-Vis (200-700 nm, in DMSO) spectrum. The structure of the title molecule was optimized at the B3LYP and PBE1PBE levels of theory using 6-311++G(d,p) basis set. The fundamental vibrational modes and chemical shifts of 1H and 13C of the present molecule were calculated using the B3LYP/6-311++G(d,p) and PBE1PBE/6-311++G(d,p) methods. UV-Vis spectrum of the title molecule was also calculated in DMSO and gas phase. The high stability and charge delocalization of DHNC arising from intramolecular hyperconjugative interaction confirmed with the NBO analysis at two DFT methods. Theoretical studies of the molecular orbitals such as HOMO-LUMO energy gap, mapped molecular electrostatic potential (MEP) surfaces and the Mulliken and NBO charges were also performed with the same levels of theory. In this work, the computed results and experimental observations support well each other.

  4. Mechanistic and kinetic study on the reactions of coumaric acids with reactive oxygen species: a DFT approach.

    PubMed

    Garzón, Andrés; Bravo, Iván; Barbero, Antonio J; Albaladejo, José

    2014-10-01

    The mechanism and kinetics of reactions between coumaric acids and a series of reactive oxygen species ((•)OX) was studied through the density functional theory (DFT). H atom abstraction from -OH and -COOH groups and addition to the nonaromatic double bond were the most representative reaction pathways chosen for which free energy barriers and rate constants were calculated within the transition state theory (TST) framework. From these calculations, it was estimated that (•)OH > (•)OCH3 > (•)OOH > (•)OOCH3 is the order of reactivity of (•)OX with any coumaric acid. The highest rate constant was estimated for p-coumaric acid + (•)OH reaction, whereas the rest of the (•)OX species are more reactive with o-coumaric acid. On the basis of the calculated rate constants, H abstraction from a -OH group should be the main mechanism for the reactions involving (•)OCH3, (•)OOH, and (•)OOCH3 radicals. Nevertheless, the addition mechanism, which sometimes is not considered in theoretical studies on reactions of phenolic compounds with electrophilic species, could play a relevant role in the global mechanism of coumaric acid + (•)OH reactions. PMID:25166496

  5. A DFT study of addition reaction between fragment ion (CH₂) units and fullerene (C₆₀) molecule.

    PubMed

    Zaragoza, Irineo Pedro; Vergara, Jaime; Pérez-Manríquez, Liliana; Salcedo, Roberto

    2011-05-01

    The theoretical study of the interaction between CH(2) and fullerene (C(60)) suggests the existence of an addition reaction mechanism; this feature is studied by applying an analysis of electronic properties. Several different effects are evident in this interaction as a consequence of the particular electronic transfer which occurs during the procedure. The addition or insertion of the methylene group results in a process, where the inclusion of CH(2) into a fullerene bond produces the formation of several geometric deformations. A simulation of these procedures was carried out, taking advantage of the dynamic semi-classical Born-Oppenheimer approximation. Dynamic aspects were analyzed at different speeds, for the interaction between the CH(2) group and the two bonds: CC (6, 6) and CC (6, 5) respectively on the fullerene (C(60)) rings. All calculations which involved electrons employed DFT as well as exchange and functional correlation. The results indicate a tendency for the CH(2) fragment to attack the CC (6, 5) bond. PMID:20658255

  6. Ab initio and DFT studies of the structure and vibrational spectra of anhydrous caffeine

    NASA Astrophysics Data System (ADS)

    Srivastava, Santosh K.; Singh, Vipin B.

    2013-11-01

    Vibrational spectra and molecular structure of anhydrous caffeine have been systematically investigated by second order Moller-Plesset (MP2) perturbation theory and density functional theory (DFT) calculations. Vibrational assignments have been made and many previous ambiguous assignments in IR and Raman spectra are amended. The calculated DFT frequencies and intensities at B3LYP/6-311++G(2d,2p) level, were found to be in better agreement with the experimental values. It was found that DFT with B3LYP functional predicts harmonic vibrational wave numbers more close to experimentally observed value when it was performed on MP2 optimized geometry rather than DFT geometry. The calculated TD-DFT vertical excitation electronic energies of the valence excited states of anhydrous caffeine are found to be in consonance to the experimental absorption peaks.

  7. Properties of noncovalent tetraphenylporphine···C60 dyads as studied by different long-range and dispersion-corrected DFT functionals.

    PubMed

    Amelines-Sarria, Oscar; Basiuk, Vladimir A; Duarte-Alaniz, Víctor; Rivera, Margarita

    2015-11-01

    The noncovalent dyad of tetraphenylporphine and C60 fullerene (H2TPP···C60) and the tetraphenylporphine dimer (H2TPP···H2TPP) were studied by density functional theory (DFT), using functionals that incorporate empirical dispersion correction (DFT-D), functionals that use a long-range correction (LC) scheme, a hybrid functional (B3LYP) and a highly parametrized empirical exchange-correlation functional (M05-2X). The results were compared to X-ray structures and interaction energies reported in previous experimental and theoretical studies. It was found that B3LYP and CAM-B3LYP functionals fail to reproduce the X-ray structures and binding energies of the TPP···C60 system. DFT-D functionals overestimated the π···π energy interactions for both systems, however, the optimized structures agree well with those observed experimentally. The LC-BLYP functional predicts geometries similar to X-ray structures; nevertheless, due to the lack of correction in the dispersion energy, the predicted energies for both model systems are low. On the other hand, the M05-2X functional exhibited the best performance. Both the structures and binding energies calculated with M05-2X are consistent with experimental and theoretical evidence reported by other authors, as well as with our experimental results obtained by means of atomic force microscopy on H2TPP thin films grown on the HOPG/C60 substrate by physical vapor deposition. PMID:26422808

  8. Interaction between fullerene-wheeled nanocar and gold substrate: A DFT study

    NASA Astrophysics Data System (ADS)

    Ahangari, M. Ghorbanzadeh; Ganji, M. Darvish; Jalali, A.

    2016-09-01

    Since the successful synthesis of nanocar and its surprising movement on the gold surface, several theoretical investigations have been devoted to explain the interaction properties as well as its movement mechanism on the substrate. All of them failed, however, to gain a clear theoretical insight into the respected challenges because of the weak computational methods implemented for this complex system including heavy metal atoms and giant size of the whole system. In this work, we have investigated the adsorption of fullerene-wheeled nanocar onto a Au (1 1 1) substrate using the comprehensive first-principles density functional theory (DFT) simulations. The binding energy between the nanocar and Au (1 1 1) surface was determined to be -9.43 eV (-217.45 kcal/mol). The net charge transfer from the nanocar to the gold substrate was calculated to be about 9.56 electrons. Furthermore, the equilibrium distances between the Au surface and the C60 molecule and nanocar chassis were estimated to be 2.20 Å and 2.30 Å, respectively. The BSSE correction was also considered in the binding energy estimation and the result show that the BSSE correction significantly affects the calculated binding energy for such systems. Finally, we have performed ab initio molecular dynamics simulation for a single C60 fullerene on the gold surface at room temperature. Our first-principles result shows that ambient condition affect remarkably on the adsorption property of fullerene on the gold surface. We also observed that the C60 fullerene wheel slips by approximately 3.90 Å within 5 ps of simulation time at 300 K.

  9. Theoretical studies of chemical reaction dynamics

    SciTech Connect

    Schatz, G.C.

    1993-12-01

    This collaborative program with the Theoretical Chemistry Group at Argonne involves theoretical studies of gas phase chemical reactions and related energy transfer and photodissociation processes. Many of the reactions studied are of direct relevance to combustion; others are selected they provide important examples of special dynamical processes, or are of relevance to experimental measurements. Both classical trajectory and quantum reactive scattering methods are used for these studies, and the types of information determined range from thermal rate constants to state to state differential cross sections.

  10. DFT Study of Solvent Effects on Conformational Equilibria and Vibrational Spectra of 4-(1-PYRROLIDINYL)PIPERAZINE

    NASA Astrophysics Data System (ADS)

    Baglayan, O.; Kesan, G.; Parlak, C.; Senyel, M.

    2012-06-01

    The optimized structural parameters (bond lengths, bond and dihedral angles), conformational equilibria and normal mode frequencies and corresponding vibrational assignments of 4-(1-Pyrrolidinyl)piperazine (4-pypp) have been examined by means of B3LYP hybrid density functional theory (DFT) method with 6-31++G(d,p) basis set. Furthermore, reliable vibrational assignments have made on the basis of potential energy distribution (PED) calculated and the thermodynamics functions, highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of 4-pypp (C_8H17N_3) have been predicted. Calculations are employed for different conformations of 4-pypp both in gas phase and in solution. Solvent effects are investigated using chloroform and dimethylsulfoxide. Results from the theoretical values are showed that the structural parameters, mole fractions of stable conformers, vibrational frequencies, IR intensities and Raman activities of 4-pypp are solvent dependent. {Keywords}: 4-(1-Pyrrolidinyl)piperazine, vibrational spectra, solvent effect, DFT.

  11. Self-assembled monolayers of methylselenolate on the Au(111) surface: A combined STM and DFT study

    NASA Astrophysics Data System (ADS)

    El-Kareh, L.; Mehring, P.; Caciuc, V.; Atodiresei, N.; Beimborn, A.; Blügel, S.; Westphal, C.

    2014-01-01

    In this study scanning tunneling microscopy (STM) and density functional theory (DFT) were used to investigate the structural formation of methylselenolate (CH3Se) self-assembled monolayers (SAMs) on the Au(111) surface. SAMs were prepared by two different methods, from solution and by exposing the Au(111) surface to gaseous dimethyldiselenide (DMDSe). For methylselenolate (MSe) on the Au(111) surface, our STM measurements revealed the presence of (4 × √3) and (3 × 2√3) rectangular striped phases. These structures were verified by DFT calculations. For both phases, the DFT calculations clearly found a bridge adsorption geometry for MSe on Au(111). Furthermore, they provide information about the electronic structure of the MSe-SAMs.

  12. Relationship between electronic properties and drug activity of seven quinoxaline compounds: A DFT study

    NASA Astrophysics Data System (ADS)

    Behzadi, Hadi; Roonasi, Payman; Assle taghipour, Khatoon; van der Spoel, David; Manzetti, Sergio

    2015-07-01

    The quantum chemical calculations at the DFT/B3LYP level of theory were carried out on seven quinoxaline compounds, which have been synthesized as anti-Mycobacterium tuberculosis agents. Three conformers were optimized for each compound and the lowest energy structure was found and used in further calculations. The electronic properties including EHOMO, ELUMO and related parameters as well as electron density around oxygen and nitrogen atoms were calculated for each compound. The relationship between the calculated electronic parameters and biological activity of the studied compounds were investigated. Six similar quinoxaline derivatives with possible more drug activity were suggested based on the calculated electronic descriptors. A mechanism was proposed and discussed based on the calculated electronic parameters and bond dissociation energies.

  13. Effect of organic molecules on hydrolysis of peptide bond: A DFT study

    NASA Astrophysics Data System (ADS)

    Makshakova, Olga; Ermakova, Elena

    2013-03-01

    The activation and inhibition effects of small organic molecules on peptide hydrolysis have been studied using a model compound dialanine and DFT approach. Solvent-assisted and non-assisted concerted mechanisms were analyzed. Several transition states for the systems: alanine dipeptide-water molecule in complexes with alcohol molecules, acetonitrile, dimethylsulfoxide, propionic, lactic and pyruvic acids and water molecules were localized. The formation of hydrogen bonds between dipeptide, reactive water molecule and molecules of solvents influences the activation energy barrier of the peptide bond hydrolytic reaction. Strong effect of organic acids on the activation energy barrier correlates with their electronegativity. Acetonitrile can act as an inhibitor of reaction. Mechanisms of regulation of the activation energy barrier are discussed in the terms of donor-acceptor interactions.

  14. DFT study on the structural and electronic properties of Pt-doped boron nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Vessally, E.; Dehbandi, B.; Edjlali, Ladan

    2016-06-01

    First-principles calculations based on density functional theory were carried out to investigate the structural and electronic properties of Pt substitution-doped boron nitride (BN) nanotubes. The electronic and structural properties were studied for substituted Pt in the boron and the nitrogen sites of the (BN) nanotube. The band gap significantly diminishes to 2.095 eV for Pt doping at the B site while the band gap diminishes to 2.231 eV for Pt doping at the N site. The band density increases in both the valence band and the conduction band after doping. The effects of the hardness and softness group 17 (halogen elements) were calculated by density functional theory (DFT).

  15. Encapsulation of fluoroethanols in pristine and Stone-Wales defect boron nitride nanotube - A DFT study

    NASA Astrophysics Data System (ADS)

    Umadevi, P.; Aiswarya, T.; Senthilkumar, L.

    2015-08-01

    The encapsulation of ethanol and fluoroethanols in pristine and Stone-Wales (SW) defect boron nitride nanotubes (BNNT) with and without hydrogen passivation has been investigated using density functional theory method (DFT). The fluoroethanols are physisorped with the charge transfer from alcohols to BNNTs. The adsorption of ethanol is weak in all forms of BNNTs. The hydrogen passivated SW defect BNNTs show strong fluoroethanols adsorption capacity. The deformation energy for SW defect tubes is reduced due to hydrogen passivation. The HOMO-LUMO gap and Fermi level of the BNNTs are altered due to fluoroethanols encapsulation, which subsequently has reduced the work function and improved the electron emission property. The study concludes that BNNTs are efficient materials for ethanol storage and fluoroethanol capture.

  16. A DFT study on SO3 capture and activation over Si- or Al-doped graphene

    NASA Astrophysics Data System (ADS)

    Esrafili, Mehdi D.; Saeidi, Nasibeh; Nematollahi, Parisa

    2016-08-01

    This study reports the adsorption and favorable reaction mechanism of SO3 reduction by CO molecule over Si- or Al-doped graphene using DFT calculations. The adsorption energy of the most stable configuration of SO3 is calculated to be about -103 and -124 kcal/mol over the Si- and Al-doped graphene, respectively. The SO3 reduction over these surfaces proceeds through the following elementary steps (a) SO3 → SO2 + Oads and (b) Oads + CO → CO2. The estimated activation energy (Eact) for the dissociation of SO3 over the Si-doped graphene is about 9 kcal/mol smaller than that on the Al-doped graphene.

  17. DFT studies on the phenol and thiophenol interaction on an undecagold cluster surface

    NASA Astrophysics Data System (ADS)

    Jayanthi, N.; Cruz, J.; Pandiyan, T.

    2008-03-01

    The interaction of Au11 clustered phenol or thiophenol was carried out by density functional theory (DFT), the results showing that the O-H or S-H bonds were activated on the Au-catalytic surface by their strong absorption. For phenol, OH bonded with Au11 while for thiophenol both benzene and sulfur interacted with Au11, suggesting that the S-H bond cleavage on thiophenol is easier than O-H on phenol; this is supported by their binding energies and the molecular orbital studies, which indicate that the phenol adsorption on the Au-surface is an orbital controlled reaction while for thiophenol both charge density transfer and orbital are involved. In addition, the spectra of the density of state (DOS) confirm that there is a mixing of the p orbitals (O or S) of phenol or thiophenol with the d orbitals of Au to form an adsorption bond.

  18. Single-walled carbon nanotubes functionalized by a series of dichlorocarbenes: DFT study

    NASA Astrophysics Data System (ADS)

    Petrushenko, Igor K.; Petrushenko, Konstantin B.

    2016-02-01

    The structural and elastic properties of neutral and ionized dichlorocarbene (CCl2) functionalized single-walled carbon nanotubes (SWCNTs) were studied using density functional theory (DFT). The Young’s modulus of ionized pristine SWCNTs is found to decrease in comparison to that of neutral models. The interesting effect of increase in Young’s modulus values of ionized functionalized SWCNTs is observed. We ascribe this feature to the concurrent processes of the bond elongation on ionization and the local deformation on cycloaddition. The strong dependence of the elasticity modulus on the number of addends is also observed. However, the CCl2-attached SWCNTs in their neutral and ionized forms remain strong enough to be suitable for the reinforcement of composites. In contrast to the elastic properties, the binding energies do not change significantly, irrespective of CCl2 coverage.

  19. Adsorption of molecular oxygen on VIIIB transition metal-doped graphene: A DFT study

    NASA Astrophysics Data System (ADS)

    Nasehnia, F.; Seifi, M.

    2014-12-01

    Adsorption of molecular oxygen with a triplet ground state on Fe-, Co-, Ni-, Ru-, Rh-, Pd-, OS-, Ir- and Pt-doped graphene is studied using density functional theory (DFT) calculations. The calculations show that O2 molecule is chemisorbed on the doped graphene sheets with large adsorption energies ranging from -0.653 eV to -1.851 eV and the adsorption process is irreversible. Mulliken atomic charge analysis of the structure shows that charge transfer from doped graphene sheets to O2 molecule. The amounts of transferred charge are between 0.375e- to 0.650e-, indicating a considerable change in the structures conductance. These results imply that the effect of O2 adsorption on transition metal-doped graphene structures can alter the possibility of using these materials as a toxic-gas (carbon monoxide, hydrogen fluoride, etc.) sensor.

  20. DFT study and Hirshfeld surface analysis of third polymorph of sulfamerazine

    NASA Astrophysics Data System (ADS)

    Patel, Mahesh K.; Tailor, Sanjay M.; Patel, Urmila H.

    2016-05-01

    The third polymorph of sulfamerazine crystallized as two molecules per asymmetric unit having orthorhombic system with space group Pna21. The ab-initio and density functional theory (DFT) are used to optimize the molecular structure and to calculate frontier molecular orbitals and Mullikan charge distributions. The optimized geometry reveals that the predicted geometry can well reproduce structural parameters. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The Hirshfeld surfaces and consequently the fingerprint analysis have been performed to study the nature of interactions and their quantitative contributions towards the crystal packing. Finally, Hirshfeld surfaces, fingerprint plots and structural overlay are employed for a comparison of the two independent molecules in the asymmetric unit of sulfamerazine and also, for a comparison of reported sulfamerazine polymorph which is in the monoclinic crystal system.

  1. Theoretical structural and vibrational study of 5-trifluoromethyluracil. A comparison with uracil

    SciTech Connect

    Rudyk, Roxana; Ramos, María E.; Checa, María A.; Brandán, Silvia A.; Chamorro, Eduardo E.

    2014-10-06

    In the present work, a comparative study on the structural and vibrational properties of the 5-trifluoromethyluracil (TFMU) derivative with those corresponding to uracil in gas and aqueous solution phases was performed combining the available H{sup 1}-NMR, C{sup 13}-NMR, F{sup 19}-NMR and FTIR spectra with Density Functional Theory (DFT) calculations. Three stable conformers were theoretically determined in both media by using the hybrid B3LYP/6-31G* method. The solvent effects were simulated by means of the self-consistent reaction field (SCRF) method employing the integral equation formalism variant (IEFPCM). Complete assignments of the vibrational spectra in both phases were performed combining the internal coordinates analysis and the DFT calculations with the Scaled Quantum Mechanics Force Field (SQMFF) methodology. The atomic charges, bond orders, solvation energies, dipole moments, molecular electrostatic potentials and force constants parameters were calculated for the three conformers of TFMU in gas phase and aqueous solution.

  2. Understanding the domino reaction between 3-chloroindoles and methyl coumalate yielding carbazoles. A DFT study.

    PubMed

    Domingo, Luis R; Sáez, José A; Emamian, Saeed R

    2015-02-21

    The molecular mechanism of the reaction between N-methyl-3-chloroindole and methyl coumalate yielding carbazole has been studied using DFT methods at the MPWB1K/6-311G(d,p) level in toluene. This reaction is a domino process that comprises three consecutive reactions: (i) a polar Diels-Alder (P-DA) reaction between indole and methyl coumalate yielding two stereoisomeric [2 + 4] cycloadducts (CAs); (ii) the elimination of HCl from these CAs affording two stereoisomeric intermediates; and (iii) the extrusion of CO2 in these intermediates, finally yielding the carbazole. This P-DA reaction proceeds in a completely regioselective and slightly exo selective fashion. In spite of the highly polar character of this P-DA reaction, it presents a high activation enthalpy of 21.8 kcal mol(-1) due to the loss of the aromatic character of the indole during the C-C bond formation. Thermodynamic calculations suggest that the P-DA reaction is the rate-determining step of this domino reaction; in addition, the initial HCl elimination in the formal [2 + 4] CAs is kinetically favoured over the extrusion of CO2. Although the P-DA reaction is kinetically and thermodynamically very unfavourable, the easier HCl and CO2 elimination from the [2 + 4] CAs together with the strong exergonic character of the CO2 extrusion makes the P-DA reaction irreversible. An ELF topological analysis of the bonding changes along the P-DA reaction supports a two-stage one-step mechanism. An analysis of the global DFT reactivity indices at the ground state of the reagents confirms the highly polar character of this P-DA reaction. Finally, the complete regioselectivity of the studied reactions can be explained using the Parr functions. PMID:25520216

  3. Nuclear magnetic resonance, vibrational spectroscopic studies, physico-chemical properties and computational calculations on (nitrophenyl) octahydroquinolindiones by DFT method.

    PubMed

    Pasha, M A; Siddekha, Aisha; Mishra, Soni; Azzam, Sadeq Hamood Saleh; Umapathy, S

    2015-02-01

    In the present study, 2'-nitrophenyloctahydroquinolinedione and its 3'-nitrophenyl isomer were synthesized and characterized by FT-IR, FT-Raman, (1)H NMR and (13)C NMR spectroscopy. The molecular geometry, vibrational frequencies, (1)H and (13)C NMR chemical shift values of the synthesized compounds in the ground state have been calculated by using the density functional theory (DFT) method with the 6-311++G (d,p) basis set and compared with the experimental data. The complete vibrational assignments of wave numbers were made on the basis of potential energy distribution using GAR2PED programme. Isotropic chemical shifts for (1)H and (13)C NMR were calculated using gauge-invariant atomic orbital (GIAO) method. The experimental vibrational frequencies, (1)H and (13)C NMR chemical shift values were found to be in good agreement with the theoretical values. On the basis of vibrational analysis, molecular electrostatic potential and the standard thermodynamic functions have been investigated. PMID:25440584

  4. Spectroscopy, NMR and DFT studies on molecular recognition of crown ether bridged chiral heterotrinuclear salen Zn(II) complex

    NASA Astrophysics Data System (ADS)

    Gao, Feng; Ruan, Wen-Juan; Chen, Jia-Mei; Zhang, Ying-Hui; Zhu, Zhi-Ang

    2005-12-01

    A barium-containing crown ether bridged chiral heterotrinuclear salen Zn(II) complex BaZn 2L(ClO 4) 2, where L is a folded dinuclear chiral ( R, R)-salen ligand, has been synthesized and characterized by elemental analysis, 1H NMR, UV-vis, IR, circular dichroism (CD) spectra, and mass spectra. As a folded dinuclear chiral host, its recognition with achiral guests (imidazole derivatives), rigid bidentate guest (1,4-diazobicyclo[2,2,2]octane, DABCO) and chiral guests (amino acid methyl esters) was investigated by means of UV-vis spectrophotometric titration, CD spectra. The association constants of D-amino acid methyl esters are found to be higher than those of their L-enantiomer. The sandwich-type binding of BaZn 2L(ClO 4) 2-DABCO supramolecular assembly was specially studied via 1H NMR titration and 1H ROESY. To understand the recognition on molecular level, density functional theory (DFT) calculations on B3LYP/LanL2DZ were performed on the minimal energy conformations of host, guests, and host-guest complexes. The minimal energy conformations were obtained by molecular mechanics (MM) optimization and molecular dynamics (MD) simulation. The results of single point energy, HOMO energy, and charges transfer were analyzed. The results of theoretical calculations are in good agreement with the experimental data.

  5. Understanding the molecular mechanism and regioselectivity in the synthesis of celecoxib via a domino reaction: A DFT study.

    PubMed

    Emamian, Saeedreza

    2015-07-01

    The molecular mechanism and energetic of the domino reaction involved in the synthesis of celecoxib, a well-known anti-inflammatory drug, were theoretically studied at the DFT-B3LYP/6-31G(*) level. The first reaction in this domino process, which is also the rate-determining step, is a complete regioselective [3+2] cycloaddition (32CA) reaction associated with the nucleophilic attack of C5 carbon atom of enamine 7 on the C3 carbon atom of nitrile imine 6, leading to cycloadduct 8. The second reaction is a rapid acid/base catalysed stepwise elimination reaction of the morpholine 9 from cycloadduct 8 affording celecoxibe 3. The results also show that neither molecular mechanism of reaction nor activation barriers are considerably affected by the inclusion of solvent. The calculated relative Gibbs free energies as well as local reactivity indices obtained using the calculated Parr functions explain the complete regioselective fashion provided by the 32CA reaction under consideration in excellent agreement with the experimental findings. PMID:26036921

  6. Complex of manganese (II) with curcumin: Spectroscopic characterization, DFT study, model-based analysis and antiradical activity

    NASA Astrophysics Data System (ADS)

    Gorgannezhad, Lena; Dehghan, Gholamreza; Ebrahimipour, S. Yousef; Naseri, Abdolhossein; Nazhad Dolatabadi, Jafar Ezzati

    2016-04-01

    The complex formation between curcumin (Cur) and Manganese (II) chloride tetrahydrate (MnCl2.4H2O) was studied by UV-Vis and IR spectroscopy. Spectroscopic data suggest that Cur can chelate Manganese cations. A simple multi-wavelength model-based method was used to define stability constant for complexation reaction regardless of the spectra overlapping of components. Also, pure spectra and concentration profiles of all components were extracted using this method. Density functional theory (DFT) was also used to view insight into complexation mechanism. Antioxidant activity of Cur and Cur-Mn(II) complex was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging method. Bond dissociation energy (BDE), the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and Molecular electrostatic potential (MEP) of Cur and the complex also were calculated at PW91/TZ2P level of theory using ADF 2009.01 package. The experimental results show that Cur has a higher DPPH radical scavenging activity than Cur-Mn(II). This observation is theoretically justified by means of lower BDE and higher HOMO and LUMO energy values of Cur ligand as compared with those of Cur-Mn(II) complex.

  7. C dbnd N sbnd N dbnd C conformational isomers of 2'-hydroxyacetophenone azine: FTIR matrix isolation and DFT study

    NASA Astrophysics Data System (ADS)

    Grzegorzek, Joanna; Mielke, Zofia; Filarowski, Aleksander

    2010-07-01

    2'-hydroxyacetophenone azine (APA) has been studied by matrix isolation infrared spectroscopy and quantum chemical calculations. The DFT/B3LYP/6-311++G(2d,2p) calculations demonstrated the existence of two conformers for the lowest energy E/ E configuration of APA, a s- trans and a gauche ones. The conformers are characterized by similar energies and differ in the value of a C dbnd N sbnd N dbnd C angle, that was calculated to be 180° for a planar s-trans conformer and 155° for a non-planar gauche one . The calculated barrier for conformational interconversion is also very low, ca. 1 kJ mol -1 for the conversion from a gauche conformer to a trans one. The FTIR spectra of an argon matrix doped with APA from a vapour above solid sample evidence the presence of both conformers that exhibit reversible interconversion at matrix temperatures. The comparison of the theoretical spectra with the experimental ones and reversible temperature dependence of the experimental spectra allowed for unambiguous spectroscopic characterization of the trans and gauche conformers. The experiment also demonstrated that a gauche conformer is more stable than a trans one. The spectra analysis indicates that transformation from a trans conformer to a gauche one weakens the intramolecular O sbnd H⋯N bonds in the molecule.

  8. DFT studies on the directing group dependent arene-alkene cross-couplings: arene activation vs. alkene activation.

    PubMed

    Zhang, Lei; Fang, De-Cai

    2015-08-01

    Due to its green-chemistry advantages, the dehydrogenative Heck reaction (DHR) has experienced enormous growth over the past few decades. In this work, two competing reaction channels were comparatively studied for the Pd(OAc)2-catalyzed DHRs of arenes with alkenes, referred to herein as the arene activation mechanism and the alkene activation mechanism, respectively, which mainly differ in the involvement of the reactants in the C-H activation step. Our calculations reveal that the commonly accepted arene activation mechanism is plausible for the desired arene-alkene cross-coupling; in contrast, the alternative alkene activation mechanism is kinetically inaccessible for the desired cross-coupling, but it is feasible for the homo-coupling of alkenes. The nature of directing groups on reactants could mainly determine the dominance of the two competing reaction routes, and therefore, influence the experimental yields. A wide range of directing groups experimentally used are examined by the density functional theory (DFT) method in this work, providing theoretical guidance for screening compatible reactants. PMID:26108375

  9. Vibrational frequency analysis, FT-IR, DFT and M06-2X studies on tert-Butyl N-(thiophen-2yl)carbamate

    NASA Astrophysics Data System (ADS)

    Sert, Yusuf; Singer, L. M.; Findlater, M.; Doğan, Hatice; Çırak, Ç.

    2014-07-01

    In this study, the experimental and theoretical vibrational frequencies of a newly synthesized tert-Butyl N-(thiophen-2yl)carbamate have been investigated. The experimental FT-IR (4000-400 cm-1) spectrum of the molecule in the solid phase have been recorded. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and bond angles) have been calculated by using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and DFT/M06-2X (the highly parametrized, empirical exchange correlation function) quantum chemical methods with the 6-311++G(d,p) basis set by Gaussian 09W software, for the first time. The vibrational frequencies have been assigned using potential energy distribution (PED) analysis by using VEDA 4 software. The computational optimized geometric parameters and vibrational frequencies have been found to be in good agreement with the corresponding experimental data, and with related literature results. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the other related molecular energy values have been calculated and are depicted.

  10. Cooperativity Assisted Shortening of Hydrogen Bonds in Crystalline Oxalic Acid Dihydrate: DFT and NBO Model Studies.

    PubMed

    Stare, Jernej; Hadži, Dušan

    2014-04-01

    The distance of ∼2.49 Å separating the carboxylic OH oxygen from the water oxygen atom in the α-polymorph of crystalline oxalic acid dihydrate is by ∼0.1 Å shorter than the average distance in carboxylic acid monohydrates. It is also by ∼0.2 Å shorter than the corresponding distance presently calculated for the heterotrimer consisting of one acid and two water molecules. The large difference between RO···O in the heterotrimer and in the crystal is attributed to the cooperative effect in the latter; this is supported by calculations carried out on clusters constituted of an increasing number of acid and water molecules. The present DFT calculations with geometry optimization include seven isolated model clusters, the largest of which contains five acid and eight water molecules. The RO···O of the short hydrogen bond shortens progressively with increasing the number of cluster constituents; in the largest cluster, it reaches 2.50 Å. This is remarkably close to both the experimental distance as well as to the distance obtained by the periodic DFT calculation. The electronic effects were studied by Natural Bond Orbital analysis, revealing an enhancement of hydrogen bonding on extending the network by increased polarization of the carbonyl group and by the increased delocalization interaction between the lone electron pair on the acceptor oxygen atom and the OH antibond orbital. The formation of circular motifs appears to be the most important factor in the cooperative shortening of the hydrogen bonds. In agreement with the measured hydrogen bond distances, inspection of the electron density reveals a notable difference in hydrogen bond shrinking tendency between the two known polymorphs of the title system. PMID:26580388

  11. De(side chain) model of epothilone: bioconformer interconversions DFT study.

    PubMed

    Rusinska-Roszak, Danuta; Lozynski, Marek

    2009-07-01

    Using ab initio methods, we have studied conformations of the de(sidechain)de(dioxy)difluoroepothilone model to quantify the effect of stability change between the exo and endo conformers of the epoxy ring. The DFT minimization of the macrolactone ring reveals four low energy conformers, although MP2 predicted five stable structures. The model tested with DFT hybride functional (B3LYP/6-31+G(d,p)) exhibits the global minimum for one of the exo forms (C), experimentally observed in the solid state, but unexpectedly with the MP2 electron correlation method for the virtual endo form (W). Using the QST3 technique, several pathways were found for the conversion of the low energy conformers to the other low energy exo representatives, as well as within the endo analog subset. The potential energy relationships obtained for several exo forms suggest a high conformational mobility between three, experimentally observed, conformers. The high rotational barrier, however, excludes direct equilibrium with experimental EC-derived endo form S. The highest calculated transition state for the conversion of the most stable exo M interligand to the endo S form is approximately a 28 kcal/mol above the energy of the former. The two-step interconversion of the exo H conformer to the endo S requires at least 28 kcal/mol. Surprisingly, we found that the transition state energy of the H form to the virtual endo W has the acceptable value of about 9 kcal/mol and the next energy barrier for free interconversion of endo W to endo S is 13 kcal/mol. PMID:19153781

  12. A comparative ab initio and DFT study of polyaniline leucoemeraldine base and its oligomers.

    PubMed

    Mishra, Abhishek Kumar; Tandon, Poonam

    2009-11-01

    Ab initio Hartree-Fock (HF) and density functional theory (DFT) calculations are being performed to investigate the geometric, vibrational, and electronic properties of the polyaniline leucoemeraldine base (PANI-LB). Vibrational spectra of PANI-LB have been analyzed using the DFT oligomer approach, and complete assignments are being reported. Lower region spectral assignments of the PANI-LB which were not being reported earlier are being done in the present work. DFT calculations with the 6-31G** basis set produce very good results of not only vibrational modes but also of energy band gap. PMID:19827802

  13. Advanced Theoretical Studies for Chemical Identification of the Heaviest Elements

    NASA Astrophysics Data System (ADS)

    Pershina, V.

    2015-06-01

    Both relativistic Dirac-Fock (DF) correlated, CCSD(T), and the density-functional theory (DFT) methods with various GGA exchange-correlation potentials agree on an increase in the M-Au bond strength from M = Cn to Fl. This means that the adsorption energy of Fl on gold, as measured by gas-phase chromatography experiments, must be larger for Fl than for Cn. For the weak (van der Waals) interactions, the trend to an increase in bonding from Cn2 to Fl2 obtained at the DFT level of theory is also confirmed by the DF CCSD(T) calculations. Thus, for comparative studies, relativistic DFT is a very reliable and efficient tool. First calculations of adsorption of TlOH and element 113OH on a hydroxylated quartz surface are reported.

  14. A theoretical study on ascorbic acid dissociation in water clusters.

    PubMed

    Demianenko, Eugeniy; Ilchenko, Mykola; Grebenyuk, Anatoliy; Lobanov, Victor; Tsendra, Oksana

    2014-03-01

    Dissociation of ascorbic acid in water has been studied by using a cluster model. It was examined by density functional theory (DFT) with the В3LYP, M06, and wB97XD functionals and a 6-311++G(d,p) basis set. The thermodynamic and kinetic characteristics of proton transfer from ascorbic acid molecule to water clusters were calculated as well as the equilibrium constants (pK a ) for the related processes. The used functionals in the DFT method together with continuum solvent models provided results close to the experimental data for the dissociation constant of ascorbic acid in aqueous solution. PMID:24567154

  15. DFT studies of the conformation and relative energies of alpha-maltotetraose (DP-4): An amylose fragment at atomic resolution

    Technology Transfer Automated Retrieval System (TEKTRAN)

    DFT optimization studies of more than one hundred conformations of a-maltotetraose have been carried out at the B3LYP/6-311++G** level of theory. The DP-4 fragments of predominately 4C1 chair residues include tightly bent forms, helix, band-flips, kinks, boat, and some 1C4 conformers. The three do...

  16. DFT Study of Uranyl Peroxo Complexes with H₂O, F⁻, OH⁻, CO₃ ²⁻, and NO₃-

    SciTech Connect

    Odoh, Samuel O.; Schreckenbach, Georg

    2013-05-06

    The structural and electronic properties of monomeric uranyl peroxo complexes with aquo, hydroxo, fluoro, carbonate, and nitrate ligands have been studied using DFT calculations with relativistic pseudopotentials. The calculated affinity of the peroxo group for the actinyl moiety far exceeds that of the other ligands tested in this work.

  17. Theoretical study of the adsorption of benzene on coinage metals

    PubMed Central

    Reckien, Werner; Eggers, Melanie

    2014-01-01

    Summary The adsorption of benzene on the M(111), M(100) and M(110) surfaces of the coinage metals copper (M = Cu), silver (M = Ag) and gold (M = Au) is studied on the basis of density functional theory (DFT) calculations with an empirical dispersion correction (D3). Variants of the Perdew–Burke–Ernzerhof functionals (PBE, RPBE and RevPBE) in combination with different versions of the dispersion correction (D3 and D3(BJ)) are compared. PBE-D3, PBE-D3(BJ) and RPBE-D3 give similar results which exhibit a good agreement with experimental data. RevPBE-D3 and RevPBE-D3(BJ) tend to overestimate adsorption energies. The inclusion of three-center terms (PBE-D3(ABC)) leads to a slightly better agreement with the experiment in most cases. Vertical adsorbate–substrate distances are calculated and compared to previous theoretical results. The observed trends for the surfaces and metals are consistent with the calculated adsorption energies. PMID:25161736

  18. Physical characteristics and optical properties of PbS nanoclusters: DFT simulation and experimental study

    NASA Astrophysics Data System (ADS)

    Dong, Yanhua; Wen, Jianxiang; Sun, Xiaolan; Shang, Yana; Wang, Tingyun

    2015-08-01

    The physical characteristics and optical properties of PbS nanoclusters are investigated by using density functional theory (DFT) of first-principles. Microstructure models of (PbS)n (n=1-9) nanoclusters and bulk materials are built on Materials Studio platform, and its energy band structures, highest occupied molecular orbital-lowest unoccupied molecular orbital gap (HOMO-LUMO gap), density of state (DOS), and optical properties are calculated, respectively. Compared to PbS bulk materials, PbS nanoclusters show a discrete energy gap as well as the DOS, because of the quantum confinement effect. It is interesting that the HOMO-LUMO gap of (PbS)n (n=1-9) shows oscillates with the increasing of the n number. However, when its size is large enough, the HOMO-LUMO gap is gradually decrease with the increasing of size (>27 atoms). And, the HOMO-LUMO gap of PbS nanoclusters of different sizes is range from 2.575 to 0.58 eV, which covers the low loss communication band of optical communication. In addition, PbS nanomaterials (NMs) with small size are synthesized by using oleylamine as ligands. Sizes of PbS NMs can be accurately controlled through control of the reaction time as well as the growth temperature. The photoluminescence (PL) spectra show strong size dependence, which is large red shift with increasing size of the NMs. This trend is basically in agreement with the theoretical calculation above. Moreover, transmission electron microscopy (TEM) further reveals the morphology of PbS NMs. PbS NMs can be used in optical fiber amplifiers and fiber lasers because of its unique optical properties in optical communication bands.

  19. Assessment of theoretical prediction of the NMR shielding tensor of 195PtClxBr(6-x)(2-) complexes by DFT calculations: experimental and computational results.

    PubMed

    Fowe, Emmanuel Penka; Belser, Peter; Daul, Claude; Chermette, Henry

    2005-04-21

    In the present work, the ZORA spin-orbit Hamiltonian, in conjunction with the gauge including orbital (GIAO) method based on DFT theory has been used to calculate 195Pt chemical shift of 195PtClxBr(6-x)(2-) complexes. Excellent agreement with experiments has been obtained for calculations bearing on optimized geometries and all electrons triple zeta + polarization (TZP) STO basis sets: the relative error with respect to experiment amounts to <1.5%. It is found that the Pt chemical shift is dominated by the paramagnetic and the spin orbit contribution, whereas the diamagnetic term remains negligible. The influence of the quality of the basis sets has been studied and found to be small, provided a basis set like TZP is used. Several calculations have been performed in order to establish the sensitivity of the chemical shift to a variation in the bond lengths. A strong dependence has been found, with an increase of the chemical shift amounting to 150 ppm pm(-1) for a distance decrease. Large sensitivity to the solvation, leading to changes in the structure, is then expected. Different tests using conductor-like screening models have been performed in order to establish the sensitivity of the chemical shift to solvation. It has been observed that the changes in the geometry are more important than charge transfers. Finally, the sensitivity of the system to the exchange-correlation functional is found rather weak, at least among the GGA functionals. PMID:19787932

  20. Spectroscopic [FT-IR and FT-Raman] and theoretical [UV-Visible and NMR] analysis on α-Methylstyrene by DFT calculations

    NASA Astrophysics Data System (ADS)

    Karthikeyan, N.; Joseph Prince, J.; Ramalingam, S.; Periandy, S.

    2015-05-01

    In the present research work, the FT-IR, FT-Raman and 13C and 1H NMR spectra of the α-Methylstyrene were recorded. The observed fundamental frequencies in finger print as well as functional group regions were assigned according to their uniqueness region. The Gaussian computational calculations are carried out by HF and DFT (B3LYP and B3PW91) methods with 6-31++G(d,p) and 6-311++G(d,p) basis sets and the corresponding results were tabulated. The impact of the presence of vinyl group in phenyl structure of the compound is investigated. The modified vibrational pattern of the molecule associated vinyl group was analyzed. Moreover, 13C NMR and 1H NMR were calculated by using the gauge independent atomic orbital (GIAO) method with B3LYP methods and the 6-311++G(d,p) basis set and their spectra were simulated and the chemical shifts linked to TMS were compared. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies were carried out. The kubo gap of the present compound was calculated related to HOMO and LUMO energies which confirm the occurring of charge transformation between the base and ligand. Besides frontier molecular orbitals (FMO), molecular electrostatic potential (MEP) was performed. The NLO properties related to Polarizability and hyperpolarizability based on the finite-field approach were also discussed.

  1. Combined experimental and DFT-TDDFT study of photo-active constituents of Canarium odontophyllum for DSSC application

    NASA Astrophysics Data System (ADS)

    Ekanayake, Piyasiri; Kooh, Muhammad Raziq Rahimi; Kumara, N. T. R. N.; Lim, Andery; Petra, Mohammad Iskandar; Voo, Nyuk Yoong; Lim, Chee Ming

    2013-10-01

    The active constituents of Canarium odontophyllum (COP) were investigated experimentally and theoretically for dye sensitized solar cell (DSSC) application. Three main flavonoid pigments (cyanidin, pelargonidin and maritimein) were detected in COP showing photo-energy conversion efficiencies of 1.43%, 0.87% and 0.60%, respectively. The molecular geometries, electronic structures, optical absorption spectra and proton affinity of these molecules were investigated with DFT/TDDFT. All three molecules displayed π→π* transition dominant in HOMO→LUMO transition. The anchoring groups onto TiO2 surface were deduced from combined experimental and calculated data. All the constituents of COP are potential sensitizers for DSSC.

