Luís M.P. Veríssimo

Diffusion coefficients in aqueous solutions of potassium chloride at high and low concentrations

Abstract Differential diffusion coefficients of potassium chloride in water at 298.15 K, and at concentrations from 0.001 M to 1 M, have been measured using a conductimetric cell and an automatic apparatus to follow diffusion. The results are discussed on the basis of the Robinson and Stokes, Onsager-Fuoss and Pikal models. The cell uses an open-ended capillary method and a conductimetric technique is used to follow the diffusion process by measuring the resistance of a solution inside the capillaries, at recorded times.

Transport properties in aqueous ethambutol dihydrochloride

Mutual diffusion coefficients, densities and viscosities are reported for aqueous solutions of ethambutol as its dihydrochloride (EMBDHC) at finite concentrations and at 298.15K. From these experimental results and by using the appropriate models (Stokes-Einstein and Hartley), the hydrodynamic radii Rh, the diffusion coefficient at infinitesimal concentration D(0) and the thermodynamic factors, FT, have been estimated, permitting us to have a better understanding of the transport behavior of ethambutol dihydrochloride in solution. Elucidation of lack of any possible drug-drug interactions in these systems was obtained by complementary (1)H nuclear magnetic resonance (NMR) spectroscopy data.

Influence of lactose on the diffusion of calcium ions at physiological temperature

Mutual diffusion coefficients for calcium chloride (0.100 mol dm(-3)) in aqueous solutions containing lactose at various concentrations (from 0.005 to 0.200 mol dm(-3)) have been measured at 37°C (physiological temperature), by using a conductimetric cell coupled to an automatic system to follow the diffusion. This cell uses an open-ended capillary method based on the measurement of the electrical resistance of a solution placed inside the capillaries at recorded times. The analysis of the CaCl2 diffusion coefficient values obtained suggests the presence of some CaCl2/lactose aggregates in the media, which are influenced by the temperature.

Characterization at 25 °C of Sodium Hyaluronate in Aqueous Solutions Obtained by Transport Techniques

Mutual diffusion coefficients, D, were determined for aqueous solutions of sodium hyaluronate (NaHy) at 25 °C and concentrations ranging from 0.00 to 1.00 g·dm−3 using the Taylor dispersion technique. From these experimental data, it was possible to estimate some parameters, such as the hydrodynamic radius Rh, and the diffusion coefficient at infinitesimal concentration, D0, of hyaluronate ion, permitting us to have a better understanding of the structure of these systems of sodium hyaluronate in aqueous solutions. The additional viscosity measurements were done and Huggins constant, kH, and limiting viscosity number, [η], were computed for interaction NaHy/water and NaHy/NaHy determination.

Effect of HP-β-cyclodextrin in the diffusion behaviour of hydrocortisone in aqueous solutions at T=298.15 K.

Binary (D) and ternary (D(11), D(22), D(12) and D(21)) mutual diffusion coefficients determined by the Taylor dispersion method are reported for two aqueous systems, pure hydrocortisone (HC/H(2)O) and HC plus HP-β-cyclodextrin (HC/HP-βCD/H(2)O), at T=298.15 K. From these data, some thermodynamic information as well as conclusions about the influence of that carbohydrate in the diffusion of this drug are given.

Limiting values of diffusion coefficients of glycine, alanine,

Abstract.The side chain effect on transport in ionic aqueous salt solutions was investigated for

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-amino butyric acid, norvaline and norleucine in a relevant physiological aqueous medium

α-amino acids glycine, alanine,

Binary Diffusion Coefficients for Aqueous Solutions of Lactic Acid

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Diffusion coefficients of paracetamol in aqueous solutions

α-amino butyric acid, norvaline, and norleucine --that together define a chemical homologous series based on the length of the characteristic side chain which increases from zero to four carbons, respectively. Binary mutual diffusion coefficients at infinitesimal concentration in aqueous solutions of NaCl (0.15 mol kg-1) are measured by means of Taylor dispersion technique for this series and significant differences were found against previous published results for identical systems in pure water. In this way, NaCl effect on the transport of each amino acid is thus assessed and discussed in terms of salting-out effects. Also, solvated Stokes hydrodynamic radii were computed for the series showing comparable results in water and NaCl solution. The new information should prove useful in the design and characterization of transport-controlled systems in physiological and pharmacological studies.Graphical abstract