1,721,700 research outputs found
Quinone methides as alkylating and cross-linking agents
No full textQuinone methides (QMs) are reactive intermediates involved in a large number of chemical and biological processes such as enzyme inhibition, DNA alkylation and cross-linking. Their electrophilicity towards amines, thiols, water, amino acids and peptides has been kinetically measured in aqueous solution. The alkylation process is often thermally and photochemically reversible and the resulting adducts may act as
QM carriers
Solution-phase chemistry. Properties, reactivity and selectivity modeled by implicit solvation models
No full textStudy of New Ternary Rare-Earth Intermetallic Germanides with Polar Covalent Bonding
No full textThe syntheses, structural characterizations and chemical bonding analyses for several ternary R–M–Ge (R = rare-earth metal; M = another metal) intermetallic compounds are reported. Each chapter of the thesis, the introductory ones part, is dedicated to the obtained achievements for a specific series of investigated compounds, which are: R2MGe6 (M= Li, Mg, Al, Cu, Zn, Pd, Ag), R4MGe10-x (M = Li, Mg), R2Pd3Ge5, Lu5Pd4Ge8, Lu3Pd4Ge4 and Yb2PdGe3. Preparation techniques included both traditional and innovative methods, like the metal flux synthesis, which turned out to be crucial for crystal growth and stabilization of some metastable compounds. Accurate crystal structure determinations were performed on the basis of both single crystal and powder diffraction data. In the case of R2LiGe6, R4MGe10-x and Lu5Pd4Ge8, the presence of non-merohedrally twinned crystals was successfully faced. The obtained structures for the R2MGe6, R2Pd3Ge5, Lu5Pd4Ge8 and Yb2PdGe3 were concisely described and rationalized according to the group–subgroup formalism. These results, combined with total energy calculations, allow presenting a correct distribution of structure modifications among the large family of the R2MGe6 compounds, leading to a deep revision of many controversial literature data. The knowledge of the correct structural models was the essential starting point to perform accurate and reliable chemical bonding investigations, mainly focusing on the far from trivial interactions between the Ge-polyanionic networks and the surrounding metals, revealing in all cases strong deviation from the Zintl description. In this framework, a comparative chemical bonding analysis for La2MGe6 (M = Li, Mg, Al, Zn, Cu, Ag, Pd) and Y2PdGe6 germanides was performed by means of cutting-edge position-space quantum chemical techniques based on QTAIM, ELI-D and their basins intersection. The accurate description of the bonding scenario required also the proposal of two new approaches: the penultimate shell correction (PSC0) and the ELI-D fine structure analysis based on its relative Laplacian. Hence, the Ge–La/Y and Ge–M (M 61⁄4Li, Mg) bonding were described as polar covalent. The Li- and Mg-containing phases were described as germanolanthantes M[La2Ge6]. Finally, thanks to these tools, a consistent picture for La/Y–M polar bonds was also presented
Study of new polar intermetallic compounds: synthesis, structural relations and real space chemical bonding analysis
No full textThe syntheses, structural characterizations and theoretical DFT-based investigations for different R–M–Ge (R = rare earth metal; M = another metal) germanides are reported. The R2PdGe6 and R2LiGe6 series, together with La2CuGe6 and La2AgGe6 compounds, were structurally characterized by single crystal X-ray diffraction, indicating the oS72-Ce2(Ga0.1Ge0.9)7 modification as the correct one. The alternative In-flux method, once optimized, produced three good quality R2PdGe6 single crystals: Pr2PdGe6 and the metastable La2PdGe6, which turned out to be mS36-La2AlGe6-type non-merohedrally twinned crystals, and the Yb2PdGe6 of oS72-Ce2(Ga0.1Ge0.9)7-type. These results were extended for a comprehensive study on the R2MGe6 (M = Li, Mg, Al, Cu, Zn, Pd, Ag, Pt, Au) family of compounds, employing symmetry-based structural rationalization and total energy calculations, revealing that the highest energy is always associated to the more reported oS18-Ce2CuGe6 structure. The knowledge of the correct structural models allowed a comparative chemical bonding analysis for La2MGe6 (M = Li, Mg, Al, Zn, Cu, Ag, Pd) and Y2PdGe6 germanides. State of the art position-space techniques (QTAIM, ELI-D and their basin intersection) were employed together with the proposal of new approaches developed during this work; i.e. the penultimate shell correction (PSC0) method and the ELI-D fine structure based on its relative Laplacian. The former was crucial to balance Ge–La polar-covalent interactions against the Ge–M ones, whereas the latter allows to reveal polyatomic bonding features. With these new tools at hand, it was possible to go beyond the Zintl picture (formally fulfilled only with M = Mg2+ and Zn2+) revealing Ge–La and Ge–M (M ≠ Li, Mg) polar-covalent interactions. For M = Li, Mg a formulation as germanolanthanate M[La2Ge6] is appropriate. In addition, a consistent picture of La/Y–M polar interactions was also described.