  2. Isolation, spectroscopic characterization, X-ray, theoretical studies as well as in vitro cytotoxicity of Samarcandin.

    PubMed

    Ghoran, Salar Hafez; Atabaki, Vahideh; Babaei, Esmaeil; Olfatkhah, Seyed Reza; Dusek, Michal; Eigner, Vaclav; Soltani, Alireza; Khalaji, Aliakbar Dehno

    2016-06-01

    Samarcandin 1, a natural sesquiterpene-coumarin, was isolated as well as elucidated from F. assa-foetida which has significant effect in Iranian traditional medicine because of its medicinal attitudes. The crystal structure of samarcandin was determined by single-crystal X-ray structure analysis. It is orthorhombic, with unit cell parameters a=10.8204 (5)Å, b=12.9894 (7)Å, c=15.2467 (9)Å, V=2142.9 (2)Å(3), space group P212121 and four symmetry equivalent molecules in the unit cell. Samarcandin was isolated in order to study for its theoretical studies as well as its cellular toxicity as anti-cancer drug against two cancerous cells. In comparison with controls, our microscopic and MTT assay data showed that samarcandin suppresses cancer cell proliferation in a dose-dependent manner with IC50=11μM and 13 for AGS and WEHI-164 cell lines, respectively. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) of the structure was computed by three functional methods and 6-311++G(∗∗) standard basis set. The optimized molecular geometry and theoretical analysis agree closely to that obtained from the single crystal X-ray crystallography. To sum up, the good correlations between experimental and theoretical studies by UV, NMR, and IR spectra were found. PMID:26998943

  3. Optical properties of phenanthrene: A DFT study for comparison between linear and nonlinear regimes

    NASA Astrophysics Data System (ADS)

    Omidi, A. R.; Dadsetani, M.

    2016-05-01

    The present study tries to determine the optical characteristics as well as the electronic structure of phenanthrene as an important nonlinear organic crystal. We have performed our calculations within the frame work of DFT. Also, we have used bootstrap exchange-correlation kernel (within the framework of TDDFT) to estimate the excitonic effects. According to the results of our study, the investigated crystal has a band structure with low dispersions which is a sign of low intermolecular interactions. In addition to the high values of linear and nonlinear susceptibilities, the crystal in question has a wide range of transparency as well as sufficient anisotropy which make it promising crystal for nonlinear optical applications. Our TDDFT calculations show that the influence of excitonic effects on optical properties can be very dramatic, particularly near the band edge. In addition, the crystal in question shows extremely small wavelengths of plasmon peaks. Furthermore, this study also covers the 2ω/ω intra- and inter-band contributions to the dominant nonlinear susceptibilities. Findings indicate that these contributions have opposite signs at higher energies and nullify each other. Our calculations show that χxxz, χxzx and χzxx have largest values of nonlinear response but χxxz is the dominant component at IR-VIS region. Moreover, the current study shows significant similarities between linear and nonlinear spectra, when we draw linear one as a function of both ω and 2ω. Finally, our simulation reproduces the experimental results very well.

  4. Torsionally controlled electronic coupling in mixed-valence oxodimolybdenum nitrosyl scorpionates--a DFT study.

    PubMed

    Romańczyk, Piotr P; Noga, Klemens; Włodarczyk, Andrzej J; Nitek, Wojciech; Broclawik, Ewa

    2010-09-01

    The density functional theory (DFT) method has been used to study the electronic communication in strongly interacting oxo-bridged di-{Mo(II,I)(NO(+))}(3+,2+) complexes stabilized by tris(3-methylpyrazol-1-yl)borate, [Tp(Me)](-) (dihydroxy 1' and its modified analogs), having fully localized valences on the two Mo centers (Class I), despite a short (ca. 3.8 A) Mo...Mo distance. Structural and electrochemical (separation between the redox potentials Delta(red/ox)E(1/2)) properties and IR spectra (in particular the nu(NO) frequencies) obtained from the B3LYP calculations for 1' are successfully related to experimental values. Strongly twisted geometry with the (O)N-Mo1...Mo2-N(O) angle close to 90 degrees (confirmed by DFT modeling performed for 1'(-1,0,+1) and X-ray diffraction study of [{Mo(NO)(Tp(Me2))(OH)}(2)(mu-O)](-) (1) presented herein) is a common, though so far not fully understood, structural feature of this class of mu-oxo species, in contrast to the closely related {Mo(V)(=O)}(3+) analogs. This study shows that the orthogonality of the local equatorial planes for the two Mo centers may be rationalized by the electronic structure, namely from the balance between the destabilizing repulsion of the Mo-based (d, pi(x)*)(b) electron pairs versus a favorable but relatively weak electron delocalization. Strongly repelling electron pairs avoid each other, which enforces the twisted geometries and blocks the electron delocalization. Steric hindrance (a nonbonding repulsion of the adjacent Tp(x) ligands and the weak hydrogen-bonding interactions, i.e., OH...ON, OH...OH, and C-H...O((NO/OH))) is shown not to be decisive since neither the removal of the inner 3-Me groups of [Tp(Me)](-) in complex 1' nor the substitution of OH groups by OCH(3) ligands did substantially influence the dihedral twist angle in the minimum energy structure. Yet the relative orientation of the {Mo(NO)}(2+,3+) cores along with the position of the bridging oxygen (significantly bent upon

  5. Comprehensive DFT and TD-DFT Studies on the Photophysical Properties of 5,6-Dichloro-1,3-Bis(2-Pyridylimino)-4,7-Dihydroxyisoindole: A New Class of ESIPT Fluorophore.

    PubMed

    Kataria, Santosh; Rhyman, Lydia; Ramasami, Ponnadurai; Sekar, Nagaiyan

    2016-09-01

    Hanson et al. [Org. Lett., 2011] reported the absorption and emission spectrum of 5,6-dichloro-1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole but the excited-state intramolecular proton transfer (ESIPT) process was not investigated. The photo-physical behaviour of 5,6-dichloro-1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole was studied using the density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The functional used was B3LYP and 6-31G(d) was the basis set for all the atoms. All the ten tautomers were studied for the absorption and emission properties. It is found that the tautomer where hydroxyl groups are syn to nitrogen of isoindoline ring is most stable and thus, responsible for the ESIPT process. The computed absorption and emission values of tautomers using TD-DFT are in good agreement with those obtained experimentally. PMID:27455833

  6. Structural and vibrational studies on (E)-2-(2-hydroxy benzyliden amino)-3-phenyl propionic acid using experimental and DFT methods

    NASA Astrophysics Data System (ADS)

    Saleem, H.; Erdogdu, Y.; Subashchandrabose, S.; Thanikachalam, V.; Jayabharathi, J.; Ramesh Babu, N.

    2012-12-01

    The structural and spectroscopic properties of (E)-2-(2-hydroxy benzyliden amino)-3-phenyl propionic acid ((E)-2-HBAPPA) has been investigated by using theoretical and experimental methods. Using the computational studies the most stable conformer was identified. Density functional theory (DFT) calculations of 16 (E)-2-HBAPPA conformers have been performed to find the optimized structure and the computed vibrational wavenumbers of the most stable one. The FT Raman and FT-IR spectra of (E)-2-HBAPPA molecule have been recorded and analyzed. A detailed interpretation of the FT-IR, FT-Raman and harmonic wavenumbers obtained at B3LYP/6-311++G(d,p) level was reported. The vibrational assignments were studied using TED method. Intra-molecular charge transfer between nitrogen and hydroxyl hydrogen (Cdbnd N⋯Hsbnd O) has been studied. First order hyperpolarizability (β0) has been calculated. Electronic excitation of (E)-2-HBAPPA was recorded in the visible region and compared with calculated TD-DFT results.

  7. The Hydrogen Catalyst Cobaloxime – a Multifrequency EPR & DFT Study of Cobaloxime’s Electronic Structure

    PubMed Central

    Niklas, Jens; Mardis, Kristy L.; Rakhimov, Rakhim R.; Mulfort, Karen L.; Tiede, David M.; Poluektov, Oleg G.

    2012-01-01

    Solar fuels research aims to mimic photosynthesis and devise integrated systems that can capture, convert, and store solar energy in the form of high-energy molecular bonds. Molecular hydrogen is generally considered an ideal solar fuel as its combustion is essentially pollution-free. Cobaloximes rank among the most promising earth-abundant catalysts for the reduction of protons to molecular hydrogen. We have used multifrequency EPR spectroscopy at X-band, Q-band, and D-band combined with DFT calculations to reveal electronic structure and establish correlations between structure, surroundings and catalytic activity of these complexes. To assess the strength and nature of ligand cobalt interactions, the BF2-capped cobaloxime, Co(dmgBF2)2, was studied in a variety of different solvents with a range of polarities and stoichiometric amounts of potential ligands to the cobalt ion. This allows the differentiation of labile and strongly coordinating axial ligands for the Co(II) complex. Labile, or weakly coordinating, ligands like methanol result in larger g-tensor anisotropy than strongly coordinating ligands like pyridine. Additionally, a coordination number effect is seen for the strongly coordinating ligands with both singly-ligated LCo(dmgBF2)2 and doubly-ligated L2Co(dmgBF2)2. The presence of two strongly coordinating axial ligands leads to the smallest g-tensor anisotropy. The relevance of the strength of the axial ligand(s) to the catalytic efficiency of Co(dmgBF2)2 is discussed. Finally, the influence of molecular oxygen and formation of Co(III) superoxide radicals LCo(dmgBF2)2O2• is studied. The experimental results are compared with a comprehensive set of DFT calculations on Co(dmgBF2)2 model systems with various axial ligands. Comparison with experimental values for the “key” magnetic parameters like g-tensor and 59Co hyperfine coupling tensor allows the determination of the conformation of the axially ligated Co(dmgBF2)2 complexes. The data presented

  8. Electrochemical and DFT study of an anticancer and active anthelmintic drug at carbon nanostructured modified electrode.

    PubMed

    Ghalkhani, Masoumeh; Beheshtian, Javad; Salehi, Maryam

    2016-12-01

    The electrochemical response of mebendazole (Meb), an anticancer and effective anthelmintic drug, was investigated using two different carbon nanostructured modified glassy carbon electrodes (GCE). Although, compared to unmodified GCE, both prepared modified electrodes improved the voltammetric response of Meb, the carbon nanotubes (CNTs) modified GCE showed higher sensitivity and stability. Therefore, the CNTs-GCE was chosen as a promising candidate for the further studies. At first, the electrochemical behavior of Meb was studied by cyclic voltammetry and differential pulse and square wave voltammetry. A one step reversible, pH-dependent and adsorption-controlled process was revealed for electro-oxidation of Meb. A possible mechanism for the electrochemical oxidation of Meb was proposed. In addition, electronic structure, adsorption energy, band gap, type of interaction and stable configuration of Meb on the surface of functionalized carbon nanotubes were studied by using density functional theory (DFT). Obtained results revealed that Meb is weakly physisorbed on the CNTs and that the electronic properties of the CNTs are not significantly changed. Notably, CNTs could be considered as a suitable modifier for preparation of the modified electrode for Meb analysis. Then, the experimental parameters affecting the electrochemical response of Meb were optimized. Under optimal conditions, high sensitivity (b(Meb)=dIp,a(Meb)/d[Meb]=19.65μAμM(-1)), a low detection limit (LOD (Meb)=19nM) and a wide linear dynamic range (0.06-3μM) was resulted for the voltammetric quantification of Meb. PMID:27612835

  9. Spectral and structural studies of the anti-cancer drug Flutamide by density functional theoretical method

    NASA Astrophysics Data System (ADS)

    Mariappan, G.; Sundaraganesan, N.

    2014-01-01

    A comprehensive screening of the more recent DFT theoretical approach to structural analysis is presented in this section of theoretical structural analysis. The chemical name of 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide is usually called as Flutamide (In the present study it is abbreviated as FLT) and is an important and efficacious drug in the treatment of anti-cancer resistant. The molecular geometry, vibrational spectra, electronic and NMR spectral interpretation of Flutamide have been studied with the aid of density functional theory method (DFT). The vibrational assignments of the normal modes were performed on the basis of the PED calculations using the VEDA 4 program. Comparison of computational results with X-ray diffraction results of Flutamide allowed the evaluation of structure predictions and confirmed B3LYP/6-31G(d,p) as accurate for structure determination. Application of scaling factors for IR and Raman frequency predictions showed good agreement with experimental values. This is supported the assignment of the major contributors of the vibration modes of the title compound. Stability of the molecule arising from hyperconjugative interactions leading to its bioactivity, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. NMR chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. The comparison of measured FTIR, FT-Raman, and UV-Visible data to calculated values allowed assignment of major spectral features of the title molecule. Besides, Frontier molecular orbital analyze was also investigated using theoretical calculations.

  10. A combined experimental and DFT study of a novel unsymmetrical azine 2-(4-methoxybenzylidene)-1-(1-(4-isobutylphenyl) ethylidene) hydrazine.

    PubMed

    Vijaya, P; Sankaran, K R

    2015-03-01

    A novel unsymmetrical azine 2-(4-methoxybenzylidene)-1-(1-(4-isobutylphenyl) ethylidene) hydrazine (UA) was prepared and characterized by IR, (1)H and (13)C NMR spectral studies. A 2D - potential energy scan (PES) of p-isobutylacetophenone (IBAP) was the portal to the conformational analysis of UA by density functional theory (DFT) methods using 6-31G(d,p) basis set by Gaussian 03 program. The theoretical IR frequencies were found to be in good agreement with the experimental values. The IR frequencies of UA were analyzed by means of Potential energy Distribution (PED %) calculation using Vibrational Energy Distribution Analysis (VEDA 4) program. The experimental NMR chemical shift values of UA were compared with the theoretical values obtained by DFT method. Nonlinear optical behavior of the unsymmetrical azine is also examined by the theoretically predicted values of dipole moment (μ), polarizability (α0) and first hyperpolarizability (βtot). Stability of the UA molecule has been analyzed using NBO analysis. The electrochemistry of UA studied experimentally by cyclic voltammetry is complemented by the computational analysis of the anionic form of the molecule UA. The determination of various global and local reactivity descriptors in the context of chemical reactivity is also performed and the electrophilicity at the vital atomic sites in UA is revealed. Bader's Atoms in molecules (AIM) theory of UA indicated the presence of intramolecular hydrogen bonding in the molecule. The molecular electrostatic potential (MEP) and HOMO-LUMO orbital analysis are also performed for the molecule UA. PMID:25528505

  11. Synthesis, conformational and theoretical studies of 1,n-di(2-formyl-4-phenylazophenoxy)alkanes

    NASA Astrophysics Data System (ADS)

    Balachander, R.; Manimekalai, A.

    2016-01-01

    1,n-di(2-Formyl-4-phenylazophenoxy)alkanes 1 and 2 and 1,3-di(2-formyl-4-phenylazophenoxymethyl)benzene 3 were synthesis and characterized by FT-IR, UV-Vis, 1H, 13C NMR and mass spectral studies. The stable conformations of 1-3 were predicted theoretically and selected geometrical parameters were derived from optimized structures. The molecular parameters of HOMO-LUMO energies, polarizability, hyperpolarizability, natural bond orbital (NBO), atom in molecule (AIM) analysis and molecular electrostatic potential (MEP) surfaces were determined by the density functional theory (DFT) method and analysed.

  12. Theoretical study on magnetic coupling interaction for Cu(II) binuclear systems with extended bridging groups

    NASA Astrophysics Data System (ADS)

    Bi, Siwei; Liu, Chengbu; Hu, Haiquan; Zhang, Changqiao

    2001-12-01

    The magnetic coupling interaction for Cu(II) binuclear systems with bridging groups C2O4 2- , C2O2( NH) 2 2- ( cis), C2O2( NH) 2 2- ( trans) and C2S2( NH) 2 2- ( trans) was studied by the broken symmetry (BS) approach within the framework of the density functional theory (DFT). The influence of different coordination atoms and geometry on magnetic coupling interaction was theoretically analyzed. Both of the calculated and experimental results were compared. The variation trends of coupling interaction calculated are in agreement with experimental ones.

  13. Fullerene Cyanation Does Not Always Increase Electron Affinity: Experimental and Theoretical Study

    SciTech Connect

    Clikeman, Tyler T.; Deng, Shihu; Popov, Alexey A.; Wang, Xue B.; Strauss, Steven H.; Boltalina, Olga V.

    2015-01-01

    The electron affinities of C70 derivatives with trifluoromethyl, methyl and cyano groups were studied experimentally and theoretically using low-temperature photoelectron spectroscopy (LT PES) and density functional theory (DFT). The electronic effects of these functional groups were determined and found to be highly dependent on the addition patterns. Substitution of CF3 for CN for the same addition pattern increases the experimental electron affinity by 70 meV per substitution. The synthesis of a new fullerene derivative, C70(CF3)10(CN)2, is reported for the first time

  14. Modelling catalyst surfaces using DFT cluster calculations.

    PubMed

    Czekaj, Izabela; Wambach, Jörg; Kröcher, Oliver

    2009-10-01

    We review our recent theoretical DFT cluster studies of a variety of industrially relevant catalysts such as TiO(2), gamma-Al(2)O(3), V(2)O(5)-WO(3)-TiO(2) and Ni/Al(2)O(3). Aspects of the metal oxide surface structure and the stability and structure of metal clusters on the support are discussed as well as the reactivity of surfaces, including their behaviour upon poisoning. It is exemplarily demonstrated how such theoretical considerations can be combined with DRIFT and XPS results from experimental studies. PMID:20057947

  15. Modelling Catalyst Surfaces Using DFT Cluster Calculations

    PubMed Central

    Czekaj, Izabela; Wambach, Jörg; Kröcher, Oliver

    2009-01-01

    We review our recent theoretical DFT cluster studies of a variety of industrially relevant catalysts such as TiO2, γ-Al2O3, V2O5-WO3-TiO2 and Ni/Al2O3. Aspects of the metal oxide surface structure and the stability and structure of metal clusters on the support are discussed as well as the reactivity of surfaces, including their behaviour upon poisoning. It is exemplarily demonstrated how such theoretical considerations can be combined with DRIFT and XPS results from experimental studies. PMID:20057947

  16. Adsorption of oxazole and isoxazole on BNNT surface: A DFT study

    NASA Astrophysics Data System (ADS)

    Kaur, Jasleen; Singla, Preeti; Goel, Neetu

    2015-02-01

    The adsorption behavior of oxazole and isoxazole heterocycles over the (6,0) zigzag and (5,5) armchair boron nitride nanotube (BNNT) has been studied within the formalism of density functional theory (DFT). The adsorption energies, the frontier molecular orbital (FMO) analysis and the structural changes at the adsorption site are indicative of covalent adsorption on the zigzag BNNT surface, while the adsorption is physical in nature on the armchair BNNT surface. The role of solvent in improving the adsorption properties over the BNNT surface is elucidated by reoptimizing the structures in aqueous phase. The solvation energy is indicative of remarkable increase in the solubility of BNNTs after adsorption of heterocyclic rings. The Density of states (DOS) Plots, natural bond orbital (NBO) analysis and the quantum molecular descriptors (QMD) are witness to the substantial changes in the electronic properties of the BNNT systems following the attachment of these heterocycles with the tube surface. The study envisages the functionalization of the BNNT as well as its applicability as carrier of the drugs containing heterocyclic rings oxazole and isoxazole with marked sensitivity to the type of adsorbate and the adsorbent.

  17. Electronic Properties of Zigzag Graphene Nanoribbons Studied by TAO-DFT.

    PubMed

    Wu, Chun-Shian; Chai, Jeng-Da

    2015-05-12

    Accurate prediction of the electronic properties of zigzag graphene nanoribbons (ZGNRs) has been very challenging for conventional electronic structure methods due to the presence of strong static correlation effects. To meet the challenge, we study the singlet-triplet energy gaps, vertical ionization potentials, vertical electron affinities, fundamental gaps, and symmetrized von Neumann entropy (i.e., a measure of polyradical character) of hydrogen-terminated ZGNRs with different widths and lengths using our recently developed thermally-assistedoccupation density functional theory (TAO-DFT) [Chai, J.-D. J. Chem. Phys. 2012, 136, 154104], a very efficient method for the study of large strongly correlated systems. Our results are in good agreement with the available experimental and high-accuracy ab initio data. The ground states of ZGNRs are shown to be singlets for all the widths and lengths investigated. With the increase of ribbon length, the singlet-triplet energy gaps, vertical ionization potentials, and fundamental gaps decrease monotonically, while the vertical electron affinities and symmetrized von Neumann entropy increase monotonically. On the basis of the calculated orbitals and their occupation numbers, the longer ZGNRs are shown to possess increasing polyradical character in their ground states, where the active orbitals are mainly localized at the zigzag edges. PMID:26894252

  18. A DFT + U study of (Rh, Nb)-codoped rutile TiO2

    NASA Astrophysics Data System (ADS)

    Ghuman, Kulbir Kaur; Singh, Chandra Veer

    2013-02-01

    A systematic study of electronic structure and band gap states is conducted to analyze the monodoping and charge compensated codoping of rutile TiO2 with Rh and Nb, using the DFT + U approach. Doping of rutile TiO2 with Rh atoms induces hybridized O 2p and Rh 4d band gap states leading to a red shift of the optical absorption edge, consistent with previous experimental studies. Since Rh monodoping may induce recombination centers, charge compensated codoping with Rh and Nb is also explored. This codoping induces an electron transfer from Nb induced states to Rh 4d states, which suppresses the formation of Rh4+, thereby leading to a reduction in recombination centers and to the formation of more stable Rh3+. A combination of band gap reduction by 0.5 eV and the elimination of band gap states that account for recombination centers makes (Rh, Nb)-codoped TiO2 a more efficient and stable photocatalyst.

  19. Electronic structure and magnetism on FeSiAl alloy: A DFT study

    NASA Astrophysics Data System (ADS)

    Cardoso Schwindt, V.; Sandoval, M.; Ardenghi, J. S.; Bechthold, P.; González, E. A.; Jasen, P. V.

    2015-09-01

    Density functional theory (DFT) calculation has been performed to study the electronic structure and chemical bonding in FeSiAl alloy. These calculations are useful to understand the magnetic properties of this alloy. Our results show that the mean magnetic moment of Fe atoms decreases due to the crystal structure and the effect of Si and Al. Depending on the environment, the magnetic moment of one Fe site (Fe1) increases to about 14.3% while of the other site (Fe2) decreases to about 25.9% (compared with pure bcc Fe). All metal-metal overlap interactions are bonding and slightly weaker than those found in the bcc Fe structure. The electronic structure (DOS) shows an important hybridization among Fe, Si and Al atoms, thus making asymmetric the PDOS with a very slight polarization of Al and Si atoms. Our study explains the importance of crystal structure in determining the magnetic properties of the alloys. FeSiAl is a good candidate for electromagnetic interference shielding combining low price and good mechanical and magnetic properties.

  20. Comparative DFT study to determine if α-oxoaldehydes are precursors for pentosidine formation.

    PubMed

    Nasiri, Rasoul; Field, Martin J; Zahedi, Mansour; Moosavi-Movahedi, Ali Akbar

    2012-03-22

    We report a comprehensive density functional theory (DFT) study of the mechanism of pentosidine formation. This work is a continuation of our earlier studies in which we proposed pathways for formation of glucosepane (J. Mol. Model. 2011, pp 1-15, DOI 10.1007/s00894-011-1161-x), GODIC (glyoxal-derived imidazolium cross-link), and MODIC (methyl glyoxal-derived imidazolium cross-link; J. Phys. Chem. 2011, 115, pp 13542-13555). Here we show that formation of pentosidine via reaction of α-oxoaldehydes with lysine and arginine in aqueous solution is possible thermodynamically and kinetically, in good agreement with the available experimental evidence. Five pathways, A-E, were characterized, as in our previous GODIC and MODIC work. In pathways A and B, a Schiff base is first formed from lysine and methyl glyoxal (MGO), and this is followed by addition of arginine and glyoxal (GO). By contrast, in pathways C, D, and E, addition of arginine to MGO occurs first, resulting in the formation of imidazolone, which then reacts with lysine and GO to give pentosidine. Our calculations show that the reaction process is highly exergonic and that the three pathways A, C, and E are competitive. These results serve to underline the potentially important role that α-oxoaldehydes play as precursors in pentosidine formation in the complex field of glycation. PMID:22335775

  1. Mechanical Properties of Metal Nitrides for Radiation Resistant Coating Applications: A DFT Study

    NASA Astrophysics Data System (ADS)

    Mota, Oscar U. Ojeda; Araujo, Roy A.; Wang, Haiyan; Çağın, Tahir

    Metal nitrides compounds like aluminum nitride (AlN), titanium nitride (TiN), tantalum nitride (TaN), hafnium nitride (HfN) and zirconium nitride (ZrN) are of great interesting because of their chemical and physical properties such as: high melting point, resistivity, thermal conductivity and extremely high hardness. They are the materials of choice for various applications like protective coating for tools, diffusion barriers or metal gate contact in microelectronics, and lately their potential applications as radiation-resistive shields. In order to assess their use for radiation tolerance we have studied the structural, mechanical and electronic properties. We have evaluated the anisotropic elastic constants and their pressure dependence for three different crystalline phases: B1-NaCl, B2-CsCl, and B3-ZnS crystal structures. In addition to these cubic polymorphs, we also have studied potential hexagonal structures of some of the same metal nitrides. All computations are carried out using first principles Density Functional Theory (DFT) approach.

  2. Bacterial nitric oxide reductase: a mechanism revisited by an ONIOM (DFT:MM) study.

    PubMed

    Attia, Amr A A; Silaghi-Dumitrescu, Radu

    2015-05-01

    Bacterial nitric oxide reductase (cNOR) is an important binuclear iron enzyme responsible for the reduction of nitric oxide to nitrous oxide in the catalytic cycle of bacterial respiration. The reaction mechanism of cNOR as well as the key reactive intermediates of the reaction are still under debate. Here, we report a computational study based on ONIOM (DFT:MM) calculations aimed at investigating the reaction mechanism of cNOR. The results suggest that the reaction proceeds via the mono-nitrosyl mechanism which starts off by the binding of an NO molecule to the heme b3 center, N-N hyponitrite bond formation as a result of the reaction with a second NO molecule was found to proceed with an exothermic energy barrier to yield a hyponitrite adduct forming an open (incomplete) ring conformation with the non-heme FeB center (O-N-N-O-FeB). N-O bond cleavage to yield N2O was shown to be the rate-limiting step with an activation barrier of 22.6 kcal mol(-1). The dinitrosyl (trans) mechanism, previously proposed by several studies, was also examined and found unfavorable due to high activation barriers of the resulting intermediates. PMID:25920393

  3. Comparative vibrational spectroscopic studies, HOMO-LUMO, NBO analyses and thermodynamic functions of p-cresol and 2-methyl-p-cresol based on DFT calculations

    NASA Astrophysics Data System (ADS)

    Balachandran, V.; Murugan, M.; Nataraj, A.; Karnan, M.; Ilango, G.

    2014-11-01

    In the present study structural properties of p-cresol, and 2-methoxy-p-cresol have been studied by using B3LYP/cc-pvdz and B3PW91/cc-pvdz of Density Functional Theory (DFT) utilizing Becke three exchange functional and Lee Yang Paar correlation functional. The Fourier transform infrared and Fourier transform Raman spectra of title molecules were recorded (solid phase). Optimized geometry, harmonic vibrational frequencies and various thermodynamic parameters of the title compounds were calculated with B3LYP/cc-pvdz, and B3PW91/cc-pvdz basis sets. Non-linear optical (NLO) behavior of the p-cresol and 2-methoxy-p-cresol were investigated by determining of electric dipole moment, polarizability α, and hyperpolarizability β using the above mentioned basis sets. The molecular properties such as ionization potential, electronegativity, chemical potential, electrophilicity have been deduced from HOMO-LUMO analysis employing the same basis sets. A detailed interpretation of the infrared and Raman spectra of title molecules were reported. UV spectrum was measured in different solvent. The energy and oscillator strength are calculated by Time Dependant Density Functional Theory (TD-DFT) results. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. The complete assignments were performed on the basis of the potential energy distribution (PED) of vibrational modes, calculated with scaled quantum mechanics (SQM) method. Finally the theoretical FT-IR, FT-Raman, and UV spectra of the title molecules have also been constructed.

  4. A DFT study on the mechanisms for the cycloaddition reactions between 1-aza-2-azoniaallene cations and acetylenes.

    PubMed

    Wang, Jing-mei; Li, Zhi-ming; Wang, Quan-rui; Tao, Feng-gang

    2013-01-01

    The mechanisms of cycloaddition reactions between 1-aza-2-azoniaallene cations 1 and acetylenes 2 have been investigated using the global electrophilicity and nucleophilicity of the corresponding reactants as global reactivity indexes defined within the conceptual density functional theory. The reactivity and regioselectivity of these reactions were predicted by analysis of the energies, geometries, and electronic nature of the transition state structures. The theoretical results revealed that the reaction features a tandem process: an ionic 1,3-dipolar cycloaddition to produce the cycloadducts 3 H-pyrazolium salts 3 followed by a [1,2]-shift affording the thermodynamically more stable adducts 4 or 5. The mechanism of the cycloaddition reactions can be described as an asynchronous concerted pathway with reverse electron demand. The model reaction has also been investigated at the QCISD/6-31++G(d,p) and CCSD(T)/6-31++G(d,p)//B3LYP/6-31++G(d,p) levels as well as by the DFT. The polarizable continuum model, at the B3LYP/6-31++G(d,p) level of theory, was used to study solvent effects on all the studied reactions. In solvent dichloromethane, all the initial cycloadducts 3 were obtained via direct ionic process as the result of the solvent effect. The consecutive [1,2]-shift reaction, in which intermediates 3 are rearranged to the five-membered heterocycles 4/5, is proved to be a kinetically controlled reaction, and the regioselectivity can be modulated by varying the migrant. The LOL function and RDG function based on localized electron analysis were used to analysis the covalent bond and noncovalent interactions in order to unravel the mechanism of the title reactions. PMID:22810049

  5. Theoretical study on a water muffler

    NASA Astrophysics Data System (ADS)

    Du, T.; Chen, Y. W.; Miao, T. C.; Wu, D. Z.

    2016-05-01

    Theoretical computation on a previously studied water muffler is carried out in this article. Structure of the water muffler is composed of two main parts, namely, the Kevlar- reinforced rubber tube and the inner-noise-reduction structure. Rubber wall of the rubber tube is assumed to function as rigid wall lined with sound absorption material and is described by a complex radial wave number. Comparison among the results obtained from theoretical computation, FEM (finite element method) simulation and experiment of the rubber tube and that of the water muffler has been made. The theoretical results show a good accordance in general tendency with the FEM simulated and the measured results. After that, parametric study on the diameter of the inner structure and that of the rubber tube is conducted. Results show that the diameter of the left inner structure has the most significant effect on the SPL of the water muffler due to its location and its effect on the diameter ratio D2/D1.

  6. CC/DFT Route toward Accurate Structures and Spectroscopic Features for Observed and Elusive Conformers of Flexible Molecules: Pyruvic Acid as a Case Study.

    PubMed

    Barone, Vincenzo; Biczysko, Malgorzata; Bloino, Julien; Cimino, Paola; Penocchio, Emanuele; Puzzarini, Cristina

    2015-09-01

    The structures and relative stabilities as well as the rotational and vibrational spectra of the three low-energy conformers of pyruvic acid (PA) have been characterized using a state-of-the-art quantum-mechanical approach designed for flexible molecules. By making use of the available experimental rotational constants for several isotopologues of the most stable PA conformer, Tc-PA, the semiexperimental equilibrium structure has been derived. The latter provides a reference for the pure theoretical determination of the equilibrium geometries for all conformers, thus confirming for these structures an accuracy of 0.001 Å and 0.1 deg for bond lengths and angles, respectively. Highly accurate relative energies of all conformers (Tc-, Tt-, and Ct-PA) and of the transition states connecting them are provided along with the thermodynamic properties at low and high temperatures, thus leading to conformational enthalpies accurate to 1 kJ mol(-1). Concerning microwave spectroscopy, rotational constants accurate to about 20 MHz are provided for the Tt- and Ct-PA conformers, together with the computed centrifugal-distortion constants and dipole moments required to simulate their rotational spectra. For Ct-PA, vibrational frequencies in the mid-infrared region accurate to 10 cm(-1) are reported along with theoretical estimates for the transitions in the near-infrared range, and the corresponding infrared spectrum including fundamental transitions, overtones, and combination bands has been simulated. In addition to the new data described above, theoretical results for the Tc- and Tt-PA conformers are compared with all available experimental data to further confirm the accuracy of the hybrid coupled-cluster/density functional theory (CC/DFT) protocol applied in the present study. Finally, we discuss in detail the accuracy of computational models fully based on double-hybrid DFT functionals (mainly at the B2PLYP/aug-cc-pVTZ level) that avoid the use of very expensive CC

  7. Density functional theoretical and NMR study of Hammett bases in acidic zeolites

    SciTech Connect

    Nicholas, J.B.; Haw, J.F.; Beck, L.W.; Krawietz, T.R.; Ferguson, D.B.

    1995-12-13

    We demonstrate here that theoretical calculations using density functional theory (DFT) accurately model proton transfer reactions between Bronsted sites in zeolites (the archetypal solid acids) and Hammett bases. The validity of the theoretical results is verified by NMR measurements of key nuclei of the same Hammett bases in zeolites HZSM-5 (MFI) and HY (FAU), the first such experiments. The accuracy of the predictions of the DFT calculations for the HZSM-5 zeolite model suggests that they may be extended to other zeolite cluster models, including those which have not yet been realized experimentally and hence are not available for NMR study. We optimized the adsorbate zeolite complexes with this angle constrained to larger values; to our surprise, the SVWN/DNP calculations resulted in the proton being transferred from p-fluoronitrobenzene back to the zeolite, even if the Si-O-Al angle was held fixed at 180{degree}. Further tests at higher levels of theory are in progress. This investigation used a choice of indicators that necessarily resulted in wide limits on zeolite acid strength, but the theoretical and experimental methodologies have been established. 21 refs., 3 figs.

  8. A DFT study of infrared spectrum of sphingomyelin lipid molecule with calcium cation

    NASA Astrophysics Data System (ADS)

    Sugimori, K.; Kawabe, H.; Nagao, H.; Nishikawa, K.

    One of the phospholipids, sphingomyelin (SM) is the most abundant component of mammalian membranes in brain and nervous tissues. It plays an important role for apoptosis, aging, and signal transduction with cations. Recently, Yappert and co-workers have shown that human lens sphingomyelin and its hydrogenated derivative, dihydrosphingomyelin (DHSM) are interacted with Ca2+ ions to develop human cataracts. In this study, we investigate conformational differences between an isolated SM/DHSM molecule and Ca2+-coordinated form by using density functional theory (DFT) calculations. B3LYP functional and 6-31G(d,p) double-zeta split-valence basis set is used for geometry optimization and normal mode analysis. One of resultant conformers of SMs has hydrogen bonding between hydroxyl and phosphate group, whereas another conformer has hydrogen bonding between hydroxyl and amide group. The red shift of calculated vibrational frequencies of amide band due to Ca2+ is compared with experimental infrared spectrum. Finally, we discuss the Ca2+-induced effects from conformational and spectroscopic point of view to compare the experimental results.

  9. Unsaturated hydrocarbons adsorbed on low coordinated Pd surface: A periodic DFT study

    NASA Astrophysics Data System (ADS)

    Belelli, Patricia G.; Ferullo, Ricardo M.; Castellani, Norberto J.

    2010-02-01

    In this work, the adsorption of several unsaturated hydrocarbon molecules on a stepped Pd(4 2 2) surface was studied. Using a periodic method based on the Density Functional Theory (DFT) formalism, different adsorption geometries for ethylene, three butene isomers ( cis/ trans-2-butene and 1-butene), acetylene and 2-butyne were investigated. The results were compared with those obtained for a free defect surface as Pd(1 1 1). The 1-butene is more stable on the free defect surface than on Pd(4 2 2). On the stepped surface, the olefins adsorb tilted towards the step and increases, in almost all the cases, the magnitude of the adsorption energy. Conversely, the 3-fold site is the most stable for the alkynes adsorption on the stepped surface, as it was found on Pd(1 1 1). The analysis of the dipole moment change indicate a charge transfer from the double bond of the olefin to the metallic surface, being higher for the Pd(1 1 1) surface. In case of the alkynes, an important back-donation is produced. Except the alkynes and the 1-butene molecule, the results show the preference of ethylene and cis/ trans-2-butene to be adsorbed on the stepped surface. These observations are related with experimental catalytic results.

  10. A DFT study on the adsorption of benzodiazepines to vermiculite surfaces.

    PubMed

    Carvalho, A J Palace; Dordio, A V; Ramalho, J P Prates

    2014-07-01

    Widespread use of pharmaceuticals such as benzodiazepines has been resulting over the last decades in the dissemination of residues of these compounds in the environment, and such fact has been raising increasing concern. The generally low efficiencies of conventional wastewater treatment processes for the removal of this type of pollutants demands for the development of alternative or complementary water and wastewater treatment technologies, among which adsorption processes have been gaining popularity, provided that cheap efficient adsorbents are found. Clay materials have been one of the popular choices in this regard. In the present study, quantum chemical calculations have been performed by periodic DFT using the projector augmented-wave (PAW) method to characterize the interactions of two benzodiazepine molecules, alprazolam and diazepam, with a surface of clay mineral, vermiculite. It was observed that both molecules interact strongly with the vermiculite surface, both through a water-bridge binding and by cation-bridge provided by the exchangeable Mg(2+) cations of the vermiculite surface. The results point to an interesting potential of vermiculite to be used efficiently as filter medium to remove these pollutants from water and wastewater. PMID:25069137

  11. A vibrational spectroscopy study on 3-aminophenylacetic acid by DFT calculations

    NASA Astrophysics Data System (ADS)

    Akkaya, Yasemin; Balci, Kubilay; Goren, Yeliz; Akyuz, Sevim

    2015-08-01

    In this study, in which the group vibrations of 3-aminophenylacetic acid were investigated by electronic structure calculations based on Density Functional Theory (DFT), the possible stable conformers of the molecule were searched through a relaxed "potential energy surface scan" carried out at B3LYP/6-31G(d) level of theory. The corresponding equilibrium geometrical and vibrational spectral data for each of the determined stable conformers and for their possible dimer structures were obtained through "geometry optimisation" and "frequency" calculations carried out at B3LYP/6-31G(d) and B3LYP/6-311G++(d,p) levels of theory. The obtained results confirmed that anharmonic wavenumbers calculated at B3LYP/6-311G++(d,p) level generally quite well agree with the experimental wavenumbers, however, harmonic wavenumbers calculated at both levels of theory need an efficient refinement for a satisfactory agreement with experiment. In particular, the harmonic wavenumbers, IR and Raman intensities refined within Scaled Quantum Mechanical Force Field (SQM FF) methodology constituted the primary data set in the interpretation of the experimental FT-IR, FT-Raman and dispersive Raman spectra of 3-aminophenylacetic acid. By the help of these refined spectral data, the effects of conformation and intermolecular hydrogen bonding on the fundamental bands observed in the experimental spectra could be correctly predicted.

