A combined theoretical and experimental study on the oxidation of fulvic acid by the sulfate radical anion

The kinetics of the reaction of sulfate radicals with the IHSS Waskish peat fulvic acid in water was investigated in the temperature range from 289.2 to 305.2 K. The proposed mechanism considers the reversible binding of the sulfate radicals by the fulvic acid. The kinetic analysis of the data allows the determination of the thermodynamic parameters ΔG° = -10.2 kcal mol-1, ΔH° = -16 kcal mol-1 and ΔS° = -20.3 cal K-1 mol-1 for the reversible association at 298.2 K. Theoretical (DFT) calculations performed with the Buffle model of the fulvic acids support the formation of H-bonded adducts between the inorganic radicals and the humic substances. The experimental enthalpy change compares well with the theoretical values found for some of the investigated adducts.Fil: David Gara, Pedro Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Bosio, Gabriela Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Gonzalez, Monica Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Russo, Nino. Università della Calabria; ItaliaFil: Del Carmen Michelini, Maria. Università della Calabria; ItaliaFil: Pis Diez, Reinaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Química Inorgánica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Química Inorgánica "Dr. Pedro J. Aymonino"; ArgentinaFil: Martire, Daniel Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Studio teorico dell'attivazione dei legami C-H e C-C mediante cationi di attinidi in fase gassosa

Dottorato di Ricerca in Metodologie Chimiche Inorganiche,XXIII Ciclo,a.a. 2009-2010Density functional theory calculations were performed to study the ability of thorium (Th+, Th2+) and uranium (U+, U2+ The potential energy surfaces were explored taking into consideration different spin states. A close description of the reaction pathways leading to different reaction products is presented, and the obtained results are compared with experimental data. ) cations to activate the C-H and C-C bonds of methane, ethane and propane in the gas-phase. Th+ activates the C-H bonds of methane and ethane, in contrast, U+ is inert in both reactions. Th2+ reacts with all three alkanes, whereas U2+ reacts with C2H6 and C3H8, with product distributions different than those of Th2+ The computed potential energy profiles, which all proceed by insertion, were used to evaluate the relationship between the energetics of the bare Th . + (2+) and U+ (2+) ions and the energies for C-H and C-C bond activation. It was found that the computed energetics for insertion are entirely consistent with the empirical model which relates insertion efficiency to the energy needed to promote the An+ (2+) ion from its ground state to a prepared divalent state with two non 5f valence electrons suitable for bond formation in {C-An+ (2+)-H} and {C-An+ (2+)-C} activated intermediates.Università della Calabri

Two State Reactivity Paradigm in Catalysis. The Example of X-H (X = O, N, C) and C-C Bonds Activation Mediated by Transition Metal Compounds

A brief review of the theoretical work carried out on the activation of O-H, N-H, C-H and C-C bonds of small prototypical molecules mediated by \u201cbare\u201d transition metal atoms and cations in gas-phase is reported. Potential energy surfaces are examined in light of the role that spin changes can play in determining the final outcome of this kind of reactions and the results are analyzed in terms of two state reactivity paradigm. The performance of Density Functional Theory, in its B3LYP formulation, in this field is discussed along with comparison with experimental findings and high level ab initio computations

Acetylene cyclotrimerization by early second-row transition metals in the gas phase. A theoretical study

The acetylene cyclotrimerization reaction mediated by the left-hand-side bare transition metal atoms Y, Zr, Nb, and Mo has been studied theoretically, employing DFT in its B3LYP formulation. The complete reaction mechanism has been analyzed, identifying intermediates and transition states. Both the ground spin state and at least one low-lying excited state have been considered to establish whether possible spin crossings between surfaces of different multiplicity can occur. Our results show that the overall reaction is highly favorable from a thermodynamic point of view and ground state transition states lie always below the energy limit represented by ground state reactants. After the activation of two acetylene molecules and formation of a bis-ligated complex, the reaction proceeds to give a metallacycle intermediate, as the alternative formation of a cyclobutadiene complex is energetically disfavored. All the examined reaction paths involve formation of a metallacycloheptatriene intermediate that in turn generates a metal-benzene adduct from which finally benzene is released. Similarities and differences in the behaviors of the considered four metal atoms have been examined. \ua9 2005 American Chemical Society

Activation of methane by the iron dimer cation. A theoretical study

A detailed investigation of the reaction mechanisms underlying the observed reactivity of the iron dimer cation with respect to methane has been performed by density functional hybrid (B3LYP) and nonhybrid (BPW91) calculations. Minima and transition states have been fully optimized and characterized along the potential energy surfaces leading to three different exit channels for both the ground and the first excited states of the dimer. A comparison with our previous work covering the reactivity of the Fe+ monomer was made to underline similarities and differences of the reaction mechanisms. Results show that geometric arrangements corresponding to bridged positions of the ligands with respect to iron atoms are always favored and stabilize intermediates, transition states and products, facilitating their formation. Binding energies of reaction products have been computed and compared with experimental measurements, and ELF analysis of the bond has been performed to rationalize trends as a function of the structure. \ua9 2006 American Chemical Society

The role of quantum chemistry in the elucidation of the elementary mechanisms of catalytic processes: From atoms, to surfaces, to enzymes

The recent activity of the laboratory of quantum and computational chemistry of the University of Calabria in the field of catalysis is shortly reviewed. Theoretical determinations of the potential energy profiles for the cyclotrimerization of acetylene catalyzed by bare and supported niobium atom and the reduction mechanism of nitrate to nitrite by nitrate reductase enzyme are presented as examples of studies in which a certain number of investigation methods mostly used in this field, are applied. \ua9 Springer-Verlag 2007