Search results for "Theoretical Chemistry"
showing 10 items of 8456 documents
Copper Induces a Core Plasmon in Intermetallic Au(144,145)–xCux(SR)60 Nanoclusters
2015
The electronic structure and optical absorption spectra of intermetallic thiol-stabilized gold-copper clusters, having 144-145 metal atoms and 60 thiols, were studied by ab initio computations. The widely known icosahedral-based cluster model from the work of Lopez-Acevedo et al. (2009) was used, and clusters doped with one to 30 copper atoms were considered. When doped inside the metal core, copper induces dramatic changes in the optical spectrum as compared to the previously studied all-gold Au144(SR)60. An intense broad absorption peak develops in the range 535-587 nm depending on the amount of doping and doping sites. This result agrees very well with recent experiments by the Dass grou…
Silver Sulfide Nanoclusters and the Superatom Model
2015
The superatom model of electron-shell closings has been widely used to explain the stability of noble-metal nanoclusters of few nanometers, including thiolate-protected Au and Ag nanoclusters. The presence of core sulfur atoms in silver sulfide (Ag–S) nanoclusters renders them a class of clusters with distinctive properties as compared to typical noble-metal clusters. Here, it is natural to ask whether the superatom model is still applicable for the Ag–S nanoclusters with mixed metal and nonmetal core atoms. To address this question, we applied density functional simulations to analyze a series of Ag–S nanoclusters: Ag14S(SPh)12(PPh3)8, Ag14(SC6H3F2)12(PPh3)8, Ag70S16(SPh)34(PhCO2)4(triphos…
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…
Synthesis, Structure and Solvatochromism of the Emission of Cyano-Substituted Oligo(phenylenevinylene)s
2001
Strongly luminescent and highly soluble oligo(phenylenevinylene)s with five benzene rings and cyano groups in different positions of the terminal styrene units were prepared by means of Horner and Knoevenagel reactions. The substitution pattern − cyanide moieties on the vinyl or on the aromatic regions, together with the effect of auxochromic groups − has distinct influences on the electronic spectra, particularly on the fluorescence. Polar solvents induce red shifts and strongly reduce the fluorescence intensity of the vinyl-substituted oligomers. Cyano substitution increases the electron affinity of the oligomers; this effect is more pronounced for molecules with vinyl cyanides and can be…
Structure ofD-ribonic acid-dimethyltin(IV) in coordinating solvents: an experimental and DFT119Sn NMR study
2006
We have investigated a newly synthesized complex of D-ribonic acid with dimethyltin(IV). The structure of the complex in solution has been characterized by means of 1 H, 13 C, and 119 Sn NMR and by DFT calculations. The comparison of experimental and computational results allowed the determination of the stable conformation in solution as well as the detection of a dimerization process. Moreover, evidence is given of active coordination of the metal by the solvent.
DFT Prediction of Enhanced Reducibility of Monoclinic Zirconia upon Rhodium Deposition.
2018
Oxides are an important class of materials and are widely used, for example, as supports in heterogeneous catalysis. In a number of industrial catalytic processes, oxide supports actively participate in chemical transformations by releasing lattice oxygen anions. While this is intuitively understood for reducible oxides, the reducibility of irreducible oxides may be modified via nanoengineering or upon inclusion of foreign species. Our calculations predict that the ability of irreducible monoclinic zirconia to release oxygen improves substantially upon deposition of rhodium. Through a comprehensive screening of Rh/ZrO2 with different size of the rhodium species, we find that a Rh adatom and…
Reactions of m-Terphenyl-Stabilized Germylene and Stannylene with Water and Methanol: Oxidative Addition versus Arene Elimination and Different React…
2015
Reactions of the divalent germylene Ge(ArMe6)2 (ArMe6 = C6H3-2,6-{C6H2-2,4,6-(CH3)3}2) with water or methanol gave the Ge(IV) insertion product (ArMe6)2Ge(H)OH (1) or (ArMe6)2Ge(H)OMe (2), respectively. In contrast, its stannylene congener Sn(ArMe6)2 reacted with water or methanol to produce the Sn(II) species {ArMe6Sn(μ-OH)}2 (3) or {ArMe6Sn(μ-OMe)}2 (4), respectively, with elimination of ArMe6H. Compounds 1–4 were characterized by IR and NMR spectroscopy as well as by X-ray crystallography. Density functional theory calculations yielded mechanistic insight into the formation of (ArMe6)2Ge(H)OH and {ArMe6Sn(μ-OH)}2. The insertion of an m-terphenyl-stabilized germylene into the O–H bond was…
Preparation of a Series of “Ru(p-cymene)” Complexes with Different N-Heterocyclic Carbene Ligands for the Catalytic β-Alkylation of Secondary Alcohol…
2008
A series of five different “(p-cymene)Ru(NHC)” complexes (NHC = imidazolin-2-ylidene, imidazolin-4-ylidene, and pyrazolin-3-ylidene) have been obtained and fully characterized. The crystal structure of two of the new complexes has been determined by X-ray diffraction methods. All five complexes have been tested in the catalytic β-alkylation of secondary alcohols with primary alcohols and the dimerization of phenylacetylene, showing an excellent activity in both processes. A clear improvement on the catalytic activity of the complexes is observed when the more basic NHC ligands are used. The pyrazolylidene-Ru complex lies among the best catalysts for the β-alkylation of secondary alcohols re…
UV-B exposure causes DNA damage and changes in protein expression in northern pike (Esox lucius) posthatched embryos.
2012
The ongoing anthropogenically caused ozone depletion and climate change has increased the amount of biologically harmful UV-B radiation, which is detrimental to fish in embryonal stages. The effects of UV-B radiation on the levels and locations of DNA damage manifested as cyclobutane pyrimidine dimers (CPDs), heat shock protein 70 (HSP70) and p53 protein in newly hatched embryos of pike were examined. Pike larvae were exposed in the laboratory to current and enhanced doses of UV-B radiation. UV-B exposure caused the formation of CPDs in a fluence rate-dependent manner, and the CPDs were found deeper in the tissues with increasing fluence rates. UV-B radiation induced HSP70 in epidermis, and…
Oncogenic BRAF and p53 Interplay in Melanoma Cells and the Effects of the HDAC Inhibitor ITF2357 (Givinostat)
2023
Oncogenic BRAF mutations have been widely described in melanomas and promote tumour progression and chemoresistance. We previously provided evidence that the HDAC inhibitor ITF2357 (Givinostat) targets oncogenic BRAF in SK-MEL-28 and A375 melanoma cells. Here, we show that oncogenic BRAF localises to the nucleus of these cells, and the compound decreases BRAF levels in both the nuclear and cytosolic compartments. Although mutations in the tumour suppressor p53 gene are not equally frequent in melanomas compared to BRAF, the functional impairment of the p53 pathway may also contribute to melanoma development and aggressiveness. To understand whether oncogenic BRAF and p53 may cooperate, a po…