Maddalena D’Amore | University of torino (original) (raw)

Papers by Maddalena D’Amore

Structure and Bonding, 2012

Electron Localization Function (ELF) and Maximum Probability Domain (MPD) analyses have been appl... more Electron Localization Function (ELF) and Maximum Probability Domain (MPD) analyses have been applied to model metal-porphyrins and show compatible and complementary results. ELF basins are quite different from MPDs, but are a necessary starting point for optimizing them. The analyses of the bond between the metal and porphyrin do not show significant differences between nontransition and transition metals. In all the cases considered, we find signatures characteristic of essentially ionic bonds.

Angewandte Chemie, 2015

The typical activation of a fourth generation Ziegler-Natta catalyst TiCl4 /MgCl2 /phthalate with... more The typical activation of a fourth generation Ziegler-Natta catalyst TiCl4 /MgCl2 /phthalate with triethyl aluminum generates Ti(3+) centers that are investigated by multi-frequency continuous wave and pulse EPR methods. Two families of isolated, molecule-like Ti(3+) species have been identified. A comparison of the experimentally derived g tensors and (35,37) Cl hyperfine and nuclear-quadrupole tensors with DFT-computed values suggests that the dominant EPR-active Ti(3+) species is located on MgCl2 (110) surfaces (or equivalent MgCl2 terminations with tetra-coordinated Mg). O2 reactivity tests show that a fraction of these Ti sites is chemically accessible, an important result in view of the search for the true catalyst active site in olefin polymerization.

Computational and Theoretical Chemistry, 2015

ABSTRACT Maximum Probability Domain (MPD) analysis has been recently applied to pure covalent and... more ABSTRACT Maximum Probability Domain (MPD) analysis has been recently applied to pure covalent and ionic crystals. The present study is devoted to a first MPD analysis of semi ionic crystals, Silicon Oxide, Aluminum Oxide and Titanium Oxide. These crystals are involved in important catalytic and photo-catalytic processes occurring on their surfaces. For this reason the study has been performed on bulk crystal and on surface slab models. Also surface neutral oxygen vacancy, the F0 surface defect, has been considered. The Electron Localization Function (ELF) analysis has also been performed, due to its holistic approach to electronic structures.

Carbon Materials: Chemistry and Physics, 2013

In carbon materials the mobile π electrons are situated in topologically different circumstances ... more In carbon materials the mobile π electrons are situated in topologically different circumstances at edge sites, and their π electronic states, essentially controlled by the network structure of sp 2 carbon, may be significantly affected. In this work, we derived topological indications about the reactivity of carbon nanotubes and fullerenes with the hydroxyl radical (OH • ), the most important oxidizing species in the troposphere. For each molecular structure, we computed the local softness, the Mulliken charges of the reacting carbons of (n,n) and (n,0) clusters, and their Huckel-type aromaticity rules, as an index to determine topologically independent sites and predicting a certain grade of reactivity of the nanotube and fullerenic carbon atoms. Using local softness, closely related to the energy gap, it was possible to separate the periodical nanotubes in three families according to their reactivity. A connection between the reactivity index ∆E and the topology was established by means of the Fukui integrated function. It resulted that for (n,0) clusters, odd n implies aromaticity, whereas even n, non-aromaticity; (n,n) clusters are in any case non-aromatic. For a better understanding of some experimental results, we also discussed how edge effects can influence topological reactivity due to the increment of the number of benzene rings in some cluster arrangements.

ChemInform, 2010

A Quantum Mechanical Study of TiCl 3 α, β and γ Crystal Phases: Geometry, Electronic Structure an... more A Quantum Mechanical Study of TiCl 3 α, β and γ Crystal Phases: Geometry, Electronic Structure and Magnetism -[DFT (B3LYP) calculations]. -(SEMENTA, L.; D'AMORE, M.; BARONE, V.; BUSICO, V.; CAUSA'*, M.; Phys. Chem. Chem.

Theoretical Chemistry Accounts, 2012

Most spectroscopic parameters are influenced by nuclear dynamics and by the chemical environment.... more Most spectroscopic parameters are influenced by nuclear dynamics and by the chemical environment. However, proper inclusion of these effects still represents a challenge in computational spectroscopy studies. In many cases, a route coupling satisfactory accuracy with reasonable computational costs consists in the integration of DFT-based methods to compute spectroscopic parameters, with ab initio molecular dynamics simulations to sample from the classical phase space of the system. Here, we discuss the application of this approach in two case studies of remarkable practical interest, namely the simulation of the absorption spectrum of 9-methyladenine, an adenine nucleoside model; and the prediction of electron spin resonance parameters for nitroxyl radicals, the prototypical spin probes. In both cases, the accuracy of the results increases significantly when the subtle interplay of intramolecular dynamics and solvent effects is introduced.

The Journal of Physical Chemistry A, 2003

The conformational behavior and magnetic properties of the R-acetylamino, N′-methylamide derivati... more The conformational behavior and magnetic properties of the R-acetylamino, N′-methylamide derivative of TOAC (4-amino-2,2,6.6-tetramethylpiperidine-1-oxyl-4-carboxylic acid) have been investigated in vacuo and in aqueous solution by an integrated computational approach including density functional, post-Hartree-Fock, and continuum solvent models. According to our computations, piperidine rings with an equatorial placement of the nitroxide moiety are more stable by about 1 kcal/mol than their axial counterparts both in vacuo and in aqueous solution. With respect to natural residues, TOAC shows a marked preference for helical conformers, which is further enhanced by polar solvents. A comparison with other C R -tetrasubstituted residues points out the difference between cyclic and open-chain substituents. The nitrogen isotropic hyperfine coupling constants (A N ) of folded TOAC conformers are similar to those of other nitroxides involving six-membered rings and are well reproduced by a composite QM/QM/PCM model. The A N values of extended TOAC conformers are significantly lower because of the constrained nearly planar structure of the piperidine ring.

