Binary Mutual Diffusion Coefficients Research Articles

Coupled mutual diffusion in aqueous calcium sulphate + sulphuric acid solutions

Taylor dispersion method was used to measure binary mutual diffusion coefficients of calcium sulphate in water at concentrations ranging 0.0000 to 0.0100 mol dm−3 and at 298.15 K. Experimental results are discussed based on the Onsager-Fuoss and Pikal models and compared with theoretical diffusion coefficients, calculated using different values of the mean distance of closest approach of ions, a. The influence parameter a on the diffusion of this system is also discussed.Ternary mutual diffusion coefficients (Dik) measured by the same technique are reported for aqueous CaSO4 + H2SO4 solutions at 298.15 K and concentrations up to 0.0100 mol dm−3. The coupled diffusion of CaSO4 (1) and H2SO4 (2) is significant, as indicated by the large negative cross-diffusion coefficients. Nernst equations are used to predict transport coefficients from limiting ionic conductivities and help to interpret both concentration dependence of the diffusion coefficients and the electrostatic mechanism for the coupled diffusion of the solutes.

Transport properties of aqueous solutions of the oncologic drug 5-fluorouracil: A fundamental complement to therapeutics

Cancer pharmacology is often markedly toxic and must be precisely dosed in order to reach the therapeutic bioavailability under strict control. Transport properties are important tools in the process of interpretation and fine-tuning pharmaceutical applications, notably for drugs that have a long record of use and have met their limits of bioavailability. 5–Fluorouracil (5-FU) is one of the most used antineoplastic agents since its discovery in 1957. In this paper, binary mutual diffusion coefficients of 5-fluorouracil, obtained from a Taylor dispersion method setup are reported for aqueous solutions up to 75 mmol.kg−1. These data were complemented by viscosity measurements. The overall information allows to compute descriptive parameters and further interpretation on the basis of well-established models.

Coupled mutual diffusion in aqueous (ammonium monovanadate + butyl-substituted sulfonated resorcinarene) solutions: An experimental and theoretical approach

Binary mutual diffusion coefficients (D) of aqueous solutions of the macrocyclic salt tetrasodium 5,11,17,23-tetrakissulfonatemethylen-2,8,14,20-tetra(butyl)resorcin[4]arene (Na4BRA) have been measured at 298.15 K by the Taylor dispersion method. The limiting diffusion coefficient of Na4BRA obtained by extrapolation of the data is used to evaluate the limiting conductivity and hydrodynamic radius of the BRA4− ion. The change in the hydrodynamic radius of sulfonated resorcinarenes with increasing the length of alkyl substituents is analysed. In the second part of this work, the effect of ammonium monovanadate on the diffusion of aqueous Na4BRA was investigated by measuring apparent ternary mutual diffusion coefficients for aqueous NH4VO3(1) + Na4BRA(2) solutions. In binary aqueous Na4BRA solutions (no added NH4VO3), the BRA4− ions diffuse at the same speed as the smaller and relatively mobile Na+ counterions to maintain electroneutrality. As the NH4VO3 concentration is raised, the main diffusion coefficient of NH4BRA drops to the tracer diffusion coefficients of BRA4− ions in supporting NH4VO3 solutions. Coupled diffusion of NH4VO3 and Na4BRA is significant. In particular, Na4BRA concentration gradients produce significant counter-current coupled flows of NH4VO3. Nernst equations are used to provide an electrostatic interpretation of the strongly coupled diffusion of Na4BRA and NH4VO3.

Mutual diffusion coefficient of concentrated trehalose aqueous solutions including supercooled regions measured by the Soret forced Rayleigh scattering method

