Search results for "ionic"

Solution Properties of Poly-Electrolytes. XI. Adsorption Effects in Aqueous Size-Exclusion Chromatog-Raphy of Polyanions

1994

Abstract Elution profiles of a series of polymer standards such as sodium poly(styrene sulphonate), poly(acrylic acid) and poly(L-glutamic acid) have been obtained from size-exclusion chromatography experiments using separately two types of hydrophilic supports. A variety of mobile phase compositions have been performed to enhance adsorption effects in order to study how this phenomenon can affect to the chromatographic separation mechanism of polyanions. Distribution coefficient values, in general greater than unity, have served to quantify the adsorption effect, as well as to analyze their dependence on eluent ionic strength, on the ionic groups of the support and on the chemical nature a…

Influence of temperature and background electrolyte on the sorption of neptunium(V) on Opalinus Clay

2012

Abstract The temperature dependence of the sorption of 8 μM neptunium(V) on Opalinus Clay (OPA, Mont Terri, Switzerland) was investigated between 40 and 80 °C and compared to previous results for 20 °C. The batch experiments were performed under ambient air conditions in synthetic pore water (pH = 7.6, I = 0.4 M) under variation of the solid-to-liquid ratio between 2 and 20 g/L. Under these conditions the sorption of Np(V) on OPA was found to be an endothermic process as the average distribution coefficient (K d ) increases continuously with increasing temperature from 23 ± 4 L/kg at 40 °C to 678 ± 254 L/kg at 80 °C. In the temperature range of 40-80 °C, the plot of log(K d ) vs. 1/T could …

Macromolecules in ordered media III. A fluorescence study on the association of poly-2-vinylpyridine with a phospholipid bilayer

2007

Association of low molecular weight poly-2-vinylpyridine taken as a polycation model with unilamellar vesicles based on dimirystoylphosphatidic acid has been experimentally investigated by means of fluorescence energy transfer experiments. The conventional profiles for the binding isotherms were obtained, confirming strong deviations from the ideality of these complex fluid composites. Two approaches, named binding and partitioning equilibrium, respectively, were used to obtain the association constant, K A; the number of phospholipids that form a binding site, N; the partition coefficient, Λ; the activity coefficient, γ; and the effective charge, v. Analysis of these parameters as a functi…

Passive Transport of Ionic Drugs through Membranes with pH-Dependent Fixed Charges

2001

We have studied both theoretically and experimentally the passive transport of ionic drugs through membranes with pH-dependent fixed charge. The system considered constitutes a simplified model for pH-controlled drug delivery through membranes of biochemical and pharmaceutical interest. The theoretical approach employed is based on the Nernst-Planck flux equations and all of the species present in the system (the neutral or ionic drug and the hydrogen and hydroxide ions) have been taken into account together with a Langmuir-type isotherm for the adsorption of the ionic drug onto the membrane surface. The membrane permeabilities of cationic, anionic, and neutral drugs through porous membrane…

Intracellular accumulation of l-Arg, kinetics of transport, and potassium leak conductance in oocytes from Xenopus laevis expressing hCAT-1, hCAT-2A,…

2004

AbstractCationic amino acid transporters play an important role in the intracellular supply of l-Arg and the generation of nitric oxide. Since the transport of l-Arg is voltage-dependent, we aimed at determining the intracellular l-Arg concentration and describing the transport of l-Arg in terms of Michaelis–Menten kinetics, taking into account membrane voltage. The human isoforms of the cationic amino acid transporters, hCAT-1, hCAT-2A, and hCAT-2B, were expressed in oocytes from Xenopus laevis and studied with the voltage clamp technique and in tracer experiments. We found that l-Arg was concentrated intracellularly by all hCAT isoforms and that influx and efflux, in the steady state of e…

The decay energy of the pure s-process nuclide ¹²³ Te

2016

Physics letters / B 758, 407 - 411 (2016). doi:10.1016/j.physletb.2016.04.059

Complex formation of Tb3+ with glycolate, D-gluconate and α-isosaccharinate in neutral aqueous perchlorate solutions

2003

Summary An electromigration technique was used for measurements of metal-ligand formation constants of non-carrier-free 160Tb3+ with glycolate, D-gluconate and α-isosaccharinate ligands. The overall ion mobilities of Tb at different concentrations of the ligands were measured in chemically inert perchlorate solutions (pH 7 and T= 298.1K) with an overall ionic strength μ = 0.1. The stepwise stoichiometric stability constants are: Tb3+/glycolate: log K 1=2.72(18), log K 2=1.73(19), log K 3= 1.12(17), Tb3+/D-gluconate: log K 1=2.96(11), log K 2=2.60(11), log K 3=1.13(9), Tb3+/α-ISA: log K 1=3.07(8), log K 2 = 2.69(11), log K 3 = 1.80(12).

Synthesis and characterization of new azoles as building blocks for functional ionic systems

2015

Polyfluoroalkyl viologen-based Ionic Liquid Crystals

2015

Quantitative characterization of the global electrophilicity power of common diene/dienophile pairs in Diels–Alder reactions

2002

Abstract The global electrophilicity power, ω, of a series of dienes and dienophiles commonly used in Diels–Alder reactions may be conveniently classified within a unique relative scale. Useful information about the polarity of transition state structures expected for a given reaction may be obtained from the difference in the global electrophilicity power, Δω, of the diene/dienophile interacting pair. Thus the polarity of the process can be related with non-polar (Δω small, pericyclic processes) and polar (Δω big, ionic processes) mechanisms.