  12. Unravelling Protein-DNA Interactions at Molecular Level: A DFT and NCI Study.

    PubMed

    González, J; Baños, I; León, I; Contreras-García, J; Cocinero, E J; Lesarri, A; Fernández, J A; Millán, J

    2016-02-01

    Histone-DNA interactions were probed computationally at a molecular level, by characterizing the bimolecular clusters constituted by selected amino acid derivatives with polar (asparagine and glutamine), nonpolar (alanine, valine, and isoleucine), and charged (arginine) side chains and methylated pyrimidinic (1-methylcytosine and 1-methylthymine) and puric (9-methyladenine and 9-methylguanine) DNA bases. The computational approach combined different methodologies: a molecular mechanics (MMFFs forced field) conformational search and structural and vibrational density-functional calculations (M06-2X with double and triple-ζ Pople's basis sets). To dissect the interactions, intermolecular forces were analyzed with the Non-Covalent Interactions (NCI) analysis. The results for the 24 different clusters studied show a noticeable correlation between the calculated binding energies and the propensities for protein-DNA base interactions found in the literature. Such correlation holded even for the interaction of the selected amino acid derivatives with Watson and Crick pairs. Therefore, the balance between hydrogen bonds and van der Waals interactions (specially stacking) in the control of the final shape of the investigated amino acid-DNA base pairs seems to be well reproduced in dispersion-corrected DFT molecular models, reinforcing the idea that the specificity between the amino acids and the DNA bases play an important role in the regulation of DNA. PMID:26765058

  13. DFT study of the chlorine promotion effect on the ethylene adsorption over iron clusters.

    PubMed

    Pahlavan, Farideh; Pakiari, Ali H

    2016-05-01

    This work explores how electronic perturbations induced by chlorine atoms can enhance the activity of iron toward ethylene. The metal clusters include Fen (n=2-4), in which each adatom (Cl) has an inclination to be adsorbed at the bridge site with electrostatic interaction. Ethylene adsorption over pure and chlorine-doped FenClm (n,m≤4) clusters is analyzed using density functional theory (DFT) calculations, in π and di-σ adsorption modes. One of the interesting features is that the adsorption mode of ethylene changes by going from trimers to tetramers. Ethylene never orients toward di-σ mode for FeFe bond in Fe2 and Fe3 series, while this orientation is preferred in tetramers. Our results demonstrate that the progressive change in the ethylene adsorption could not be sustained with increasing portion of chlorine in metal cluster. In this study, we attempt to provide a sensible justification for this phenomenon by the natural bond orbital (NBO) and quantum theory of atoms-in-molecules (QTAIM) analyses. PMID:27041445

  14. A vibrational spectroscopy study on 3-aminophenylacetic acid by DFT calculations.

    PubMed

    Akkaya, Yasemin; Balci, Kubilay; Goren, Yeliz; Akyuz, Sevim

    2015-08-01

    In this study, in which the group vibrations of 3-aminophenylacetic acid were investigated by electronic structure calculations based on Density Functional Theory (DFT), the possible stable conformers of the molecule were searched through a relaxed "potential energy surface scan" carried out at B3LYP/6-31G(d) level of theory. The corresponding equilibrium geometrical and vibrational spectral data for each of the determined stable conformers and for their possible dimer structures were obtained through "geometry optimisation" and "frequency" calculations carried out at B3LYP/6-31G(d) and B3LYP/6-311G++(d,p) levels of theory. The obtained results confirmed that anharmonic wavenumbers calculated at B3LYP/6-311G++(d,p) level generally quite well agree with the experimental wavenumbers, however, harmonic wavenumbers calculated at both levels of theory need an efficient refinement for a satisfactory agreement with experiment. In particular, the harmonic wavenumbers, IR and Raman intensities refined within Scaled Quantum Mechanical Force Field (SQM FF) methodology constituted the primary data set in the interpretation of the experimental FT-IR, FT-Raman and dispersive Raman spectra of 3-aminophenylacetic acid. By the help of these refined spectral data, the effects of conformation and intermolecular hydrogen bonding on the fundamental bands observed in the experimental spectra could be correctly predicted. PMID:25854610

  15. Effects of ionization on stability of 1-methylcytosine - DFT and PCM studies.

    PubMed

    Raczyńska, Ewa D; Michalec, Piotr; Zalewski, Marcin; Sapuła, Mariusz

    2016-07-01

    Consequences of ionization were studied by quantum-chemical methods (DFT and PCM) for 1-methylcytosine (MC)-a model of the nucleobase cytosine (C) connected with sugar in DNA. For calculations, three prototropic tautomers (one amino and two imino forms) and two imino zwitterions were considered, including conformational or configurational isomerism of exo heterogroups. Ionization and interactions between neighboring groups affect intramolecular proton-transfers, geometric and thermodynamic parameters, and electron delocalization for individual isomers. We discovered that an imino isomer is present in the isomeric mixture in the highest amount for positively ionized MC. Its contribution in neutral and negatively ionized MC is considerably smaller. Acid-base parameters for selected radical ions were estimated in the gas phase and compared to those of neutral MC. Gas-phase acidity of radical cations is close to that of the conjugate acid of MC, and gas-phase basicity of radical anions is close to that of the conjugate base of MC. Various routes of amino-imino conversion between neutral and ionized isomers were considered. Energetic-barrier for intramolecular proton-transfer in MC is close to that in the parent system-formamidine. PMID:27259531

  16. Phosphorus-stabilized titanium carbene complexes: synthesis, reactivity and DFT studies.

    PubMed

    Lafage, Mathieu; Heuclin, Hadrien; Le Goff, Xavier-Frédéric; Saffon-Merceron, Nathalie; Mézailles, Nicolas

    2014-12-15

    The synthesis of two novel titanium carbene complexes from the bis(thiophosphinoyl)methanediide geminal dianion 1 (SCS(2-) ) is described. Dianion 1 reacts cleanly with 0.5 equivalents of [TiCl4 (thf)2 ] to afford the bis-carbene complex [(SCS)2 Ti] (2) in 86 % yield. The mono-carbene complex [(SCS)TiCl2 (thf)] (3) can also be obtained by using an excess of [TiCl4 (thf)2 ]. The structures of 2 and 3 are confirmed by X-ray crystallography. A strong nucleophilic reactivity towards various electrophiles (ketones and aldehydes) is observed. The reaction of 3 with N,N'-dicyclohexylcarbodiimide (DCC) and phenyl isocyanate leads to the formation of two novel diphosphinoketenimines 8 a and 8 b. The bis-titanium guanidinate complex 9 is trapped as the by-product of the reaction with DCC. The X-ray crystal structures of 8 a and 9 are presented. The mechanism of the reaction between complex 3 and DCC is rationalized by DFT studies. PMID:25339253

  17. DFT study of interactions between calcium hydroxyl ions and pyrite, marcasite, pyrrhotite surfaces

    NASA Astrophysics Data System (ADS)

    Zhao, Cuihua; Chen, Jianhua; Li, Yuqiong; Huang, De wei; Li, Weizhou

    2015-11-01

    The interaction between CaOH+ ions and pyrite, marcasite and pyrrhotite surfaces was studied using density functional theory (DFT) calculations. The calculated results show that the adsorption energy of CaOH+ on the marcasite surface is the largest, -384.65 kJ/mol; then pyrrhotite, -346.61 kJ/mol; pyrite, -276.62 kJ/mol. After CaOH+ adsorption, oxygen atom is bonded to one iron atom, calcium atom is bonded to two sulfur atoms of pyrite surface. And there exists a Casbnd Fe2 anti-bonding on the pyrite surface. For marcasite, oxygen atom is bonded to one iron atom, calcium atom is bonded to two sulfur atoms of marcasite surface. As for pyrrhotite, calcium atom is only attached to three sulfur atoms of pyrrhotite surface. The charge transfers occur from CaOH+ to sulfides surfaces. The value of charge transfer from CaOH+ to marcasite surface is the largest, then pyrite, pyrrhotite in order. However, formation of Casbnd Fe2 anti-bonding on the pyrite surface weakens the reaction of CaOH+ with pyrite.

  18. DFT model cluster studies of O₂ adsorption on hydrogenated titania sub-nanoparticles.

    PubMed

    Andreev, Alexey S; Kuznetsov, Vyacheslav N; Chizhov, Yuri V

    2013-11-01

    In the present paper, we examine the general applicability of different TiO2 model clusters to study of local chemical events on TiO2 sub-nanoparticles. Our previous DFT study of TiO2 activation through H adsorption and following deactivation by O2 adsorption using small amorphous Ti8O16 cluster were complemented by examination of rutile-type and spherical Ti15O30 nanoclusters. The obtained results were thoroughly compared with experimental data and results of related computational studies using other TiO2 models including periodic structures. It turned out that all considered model TiO2 model systems provide qualitatively similar results. It was shown that atomic hydrogen is adsorbed with negligible activation energy on surface O atoms, which is accompanied by the appearance of reduced Ti(3+) species and corresponding localized band gap 3d-Ti states. Oxygen molecule is adsorbed on Ti(3+) sites spontaneously forming molecular O2 (-) species by capturing an extra electron of Ti(3+) ion, which results in disappearance of Ti(3+) species and corresponding band gap states. Calculated g-tensor values of Ti(3+) and O2 (-) species agree well with the results of EPR studies and do not depend on the used TiO2 model cluster. Additionally, it was shown that the various cluster calculations provide results comparable with the calculations of periodic structures with respect to the modeling of chemical processes under study. As a whole, the present study approves the validity of molecular cluster approach to study of local chemical events on TiO2 sub-nanoparticles. PMID:24085538

  19. Experimental and theoretical studies in nonlinear aeroelasticity

    NASA Astrophysics Data System (ADS)

    Attar, Peter Joseph

    Experimental and theoretical studies are conducted in the field of nonlinear aeroelasticity. Specifically two aeroelastic configurations, a flapping flag and a delta wing, are investigated and correlations between theory and experiment are presented. Two nonlinear structural theories are used to describe the structural behavior of the two models which are studied. The delta wing structural behavior is modeled using the nonlinear plate theory of von Karman. The nonlinearity in this model is due to the coupling between the out-of-plane and in-plane deflections and the model allows for moderately large out-of-plane plate deflections. The flapping flag structural model is a nonlinear beam theory which includes nonlinearities due to both large curvature and inertia. The axial deflection in this model is related to the out-of-plane deflection using an axially inextensible theory. The aerodynamic theory used is potential flow theory, which is applicable to low speed flows. The equation which describes potential flow is the Laplace equation, which is a linear partial differential equation. The Laplace equation is solved using a vortex lattice method. Aeroelastic solutions are found using both the classic small disturbance linearized fluid-structure interface boundary condition and the exact nonlinear boundary condition. The aeroelastic model which includes the nonlinear boundary conditions also includes a free wake solution. Several reduced order methods are explored. Normal mode solutions, both for the structural and aerodynamic models, are studied along with a proper orthogonal decomposition model for the aerodynamic flow. A brief description of a parallel implementation of the aeroelastic simulation code is also given and the parallel speedup is shown to be nearly linear for a certain class of problems. Correlation between theory and experiment is presented for both the delta wing and flapping flag model. Several steady angle of attack cases were investigated for the

  20. Studies of the electronic structure and biological activity of chosen 1,4-benzodiazepines by 35Cl NQR spectroscopy and DFT calculations

    NASA Astrophysics Data System (ADS)

    Bronisz, K.; Ostafin, M.; Poleshchuk, O. Kh.; Mielcarek, J.; Nogaj, B.

    2006-11-01

    Selected derivatives of 1,4-benzodiazepine: lorazepam, lormetazepam, oxazepam and temazepam, used as active substances in anxiolytic drugs, have been studied by 35Cl NQR method in order to find the correlation between electronic structure and biological activity. The 35Cl NQR resonance frequencies ( νQ) measured at 77 K have been correlated with the following parameters characterising their biological activity: biological half-life period ( t0.5), affinity to benzodiazepine receptor (IC 50) and mean dose equivalent. The results of experimental study of some benzodiazepine derivatives by nuclear quadrupole resonance of 35Cl nuclei are compared with theoretical results based on DFT calculations which were carried out by means of Gaussian'98 W software.

  1. Experimental and DFT studies of (E)-2-[2-(2,6-dichlorophenyl)ethenyl]-8-hydroxyquinoline: Electronic and vibrational properties

    NASA Astrophysics Data System (ADS)

    Sun, Wenqi; Yuan, Guozan; Liu, Jingxin; Ma, Li; Liu, Chengbu

    2013-04-01

    The title molecule (E)-2-[2-(2,6-dichlorophenyl)ethenyl]-8-hydroxyquinoline (DPEQ) was synthesized and characterized by FT-IR, UV-vis, NMR spectroscopy. The molecular geometry, vibrational frequencies and gauge independent atomic orbital (GIAO) 1H and 13C NMR chemical shift values of the compound in the ground state have been calculated by using the density functional theory (DFT) method. All the assignments of the theoretical frequencies were performed by potential energy distributions using VEDA 4 program. The calculated results indicate that the theoretical vibrational frequencies, 1H and 13C NMR chemical shift values show good agreement with experimental data. The electronic properties like UV-vis spectral analysis and HOMO-LUMO analysis of DPEQ have been reported and compared with experimental data. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with molecular electrostatic potential (MEP).

  2. DFT and ab initio study of structure of dyes derived from 2-hydroxy and 2,4-dihydroxy benzoic acids

    NASA Astrophysics Data System (ADS)

    Dabbagh, Hossein A.; Teimouri, Abbas; Najafi Chermahini, Alireza; Shahraki, Maryam

    2008-02-01

    We present a detailed analysis of the structural, infrared spectra and visible spectra of a series of azo dyes preparation of salicylic acid and 2,4-dihydroxy benzoic acid derivatives as the coupling component. The preparation of these azo dyes with salicylic acid and 2,4-dihydroxy benzoic acid derivatives (salicylic acid, methyl salicylate, ethyl salicylate, butyl salicylate, methyl 2,4-dihydroxy benzoate, ethyl 2,4-dihydroxy benzoate, salicylaldehyde, salicylamide, 2,4-dihydroxy benzamide, salicylaldoxime) have been investigated theoretically by performing HF and DFT levels of theory using the standard 6-31G* basis set. The optimized geometries and calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational spectral data obtained from solid phase FT-IR spectra are assigned modes based on the results of the theoretical calculations. The observed spectra are found to be in good agreement with the calculations.

  3. Alignment of the dye's molecular levels with the TiO2 band edges in dye-sensitized solar cells: a DFT TDDFT study

    NASA Astrophysics Data System (ADS)

    DeAngelis, Filippo; Fantacci, Simona; Selloni, Annabella

    2008-10-01

    We present a theoretical study of the lineup of the LUMO of Ru(II)-polypyridyl (N3 and N719) molecular dyes with the conduction band edge of a TiO2 anatase nanoparticle. We use density functional theory (DFT) and the Car-Parrinello scheme for efficient optimization of the dye-nanoparticle systems, followed by hybrid B3LYP functional calculations of the electronic structure and time-dependent DFT (TDDFT) determination of the lowest vertical excitation energies. The electronic structure and TDDFT calculations are performed in water solution, using a continuum model. Various approximate procedures to compute the excited state oxidation potential of dye sensitizers are discussed. Our calculations show that the level alignment for the interacting nanoparticle-sensitizer system is very similar, within about 0.1 eV, to that for the separated TiO2 and dye. The excellent agreement of our results with available experimental data indicates that the approach of this work could be used as an efficient predictive tool to help the optimization of dye-sensitized solar cells.

  4. Base release in nucleosides induced by low-energy electrons: a DFT study.

    PubMed

    Li, Xifeng; Sanche, Léon; Sevilla, Michael D

    2006-06-01

    Low-energy electrons are known to induce strand breaks and base damage in DNA and RNA through fragmentation of molecular bonding. Recently the glycosidic bond cleavage of nucleosides by low-energy electrons has been reported. These experimental results call for a theoretical investigation of the strength of the C(1)'-N link in nucleosides (dA, dC and dT) between the base and deoxyribose before and after electron attachment. Through density functional theory (DFT) calculations, we compare the C(1)'-N bond strength, i.e., the bond dissociation energy of the neutral and its anionic radical, and find that an excess electron effectively weakens the C(1)'- N bond strength in nucleosides by 61-75 kcal/mol in the gas phase and 76-83 kcal/mol in the solvated environment. As a result, electron-induced fragmentation of the C(1)'-N bond in the gas phase is exergonic for dA (DeltaG=-14 kcal/mol) and for dT (DeltaG=-6 kcal/mol) and is endergonic (DeltaG=+1 kcal/ mol) only for dC. In the gas phase all the anionic nucleosides are found to be in valence states. Solvation is found to increase the exergonic nature by an additional 20 kcal, making the fragmentation both exothermic and exergonic for all nucleoside anion radicals. Thus C(1)'-N bond breaking in nucleoside anion radicals is found to be thermodynamically favorable both in the gas phase and under solvation. The activation barrier for the C(1)'-N bond breaking process was found to be about 20 kcal/mol in every case examined, suggesting that a 1 eV electron would induce spontaneous cleavage of the bond and that stabilized anion radicals on the DNA strand would undergo base release at only a modest rate at room temperature. These results suggest that base release from nucleosides and DNA is an expected consequence of low-energy electron-induced damage but that the high barrier would inhibit this process in the stable anion radicals. PMID:16802873

  5. Synthesis, experimental spectra (IR & Raman and NMR), vibrational analysis and theoretical DFT investigations of N-(5-(4-methylbenzoyl)-2-oxo-4-(4-methylphenyl)pyrimidine-1(2H)-yl)-4-methylbenzamide

    NASA Astrophysics Data System (ADS)

    Aydın, Lütfiye; Şahan, Emine; Önal, Zülbiye; Özpozan, Talat

    2014-08-01

    The title molecule, N-(5-(4-methylbenzoyl)-2-oxo-4-(4-methylphenyl)pyrimidine-1(2H)-yl)-4-methylbenzamide (C27H23N3O3), was synthesized and characterized by elemental analysis, IR, Raman, 1H and 13C NMR spectral data. To determine conformational flexibility, potential energy surfaces of the title compound were obtained by DFT regarding the selected degree of torsional freedom, which was varied from 0° to 360° in 6° and 20° steps. The ten conformers of the title compound were determined and it was found that the conformer 1 basis the most stable one. All conformers were also optimized by using the density functional theory (DFT/B3LYP) method with the 6-31G(d,p), 6-311G(d,p) and cc-pVDZ basis sets in the ground state. Potential energy distribution was calculated with the 6-31G(d,p) basis set. The vibrational spectra were recorded in solid phase IR and Raman spectra were compared based on the results of the theoretical calculations. The formation of hydrogen bonds was explained using natural bond orbital (NBO) analysis and spectroscopic analysis. NMR analysis and frontier molecular orbitals (FMOs) were also investigated by DFT.

  6. Experimental, theoretical and docking studies of 2-hydroxy Schiff base type compounds derived from 2-amino-4-chlorobenzenethiol

    NASA Astrophysics Data System (ADS)

    Kusmariya, Brajendra S.; Mishra, A. P.

    2015-12-01

    We report here synthesis, DFT, Docking and Fluorescence studies of three Schiff base organic compounds viz. 2-{(E)-[(5-chloro-2-sulfanylphenyl)imino]methyl}phenol (1); 2,4-dichloro-6-{(E)-[(5-chloro-2-sulfanylphenyl)imino]methyl}phenol (2) and 2-{(E)-[(5-chloro-2-sulfanylphenyl) imino] methyl}-5-(diethylamino) phenol (3). These compounds have been characterized by elemental, FTIR, electronic and 1H NMR spectral techniques. Spectroscopic studies reveal that all the compounds exist in enol-form in the solid state whereas keto and enol, both forms exist in solution. The fluorescence behavior has been studied in DMF solvents and 1 &2 compound exhibit more efficient fluorescence properties. The molecular geometry of all the compounds in the ground state has been computed using the Hartree-Fock (HF) and density functional theory (DFT) with the 6-31++G basis set. The theoretical electronic absorption spectra of the compounds have been predicted using TD-DFT and TD-HF methods and compared with experimental spectral results. The predicted nonlinear optical properties of all the compounds are higher than those of urea. In addition to DFT calculations; frequency calculations, mulliken charge distribution, HOMO-LUMO and molecular electrostatic potential (MEP) have also been computed at the same level of theory. Molecular docking studies of the compounds in the active site of CAII (PDB code: 1CNX) have been performed to predict their possible binding modes in the active site of target carbonic anhydrase II enzyme.

  7. Alcohol cold starting - A theoretical study

    NASA Technical Reports Server (NTRS)

    Browning, L. H.

    1983-01-01

    Two theoretical computer models have been developed to study cold starting problems with alcohol fuels. The first model, a droplet fall-out and sling-out model, shows that droplets must be smaller than 50 microns to enter the cylinder under cranking conditions without being slung-out in the intake manifold. The second model, which examines the fate of droplets during the compression process, shows that the heat of compression can be used to vaporize small droplets (less than 50 microns) producing flammable mixtures below freezing ambient temperatures. While droplet size has the greater effect on startability, a very high compression ratio can also aid cold starting.

  8. Partial vs. integer electron transfer in molecular assemblies: On the importance of multideterminant theoretical description and the necessity to find a solution within DFT

    SciTech Connect

    Geskin, Victor; Cornil, Jérôme; Stadler, Robert

    2015-01-22

    Nonequilibrium Green's function techniques (NEGF) combined with density functional theory (DFT) calculations have become a standard tool for the description of electron transport through single molecule nanojunctions in the coherent tunneling (CT) regime. However, the applicability of these methods for transport in the Coulomb blockade (CB) regime is questionable. For a molecular assembly model, with multideterminant calculations as a benchmark, we show how a closed-shell ansatz, the usual ingredient of mean-field methods, fails to properly describe the step like electron-transfer characteristic in weakly coupled systems. Detailed analysis of this misbehavior allows us to propose a practical scheme to extract the addition energies in the CB regime for single-molecule junctions from NEGF DFT within the local-density approximation (closed shell). We show also that electrostatic screening effects are taken into account within this simple approach.

  9. Experimental (FT-IR and FT-Raman) and theoretical (HF and DFT) investigation, IR intensity, Raman activity and frequency estimation analyses on 1-bromo-4-chlorobenzene

    NASA Astrophysics Data System (ADS)

    Udayakumar, V.; Periandy, S.; Ramalingam, S.

    2011-09-01

    The FT-IR and FT-Raman spectra of 1-bromo-4-chlorobenzene (1-Br-4-CB) have been recorded using Bruker IFS 66V spectrometer in the region of 4000-100 cm -1. Ab-initio-HF (HF/6-311+G (d, p)) and DFT (B3LYP/6-31++G (d, p)/6-311++G (d, p)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities. The vibrational frequencies are calculated and scaled values are compared with FT-IR and FT-Raman experimental values. Comparison of simulated spectra with the experimental spectra provides important information, the computational method have the ability to describe the vibrational methods. The frequency estimation analysis on HF and DFT is made. The impact of di-substituted halogens on the benzene molecule has also been discussed.

  10. Experimental (FT-IR and FT-Raman) and theoretical (HF and DFT) investigation, IR intensity, Raman activity and frequency estimation analyses on 1-bromo-4-chlorobenzene.

    PubMed

    Udayakumar, V; Periandy, S; Ramalingam, S

    2011-09-01

    The FT-IR and FT-Raman spectra of 1-bromo-4-chlorobenzene (1-Br-4-CB) have been recorded using Bruker IFS 66V spectrometer in the region of 4000-100 cm(-1). Ab-initio-HF (HF/6-311+G (d, p)) and DFT (B3LYP/6-31++G (d, p)/6-311++G (d, p)) calculations have been performed giving energies, optimized structures, harmonic vibrational frequencies, depolarization ratios, IR intensities, Raman activities. The vibrational frequencies are calculated and scaled values are compared with FT-IR and FT-Raman experimental values. Comparison of simulated spectra with the experimental spectra provides important information, the computational method have the ability to describe the vibrational methods. The frequency estimation analysis on HF and DFT is made. The impact of di-substituted halogens on the benzene molecule has also been discussed. PMID:21550298

  11. Electron density distribution in cladribine (2-chloro-2‧-deoxyadenosine) - A drug against leukemia and multiple sclerosis - Studied by multinuclear NQR spectroscopy and DFT calculations

    NASA Astrophysics Data System (ADS)

    Latosińska, J. N.; Latosińska, M.; Seliger, J.; Žagar, V.; Kazimierczuk, Z.

    2009-07-01

    2-Chloro-2'-deoxyadenosine (Cladribine) chemotherapeutic drug has been studied experimentally in solid state by 35Cl NQR and NMR-NQR double resonance and theoretically by the Density Functional Theory. Fifteen resonance frequencies on 14N have been detected and assigned to particular nitrogen sites in the 2-CdA molecule. The effects of tautomerism, regioisomerism, conformations and molecular aggregations, related to intermolecular hydrogen bond formation, on the NQR parameters have been analysed within the DFT and AIM ( Atoms in Molecules) formalism. The properties of the whole molecule, the so-called global reactivity descriptors, have been calculated for a comparison of both syn and anti conformations of 2-CdA molecule to check the effect of crystal packing on molecular conformation.

  12. Main chemical species and molecular structure of deep eutectic solvent studied by experiments with DFT calculation: a case of choline chloride and magnesium chloride hexahydrate.

    PubMed

    Zhang, Chao; Jia, Yongzhong; Jing, Yan; Wang, Huaiyou; Hong, Kai

    2014-08-01

    The infrared spectrum of deep eutectic solvent of choline chloride and magnesium chloride hexahydrate was measured by the FTIR spectroscopy and analyzed with the aid of DFT calculations. The main chemical species and molecular structure in deep eutectic solvent of [MgClm(H2O)6-m]2-m and [ChxCly]x+y complexes were mainly identified and the active ion of magnesium complex during the electrochemical process was obtained. The mechanism of the electrochemical process of deep eutectic solvent of choline chloride and magnesium chloride hexahydrate was well explained by combination theoretical calculations and experimental. Besides, based on our results we proposed a new system for the dehydration study of magnesium chloride hexahydrate. PMID:25031082

  13. New insight into the structure of saturated chlorine layer on Ag(1 1 1): LT-STM and DFT study

    NASA Astrophysics Data System (ADS)

    Andryushechkin, B. V.; Cherkez, V. V.; Gladchenko, E. V.; Zhidomirov, G. M.; Kierren, B.; Fagot-Revurat, Y.; Malterre, D.; Eltsov, K. N.

    2013-02-01

    Atomic structures formed on the Ag(1 1 1) surface as a result of molecular chlorine adsorption have been studied with a low-temperature scanning tunneling microscopy (LT-STM) in a combination with DFT calculations. We have found that saturated chlorine coverage on Ag(1 1 1) is a complex system consisting of two different structural phases: small anti-phase domains of a (3 × 3) reconstruction and nanoclusters Ag3Cl7.

  14. 27ps DFT Molecular Dynamics Simulation of a-maltose: A Reduced Basis Set Study.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    DFT molecular dynamics simulations are time intensive when carried out on carbohydrates such as alpha-maltose, requiring up to three or more weeks on a fast 16-processor computer to obtain just 5ps of constant energy dynamics. In a recent publication [1] forces for dynamics were generated from B3LY...

  15. DFT STUDY OF ALPHA-MALTOSE: INFLUENCE OF HYDROXYL ORIENTATIONS ON THE GLYCOSIDIC BOND

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The result of DFT geometry optimization of 68 unique alpha-maltose conformers at the B3LYP/6-311++G** level of theory is described. Particular attention is paid to the hydroxyl group rotational positions and their influence on the glycosidic bond dihedral angles. The orientation of lone pair elect...

  16. Comparative theoretical studies of energetic azo s-triazines.

    PubMed

    Wang, Fang; Du, Hong-chen; Zhang, Jian-ying; Gong, Xue-dong

    2011-10-27

    In this work, the properties of the synthesized high-nitrogen compounds 4,4',6,6'-tetra(azido)azo-1,3,5-triazine (TAAT) and 4,4',6,6'-tetra(azido)hydrazo-1,3,5-triazine (TAHT), and a set of designed bridged triazines with similar bridges were studied theoretically to facilitate further developments for the molecules of interests. The gas-phase heats of formation were predicted based on the isodesmic reactions by using the DFT-B3LYP/AUG-cc-PVDZ method. The estimates of the condensed-phase heats of formation and heats of sublimation were estimated in the framework of the Politzer approach. Calculation results show that the method gives a good estimation for enthalpies, in comparison with available experimental data for TAAT and TAHT. The crystal density has been computed using molecular packing calculations. The calculated detonation velocities and detonation pressures indicate that -NF(2), -NO(2), -N═N-, and -N═N(O)- groups are effective structural units for improving the detonation performance of the bridged triazines. The synthesized TAAT and TAHT are not preferred energetic materials due to their inferior detonation performance. The p→π conjugation effect between the triazine rings and bridges makes the molecule stable as a whole. The electrostatic behavior of the bridged triazines is characterized by an anomalous surface potential imbalance when incorporating the strongly electron-withdrawing -NF(2) and -NO(2) groups into the molecule. An analysis of the bond dissociation energies shows that all these derivatives have good thermal stability over RDX and HMX, and the -NH-NH- bridge is more helpful for improving the stability than -N═N(O)- and -N═N- bridges. Considering the detonation performance and thermal stability, three bridged triazines may be considered as the potential candidates of high-energy density materials (HEDMs). PMID:21910431

  17. Structural and spectroscopic characterization of ettringite mineral -combined DFT and experimental study

    NASA Astrophysics Data System (ADS)

    Scholtzová, Eva; Kucková, Lenka; Kožíšek, Jozef; Tunega, Daniel

    2015-11-01

    The structure of the ettringite mineral was studied by means of FTIR spectroscopy and single crystal X-ray diffraction method. The experimental study was combined with the first principle calculations based on density functional theory (DFT) method. Predicted structural parameters (unit cell vectors and positions of heavy atoms) are in a very good agreement with the experimental data. Moreover, calculations also enabled to refine the positions of the hydrogen atoms not determined precisely by the single crystal X-ray measurement. The detailed analysis of the hydrogen bonds in the ettringite structure was performed and several groups of the hydrogen bonds were classified. It was found that the water molecules from the coordination sphere of Ca2+ cations act as proton donors in moderate O-H···O hydrogen bonds with SO 32- anions. Further, multiple O-H···O hydrogen bonds were identified among water molecules themselves. In addition, also hydroxyl groups from the [Al(OH)6]3- octahedral units are involved in the weak O-H···O hydrogen bonding with the water molecules. The calculated vibrational spectrum showed all typical features observed in the experimental FTIR spectrum. Moreover, performing the analysis of the calculated spectrum, all vibrational modes were distinguished and assigned. Such a complete analysis of the measured IR and/or Raman spectra is not fully possible, specifically for the region below 1500 cm-1, which is characterized by a complex curve with many overlapped bands. A comparison of the vibrational spectra of ettringite and thaumasite (mineral structurally similar to ettringite) revealed the origin of the most important differences between them.

  18. Theoretical studies of viral capsid proteins.

    PubMed

    Phelps, D K; Speelman, B; Post, C B

    2000-04-01

    Recent results in structural biology and increases in computer power have prompted initial theoretical studies on capsids of nonenveloped icosahedral viruses. The macromolecular assembly of 60 to 180 protein copies into a protein shell results in a structure of considerable size for molecular dynamics simulations. Nonetheless, progress has been made in examining these capsid assemblies from molecular dynamics calculations and kinetic models. The goals of these studies are to understand capsid function and structural properties, including quarternary structural stability, effects of antiviral compounds that bind the capsid and the self-assembly process. The insight that can be gained from the detailed information provided by simulations is demonstrated in studies of human rhinovirus; an entropic basis for the antiviral activity of hydrophobic compounds, predicted from calculated compressibility values, has been corroborated by experimental measurements on poliovirus. PMID:10753813

  19. Theoretical studies of hadrons and nuclei

    SciTech Connect

    COTANCH, STEPHEN R

    2007-03-20

    This report details final research results obtained during the 9 year period from June 1, 1997 through July 15, 2006. The research project, entitled Theoretical Studies of Hadrons and Nuclei , was supported by grant DE-FG02-97ER41048 between North Carolina State University [NCSU] and the U. S. Department of Energy [DOE]. In compliance with grant requirements the Principal Investigator [PI], Professor Stephen R. Cotanch, conducted a theoretical research program investigating hadrons and nuclei and devoted to this program 50% of his time during the academic year and 100% of his time in the summer. Highlights of new, significant research results are briefly summarized in the following three sections corresponding to the respective sub-programs of this project (hadron structure, probing hadrons and hadron systems electromagnetically, and many-body studies). Recent progress is also discussed in a recent renewal/supplemental grant proposal submitted to DOE. Finally, full detailed descriptions of completed work can be found in the publications listed at the end of this report.

  20. DFT study of structure, IR and Raman spectra of the fluorescent "Janus" dendron built from cyclotriphosphazene core

    NASA Astrophysics Data System (ADS)

    Furer, V. L.; Vandyukova, I. I.; Vandyukov, A. E.; Fuchs, S.; Majoral, J. P.; Caminade, A. M.; Kovalenko, V. I.

    2011-11-01

    The FTIR and FT-Raman spectra of the zero generation dendron, possessing five fluorescent dansyl terminal groups, cyclotriphosphazene core, and one carbamate function G0v were studied. The structural optimization and normal mode analysis were performed for G0v dendron on the basis of the density functional theory (DFT). The calculated geometrical parameters and harmonic vibrational frequencies are predicted in a good agreement with the experimental data. It was found that dendron molecule G0v has a concave lens structure with slightly non-planar cyclotriphosphazene core. The experimental IR and Raman spectra of G0v dendron were interpreted by means of potential energy distributions. Relying on DFT calculations a complete vibrational assignment is proposed. The frequency of ν(N-H) band in the IR spectrum reveal the presence of H-bonds in the G0v dendron.

  1. Density functional theory (DFT) study of triphenylamine-based dyes for their use as sensitizers in molecular photovoltaics.

    PubMed

    Baldenebro-López, Jesús; Castorena-González, José; Flores-Holguín, Norma; Almaral-Sánchez, Jorge; Glossman-Mitnik, Daniel

    2012-01-01

    In this work we studied three dyes which are proposed for potential photovoltaic applications and named Dye7, Dye7-2t and Dye7-3t. The Density Functional Theory (DFT) was utilized, using the M05-2X hybrid meta-GGA functional and the 6-31+G(d,p) basis set. This level of calculation was used to find the optimized molecular structure and to predict the main molecular vibrations, the absorption and emission spectra, the molecular orbitals energies, dipole moment, isotropic polarizability and the chemical reactivity parameters that arise from Conceptual DFT. Also, the pK(a) values were calculated with the semi-empirical PM6 method. PMID:22605987

  2. Water adsorption on a copper formate paddlewheel model of CuBTC: A comparative MP2 and DFT study

    NASA Astrophysics Data System (ADS)

    Toda, Jordi; Fischer, Michael; Jorge, Miguel; Gomes, José R. B.

    2013-11-01

    Simultaneous adsorption of two water molecules on open metal sites of the HKUST-1 metal-organic framework (MOF), modeled with a Cu2(HCOO)4 cluster, was studied by means of density functional theory (DFT) and second-order Moller-Plesset (MP2) approaches together with correlation consistent basis sets. Experimental geometries and MP2 energetic data extrapolated to the complete basis set limit were used as benchmarks for testing the accuracy of several different exchange-correlation functionals in the correct description of the water-MOF interaction. M06-L and some LC-DFT methods arise as the most appropriate in terms of the quality of geometrical data, energetic data and computational resources needed.

  3. The guanidine and maleic acid (1:1) complex. The additional theoretical and experimental studies

    NASA Astrophysics Data System (ADS)

    Drozd, Marek; Dudzic, Damian

    2012-04-01

    On the basis of experimental literature data the theoretical studies for guanidinium and maleic acid complex with using DFT method are performed. In these studies the experimental X-ray data for two different forms of investigated crystal were used. During the geometry optimization process one equilibrium structure was found, only. According to this result the infrared spectrum for one theoretical molecule was calculated. On the basis of potential energy distribution (PED) analysis the clear-cut assignments of observed bands were performed. For the calculated molecule with energy minimum the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were obtained and graphically illustrated. The energy difference (GAP) between HOMO and LUMO was analyzed. Additionally, the nonlinear properties of this molecule were calculated. The α and β (first and second order) hyperpolarizability values are obtained. On the basis of these results the title crystal was classified as new second order NLO generator.

  4. Theoretical pluralism in psychoanalytic case studies

    PubMed Central

    Willemsen, Jochem; Cornelis, Shana; Geerardyn, Filip M.; Desmet, Mattias; Meganck, Reitske; Inslegers, Ruth; Cauwe, Joachim M. B. D.

    2015-01-01

    The aim of this study is to provide an overview of the scientific activity of different psychoanalytic schools of thought in terms of the content and production of case studies published on ISI Web of Knowledge. Between March 2013 and November 2013, we contacted all case study authors included in the online archive of psychoanalytic and psychodynamic case studies (www.singlecasearchive.com) to inquire about their psychoanalytic orientation during their work with the patient. The response rate for this study was 45%. It appears that the two oldest psychoanalytic schools, Object-relations psychoanalysis and Ego psychology or “Classical psychoanalysis” dominate the literature of published case studies. However, most authors stated that they feel attached to two or more psychoanalytic schools of thought. This confirms that the theoretical pluralism in psychoanalysis stretches to the field of single case studies. The single case studies of each psychoanalytic school are described separately in terms of methodology, patient, therapist, or treatment features. We conclude that published case studies features are fairly similar across different psychoanalytic schools. The results of this study are not representative of all psychoanalytic schools, as some do not publish their work in ISI ranked journals. PMID:26483725

  5. Experimental and DFT studies of the conversion of ethanol and acetic acid on PtSn-based catalysts.

    PubMed

    Alcala, Rafael; Shabaker, John W; Huber, George W; Sanchez-Castillo, Marco A; Dumesic, James A

    2005-02-17

    Reaction kinetics studies were conducted for the conversions of ethanol and acetic acid over silica-supported Pt and Pt/Sn catalysts at temperatures from 500 to 600 K. Addition of Sn to Pt catalysts inhibits the decomposition of ethanol to CO, CH4, and C2H6, such that PtSn-based catalysts are active for dehydrogenation of ethanol to acetaldehyde. Furthermore, PtSn-based catalysts are selective for the conversion of acetic acid to ethanol, acetaldehyde, and ethyl acetate, whereas Pt catalysts lead mainly to decomposition products such as CH4 and CO. These results are interpreted using density functional theory (DFT) calculations for various adsorbed species and transition states on Pt(111) and Pt3Sn(111) surfaces. The Pt3Sn alloy slab was selected for DFT studies because results from in situ (119)Sn Mössbauer spectroscopy and CO adsorption microcalorimetry of silica-supported Pt/Sn catalysts indicate that Pt-Sn alloy is the major phase present. Accordingly, results from DFT calculations show that transition-state energies for C-O and C-C bond cleavage in ethanol-derived species increase by 25-60 kJ/mol on Pt3Sn(111) compared to Pt(111), whereas energies of transition states for dehydrogenation reactions increase by only 5-10 kJ/mol. Results from DFT calculations show that transition-state energies for CH3CO-OH bond cleavage increase by only 12 kJ/mol on Pt3Sn(111) compared to Pt(111). The suppression of C-C bond cleavage in ethanol and acetic acid upon addition of Sn to Pt is also confirmed by microcalorimetric and infrared spectroscopic measurements at 300 K of the interactions of ethanol and acetic acid with Pt and PtSn on a silica support that had been silylated to remove silanol groups. PMID:16851198

  6. Theoretical study of the regioselective cyclization of enaminones in the construction of benzofurans and indoles.

    PubMed

    Herrera, Rafael; Méndez, Francisco; Jiménez, Fabiola; Cruz, M Carmen; Tamariz, Joaquín

    2016-05-01

    A theoretical study was undertaken regarding the regioselective Lewis acid-promoted intramolecular cyclization of novel enaminones 1-3 leading to the corresponding benzofurans 4-5 and indoles 6. The density functional theory (DFT) and hard and soft acids and bases (HSAB) principle provided data to describe the electronic effects of the substituents in the reactivity of the benzene ring and the enaminone moiety. The condensed and local Fukui functions for nucleophilic and electrophilic attacks of the reactants accounted for the experimentally observed preference, in regard to precursors 1-3, of the cyclization between the C6' carbon (rather than the C2' carbon) of the benzene ring and the C3 center of the enaminone moiety. Graphical Abstract A theoretical study (DFT/HSAB) describes the electronic effects of the substituents in the reactivity of the benzene ring and the enaminone moiety of enaminones I to explain their Lewis acid-promoted regioselective intramolecular cyclization, which exclusively leads to the corresponding benzofurans and indoles II. PMID:27132239

  7. Experimental and theoretical spectroscopic studies of anticancer drug rosmarinic acid using HF and density functional theory

    NASA Astrophysics Data System (ADS)

    Mariappan, G.; Sundaraganesan, N.; Manoharan, S.

    2012-11-01

    In this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of anticancer drug of rosmarinic acid. The optimized molecular structure, atomic charges, vibrational frequencies, natural bond orbital analysis and ultraviolet-visible spectral interpretation of rosmarinic acid have been studied by performing HF and DFT/B3LYP/6-31G(d,p) level of theory. The FT-IR (solid and solution phase), FT-Raman (solid phase) spectra were recorded in the region 4000-400 and 3500-50 cm-1, respectively. The UV-Visible absorption spectra of the compound that dissolved in ethanol were recorded in the range of 200-800 nm. The scaled wavenumbers are compared with the experimental values. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The formation of hydrogen bond was investigated in terms of the charge density by the NBO calculations. Based on the UV spectra and TD-DFT calculations, the electronic structure and the assignments of the absorption bands were carried out. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis were investigated using theoretical calculations.

  8. Semi- and thiosemicarbazide Mn(II) complexes: Characterization, DFT and biological studies

    NASA Astrophysics Data System (ADS)

    Yousef, T. A.; Alduaij, O. K.; Ahmed, Sara F.; Abu El-Reash, G. M.; El-Gammal, O. A.

    2016-09-01

    One NO and two NOS donor ligands have been prepared by addition ethanolic suspension of 2-hydrazino-2-oxo-N-phenyl-acetamide to phenyl isocyanate (H2PAPS), phenyl isothiocyanate (H2PAPT) and benzoyl isothiocyanate (H2PABT). The Mn (II) complexes were prepared from the chloride salt and characterized by conventional techniques. The isolated complexes were assigned the formulaes, [Mn(HPAPS)2], [Mn(HPAPT)Cl] and [Mn(HPABT)Cl(H2O)2], respectively. The IR study of ligands and their complexes shows that H2PAPS behaves as a mononegative tridentate via both CO of hydrazide moiety in keto and deprotonated enol form and CN (azomethine) due to enolization of CO cyanate moiety without deprotonation. H2PAPT behaves as mononegative tridentate via CO of hydrazide moiety, deprotonated thiol CS and NH group. Finally H2PABT behaves as mononegative tridentate via deprotonated enolized CO of hydrazide moiety, CO of benzoyl moiety and NH group. The IR spectra of ligands from DFT calculations are compared with those obtained experimentally. Also, HOMO, LUMO, the bond lengths, bond angles, and dipole moments have been calculated. The calculated HOMO-LUMO energy gap reveals that charge transfer occurs within the molecule. The binding energy values display the high stability of complexes. The kinetic and thermodynamic parameters were determined by Coats-Redfern and Horowitz-Metzger methods. The antibacterial activities were also tested against Bacillus subtilis and Escherichia coli bacteria. Finally, the antitumor activities of the Ligands and their Mn(II) complexes have been evaluated against liver (HePG2) and breast (MCF-7) cancer cells.