A systematic study on the existence of R2Pd3Ge5 (R = La-Nd, Sm, Gd-Lu) was conducted and the desired phase was revealed to exist with R = La-Nd, Sm, Yb crystallizing with the oI40-U2Co3Si5 structure. A Bärnighausen tree was constructed in order to rationalize the related crystal structures of the RPd2Ge2, RPdGe3 and R2Pd3Ge5 ternary compounds, enriching the large family of the BaAl4 derivatives. After magnetization and susceptibility measurements Yb2Pd3Ge5 was described as a paramagnet with μeff close to 0.8 μB/Yb-atom, suggesting a nearly divalent Yb state.
The new Lu5Pd4Ge8 and Lu3Pd4Ge4 intermetallics were synthesized. The former crystallizes with non-merohedral monoclinic twinned crystals (P21/m, mP34) and the latter is orthorhombic (Immm, oI22). COHP- and preliminary ELI-D-based chemical bonding analysis revealed the expected Ge-covalent fragments and in addition Ge–Lu, Ge–Pd and Pd-Lu polar-covalent interactions. These findings, together with the aforementioned results for La2MGe6 compounds, indicate the importance of these interactions within ternary rare-earth germanides.
Finally, the existence of R4MgGe10-x and R4LiGe10-x phases along the R series was investigated. X-ray single crystal diffraction experiments show that all the phases, obtained with R = La-Nd, Sm, Gd-Dy, are non-merohedrally twinned with mS60-La4MgGe10-x structure.
The presented results constitute a step forward in the comprehension of composition-structure-properties relationships and a good playground for further studies on analogous systems
Modeling Substituent and Conformational Effects on the Reactivity of Antitumor Agents Containing a Cyclopropylcyclohexadienone Subunit
No full textCollezione di antichità di Palazzo Lancellotti ai Coronari: archeologia, architettura, restauro
No full textla lingua del volume è in italiano e in ingles
Synthesis, spectroscopic characterization and chemical reactions of stable o-QM on solid phase
No full textA novel approach towards quinone methides stabilization
has been achieved by anchoring the reactive o-QM intermediate on solid phase (RTHP). The reactivity and selectivity of supported o-QM towards N and S centered nucleophiles have been explored
ground state
No full textThe chemical bonding, structural and magnetic properties of EuPdSn2 have been investigated by DFT, synchrotron X-ray and neutron powder diffraction and 151Eu Mössbauer spectroscopy. As a result, no structural transition is observed in the thermal range of 5-290 K, whereas ferromagnetic and antiferromagnetic orderings are found to coexist below 12 K and compete in the ground state. This magnetic phase separation is likely triggered by the minimization of the global energy resulting from the coexistence of the different magnetic configurations. Chemical bonding analysis in position space reveals the presence of heteroatomic 4a- and 5a-bonds, involving each species, and two-atomic Eu-Pd polar covalent interactions building up graphite-like distorted honeycomb layers.Fil: Martinelli, A.. Università degli Studi di Genova; ItaliaFil: Ryan, Dominic. McGill University; CanadáFil: Sereni, Julian Gustavo Renzo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Ritter, Clemens. Institut Laue Langevin; FranciaFil: Leineweber, Andreas. No especifíca;Fil: Curlık, Ivan. No especifíca;Fil: Freccero, Riccardo. Università degli Studi di Genova; ItaliaFil: Giovannini, Mauro. Università degli Studi di Genova; Itali
Modeling Acid and Cationic Catalysis on the Reactivity of Duocarmycins
No full textSeveral catalyzed alkylation reactions of 9-methyladenine by a model [CPI, cyclopropa[c]pyrrolo-[3,2-e]indol-4(5H)-one] of duocarmycin anticancer drugs have been compared to the uncatalyzed reaction in gas phase and in water solvent bulk, using density functional theory at the B3LYP level with the 6-31+G(d,p) basis set and C-PCM solvation model. The effect on the CPI reactivity induced by water, formic and phosphoric acids (general acid catalysis), H3O+ (specific acid catalysis), sodium, and ammonium cation complexation (cationic catalysis) has been investigated
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