Search results for "ionic"

Non-conventional methods and media for the activation and manipulation of carbon nanoforms

2013

Very often, chemical transformations require tedious and long procedures, which, sometimes, can be avoided using alternative methods and media. New protocols, enabling us to save time and solvents, allow us also to explore new reaction profiles. This Tutorial Review focuses on the physical and chemical behavior of carbon nanoforms, CNFs (fullerenes, nanotubes, nanohorns, graphene, etc.) when non-conventional methods and techniques, such as microwave irradiation, mechano-chemistry or highly ionizing radiations are employed. In addition, the reactivity of CNFs in non-conventional media such as water, fluorinated solvents, supercritical fluids, or ionic liquids is also discussed.

Growth and field crystallization of anodic films on Ta–Nb alloys

2012

The growth behavior of amorphous anodic films on Ta–Nb solid solution alloys has been investigated over a wide composition range at a constant current density of 50 Am−2 in 0.1 mol dm−3 ammonium pentaborate electrolyte. The anodic films consist of two layers, comprising a thin outer Nb2O5 layer and an inner layer consisting of units of Ta2O5 and Nb2O5. The outer Nb2O5 layer is formed as a consequence of the faster outward migration of Nb5+ ions, compared with Ta5+ ions, during film growth under the high electric field. Their relative migration rates are independent of the alloy composition. The formation ratio, density, and capacitance of the films show a linear relation to the alloy compos…

STRATEGIE PER IL MIGLIORAMENTO DELLA PRODUZIONE E LO SVILUPPO DI MOLECOLE AD ATTIVITÀ ANTIBIOTICA DI ORIGINE NATURALE O DI SINTESI CHIMICA

The emergence of multi-drug resistant (MDR) bacterial strains is an urgent problem derived from the widespread and uncontrolled use of antibiotics. Therefore, new arrays of lead compounds exerting antimicrobial activity are necessary to contrast the spreading of MDR pathogens. Between 1980 and 2003, the interest in scientific research programs aimed to the new drug discovery by large pharmaceutical companies progressively decreased due to increasing costs in the respect of i) the low discovery rate of new leads, ii) the small amounts of product recovery needing process optimization and, finally, iii) regulatory obstacles associated with long-lasting pre-clinical and clinical trials for ther…

Ontogeny of the human amygdala.

2003

Data on the fetal development of the human amygdala is reviewed with special reference to major ontogenetic events. In the fifth gestational month, the inferior portion of the amygdala reveals cell-dense columns merging with the ganglionic eminence (proliferative zone) in Nissl-stained sections. These columns contain vimentin-positive fibers and can therefore be regarded as migrational routes. In the sixth and seventh months, distinct reorganization of the cytoarchitectonics takes place. The sequential occurrence of afferens can be visualized using anti-GAP-43; moreover, outgrowing axons appear to reach the periphery of the ganglionic eminence. The latter may thus represent an intermediate …

Young neurons from medial ganglionic eminence disperse in adult and embryonic brain.

1999

In this study, we identified neuronal precursors that can disperse through adult mammalian brain tissue. Transplanted neuronal precursors from embryonic medial ganglionic eminence (MGE), but not from lateral ganglionic eminence (LGE) or neocortex, dispersed and differentiated into neurons in multiple adult brain regions. In contrast, only LGE cells were able to migrate efficiently from the adult subventricular zone to the olfactory bulb. In embryonic brain slices, MGE cells migrated extensively toward cortex. Our results demonstrate that cells in different germinal regions have unique migratory potentials, and that adult mammalian brain can support widespread dispersion of specific populati…

Novel polyaminoacidic copolymers as nonviral gene vectors

2000

Human gene therapy is one of the most promising methods developed in recent years, providing great potential for the treatment of a variety of diseases. Complexes formed between DNA and cationic polymers are attracting increasing attention as novel synthetic vectors for the delivery of genes. We have synthesized polycations with quaternary ammonium groups in their side chains for self-assembly with calf thymus DNA. This paper describes the functionalization of α,β-polyasparthydrazide (PAHy), a synthetic macromolecule having many potential applications in the field of biomedical sciences, with glycidyltrimethylammonuim chloride (GTA) in order to introduce positive charges into their chains. …

Solution properties of polyelectrolytes. III. Effect of sodium polystyrene sulfonate concentration on viscometric and size exclusion chromatographic …

1988

The effect of sodium polystyrene sulfonate concentration on the shape of its molecules in aqueous solution at different NaNO3 ionic strengths has been analyzed by viscometry and size-exclusion chromatography (s.e.c). An equation has been developed which predicts the intrinsic viscosity, [η] p.cp.cs, at finite concentration of both polyion (cp) and electrolyte (cs). The experimental results obtained by both techniques can be accounted for in terms of the theory. Several factors involved in the elution mechanism have been considered and the variation of the slopes of s.e.c. calibration curves with cp and cs has been discussed in terms of polyion conformation changes.

Geminal ionic liquids: a combined approach to investigate their three-dimensional organisation.

2009

Different investigations, such as 1D and 2D NMR spectroscopy, resonance light scattering spectroscopy and molecular dynamics simulations, have been jointly used to achieve a deeper understanding of the degree of structural order in two geminal ionic liquids. In particular, 3,3'-di-n-butyl-1,1'-(1,3-phenylenedimethylene)diimidazolium and 3,3'-di-n-butyl-1,1'-(1,4-phenylenedimethylene)diimidazolium bis[bis(trifluoromethanesulfonyl)imide] have been studied. These geminal ionic liquids were chosen because of the presence of both a rigid phenylenedimethylene link between two imidazolium rings, which should give a high degree of order to the solvent system, and the different shapes of the two cat…

Ultrasonic and Volumetric Properties of 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate Ionic Liquid with 2-Propanol or Tetrahydrofuran at Seve…

2011

Densities and speeds of sound of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate mixtures with 2-propanol and tetrahydrofuran (THF), as well as of the pure components, have been measured over the whole range of compositions at T = (278.15 to 328.15) K and P = (101 ± 2) kPa. From these experimental data, the excess molar volume, excess speed of sound, and excess isentropic compressibility have been calculated and fitted to an extended version of the Redlich–Kister equation, which takes into account the dependence on composition and temperature simultaneously. The Prigogine–Flory–Patterson theory has also been used to explain the behavior of these systems.

The mechanism of ionic diels-alder reactions. A dft study of the oxa-povarov reaction

2014

The mechanism of the oxa-Povarov reaction of a cationic aryl oxonium with cyclopentene and styrene has been studied using DFT methods at the B3LYP/6-31G* level as a reaction model of ionic Diels–Alder (I-DA) reactions. Oxa-Povarov reactions are initialized by an I-DA reaction between the cationic aryl oxonium and alkenes to yield the corresponding formal [4+ + 2] cycloadducts. The last step is a rapid loss of a proton giving chromans. While the I-DA reaction with cyclopentene takes place through a two-stage one-step mechanism, the presence of a phenyl substituent on styrene makes the mechanism of the I-DA reaction stepwise. An electron localization function (ELF) bonding analysis of selecte…