  9. DFT study on the galvanic interaction between pyrite (100) and galena (100) surfaces

    NASA Astrophysics Data System (ADS)

    Ke, Baolin; Li, Yuqiong; Chen, Jianhua; Zhao, Cuihua; Chen, Ye

    2016-03-01

    The galvanic interaction between pyrite and galena surface has been investigated using density functional theory (DFT) method. The calculated results show that galvanic interactions between pyrite and galena surface are decreased with the increase of contact distance. The galvanic interactions still occurs even the distance larger than the sum of two atoms radius (≈2.8 Å), and the limit distance of galvanic interaction between galena and pyrite surface is about 10 Å, which is consistent with the quantum tunneling effect. Through Mulliken charge population calculation, it is found that electrons transfer from galena to pyrite. For galena surface, Pb 6s and 6p states lose electrons and S 3p state loses a small amount of electrons, which causes the electron loss of galena. For pyrite surface, Fe 4p state obtains large numbers of electrons, resulting in the decrease of positive charge of Fe atom. However, the 3p state of S atom loses a small numbers of electrons. The reactivity of mineral surface has also been studied by calculating the frontier orbitals of minerals. Results suggest that the highest occupied molecular orbital (HOMO) coefficients of galena are increased whereas those of pyrite are decreased with the enhancing galvanic interaction, indicating that the oxidation of galena surface would be enhanced due to the galvanic interaction. The Fukui indices and dual descriptor values of surface atoms suggest that the nucleophilicity of the galena surface increases, meanwhile, the electrophilicity of pyrite surface increases with the decrease of the contact distance. In addition, the density of states (DOS) of atoms results show that the activity of electrons in Pb 6s and 6p orbitals enhances while the activity of electrons in Fe 3d orbitals weaken due to the galvanic contact between minerals.

  10. Experimental and DFT studies on the antioxidant activity of a C-glycoside from Rhynchosia capitata

    NASA Astrophysics Data System (ADS)

    Praveena, R.; Sadasivam, K.; Kumaresan, R.; Deepha, V.; Sivakumar, Raman

    2013-02-01

    Rhynchosia capitata (=Glycine capitata) Heyne ex roth, was found to possess polyphenolics including flavonoids, which acts as potential antioxidant. The study of ethanolic extract of roots and leaves reveals that the leaves possess high polyphenolics including flavonoids than roots. This was also confirmed by DPPH radical scavenging activity. Leaf powder of the plant was extracted with different solvents by soxhlet apparatus in the order of increasing polarity. The DPPH scavenging activity of methanol fraction was found to be high compared to the crude extract and other fractions. Nitric oxide scavenging activity was dominant in chloroform fraction compared to methanol fraction. Presence of flavonoids especially vitexin, a C-glycoside in methanol and chloroform fractions were confirmed by high pressure thin layer chromatography (HPTLC) analysis. The structural and molecular characteristics of naturally occurring flavonoid, vitexin was investigated in gas phase using density functional theory (DFT) approach with B3LYP/6-311G(d,p) level of theory. Analysis of bond dissociation enthalpy (BDE) reveals that the OH site that requires minimum energy for dissociation is 4'-OH from B-ring. To explore the radical scavenging activity of vitexin, the adiabatic ionization potential, electron affinity, hardness, softness, electronegativity and electrophilic index properties were computed and interpreted. The nonvalidity of Koopman's theorem has been verified by the computation of Eo and Ev energy magnitudes. Interestingly, from BDE calculations it was observed that BDE for 4'-OH, 5-OH and 7-OH are comparatively low for vitexin than its aglycone apigenin and this may be due to the presence of C-8 glucoside in vitexin. To substantiate this, plot of frontier molecular orbital and spin density distribution analysis for neutral and the corresponding radical species for the compound vitexin have been presented.

  11. Using Defects in Materials to Store Energy: a Theoretical Study

    NASA Astrophysics Data System (ADS)

    Lu, I.-Te; Bernardi, Marco

    We study the energy stored by defects in materials using density functional theory (DFT) calculations. Leveraging experimental data to estimate the energy density of defects, expressed as the defect formation energy per unit volume (units of MJ/L) or weight (units of MJ/kg), we identify candidates for high energy density storage, including tungsten, diamond, graphite, silicon, and graphene. DFT calculations are applied to these materials to study the formation energy of vacancies, interstitials, and Frenkel pairs. Our results indicate that the energy density stored by defects in these materials, with experimentally accessible non-equilibrium defect concentrations, can be higher than that of common energy storage technologies such as lithium batteries and supercapacitors. We discuss storage of solar energy and electrical energy (through ion bombardment) using defects.

  12. Threshold photodetachment of HOCO-: a theoretical study

    NASA Astrophysics Data System (ADS)

    Miyabe, S.; Haxton, D. J.; Lawler, K. V.; Lawler, A. E.; McCurdy, C. W.; Rescigno, T. N.

    2011-05-01

    The HOCO radical is an important intermediate in combustion. Information about its electronic structure has been obtained from studies of the photodetachment of HOCO-. We present the results of a theoretical study of HOCO- photodetachment, with a view toward understanding the origin of two peaks observed in the photoelectron kinetic energy spectrum very close to threshold. Fixed-nuclei variational electron-HOCO scattering calculations are used to compute photodetachment cross sections and laboratory-frame photoelectron angular distributions. We show that the observed peaks cannot, as previously assumed, be narrow shape resonances and argue that they can be attributed to vibrational Feshbach resonances of dipole-bound trans-HOCO-. LBNL, UC Davis. Work performed under auspices of US DOE and supported by OBES, Division of Chemical Sciences.

  13. Theoretical studies on flapped delta wings

    NASA Technical Reports Server (NTRS)

    Oh, S.; Tavella, D.; Roberts, L.

    1988-01-01

    The effects of leading edge flaps on the aerodynamic characteristics of a low aspect-ratio delta wing are studied theoretically. As an extension of the classical crossflow plane analysis and in order to include separated shear layers, an analogy between three dimensional steady conical and two dimensional unsteady self-similar flows is explored. This analogy provides a simple steady-unsteady relationship. The criteria for the validity of the steady-unsteady analogy are also examined. Two different theoretical techniques are used to represent the separated shear layers based on the steady-unsteady analogy, neglecting the trailing edge effect. In the first approach, each vortex system is represented by a pair of concentrated vortices connected to the separation points by straight feeding sheets. In the second approach, the vortex cloud method is adopted for simulating the flow field in the crossflow plane. The separated shear layers are replaced with a cloud of discrete vortices and the boundary element method is employed to represent the wing trace by a vorticity distribution. A simple merging scheme is used to model the core region of the vortical flow as a single vortex by imposing a restriction on the shear layer rotation angle. The results are compared with experiments and with results from 3-D panel calculations.

  14. Theoretical Study on Standing Wave Thermoacoustic Engine

    NASA Astrophysics Data System (ADS)

    Kalra, S.; Desai, K. P.; Naik, H. B.; Atrey, M. D.

    Applications of thermoacoustic engines are not limited to driving pulse tube cryocoolers. The performance of a thermoacoustic engine is governed by various design parameters like type of resonator, stack geometry, frequency, type of working gas etc. and various operating parameters like heat input, charging pressure etc. It is very important to arrive at an optimum configuration of the engine for which a theoretical model is required. In the present work, a theoretical analysis, based on linear acoustic theory of a standing wave type half wavelength thermoacoustic engine is carried out using DeltaEC software. The system dimensions like length of resonator, stack, hot and cold heat exchangers are fixed with a helium-argon mixture as the working gas and a parallel plate type stack. Later on, two plate spacings, corresponding to helium-argon mixture and nitrogen gas, are used for carrying out analysis with helium, argon, nitrogen, carbon dioxide and helium-argon mixture as working gases of the system. The effect of charging pressure on the performance of the system is studied in terms of resonating frequency, onset temperature, pressure amplitude, acoustic power and efficiency. The conclusions derived from the analysis are reported in the paper.

  15. Synthesis, structural, conformational and DFT studies of N-3 and O-4 alkylated regioisomers of 5-(hydroxypropyl)pyrimidine

    NASA Astrophysics Data System (ADS)

    Salihović, Mirsada; Osmanović, Amar; Špirtović-Halilović, Selma; Roca, Sunčica; Meščić, Andrijana; Vujisić, Ljubodrag; Trifunović, Snežana; Završnik, Davorka; Sofić, Emin

    2015-07-01

    Because of the great pharmacological potential of the pyrimidine motif, novel C-5 substituted N-3 acyclic and O-4 acyclic pyrimidine derivatives were prepared as an interesting class of compounds for biological evaluation. Introduction of the 2,3-dihydroxypropyl (DHP) and penciclovir (PCV)-like side chains to 2-methoxypyrimidin-4-one (2) afforded a mixture of N- and O-acyclic pyrimidine nucleosides in the ratio of 54: 29 (3:4) and 57:21 (5:6) with N-3 isomer being dominant. Distinction between N- and O-alkylated pyrimidine moiety was deduced from extensive experimental FT-IR, HPLC-MS and 1D (1H, 13C) and 2D (COSY, HMQC and HMBC) NMR analyses. The N-, O-regioisomers were also examined by computational method at density functional theory (DFT) RB3LYP/6-31G(d), 6-31G∗∗ and 6-31+G∗ levels. DFT global chemical reactivity descriptors (total energy, chemical hardness, electronic chemical potential and electrophilicity) were calculated for the isomers and used to predict and describe their relative stability and reactivity. The chemical reactivity indices were related to the C2sbnd N3sbnd C4 bond angle. Theoretical predictions can be used to compare chemical reactivity and stability with future biological evaluation and behaviour of these compounds.

  16. Weakly bound PTCDI and PTCDA dimers studied by using MP2 and DFT methods with dispersion correction.

    PubMed

    Oltean, Mircea; Mile, George; Vidrighin, Mihai; Leopold, Nicolae; Chiş, Vasile

    2013-09-01

    Potential energy curves along the inter-planar coordinates have been calculated for the dimers of two perylene derivatives (PTCDI and PTCDA) by using MP2 and dispersion corrected DFT (DFT-D) methods with B3LYP, B97 and PBE0 density functionals. The performance of dispersion-correcting potentials (DCPs) for describing intermolecular van der Waals interactions was also tested in conjunction with PBE0 and B971 functionals. Analytical potential energy curves were derived at different levels of theory by fitting the calculated data to modified Morse, Murrell-Sorbie, Buckingham and Lennard-Jones potentials. Potential energy surfaces for the two types of dimers were explored at the PBE0-DCP/6-31+G(d,p) level of theory in order to assess the effects of geometrical perturbations (displacements and/or rotations) on the stability of the dimers. Two minima were located for each perylene derivative, depending on the starting geometries of the dimers. Inter-monomer geometrical parameters of fully and partially optimized dimeric structures, as well as their relative stability, are discussed in comparison to available experimental data and other theoretical results on these or similar compounds. PMID:23852032

  17. How Many Conformations of Enzymes Should Be Sampled for DFT/MM Calculations? A Case Study of Fluoroacetate Dehalogenase

    PubMed Central

    Li, Yanwei; Zhang, Ruiming; Du, Likai; Zhang, Qingzhu; Wang, Wenxing

    2016-01-01

    The quantum mechanics/molecular mechanics (QM/MM) method (e.g., density functional theory (DFT)/MM) is important in elucidating enzymatic mechanisms. It is indispensable to study “multiple” conformations of enzymes to get unbiased energetic and structural results. One challenging problem, however, is to determine the minimum number of conformations for DFT/MM calculations. Here, we propose two convergence criteria, namely the Boltzmann-weighted average barrier and the disproportionate effect, to tentatively address this issue. The criteria were tested by defluorination reaction catalyzed by fluoroacetate dehalogenase. The results suggest that at least 20 conformations of enzymatic residues are required for convergence using DFT/MM calculations. We also tested the correlation of energy barriers between small QM regions and big QM regions. A roughly positive correlation was found. This kind of correlation has not been reported in the literature. The correlation inspires us to propose a protocol for more efficient sampling. This saves 50% of the computational cost in our current case. PMID:27556449

  18. How Many Conformations of Enzymes Should Be Sampled for DFT/MM Calculations? A Case Study of Fluoroacetate Dehalogenase.

    PubMed

    Li, Yanwei; Zhang, Ruiming; Du, Likai; Zhang, Qingzhu; Wang, Wenxing

    2016-01-01

    The quantum mechanics/molecular mechanics (QM/MM) method (e.g., density functional theory (DFT)/MM) is important in elucidating enzymatic mechanisms. It is indispensable to study "multiple" conformations of enzymes to get unbiased energetic and structural results. One challenging problem, however, is to determine the minimum number of conformations for DFT/MM calculations. Here, we propose two convergence criteria, namely the Boltzmann-weighted average barrier and the disproportionate effect, to tentatively address this issue. The criteria were tested by defluorination reaction catalyzed by fluoroacetate dehalogenase. The results suggest that at least 20 conformations of enzymatic residues are required for convergence using DFT/MM calculations. We also tested the correlation of energy barriers between small QM regions and big QM regions. A roughly positive correlation was found. This kind of correlation has not been reported in the literature. The correlation inspires us to propose a protocol for more efficient sampling. This saves 50% of the computational cost in our current case. PMID:27556449

  19. Synthesis, crystal structure and DFT studies of a dual fluorescent ketamine: Structural changes in the ground and excited states

    NASA Astrophysics Data System (ADS)

    Latha, V.; Balakrishnan, C.; Neelakantan, M. A.

    2015-07-01

    A fluorescent probe 2Z,2‧Z-3,3‧-(4,4‧-methylenebis(4,1-phenylene) bis(azanediyl))bis (1,3-diphenylprop-2-en-1-one) (L) was synthesized and characterized by IR, 1H NMR, ESI-mass, UV-visible and fluorescence spectral techniques. The single crystal analysis illustrates the existence of L in ketamine form. The crystal structure is stabilized by intramolecular and intermolecular hydrogen bonding. The thermal stability of L was studied by TG analysis. The fluorescence spectrum of L shows dual emission, and is due to excited state intramolecular proton transfer (ESIPT) process. This is supported by the high Stokes shift value. Electronic structure calculations of L in the ground and excited state have been carried out using DFT and TD-DFT at B3LYP/6-31G (d,p) level, respectively. The vibrational spectrum was computed at this level and compared with experimental values. Major orbital contributions for the electronic transitions were assigned with the help of TD-DFT. The changes in the Mulliken charge, bond lengths and bond angles between the ground and excited states of the tautomers demonstrate that twisted intramolecular charge transfer (TICT) process occurs along with ESIPT in the excited state.

  20. Theoretical studies of 2-quinolinol: Geometries, vibrational frequencies, isomerization, tautomerism, and excited states

    NASA Astrophysics Data System (ADS)

    Pan, Yi; Lau, Kai-Chung; Al-Mogren, Muneerah Mogren; Mahjoub, Ahmed; Hochlaf, Majdi

    2014-10-01

    We treat theoretically 2-quinolinol(lactam), an analog of carbostyril and DNA bases. We characterized the ground state structure of 2-quinolinol and its isomer(lactim) using density functional theory(DFT). The reaction profile and energetics for lactam-lactim tautomerization and cis-lactim to trans-lactim isomerization predicted with explicitly correlated methods. We explored the pattern of the lowest singlet and triplet manifolds of states and electronic S1 ← S0 transitions using multiconfigurational methodologies. The theoretical results are compared with available experimental data and used to interpret the on-going photoelectron study of 2-quinolinol. Our analysis should help to understand the effect of tautomerism and aromaticity on the DNA bases.

  1. Theoretical and experimental studies of 3β-acetoxy-5α-cholestan-6-one oxime

    NASA Astrophysics Data System (ADS)

    Khan, Azhar U.; Avecillia, Fernando; Malik, Nazia; Khan, Md. Shahzad; Khan, Mohd Shahid; Mushtaque, Md.

    2016-10-01

    Steroidal oxime (3β-acetoxy-5α-cholestan- 6-one oxime) has been synthesized using microwave-induced reaction in 3.5 min using saturated steroidal ketone and aqueous hydroxylamine hydrochloride in ethanol. The structure of the compound was elucidated by UV, IR, 1H NMR and X-ray single crystal structure. The computational quantum chemical studies like, IR, UV analysis were performed by density functional theory (DFT) at Becke-3-Lee-Yang-Parr(B3LYP) exchange-correlation functional in combination with 6-31++G(d,p) basis sets. The harmonic vibrational frequencies, the optimized geometric parameters have been interpreted and compared with experimental values. Theoretical wavelength at 214.88 cm-1 correspond to the experimental value 214.0 cm-1. The nature of this transition is n → π*. The theoretical results are in good agreement with experiment results.

  2. Structural studies of homoisoflavonoids: NMR spectroscopy, X-ray diffraction, and theoretical calculations

    NASA Astrophysics Data System (ADS)

    Sievänen, Elina; Toušek, Jaromír; Lunerová, Kamila; Marek, Jaromír; Jankovská, Dagmar; Dvorská, Margita; Marek, Radek

    2010-08-01

    In this article we present a detailed structural investigation for five homoisoflavonoids, molecules important from the pharmacological point of view. For studying the electron distribution as well as its influence on the physicochemical properties, NMR spectroscopy, X-ray diffraction, and theoretical calculations have been used. Nuclear magnetic shieldings obtained by using DFT calculations for optimized molecular geometries are correlated with the experimentally determined chemical shifts. The theoretical data are well in agreement with the experimental values. The single crystal X-ray structures of homoisoflavonoid derivatives 1, 3, and 4 have been solved. The molecular geometries and crystal packing determined by X-ray diffraction are used for characterizing the intermolecular interactions. Electron distribution is crucial for the stability of radicals and hence the antioxidant efficiency of flavonoid structures. The hydrogen bonding governs the formation of complexes of homoisoflavonoids with biological targets.

  3. Theoretical study of pyridoxine (vitamin B6) photolysis.

    PubMed

    Wu, Min; Xu, Qi; Strid, Ake; Martell, Jaime M; Eriksson, Leif A

    2011-11-24

    Two different reaction types for the photolysis of pyridoxine-aromatic ring-opening and photodissociation-have been studied in the Density Functional Theory (DFT) framework. Our results show that neither photolytic ring-opening, dehydroxymethylation, demethylation nor dehydroxylation from the aromatic ring can be induced spontaneously in UV-irradiated pyridoxine, due to the high barriers along the reaction coordinates in the excited states. However, the simultaneous dehydroxylation of the C4-bound hydroxymethyl group and dehydrogenation of the ring bound hydroxyl substituent, selectively generating ortho-quinone methide and water, does occur after UV exposure. The findings correlate very well with available experimental data. The geometries of pyridoxine, its various transition states and products are optimized in the ground and first excited states in vacuum within the TD-DFT formalism. PMID:21995706

  4. Theoretical Studies of Accreting Neutron Stars

    NASA Technical Reports Server (NTRS)

    Taam, Ronald E.

    2003-01-01

    Among the newly discovered classes of X-ray sources which have attracted wide attention are close binary systems in which mass is transferred via Roche lobe overflow from a low mass donor star to its neutron star companion. Many of these sources exhibit intense bursts of X-ray radiation as well as periodic and quasi-periodic phenomena. Intensive analysis of these sources as a class has provided insight into the accretion process in binary star systems and into the magnetic field, rotational, and nuclear evolution of the underlying neutron star. In this proposal we have focused on theoretical studies of the hydrodynamical and nuclear processes that take place on the surface of accreting neutron stars in these systems. The investigation of these processes is critical for providing an understanding of a number of outstanding problems related to their transient behavior and evolution.

  5. Propagation studies using a theoretical ionosphere model

    NASA Technical Reports Server (NTRS)

    Lee, M.

    1973-01-01

    The mid-latitude ionospheric and neutral atmospheric models are coupled with an advanced three dimensional ray tracing program to see what success would be obtained in predicting the wave propagation conditions and to study to what extent the use of theoretical ionospheric models is practical. The Penn State MK 1 ionospheric model, the Mitra-Rowe D region model, and the Groves' neutral atmospheric model are used throughout this work to represent the real electron densities and collision frequencies. The Faraday rotation and differential Doppler velocities from satellites, the propagation modes for long distance high frequency propagation, the group delays for each mode, the ionospheric absorption, and the spatial loss are all predicted.

  6. Theoretical Study of Negative Molecular Ions

    NASA Astrophysics Data System (ADS)

    Simons, Jack

    2011-05-01

    Although this review provides references to tabulations of molecular electron affinities, primarily it focuses on explaining why theory plays an important role in understanding the behavior of anions, explaining the challenges that anions pose to theory, making connections between the theories used to compute electron affinities and the potentials (e.g., charge-dipole, charge-quadrupole, valence attraction and exchange repulsion, dispersion, and polarization) that govern the electron-molecule interaction, and discussing how species with negative electron affinities may possess metastable anion states and how such states should be treated. In addition to references to published literature, many links are given to websites of practicing theoretical chemists who study molecular anions; these links (which appear in boldface) offer the reader a broad avenue to access much more information about molecular anions than can be covered in a review or even through conventional literature sources.

  7. Experimental (FT-IR, NMR and UV) and theoretical (M06-2X and DFT) investigation, and frequency estimation analyses on (E)-3-(4-bromo-5-methylthiophen-2-yl)acrylonitrile

    NASA Astrophysics Data System (ADS)

    Sert, Yusuf; Balakit, Asim A.; Öztürk, Nuri; Ucun, Fatih; El-Hiti, Gamal A.

    2014-10-01

    The spectroscopic properties of (E)-3-(4-bromo-5-methylthiophen-2-yl)acrylonitrile have been investigated by FT-IR, UV, 1H and 13C NMR techniques. The theoretical vibrational frequencies and optimized geometric parameters (bond lengths and angles) have been calculated using density functional theory (DFT/B3LYP: Becke, 3-parameter, Lee-Yang-Parr) and DFT/M06-2X (the highly parameterized, empirical exchange correlation function) quantum chemical methods with 6-311++G(d,p) basis set by Gaussian 03 software, for the first time. The assignments of the vibrational frequencies have been carried out by potential energy distribution (PED) analysis by using VEDA 4 software. The theoretical optimized geometric parameters and vibrational frequencies were in good agreement with the corresponding experimental data, and with the results in the literature. 1H and 13C NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. The electronic properties, such as excitation energies, oscillator strength wavelengths were performed by B3LYP methods. In addition, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energies and the other related molecular energy values have been calculated and depicted.

  8. Theoretical Study of Fe(CO)n-

    NASA Technical Reports Server (NTRS)

    Ricca, Alessandra; Baushlicher, Charles W., Jr.

    1995-01-01

    The structures and CO binding energies are computed for Fe(CO)n- using a hybrid density functional theory (DFT) approach. The structures and ground states can be explained in terms of maximizing the Fe to CO 2pi* donation and minimizing Fe-CO 5 sigma repulsion. The trends in the CO binding energies for Fe(CO)n- and the differences between the trends for Fe(CO)n- and Fe(CO)n are also explained. For Fe(CO)n-, the second, third, and fourth CO bonding energies are in good agreement with experiment, while the first is too small. The first CO binding is also too small using the coupled cluster singles and doubles approach including a perturbation estimate of the connected triple excitations.

  9. Experimental and theoretical study of ornidazole

    NASA Astrophysics Data System (ADS)

    Rajesh, P.; Gunasekaran, S.; Gnanasambandan, T.; Seshadri, S.

    2016-01-01

    The Fourier transform infrared (FT-IR) and the Fourier transform Raman (FT-Raman) spectra of the title molecule in solid phase were recorded in the region 4000-400 cm- 1 and 4000-100 cm- 1 respectively. The geometrical parameters and energies were investigated with the help of Density Functional Theory (DFT) employing B3LYP method and 6-31G (d, p) basis set. The analysis was supported by electrostatic potential maps and calculation of HOMO-LUMO. UV, FT-IR and FT-Raman spectra of ornidazole were calculated and compared with experimental results. Thermodynamic properties like entropy, heat capacity, have been calculated for the molecule. The predicted first hyperpolarizability also shows that the molecule might have a reasonably good non-linear optical (NLO) behavior. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis.

  10. Spectroscopic (FT-IR and UV-Vis) and theoretical (HF and DFT) investigation of 2-Ethyl-N-[(5-nitrothiophene-2-yl)methylidene]aniline

    NASA Astrophysics Data System (ADS)

    Ceylan, Ümit; Tarı, Gonca Özdemir; Gökce, Halil; Ağar, Erbil

    2016-04-01

    Crystal structure of the title compound, 2-Ethyl-N-[(5-nitrothiophene-2-yl)methylidene]aniline, C13H12N2O2S, has been synthesized and characterized by FT-IR and UV-Vis spectrum. The compound crystallized in the monoclinic space group P 21/c with a = 11.3578 (4) Å, b = 7.4923 (2) Å, c = 14.9676 (6) Å and β = 99.589 (3)° and Z = 4 in the unit cell. The molecular geometry was also calculated using the Gaussian 03 software and structure was optimized using the HF and DFT/B3LYP methods with the 6-311++G(d,p) basis set in ground state. Using the TD-DFT method, the electronic absorption spectra of the title compound was computed in both the gas phase and ethanol solvent. The harmonic vibrational frequencies of the title compound were calculated using the same methods with the 6-311++G(d,p) basis set. The calculated results were compared with the experimental determination results of the compound. It was seen that the optimized structure was in excellent agreement with the X-ray crystal structure. The energetic behaviors of the title compound in solvent media were examined using the HF and DFT/B3LYP methods with the 6-311++G(d,p) basis set applying the polarizable continuum model (PCM). In addition, the molecular orbitals (FMOs) analysis, molecular electrostatic potential (MEP), nonlinear optical and thermodynamic properties of the title compound were performed using the same methods with the 6-311++G(d,p) basis set.

  11. The mechanism of hydrogen evolution in Cu(bztpen)-catalysed water reduction: a DFT study.

    PubMed

    Liao, Rong-Zhen; Wang, Mei; Sun, Licheng; Siegbahn, Per E M

    2015-06-01

    The mechanism of water reduction catalysed by a mononuclear copper complex Cu(bztpen) (bztpen = N-benzyl-N,N',N'-tris(pyridine-2-ylmethyl)ethylenediamine) has been elucidated by DFT calculations, revealing that hydrogen evolution proceeds via coupling of a Cu(ii)-hydride and a pendant pyridinium, and providing important implications for the future design of new catalytic systems for water reduction. PMID:25928325

  12. Enantiomerization of Allylic Trifluoromethyl Sulfoxides Studied by HPLC Analysis and DFT Calculations.

    PubMed

    Bailly, Laetitia; Petit, Emilie; Maeno, Mayaka; Shibata, Norio; Trapp, Oliver; Cardinael, Pascal; Chataigner, Isabelle; Cahard, Dominique

    2016-02-01

    Enantiomerization of allylic trifluoromethyl sulfoxides occurs spontaneously at room temperature through the corresponding allylic trifluoromethanesulfenates via a [2,3]-sigmatropic rearrangement. Dynamic enantioselective high-performance liquid chromatography (HPLC) analysis revealed the stereodynamics of these sulfoxides ranging from chromatographic resolution to peak coalescence at temperatures between 5 and 53 °C. The rate constant of enantiomerization and activation parameters were determined and compared with Density Functional Theory (DFT) calculations. PMID:26689286

  13. A computational DFT study of structural transitions in textured solid-fluid interfaces

    NASA Astrophysics Data System (ADS)

    Yatsyshin, Petr; Parry, Andrew O.; Kalliadasis, Serafim

    2015-11-01

    Fluids adsorbed at walls, in capillary pores and slits, and in more exotic, sculpted geometries such as grooves and wedges can exhibit many new phase transitions, including wetting, pre-wetting, capillary-condensation and filling, compared to their bulk counterparts. As well as being of fundamental interest to the modern statistical mechanical theory of inhomogeneous fluids, these are also relevant to nanofluidics, chemical- and bioengineering. In this talk we will show using a microscopic Density Functional Theory (DFT) for fluids how novel, continuous, interfacial transitions associated with the first-order prewetting line, can occur on steps, in grooves and in wedges, that are sensitive to both the range of the intermolecular forces and interfacial fluctuation effects. These transitions compete with wetting, filling and condensation producing very rich phase diagrams even for relatively simple geometries. We will also discuss practical aspects of DFT calculations, and demonstrate how this statistical-mechanical framework is capable of yielding complex fluid structure, interfacial tensions, and regions of thermodynamic stability of various fluid configurations. As a side note, this demonstrates that DFT is an excellent tool for the investigations of complex multiphase systems. We acknowledge financial support from the European Research Council via Advanced Grant No. 247031.

  14. H-aggregation of the amphiphilic dye TDPI: Photophysical, electrochemical, DFT and SAXS studies

    NASA Astrophysics Data System (ADS)

    Vicente, Juliano; Goulart, Juliana S.; Premazzi, Melissa C. A.; Sobrinho, Alan G. P.; Silva Neto, Adalberto A.; Azeredo, Marcella C. S.; Domingos, Josiel B.; Miranda, Fabio S.

    2014-04-01

    A new amphiphilic dye 2,4,5-tris(1-dodecylpyridinium-4-yl)imidazol-1-ide tetrafluoroborate (TDPI) was synthesized and characterized by 1H and 13C NMR, ESI-TOF mass spectra and elemental analysis. The photophysical behavior of TDPI was investigated by means of UV-Vis and fluorescence spectroscopy techniques. The results show a solvent-dependent blue-shift absorption and emission which were assigned to an H-aggregation. The calculated dimerization aggregation constant is 10 times bigger in dichloromethane than in acetonitrile, which is probably due to stronger ionic pair stabilization in low dielectric media. The structural characteristics of the formed aggregate were also investigated by SAXS analysis, revealing a surface fractal structure for all solvents. DFT calculations were used to investigate the photophysical properties of the monomer and the aggregate dimer. The TD-DFT calculations successfully described the electronic spectra of the monomer, but failed to simulate the dimer spectra as expected for this type of system. However, the TD-DFT of the dimer corroborates the experimental observed blue-shift tendency.

  15. A silver complex with tryptophan: Synthesis, structural characterization, DFT studies and antibacterial and antitumor assays in vitro

    NASA Astrophysics Data System (ADS)

    Carvalho, Marcos A.; de Paiva, Raphael E. F.; Bergamini, Fernando R. G.; Gomes, Alexandre F.; Gozzo, Fábio C.; Lustri, Wilton R.; Formiga, André L. B.; Shishido, Silvia M.; Ferreira, Carmen V.; Corbi, Pedro P.

    2013-01-01

    The synthesis, spectroscopic characterization and biological assays of a new silver(I) complex with L-tryptophan (TRP) are presented. Elemental and thermal analyses and ESI-QTOF mass spectrometric measurements of the solid compound suggest the composition AgC11H11N2O2. Infrared and solid-state NMR analyses indicate coordination of TRP to Ag(I) ion through the nitrogen of the NH2 group and also through the oxygen of carboxylate group. Theoretical (DFT) calculations permit proposing an optimized geometry for the complex. Antibacterial assays indicated that the Ag-TRP complex is effective against Staphylococcus aureus and Enterococcus faecalis (Gram-positive), and Pseudomonas aeruginosa and Escherichia coli (Gram-negative) bacterial strains. The complex was also cytotoxic against Panc-1 (human pancreatic carcinoma) and SK-Mel 103 (human melanoma) cells.

  16. Effect of meso-substituents on the electronic transitions of BODIPY dyes: DFT and RI-CC2 study

    NASA Astrophysics Data System (ADS)

    Petrushenko, I. K.; Petrushenko, K. B.

    2015-03-01

    In this work, the influence of substituents on the electronic transitions of model 8-R-BODIPY dyes (R = NMe2, NH2, OH, CH3, H, F, SH, Cl, Br, CF3, CN, and NO2) was investigated theoretically using time-dependent density functional theory (TD-DFT) and ab initio coupled-cluster doubles (CC2) quantum chemical calculations. Quantum chemical modeling shows a direct relationship between the electron donating and electron withdrawing character of substituents expressed by Hammett substituent constants (σp) and changes in energy of the HOMO-LUMO gap modulating spectral shifts of the S0 → S1 transition. Good linear correlations of the calculated LUMO energies and σp as well as the shape of the HOMO and LUMO allow to obtain a reasonable explanation for the observed effects of substituents.

  17. Methanethiolate Adsorption Site on Au(111): A Combined STM/DFT Study at the Single-Molecule Level

    SciTech Connect

    Maksymovych, P.; Sorescu, D.C.; Yates, J.T.

    2006-10-26

    The chemisorptive bonding of methanethiolate (CH3S) on the Au(111) surface has been investigated at a single-molecule level using low-temperature scanning tunneling microscopy (LT-STM) and density functional theory (DFT). The CH3S species were produced by STM-tip-induced dissociation of methanethiol (CH3SH) or dimethyl disulfide (CH3SSCH3) at 5 K. The adsorption site of an isolated CH3S species was assigned by comparing the experimental and calculated STM images. We conclude that the S-headgroup of chemisorbed CH3S adsorbs on the 2-fold coordinated bridge site between two Au atoms, consistent with theoretical predictions for CH3S on the nondefective Au(111) surface. Our assignment is also supported by the freezing of the tip-induced rotational dynamics of a single CH3SH molecule upon conversion to CH3S via deprotonation.

  18. Structural, vibrational and theoretical studies of L-histidine bromide

    NASA Astrophysics Data System (ADS)

    Ahmed, A. Ben; Feki, H.; Abid, Y.; Boughzala, H.; Mlayah, A.

    2008-10-01

    This paper presents the results of our calculations of the geometric parameters, vibrational spectra and hyperpolarizability of a non linear optical material, L-histidine bromide. Due to the lack of sufficiently precise information on the geometric structure available in literature, theoretical calculations were preceded by re-determination of the crystal X-ray structure. Single crystals of L-histidine bromide have been grown by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in the non-Centro symmetric space group P2 12 12 1 of the orthorhombic system. Raman spectra have been recorded in the range [200-3500 cm -1]. All observed vibrational bands have been discussed and assigned to normal mode or to combinations and overtones on the basis of our calculations. The optimized geometric bond lengths and bond angles obtained by using HF and DFT (B3LYP and BLYP) show good agreement with the experimental data. Comparison between the measured and the calculated vibrational frequencies indicate that B3LYP is superior to the scaled HF approach for molecular vibrational problems. To investigate microscopic second order non linear optical properties of L-histidine bromide, the electric dipole μ, the polarizability α and the hyperpolarizability β were computed using DFT//B3LYP/6-31G(d) method. According to our calculations, the title compound exhibits non-zero β value revealing microscopic second order NLO behaviour.

  19. Comparative studies of the spectroscopy of CuCl2: DFT versus standard ab initio approaches.

    PubMed

    Ramírez-Solís, A; Poteau, R; Vela, A; Daudey, J P

    2005-04-22

    The X2Pi g-2Sigma g+, X2Pi g-2Delta g, X2Pi g-2Sigma u+, X2Pi g-2Pi u transitions on CuCl2 have been studied using several exchange-correlation functionals from the various types of density functional theory (DFT) approaches like local density approximation (LDA), generalized gradient approximation (GGA), hybrid and meta-GGA. The results are compared with the experience and with those coming from the most sophisticated nondynamic and dynamic electronic correlation treatments using the same relativistic effective core potentials and especially developed basis sets to study the electronic structure of the five lowest states and the corresponding vertical and adiabatic transition energies. The calculated transition energies for three of the hybrid functionals (B3LYP, B97-2, and PBE0) are in very good agreement with the benchmark ab initio results and experimental figures. All of the other functionals largely overestimate the X2Pi g-2Sigma g+ and X2Pi g-2Delta g transition energies, many of them even placing the 2Delta g ligand field state above the charge transfer 2Pi u and 2Sigma u+ states. The relative weight of the Hartree-Fock exchange in the definition of the functional used appears to play a key role in the accurate description of the LambdaSSigma density defined by the orientation of the 3d hole (sigma, pi, or delta) on Cu in the field of both chlorine atoms, but no simple connection of this weight with the quality of the spectra has been found. Mulliken charges and spin densities are carefully analyzed; a possible link between the extent of spin density on the metal for the X2Pi g state and the performance of the various functionals was observed, suggesting that those that lead to the largest values (close to 0.65) are the ones that best reproduce these four transitions. Most functionals lead to a remarkably low ionicity for the three ligand field states even for the best performing functionals, compared to the complete active space (SCF) (21, 14) ab initio

  20. Comparative studies of the spectroscopy of CuCl2: DFT versus standard ab initio approaches

    NASA Astrophysics Data System (ADS)

    Ramírez-Solís, A.; Poteau, R.; Vela, A.; Daudey, J. P.

    2005-04-01

    The XΠg2-Σg +2, XΠg2-Δg2, XΠg2-Σu +2, XΠg2-Πu2 transitions on CuCl2 have been studied using several exchange-correlation functionals from the various types of density functional theory (DFT) approaches like local density approximation (LDA), generalized gradient approximation (GGA), hybrid and meta-GGA. The results are compared with the experience and with those coming from the most sophisticated nondynamic and dynamic electronic correlation treatments using the same relativistic effective core potentials and especially developed basis sets to study the electronic structure of the five lowest states and the corresponding vertical and adiabatic transition energies. The calculated transition energies for three of the hybrid functionals (B3LYP, B97-2, and PBE0) are in very good agreement with the benchmark ab initio results and experimental figures. All of the other functionals largely overestimate the XΠg2-Σg +2 and XΠg2-Δg2 transition energies, many of them even placing the Δg2 ligand field state above the charge transfer Πu2 and Σu +2 states. The relative weight of the Hartree-Fock exchange in the definition of the functional used appears to play a key role in the accurate description of the ΛSΣ density defined by the orientation of the 3d hole (σ, π, or δ) on Cu in the field of both chlorine atoms, but no simple connection of this weight with the quality of the spectra has been found. Mulliken charges and spin densities are carefully analyzed; a possible link between the extent of spin density on the metal for the XΠg2 state and the performance of the various functionals was observed, suggesting that those that lead to the largest values (close to 0.65) are the ones that best reproduce these four transitions. Most functionals lead to a remarkably low ionicity for the three ligand field states even for the best performing functionals, compared to the complete active space (SCF) (21, 14) ab initio values. These findings show that not only large

  1. Theoretical study of electron-phonon superconductivity

    NASA Astrophysics Data System (ADS)

    Moussa, Jonathan Edward

    This theoretical study of superconductivity examines some of the limiting factors that constrain the Tc of conventional, phonon-mediated superconductors. For materials with wide-bandwidth metallic states, electronic instabilities that are theoretically challenging to deal with can be avoided. In this case, structural instability can still result from phonon softening caused by strong electron-phonon coupling of electrons at the Fermi level. Superconductivity is also limited by the total electron-phonon coupling available within a material given the hypothetical ability to arbitrarily dope the material. This limit is studied by deriving a generalization of the McMillan-Hopfield parameter, h˜ (E), which measures the strength of electron-phonon coupling including anisotropy effects and rigid-band doping of the Fermi level to E. I examine these bounds for some covalent superconductors including MgB2, where Tc has reached the limit set by total electron-phonon coupling strength, and boron-doped diamond, which is far from any bounds. To consider the possibility of increasing the Tc of boron-doped diamond, calculations of electron-phonon coupling are performed for boron-doped diamond structures without electronically compensating defects over a wide range of boron concentration. The effects of boron substitutional disorder are incorporated through the use of randomly generated supercells, leading to a disorder-broadened distribution of results. After averaging over disorder, this study predicts a maximum bulk Tc near 55 K for boron concentrations between 20% -- 30%, assuming the validity of the simple structural model used and a Coulomb pseudopotential of micro* = 0.12. Considering only the largest electron-phonon coupling values of the distribution, superconductivity may still percolate through the material at higher temperatures, up to 80 K, through the regions of large coupling. A synthesis path is proposed to experimentally access higher levels of boron concentration

  2. Optical Absorption Spectra and Electronic Properties of Symmetric and Asymmetric Squaraine Dyes for Use in DSSC Solar Cells: DFT and TD-DFT Studies.

    PubMed

    El-Shishtawy, Reda M; Elroby, Shaaban A; Asiri, Abdullah M; Müllen, Klaus

    2016-01-01

    The electronic absorption spectra, ground-state geometries and electronic structures of symmetric and asymmetric squaraine dyes (SQD1-SQD4) were investigated using density functional theory (DFT) and time-dependent (TD-DFT) density functional theory at the B3LYP/6-311++G** level. The calculated ground-state geometries reveal pronounced conjugation in these dyes. Long-range corrected time dependent density functionals Perdew, Burke and Ernzerhof (PBE, PBE1PBE (PBE0)), and the exchange functional of Tao, Perdew, Staroverov, and Scuseria (TPSSh) with 6-311++G** basis set were employed to examine optical absorption properties. In an extensive comparison between the optical data and DFT benchmark calculations, the BEP functional with 6-311++G** basis set was found to be the most appropriate in describing the electronic absorption spectra. The calculated energy values of lowest unoccupied molecular orbitals (LUMO) were 3.41, 3.19, 3.38 and 3.23 eV for SQD1, SQD2, SQD3, and SQD4, respectively. These values lie above the LUMO energy (-4.26 eV) of the conduction band of TiO₂ nanoparticles indicating possible electron injection from the excited dyes to the conduction band of the TiO₂ in dye-sensitized solar cells (DSSCs). Also, aromaticity computation for these dyes are in good agreement with the data obtained optically and geometrically with SQD4 as the highest aromatic structure. Based on the optimized molecular geometries, relative positions of the frontier orbitals, and the absorption maxima, we propose that these dyes are suitable components of photovoltaic DSSC devices. PMID:27043556

  3. Optical Absorption Spectra and Electronic Properties of Symmetric and Asymmetric Squaraine Dyes for Use in DSSC Solar Cells: DFT and TD-DFT Studies

    PubMed Central

    El-Shishtawy, Reda M.; Elroby, Shaaban A.; Asiri, Abdullah M.; Müllen, Klaus

    2016-01-01

    The electronic absorption spectra, ground-state geometries and electronic structures of symmetric and asymmetric squaraine dyes (SQD1–SQD4) were investigated using density functional theory (DFT) and time-dependent (TD-DFT) density functional theory at the B3LYP/6-311++G** level. The calculated ground-state geometries reveal pronounced conjugation in these dyes. Long-range corrected time dependent density functionals Perdew, Burke and Ernzerhof (PBE, PBE1PBE (PBE0)), and the exchange functional of Tao, Perdew, Staroverov, and Scuseria (TPSSh) with 6-311++G** basis set were employed to examine optical absorption properties. In an extensive comparison between the optical data and DFT benchmark calculations, the BEP functional with 6-311++G** basis set was found to be the most appropriate in describing the electronic absorption spectra. The calculated energy values of lowest unoccupied molecular orbitals (LUMO) were 3.41, 3.19, 3.38 and 3.23 eV for SQD1, SQD2, SQD3, and SQD4, respectively. These values lie above the LUMO energy (−4.26 eV) of the conduction band of TiO2 nanoparticles indicating possible electron injection from the excited dyes to the conduction band of the TiO2 in dye-sensitized solar cells (DSSCs). Also, aromaticity computation for these dyes are in good agreement with the data obtained optically and geometrically with SQD4 as the highest aromatic structure. Based on the optimized molecular geometries, relative positions of the frontier orbitals, and the absorption maxima, we propose that these dyes are suitable components of photovoltaic DSSC devices. PMID:27043556

  4. TD-DFT study of the light-induced spin crossover of Fe(III) complexes.

    PubMed

    Saureu, Sergi; de Graaf, Coen

    2016-01-14

    Two light-induced spin-crossover Fe(III) compounds have been studied with time-dependent density functional theory (TD-DFT) to investigate the deactivation mechanism and the role of the ligand-field states as intermediates in this process. The B3LYP* functional has previously shown its ability to accurately describe (light-induced) spin-crossover in Fe(II) complexes. Here, we establish its performance for Fe(III) systems using [Fe(qsal)2](+) (Hqsal = 2-[(8-quinolinylimino)methyl]phenol) and [Fe(pap)2](+) (Hpap = 2-(2-pyridylmethyleneamino)phenol) as test cases comparing the B3LYP* results to experimental information and to multiconfigurational wave function results. In addition to rather accurate high spin (HS) and low spin (LS) state geometries, B3LYP* also predicts ligand-to-metal charge transfer (LMCT) states with large oscillator strength in the energy range where the UV-VIS spectrum shows an intense absorption band, whereas optically allowed π-π* excitations on the ligands were calculated at higher energy. Subsequently, we have generated a two-dimensional potential energy surface of the HS and LS states varying the Fe-N and Fe-O distances. LMCT and metal centered (MC) excited states were followed along the approximate minimal energy path that connects the minima of the HS and LS on this surface. The (2)LMCT state has a minimum in the same region as the initial LS state, where we also observe a crossing with the intermediate spin (IS) state. Upon the expansion of the coordination sphere of the Fe(III) ion, the IS state crosses with the HS state and further expansion of the coordination sphere leads to the excited spin state trapping as observed in experiment. The calculation of the intersystem crossing rates reveals that the deactivation from (2)LMCT → IS → HS competes with the (2)LMCT → IS → LS pathway, in line with the low efficiency encountered in experiments. PMID:26660866

  5. Theoretical and Experimental Studies of Radiative Shocks

    NASA Astrophysics Data System (ADS)

    Michaut, C.; Vinci, T.; Boireau, L.; Koenig, M.; Bouquet, S.; Benuzzi-Mounaix, A.; Osaki, N.; Herpe, G.; Falize, E.; Loupias, B.; Atzeni, S.

