Carlo Canepa

Silica gel functionalized with amino groups as a new catalyst for Knoevenagel condensation under heterogeneous catalysis conditions

Abstract Knoevenagel condensation has been carried out under heterogeneous catalysis conditions using amino groups immobilized on silica gel: the results show that the catalytic support is recoverable without regeneration, and that the matrix probably participates to the catalysis mechanism.

Amino groups immobilized on silica gel: an efficient and reusable heterogeneous catalyst for the Knoevenagel condensation

Silica gel functionalized with amino groups is a useful insoluble catalyst for the Knoevenagel condensation: the reaction can be carried out under continuous-flow conditions and good yields are obtained when aromatic aldehydes, cyclohexanone, and acetophenone react with ethyl acetoacetate, ethyl cyanoacetate, and malononitrile. Lower yields are obtained in the case of ethyl benzoylacetate and acetylacetone; this fact and the easy dehydration of the aldol intermediate strongly suggest the participation of the residual free silanol groups of the matrix in the catalysis mechanism.

Gas-phase ion chemistry of silane with ethane and ethyne

Abstract Silane–ethane and silane–ethyne systems have been studied by ion trap mass spectrometry and the variation of the abundances, with reaction time, of the ions containing silicon and carbon together in 5:1, 1:1 and 1:5 mixtures, have been reported. The best ion yield, which increases with the total pressure, is observed for 1:1 silane–ethyne mixture. Reaction mechanisms and rate constants of the first nucleation processes have been determined. In SiH 4 –C 2 H 2 systems, the formation of ions containing new SiC bonds occurs starting mainly from Si m H n + ions in the first steps, whereas the Si m C n H p + cluster species further reacts with high efficiency in processes with ethyne.

An AB initio theoretical study of the structure and stability of 1-fluoropropenide and 1,1-difluoropropenide and of the corresponding monomeric lithiated species

Abstract The electron distribution and HOMO polarization induce in the title compounds a different behaviour toward both hard and soft electrophiles: the results explain the observed α selectivity in difluoroallyllithium, while monofluoroallyllithium is predicted to show a less pronounced preference for the same site of attack.

Effect of lithium complexation by 12-crown-4 on the regioselectivity of the attack of gem-dichloroallyl-lithium on some carbonyl compounds

Abstract Substituted benzaldehydes and acetophenone preferentially attack the γ position of gem-dichloro allyl anion, but show a significantly increased α-selectivity if 12-crown-4 is present. This behaviour is discussed on the basis of theoretical computations.

Effect of the cation in the regioselectivity control in reactions of 3,3-dichloroallyl metals with substituted benzaldehydes

Abstract gem-Dichloroallyl-lithium and gem-dichloroallyl-potassium, produced respectively upon treatment of 3,3-dichloropropene with lithium diisopropylamide alone or in the presence of potassium tert-butoxide, show opposite regioselectivity in the reactions with substituted benzaldehydes.

Non-linear optical properties of β-D-fructopyranose calcium chloride MOFs: an experimental and theoretical approach

The second harmonic generation (SHG) properties of two MOFs, obtained from fructose and calcium chloride, were studied using a Non-Linear Optics Multimodal microscope. The first-order hyperpolarizability and the second-order susceptibility were calculated at the DFT level of theory. Moreover, a semi-classical approach to non-linearities in the optical behaviour was used in order to determine the features responsible for the SHG. The MOFs were synthesized both in ethanol and by solid–solid interaction, with a simple, rapid and low-cost methodology with no environmental impact, and were characterized with IR and RAMAN spectroscopy and both the single-crystal and powder X-ray diffraction. Both the metal–carbohydrate-based MOFs show an interesting SHG intensity: in particular, compound 1 shows an average SH intensity more than twice that of sucrose, in agreement with the theoretical results. A favourable combination of optical properties, transparency, thermal and chemical stability makes compound 1 a potential candidate for applications in electro-optics devices.

A stationary‐wave model of enzyme catalysis

An expression for the external force driving a system of two coupled oscillators in the condensed phase was derived in the frame of the Debye theory of solids. The time dependence and amplitude of the force is determined by the size of the cell embedding the coupled oscillators and its Debye temperature (θD). The dynamics of the driven system of oscillators were followed in the two regimes of (a) low θD and cell diameter, as a model of liquid water, and (b) large θD and cell diameter, as a model of the core of a protein. The response in potential energy of the reference oscillator was computed for all possible values of the internal parameters of the system under investigation. For protein cores, the region in the parameter space of high maximum potential energy of the reference oscillator is considerably extended with respect to the corresponding simulation for water.

A statistical mechanics/density functional approach to the thermodynamics of liquids

This study describes an accurate partition function obtained evaluating the configurational integral of molecular solutes with a computationally feasible method. The key features of this method include the partition function’s factors for translation (calculated according to the approach of the Lennard-Jones–Devonshire theory of liquids) and libration. The proposed molecular partition function has been successfully tested computing entropies of vaporization and molar heat capacities at constant volume for the four common liquids dichloromethane, acetonitrile, methanol, and water. The formulation of pressure-dependent properties is also given through a virial equation, and the evaluation of its simplest term allows the estimate of enthalpies of vaporization. Structural parameters needed by the theory, such as binding energies of particles to the bulk, have been obtained through density functional theory calculations on monomers, dimers, and clusters of the four test liquids.

Ab initio theoretical study of the monomer-dimer equilibrium in lithium and sodium gem-difluoro allyl and methyl systems

Abstract Non-empirical free energy calculations on lithium and sodium gem-dichloroallyl and dichloromethyl systems show that the dimeric structures are favoured for both species, but to a significantly lesser extent than in the analogous difluoro systems previously studied. The two dichloromethyl systems show geometric and energetic features very close to those found in the larger systems, whose vinylic part is not directly involved in the dimerization process. In both cases about the same dimerization free energies are computed for the lithium and sodium systems (ca.−24 kcal mol−1). Dichloromethyl is then used as a model for dichloroallyl to investigate, for two different dimerization equations, the structural and energetic effects of the interaction with the counterion of a discrete number of water molecules (used as a model for ether). The sign of the energy differences obtained by taking into account this interaction is reversed, and, in the case of lithium, the equilibrium is now clearly in favour of the monomeric species (by ca. 16 or 20 kcal mol−1, depending on the equation considered). The inclination to dimerize of the sodium systems is less clearly set, because smaller approximate ΔG values are estimated (close to zero or ca. 7 kcal mol−1, depending again on the equation considered). This picture contrasts the results previously published for the analogous difluoro compounds, for which approximate ΔG values ranging from -13 to -18 kcal mol−1 had been obtained.