Search results for "ionic"

Dielectric characterization and ionic conductivity of α-LiIO3 crystals related to the growth conditions

2000

Abstract The dielectric response of α-LiIO3 has been studied at room temperature between 20 Hz and 1 MHz with various types of electrodes and compared to the results in the literature. By changing the sample thickness, a relaxation of space charges is clearly identified and the bulk ionic conductivity is deduced from the admittance diagram. Finally a comparison is carried out between chromium doped and undoped crystals obtained from acid and neutral growth solutions.

Dielectric response of α-LiIO3 acid type crystals

1998

Abstract α-LiIO 3 is often used as non-linear optical material. In view of its preparation, low pH aqueous solutions are used as mother solutions, which give crystals with some hydrogen incorporated to the lattice. Thus, dielectric characterization appears as a very important tool. In this work, the dielectric properties of acid type α-LiIO 3 crystals (conductivity, permittivity, loss-angle tangent) are investigated as functions of temperature and frequency, through an original method allowing seemingly continuous measurements and avoiding space charge contributions to the measurements. The results show the dipolar and low frequency conductivity contributions to the dielectric response. The…

Complex permittivity of FeCl3/AOT/CCl4 microemulsions probed by AC impedance spectroscopy

2009

Abstract The complex permittivity of FeCl 3 /AOT/CCl 4 microemulsions in the 1–10 5  Hz frequency range has been measured by the conventional AC complex impedance technique. Measurements as a function of the volume fraction of the dispersed phase (FeCl 3  + AOT) and temperature at fixed salt-to-AOT molar ratio ( R , R  = 0.5) show that the entrapment of FeCl 3 clusters significantly enhances the local permittivity of the AOT reverse micelles and the number density of charge carriers resulting from the peculiar state of the confined inorganic salt. An estimate of the apparent static permittivity of the FeCl 3 ionic clusters entrapped in the core of AOT reverse micelles gives the very high an…

The Electrostatic Expansion of Linear Polyelectrolytes:  Effects of Gegenions, Co-ions, and Hydrophobicity

1997

The molar mass and ionic strength dependence of the dimensions of hydrophobically modified poly(vinylpyridinium) cations are demonstrated to be almost perfectly described by a theoretical expression derived on the basis of only excluded volume considerations. Generally, the effective charge density of the polyions decreases significantly with increasing hydrophobicity and with increasing polarizability of the gegenions. Unexpectedly, the intrinsic excluded volume effect which becomes dominating at high ionic strength not only depends on the hydrophobicity of the polyion but also significantly increases with decreasing polarizability of the gegenions (i.e., if the iodide gegenions are replac…

Long-term expression of the human alpha1-antitrypsin gene in mice employing anionic and cationic liposome vector.

1997

The complete process of gene therapy involves three important steps: targeting, delivery, and gene expression. Since each step can be related to the pharmacological concept of affinity, bioavailability, and intrinsic capacity, this commentary examines, from this perspective, the efficiency of anionic and cationic liposomes as vectors for the in vivo gene transfer of the human alpha1-antitrypsin gene. Small liposomes represent the first generation of liposomes destined for the liver parenchymal cell. Although the final efficiency of gene transfer is low, we found that small liposomes are a kind of high-affinity hepatocyte-destined vector because the dose range for mediating the response is t…

The ionic dependence of calcium efflux from guinea pig auricles.

1968

Über eine mangelnde Parallelität zwischen Ionenpumpenhemmung und Kontraktionskraftsteigerung

1964

Δ 5-Pregnen-3,20-dione-N,N'-ethylpyrrolidine-bisguanylhydrazone and Δ5-pregnen-3β-hydroxy-20-one-N,N'-ethyl-pyrrolidine-monoguanylhydrazone inhibit the activity of the ionic pump of cold-stored erythrocytes of guinea-pigs. The contractile force of isolated guinea-pig auricles is decreased by the mono-derivate and increased by the bis-derivate in spite of the similar action upon the pumping mechanism.

Quantitative structure-retention relationships for ionic and non-ionic compounds in biopartitioning micellar chromatography

2004

Quantitative structure–retention relationships, QSRRs, represent a powerful tool in chromatography. The objectives of QSRR studies are to predict the chromatographic retention behaviour of solutes based on their structural properties, to elucidate retention mechanisms, to optimize the separation of complex mixtures or to prepare experimental designs. In this paper, using the retention factors of 151 structurally unrelated solutes that cover a wide range of hydrophobicity, molecular size, hydrogen bonding properties and ionization degrees obtained in biopartitioning micellar chromatography (BMC) at different Brij35 micellar concentrations, several multivariate QSRR models are tested. It is d…

Biopartitioning micellar chromatography to predict skin permeability

2003

Dermal absorption of chemicals is an area of increasing interest to the pharmaceutical and cosmetic industries, as well as in dermal exposure and risk assessment processes. In this paper the capability of biopartitioning micellar chromatography (BMC) as an in vitro technique to describe compound percutaneous absorption is evaluated. A multivariate study (principal component analysis, partial least squares) is performed in order to evaluate the importance of some physicochemical variables on the skin permeability constant values. From these results, a quantitative retention-activity relationship model for predicting the skin permeability constants that uses the BMC retention data and melting…

Designing fluorous domains. Synthesis of a series of pyridinium salts bearing a perfluoroalkylated azole moiety

2006

The synthesis of a series of N-methylpyridinium salts bearing a perfluoroalkylated 1,2,4-oxadiazole or 1,2,4-triazole moiety is reported. X-Ray structures of representative perfluoroalkyl-triazolylpyridine (15) and methyl- pyridinium iodide salt (5a) are reported. Their crystal packing clearly shows segregation between the aromatic and parallel double layer fluorinated regions.