    2007-01-01

    This paper deals with the radiative shock from both theoretical and numerical points of view. It is based on the whole experimental results obtained at Laboratoire d'Utilisation des Lasers Intenses (LULI, École Polytechnique). Radiative shocks are high-Mach number shocks with a strong coupling between radiation and hydrodynamics which leads to a structure governed by a radiative precursor. These shocks are involved in various astrophysical systems: stellar accretion shocks, pulsating stars, interaction between supernovae and the interstellar medium. In laboratory, these radiative shocks are generated using high power lasers. New diagnostics have been implemented to study the geometrical shape of the shock and the front shock density. Data were obtained varying initial conditions for different laser intensities and temperature. The modeling of these phenomena is mainly performed through numerical simulations (1D and 2D) and analytical studies. We exhibit results obtained from several radiative hydrodynamics codes. As a result, it is possible to discuss about the influence of the geometry and physical parameters introduced in the 1D and 2D models.

  6. Molecular structure and vibrational study of diprotonated guanazolium using DFT calculations and FT-IR and FT-Raman spectroscopies

    NASA Astrophysics Data System (ADS)

    Guennoun, L.; Zaydoun, S.; El jastimi, J.; Marakchi, K.; Komiha, N.; Kabbaj, O. K.; El Hajji, A.; Guédira, F.

    2012-11-01

    The purpose of this manuscript is to discuss our investigations of diprotonated guanazolium chloride using vibrational spectroscopy and quantum chemical methods. The solid phase FT-IR and FT-Raman spectra were recorded in the regions 4000-400 cm-1 and 3600-50 cm-1 respectively, and the band assignments were supported by deuteration effects. Different sites of diprotonation have been theoretically examined at the B3LYP/6-31G∗ level. The results of energy calculations show that the diprotonation process occurs with the two pyridine-like nitrogen N2 and N4 of the triazole ring. The molecular structure, harmonic vibrational wave numbers, infrared intensities and Raman activities were calculated for this form by DFT/B3LYP methods, using a 6-31G∗ basis set. Both the optimized geometries and the theoretical and experimental spectra for diprotonated guanazolium under a stable form are compared with theoretical and experimental data of the neutral molecule reported in our previous work. This comparison reveals that the diprotonation occurs on the triazolic nucleus, and provide information about the hydrogen bonding in the crystal. The scaled vibrational wave number values of the diprotonated form are in close agreement with the experimental data. The normal vibrations were characterized in terms of potential energy distribution (PED) using the VEDA 4 program.

  7. A DFT study on the Cu (1 1 1) surface for ethyl acetate synthesis from ethanol dehydrogenation

    NASA Astrophysics Data System (ADS)

    Li, Ruzhen; Zhang, Minhua; Yu, Yingzhe

    2012-07-01

    Copper-based catalysts have shown excellent catalytic performances. Despite extensive studies in the field, the microscopic mechanism of ethanol dehydrogenation to ethyl acetate (EA) on Cu-based catalysts remains controversial. Aiming to provide insight into the catalytic roles of Cu, density functional theory (DFT) calculations have been performed to study the elementary reactions involved in ethanol dehydrogenation to EA on Cu surfaces. In this work, the adsorption properties of ethanol, ethoxy, acetaldehyde, acetyl and EA on the Cu (1 1 1) catalyst surface were investigated. Based on two pathways, many transition states involved are located. The results show that the route proposed by Colley is more likely to happen.

  8. Investigating Superoxide Transfer through a μ-1,2-O2 Bridge between Nonheme Ni(III)-Peroxo and Mn(II) Species by DFT Methods to Bridge Theoretical and Experimental Views.

    PubMed

    Cho, Kyung-Bin; Cho, Jaeheung; Shaik, Sason; Nam, Wonwoo

    2014-07-17

    Previously, a fast unprecedented O2(•-) transfer reaction has been observed experimentally when adding a Mn(II) complex into a solution containing a Ni(III)-peroxo complex. Due to the fast reaction rate, no intermediates were observed. We have investigated this reaction with density functional theory (DFT) and show that DFT is unusually problematic in reproducing the correct spin state for the investigated Ni(III)-peroxo complex, something which calls for examination of all previous Ni-dioxygen studies. Surprisingly, the BP86 functional is shown to yield energies more in agreement with known experiments than B3LYP. The calculations reveal for the first time an intermediate structure in a complete O2(•-) transfer reaction, shown here to be a short-lived bridging Ni-(μ-1,2-O2)-Mn structure. PMID:26277812

  9. Guanidine complexes of platinum: a theoretical study.

    PubMed

    Marin-Luna, Marta; Sanchez-Sanz, Goar; O'Sullivan, Patrick; Rozas, Isabel

    2014-07-24

    We have studied theoretically the complexes of model N-phenylguanidine/ium derivatives with PtCl3(-) and PtCl2 in different coordinating modes (mono- and bidentate) with different N atoms of the guanidine/ium moiety using the B3LYP/6-31+G** and LANL2DZ mixed basis set. This will aid the understanding of the complexation between platinum and the guanidine or guanidinium moiety in order to design dual anticancer agents that combine a guanidine-based DNA minor groove binder and a cisplatin-like moiety. Calculated interaction and relative energies, analysis of the electron density, and examination of the orbital interactions indicate that the most stable type of complex is that with a monodentate interaction between PtCl3(-) and guanidinium established through one of the NH2 groups. Next, we optimized the structure of three bis-guanidinium diaromatic systems developed in our group as DNA minor groove binders and their complexation with PtCl3(-), finding that the formation of Pt complexes of these minor groove binders is favorable and would produce stable monodentate coordinated systems. PMID:24988181

  10. Theoretical study of Δ-3-(+)-carene oxidation.

    PubMed

    Baptista, Leonardo; Fernandes Francisco, Lilian; Dias, Jacques Fernandes; da Silva, Edilson Clemente; Ferreira dos Santos, Claudio Vinicius; Gil de Mendonça, Felipe Simões; Arbilla, Graciela

    2014-09-28

    In this work, the rate-limiting steps of Δ(3)-carene oxidation by ozone and OH radicals were studied. The thermochemical and kinetic parameters were evaluated using the B3LYP, PBE1PBE and BHandHLYP functionals, coupled cluster methods and the 6-311G(d,p) and 6-311++G(d,p) basis sets. The attack on the double bond may occur in different orientations, leading to different oxidation products. The rate coefficients of each step of the reactions were evaluated using conventional canonical transition-state theory and variational canonical transition-state theory whenever necessary. The theoretical rate coefficient for the ozonolysis mechanism, evaluated at the CCSD(T)/6-31G(d,p)//PBE1PBE/6-311++G(d,p) level, was 2.08 × 10(-17) cm(3) molecule(-1) s(-1). The coefficient for the oxidation initialised by the OH radical, calculated at the BHandHLYP/6-311++G(d,p) level, was 5.06 × 10(-12) cm(3) molecule(-1) s(-1). These values are in reasonable agreement with the experimental results. The importance of these reactions in atmospheric chemistry is discussed. PMID:25102281

  11. A new series of Schiff bases derived from sulfa drugs and indole-3-carboxaldehyde: Synthesis, characterization, spectral and DFT computational studies

    NASA Astrophysics Data System (ADS)

    Ebrahimi, H.; Hadi, J. S.; Al-Ansari, H. S.

    2013-05-01

    A new series of Schiff bases were synthesized for the first time by the condensation of indole-3-carboxaldehyde with various sulfa drugs including sulfanilamide, sulfapyridine, sulfadiazine, sulfamerazine, sulfamethoxazole, sulfamethoxypyridazine and sulfacetamide sodium in ethanol (1:1). The structure of Schiff bases were experimentally characterized by using IR, 1H NMR, 13C NMR and mass spectroscopic methods. The structural and electronic properties of the studied molecules were investigated theoretically by performing density functional theory (DFT) to access reliable results to the experimental values. The molecular geometry, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and Mulliken atomic charges of the studied molecules have been calculated at the B3LYP method and standard 6-31 + G(d,p) basis set starting from optimized geometry. The theoretical 13C chemical shift results were also calculated using the gauge independent atomic orbital (GIAO) approach and their respective linear correlations were obtained. The comparison of the results indicates that B3LYP/6-31 + G(d,p) yields good agreement with the observed chemical shifts.

  12. The effect of Cu(2+) chelation on the direct photolysis of oxytetracycline: A study assisted by spectroscopy analysis and DFT calculation.

    PubMed

    Jin, Xin; Qiu, Shanshan; Wu, Ke; Jia, Mingyun; Wang, Fang; Gu, Chenggang; Zhang, Aiqian; Jiang, Xin

    2016-07-01

    The extensive usage of OTC and Cu(2+) in livestock and poultry industry caused high residues in natural environment. Co-contamination of OTC and Cu(2+) was a considerable environmental problem in surface waters. In this study, Cu(2+) mediated direct photolysis of OTC was studied. Cu(2+) chelating with OTC was found to greatly inhibit OTC photodegradation. To reveal the chelation mechanism of OTC-Cu complexes, multiple methods including UV-Vis absorption spectra, Infrared (IR) spectra, mass spectroscopy, and density functional theoretical (DFT) modeling were performed. Four OTC-Cu complexes were proposed. Cu(2+) preferably bond to O11O12 site with the binding constants logK = 8.19 and 7.86 for CuHL+ and CuL±, respectively. The second chelating site was suggested to be O2O3 with the binding constants of logK = 4.41 and 4.62 for Cu2HL3+ and Cu2L2+, respectively. The suppressed quantum yield of OTC by Cu2+ chelation was accused for their intra-/inter-molecular electron transfer, by which the energy in activated states was distributed. The occurrence of electron transfer between BCD ring and A ring also from BCD ring to Cu was evidenced by the TD-DFT result only for the OTC-Cu complexes. Besides, the cyclic voltammetry measurement also suggested one OTC-Cu(II)/OTC-Cu(I) redox couple. These results suggested that the persistence of OTC in environmental surface waters will probably be underestimated for neglecting the chelating effect of Cu2+. The photolysis quantum yield of OTC-Cu complexes, as well as the specific molar absorption constants, the equilibrium binding constants of Cu2+ with OTC could contribute to more accurate kinetic models of OTC. PMID:27155101

  13. DFT studies on the vibrational and electronic spectra of acetylsalicylic acid

    NASA Astrophysics Data System (ADS)

    Ye, Yunfeng; Tang, Guodong; Han, Yonghong; Culnane, Lance F.; Zhao, Jianyin; Zhang, Yu

    2016-05-01

    The following is a theoretical and experimental study on the vibrational and electronic properties of acetylsalicylic acid (ASA). Vibrational information was obtained by FT-IR and Raman spectroscopy which agree well with harmonic vibrational frequency calculations. The calculations were carried out using density functional theory B3LYP methods with 6-311G** and LANL2DZ basis sets. The vibrational assignments were calculated by Gaussview. Absorption UV-Vis experiments of ASA reveal three maximum peaks at 203, 224 and 277 nm, which are in agreement with calculated electronic transitions using TD-B3LYP/6-311G**.

  14. Acylation and deacylation mechanism of Helicobacter pylori AmiF formamidase: A computational DFT study

    NASA Astrophysics Data System (ADS)

    He, Rongxing; Yang, Qinlei; Li, Ming

    2014-04-01

    The acylation and deacylation mechanisms of Helicobacter pylori AmiF formamidase were investigated using DFT method. In the constructed active site, residues Glu60, Glu141 and His167 were taken into account besides Lys133 and Cys166. Calculations provided insight on the details of mechanism and explained crucial roles played by Glu60, Glu141 and His167. For acetylation, we proposed a new stepwise mechanism in which the thiol group first attacks the carbon atom of formamide and produces tetrahedral intermediate. In deacylation, Glu60 activates a water molecule to perform nucleophilic attack and then forms an intermediate, which is different from the usually suggested mechanism.

  15. TD-DFT study on electron transfer mobility and intramolecular hydrogen bond of substituted indigo derivatives

    NASA Astrophysics Data System (ADS)

    Ma, Chi; Li, Hui; Yang, Yonggang; Li, Donglin; Liu, Yufang

    2015-10-01

    The density functional theory (DFT) and time-dependent density functional theory (TDDFT) method were carried out to investigate the ground and excited states of indigo and its derivative molecules. The results demonstrate that the intramolecular hydrogen bond I is weakened and the intramolecular hydrogen bond II is strengthened upon photo-excitation to the S1 state. In the absorption spectra, the substitution at R4R4, of indigo causes a significant redshift. In addition, the halogen substitution obviously increases the electron transfer mobility of indigo. It is proved that the halogen substitution may be a new method to design high performance organic semiconductors.

  16. DFT study of electronic transfer properties of carboxyl and nitro substituted benzene

    NASA Astrophysics Data System (ADS)

    M, Megala.; Rajkumar, Beulah J. M.

    2015-06-01

    The electronic and optical transfer properties of Benzene, Benzoic Acid (BA), Nitrobenzene (NB) and Para Nitro Benzoic Acid (PNBA) at ground and first excited state has been investigated by the Density functional theory (DFT)and Time Dependent Density Functional Theory (TDDFT) using SVWN functional/3-21G basis set respectively. Possible intra-molecular charge transfer and n to π* transitions in the ground and the first excitation states have been predicted by the molecular orbitals and the Natural Bond Orbital (NBO) analysis. The simulated absorption spectra have been generated and the result compared with existing experimental results.

  17. DFT study of electronic transfer properties of carboxyl and nitro substituted benzene

    SciTech Connect

    Megala, M.; Rajkumar, Beulah J. M.

    2015-06-24

    The electronic and optical transfer properties of Benzene, Benzoic Acid (BA), Nitrobenzene (NB) and Para Nitro Benzoic Acid (PNBA) at ground and first excited state has been investigated by the Density functional theory (DFT)and Time Dependent Density Functional Theory (TDDFT) using SVWN functional/3-21G basis set respectively. Possible intra-molecular charge transfer and n to π* transitions in the ground and the first excitation states have been predicted by the molecular orbitals and the Natural Bond Orbital (NBO) analysis. The simulated absorption spectra have been generated and the result compared with existing experimental results.

  18. A facile approach towards synthesis, characterization, single crystal structure, and DFT study of 5-bromosalicylalcohol

    NASA Astrophysics Data System (ADS)

    Rastogi, Rupali; Tarannum, Nazia; Butcher, R. J.

    2016-03-01

    5-Bromosalicylalcohol was prepared by the interaction of NaBH4 and 5-bromosalicylaldehyde. The use of sodium borohydride makes the reaction easy, facile, economic and does not require any toxic catalyst. The compound is characterized by FTIR, 1H NMR, 13C NMR, TEM and ESI-mass spectra. Crystal structure is determined by single crystal X-ray analysis. Quantum mechanical calculations of geometries, energies and thermodynamic parameters are carried out using density functional theory (DFT/B3LYP) method with 6-311G( d, p) basis set. The optimized geometrical parameters obtained by B3LYP method show good agreement with experimental data.

  19. DFT-based molecular modeling, NBO analysis and vibrational spectroscopic study of 3-(bromoacetyl)coumarin

    NASA Astrophysics Data System (ADS)

    Sajan, D.; Erdogdu, Y.; Reshmy, R.; Dereli, Ö.; Kurien Thomas, K.; Hubert Joe, I.

    2011-11-01

    The NIR-FT Raman and FT-IR spectra of 3-(bromoacetyl)coumarin (BAC) molecule have been recorded and analyzed. Density functional theory (DFT) calculation of two BAC conformers has been performed to find the optimized structures and computed vibrational wavenumbers of the most stable one. The obtained vibrational wavenumbers and optimized geometric parameters were seen to be in good agreement with the experimental data. Characteristic vibrational bands of the pyrone ring and methylene and carbonyl groups have been identified. The lowering of HOMO-LUMO energy gap clearly explains the charge transfer interactions taking place within the molecule.

  20. Formation of the cerium orthovanadate CeVO4 : DFT+U study

    NASA Astrophysics Data System (ADS)

    da Silva, Juarez L. F.; Ganduglia-Pirovano, M. Verónica; Sauer, Joachim

    2007-09-01

    We report density functional theory calculations of the structural, electronic, and thermodynamic properties of cerium orthovanadate ( CeVO4 ) employing the local density approximation (LDA), generalized gradient approximation (GGA-PBE), LDA+U , and GGA-PBE+U functionals. The LDA+U , GGA-PBE+U , LDA, and GGA-PBE equilibrium volumes deviate by -2.4% , +3.6% , -7.4% , and -0.8% , respectively, from experimental results. DFT+U (DFT) predicts an antiferromagnetic (ferromagnetic) insulating (metallic) ground state, which is in agreement with experimental observations. DFT+U yields Ce and V ions in the III+ and V+ oxidation state, respectively. CeVO4 can be obtained by the reaction between Ce2O3 and V2O5 [ (1)/(2)Ce2O3(s)+(1)/(2)V2O5(s)→CeVO4(s) ] under an inert atmosphere, which is described as exoenergetic (∣ΔH0∣=1.6-1.8eV) by all functionals. The reaction (1)/(2)Ce2O3(s)+(1)/(2)V2O5(s)→CeO2(s)+VO2(s) is exoenergetic with ∣ΔH0∣=0.75 , 0.25, 1.70, and 1.24eV for LDA+U , GGA-PBE+U , LDA, and GGA-PBE, respectively. Hence, VV+ is more easily reduced to VIV+ than CeIV+ to CeIII+ , but the difference is small as obtained with DFT+U , PBE+U , in particular. The variation of this reaction energy is due to the different performance of the various approaches for the description of the change in oxidation state of cerium, IV+ to III+ [J. L. F. Da Silva , Phys. Rev. B 75, 045121 (2007)]. The small difference between the VV and CeIV reducibilities may have consequences for the use of CeO2 as support of V2O5 catalysts in selective oxidation.

  1. High-pressure behavior of solid nitrobenzene: Combined Raman spectroscopy and DFT-D calculations study

    NASA Astrophysics Data System (ADS)

    Wang, Wen-Peng; Liu, Fu-Sheng; Liu, Qi-Jun; Zhang, Lin-Ji; Wang, Yi-Gao; Liu, Zheng-Tang

    2016-09-01

    Nitrobenzene (NB), a simplest structure of the aromatic nitro compounds, was investigated as a model for understanding structural properties in nitro derivatives of benzene and anilines. Using the Raman spectroscopic technique, the vibrational modes of solid NB were examined under hydrostatic compression up to 10 GPa. The Raman spectra indicated that a subtle phase transition occurred around 5 GPa. Also, the dispersion corrected density functional theory (DFT-D) calculations were performed to provide further insight into pressure effects on the molecular geometry. The calculated data suggested that NB molecules were distorted, and molecular conformation was readjusted when the phase transition with vibrational changes took place under high-pressure.

  2. Synthesis and characterization of three novel Schiff base compounds: Experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Taslı, P. T.; Bayrakdar, A.; Karakus, O. O.; Kart, H. H.; Koc, Y.

    2015-09-01

    In this study, three novel Schiff base compounds such as N-(4-nitrobenzyl)-4-methyl bromo aniline ( 1a), N-(2,4-dimethoxybenzyl)-4-methyl bromoaniline ( 2a), SN-((1H-indol-3-yl) methylene)-4- methyl bromoaniline ( 3a) are synthesized and characterized by using the spectroscopic methods of UV, IR and 1H-NMR. Molecular geometry and spectroscopic properties of synthesized compounds are also analyzed by using ab initio calculation methods based on the density functional theory (DFT) in the ground state. The extensive theoretical and experimental FT-IR and UV-vis spectrometry studies of synthesized compounds are performed. The optimized molecular structure and harmonic vibrational frequencies are studied by using B3LYP/6-311++G(d,p) method. Moreover, electronic structures are investigated by using the time dependent density functional theory (TD-DFT) while the energy changes of the parent compounds are examined in a solvent medium by using the polarizable continuum model (PCM). Additionally, the frontier molecular orbital analysis is performed for the Schiff base compounds. The electronic properties of each compound such as; chemical hardness, chemical softness, ionization potential, electron affinity, electronegativity and chemical potential are investigated by utilizing the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies.

  3. The guanidine and benzoic acid (1:1) complex. The polarized vibrational studies and theoretical investigations

    NASA Astrophysics Data System (ADS)

    Drozd, M.; Dudzic, D.

    2015-03-01

    The structure of guanidinium benzoate was discovered by Silva et al. On the basis of these X-ray crystallographic studies the detailed DFT investigation are performed. According to this result the infrared spectrum for one theoretical molecule was calculated. On the basis of potential energy distribution (PED) analysis the clear-cut assignments of observed bands were performed. For the calculated molecule with energy minimum the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were obtained. The energy difference between HOMO and LUMO was analyzed. According to theoretical calculations the direction of dipole moments (TDM) for bands observed in infrared spectra are analyzed. Verification of theoretical TDM behaviors is performed on the basis of experimental polarized specular reflection infrared spectra. The detailed assignments of observed bands is presented. Both theoretical and experimental spectra are compared. Crucial role of three different hydrogen bonds is studied in detail. Additionally, on the basis of differential scanning calorimetric study no phase transition was found in investigated crystal in the range 100-400 K.

  4. Influence of anthraquinone scaffold on E/Z isomer distribution of two thiosemicarbazone derivatives. 2D NMR and DFT studies

    NASA Astrophysics Data System (ADS)

    Marković, Violeta; Joksović, Milan D.; Marković, Svetlana; Jakovljević, Ivan

    2014-01-01

    A distribution of possible isomeric and tautomeric forms of two tautomerizable anthraquinone-thiosemicarbazones with pronounced cytotoxic potential was investigated using 2D NMR and DFT studies. Conformational analysis of the E and Z isomers of both thiosemicarbazones was performed to find out the most stable conformation for each molecule. It was found that superior stability of E-isomers results from ten-membered intramolecular hydrogen bond between thiosemicarbazone N2H and anthraquinone carbonyl group. This hydrogen bond is stronger than that between thiosemicarbazone N2H and ester oxygen, owing to the large partial negative charge on the anthraquinone oxygen.

  5. A DFT study on CO oxidation catalyzed by subnanometer AlCu n ( n = 1-3) clusters

    NASA Astrophysics Data System (ADS)

    Dong, Xiaona; Guo, Ling; Wen, Caixia; Ren, Ningning; Niu, Shuangshu

    2014-07-01

    Through the first-principle density-functional theory (DFT) calculations, we have made an exhaustive study of the mechanism of CO oxidation catalyzed by AlCu n ( n = 1-3) clusters on gas phase. It is shown that mixing two different metals (Al and Cu) can have beneficial effects on the catalytic activity than monometallic Cu n + 1 ( n = 1-3) cluster toward the reaction of CO oxidation and the alloyed AlCu3 cluster is proposed as the best effective nanocatalysts.

  6. Theoretical Study of a Spherical Plasma Focus

    NASA Astrophysics Data System (ADS)

    Ay, Yasar

    A theoretical model is developed for two concentric electrodes spherical plasma focus device in order to investigate the plasma sheath dynamics, radiative emission, and the ion properties. The work focuses on the model development of the plasma sheath dynamics and its validation, followed by studying of the radiation effects and the beam-ion properties in such unique geometry as a pulsed source for neutrons, soft and hard x-rays, and electron and ion beams. Chapter 1 is an introduction on fusion systems including plasma focus. Chapter 2 is an extensive literature survey on plasma focus modeling and experiments including the various radiations and their mechanism. Chapter 3 details modeling and validation of the plasma sheath dynamics model with comparison between hydrogen, deuterium, tritium and deuterium-tritium mixture for the production of pulsed neutrons. Chapter 4 is a study of the radiative phase, in which neutron yield is investigated, as well as the predicted beam-ion properties. Chapter 5 summarizes and discusses the results. Chapter 6 provides concluding remarks and proposed future works. The phases of the developed model are the rundown phase I, rundown phase II, the reflected phase and a radiative phase. The rundown phase I starts immediately after the completion of the gas breakdown and ends when the current sheath reaches the equator point of the spherical shape. Then immediately followed by rundown phase II to start and it ends when the shock front hits the axis, which is the beginning of the reflected shock phase. Reflected shock front moves towards the incoming current sheath and meets it which is both the end of the reflected shock phase and the beginning of the radiative phase. After the reflected shock front and the current sheath meet, the current sheath continues to move radially inward by compressing the produced plasma column until it reaches the axis. Since the discharge current contains important information about the plasma dynamic

  7. Computational and theoretical studies of globular proteins

    NASA Astrophysics Data System (ADS)

    Pagan, Daniel L.

    Protein crystallization is often achieved in experiment through a trial and error approach. To date, there exists a dearth of theoretical understanding of the initial conditions necessary to promote crystallization. While a better understanding of crystallization will help to create good crystals suitable for structure analysis, it will also allow us to prevent the onset of certain diseases. The core of this thesis is to model and, ultimately, understand the phase behavior of protein particles in solution. Toward this goal, we calculate the fluid-fluid coexistence curve in the vicinity of the metastable critical point of the modified Lennard-Jones potential, where it has been shown that nucleation is increased by many orders of magnitude. We use finite-size scaling techniques and grand canonical Monte Carlo simulation methods. This has allowed us to pinpoint the critical point and subcritical region with high accuracy in spite of the critical fluctuations that hinder sampling using other Monte Carlo techniques. We also attempt to model the phase behavior of the gamma-crystallins, mutations of which have been linked to genetic cataracts. The complete phase behavior of the square well potential at the ranges of attraction lambda = 1.15 and lambda = 1.25 is calculated and compared with that of the gammaII-crystallin. The role of solvent is also important in the crystallization process and affects the phase behavior of proteins in solution. We study a model that accounts for the contribution of the solvent free-energy to the free-energy of globular proteins. This model allows us to model phase behavior that includes solvent.

  8. Systematic DFT-GGA study of hydrogen adsorption on transition metals

    NASA Astrophysics Data System (ADS)

    Vasić, D.; Ristanović, Z.; Pašti, I.; Mentus, S.

    2011-12-01

    Computational study of hydrogen adsorption on (111) surface of transition metals with face centered cubic (fcc) lattice is reported and the results are compared with available experimental and theoretical data. In addition, dissociative adsorption of hydrogen on Pt(111), Pt(100) and Pt(110) is studied in the range of coverage from 0.25 to 1 monolayer. In the case of Pt(111) preferential adsorption site was found to be three-coordinated fcc-hollow site, while on Pt(100) and Pt(110) surface hydrogen settles on two-coordinated bridge and short bridge site, respectively. Hydrogen adsorption energy was found to decrease with the increasing coverage. Structural changes of studied Pt surfaces upon hydrogen adsorption have been compared with the experimental data existing in the literature and good qualitative agreement has been obtained.

  9. QM(DFT) and MD studies on formation mechanisms of C60 fullerenes

    NASA Astrophysics Data System (ADS)

    Hua, Xinlei; Cagin, Tahir; Che, Jianwei; Goddard, William A., III

    2000-06-01

    One of the most puzzling aspects of fullerenes is how such complicated symmetric molecules are formed from a gas of atomic carbons, namely, the atomistic or chemical mechanisms. Are the atoms added one by one or as molecules (C2, C3)? Is there a critical nucleus beyond which formation proceeds at gas kinetic rates? What determines the balance between forming buckyballs, buckytubes, graphite and soot? The answer to these questions is extremely important in manipulating the systems to achieve particular products. A difficulty in current experiments is that the products can only be detected on time scales of microseconds long after many of the important formation steps have been completed. Consequently, it is necessary to use simulations, quantum mechanics and molecular dynamics, to determine these initial states. Experiments serve to provide the boundary conditions that severely limit the possibilities. Using quantum mechanical methods (density functional theory (DFT)) we derived a force field (MSXX FF) to describe one-dimensional (rings) and two-dimensional (fullerene) carbon molecules. Combining DFT with the MSXX FF, we calculated the energetics for the ring fusion spiral zipper (RFSZ) mechanism for formation of C60 fullerenes. Our results shows that the RFSZ mechanism is consistent with the quantum mechanics (with a slight modification for some of the intermediates).

  10. Synthesis, X-ray Structure, Spectroscopic Properties and DFT Studies of a Novel Schiff Base

    PubMed Central

    Chen, Kew-Yu; Tsai, Hsing-Yang

    2014-01-01

    A series of Schiff bases, salicylideneaniline derivatives 1–4, was synthesized under mild conditions and characterized by 1H NMR, HRMS, UV-Vis and fluorescence spectra, and single-crystal X-ray diffraction. In solid and aprotic solvents 1–4 exist mainly as E conformers that possess an intramolecular six-membered-ring hydrogen bond. A weak intramolecular C–H···F hydrogen bond is also observed in fluoro-functionalized Schiff base 4, which generates another S(6) ring motif. The C–H···F hydrogen bond further stabilizes its structure and leads it to form a planar configuration. Compounds 1–3 exhibit solely a long-wavelength proton-transfer tautomer emission, while dipole-functionalized Schiff base 4 shows remarkable dual emission originated from the excited-state intramolecular charge transfer (ESICT) and excited-state intramolecular proton transfer (ESIPT) states. Furthermore, the geometric structures, frontier molecular orbitals (MOs) and the potential energy curves for 1–4 in the ground and the first singlet excited state were fully rationalized by density functional theory (DFT) and time-dependent DFT calculations. PMID:25329613

  11. Understanding the polar mechanism of the ene reaction. A DFT study.

    PubMed

    Domingo, Luis R; Aurell, Maria J; Pérez, Patricia

    2014-10-14

    The molecular mechanism of ene reactions has been characterised by DFT methods at the MPWB1K/6-311G(d,p) level of theory. Most reactions take place along a two-stage one-step mechanism in which the C-C bond formation takes place before the hydrogen transfer process. A very good correlation between the polar character of the reaction measured by the global electron density transfer at the transition state and the activation energy has been found. This behaviour allows establishing a useful classification of ene reactions in N-ene having a very high activation energy, P-ene reactions having activation energies between 35 and 20 kcal mol(-1), and H-ene reactions having activation energies below 20 kcal mol(-1). ELF topological analysis allows the characterisation of the two-stage one-step mechanism associated with a two-centre nucleophilic/electrophilic interaction. Formation of the C-C single bond is achieved by the C-to-C coupling of two pseudoradical centres formed at the two interacting carbon atoms in the first stage of the reaction. This topological analysis establishes that bonding changes are non-concerted. Finally, a DFT reactivity analysis makes it possible to characterise the electrophilic/nucleophilic behaviour of the reagents involved in ene reactions, and consequently, to predict the feasibility of ene reactions. PMID:25139695

  12. Dithizone and its oxidation products: a DFT, spectroscopic, and X-ray structural study.

    PubMed

    von Eschwege, Karel G; Conradie, Jeanet; Kuhn, Annemarie

    2011-12-29

    Air oxidation of ortho-fluorodithizone resulted in the first X-ray resolved structure of a disulfide of dithizone, validating the last outstanding X-ray structure in the oxidation of dithizone, H(2)Dz, which proceeds via the disulfide, (HDz)(2), to the deprotonated dehydrodithizone tetrazolium salt, Dz. Density functional theory calculations established the energetically favored tautomers along the entire pathway; in gas phase and in polar as well as nonpolar solvent environments. DFT calculations using the classic pure OLYP and PW91, or the newer B3LYP hybrid functional, as well as MP2 calculations, yielded the lowest energy structures in agreement with corresponding experimental X-ray crystallographic results. Atomic charge distribution patterns confirmed the cyclization reaction pathway and crystal packing of Dz. Time dependent DFT for the first time gave satisfactory explanation for the solvatochromic properties of dithizone, pointing to different tautomers that give rise to the observed orange color in methanol and green in dichloromethane. Concentratochromism of H(2)Dz was observed in methanol. Computed orbitals and oscillators are in close agreement with UV-visible spectroscopic experimental results. PMID:22103321

  13. NMR J-coupling constants in cisplatin derivatives studied by molecular dynamics and relativistic DFT.

    PubMed

    Sutter, Kiplangat; Truflandier, Lionel A; Autschbach, Jochen

    2011-06-01

    Solvent effects on J((195)Pt-(15)N) one-bond nuclear spin-spin coupling constants (J(PtN)) of cisplatin [cis-diamminedichloroplatinum(II)] and three cisplatin derivatives are investigated using a combination of density functional theory (DFT) based ab initio molecular dynamics (aiMD) and all-electron relativistic DFT NMR calculations employing the two-component relativistic zeroth-order regular approximation (ZORA). Good agreement with experiment is obtained when explicit solvent molecules are considered and when the computations are performed with a hybrid functional. Spin-orbit coupling causes only small effects on J(PtN) . Key factors contributing to the magnitude of coupling constants are elucidated, with the most significant being the presence of solvent as well as the quality of the density functional and basis set combination. The solvent effects are of the same magnitude as J(PtN) calculated for gas-phase geometries. However, the trends of J(PtN) among the complexes are already present in the gas phase. Results obtained with a continuum solvent model agree quite well with the aiMD results, provided that the Pt solvent-accessible radius is carefully chosen. The aiMD results support the existence of a partial hydrogen-bond-like inverse-hydration-type interaction affording a weak (1)J(Pt⋅⋅⋅H(w)) coupling between the complexes and the coordinating water molecule. PMID:21381179

  14. An experimental NEXAFS and computational TDDFT and ΔDFT study of the gas-phase core excitation spectra of nitroxide free radical TEMPO and its analogues.

    PubMed

    Ljubić, Ivan; Kivimäki, Antti; Coreno, Marcello

    2016-04-21

    Core-hole spectroscopy adds to the fundamental understanding of the electronic structure of stable nitroxide free radicals thus paving way for a sensible design of new analogues with desired functionalities. We study the gas-phase C 1s, N 1s and O 1s excitation spectra of three nitroxide free radicals - TEMPO and two of its amide-substituted analogues - using the experimental NEXAFS technique and the theoretical TDDFT and ΔDFT methods in the unrestricted setting. The short-range corrected SRC1-BLYP and SRC2-BLYP exchange-correlation functionals are used with TDDFT, and the standard B3LYP functional with ΔDFT. The TDDFT-based detailed spectral assignment includes the valence, mixed valence-Rydberg and Rydberg portions of the spectra from the onset of absorptions to the vicinity of the core-ionization thresholds. The relative overlaps between the experimental and TDDFT-modelled spectra are reasonably good, in the range of 0.7-0.8, 0.6-0.8, and 0.7-0.8 for the C 1s, N 1s, and O 1s spectra, respectively. The extent of spin contamination within the unrestricted framework and its effect on the accuracy of the calculated excitation energies and dipole intensities are discussed in detail. It is concluded that, despite the sizeable spin contamination, the presently used methods are capable of predicting the core-excitation spectra of comparatively large free radical species fairly reliably over a wide spectral range. PMID:27020039

  15. Theoretical study of the ammonia nitridation rate on an Fe (100) surface: A combined density functional theory and kinetic Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Yeo, Sang Chul; Lo, Yu Chieh; Li, Ju; Lee, Hyuck Mo

    2014-10-01

    Ammonia (NH3) nitridation on an Fe surface was studied by combining density functional theory (DFT) and kinetic Monte Carlo (kMC) calculations. A DFT calculation was performed to obtain the energy barriers (Eb) of the relevant elementary processes. The full mechanism of the exact reaction path was divided into five steps (adsorption, dissociation, surface migration, penetration, and diffusion) on an Fe (100) surface pre-covered with nitrogen. The energy barrier (Eb) depended on the N surface coverage. The DFT results were subsequently employed as a database for the kMC simulations. We then evaluated the NH3 nitridation rate on the N pre-covered Fe surface. To determine the conditions necessary for a rapid NH3 nitridation rate, the eight reaction events were considered in the kMC simulations: adsorption, desorption, dissociation, reverse dissociation, surface migration, penetration, reverse penetration, and diffusion. This study provides a real-time-scale simulation of NH3 nitridation influenced by nitrogen surface coverage that allowed us to theoretically determine a nitrogen coverage (0.56 ML) suitable for rapid NH3 nitridation. In this way, we were able to reveal the coverage dependence of the nitridation reaction using the combined DFT and kMC simulations.

  16. Theoretical study of the ammonia nitridation rate on an Fe (100) surface: A combined density functional theory and kinetic Monte Carlo study

    SciTech Connect

    Yeo, Sang Chul; Lee, Hyuck Mo; Lo, Yu Chieh; Li, Ju

    2014-10-07

    Ammonia (NH{sub 3}) nitridation on an Fe surface was studied by combining density functional theory (DFT) and kinetic Monte Carlo (kMC) calculations. A DFT calculation was performed to obtain the energy barriers (E{sub b}) of the relevant elementary processes. The full mechanism of the exact reaction path was divided into five steps (adsorption, dissociation, surface migration, penetration, and diffusion) on an Fe (100) surface pre-covered with nitrogen. The energy barrier (E{sub b}) depended on the N surface coverage. The DFT results were subsequently employed as a database for the kMC simulations. We then evaluated the NH{sub 3} nitridation rate on the N pre-covered Fe surface. To determine the conditions necessary for a rapid NH{sub 3} nitridation rate, the eight reaction events were considered in the kMC simulations: adsorption, desorption, dissociation, reverse dissociation, surface migration, penetration, reverse penetration, and diffusion. This study provides a real-time-scale simulation of NH{sub 3} nitridation influenced by nitrogen surface coverage that allowed us to theoretically determine a nitrogen coverage (0.56 ML) suitable for rapid NH{sub 3} nitridation. In this way, we were able to reveal the coverage dependence of the nitridation reaction using the combined DFT and kMC simulations.

  17. Synthesis, spectroscopic (UV-vis and GIAO NMR), crystallographic and theoretical studies of triazine heterocyclic derivatives

    NASA Astrophysics Data System (ADS)

    Khan, Salman A.; Obaid, Abdullah Y.; Al-Harbi, Laila M.; Arshad, Muhammad Nadeem; Şahin, Onur; Ersanlı, Cem Cüneyt; Abdel-Rehman, R. M.; Asiri, Abdullah M.; Hursthouse, Michael B.

    2015-09-01

    This work presents the synthesis and characterization of triazine heterocyclic derivatives. The spectroscopic properties like nuclear magnetic resonance [NMR, (1H and 13C)] were recorded in CDCl3 solution and Ultraviolet-Visible (UV-vis) absorption spectrums of compounds, 5,6-diphenyl-[1,2,4]triazin-3-ylamine (1), (5,6-diphenyl-[1,2,4]triazin-3-yl)-hydrazine (2) and 5,6-diphenyl-4H-[1,2,4] triazine-3-thione (3), were recorded in the range of 200-800 nm, using chloroform as base solvent. Molecular geometry of compounds with triazine heterocyclic derivative in the ground state have been calculated using the density functional theory (DFT) with 6-31G(d,p) basis set and compared with the X-ray experimental data. The calculated results show that the optimized geometry can well reproduce the crystal structures. Total static dipole moment (μ), the average linear polarizability (α) and the first hyperpolarizability (β) values of the investigated molecules have been computed using the same methods. The energetic behavior of compounds in solvent media has been examined using B3LYP method with the 6-31G(d,p) basis set by applying the polarizable continuum model (PCM). The total energy of compounds decreases with increasing polarity of the solvent. Frontier molecular orbitals and the molecular electrostatic potential (MEP), 1H NMR, and 13C NMR of three triazine derivatives were investigated using theoretical calculations. The linear polarizabilities and first hyperpolarizabilities of the studied molecules indicate that the compounds 1-3 can be used as a good nonlinear optical material (NLO). Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. Comparison of the NMR chemical shifts, absorption wavelengths with the experimental values revealed that DFT and time dependent-density functional theory (TD-DFT) method produce generally closer to good results.