Physical Chemistry Chemical Physics, 2009

The electronic structure of different magnetic states of a, b and g modifications of TiCl 3 has b... more The electronic structure of different magnetic states of a, b and g modifications of TiCl 3 has been computed employing the density functional theory with periodic boundary conditions and localized Gaussian basis sets. The analysis of the density of the electronic states (DOS) and of the spin density makes it possible to classify these halides as Mott-Hubbard insulators, where the band gap appears a result of large on-site Coulomb interaction. For each crystalline phase, the relative stability of different magnetic states has been analyzed in terms of exchange mechanisms. The electronic population data along with the spin density maps support the assumption of a d 1 Titanium ion in a distorted octahedral crystal field, notwithstanding the not fully ionic character of TiCl 3 modifications. Dispersion forces are particularly important for this material: a classical correction (of the type f(R)/R 6 ) has been added to the DFT energies and gradients, providing a good agreement with structural data.

Macromolecules, 2004

Model conformations of polytetrafluoroethylene (PTFE) chains containing various amounts of helix ... more Model conformations of polytetrafluoroethylene (PTFE) chains containing various amounts of helix reversal defects suitable for the high-temperature form I of PTFE have been modeled using semiempirical methods implemented in the Gaussian package, which makes use of the PM3 Hamiltonian. In these disordered conformations, ordered portions of chains in right-and left-handed 15/7 helical conformation succeed each other statistically along the chain. The Fourier transform of model chains containing various amounts of helix reversal defects obtained through the QM approach are then compared with the experimental X-ray fiber diffraction patterns of PTFE. Straight and slim model chains of PTFE containing helix reversal defects may be obtained at a low cost of internal energy and with small lateral encumbrance. For the minimum energy conformers the defect is always localized into a small region involving only 4 -CF 2-units, with the internal variables placed at the junction between the two enantiomorphic portions of chain, deviating only slightly from their average values in the defect-free portions of chains. Two consecutive helix reversals do not interact with each other if they are separated by more than three dihedral angles, and their contributions to internal energy can be considered as additive. The energy cost is ∼2.3 kcal/mol for each reversal. The disordered conformations of PTFE chains account for the X-ray fiber diffraction patterns of form I of PTFE at temperatures higher than 30°C. With increasing temperature an increase of the frequency of helix reversal defects is observed according to predictions of QM energy and Fourier transform calculations.

Journal of the American Chemical Society, 2006

We report here the main results of a successful attempt to predict some macroscopic properties of... more We report here the main results of a successful attempt to predict some macroscopic properties of representative polymers of technological relevance both in regular and disordered forms by using first principle quantum mechanical approaches at microscopic level. Until now, the prediction of the structural and thermal properties of those polymers has been mostly a domain of molecular mechanics methods. To overcome the limits of those classical computational tools whenever physical properties are significantly influenced by stereoelectronic effects (e.g., electron rich substituents), we employed methods rooted in the Density Functional Theory (DFT). A general computational strategy including the proper choice of periodic boundary conditions (PBC), functional, basis set, and model system size, has been tested and validated for saturated polymers such as polyethylene and isotactic/syndiotactic polypropylenes. On the basis of these results, a comprehensive study of poly(tetrafluoroethylene) (PTFE) chains in both regular periodic and disordered conformations has been performed. A statistical approach has been next applied to obtain the thermal concentration of defects and to reproduce the thermal behavior of the investigated polymer. At the end, a very good agreement with experimental X-ray diffraction and IR results has been achieved, definitely reaching a good understanding of the widely studied disorder phenomenon determining the main technological properties of poly(tetrafluoroethylene) (the trade Teflon) and, at the same time, identifying the proper computational tools to investigate perfluoro-compounds and other complex polymeric systems.

Journal of Catalysis, 2012

The adsorption of TiCl4 on the surfaces of MgCl2 crystals has been investigated by means of state... more The adsorption of TiCl4 on the surfaces of MgCl2 crystals has been investigated by means of state-of-the-art periodic hybrid DFT methods, as the first step of a comprehensive study aiming to elucidate the structure of the active species in industrial MgCl2-supported Ziegler-Natta catalysts for ethene and propene polymerization. A first distinctive feature of the approach was the thorough evaluation of

Chemistry of Materials, 2008

ABSTRACT n-Butylammonium ions intercalated in a layered aluminophosphate (AlPO-ntu) with kanemite... more ABSTRACT n-Butylammonium ions intercalated in a layered aluminophosphate (AlPO-ntu) with kanemite-type structure (hereafter AlPO-kan) have been studied by IR spectroscopy and modeled with density functional theory (DFT) calculations. This joint approach clarified the local structure of the inorganic/organic interface, not yet described. The acidity of the surface hyroxyls was investigated with a finite cluster model, while the structure and the theoretical IR spectra were obtained with 3D and 2D periodic boundary conditions. In the structure here optimized, each organic ion forms three hydrogen bonds with the surface phosphate and aluminate oxygens; the theoretical frequencies, including anharmonic corrections on the main stretching modes, were compared to the experimental IR spectra. The very satisfactory agreement confirms the optimized structure and allowed all the observed peaks to be assigned, providing for the first time a clear-cut interpretation of the broad and complex absorption at 2800−1700 cm−1 in terms of Fermi-type resonances.