Search results for " DFT."
showing 10 items of 87 documents
Butene Isomerization and Double-Bond Migration on the H-ZSM-5 Outer Surface: A Density Functional Theory Study
2011
Isomerization of trans-but-2-ene to cis-but-2-ene and double bond migration of trans-but-2-ene to but-1-ene have been investigated by means of density functional theory calculations on a suitable model of H-ZSM-5 surface. The study has been afforded on outer surface sites by considering the hydroxyl group of either a SiO2(OH)2 or a AlO2H(OH)2 moiety. On these outer surface sites, one alkoxide species occurs as a stable intermediate both along the isomerization and double bond migration pathways. The latter process could also occur via a single-step mechanism, which involves a six-center transition state. The energy barriers of the outer surface processes above do not take any advantage by t…
B-DNA Structure and Stability as Function of Nucleic Acid Composition. Dispersion-Corrected DFT Study of Dinucleoside-Monophosphate Single and Double…
2013
actions of the sugar-phosphate skeleton with water; (6) hydrophobic interactions of the DNA cylindrical core, made up by the hydrogen-bonded and stacked nitrogen bases, with the water solvent. Recently, there has been increasing effort in developing and applying quantum chemical methods able to reproduce the structure of native B-DNA and to correctly describe the energy involved in the intrastrand and interstrand noncovalent interactions between the nucleotide monomers. This topic has been approached by both wave function methods and density functional theory. [2] Water solvent and sodium counterions also play an important role in the formation and relative stabilization of the double-helic…
π-Conjugated diimidazolium salts: rigid structure to obtain organized materials.
2015
Phenylene ethynylene based diimidazolium salts differing in the alkyl chain length borne on the imidazolium ion and anion nature were synthesized. Their properties were studied both in solution and in the solid state. Salts obtained were able to aggregate in organic solvent solution. Aggregate formation was studied by performing concentration dependent measurements using UV-vis, fluorescence and Resonance Light Scattering. Furthermore, features of the aggregates were also investigated in the solid state by means of fluorescence and Scanning Electron Microscopy measurements. Finally, Density Functional Theory calculations were performed to obtain insights into the interaction geometry in the…
Two New Flavonoids fromBonannia graeca: a DFT-NMR Combined Approach in Solving Structures
2007
Two new cyclized C-geranylated flavonoids, the dihydroflavonol bonanniol C (4a) and the flavanone bonannione B (6a), were isolated as minor compounds from the aerial parts of Bonannia graeca (Umbelliferae). Their structures were elucidated by a combined approach of extensive spectroscopic means and quantum mechanical methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
l-Arabinose Conformers Adsorption on Ruthenium Surfaces: A DFT Study
2012
Adsorption of 5 L-arabinose tautomers – one acyclic and four cyclic (α and β, pyranose and furanose) species – on a ruthenium surface was studied as a precursor-process of the, nowadays more and more, industrially important sugar catalytic hydrogenation on metal surfaces in water medium. The study was mostly referred to a 37-atom metal catalyst fragment, even though border-effects on the adsorption processes were also checked employing a 61-atom metal fragment. In order to figure out conformational effects on the title process the tautomer flexibility was, at first, investigated by the genetic-algorithm based code Balloon, considering the conformational spaces of the different aquo tautomer…
DFT insights into the oxygen-assisted selective oxidation of benzyl alcohol on manganese dioxide catalysts
2020
Abstract The reactivity pattern of the MnO2 catalyst in the selective aerobic oxidation of benzyl alcohol is assessed by density functional theory (DFT) analysis of adsorption energies and activation barriers on a model Mn4O8 cluster. DFT calculations predict high reactivity of defective Mn(IV) sites ruling a surface redox mechanism, L-H type, involving gas-phase oxygen. Bare and promoted (i.e., CeOx and FeOx) MnOx materials with high surface exposure of Mn(IV) sites were synthesized to assess kinetic and mechanistic issues of the selective aerobic oxidation of benzyl alcohol on real catalysts (T, 333–363 K). According to DFT predictions, the experimental study shows: i) comparable activity…
Synthesis of Unexpected Dimethyl 2-(4-Chlorophenyl)-2,3-dihydropyrrolo[2,1-a]isoquinoline-1,3-dicarboxylate via Hydrolysis/Cycloaddition/Elimination …
2021
Hydrolysis/[3 + 2] cycloaddition/elimination cascades employed for the synthesis of unexpected tricyclic compound derived from isoquinoline. Reaction of ethylene derivative 1 with the isoquinoline ester iminium ion 2 in alkaline medium (MeOH/NEt3) under reflux for 1 h resulted in the formation of the fused pyrrolo[2,1-a]isoquinoline derivative 3. Its structure was elucidated by X-ray single crystal and other spectrophotometric tools. Hirshfeld calculations for 3 and its crystal structure analysis revealed the importance of the short O…H (19.1%) contacts and the relatively long H…C (17.1%), Cl…H (10.6%) and C…C (6.1%) interactions in the molecular packing. DFT calculations were used to compu…
Identification of mixed bromidochloridotellurate anions in disordered crystal structures of (bdmim)2[TeX2Y4] (X, Y = Br, Cl; bdmim = 1-butyl-2,3-dime…
2014
The discrete mixed [TeBrxCl6−x]2− anions in their disordered crystal structures have been identified by using the phases prepared by the reaction of 1-butyl-2,3-dimethylimidazolium halogenides (bdmim)X with tellurium tetrahalogenides TeX4 (X = Cl, Br) as examples. Homoleptic (bdmim)2[TeX6] [X = Cl (1), Br (2)] and mixed (bdmim)2[TeBr2Cl4] (3), and (bdmim)2[TeBr4Cl2] (4) are formed depending on the choice of the reagents, and their crystal structures have been determined by single-crystal X-ray diffraction. The coordination environments of tellurium in all hexahalogenidotellurates are almost octahedral. Because of the crystallographic disorder, the mixed [TeBr2Cl4]2− and [TeBr4Cl2]2− anions …
Direct detection of 17O NMR in [Gd(DOTA)]- by NMR Spectroscopy
2015
The 17O NMR spectrum of the non-coordinated carboxyl oxygen in the GdIII-DOTA (DOTA = tetraazacyclododecanetetraacetic acid) complex has been observed experimentally. Its line width is essentially unaffected by paramagnetic relaxation due to gadolinium, and is only affected by the quadrupole pathway. The results are supported by the relevant parameters (hyperfine and quadrupole coupling constants) calculated by relativistic DFT methods. This finding opens up new avenues for investigating the structure and reactivity of paramagnetic GdIII complexes used as contrast agents in magnetic resonance imaging.
Stability, electronic structure, and optical properties of protected gold-doped silver Ag29-xAux (x = 0-5) nanoclusters
2017
In this work, we used density functional theory (DFT) and linear response time-dependent DFT (LR-TDDFT) to investigate the stability, electronic structure, and optical properties of Au-doped [Ag29−xAux(BDT)12(TPP)4]3− nanoclusters (BDT: 1,3-benzenedithiol; TPP triphenylphosphine) with x = 0–5. The aim of this work is to shed light on the most favorable doped structures by comparing our results with previously published experimental data. The calculated relative energies, ranging between 0.8 and 10 meV per atom, indicate that several doped Ag29−xAux nanoclusters are likely to co-exist at room temperature. However, only the Au-doped [Ag29−xAux(BDT)12(TPP)4]3− nanoclusters that have direct bon…