  18. Synthesis, characterization, DFT and biological studies of isatinpicolinohydrazone and its Zn(II), Cd(II) and Hg(II) complexes

    NASA Astrophysics Data System (ADS)

    El-Gammal, O. A.; Rakha, T. H.; Metwally, H. M.; Abu El-Reash, G. M.

    2014-06-01

    Isatinpicolinohydrazone (H2IPH) and its Zn(II), Cd(II) and Hg(II) complexes have been synthesized and investigated using physicochemical techniques viz. IR, 1H NMR, 13C NMR, UV-Vis spectrometric methods and magnetic moment measurements. The investigation revealed that H2IPH acts as binegative tetradentate in Zn(II), neutral tridentate in Cd(II) and as neutral bidentate towards Hg(II) complex. Octahedral geometry is proposed for all complexes. The bond length, bond angle, chemical reactivity, energy components (kcal/mol), binding energy (kcal/mol) and dipole moment (Debyes) for all the title compounds were evaluated by DFT and also MEP for the ligand is shown. Theoretical infrared intensities of H2IPH and also the theoretical electronic spectra of the ligand and its complexes were calculated. The thermal behavior and the kinetic parameters of degradation were determined using Coats-Redfern and Horowitz-Metzger methods. The in vitro antibacterial studies of the complexes proved them as growth inhibiting agents. The DDPH antioxidant of the compounds have been screened. Antitumor activity, carried out in vitro on human mammary gland (breast) MCF7, have shown that Hg(II) complex exhibited potent activity followed by Zn(II), Cd(II) complexes and the ligand.

  19. Electronic structure of interstitial hydrogen in lutetium oxide from DFT+U calculations and comparison study with μ SR spectroscopy

    NASA Astrophysics Data System (ADS)

    da Silva, E. Lora; Marinopoulos, A. G.; Vieira, R. B. L.; Vilão, R. C.; Alberto, H. V.; Gil, J. M.; Lichti, R. L.; Mengyan, P. W.; Baker, B. B.

    2016-07-01

    The electronic structure of hydrogen impurity in Lu2O3 was studied by first-principles calculations and muonium spectroscopy. The computational scheme was based on two methods which are well suited to treat defect calculations in f -electron systems: first, a semilocal functional of conventional density-functional theory (DFT) and secondly a DFT+U approach which accounts for the on-site correlation of the 4 f electrons via an effective Hubbard-type interaction. Three different types of stable configurations were found for hydrogen depending upon its charge state. In its negatively charged and neutral states, hydrogen favors interstitial configurations residing either at the unoccupied sites of the oxygen sublattice or at the empty cube centers surrounded by the lanthanide ions. In contrast, the positively charged state stabilized only as a bond configuration, where hydrogen binds to oxygen ions. Overall, the results between the two methods agree in the ordering of the formation energies of the different impurity configurations, though within DFT+U the charge-transition (electrical) levels are found at Fermi-level positions with higher energies. Both methods predict that hydrogen is an amphoteric defect in Lu2O3 if the lowest-energy configurations are used to obtain the charge-transition, thermodynamic levels. The calculations of hyperfine constants for the neutral interstitial configurations show a predominantly isotropic hyperfine interaction with two distinct values of 926 MHz and 1061 MHz for the Fermi-contact term originating from the two corresponding interstitial positions of hydrogen in the lattice. These high values are consistent with the muonium spectroscopy measurements which also reveal a strongly isotropic hyperfine signature for the neutral muonium fraction with a magnitude slightly larger (1130 MHz) from the ab initio results (after scaling with the magnetic moments of the respective nuclei).

  20. Effect of Base Stacking on the Acid-Base Properties of the Adenine Cation Radical [A•+] in Solution: ESR and DFT Studies

    PubMed Central

    Adhikary, Amitava; Kumar, Anil; Khanduri, Deepti

    2015-01-01

    In this study, the acid–base properties of the adenine cation radical are investigated by means of experiment and theory. Adenine cation radical (A•+) is produced by one-electron oxidation of dAdo and of the stacked DNA-oligomer (dA)6 by Cl2•− in aqueous glass (7.5 M LiCl in H2O and in D2O) and investigated by ESR spectroscopy. Theoretical calculations and deuterium substitution at C8–H and N6–H in dAdo aid in our assignments of structure. We find the pKa value of A•+ in this system to be ca. 8 at 150 K in seeming contradiction to the accepted value of ≤ 1 at ambient temperature. However, upon thermal annealing to ≥160 K, complete deprotonation of A•+ occurs in dAdo in these glassy systems even at pH ca. 3. A•+ found in (dA)6 at 150 K also deprotonates on thermal annealing. The stability of A•+ at 150 K in these systems is attributed to charge delocalization between stacked bases. Theoretical calculations at various levels (DFT B3LYP/6-31G*, MPWB95, and HF-MP2) predict binding energies for the adenine stacked dimer cation radical of 12 to 16 kcal/mol. Further DFT B3LYP/6-31G* calculations predict that, in aqueous solution, monomeric A•+ should deprotonate spontaneously (a predicted pKa of ca. −0.3 for A•+). However, the charge resonance stabilized dimer AA•+ is predicted to result in a significant barrier to deprotonation and a calculated pKa of ca. 7 for the AA•+ dimer which is 7 pH units higher than the monomer. These theoretical and experimental results suggest that A•+ isolated in solution and A•+ in adenine stacks have highly differing acid–base properties resulting from the stabilization induced by hole delocalization within adenine stacks. PMID:18611019

  1. Theoretical Studies in Elementary Particle Physics

    SciTech Connect

    Collins, John C.; Roiban, Radu S

    2013-04-01

    This final report summarizes work at Penn State University from June 1, 1990 to April 30, 2012. The work was in theoretical elementary particle physics. Many new results in perturbative QCD, in string theory, and in related areas were obtained, with a substantial impact on the experimental program.

  2. Dry (CO2) reforming of methane over Pt catalysts studied by DFT and kinetic modeling

    NASA Astrophysics Data System (ADS)

    Niu, Juntian; Du, Xuesen; Ran, Jingyu; Wang, Ruirui

    2016-07-01

    Dry reforming of methane (DRM) is a well-studied reaction that is of both scientific and industrial importance. In order to design catalysts that minimize the deactivation and improve the selectivity and activity for a high H2/CO yield, it is necessary to understand the elementary reaction steps involved in activation and conversion of CO2 and CH4. In our present work, a microkinetic model based on density functional theory (DFT) calculations is applied to explore the reaction mechanism for methane dry reforming on Pt catalysts. The adsorption energies of the reactants, intermediates and products, and the activation barriers for the elementary reactions involved in the DRM process are calculated over the Pt(1 1 1) surface. In the process of CH4 direct dissociation, the kinetic results show that CH dissociative adsorption on Pt(1 1 1) surface is the rate-determining step. CH appears to be the most abundant species on the Pt(1 1 1) surface, suggesting that carbon deposition is not easy to form in CH4 dehydrogenation on Pt(1 1 1) surface. In the process of CO2 activation, three possible reaction pathways are considered to contribute to the CO2 decomposition: (I) CO2* + * → CO* + O*; (II) CO2* + H* → COOH* + * → CO* + OH*; (III) CO2* + H* → mono-HCOO* + * → bi-HCOO* + * [CO2* + H* → bi-HCOO* + *] → CHO* + O*. Path I requires process to overcome the activation barrier of 1.809 eV and the forward reaction is calculated to be strongly endothermic by 1.430 eV. In addition, the kinetic results also indicate this process is not easy to proceed on Pt(1 1 1) surface. While the CO2 activation by H adsorbed over the catalyst surface to form COOH intermediate (Path II) is much easier to be carried out with the lower activation barrier of 0.746 eV. The Csbnd O bond scission is the rate-determining step along this pathway and the process needs to overcome the activation barrier of 1.522 eV. Path III reveals the CO2 activation through H adsorbed over the catalyst

  3. Experimental and DFT studies on the vibrational spectra of 1H-indene-2-boronic acid

    NASA Astrophysics Data System (ADS)

    Alver, Özgur; Kaya, Mehmet Fatih

    2014-11-01

    Stable conformers and geometrical molecular structures of 1H-indene-2-boronic acid (I-2B(OH)2) were studied experimentally and theoretically using FT-IR and FT-Raman spectroscopic methods. FT-IR and FT-Raman spectra were recorded in the region of 4000-400 cm-1, and 3700-400 cm-1, respectively. The optimized geometric structures were searched by Becke-3-Lee-Yang-Parr (B3LYP) hybrid density functional theory method with 6-31++G(d,p) basis set. Vibrational wavenumbers of I-2B(OH)2 were calculated using B3LYP density functional methods including 6-31++G(d,p) basis set. Experimental and theoretical results show that density functional B3LYP method gives satisfactory results for predicting vibrational wavenumbers except OH stretching modes which is probably due to increasing unharmonicity in the high wave number region and possible intra and inter molecular interaction at OH edges. To support the assigned vibrational wavenumbers, the potential energy distribution (PED) values were also calculated using VEDA 4 (Vibrational Energy Distribution Analysis) program.

  4. Experiment and DFT studies on radioiodine removal and storage mechanism by imidazolium-based ionic liquid.

    PubMed

    Cao, Bobo; Liu, Shuangyue; Du, Dongmei; Xue, Zhimin; Fu, Hui; Sun, Haitao

    2016-03-01

    In order to remove and store radioactive substances effectively, studies on the mechanisms of radioiodine captured by ionic liquids (ILs) with a fixed cation (1-butyl-3-methyl-imidazolium cation [Bmim]+) were carried out in experimental and theoretical methods. Fourier transform infrared attenuated total reflectance (FT-IR ATR) spectra of 2BP8HQ and ultraviolet-visible (UV/vis) spectroscopy were used to investigate the kinetic process of radioiodine removal by ILs in experiment. Corresponding theoretical investigations on the structures and formation mechanisms of ILs, bare anions and complexes as well as hydrogen bonds was carried using density functional theory. The electrostatic potential was used in configuration design and construction. Charge distribution was used to show the variation of atom charge density, Interaction energy and vibration frequency change were performed to explore possible mechanisms on the halogen bond formation between radioiodine molecule and bare anion or anion in ILs when radioiodine captured by ILs. In order to characterize halogen bonds both natural bond orbital analysis and atoms in molecules analysis were performed. Both experimental and computational results showed that radioiodine could be captured by ILs with a 1:1mol stoichiometry. It was noteworthy that [Bmim][Br], [Bmim][I] and [Bmim][Cl], containing high radioiodine capture efficiency anions, were better candidates in removal and reliable storage of radioiodine for their capture efficiencies of over 80% in 5h. PMID:26774640

  5. Synthesis, characterization and DFT studies of two new silver(I) complexes with 3,4-lutidine

    NASA Astrophysics Data System (ADS)

    Soliman, Saied M.; Assem, Rania; Abu-Youssef, Morsy A. M.; Kassem, Taher S.

    2015-04-01

    The synthesis, characterization and molecular structure of two new Ag(I) complexes with 3,4-lutidine (34lut) have been reported. The [Ag(34lut)3(OAC)]; 1 and [Ag(34lut)2(TFA)]; 2 complexes, where OAC and TFA are acetate and trifluoroacetate respectively, have been characterized using elemental analysis, FTIR, NMR and mass spectra. Their molecular structures were calculated using DFT quantum chemical calculations. Both 1 and 2 were found to have distorted tetrahedral geometry around the Ag(I). The spectroscopic properties of the studied complexes have been calculated using the same level of theory. The Infrared vibrational frequencies of the COO stretches confirmed that the OAC is monodentate in 1 while the TFA is bidentate in 2. The calculated polarizability (α0) and HOMO-LUMO energy gap (ΔE) values indicated that 1 has higher NLO activity than 2. The electronic spectra of these complexes are calculated using the TD-DFT calculations. The calculated 1H NMR chemical shift values using GIAO approach showed good correlations with the experimental data. The interaction energies using the second order perturbation theory have been used to study the different intramolecular charge transfer interactions in the studied complexes. The NBO calculations indicated that both the Agsbnd O bonds are almost identical in 2 but not in 1.

  6. Effects of metal elements in catalytic growth of carbon nanotubes/graphene: A first principles DFT study

    NASA Astrophysics Data System (ADS)

    Li, Jingde; Croiset, Eric; Ricardez-Sandoval, Luis

    2014-10-01

    Role of metals in the catalytic Chemical Vapor Deposition (CVD) growth of carbon nanotubes (CNTs) or graphene was investigated using DFT. Crucial processes involved in the growth of CNTs/graphene: methane dissociation to produce C, C diffusion and nucleation kinetics were studied on the (1 1 1) surface of different transition metals, i.e., Fe, Co, Ni, and Cu. Based on the DFT calculation results, the present study explains why Ni-based catalyst is a suitable CVD substrate for growing CNTs: it has a moderate reactivity towards methane dissociation; low energy barrier for C atom surface diffusion, which makes C to diffuse easily to the metal/CNTs edges and contribute to CNTs growth; relatively high nucleation barriers, making it more resistant for deactivation caused by the cover of carbon clusters. Meanwhile, this study also shows that Cu may be an appropriate catalyst for graphene synthesis due to the particularly low diffusion and nucleation barriers of C atoms on Cu, which suggest that C atoms tend to be more uniformly distributed and nucleate easily on the Cu surface. Key limitation of Cu is the low reactivity of this metal towards methane dissociation. Since Fe and Ni are very reactive towards Csbnd H bond breaking, Cu based alloys, e.g. Cu8Ni, were proposed as a suitable catalyst for graphene production.

  7. Theoretical study on mechanical properties of polyethylene-SWCNT complexes

    NASA Astrophysics Data System (ADS)

    Petrushenko, Igor K.

    2016-01-01

    This paper studies the mechanical properties of polyethylene (PE)-Single-walled carbon nanotube (SWCNT) complexes by using density functional theory (DFT). At the PBE/SVP level, the Young’s modulus of the complexes is obtained as a function of PE content. It is established that, with increasing number of PE chains attached to the SWCNTs, the Young’s modulus monotonically decreases. The density of states (DOS) results show that no orbital hybridization exists between the PE chains and nanotubes. The results of this work are of importance for the design of composite materials employing SWCNTs.

  8. Metric for the measurement of the quality of complex beams: a theoretical study.

    PubMed

    Kaim, Sergiy; Lumeau, Julien; Smirnov, Vadim; Zeldovich, Boris; Glebov, Leonid

    2015-04-01

    We present a theoretical study of various definitions of laser beam width in a given cross section. Quality of the beam is characterized by dimensionless beam propagation products (BPPs) Δx·Δθ(x)/λ, which are different for the 21 definitions presented, but are close to 1. Six particular beams are studied in detail. In the process, we had to review the properties for the Fourier transform of various modifications and the relationships between them: physical Fourier transform (PFT), mathematical Fourier transform (MFT), and discrete Fourier transform (DFT). We found an axially symmetric self-MFT function, which may be useful for descriptions of diffraction-quality beams. In the appendices, we illustrate the thesis "the Fourier transform lives on the singularities of the original." PMID:26366763

  9. A combined experimental and theoretical study of the thermal cycloaddition of aryl azides with activated alkenes.

    PubMed

    Zeghada, Sarah; Bentabed-Ababsa, Ghenia; Derdour, Aïcha; Abdelmounim, Safer; Domingo, Luis R; Sáez, José A; Roisnel, Thierry; Nassar, Ekhlass; Mongin, Florence

    2011-06-01

    Reactions were performed from aryl azides on the one hand, and activated alkenes coming from β-dicarbonyl compounds or malonodinitrile on the other hand, either with recourse to conventional heating or to microwave activation, to afford 1-aryl-1H-1,2,3-triazoles. The mechanism and the regioselectivity of the reactions involving β-dicarbonyl compounds have been theoretically studied using DFT methods at the B3LYP/6-31G* level: they are domino processes comprising a tautomeric equilibrium of the β-dicarbonyl compounds with their enol forms, a 1,3-dipolar cycloaddition of the enol forms with the aryl azides (high activation energy), and a dehydration process (lower activation energy). The effect of non-conventional activation methods on the degradation of 1,2,3-triazolines was next studied experimentally. Finally, some of the 1,2,3-triazoles such synthesized were evaluated for their bactericidal and cytotoxic activities. PMID:21494704

  10. The structure, vibrational spectra and nonlinear optical properties of the L-lysine × tartaric acid complex—Theoretical studies

    NASA Astrophysics Data System (ADS)

    Drozd, M.; Marchewka, M. K.

    2006-05-01

    The room temperature X-ray studies of L-lysine × tartaric acid complex are not unambiguous. The disorder of three atoms of carbon in L-lysine molecule is observed. These X-ray studies are ambiguous. The theoretical geometry study performed by DFT methods explain the most doubts which are connected with crystallographic measurements. The theoretical vibrational frequencies and potential energy distribution (PED) of L-lysine × tartaric acid were calculated by B3LYP method. The calculated frequencies were compared with experimental measured IR spectra. The complete assignment of the bands has been made on the basis of the calculated PED. The restricted Hartee-Fock (RHF) methods were used for calculation of the hyperpolarizability for investigated compound. The theoretical results are compared with experimental value of β.

  11. Theoretical study of NMR, infrared and Raman spectra on triple-decker phthalocyanines

    NASA Astrophysics Data System (ADS)

    Suzuki, Atsushi; Oku, Takeo

    2016-02-01

    Electronic structures and magnetic properties of multi-decker phthalocyanines were studied by theoretical calculation. Electronic structures, excited processes at multi-states, isotropic chemical shifts of 13C, 14N and 1H-nuclear magnetic resonance (NMR), principle V-tensor in electronic field gradient (EFG) tensor and asymmetry parameters (η), vibration mode in infrared (IR) and Raman spectra of triple-decker phthalocyanines were calculated by density functional theory (DFT) and time-dependent DFT using B3LYP as basis function. Electron density distribution was delocalized on the phthalocyanine rings with electron static potential. Considerable separation of chemical shifts in 13C, 14N and 1H-NMR was originated from nuclear spin interaction between nitrogen and carbon atoms, nuclear quadrupole interaction based on EFG and η of central metal under crystal field. Calculated optical absorption at multi-excited process was derived from overlapping π-orbital on the phthalocyanine rings. The vibration modes in IR and Raman spectra were based on in-plane deformation and stretching vibrations of metal-ligand coordination bond on the deformed structure.

  12. Theoretical and experimental studies of reentry plasmas

    NASA Technical Reports Server (NTRS)

    Dunn, M. G.; Kang, S.

    1973-01-01

    A viscous shock-layer analysis was developed and used to calculate nonequilibrium-flow species distributions in the plasma layer of the RAM vehicle. The theoretical electron-density results obtained are in good agreement with those measured in flight. A circular-aperture flush-mounted antenna was used to obtain a comparison between theoretical and experimental antenna admittance in the presence of ionized boundary layers of low collision frequency. The electron-temperature and electron-density distributions in the boundary layer were independently measured. The antenna admittance was measured using a four-probe microwave reflectometer and these measured values were found to be in good agreement with those predicted. Measurements were also performed with another type of circular-aperture antenna and good agreement was obtained between the calculations and the experimental results. A theoretical analysis has been completed which permits calculation of the nonequilibrium, viscous shock-layer flow field for a sphere-cone body. Results are presented for two different bodies at several different altitudes illustrating the influences of bluntness and chemical nonequilibrium on several gas dynamic parameters of interest. Plane-wave transmission coefficients were calculated for an approximate space-shuttle body using a typical trajectory.

  13. Microwave Assisted Synthesis, Antifungal Activity, and DFT Study of Some Novel Triazolinone Derivatives

    PubMed Central

    Sun, Na-Bo; Jin, Jian-Zhong; He, Fang-Yue

    2015-01-01

    A series of some novel 1,2,4-triazol-5(4H)-one derivatives were designed and synthesized under microwave irradiation via multistep reaction. The structures of 1,2,4-triazoles were confirmed by 1H NMR, MS, FTIR, and elemental analysis. The antifungal activities of 1,2,4-triazoles were determined. The antifungal activity results indicated that the compounds 5c, 5f, and 5h exhibited good activity against Pythium ultimum, and the compounds 5b and 5c displayed good activity against Corynespora cassiicola. Theoretical calculation of the compound 5c was carried out with B3LYP/6-31G (d). The full geometry optimization was carried out using 6-31G(d) basis set, and the frontier orbital energy and electrostatic potential were discussed, and the structure-activity relationship was also studied. PMID:25861651

  14. Theoretical studies of Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Das, Kunal Kashyap

    This thesis is a theoretical study of Bose-Einstein Condensation (BEC) in harmonically-trapped, weakly-interacting dilute gases. The motivation for this study is the experimental realization of BEC in trapped alkali gases since 1995. The weak inter-particle interactions and diluteness of the gases allow for a fairly accurate mean-field treatment and justifies a discrete quasi-particle description as we use in this work. This thesis considers three specific topics in the rapidly growing field of BEC theory: (i) interference effects in BEC, (ii) interaction-induced energy shifts and damping of excitations of condensates and (iii) the properties of highly anisotropic condensates. The results are summarized here: i. We show that if two multiply occupied boson modes are in eigenstates of the Hermitian relative phase operator, then the visibility of fringes formed by the interference between the modes is necessarily less than unity. For large total occupation numbers the visibility V ≤ pi/4. States with definite relative phase and unit visibility do exist. They are related to coherent states and are not orthogonal (not eigenstates of a Hermitian phase operator). This visibility limitation may make it possible to investigate experimentally the physical role of the relative phase eigenstates in interference measurements on BEC. ii. We evaluate analytically the asymptotic energy shifts of the high energy Bogoliubov quasi-particle modes. In spherical geometry, those modes display a 1/ n dependence on their number of radial nodes n but only a weak dependence on their angular momenta l. We obtain similar results for cylindrical geometry. We derive an implicit equation for the widths or decay rates gamma of the modes from an assumption of exponential decay. We use the equation to do a detailed numerical study of the trends in the behavior of the widths as a function of temperature, energy, particle number and scattering lengths. In particular, we find that widths due to

  15. A 45Sc-NMR and DFT calculation study of crystalline scandium compounds

    NASA Astrophysics Data System (ADS)

    Bräuniger, Thomas; Hofmann, Andreas J.; Moudrakovski, Igor L.; Hoch, Constantin; Schnick, Wolfgang

    2016-01-01

    A series of scandium compounds, namely ScPO4, ScOF, Li3Sc(BO3)2, and CaSc2O4, were prepared according to procedures described in the literature, and then characterised by powder X-ray diffraction and solid-state 45Sc-NMR spectroscopy. By computer fitting, the quadrupolar interaction parameters χ and η, as well as the isotropic chemical shifts δiso were extracted from the NMR spectra. For comparison and site assignment of 45Sc, density functional theory (DFT) calculations of the EFG tensor were carried out with the CASTEP code. For the compounds with a well-defined formal coordination number (CN), a convincing linear correlation between CN and isotropic chemical shift could be established.

  16. Beyond the constant Lorenz number for separating thermal conductivities of electrons and phonons: A DFT study

    NASA Astrophysics Data System (ADS)

    Chen, Mingxing; Podloucky, Raimund

    2013-03-01

    Lorenz number is an important quantity for separating thermal conductivities of electrons and phonons in the field of thermoelectrics, which is material- and temperature-dependent. Combing DFT calculations with Boltzmann transport equations, we have derived the Lorenz number for realistic compound BaAu6Ge40, a good thermoelectric material. It is demonstrated that using the constant Lorenz number of the Wiedemann-Franz law for simple metals leads to strong discrepancies, in particular at higher temperatures. The results suggest that one has to rethink the way of extracting both κel and κph as usually done based on the measured electrical conductivity. We propose a strategy of correcting the Wiedemann-Franz Lorenz number that subtracts the metallic limiting value by S2 as obtained from Seebeck measurements. The authors gratefully acknowledge the support by the Austrian Science Foundation FWF under project nr. P22295-N20.

  17. First-principles DFT +G W study of oxygen-doped CdTe

    NASA Astrophysics Data System (ADS)

    Flores, Mauricio A.; Orellana, Walter; Menéndez-Proupin, Eduardo

    2016-05-01

    The role of oxygen doping in CdTe is addressed by first-principles calculations. Formation energies, charge transition levels, and quasiparticle defect states are calculated within the DFT+G W formalism. The formation of a new defect is identified, the (OTe-TeCd) complex.Thiscomplex is energetically favored over both isovalent (OTe) and interstitial oxygen (Oi), in the Te-rich limit. We find that the incorporation of oxygen passivates the harmful deep energy levels associated with (TeCd), suggesting an improvement in the efficiency of CdTe based solar cells. Substitutional (OCd) is only stable in the neutral charge state and undergoes a Jahn-Teller distortion. We also investigate the diffusion profiles of interstitial oxygen and find a low-energy diffusion barrier of only 0.14 eV between two structurally distinct interstitial sites.

  18. DFT studies of 5-fluorouracil tautomers on a silicon graphene nanosheet

    NASA Astrophysics Data System (ADS)

    Yaraghi, Afshin; Ozkendir, O. Murat; Mirzaei, Mahmoud

    2015-09-01

    We have performed density functional theory (DFT) calculations to evaluate properties for tautomers of 5-fluorouracil (FU), as an anticancer medicine, in the free form and in the hybridized form with a representative silicon graphene (SiG) nanosheet. All the structures have been fully relaxed to obtain the optimized geometries and energy parameters. The results indicated that the total and binding energies have good clues to determine the properties of tautomers and hybrid structures. Moreover, quadrupole coupling constants (CQ) have been evaluated for the optimized structures to run an atomic level characterization of the investigated structures. The obtained results indicated that the properties for fluorine atoms are characteristically changed through tautomerism and hybridization processes.

  19. Vibrational spectroscopic and non-linear optical activity studies on nicotinanilide : A DFT approach

    NASA Astrophysics Data System (ADS)

    Premkumar, S.; Jawahar, A.; Mathavan, T.; Dhas, M. Kumara; Benial, A. Milton Franklin

    2015-06-01

    The molecular structure of nicotinanilide was optimized by the DFT/B3LYP method with cc-pVTZ basis set using Gaussian 09 program. The first order hyperpolarizability of the molecule was calculated, which exhibits the higher nonlinear optical activity. The natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction, which leads to the higher nonlinear optical activity of the molecule. The Frontier molecular orbitals analysis of the molecule shows that the delocalization of electron density occurs within the molecule. The lower energy gap indicates that the hydrogen bond formation between the charged species. The vibrational frequencies were calculated and assigned on the basis of potential energy distribution calculation using the VEDA 4.0 program and the corresponding vibrational spectra were simulated. Hence, the nicotinanilide molecule can be a good candidate for second-order NLO material.

  20. DFT calculations, spectroscopy and antioxidant activity studies on (E)-2-nitro-4-[(phenylimino)methyl]phenol

    NASA Astrophysics Data System (ADS)

    Temel, Ersin; Alaşalvar, Can; Gökçe, Halil; Güder, Aytaç; Albayrak, Çiğdem; Alpaslan, Yelda Bingöl; Alpaslan, Gökhan; Dilek, Nefise

    2015-02-01

    We have reported synthesis and characterization of (E)-2-nitro-4-[(phenylimino)methyl]phenol by using X-ray crystallographic method, FT-IR and UV-vis spectroscopies and density functional theory (DFT). Optimized geometry and vibrational frequencies of the title compound in the ground state have been computed by using B3LYP with the 6-311G+(d,p) basis set. HOMO-LUMO energy gap, Non-linear optical properties and NBO analysis of the compound are performed at B3LYP/6-311G+(d,p) level. Additionally, as remarkable properties, antioxidant activity of the title compound (CMPD) has been determined by using different antioxidant test methods i.e. ferric reducing antioxidant power (FRAP), hydrogen peroxide scavenging (HPSA), free radical scavenging (FRSA) and ferrous ion chelating activities (FICA). When compared with standards (BHA, BHT, and α-tocopherol), we have concluded that CPMD has effective FRAP, HPSA, FRSA and FICA.

  1. DFT STUDY OF HYDROGEN STORAGE ON Li- AND Na-DOPED C59B HETEROFULLERENE

    NASA Astrophysics Data System (ADS)

    Zahedi, Ehsan; Mozaffari, Majid

    2014-05-01

    Effect of light alkali metal (Li and Na) decorated on the C59B heterofullerene for hydrogen storage is considered using DFT-MPW1PW91 method. Results show that Li and Na atoms strongly prefer to adsorb on top of five-member and six-member ring where a carbon atom is replaced by a boron atom. Significant charge transfer from the alkali metal to the C59B compensates for the electron deficiency of C59B and makes the latter aromatic in nature. Corrected binding energies of hydrogen molecule on the alkali-doped C59B using counterpoise method, structural properties and NBO analysis indicate that first hydrogen molecule is adsorbed physically and does not support minimal conditions of DOE requirement. Finally, positive values of binding energies for the adsorption of a second hydrogen molecule show that alkali doped C59B are capable of storing a maximum of one hydrogen molecule.

  2. First-principles DFT +GW study of oxygen vacancies in rutile TiO2

    NASA Astrophysics Data System (ADS)

    Malashevich, Andrei; Jain, Manish; Louie, Steven G.

    2014-02-01

    We perform first-principles calculations of the quasiparticle defect states, charge transition levels, and formation energies of oxygen vacancies in rutile titanium dioxide. The calculations are done within the recently developed combined DFT +GW formalism, including the necessary electrostatic corrections for the supercells with charged defects. We find the oxygen vacancy to be a negative U defect, where U is the defect electron addition energy. For Fermi level values below ˜2.8 eV (relative to the valence-band maximum), we find the +2 charge state of the vacancy to be the most stable, while above 2.8 eV we find that the neutral charge state is the most stable.

  3. Radical reactions of C 60Ph 5Cl: EPR study and DFT calculations

    NASA Astrophysics Data System (ADS)

    Kalina, O. G.; Tumanskii, B. L.; Chistyakov, A. L.; Stankevich, I. V.; Birkett, P. R.; Taylor, R.

    2003-10-01

    UV-irradiation of a toluene solution of C 60Ph 5Cl leads to the formation of the stable rad C 60Ph 5 cyclopentadienyl-type fullerenyl radical. Under UV-irradiation of a toluene solution of C 60Ph 5Cl containing Hg[P(O)(OPr i) 2] 2 (Pr i=CH(CH 3) 2), three isomers of the adducts of phosphoryl radicals with C 60Ph 5Cl are formed. Density functional (DFT) approach with the B3LYP functional was used for estimating of the enthalpies of the formation and hyperfine coupling constants for all possible adducts of phosphoryl radicals with C 60Ph 5Cl. Biradical particles rad C 60Ph 5[P(O)(OPr i) 2]- rad C 60Ph 5[P(O)(OPr i) 2] with a distance between unpaired electrons of about 10.5 Å, are also obtained.

  4. Arsenic incorporation into FeS 2 pyrite and its influence on dissolution: A DFT study

    NASA Astrophysics Data System (ADS)

    Blanchard, Marc; Alfredsson, Maria; Brodholt, John; Wright, Kate; Catlow, C. Richard A.

    2007-02-01

    FeS 2 pyrite can incorporate large amounts of arsenic (up to ca. 10 wt%) and hence has a strong impact on the mobility of this toxic metalloid. Focussing on the lowest arsenic concentrations for which the incorporation occurs in solid solution, the substitution mechanisms involved have been investigated by assuming simple incorporation reactions in both oxidising and reducing conditions. The solution energies were calculated by Density Functional Theory (DFT) calculations and we predict that the formation of AsS dianion groups is the most energetically favourable mechanism. The results also suggest that the presence of arsenic will accelerate the dissolution and thus the generation of acid drainage, when the crystal dissolves in oxidising conditions.

  5. A DFT study of electron or hole localization in a peptide containing asparagin

    NASA Astrophysics Data System (ADS)

    Houée-Levin, C.; Bergès, J.

    2002-09-01

    The mechanisms of protein degradation induced by ionisation are of great interest for radiobiology, improvement of mass spectroscopy and industrial processes such as radio sterilisation. Sequences containing asparagin are very sensitive especially if surrounded by glycine. Very few techniques allow a satisfying understanding of the processes induced by creation of an anionic or cationic site in a peptide. We used the methods of quantum chemistry (DFT/B3LYP with 6-31G^* basis set) to characterise the geometry modifications induced in the cations or in the anions derived from peptide Gly Asn Gly. The cationic sites are localised mostly close to the first peptidic bond and induce a lengthening of the Ca C(O) bond. Conversely the anionic sites are localised on a carbonyl function. Implications are discussed considering the radiolytic products and the proposed mechanisms.

  6. Vibrational spectroscopic and non-linear optical activity studies on nicotinanilide : A DFT approach

    SciTech Connect

    Premkumar, S.; Mathavan, T.; Dhas, M. Kumara; Benial, A. Milton Franklin; Jawahar, A.

    2015-06-24

    The molecular structure of nicotinanilide was optimized by the DFT/B3LYP method with cc-pVTZ basis set using Gaussian 09 program. The first order hyperpolarizability of the molecule was calculated, which exhibits the higher nonlinear optical activity. The natural bond orbital analysis confirms the presence of intramolecular charge transfer and the hydrogen bonding interaction, which leads to the higher nonlinear optical activity of the molecule. The Frontier molecular orbitals analysis of the molecule shows that the delocalization of electron density occurs within the molecule. The lower energy gap indicates that the hydrogen bond formation between the charged species. The vibrational frequencies were calculated and assigned on the basis of potential energy distribution calculation using the VEDA 4.0 program and the corresponding vibrational spectra were simulated. Hence, the nicotinanilide molecule can be a good candidate for second-order NLO material.

  7. DFT Study of Oxygen Reduction Reaction on N-substituted Carbon Electrodes. Adsorption

    NASA Astrophysics Data System (ADS)

    Kobayashi, Hisayoshi; Tomoya, Nakzono; Miyazaki, Soichi; Miura, Toshiko; Takeuchi, Nobuyuki; Yamabe, Tokio

    2011-05-01

    Carbon alloys attract attention as metal-free cathode catalysts. Mechanisms of oxygen reduction reactions are investigated using the DFT calculations and molecular models such as N-substituted coronene, circum pyrene, and corannulene. The overall oxygen reduction reaction (ORR) is decomposed into five elementary reactions. Adsorption of O2 is important as the first step of reduction, and it depends strongly on the spin density on C atoms, introduced by the N atom. Secondly the peripheral C atoms have an advantage due to the rehybridization freedom to the sp3 configuration. Based on the reversible electrode potential (REP) for each elementary reaction, the overpotential is expected for the first reduction of O2 to OOH and the final reduction of OH to H2O. These features indicate that N-substituted carbon electrode resembles Pt electrode compared to other less active metals, such as Au.

  8. Chemical shielding properties for BN, BP, AlN, and AlP nanocones: DFT studies

    NASA Astrophysics Data System (ADS)

    Mirzaei, Mahmoud; Yousefi, Mohammad; Meskinfam, Masoumeh

    2012-06-01

    The properties of boron nitride (BN), boron phosphide (BP), aluminum nitride (AlN), and aluminum phosphide (AlP) nanocones were investigated by density functional theory (DFT) calculations. The investigated structures were optimized and chemical shielding (CS) properties including isotropic and anisotropic CS parameters were calculated for the atoms of the optimized structures. The magnitudes of CS parameters were observed to be mainly dependent on the bond lengths of considered atoms. The results indicated that the atoms could be divided into atomic layers due to the similarities of their CS properties for the atoms of each layer. The trend means that the atoms of each layer detect almost similar electronic environments. Moreover, the atoms at the apex and mouth of nanocones exhibit different properties with respect to the other atomic layers.

  9. Spectroscopic and DFT study of atenolol and metoprolol and their copper complexes

    NASA Astrophysics Data System (ADS)

    Cozar, O.; Szabó, L.; Cozar, I. B.; Leopold, N.; David, L.; Căinap, C.; Chiş, V.

    2011-05-01

    IR, Raman and surface-enhanced Raman scattering (SERS) spectra of atenolol (ATE) and metoprolol (MET) were recorded and assigned on the basis of density functional theory (DFT) calculations. A reliable assignment of vibrational IR and Raman bands of the two compounds was possible by a proper choice of models used in quantum chemical calculations. Both molecules are adsorbed to the silver surface mainly through the oxygen atoms and π-electrons of the phenyl ring. The coordination mode of the metal ions in Cu(II)-ATE and -MET compounds was also derived from IR and EPR spectra. EPR spectra give evidence for a square-planar arrangement around the copper (II) ion in the case of Cu-ATE complex, with a N 2O 2 chromophore. Only oxygen atoms are involved in the cooper coordination for Cu-MET complex, and two types of local symmetries with d and d as ground states for paramagnetic electron coexist.

  10. NO Chemisorption on Cu/SSZ-13: a Comparative Study from Infrared Spectroscopy and DFT Calculations

    SciTech Connect

    Zhang, Renqin; McEwen, Jean-Sabin; Kollar, Marton; Gao, Feng; Wang, Yilin; Szanyi, Janos; Peden, Charles HF

    2014-11-07

    The locations and energies of Cu ions in a Cu/SSZ-13 zeolite catalyst were investigated by density functional theory (DFT) calculations. For 'naked' Cu2+ ions (i.e., Cu2+ ions with no ligands in their coordination spheres other than zeolite lattice oxygen atoms), the more energetically favorable sites are within a 6-membered ring. However, with the presence of various adsorbates, the energy difference between 6- and 8-membered ring locations greatly diminishes. Specifically, Cu2+ ions are substantially stabilized by -OH ligands (as [CuII(OH)]+), making the extra-framework sites in an 8-membered ring energetically more favorable than 6-membered ring sites. Under fully dehydrated high vacuum conditions with different Si/Al and Cu/Al ratios, three chemisorbed NO species coexist upon exposure of NO to Cu/SSZ-13: NO+, Cu2+-NO and Cu+-NO. The relative signal intensities for these bands vary greatly with Si/Al ratios. The vibrational frequency of chemisorbed NO was found to be very sensitive to the location of Cu2+ ions. On the one hand, with the aid from DFT calculations, the nature for these vibrations can be assigned in detail. On the other hand, the relative intensities for various Cu2+-NO species provide a good measure of the nature of Cu2+ ions as functions of Si/Al and Cu/Al ratios and the presence of humidity. These new findings cast doubt on the generally accepted proposal that only Cu2+ ions located in 6-membered rings are catalytically active for NH3-SCR.

  11. UV resonance Raman and DFT studies of arginine side chains in peptides: insights into arginine hydration.

    PubMed

    Hong, Zhenmin; Wert, Jonathan; Asher, Sanford A

    2013-06-20

    We examined the UV resonance Raman (UVRR) spectra of four models of the Arg side chain, guanidinium (Gdn), ethylguanidinium (EG), arginine (Arg), and Ac-Arg-OMe (AAO) in H2O and D2O, in order to identify spectral markers that report on the environment of the Arg side chain. To elucidate the resonance Raman enhancement mechanism of the Arg side chain, we used density functional theory (DFT) to calculate the equilibrium geometries of the electronic ground state and the first excited state. We determined the vibrational mode frequencies of the ground state and the first derivative of the first electronic excited state potential energy with respect to each vibrational normal mode of the electronic ground state at the electronic ground state equilibrium geometry. The DFT calculations and the potential energy distributions reveal that, in addition to the Gdn group C-N stretching vibrations, the C-N bond stretching vibration of the Gdn group-methylene linkage is also strongly resonance-enhanced in EG, Arg, and AAO. From the UVRR spectra, we find that the Raman cross section and frequency of the ~1170 cm(-1) vibration of the Arg side chain depends on its hydration state and can be used to determine the hydration state of the Arg side chain in peptides and proteins. We examined the hydration of the Arg side chain in two polyAla peptides and found that in the α-helical conformation the Arg side chain in the AEP peptide (sequence: A9RA3EA4RA2) is less hydrated than that in the AP peptide (sequence: A8RA4RA4RA2). PMID:23676082

  12. UV Resonance Raman and DFT Studies of Arginine Side Chains in Peptides: Insights into Arginine Hydration

    PubMed Central

    Hong, Zhenmin; Wert, Jonathan; Asher, Sanford A.

    2013-01-01

    We examined the UV resonance Raman (UVRR) spectra of four models of the arg side chain, guanidinium (gdn), ethylguanidinium (EG), arginine (arg) and Ac-arg-OMe (AAO) in H2O and D2O, in order to identify spectral markers that report on the environment of the arg side chain. To elucidate the resonance Raman enhancement mechanism of the arg side chain, we used DFT to calculate the equilibrium geometries of the electronic ground state and the first excited state. We determined the vibrational mode frequencies of the ground state and the first derivative of the first electronic excited state potential energy with respect to each vibrational normal mode of the electronic ground state at the electronic ground state equilibrium geometry. The DFT calculations and the potential energy distributions reveal that, in addition to the gdn group C-N stretching vibrations, the C-N bond stretching vibration of the gdn group-methylene linkage is also strongly resonance enhanced in EG, arg and AAO. From the UVRR spectra, we find that the Raman cross section and frequency of the ~1170 cm−1 vibration of the arg side chain depends on its hydration state and can be used to determine the hydration state of the arg side chain in peptides and proteins. We examined the hydration of the arg side chain in two polyala peptides and found that in the α-helical conformation the arg side chain in the AEP peptide (sequence: A9RA3EA4RA2) is less hydrated than that in the AP peptide (sequence: A8RA4RA4RA2). PMID:23676082

  13. Ab initio and DFT study of 31P-NMR chemical shifts of sphingomyelin and dihydrosphingomyelin lipid molecule

    NASA Astrophysics Data System (ADS)

    Sugimori, K.; Kawabe, H.; Nagao, H.; Nishikawa, K.

