Biomedical subjects

Ivo Cacelli

Publications and source records attributed to Ivo Cacelli.

6 recordsLinked to original sources

PubMed2006

A two-state computational investigation of methane C--H and ethane C--C oxidative addition to [CpM(PH3)]n+ (M = Co, Rh, Ir; n = 0, 1).

Reductive elimination of methane from methyl hydride half-sandwich phosphane complexes of the Group 9 metals has been investigated by DFT calculations on the model system [CpM(PH(3))(CH(3))(H)] (M = Co, Rh, Ir). For each metal, the unsaturated product has a triplet ground state; thus, spin crossover occurs during the reaction. All relevant stationary points on the two potential energy surfaces (PES) and the minimum energy crossing point (MECP) were optimized. Spin crossover occurs very near the sigma-CH(4) complex local minimum for the Co system, whereas the heavier Rh and Ir systems remain in the singlet state until the CH(4) molecule is almost completely expelled from the metal coordination sphere. No local sigma-CH(4) minimum was found for the Ir system. The energetic profiles agree with the nonexistence of the Co(III) methyl hydride complex and with the greater thermal stability of the Ir complex relative to the Rh complex. Reductive elimination of methane from the related oxidized complexes [CpM(PH(3))(CH(3))(H)](+) (M = Rh, Ir) proceeds entirely on the spin doublet PES, because the 15-electron [CpM(PH(3))](+) products have a doublet ground state. This process is thermodynamically favored by about 25 kcal mol(-1) relative to the corresponding neutral system. It is essentially barrierless for the Rh system and has a relatively small barrier (ca. 7.5 kcal mol(-1)) for the Ir system. In both cases, the reaction involves a sigma-CH(4) intermediate. Reductive elimination of ethane from [CpM(PH(3))(CH(3))(2)](+) (M = Rh, Ir) shows a similar thermodynamic profile, but is kinetically quite different from methane elimination from [CpM(PH(3))(CH(3))(H)](+): the reductive elimination barrier is much greater and does not involve a sigma-complex intermediate. The large difference in the calculated activation barriers (ca. 12.0 and ca. 30.5 kcal mol(-1) for the Rh and Ir systems, respectively) agrees with the experimental observation, for related systems, of oxidatively induced ethane elimination when M = Rh, whereas the related Ir systems prefer to decompose by alternative pathways.

Journal Article↗

PubMed2005

Atomistic simulation of a nematogen using a force field derived from quantum chemical calculations.

Bulk phase atomistic computer simulations of 4-n-pentyl-4'-cyanobiphenyl (5CB) were performed with a specific force field obtained from ab initio and DFT calculations. The intermolecular potential was previously derived through the fragmentation reconstruction method (FRM), developed in our group. The description of some intramolecular interactions, like the torsional potential between the phenyl rings and at the aryl-alkyl linkage, is achieved through accurate DFT studies. Lengthy ( approximately 40 ns) molecular dynamics (MD) simulations were then carried out at constant atmospheric pressure and different temperatures. The system was stable in the experimental crystalline structure up to 285 K, where the early stage of the melting process appears with the loss of positional order. At higher temperatures (between 290 and 305 K) a kinetically stable, orientationally ordered phase is obtained. This nematic phase was reached starting with three initial configurations, differing in their orientational order parameter. The calculated values of thermodynamic and structural properties of each phase were in fairly good agreement with the relevant experimental data.

Journal Article↗

PubMed2004

Computer simulation of solid and liquid benzene with an atomistic interaction potential derived from ab initio calculations.

Molecular dynamics atomistic simulations of solid and liquid benzene have been performed, employing a model intermolecular potential derived from quantum mechanical calculations. The ab initio database includes approximately 200 geometries of the benzene dimer with interaction energies computed at the MP2 level of theory. The accuracy of the modeled force field results is satisfactory. The thermodynamic and structural properties, calculated in the condensed phases, are compared with experimental data and previous simulation results. Single particle and collective dynamical properties are also investigated through the calculation of translational and rotational diffusion coefficients, reorientational dynamics, and viscosities. The agreement of these data with experimental measurements confirms the reliability of the proposed force field.

Journal Article↗

PubMed2004

[(NH3)5Ru(1,2,4,5-tetrazine)]2+: synthesis and experimental and theoretical study of its solvatochromism in the visible spectral region.

The title compound has been first synthesized and fully characterized as both tetraphenylborate and perchlorate salt. Its 300-900 nm absorption spectrum, recorded in nitromethane, water, and dimethyl sulfoxide, reveals the peculiar existence of two distinct bands whose intensities depend on the solvent donor number. This feature can be attributed to two separate metal-to-ligand charge-transfer transitions, in agreement with the theoretical predictions obtained by extensive configuration interaction calculations, which take into account the solvent effects. The calculation of the potential energy curves of the ground and excited states along the Ru-tetrazine coordinate allows the interpretation of the relative intensities of the observed bands, as well as the interpretation of their line-shape profiles.

Journal Article↗

PubMed2003

Analysis of electron transfer in substituted biphenylmethane.

We present an analysis of electron transfer in a molecular structure containing two phenyl rings connected by a methylene barrier, with the addition of a donor group (NH(2)) on one ring and an acceptor group (NO(2)) on the other. Such molecules are among those currently being considered for the implementation of molecular circuits for information processing. We have performed both a study of the response of electron polarization to the application of an external electrostatic perturbation, and an analysis of the time-dependent behavior of electron transfer across the barrier. A detailed evaluation of the electron affinity and of the ionization energy of the molecular structure under investigation has also been performed, obtaining results that show the inadequacy of representations in terms of simple HOMO and LUMO orbitals.

Benzhydryl Compounds↗

PubMedDate not supplied

Theoretical prediction of the Abraham hydrogen bond acidity and basicity factors from a reaction field method.

A new methodology for the theoretical evaluation of the hydrogen bond acidity SigmaalphaH2 and basicity SigmabetaH2 Abraham descriptors is presented. The first step is a quantum mechanical calculation at the Hartree-Fock level using a moderate basis set, including the solute-solvent interaction through a Reaction Field method, namely the Polarizable Continuum Model (PCM). The density charge on the surface of the cavity surrounding the solute, which contains the signature of the specificity of the molecule, is then translated into effective atomic charges through a suitable algorithm. These atomic charges can be related to the acidity and basicity properties of the molecule by a proper parametrization of empirical atomic factors, which account for the specific H-bonding capabilities of the individual atoms and group of atoms. The Abraham descriptors can be then evaluated with a high degree of accuracy for a large number of classes of molecules. Calculations performed for a set of 55 compounds give a standard deviation of 0.029 and 0.044 for SigmaalphaH2 and SigmabetaH2, respectively. The correlation coefficients are 0.994 and 0.974.

Acids↗