Some thoughts on electrospray ionization mechanisms

Electrospray ionization (ESI) mechanisms are highly complex, due to a series of physical and chemical phenomena taking place on a complex system, as a solution is. In fact, even if the solution of an analyte in a protic medium can be considered at first sight to be a two-component system, the presence of solvent dissociation equilibria and the possible interactions solvent-solvent dissociation products, solvent dissociation products-analyte make this system highly complex, also for the presence of possible ionic compounds (for example, Na(+), K(+)) which strongly affect the above equilibria. A high number of research articles have been published, mainly devoted to charged droplet production and to gas-phase ion generation. They all show the high complexity of the processes affecting electrospray measurements related to either the chemical equilibria present in the condensed phase and to electrolysis processes at the emitter tip or to the processes occurring in the sprayed droplets. As a result, the chemical composition inside the small droplets from which the analyte ions are generated can be significantly different from those in sprayed solution. In this review, after a short survey of the proposed ESI mechanisms, some experiments are described. They were performed to examine if ion mobility in solution, before the formation of the sprayed charged droplets, can affect the ESI results. The data, obtained by studying both inorganic and organic analytes, indicate that the ESI spectra are dependent on the analyte dimension and charge state which, as a consequence, affect their ion mobility in solution.     

Kondo lattice state within the slave boson approach: spin-split masses and effective interaction among heavy quasiparticles

We provide a brief overview of our Hamiltonian approach to the the Kondo-lattice state at both finite Coulomb interaction U and nonzero applied magnetic field. In the mean-field approximation we introduce the spindependent effective masses, as well as calculate the effective Kondo (hybridization) temperature as a function of U. The effective interaction coming from the slave-boson exchange is shown to contain both the local (intraband) pairing and the Kondo (interband) interaction.     

Luminescence of porous silicon derived nanocrystals dispersed in water: dependence on initial porous silicon oxidation

Aqueous solutions of silicon nanocrystals have been obtained, by sonication, from porous Si (p-Si) aged in air for various times. The photoluminescence of these solutions changes with the aging time of p-Si. These changes correlate with nanocrystal core dimensions, i.e. with the oxidation of the nanocrystals. Infrared spectra show that the reaction with water depends on the age of the starting p-Si sample, since the native superficial oxide layer on p-Si inhibits these reactions.     

Synthesis of 8-arylated catechin and epicatechin derivatives via Suzuki cross-coupling

8-Arylated catechin and epicatechin derivatives have been prepared in good to excellent yields via Suzuki cross-coupling in the presence of Pd₂(dba)₃ as the Pd(0) source and Sphos as the phosphine ligand.     

TiO2-based photocatalysts impregnated with metallo-porphyrins employed for degradation of 4-nitrophenol in aqueous solutions: role of metal and macrocycle

Photodegradation of organic compounds in water solutions by means of economically advantageous and environment-friendly processes is a topic of growing interest. In recent years a great attention has been devoted to TiO₂-based photocatalysts for the oxidative degradation of various organic pollutants. In this context, we have prepared new photo-catalytic polycrystalline TiO₂ systems impregnated with sensitizers, i.e., copper, iron or manganese porphyrins, and investigated their photoactivity for 4-nitrophenol oxidation compared with that of bare TiO₂. A significant improvement of the photoreactivity was observed in the case of TiO₂ impregnated with copper porphyrin, while only a slight beneficial effect was observed in the case of iron porphyrin. In contrast, the presence of manganese porphyrin appeared to be detrimental.