    One of the phospholipids, sphingomyelin (SM, N-acyl-sphingosine-1-phosphorylcholine) is the most abundant component of mammalian membranes in brain, nervous tissues, and human ocular lens. It plays an important role for apoptosis, aging, and signal transduction. Recently, Yappert and coworkers have shown that human lens sphingomyelin and its hydrogenated derivative, dihydrosphingomyelin (DHSM) are interacted with Ca2+ ions to develop human cataracts. Previously, we have investigated conformational differences between an isolated SM/DHSM molecule and Ca2+-coordinated form by using density functional theory (DFT) for geometry optimization and normal mode analysis. As a result, one of stable conformers of SMs has a hydrogen bonding between hydroxyl group and phosphate group, whereas another conformer has a hydrogen bonding between hydroxyl and phosphate amide group. In this study, 31P-Nuclear Magnetic Resonance (NMR) shielding constants of the obtained conformers are investigated by using ab initio and DFT with NMR-gauge invariant atomic orbitals (NMR-GIAO) calculations. The experimental 31P-NMR chemical shifts of SMs and DHSMs have significant small value around 0.1 ppm. We consider the relative conformational changes between SMs and DHSMs affect the slight deviations of 31P-NMR chemical shifts, and discuss intramolecular hydrogen bondings and the solvent effect in relation to NMR experimental reference.

  14. A DFT study of 2-aminopurine-containing dinucleotides: prediction of stacked conformations with B-DNA structure.

    PubMed

    Smith, Darren A; Holroyd, Leo F; van Mourik, Tanja; Jones, Anita C

    2016-05-25

    The fluorescence properties of dinucleotides incorporating 2-aminopurine (2AP) suggest that the simplest oligonucleotides adopt conformations similar to those found in duplex DNA. However, there is a lack of structural data for these systems. We report a density functional theory (DFT) study of the structures of 2AP-containing dinucleotides (deoxydinucleoside monophosphates), including full geometry optimisation of the sugar-phosphate backbone. Our DFT calculations employ the M06-2X functional for reliable treatment of dispersion interactions and include implicit aqueous solvation. Dinucleotides with 2AP in the 5'-position and each of the natural bases in the 3'-position are examined, together with the analogous 5'-adenine-containing systems. Computed structures are compared in detail with typical B-DNA base-step parameters, backbone torsional angles and sugar pucker, derived from crystallographic data. We find that 2AP-containing dinucleotides adopt structures that closely conform to B-DNA in all characteristic parameters. The structures of 2AP-containing dinucleotides closely resemble those of their adenine-containing counterparts, demonstrating the fidelity of 2AP as a mimic of the natural base. As a first step towards exploring the conformational heterogeneity of dinucleotides, we also characterise an imperfectly stacked conformation and one in which the bases are completely unstacked. PMID:27186599

  15. UV-Vis spectroscopic study and DFT calculation on the solvent effect of trimethoprim in neat solvents and aqueous mixtures

    NASA Astrophysics Data System (ADS)

    Almandoz, M. C.; Sancho, M. I.; Duchowicz, P. R.; Blanco, S. E.

    2014-08-01

    The solvatochromic behavior of trimethoprim (TMP) was analyzed using UV-Vis spectroscopy and DFT methods in neat and binary aqueous solvent mixtures. The effects of solvent dipolarity/polarizability and solvent-solute hydrogen bonding interactions on the absorption maxima were evaluated by means of the linear solvation energy relationship concept of Kamlet and Taft. This analysis indicated that both interactions play an important role in the position of the absorption maxima in neat solvents. The simulated absorption spectra of TMP and TMP:(solvent)n complexes in ACN and H2O using TD-DFT methods were in agreement with the experimental ones. Binary aqueous mixtures containing as co-solvents DMSO, ACN and EtOH were studied. Preferential solvation was detected as a nonideal behavior of the wavenumber curve respective to the analytical mole fraction of co-solvent in all binary systems. TMP molecules were preferentially solvated by the organic solvent over the whole composition range. Index of preferential solvation, as well as the influence of solvent parameters were calculated as a function of solvent composition.

  16. Molecular structure of 2-chloromethyl-1H-benzimidazole hydrochloride: Single crystal, spectral, biological studies, and DFT calculations

    NASA Astrophysics Data System (ADS)

    Abdel Ghani, Nour T.; Mansour, Ahmed M.

    2012-02-01

    In the present work, structural studies on 2-chloromethyl-1H-benzimidazole hydrochloride have been performed extensively by X-ray crystallography, 1H NMR, FT-IR, UV/vis, and elemental analysis. The title compound crystallizes in a monoclinic space group P21/c with a = 7.1982 (3) Å, b = 9.4513 (5) Å, c = 14.0485 (7) Å and β = 102.440 (3)° forming an infinite chain structure parallel to " b" axis through the intermolecular hydrogen bond. Optimized geometrical structure, harmonic vibrational frequencies, natural bonding orbital (NBO) and frontier molecular orbitals (FMO) were obtained by DFT/B3LYP method combined with 6-31G(d) basis set. TD-DFT calculations help to assign the electronic transitions. The 1H NMR chemical shifts were computed at the B3LYP/6-311 + G(2d,p) level of theory in different solvents by applying GIAO method using the polarizable continuum model (PCM). The title compound was screened for its antibacterial activity referring to Tetracycline as a standard antibacterial agent.

  17. Ab initio DFT study of bisphosphonate derivatives as a drug for inhibition of cancer: NMR and NQR parameters.

    PubMed

    Aghabozorg, Hussein; Sohrabi, Beheshteh; Mashkouri, Sara; Aghabozorg, Hamid Reza

    2012-03-01

    DFT computations were carried out to characterize the (17)Oand (2)H electric field gradient, EFG, in various bisphosphonate derivatives. The computations were performed at the B3LYP level with 6-311++G (d,P) standard basis set. Calculated EFG tensors were used to determine the (17)O and (2)H nuclear quadrupole coupling constant, χ and asymmetry parameter, η. For better understanding of the bonding and electronic structure of bisphosphonates, isotropic and anisotropic NMR chemical shieldings were calculated for the (13)C, (17)O and (31)P nuclei using GIAO method for the optimized structure of intermediate bisphosphonates at B3LYP level of theory using 6-311++G (d, p) basis set. The results showed that various substituents have a strong effect on the nuclear quadrupole resonance (NQR) parameters (χ, η) of (17)O in contrast with (2)H NQR parameters. The NMR and NQR parameters were studied in order to find the correlation between electronic structure and the activity of the desired bisphosphonates. In addition, the effect of substitutions on the bisphosphonates polarity was investigated. Molecular polarity was determined via the DFT calculated dipole moment vectors and the results showed that substitution of bromine atom on the ring would increase the activity of bisphosphonates. PMID:21633790

  18. Study of molecular structure, vibrational, electronic and NMR spectra of oncocalyxone A using DFT and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Joshi, Bhawani Datt; Srivastava, Anubha; Honorato, Sara Braga; Tandon, Poonam; Pessoa, Otília Deusdênia Loiola; Fechine, Pierre Basílio Almeida; Ayala, Alejandro Pedro

    2013-09-01

    Oncocalyxone A (C17H18O5) is the major secondary metabolite isolated from ethanol extract from the heartwood of Auxemma oncocalyx Taub popularly known as “pau branco”. Oncocalyxone A (Onco A) has many pharmaceutical uses such as: antitumor, analgesic, antioxidant and causative of inhibition of platelet activation. We have performed the optimized geometry, total energy, conformational study, molecular electrostatic potential mapping, frontier orbital energy gap and vibrational frequencies of Onco A employing ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d, p) basis set. Stability of the molecule arising from hyperconjugative interactions and/or charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV-vis spectrum of the compound was recorded in DMSO and MeOH solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using IEF-PCM and 6-31G basis set. The 13C NMR chemical shifts have been calculated with the B3LYP/6-311++G(d, p) basis set and compared with the experimental values. These methods have been used as tools for structural characterization of Onco A.

  19. Electron Transport and Nonlinear Optical Properties of Substituted Aryldimesityl Boranes: A DFT Study

    PubMed Central

    Pandith, Altaf Hussain; Islam, Nasarul

    2014-01-01

    A comprehensive theoretical study was carried out on a series of aryldimesityl borane (DMB) derivatives using Density Functional theory. Optimized geometries and electronic parameters like electron affinity, reorganization energy, frontiers molecular contours, polarizability and hyperpolarizability have been calculated by employing B3PW91/6-311++G (d, p) level of theory. Our results show that the Hammett function and geometrical parameters correlates well with the reorganization energies and hyperpolarizability for the series of DMB derivatives studied in this work. The orbital energy study reveals that the electron releasing substituents increase the LUMO energies and electron withdrawing substituents decrease the LUMO energies, reflecting the electron transport character of aryldimesityl borane derivatives. From frontier molecular orbitals diagram it is evident that mesityl rings act as the donor, while the phenylene and Boron atom appear as acceptors in these systems. The calculated hyperpolarizability of secondary amine derivative of DMB is 40 times higher than DMB (1). The electronic excitation contributions to the hyperpolarizability studied by using TDDFT calculation shows that hyperpolarizability correlates well with dipole moment in ground and excited state and excitation energy in terms of the two-level model. Thus the results of these calculations can be helpful in designing the DMB derivatives for efficient electron transport and nonlinear optical material by appropriate substitution with electron releasing or withdrawing substituents on phenyl ring of DMB system. PMID:25479382

  20. Experimental and theoretical spectroscopic and structural study of A-ring substituted camptothecins

    NASA Astrophysics Data System (ADS)

    Ivanova, Bojidarka B.; Spiteller, Michael

    2012-03-01

    The molecular architecture design and physical properties of seven camptothecin (CPT) alkaloids, structurally related to irinotecan (CPT-11), substituted with the cyclic bulk N-aliphatic substituents at A-ring as well as their different protonated forms were studied. The correlation between the molecular geometry and physical properties of the neutral lactone form and different possible cationic forms was elucidated, using the electronic absorptions (EAs), circular dichroic (CD) and Raman spectroscopy within the far-IR region as well as electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry and nuclear magnetic resonance methods. The electronic structures, and properties of the neutral CPTs, their mono- and diprotonated forms as well as molecular ion fragments, obtained by the mass spectrometric data are predicted theoretically using the DFT method.

  1. Theoretical study on the mechanism and kinetics of acetaldehyde and hydroperoxyl radical: An important atmospheric reaction

    NASA Astrophysics Data System (ADS)

    Farnia, Solaleh; Vahedpour, Morteza; Abedi, Mostafa; Farrokhpour, Hossein

    2013-09-01

    A systematic theoretical study was performed on the mechanism and kinetics of the atmospheric reaction of acetaldehyde (CH3CHO) and hydroperoxyl radical (HO2) in the gas phase. The DFT-B3LYP/6-311++G(3df,3pd) and CCSD(T)/6-311++G(d,p) methods were employed for calculations. Based on the calculations, this reaction leads to four different products through radical addition and hydrogen abstraction mechanisms which are very important in atmospheric and combustion chemistry. The favorable reaction paths begin with α-hydroxyethylperoxy radical, CH3CH(OO)OH, in a exothermic process and finally leads to the product P1 (CH3COOH + OH). The overall rate constants for favorite reaction paths have been calculated at different temperatures (200-2500 K).

  2. Protonation effects on the UV/Vis absorption spectra of imatinib: A theoretical and experimental study

    NASA Astrophysics Data System (ADS)

    Grante, Ilze; Actins, Andris; Orola, Liana

    2014-08-01

    An experimental and theoretical investigation of protonation effects on the UV/Vis absorption spectra of imatinib showed systematic changes of absorption depending on the pH, and a new absorption band appeared below pH 2. These changes in the UV/Vis absorption spectra were interpreted using quantum chemical calculations. The geometry of various imatinib cations in the gas phase and in ethanol solution was optimized with the DFT/B3LYP method. The resultant geometries were compared to the experimentally determined crystal structures of imatinib salts. The semi-empirical ZINDO-CI method was employed to calculate the absorption lines and electronic transitions. Our study suggests that the formation of the extra near-UV absorption band resulted from an increase of imatinib trication concentration in the solution, while the rapid increase of the first absorption maximum could be attributed to both the formation of imatinib trication and tetracation.

  3. Vibrational spectra of palladium 5-nitrofuryl thiosemicarbazone complexes: Experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Gambino, Dinorah; Otero, Lucía; Vieites, Marisol; Boiani, Mariana; González, Mercedes; Baran, Enrique J.; Cerecetto, Hugo

    2007-10-01

    The vibrational spectroscopic behavior of a series of 16 palladium(II) complexes with 8 bioactive nitrofuran containing thiosemicarbazones as ligands has been studied in the solid state. The IR and Raman spectra of these complexes and the free nitrofuran thiosemicarbazone ligands were recorded and analyzed. Experimental spectra were satisfactorily described by density functional theory (DFT) calculations. The combination of experimental and theoretical methods allowed us to perform the characterization of the main vibrations that show the mode of coordination of the thiosemicarbazone moiety to palladium even though these vibration bands are located in spectral regions showing a complicated pattern due to the presence of vibrations of the nitrofuran moiety and combination modes involving furan vibrations. A characteristic vibrational spectroscopic pattern has been defined for Pd(II) 5-nitrofuryl thiosemicarbazone complexes. This systematic knowledge may be useful for the analysis of the spectroscopic behavior of other coordination compounds holding the 5-nitrofuran thiosemicarbazone moiety.

  4. Theoretical molecular studies of astrophysical interest

    NASA Technical Reports Server (NTRS)

    Flynn, George

    1991-01-01

    When work under this grant began in 1974 there was a great need for state-to-state collisional excitation rates for interstellar molecules observed by radio astronomers. These were required to interpret observed line intensities in terms of local temperatures and densities, but, owing to lack of experimental or theoretical values, estimates then being used for this purpose ranged over several orders of magnitude. A problem of particular interest was collisional excitation of formaldehyde; Townes and Cheung had suggested that the relative size of different state-to-state rates (propensity rules) was responsible for the anomalous absorption observed for this species. We believed that numerical molecular scattering techniques (in particular the close coupling or coupled channel method) could be used to obtain accurate results, and that these would be computationally feasible since only a few molecular rotational levels are populated at the low temperatures thought to prevail in the observed regions. Such calculations also require detailed knowledge of the intermolecular forces, but we thought that those could also be obtained with sufficient accuracy by theoretical (quantum chemical) techniques. Others, notably Roy Gordon at Harvard, had made progress in solving the molecular scattering equations, generally using semi-empirical intermolecular potentials. Work done under this grant generalized Gordon's scattering code, and introduced the use of theoretical interaction potentials obtained by solving the molecular Schroedinger equation. Earlier work had considered only the excitation of a diatomic molecule by collisions with an atom, and we extended the formalism to include excitation of more general molecular rotors (e.g., H2CO, NH2, and H2O) and also collisions of two rotors (e.g., H2-H2).

  5. Recent Theoretical Studies On Excitation and Recombination

    NASA Technical Reports Server (NTRS)

    Pradhan, Anil K.

    2000-01-01

    New advances in the theoretical treatment of atomic processes in plasmas are described. These enable not only an integrated, unified, and self-consistent treatment of important radiative and collisional processes, but also large-scale computation of atomic data with high accuracy. An extension of the R-matrix work, from excitation and photoionization to electron-ion recombination, includes a unified method that subsumes both the radiative and the di-electronic recombination processes in an ab initio manner. The extensive collisional calculations for iron and iron-peak elements under the Iron Project are also discussed.

  6. A quantum theoretical study of polyimides

    NASA Technical Reports Server (NTRS)

    Burke, Luke A.

    1987-01-01

    One of the most important contributions of theoretical chemistry is the correct prediction of properties of materials before any costly experimental work begins. This is especially true in the field of electrically conducting polymers. Development of the Valence Effective Hamiltonian (VEH) technique for the calculation of the band structure of polymers was initiated. The necessary VEH potentials were developed for the sulfur and oxygen atoms within the particular molecular environments and the explanation explored for the success of this approximate method in predicting the optical properties of conducting polymers.

  7. Synthesis, characterization, investigation of biological activity and theoretical studies of hydrazone compounds containing choloroacetyl group

    NASA Astrophysics Data System (ADS)

    Cukurovali, Alaaddin; Yilmaz, Engin

    2014-10-01

    In this study, three new hydrazide-hydrazone derivative compounds which contain choloroacetyl group have been synthesized and characterized. In the characterization, spectral techniques such as IR, 1H NMR, 13C NMR and UV-Vis spectroscopy techniques were used. Antibacterial effects of the synthesized compounds were investigated against Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853. In the theoretical calculations Gaussian 09 software was used with the DFT/6-311+(d,p) basis set. Experimental X-ray analysis of compounds has not been studied. Theoretical bond lengths of synthesized compounds were compared with experimental bond lengths of a similar compound. Theoretical and experimental bond lengths are in good agreement with R2: 0.896, 0.899 and 0.900 for compounds 1, 2, and 3, respectively. For antibacterial activity, the most effective one was found to be N‧-(4-bromobenzylidene)-2-chloro-N-(4-(3-methyl-3-phenylcyclobutyl)-thiazol-2-yl) acetohydrazide against P.aeroginaosa ATTC 27853, among the studied compounds.

  8. An experimental and theoretical investigation of free Oxazole in conjunction with the DFT analysis of Oxazole⋯(H2O)n complexes.

    PubMed

    Yurdakul, Şenay; Badoğlu, Serdar; Özkurt, Lütfiye

    2016-06-01

    The mid-IR spectrum of Oxazole (Oxa) is recorded. This spectrum is interpreted with the help of B3LYP/6-311++G(d,p) calculations and potential energy distribution (PED) analysis. The experimental spectrum is concordant with the theoretical data. Geometrical parameters and the atomic charges are also theoretically obtained and presented. Solvent effects on the geometrical parameters, vibrational frequencies, and electronic properties of Oxa are analyzed theoretically in chloroform, ethanol, and water. Besides, hydrogen bonded Oxa⋯(H2O)n (n=1, 2,…, 10) complexes are investigated within the PCM solvation model. It is found that the interaction energies in Oxa⋯(H2O)n complexes are influenced by the number of water molecules, and by the arrangement of water molecules. PMID:26978786

  9. An experimental and theoretical investigation of free Oxazole in conjunction with the DFT analysis of Oxazole ⋯(H2O)n complexes

    NASA Astrophysics Data System (ADS)

    Yurdakul, Şenay; Badoğlu, Serdar; Özkurt, Lütfiye

    2016-06-01

    The mid-IR spectrum of Oxazole (Oxa) is recorded. This spectrum is interpreted with the help of B3LYP/6-311 ++G(d,p) calculations and potential energy distribution (PED) analysis. The experimental spectrum is concordant with the theoretical data. Geometrical parameters and the atomic charges are also theoretically obtained and presented. Solvent effects on the geometrical parameters, vibrational frequencies, and electronic properties of Oxa are analyzed theoretically in chloroform, ethanol, and water. Besides, hydrogen bonded Oxa ⋯(H2O)n (n = 1, 2,…, 10) complexes are investigated within the PCM solvation model. It is found that the interaction energies in Oxa ⋯(H2O)n complexes are influenced by the number of water molecules, and by the arrangement of water molecules.

  10. Electronic and geometrical properties of monoatomic and diatomic 2D honeycomb lattices. A DFT study

    NASA Astrophysics Data System (ADS)

    Rojas, Ángela; Rey, Rafael; Fonseca, Karen; Grupo de Óptica e Información Cuántica Team

    Since the discovery of graphene by Geim and Novoselov at 2004, several analogous systems have been theoretically and experimentally studied, due to their technological interest. Both monoatomic lattices, such as silicine and germanene, and diatomic lattices (h-GaAs and h-GaN) have been studied. Using Density Functional Theory we obtain and confirm the chemical stability of these hexagonal 2D systems through the total energy curves as a function of interatomic distance. Unlike graphene, silicine and germanene, gapless materials, h-GaAs and h-GaN exhibit electronic gaps, different from that of the bulk, which could be interesting for the industry. On the other hand, the ab initio band structure calculations for graphene, silicene and germanene show a non-circular cross section around K points, at variance with the prediction of usual Tight-binding models. In fact, we have found that Dirac cones display a dihedral group symmetry. This implies that Fermi speed can change up to 30 % due to the orientation of the wave vector, for both electrons and holes. Traditional analytic studies use the Dirac equation for the electron dynamics at low energies. However, this equation assumes an isotropic, homogeneous and uniform space. Authors would like to thank the División de Investigación Sede Bogotá for their financial support at Universidad Nacional de Colombia. A. M. Rojas-Cuervo would also like to thank the Colciencias, Colombia.

  11. Electronic structure of copper phthalocyanine: An experimental and theoretical study of occupied and unoccupied levels

    SciTech Connect

    Evangelista, Fabrizio; Carravetta, Vincenzo; Stefani, Giovanni; Jansik, Branislav; Alagia, Michele; Stranges, Stefano; Ruocco, Alessandro

    2007-03-28

    An experimental and theoretical study of the electronic structure of copper phthalocyanine (CuPc) molecule is presented. We performed x-ray photoemission spectroscopy (XPS) and photoabsorption [x-ray absorption near-edge structure (XANES)] gas phase experiments and we compared the results with self-consistent field, density functional theory (DFT), and static-exchange theoretical calculations. In addition, ultraviolet photoelectron spectra (UPS) allowed disentangling several outer molecular orbitals. A detailed study of the two highest occupied orbitals (having a{sub 1u} and b{sub 1g} symmetries) is presented: the high energy resolution available for UPS measurements allowed resolving an extra feature assigned to vibrational stretching in the pyrrole rings. This observation, together with the computed DFT electron density distributions of the outer valence orbitals, suggests that the a{sub 1u} orbital (the highest occupied molecular orbital) is mainly localized on the carbon atoms of pyrrole rings and it is doubly occupied, while the b{sub 1g} orbital, singly occupied, is mainly localized on the Cu atom. Ab initio calculations of XPS and XANES spectra at carbon K edge of CuPc are also presented. The comparison between experiment and theory revealed that, in spite of being formally not equivalent, carbon atoms of the benzene rings experience a similar electronic environment. Carbon K-edge absorption spectra were interpreted in terms of different contributions coming from chemically shifted C 1s orbitals of the nonequivalent carbon atoms on the inner ring of the molecule formed by the sequence of CN bonds and on the benzene rings, respectively, and also in terms of different electronic distributions of the excited lowest unoccupied molecular orbital (LUMO) and LUMO+1. In particular, the degenerate LUMO appears to be mostly localized on the inner pyrrole ring.

  12. Study of gas-phase O-H bond dissociation enthalpies and ionization potentials of substituted phenols - Applicability of ab initio and DFT/B3LYP methods

    NASA Astrophysics Data System (ADS)

    Klein, Erik; Lukeš, Vladimír

    2006-11-01

    In this paper, the study of phenol and 37 compounds representing various ortho-, para-, and meta-substituted phenols is presented. Molecules and their radical structures were studied using ab initio methods with inclusion of correlation energy and DFT in order to calculate the O-H bond dissociation enthalpies (BDEs) and vertical ionization potentials (IPs). Calculated BDEs and IPs were compared with available experimental values to ascertain the suitability of used methods, especially for the description of the substituent induced changes in BDE and IP. MP2, MP3, and MP4 methods do not give reliable results, since they significantly underestimate substituent induced changes in BDE and do not reflect distinct effect of substituents related to para and meta position correctly. DFT/B3LYP method reflects the effect of substituents on BDE satisfactorily, though ΔBDEs are in narrower range than experimental values. BDE of phenol was calculated also using CCSD(T) method in various basis sets. Both, DFT and HF methods describe the effect of substituents on IP identically. However, DFT considerably underestimates individual values. HF method gives IPs in very good agreement with experimental data. Obtained results show that dependences of BDEs and IPs on Hammett constants of the substituents are linear. Linearity of DFT BDE vs. IP dependence is even better than the dependences on Hammett constants and obtained equations allow estimating of O-H BDEs of meta- and para-substituted phenols from calculated IPs.

  13. Vibrational spectroscopic study, charge transfer interaction and nonlinear optical properties of L-asparaginium picrate: A density functional theoretical approach

    NASA Astrophysics Data System (ADS)

    Elleuch, Nabil; Amamou, Walid; Ben Ahmed, Ali; Abid, Younes; Feki, Habib

    2014-07-01

    Single crystals of L-asparaginium picrate (LASP) were grown by slow evaporation technique at room temperature and were the subject of an X-ray powder diffraction study to confirm the crystalline nature of the synthesized compound. FT-IR and Raman spectra were recorded and analyzed with the aid of the density functional theory (DFT) calculations in order to make a suitable assignment of the observed bands. The optimum molecular geometry, normal mode wavenumbers, infrared and Raman intensities and the first hyperpolarizability were investigated with the help of B3LYP method using 6-31G(d) basis set. The theoretical FT-IR and Raman spectra of LASP were simulated and compared with the experimental data. A good agreement was shown and a reliable vibrational assignment was made. Natural bond orbital (NBO) analysis was carried out to demonstrate the various inter and intramolecular interactions that are responsible for the stabilization of the title compound leading to high NLO activity. A study on the electronic properties was performed by time-dependent DFT (TD-DFT) approach. The lowering in the HOMO and LUMO energy gap explains the eventual charge transfer interactions that take place within the molecules.

  14. Mesomorphic, micro-Raman and DFT studies of new calamitic liquid crystals; methyl 4-[4-(4-alkoxy benzoyloxy)benzylideneamino]benzoates

    NASA Astrophysics Data System (ADS)

    Nandi, Rajib; Singh, Hemant Kumar; Singh, Sachin Kumar; Singh, Bachcha; Singh, Ranjan K.

    2014-07-01

    The mesomorphic properties of newly synthesized homologous series of calamitic liquid crystals; methyl 4-[4-(4-alkoxy benzoyloxy)benzylideneamino]benzoates, H2n+1CnOC6H4COOC6H4C(H)dbnd N C6H4COOCH3; n = 6, 8, 10, 12, 14, 16 (MABBAB-n) containing ester and Schiff base groups as linker have been studied by temperature dependent micro-Raman study, differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). All members of this series exhibit enantiotropic smectic A (SmA) mesophase with oily streak and focal conic textures. Analyses of Raman marker bands of phenyl rings, Schiff base and ester groups of MABBAB-10 confirm the phase transitions. The Raman study also gives an evidence of breaking of weak intermolecular hydrogen bonds associated with ester groups and formation of new hydrogen bonds through Cdbnd N bond at Cr → SmA phase transition. The monomer and dimer were optimized and vibrational assignment of MABBAB-10 was also done with density functional theoretical (DFT) technique to understand the experimental results.

  15. Electronic and magnetic properties of silicon supported organometallic molecular wires: a density functional theory (DFT) study.

    PubMed

    Liu, Xia; Tan, Yingzi; Li, Xiuling; Wu, Xiaojun; Pei, Yong

    2015-08-28

    The electronic and magnetic properties of transition metal (TM = Sc, Ti, V, Cr and Mn) atom incorporated single and double one-dimensional (1D) styrene molecular wires confined on the hydrogen-terminated Si(100) surface are explored for the first time by means of spin-polarized density functional theory, denoted as Si-[TM(styrene)]. It is unveiled that TM atoms bind asymmetrically to the adjacent phenyl rings, which leads to novel electronic and magnetic properties in stark contrast to the well-studied gas phase TM-benzene molecular wires. Si-[Mn(styrene)]∞ and Si-[Cr(styrene)]∞ single molecular wires (SMWs) are a ferromagnetic semiconductor and half metal, respectively. Creation of H-atom defects on the silicon surface can introduce an impurity metallic band, which leads to novel half-metallic magnetism of a Si-[Mn(styrene)]∞ system. Moreover, double molecular wires (DMWs) containing two identical or hetero SMWs are theoretically designed. The [Mn(styrene)]∞-[Cr(styrene)]∞ DMW exhibits half-metallic magnetism where the spin-up and spin-down channels are contributed by two single molecular wires. Finally, we demonstrate that introducing a TM-defect may significantly affect the electronic structure and magnetic properties of molecular wires. These studies provide new insights into the structure and properties of surface supported 1-D sandwiched molecular wires and may inspire the future experimental synthesis of substrate confined organometallic sandwiched molecular wires. PMID:26219748

  16. Interaction of water molecules with hexagonal 2D systems. A DFT study

    NASA Astrophysics Data System (ADS)

    Rojas, Ángela; Rey, Rafael

    Over the years water sources have been contaminated with many chemical agents, becoming issues that affect health of the world population. The advances of the nanoscience and nanotechnology in the development new materials constitute an alternative for design molecular filters with great efficiencies and low cost for water treatment and purification. In the nanoscale, the process of filtration or separation of inorganic and organic pollutants from water requires to study interactions of these atoms or molecules with different nano-materials. Specifically, it is necessary to understand the role of these interactions in physical and chemical properties of the nano-materials. In this work, the main interest is to do a theoretical study of interaction between water molecules and 2D graphene-like systems, such as silicene (h-Si) or germanene (h-Ge). Using Density Functional Theory we calculate total energy curves as function of separation between of water molecules and 2D systems. Different spatial configurations of water molecules relative to 2D systems are considered. Structural relaxation effects and changes of electronic charge density also are reported. Universidad Nacional de Colombia.

  17. The performance of selected semi-empirical and DFT methods in studying C60 fullerene derivatives

    NASA Astrophysics Data System (ADS)

    Sikorska, Celina; Puzyn, Tomasz

    2015-11-01

    The capability of reproducing the open circuit voltages (V oc) of 15 representative C60 fullerene derivatives was tested using the selected quantum mechanical methods (B3LYP, PM6, and PM7) together with the two one-electron basis sets. Certain theoretical treatments (e.g. PM6) were found to be satisfactory for preliminary estimates of the open circuit voltages (V oc), whereas the use of the B3LYP/6-31G(d) approach has been proven to assure highly accurate results. We also examined the structural similarity of 19 fullerene derivatives by employing principle component analysis (PCA). In order to express the structural features of the studied compounds we used molecular descriptors calculated with semi-empirical (PM6 and PM7) and density functional (B3LYP/6-31G(d)) methods separately. In performing PCA, we noticed that semi-empirical methods (i.e. PM6 and PM7) seem satisfactory for molecules, in which one can distinguish the aromatic and the aliphatic parts in the cyclopropane ring of PCBM (phenyl-C61-buteric acid methyl ester) and they significantly overestimate the energy of the highest occupied molecular orbital (E HOMO). The use of the B3LYP functional, however, is recommended for studying methanofullerenes, which closely resemble the structure of PCBM, and for their modifications.

  18. Theoretical and experimental NMR studies on muscimol from fly agaric mushroom (Amanita muscaria)

    NASA Astrophysics Data System (ADS)

    Kupka, Teobald; Wieczorek, Piotr P.

    2016-01-01

    In this article we report results of combined theoretical and experimental NMR studies on muscimol, the bioactive alkaloid from fly agaric mushroom (Amanita muscaria). The assignment of 1H and 13C NMR spectra of muscimol in DMSO-d6 was supported by additional two-dimensional heteronuclear correlated spectra (2D NMR) and gauge independent atomic orbital (GIAO) NMR calculations using density functional theory (DFT). The effect of solvent in theoretical calculations was included via polarized continuum model (PCM) and the hybrid three-parameter B3LYP density functional in combination with 6-311++G(3df,2pd) basis set enabled calculation of reliable structures of non-ionized (neutral) molecule and its NH and zwitterionic forms in the gas phase, chloroform, DMSO and water. GIAO NMR calculations, using equilibrium and rovibrationally averaged geometry, at B3LYP/6-31G* and B3LYP/aug-cc-pVTZ-J levels of theory provided muscimol nuclear magnetic shieldings. The theoretical proton and carbon chemical shifts were critically compared with experimental NMR spectra measured in DMSO. Our results provide useful information on its structure in solution. We believe that such data could improve the understanding of basic features of muscimol at atomistic level and provide another tool in studies related to GABA analogs.

  19. Theoretical and experimental NMR studies on muscimol from fly agaric mushroom (Amanita muscaria).

    PubMed

    Kupka, Teobald; Wieczorek, Piotr P

    2016-01-15

    In this article we report results of combined theoretical and experimental NMR studies on muscimol, the bioactive alkaloid from fly agaric mushroom (Amanita muscaria). The assignment of (1)H and (13)C NMR spectra of muscimol in DMSO-d6 was supported by additional two-dimensional heteronuclear correlated spectra (2D NMR) and gauge independent atomic orbital (GIAO) NMR calculations using density functional theory (DFT). The effect of solvent in theoretical calculations was included via polarized continuum model (PCM) and the hybrid three-parameter B3LYP density functional in combination with 6-311++G(3df,2pd) basis set enabled calculation of reliable structures of non-ionized (neutral) molecule and its NH and zwitterionic forms in the gas phase, chloroform, DMSO and water. GIAO NMR calculations, using equilibrium and rovibrationally averaged geometry, at B3LYP/6-31G* and B3LYP/aug-cc-pVTZ-J levels of theory provided muscimol nuclear magnetic shieldings. The theoretical proton and carbon chemical shifts were critically compared with experimental NMR spectra measured in DMSO. Our results provide useful information on its structure in solution. We believe that such data could improve the understanding of basic features of muscimol at atomistic level and provide another tool in studies related to GABA analogs. PMID:26312739

  20. Theoretical study of adsorption and dissociation of NH3 on pentanuclear Fe(111) surface

    NASA Astrophysics Data System (ADS)

    Purwiandono, G.; Triyono; Wijaya, K.

    2016-02-01

    Theoretical study regarding the adsorption and dissociation of NH3 molecule on Fe(111) surface has been carried out. The method used was DFT-B3LYP, and the basis sets used were ECP and 6-311G**. This research aimed at giving the theoretical understanding of adsorption and dissociation of NH3 molecule on Fe(111) surface. The adsorption and dissociation were studied based on the energetic parameter, bond length, electron population, vibration and orbital interaction. The result of theoretical calculation revealed that the on top position is the interaction position with the minimum energy for the adsorption of NH3 molecule on Fe(111) surface. The analysis of electron population of the two composing molecular orbitals indicated that the transfer of electron has an important role in the mechanism of adsorption. The visualization of molecular orbital showed that the transfer of electron occurred in the electron pairs of the interacting orbital. Relating to the adsorption mechanism and the overlapping of interaction orbitals, NH3 molecule provides the Highest Occupied Molecular Orbital (HOMO) as the interaction pair for the Lowest Unoccupied Molecular Orbital (LUMO) on Fe surface. The insignificant difference between the oxidation state of N and H atoms as well as the higher hemolytic N-H bond dissociation energy (compared to heterolytic dissociation) cause the adsorption mechanism of NH3 on Fe(111) model to occur through homolytic-dissociative chemisorption.

  1. Charge neutralization as studied experimentally and theoretically

    NASA Technical Reports Server (NTRS)

    Linson, L. M.

    1982-01-01

    Problems regarding an isolated sphere which emits negative charge are considered. Such a sphere could charge up to large potentials which would inhibit the electron beam from leaving the vicinity of the body. In order to avoid charging to high potentials, a vehicle must attract a return current equal to the emitted current. The present investigation is concerned with theoretical models of some processes believed to be important for the vehicle neutralization problem under various conditions. Attention is given to general time-scale considerations, the low-altitude regime, the high-altitude regime, vehicle-induced discharge, and beam-plasma discharge. The general pattern which emeres as a result of measurements is that below altitudes of approximately 125 + or - 5 km the vehicle potential rarely rises more than several tens of volts.

  2. Stability and spatial arrangement of the 2,4-dichlorophenoxyacetic acid and β-cyclodextrin inclusion compound: A theoretical study

    NASA Astrophysics Data System (ADS)

    Pereira, Robson A.; Anconi, Cleber P. A.; Nascimento, Clebio S.; De Almeida, Wagner B.; Dos Santos, Hélio F.

    2015-07-01

    The present letter reports results from a comprehensive theoretical analysis of the inclusion process involving 2,4-dichlorophenoxyacetic acid (2,4-D) and β-cyclodextrin (β-CD) for which the experimental data of formation is available. Spatial arrangement and stabilization energies were evaluated in gas phase and aqueous solution through density functional theory (DFT) and through the use of SMD implicit solvation approach. The discussed methodology was applied to predict the stability and identify the most favorable form (deprotonated or neutral) as well as the most probable spatial arrangement of the studied inclusion compound.

  3. Determination of the crotonaldehyde structures on Pt and PtSn surface alloys from a combined experimental and theoretical study

    NASA Astrophysics Data System (ADS)

    Haubrich, Jan; Loffreda, David; Delbecq, Françoise; Jugnet, Yvette; Sautet, Philippe; Krupski, Aleksander; Becker, Conrad; Wandelt, Klaus

    2006-12-01

    A complementary experimental and theoretical study of the alloying effects of Sn on the molecule-surface bonding of crotonaldehyde on Pt(1 1 1) is presented. By comparing high-resolution electron energy loss spectroscopy (HREELS) data and density-functional theory (DFT) calculations of vibrational spectra from a complete set of possible adsorption configurations of crotonaldehyde on the Pt(1 1 1) and Pt 2Sn(1 1 1) surfaces, we are able to identify the adsorption structures present on the surface. An interpretation of the HREELS spectra for these highly complex systems is proposed and the effect of alloying with Sn on the molecule-surface interactions is addressed.

  4. Theoretical study of the surface properties of poly(dimethylsiloxane) and poly(tetrafluoroethylene).

    PubMed

    Michalkova, Andrea; Tulyani, Sonia; Beals, James; Leszczynski, Jerzy

    2012-01-01

    Molecular dynamics (MD) simulations of poly(dimethylsiloxane) (PDMS) and poly(tetrafluoroethylene) (PTFE) were carried out to determine their surface properties and energies. This study helps to gain better insight into the molecular modeling of PDMS and PTFE, in particular how different approaches affect calculations of surface energy. Current experimental and theoretical data were used to further understand the surface properties of PDMS and PTFE as well as to validate and verify results obtained from the combination of density functional theory (DFT) calculations (including periodic boundary conditions) and MD simulations. Detailed analysis of the structure and electronic properties (by calculation of the projected density of states) of the bulk and surface models of PDMS and PTFE was performed. The sensitivity of the surface energy calculation of these two polymers to the chemistry and model preparation was indicated. The balance between the molecular density, weight (which also reflects bond orientation in the surface region), bond flexibility, and intramolecular interactions including bond stretching was revealed to govern the results obtained. In modeling, the structural organization of polymer near a given surface (types and number of end groups and broken bonds due to application of different cut offs of the periodic structure) also significantly affects the final results. Besides the structural differences, certain simulation parameters, such the DFT functionals and simulation boxes utilized, play an important role in determining surface energy. The models used here were shown to be sufficient due to their good agreement with experimental and other theoretical data related to surface properties and surface energies. PMID:21523541

  5. Metal coordination study at Ag and Cd sites in crown thioether complexes through DFT calculations and hyperfine parameters.

    PubMed

    do Nascimento, Rafael R; Lima, Filipe C D A; Gonçalves, Marcos B; Errico, Leonardo A; Rentería, Mario; Petrilli, Helena M

    2015-04-01

    Structural and electronic properties of [C12H24S6X], [C13H26S6OX], and [C14H28S6OX] (X: Ag(+), Cd(2+)) crown thioether complexes were investigated within the framework of the density functional theory (DFT) using the projector augmented wave (PAW) method. The theoretical results were compared with time-differential perturbed γ-γ angular correlations (TDPAC) experiments reported in the literature using the (111)Ag→(111)Cd probe. In the case of X=Ag(+), a refinement of the structure was performed and the predicted equilibrium structures compared with available X-ray diffraction experimental data. Structural distortions induced by replacing Ag(+) with Cd(2+) were investigated as well as the electric-field gradient (EFG) tensor at the Cd(2+) sites. Our results suggest that the EFG at Cd(2+) sites corresponds to the Ag(+) coordination sphere structure, i.e., before the structural relaxations of the molecule with X=Cd(2+) are completed. The results are discussed in terms of the characteristics of the TDPAC (111)Ag→(111)Cd probe and the time window of the measurement, and provide an interesting tool with which to probe molecular relaxations. PMID:25814377

  6. Molecular structure, vibrational spectra (FTIR and FT Raman) and natural bond orbital analysis of 4-Aminomethylpiperidine: DFT study

    NASA Astrophysics Data System (ADS)

    Mahalakshmi, G.; Balachandran, V.

    2014-10-01

    The FT-IR and FT-Raman spectra of 4-Aminomethylpiperidine have been recorded using Perkin Elmer Spectrophotometer and Nexus 670 spectrophotometer. The equilibrium geometrical parameters, various bonding features, the vibrational wavenumbers, the infrared intensities and the Raman scattering activities were calculated using Hartree-Fock and density functional method (B3LYP) with 6-311+G(d,p) basis set. Detailed interpretations of the vibrational spectra have been carried out with the aid of the normal coordinate analysis. The spectroscopic and natural bonds orbital (NBO) analysis confirms the occurrence of intra molecular hydrogen bonds, electron delocalization and steric effects. The changes in electron density in the global minimum and in the energy of hyperconjugative interactions of 4-Aminomethylpiperidine (4AMP) were calculated. The theoretical UV-Visible spectrum of the compound was computed in the region 200-400 nm by time-dependent TD-DFT approach. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. The dipole moment (μ) and polarizability (α), anisotropy polarizability (Δα) and hyperpolarizability (β) of the molecule have been reported.

  7. Structural, DFT and biological studies on Cr(III) complexes of semi and thiosemicarbazide ligands derived from diketo hydrazide

    NASA Astrophysics Data System (ADS)

    Yousef, T. A.; Alduaij, O. K.; Ahmed, Sara F.; Abu El-Reash, G. M.; El-Gammal, O. A.

    2016-12-01

    Three ligands have been prepared by addition ethanolic suspension of 2-hydrazino-2-oxo-N-phenyl-acetamide to phenyl isocyanate (H2PAPS), phenyl isothiocyanate (H2PAPT) and benzoyl isothiocyanate (H2PABT). The Cr(III) chloride complexes were prepared and characterized by conventional techniques. The data confirmed that the complexes have the following formulaes, [Cr(H2PAPS)Cl3], [Cr(HPAPT)Cl2(H2O)2] and [Cr(HPABT)Cl2(H2O)]. The IR spectra of complexes shows that H2PAPS behaves as neutral tridentate via both CO of hydrazide moiety and Cdbnd N(azomethine) due to enolization of CO isocyanate without deprotonation. H2PAPT suggests the coordination as mononegative bidentate via both CO of hydrazide moiety in keto and deprotonated enolic oxygen atoms. H2PABT act as mononegative tridentate via carbonyl oxygen (Cdbnd O)3, the deprotonated enolic oxygen atom (dbnd Csbnd Osbnd)1 and NH1 groups. The experimental IR data of ligands are compared with those obtained theoretically from DFT calculations. Also, the bond lengths, bond angles, HOMO, LUMO and dipole moments have been calculated. The calculated HOMO-LUMO energy gap reveals that charge transfer occurs within the ligand molecules. The calculated values of binding energies indicates the higher stability of metal complexes than of ligands. Also, the kinetic and thermodynamic parameters for the different thermal degradation steps of the complexes were determined by Coats-Redfern and Horowitz-Metzger methods.

  8. Structural, vibrational spectroscopic and nonlinear optical activity studies on 2-hydroxy- 3, 5-dinitropyridine: A DFT approach

    SciTech Connect

    Asath, R. Mohamed; Premkumar, S.; Mathavan, T.; Dhas, M. Kumara; Benial, A. Milton Franklin; Jawahar, A.

    2015-06-24

    The conformational analysis was carried out for 2-Hydroxy- 3, 5-dinitropyridine molecule using potential energy surface scan and the most stable optimized conformer was predicted. The vibrational frequencies and Mulliken atomic charge distribution were calculated for the optimized geometry of the molecule 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. In the Frontier molecular orbitals analysis, the molecular reactivity, kinetic stability, intramolecular charge transfer studies and the calculation of ionization energy, electron affinity, global hardness, chemical potential, electrophilicity index and softness values of the title molecule were carried out. The nonlinear optical activity of the molecule was studied by means of first order hyperpolarizability, which was computed as 7.64 times greater than urea. The natural bond orbital analysis was performed to confirm the nonlinear optical activity of the molecule.

  9. Structural, vibrational spectroscopic and nonlinear optical activity studies on 2-hydroxy- 3, 5-dinitropyridine: A DFT approach

    NASA Astrophysics Data System (ADS)

    Asath, R. Mohamed; Premkumar, S.; Jawahar, A.; Mathavan, T.; Dhas, M. Kumara; Benial, A. Milton Franklin

    2015-06-01

    The conformational analysis was carried out for 2-Hydroxy- 3, 5-dinitropyridine molecule using potential energy surface scan and the most stable optimized conformer was predicted. The vibrational frequencies and Mulliken atomic charge distribution were calculated for the optimized geometry of the molecule 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. In the Frontier molecular orbitals analysis, the molecular reactivity, kinetic stability, intramolecular charge transfer studies and the calculation of ionization energy, electron affinity, global hardness, chemical potential, electrophilicity index and softness values of the title molecule were carried out. The nonlinear optical activity of the molecule was studied by means of first order hyperpolarizability, which was computed as 7.64 times greater than urea. The natural bond orbital analysis was performed to confirm the nonlinear optical activity of the molecule.

  10. A comparative DFT study on aquation and nucleobase binding of ruthenium (II) and osmium (II) arene complexes.

    PubMed

    Wang, Hanlu; Zeng, Xingye; Zhou, Rujin; Zhao, Cunyuan

    2013-11-01

    The potential energy surfaces of the reactions of organometallic arene complexes of the type [(η (6)-arene)M(II)(pic)Cl] (where pic = 2-picolinic acid, M = Ru or Os) were examined by a DFT computational study. Among the seven density functional methods, hybrid exchange functional B3LYP outperforms the others to explain the aquation of the complexes. The reactions and binding energies of Ru(II) and Os(II) arene complexes with both 9EtG and 9EtA were studied to gain insight into the reactivity of these types of organometallic complexes with DNA. The obtained data rationalize experimental observation, contributing to partly understanding the potential biological and medical applications of organometallic complexes. PMID:24037457

  11. A complete synergy on the experimental and theoretical study of the pyridine derivatives - 2-Hydroxy-5-Nitropyridine and 2-Chloro-5-Nitropyridine

    NASA Astrophysics Data System (ADS)

    Sangeetha, M.; Mathammal, R.

    2016-08-01

    The present work signifies the spectroscopic study (FTIR and FT-Raman) of the chosen compounds 2-Hydroxy-5-Nitropyridine (2H5NP) and 2-Chloro-5-Nitropyridine (2Cl5NP). Density Functional Theory (DFT) is implemented for the calculation of the molecular geometries, normal modes of vibrations, and electronic properties such as band gap energy, Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO). NMR chemical shifts are obtained experimentally and calculated theoretically with the help of Gauge Invariant Atomic Orbital (GIAO) method. Furthermore, the Natural Bond Orbital (NBO) analysis, Molecular Electrostatic Potential (MEP) surface maps and Mulliken charge analysis is performed and discussed in detail. The theoretical calculations are performed with the aid of DFT method using the functional B3LYP and basis set 6-31+G (d,p). The detailed study of the chosen compounds helps in understanding the structural, physical and chemical properties for the further application in the field of pharmaceutics.

  12. Structural, spectroscopic and DFT study of 4-methoxybenzohydrazide Schiff bases. A new series of polyfunctional ligands

    NASA Astrophysics Data System (ADS)

    Ferraresi-Curotto, Verónica; Echeverría, Gustavo A.; Piro, Oscar E.; Pis-Diez, Reinaldo; González-Baró, Ana C.

    2015-02-01

    Five Schiff bases obtained from condensation of 4-methoxybenzohydrazide with related aldehydes, namely o-vanillin, vanillin, 5-bromovanillin, 5-chlorosalicylaldehyde and 5-bromosalicylaldehyde were prepared. A detailed structural and spectroscopic study is reported. The crystal structures of four members of the family were determined and compared with one another. The hydrazones obtained from 5-chlorosalicylaldehyde and 5-bromosalicylaldehyde resulted to be isomorphic to each other. The solid-state structures are stabilized by intra-molecular Osbnd H⋯N interactions in salicylaldehyde derivatives between the Osbnd H moiety from the aldehyde and the hydrazone nitrogen atom. All crystals are further stabilized by inter-molecular H-bonds mediated by the crystallization water molecule. A comparative analysis between experimental and theoretical results is presented. The conformational space was searched and geometries were optimized both in gas phase and including solvent effects. The structure is predicted for the compound for which the crystal structure was not determined. Infrared and electronic spectra were measured and assigned with the help of data obtained from computational methods based on the Density Functional Theory.

  13. DFT based study of transition metal nano-clusters for electrochemical NH3 production.

    PubMed

    Howalt, J G; Bligaard, T; Rossmeisl, J; Vegge, T

    2013-05-28

    Theoretical studies of the possibility of producing ammonia electrochemically at ambient temperature and pressure without direct N2 dissociation are presented. Density functional theory calculations were used in combination with the computational standard hydrogen electrode to calculate the free energy profile for the reduction of N2 admolecules and N adatoms on transition metal nanoclusters in contact with an acidic electrolyte. This work has established linear scaling relations for the dissociative reaction intermediates NH, NH2, and NH3. In addition, linear scaling relations for the associative reaction intermediates N2H, N2H2, and N2H3 have been determined. Furthermore, correlations between the adsorption energies of N, N2, and H have been established. These scaling relations and the free energy corrections are used to establish volcanoes describing the onset potential for electrochemical ammonia production and hence describe the potential determining steps for the electrochemical ammonia production. The competing hydrogen evolution reaction has also been analyzed for comparison. PMID:23598667

  14. The ionic states of iodobenzene studied by photoionization and ab initio configuration interaction and DFT computations

    SciTech Connect

    Palmer, Michael H. E-mail: tr01@staffmail.ed.ac.uk E-mail: nykj@phys.au.dk E-mail: desimone@iom.cnr.it Ridley, Trevor; Hoffmann, Søren Vrønning; Jones, Nykola C.; Coreno, Marcello; Grazioli, Cesare; Biczysko, Malgorzata; Baiardi, Alberto

    2015-04-07

    New valence electron photoelectron spectra of iodobenzene obtained using synchrotron radiation have been recorded. Ionization energies (IEs) determined using multi-configuration SCF calculation (MCSCF) procedures confirmed the adiabatic IE order as: X{sup 2}B{sub 1}theoretical studies. The calculated Franck-Condon vibrational spectral envelopes, including hot band contributions, for the first four ionic states reproduce the observed peak positions and intensities with reasonable accuracy. In order to simulate the observed spectra, different bandwidths are required for different states. The increase in the required bandwidths for the A{sup 2}A{sub 2} and B{sup 2}B{sub 2} states is attributed to internal conversion to lower-lying states. The presence of relatively high intensity sequence bands leads to asymmetry of each of the X{sup 2}B{sub 1} state bands.

  15. Mono- and multiply-functionalized fullerene derivatives through 1,3-dipolar cycloadditions: A DFT study

    NASA Astrophysics Data System (ADS)

    Anafcheh, Maryam; Ghafouri, Reza

    2014-02-01

    We have performed a computational study to investigate the electronic and chemical properties of mono- and multiply-functionalized fullerene derivatives through the [2+3] cycloaddition reactions of 1,3 dipoles such as nitriloxide (HCåN+-O-), azide (NåN+-NH-) and azomethine ylides (H2C-NH-CH2-) with C60 fullerene. The 1,3-dipolar cycloadditions (1,3 DCs) of one to six dipoles with a C60 molecule are theoretically investigated in terms of geometry, energies, electronic structures, stability and the electrophilicity index. Negative values of reaction energies Er are obtained, which indicate the exothermic character of the adsorption process. Generally, absolute values of Er for the C60/(H2C-NH-CH2-)n compounds are always larger than those of their corresponding compounds C60/(HCåN+-O-)n and C60/(NåN+-NH-)n. The results indicate that the successive 1,3-DC reactions of nitriloxides (HCåN+-O-) and azides (NåN+-NH-), n=1,2, 4 and 6 on the exterior surface of fullerene increases the electrophilicity while the reverse trend is observed for C60/(H2C-NH-CH2-)n. Furthermore, electrophilicity values for the C60/(HCåN+-O-)n and C60/(NåN+-NH-)n compounds are always greater than those of C60.

  16. Very strong intramolecular hydrogen bonding of 1,2-dithenoylcyclopentadiene; DFT and spectroscopic studies

    NASA Astrophysics Data System (ADS)

    Nekoei, A.-R.; Tayyari, S. F.; Vakili, M.

    2014-10-01

    Structure and intramolecular hydrogen bond (IHB) of 1,2-dithenoylcyclopentadiene (DTCP) have been investigated with quantum mechanical calculations using density functional theory at B3LYP level using some Pople-style basis sets augmented with polarized and diffuse functions. The full isomeric and conformational analyses have been done, and the relative stabilities for different chelated and non-chelated enol and different keto forms have been reported. The estimated IHB energy and the barrier height for proton transfer (19.34 and 0.31 kcal/mol, respectively), together with the value of 0.082 Å for the Q Gilli’s symmetry coordinate and the σ-skeleton of the molecule (O⋯O distance of 1.463 Å), confirm a very strong, nearly symmetric, linear and short distance resonance assisted IHB (RAHB) in DTCP. The values of 18.29 ppm for the enolated proton chemical shift and 1128 cm-1 for out-of-plain bending of the OH bond, besides investigations on other IR and Raman bands associated with the IHB strength and electron delocalization in different segments of the molecule, confirm the results of the theoretical studies and a very strong RAHB in DTCP.

  17. Understanding the mechanism of the intramolecular stetter reaction. A DFT study.

    PubMed

    Domingo, Luis R; Zaragozá, Ramón J; Saéz, Jose A; Arnó, Manuel

    2012-01-01

    The mechanism of the N-heterocyclic carbene (NHC)-catalyzed intramolecular Stetter reaction of salicylaldehyde 1 to yield chromanone 3 has been theoretically studied at the B3LYP/6-31G** level. This NHC-catalyzed reaction takes place through six elementary steps, which involve: (i) formation of the Breslow intermediate IN2; (ii) an intramolecular Michael-Type addition in IN2 to form the new C-C s bond; and (iii) extrusion of the NHC catalyst from the Michael adduct to yield chromanone 3. Analysis of the relative free energies in toluene indicates that while formation of Breslow intermediate IN2 involves the rate-determining step of the catalytic process, the intramolecular Michael-type addition is the stereoselectivity determining step responsible for the configuration of the stereogenic carbon a to the carbonyl of chromanone 3. An ELF analysis at TSs and intermediates involved in the Michael-type addition allows for the characterization of the electronic changes along the C-C bond-formation. PMID:22301721

  18. Antioxidant behavior of mearnsetin and myricetin flavonoid compounds — A DFT study

    NASA Astrophysics Data System (ADS)

    Sadasivam, K.; Kumaresan, R.

    2011-06-01

    The molecular characteristics of two naturally occurring flavonoid compounds mearnsetin and myricetin have been computed using density functional theory (DFT) approach with B3LYP/6-311G(d,p) level of theory. The computation and analysis of bond dissociation enthalpy magnitudes for all the OH sites for both the compounds clearly denotes the contribution of the B-ring for the antioxidant activity. The analysis has also indicated the higher values of BDE on the C5-OH radical species in both the compounds. The computed vibrational frequency analysis indicates the absence of imaginary frequency in the neutral as well as radical species of both the flavonoid compounds. The ionisation potential (IP) analysis was found to be within the range of the IP of synthetic food additives. In addition, various molecular descriptors such as electron affinity, hardness, softness, electronegativity, electrophilic index have also been calculated and the validity of Koopman's theorem is verified. The plot of frontier molecular orbital and spin density distribution analysis for neutral and the corresponding radical species for both the compounds have been computed and interpreted. The polar nature and their polarizing capacity are well established through the analysis of dipole moment and polarisability magnitudes.

  19. Relaxations of fluorouracil tautomers by decorations of fullerene-like SiCs: DFT studies

    NASA Astrophysics Data System (ADS)

    Kouchaki, Alireza; Gülseren, Oğuz; Hadipour, Nasser; Mirzaei, Mahmoud

    2016-06-01

    Decorations of silicon carbide (SiC) fullerene-like nanoparticles by fluorouracil (FU) and its tautomers are investigated through density functional theory (DFT) calculations. Two models of fullerene-like particles including Si12C8 and Si8C12 are constructed to be counterparts of decorated hybrid structures, FU@Si12C8 and FU@Si8C12, respectively. The initial models including original FU and tautomeric structures and SiC nanoparticles are individually optimized and then combined for further optimizations in the hybrid forms. Covalent bonds are observed for FU@Si12C8 hybrids, whereas non-covalent interactions are seen for FU@Si8C12 ones. The obtained properties indicated that Si12C8 model could be considered as a better counterpart for interactions with FU structures than Si8C12 model. The results also showed significant effects of interactions on the properties of atoms close to the interacting regions in nanoparticles. Finally, the tautomeric structures show different behaviors in interactions with SiC nanoparticles, in which the SiC nanoparticles could be employed to detect the situations of tautomeric processes for FU structures.

  20. Molecular self-assembly in substituted alanine derivatives: XRD, Hirshfeld surfaces and DFT studies

    NASA Astrophysics Data System (ADS)

    Rajalakshmi, Periasamy; Srinivasan, Navaneethakrishnan; Sivaraman, Gandhi; Razak, Ibrahim Abdul; Rosli, Mohd Mustaqim; Krishnakumar, Rajaputi Venkatraman

    2014-06-01

    The molecular assemblage in the crystal structures of three modified chiral amino acids, two of which are isomeric D- and L-pairs boc-L-benzothienylalanine (BLA), boc-D-benzothienylalanine (BDA) and the other boc-D-naphthylalanine (NDA) differing from this pair very slightly in the chemical modification introduced, is accurately described. The aggregation of amino acid molecules is similar in all the crystals and may be described as a twisted double helical ladder in which two complementary long helical chains formed through O-H⋯O hydrogen bonds are interconnected through the characteristic head-to-tail N-H⋯O hydrogen bonds. Thus the molecular aggregation enabled through classical hydrogen bonds may be regarded as a mimic of the characteristic double helical structure of DNA. Also, precise structural information involving these amino acid molecules with lower symmetry exhibiting higher trigonal symmetry in their self-assembly is expected to throw light on the nature and strength of intermolecular interactions and their role in self-assembly of molecular aggregates, which are crucial in developing new or at least supplement existing crystal engineering strategies. Single crystal X-ray analysis and their electronic structures were calculated at the DFT level with a detailed analysis of Hirshfeld surfaces and fingerprint plots facilitating a comparison of intermolecular interactions in building different supramolecular architectures.

  1. Reaction of Stabilized Criegee Intermediates from Ozonolysis of Limonene with Water: Ab Initio and DFT Study

    PubMed Central

    Jiang, Lei; Lan, Ru; Xu, Yi-Sheng; Zhang, Wen-Jie; Yang, Wen

    2013-01-01

    The mechanism of the chemical reaction of H2O with three stabilized Criegee intermediates (stabCI-OO, stabCI-CH3-OO and stabCIx-OO) produced via the limonene ozonolysis reaction has been investigated using ab initio and DFT (Density Functional Theory) methods. It has been shown that the formation of the hydrogen-bonded complexes is followed by two different reaction pathways, leading to the formation of either OH radicals via water-catalyzed H migration or of α-hydroxy hydroperoxide. Both pathways were found to be essential sources of atmospheric OH radical and H2O2 making a significant contribution to the formation of secondary aerosols in the Earth’s atmosphere. The activation energies at the CCSD(T)/6-31G(d) + CF level of theory were found to be in the range of 14.70–21.98 kcal mol−1. The formation of α-hydroxy hydroperoxide for the reaction of stabCIx-OO and H2O with the activation energy of 14.70 kcal mol−1 is identified as the most favorable pathway. PMID:23481640

  2. A comparative DFT study of the structural and electronic properties of nonpolar GaN surfaces

    NASA Astrophysics Data System (ADS)

    González-Hernández, Rafael; González-García, Alvaro; Barragán-Yani, Daniel; López-Pérez, William

    2014-09-01

    A comparative analysis of the geometry and the electronic characteristics of nonpolar GaN surfaces was carried out using density-functional theory (DFT) with different approximations for the exchange-correlation energy (LDA, PBE, PBEsol, RPBE, TPSS, revTPSS, and HSE). The obtained data show that the GaN(1 0 1bar 0) (m-plane) is more energetically stable than the GaN(1 1 2bar 0) (a-plane) surface. However, these surfaces have similar surface relaxation geometry, with a Ga-N surface bond-length contraction of around 6-7% and a Ga-N surface rotational angle in the range of 6-9°. Our results show that the use of different exchange-correlation functionals does not significantly change the surface energy and surface geometry. In addition, we found the presence of surface intra-gap states that reduce the band gap of the nonpolar GaN surface with respect to the bulk value, in agreement with recent photoelectron and surface optical spectroscopy experiments.

  3. Adsorption of nonmetallic elements on defect-free MgO(001) surface - DFT study

    NASA Astrophysics Data System (ADS)

    Pašti, Igor A.; Baljozović, Miloš; Skorodumova, Natalia V.

    2015-02-01

    Adsorption of 11 non-metals (H, B, C, N, O, F, Si, P, S, Cl and Br) on defect-free MgO(001) surface was investigate using DFT approach. Adsorption energies were found to be between - 0.56 eV (hydrogen adsorption) and - 2.63 eV (carbon adsorption). Charge transfer from substrate to adsorbate was observed to follow the periodicity in the Periodic Table of Elements, as increases from left to right and decreases from top to bottom. All investigated adsorbates prefer oxygen sites on MgO surface. The analysis of adsorbate-MgO(001) electronic structure suggested that the electronic structure of the O adsorption center and adsorbate atom is molecule-like and there is no strong interaction with MgO electronic bands. Based on the obtained dataset for adsorption energies of selected non-metallic adsorbates (X) the reactivity of MgO towards the bond cleavage in the cases of X-X, H-X and HO-X bonds was discussed. Obtained results point to weak reactivity of MgO(001) towards atomic adsorption and low activity for bond cleavage. However, these results can be used as a starting point for the functionalization of MgO, particularly in the cases where bond cleavage activity and surface-mediated stabilization of dissociation products are desired.

  4. DFT computational study on decarboxylation mechanism of salicylic acid and its derivatives in the anionic state

    NASA Astrophysics Data System (ADS)

    Gao, Lu; Hu, Yanying; Zhang, Huitu; Liu, Yanchun; Song, Zhidan; Dai, Yujie

    2016-07-01

    The mechanisms of the decarboxylation of salicylic acid anion and its ortho substituted derivatives in gas phase and aqueous solution have been investigated by B3LYP method of DFT theory using the 6-31++G (d,p) basis set. The decarboxylation process includes hydrogen transfers from hydroxyl to carboxyl group and from carboxyl to the α-C of the aryl ring. The mechanism suggested is a pseudo-unimolecular decomposition of the salicylic acid anion and the hydrogen transfer from carboxyl to the α-C of the aryl ring is the rate determining step. Compared with the decarboxylation process in gas phase, the energy barriers in aqueous solution approximately declined by 25%-31%with the water mediation of the hydrogen transfer from carboxyl to the α-C of the aryl ring. The effects of substituents at the ortho position on the decarboxylation process were also investigated. Both the electron donating CH3 and withdrawing group NO2 at the ortho position of carboxyl group can further reduce the reaction energy barriers of the decarboxylation of salicylic acid anions.

  5. Understanding the cooperative NHC/LA catalysis for stereoselective annulation reactions with homoenolates. A DFT study.

    PubMed

    Domingo, Luis R; Zaragozá, Ramón J; Arnó, Manuel

    2011-10-01

    The role of Ti(Oi-Pr)(4) Lewis acid (LA) in the cooperative N-heterocyclic carbene (NHC)/LA catalyzed addition of enals to enones to yield cis-cyclopentenes has been investigated using DFT methods at the B3LYP/6-31G** computational level. Ti(IV) effectively catalyzes the reaction by formation of a complex with cinnamaldehyde 1, which favors the nucleophilic attack of NHC 5 on 1, and the subsequent proton abstraction to yield the extended Ti(IV)-Breslow intermediate 21. The nature of the metal involved in the LA catalyst plays a relevant role due to the more basic character of NHCs than aldehydes. Thus, strong LAs, such as Zn(OTf)(2), prevent the catalytic behavior of NHCs to form a very stable complex. The subsequent formation of a complex between chalcone 2 and the extended Ti(IV)-Breslow intermediate 21 favors the cis stereoselective C-C bond-formation. Analysis of the structures of Ti(IV)-complex precursors for the cis and trans C-C bond-formation steps allows for an explanation of the unexpected cis stereoselectivity. PMID:21842074

  6. DFT study of the energetic and noncovalent interactions between imidazolium ionic liquids and hydrofluoric acid.

    PubMed

    Velarde, Marco V; Gallo, Marco; Alonso, P A; Miranda, A D; Dominguez, J M

    2015-04-16

    In this work, we evaluated the energetic interactions between imidazolium ionic liquids (ILs) and hydrofluoric acid, as well as the cation-anion interactions in ILs. We used DFT calculations that include dispersion corrections employing the PBE and M06 functionals. We tested 22 ILs, including [C4MIM][PF6], [C4MIM][NTf2], and [C4MIM][CH3COO], obtaining interaction energies in the range of -27 to -13 kcal/mol with the PBE functional. The NCI (noncovalent interaction) index developed by Yang and collaborators ( J. Am. Chem. Soc. 2010 , 132 , 6498 - 6506 ; J. Chem. Theory Comput. 2011 , 7 , 625 - 632 ) also was used for mapping the key noncovalent interactions (hydrogen bonds, van der Waals, and steric repulsions) between the anions and cations of ILs and also for interactions of ILs with hydrofluoric acid (HF). The results obtained show that the anions have a stronger effect with respect to cations in their capacity for interacting with hydrofluoric acid, and the strongest interaction energies occur in systems where the key noncovalent interactions are mainly hydrogen bonds. The [C4MIM][PF6], [C4MIM][NTf2], and [C4MIM][BF4] ionic liquids displayed the weakest cation-anion interactions. PMID:25803741

  7. Effect of carbon on the Ni catalyzed methane cracking reaction: A DFT study

    NASA Astrophysics Data System (ADS)

    Li, Jingde; Croiset, Eric; Ricardez-Sandoval, Luis

    2014-08-01

    To understand the effects of carbon atoms on the Ni catalyzed methane cracking reactions, methane dissociation on clean, surface-carbon-covered, and subsurface-carbon-accumulated Ni(1 1 1) surfaces were investigated using density functional theory (DFT). The results show that the existence of surface and subsurface C atoms destabilized the adsorption of the surface hydrocarbon species when compared to the clean Ni(1 1 1) surface. The projected density state (PDOS) analysis shows that the deposition of C atoms on and into the Ni surface modified the electronic structure of the Ni surface, and thus reduced the catalytic activity of the bonded Ni atoms. Moreover, it was found that the presence carbon atoms increase the CHx (x = 4-1) species activation barriers especially on the surface carbon covered (1/4 ML) Ni(1 1 1) surface, where CHx (x = 4-1) species encounter highest energy barrier for dissociation due to the electronic deactivation induced by Csbnd Ni bonding and the strong repulsive carbon sbnd CHx interaction. The calculations also show that CHx dissociation barriers are not affected by its neighboring C atom at low surface carbon coverage (1/9 ML). This work can be used to estimate more realistic kinetic parameters for this system.

  8. Hydrogenation of CO2 to formic acid over a Cu-embedded graphene: A DFT study

    NASA Astrophysics Data System (ADS)

    Sirijaraensre, J.; Limtrakul, J.

    2016-02-01

    DFT calculations were used to investigate the properties of the atomic copper embedded in the surface of graphene (Cu/dG) and the catalytic reaction pathway for the CO2 hydrogenation to formic acid (FA). The Cu/dG was active for the adsorption of the hydrogen molecule (H2), and provided a reaction site for the heterolytic cleavage of H2, leading to the formation of Cu-H deposited on a singly hydrogenated vacancy graphene (Cu-H/H-dG). The protonation of CO2 takes place facilely over the generated metal-hydride species (Cu-H). Under the dilution of H2, the catalytic process would be hampered by the formation of copper-formate deposited on the H-dG due mainly to the very high energy demand for the transformation of the copper-formate to FA through the protonation from the H-dG. It was further found that the presence of H2 in the system plays a significant role in producing the FA on the Cu/dG catalyst. The copper-formate species can be converted into formic acid via the heterolytic cleavage of the second hydrogen molecule, yielding the FA and Cu-H species.

  9. A DFT study of rocksalt proxy copper monochalcogenide structures - Implications for possible high-Tc superconductivity

    NASA Astrophysics Data System (ADS)

    Grant, P. M.; Hammond, R. H.; W2AGZ Technologies/GLAM, Stanford University Collaboration

    2014-03-01

    We report findings derived from a series of DFT calculations on the structural stability and paramagnetic ground states of four idealized copper monochalcogenide (CuO, CuS, CuSe, CuTe) rocksalt structures. Note that none of these target compounds occur naturally, but can possibly be fabricated using ``forced epitaxy'' MBE methods, as has been done to grow CuO tetragonal rocksalt films 5-6 monolayers thick.[1,2] Therefore, we treat all examples we report herein as proxies intended to explore candidate implications for possible future high-TC materials. In particular, we find, as might be expected from the long accepted Van Vleck-Anderson-Hubbard formalism describing antiferromagnetic insulators, the Neel temperature scales upward roughly as the width of the spin-carrying bands near or adjacent to the Fermi level or energy gap. We conclude such trend might result in higher superconducting transition temperatures should this be mediated by carrier-spin excitation/fluctuation driven pairing scaled by TN. Finally, we briefly discuss synthetic paths to realizing actual embodiments of our proxy exercises.

  10. Insight into deactivation of commercial SCR catalyst by arsenic: an experiment and DFT study.

    PubMed

    Peng, Yue; Li, Junhua; Si, Wenzhe; Luo, Jinming; Dai, Qizhou; Luo, Xubiao; Liu, Xin; Hao, Jiming

    2014-12-01

    Fresh and arsenic-poisoned V2O5–WO3/TiO2 catalysts are investigated by experiments and DFT calculations for SCR activity and the deactivation mechanism. Poisoned catalyst (1.40% of arsenic) presents lower NO conversion and more N2O formation than fresh. Stream (5%) could further decrease the activity of poisoned catalyst above 350 °C. The deactivation is not attributed to the loss of surface area or phase transformation of TiO2 at a certain arsenic content, but due to the coverage of the V2O5 cluster and the decrease in the surface acidity: the number of Lewis acid sites and the stability of Brønsted acid sites. Large amounts of surface hydroxyl induced by H2O molecules provide more unreactive As–OH groups and give rise to a further decrease in the SCR activity. N2O is mainly from NH3 unselective oxidation at high temperatures since the reducibility of catalysts and the number of surface-active oxygens are improved by As2O5. Finally, the reaction pathway seems unchanged after poisoning: NH3 adsorbed on both Lewis and Brønsted acid sites is reactive. PMID:25380546

  11. First-principles DFT+GW study of oxygen doped CdTe

    NASA Astrophysics Data System (ADS)

    Orellana, Walter; Flores, Mauricio A.; Menéndez-Proupin, Eduardo

    The role of oxygen doping in CdTe is addressed by first-principles calculations. Formation energies, charge transition levels and quasiparticle defect states are calculated within the DFT+GW formalism. The formation of a new defect is identified, the (OTe -TeCd) complex. This complex is energetically favored over both isovalent (OTe) and interstitial oxygen (Oi). We find that incorporation of oxygen passivates the harmful deep energy levels derived from Te antisites, suggesting an improvement in the efficiency of CdTe based solar cells. Our calculations indicate that both (OTe) and (Oi) have low formation energies. Moreover, (OCd) is only stable in the neutral charge state and undergoes a Jahn-Teller distortion. The (VCd - OTe) complex is found to be a shallow acceptor with a high formation energy. We also report an oxygen-related interstitial defect, which plays a key role in the diffusion mechanism of oxygen in CdTe. Support by FONDECYT Grant No. 1130437 is acknowledged. Powered@NLHPC: This research was partially supported by the supercomputing infrastructure of the NLHPC (ECM-02).

  12. Electronic structure, hydrogen bonding and spectroscopic profile of a new 1,2,4-triazole-5(4H)-thione derivative: A combined experimental and theoretical (DFT) analysis

    NASA Astrophysics Data System (ADS)

    Al-Tamimi, Abdul-Malek S.

    2016-09-01

    Density functional theory has been implemented to study the electronic structure, molecular properties and vibrational spectra of 3-(adamantan-1-yl)-4-(4-chlorophenyl)-1H-1,2,4-triazole-5(4H)-thione, a novel 1,2,4-triazole-5(4H)-thione derivative. Hydrogen bonded dimer of the title molecule has been studied using B3LYP, M06-2X and X3LYP functionals at 6-311++ G(d,p) level of theory. The intermolecular hydrogen bonding has been studied using NBO analysis of the dimer. Bader's AIM theory was also used to evaluate the strength as well as the hydrogen bonding characteristics. Experimental FT-IR and FT-Raman spectra of the title molecule were related with the spectral data obtained with DFT/B3LYP method. The 1H NMR chemical shifts of the title molecule were calculated by the GIAO method and compared with experimental results. Dipole moment, polarizability (α), first order static hyperpolarizability (β) along with molecular electrostatic potential surface have been calculated. Frequency-dependent first hyperpolarizabilities, β(-2ω;ω,ω) and β(-ω;ω,0) have also been evaluated to study the non-linear optical behavior of the title compound. UV-Vis spectrum of the title molecule was recorded and TD-DFT method has been used to calculate six lowest excited states and the corresponding excitation energies.

  13. Embedded coding technique - Principles and theoretical studies

    NASA Astrophysics Data System (ADS)

    Darnell, M.; Honary, B. K.; Zolghadr, F.

    1988-02-01

    In the paper the principles of embedded array codes, which employ a combination of forward error correction and detection (FEC/FED) for error control in an ARQ environment, are introduced. In this scheme a concatenated code with an inner code for error correction and an outer code for error detection is used. A retransmission of the erroneous information packets is requested if the outer code decoder detects the presence of any errors after the initial correction has been performed by the inner decoder. The theoretical expressions for the reliability and throughput efficiency of the system are derived. The performance of the system is analyzed and compared with that of a conventional array code. It is shown that the embedded scheme yields high reliability over a wide range of input bit error rates. A system of this type has many practical applications in situations where the transmission capacity of the communication channel varies with time; for example, on meteor-burst or HF(2-30 MHz) radio links.

  14. Electronic and magnetic properties of silicon supported organometallic molecular wires: a density functional theory (DFT) study

    NASA Astrophysics Data System (ADS)

    Liu, Xia; Tan, Yingzi; Li, Xiuling; Wu, Xiaojun; Pei, Yong

    2015-08-01

    The electronic and magnetic properties of transition metal (TM = Sc, Ti, V, Cr and Mn) atom incorporated single and double one-dimensional (1D) styrene molecular wires confined on the hydrogen-terminated Si(100) surface are explored for the first time by means of spin-polarized density functional theory, denoted as Si-[TM(styrene)]. It is unveiled that TM atoms bind asymmetrically to the adjacent phenyl rings, which leads to novel electronic and magnetic properties in stark contrast to the well-studied gas phase TM-benzene molecular wires. Si-[Mn(styrene)]∞ and Si-[Cr(styrene)]∞ single molecular wires (SMWs) are a ferromagnetic semiconductor and half metal, respectively. Creation of H-atom defects on the silicon surface can introduce an impurity metallic band, which leads to novel half-metallic magnetism of a Si-[Mn(styrene)]∞ system. Moreover, double molecular wires (DMWs) containing two identical or hetero SMWs are theoretically designed. The [Mn(styrene)]∞-[Cr(styrene)]∞ DMW exhibits half-metallic magnetism where the spin-up and spin-down channels are contributed by two single molecular wires. Finally, we demonstrate that introducing a TM-defect may significantly affect the electronic structure and magnetic properties of molecular wires. These studies provide new insights into the structure and properties of surface supported 1-D sandwiched molecular wires and may inspire the future experimental synthesis of substrate confined organometallic sandwiched molecular wires.The electronic and magnetic properties of transition metal (TM = Sc, Ti, V, Cr and Mn) atom incorporated single and double one-dimensional (1D) styrene molecular wires confined on the hydrogen-terminated Si(100) surface are explored for the first time by means of spin-polarized density functional theory, denoted as Si-[TM(styrene)]. It is unveiled that TM atoms bind asymmetrically to the adjacent phenyl rings, which leads to novel electronic and magnetic properties in stark contrast to

  15. Theoretical and spectroscopic studies on molecular structure and hydrogen bonding of 2-trifluoroacetylphenol.

    PubMed

    Moosavi-Tekyeh, Zainab; Tayyari, Sayyed Faramarz

    2015-01-25

    The molecular structure, intramolecular hydrogen bonding, and vibrational frequencies of 2-trifluoroacetylphenol (TFAP), were investigated by means of density functional theory (DFT) calculations and NMR, IR, and Raman spectroscopy techniques. The calculated theoretical and observed experimental results were compared with the corresponding data for salicylaldehyde (SA). Calculations were performed at the B3LYP level, using 6-311++G(**) basis set. The observed vibrational frequencies of TFAP were assigned with aid of theoretical calculations. The scaled frequencies at the B3LYP/6-311++G(**) level are in good agreement with the corresponding observed values by acceptable deviations. To investigate the effect of CF3 group on the hydrogen bond strength, the charge distributions, steric effects, and electron delocalization in TFAP and SA are studied using the natural bond orbital (NBO) analysis. The computations were further complemented with an atoms-in-molecules (AIM) topological analysis to characterize the nature of the intramolecular hydrogen bond, IHB, in the considered molecules. The contradiction between experimental and theoretical results was interpreted by considering the opposite effects of steric effect and electron withdrawing nature of CF3 group. PMID:25150433

  16. A new supramolecular compound of chrome(III): Synthesis, spectroscopic characterization, X-ray crystal structure, DFT, and solution studies

    NASA Astrophysics Data System (ADS)

    Eshtiagh-Hosseini, Hossein; Yousefi, Zakieh; Mirzaei, Masoud; Chen, Ya-Guang; Ali Beyramabadi, S.; Shokrollahi, Ardeshir; Aghaei, Roghayyeh

    2010-06-01

    A new supramolecular compound of Cr(III) atom was synthesized and characterized by using elemental analysis, FTIR spectroscopy, UV-vis, and single crystal X-ray diffraction method. The chemical formula and space group of the resulting compound is (2-apymH)[Cr(pydc) 2]·2H 2O ( 1) (pydc = 2,6-pyridinedicarboxylate, 2-apym = 2-aminopyrimidine) and P2 1/ c where the final R value is 0.0157 for 3896 reflections collected. The [Cr(pydc) 2] - anions and the (2-apymH) + moiety form a three-dimensional solid state structure by a variety of noncovalent interactions such as ion pairing and hydrogen bonds interactions. On the basis of crystallographic data, it can be seen that Cr(III) atom is six-coordinated by two (pydc) 2- groups. With respect to bond lengths and angles, it is observed that coordination sphere around Cr(III) atom is a distorted octahedral. Furthermore, DFT calculation and solution study have been completely performed on 1 where corresponding data showed that obtained results from DFT and solution studies have good agreement with X-ray crystallography results. The optimized geometry confirms that the C-O (bonded) bond length of (pydc) 2- ligand in its complex form has been increased compared with the free ligand. The evidence shows that C-O (bonded) is weakened upon formation of complex, while C dbnd O (free) converted to double bond. Anionic complex possesses 90 occupied molecular orbitals and 3 half-occupied ones (91-93). A comparison between the stoichiometry of the crystalline complex in pydcH 2-2-apym-Cr system and the results obtained from solution studies clearly revealed that the CrL 2QH is the most abundant species existing in aqueous solution possesses a stoichiometry similar to that of the complex which was obtained in the solid state.

  17. DFT studies on the mechanism of alcohol oxidation by the (bpy)Cu(I)-TEMPO/NMI catalytic system.

    PubMed

    Cheng, Lin; Li, Jie; Zhang, Qiancheng; Ma, Lisha; Yang, Jucai

    2015-04-28

    Density functional theory (DFT) calculations have been performed to investigate the oxidation of alcohol to acetaldehyde, catalyzed by the (bpy)Cu(I)-TEMPO/NMI catalytic system. Three pathways (path A, path B and path C) are presented. Our calculations indicate that path B is the favourable pathway. In path B, the alcohol coordinating to the Cu(I) center provides a H atom to TEMPO to form TEMPOH. Another TEMPO then replaces TEMPOH to abstract the H atom from the Cα-H of the alcoholate (RCH2O(-)) to generate the aldehyde product. On the basis of the studied pathway, a possible mechanism is presented to explain the experimental observations. PMID:25799480

  18. Synthesis, structure and DFT study of cymantrenyl Fischer carbene complexes of group VI and VII transition metals

    NASA Astrophysics Data System (ADS)

    Fraser, Roan; van Rooyen, Petrus H.; Landman, Marilé

    2016-02-01

    Bi- and trimetallic carbene complexes of group VI and VII transition metals (Cr, Mo, W, Mn and Re), with CpMn(CO)3 as the initial synthon, have been synthesised according to the classical Fischer methodology. Crystal structures of the novel carbene complexes with general formula [Mx(CO)y-1{C(OEt)(MnCp(CO)3)}], where x = 1 then y = 3 or 6; x = 2 then y = 10, of the complexes are reported. A density functional theory (DFT) study was undertaken to determine natural bonding orbitals (NBOs) and conformational as well as isomeric aspects of the polymetallic complexes. Application of the second-order perturbation theory (SOPT) of the natural bond orbital (NBO) method revealed stabilizing interactions between the methylene C-H bonds and the carbonyl ligands of the carbene metal moiety. These stabilization interactions show a linear decrease for the group VI metal carbene complexes down the group.

  19. DFT study of isocyanate chemisorption on Cu(100): Correlation between substrate-adsorbate charge transfer and intermolecular interactions

    NASA Astrophysics Data System (ADS)

    Belelli, Patricia G.; Garda, Graciela R.; Ferullo, Ricardo M.

    2011-07-01

    The adsorption of isocyanate (- NCO) species on Cu(100) was studied using the density functional theory (DFT) and the periodic slab model. The calculations indicate that at low and intermediate coverages NCO adsorbs preferentially on bridge and hollow sites. Work function and dipole moment changes show a significant negative charge transfer from Cu to NCO. The resulting charged NCO species interact repulsively among themselves being these dipole-dipole interactions particularly intensive when they are adsorbed in adjacent sites. Consequently, isocyanates tend to be separated from each other generating the vacant sites required for the dissociation to N and CO. This condition for NCO dissociation has been suggested in the past from experimental observations. A comparison was also performed with the NCO adsorption on Pd(100). In particular, the calculated minimal energy barrier for NCO dissociation was found to be higher on Cu(100) than on Pd(100) in accord with the well known higher NCO stability on Cu(100).

  20. Intramolecular photoinduced proton transfer in 2-(2‧-hydroxyphenyl)benzazole family: A TD-DFT quantum chemical study

    NASA Astrophysics Data System (ADS)

    Roohi, Hossein; Mohtamedifar, Nafiseh; Hejazi, Fahemeh

    2014-11-01

    In this work, intramolecular photoinduced proton transfer in 2-(2‧-hydroxyphenyl)benzazole family (HBO, HBI and HBT) was investigated using TD-DFT calculations at PBE1PBE/6-311++G(2d,2p) level of theory. The potential energy surfaces were employed to explore the proton transfer reactions in both states. In contrast to the ground state, photoexcitation from S0 state to S1 one encourages the operation of the excited-state intramolecular proton transfer process. Structural parameters, H-bonding energy, absorption and emission bands, vertical excitation and emission energies, oscillator strength, fluorescence rate constant, dipole moment, atomic charges and electron density at critical points were calculated. Molecular orbital analysis shows that vertical S0 → S1 transition in the studied molecules corresponds essentially to the excitation from HOMO (π) to LUMO (π∗). Our calculated results are in good agreement with the experimental observations.