We measured the binary mutual diffusion (interdiffusion) coefficient of trehalose aqueous solutions D in the concentration range from 0.1 to 0.8 mass fraction and the temperature range from 25 to 50 °C including supercooled regions under atmospheric pressure. The experimental apparatus was based on the Soret forced Rayleigh scattering (SFRS) technique, which uses the Soret effect to create a periodic spatial concentration modulation (Δw <10−5) of micrometer-order fringe spacing in a disaccharide aqueous solution due to the absorption of an optical interference grating generated by two crossing pulsed excitation laser beams (ΔT <10−2 °C). The decay of the mass diffusion process is monitored by the diffraction intensity of a probing laser beam within a few milliseconds. These characteristics of SFRS enabled us to measure highly viscous disaccharide aqueous solutions under supercooled states. The uncertainties of the experimental results were estimated to be within ±3% for low concentration and ±9% for high concentration (w > 0.55). The experimental results demonstrated that the rate of decrease in the mutual diffusion coefficient with the increasing concentration is more pronounced in supercooled regions than in dilute normal regions. We also measured the mutual diffusion coefficient of sucrose aqueous solutions at 30 °C in the supercooled regions to compare the results with those obtained from trehalose. We observed that the mutual diffusion coefficient of the trehalose aqueous solutions were smaller than those of sucrose with the increasing concentration, the ratio of Dtrehalose to Dsucrose showed an almost linear concentration-dependence towards the values that were less than half. Our findings suggest that trehalose can be more effective than sucrose in terms of the relaxation of the composition near their glass transitions.

Limiting diffusion coefficients of [Formula: see text],[Formula: see text]-amino acids in water and in sodium chloride aqueous solutions at 298.15 K.

Transport properties of model compounds in aqueous solutions such as amino acids can provide valuable information in order to understand the complex interactions in aqueous solutions as well as the protein stability in water and the relevant factors involved. Informations about the diffusion of amino acids in water and in aqueous solutions of sodium chloride are very scarce, especially for the 5-aminopentanoic acid and 6-aminohexanoic acid. In this study, limiting binary mutual diffusion coefficients at 298.15 K of 5-aminopentanoic and 6-aminohexanoic acids in aqueous solutions of NaCl 0.15 mol kg-1, using the Taylor dispersion technique, were determined and the results compared with the limiting binary mutual diffusion coefficients for 2-aminopentanoic acid, and 2-aminohexanoic acid, obtained in the same experimental conditions. The discussion of the properties of the selected amino acids is centered on the positions of the ionic groups in the hydrocarbon chain and, in addition, we have discussed the effects of NaCl on their structures and properties. The data on diffusion properties are supported by 1H, 13C and 23Na NMR experiments, which we have obtained for 5-aminopentanoic and 6-aminohexanoic acids, in aqueous solution, also in the presence of NaCl.

Coupled mutual diffusion in aqueous sodium (salicylate + sodium chloride) solutions at 25 °C

Taylor dispersion is used to measure the binary mutual diffusion coefficient (D) of aqueous solutions of sodium salicylate (NaSal), a non-steroidal anti-inflammatory drug (NSAID). The D° value estimated by extrapolation to zero NaSal concentration is used to calculate the limiting mobility of the Sal− ion for comparison with the value determined previously from conductivity data. Salt effects on NSAID diffusion are studied by measuring the ternary mutual diffusion coefficients (Dik) of aqueous NaSal(C1) + NaCl(C2) solutions, including results for the diffusion of NaSal in physiological saline solutions with C2 = 0.15 mol dm−3. As the NaCl:NaSal ratio increases, NaSal diffusion coefficient D11 changes from the binary diffusion coefficient of aqueous NaSal (a weighted average of the Na+ and Sal− diffusion coefficients) to the tracer diffusion coefficient of the Sal− ion in NaCl solutions. Coupled diffusion in the solutions is analysed by using Nernst-Planck equations to calculate the fluxes of ions migrating in the electric field (diffusion potential) generated by NaSal and NaCl concentration gradients.

Diffusion and structural behaviour of the dl-2-aminobutyric acid

dl-2-Aminobutyric acid (α-aminobutyric acid or AABA) is a non-protein amino acid with important physiological properties, and with considerable relevance in different areas, such as fundamental research and pharmaceutical industry. In this paper, the binary mutual diffusion coefficients of AABA in non-buffered aqueous solutions (0.001–0.100) mol·dm−3 at 298.15 K were measured. From these diffusion data, limiting values at infinitesimal concentration, D0, as well as those of the thermodynamic factors, FT, and activity coefficients, γ, were estimated. These data for AABA were compared with the data previously obtained for dl-4-aminobutyric acid (GABA). The difference of the behaviour of these transport properties for both amino-acids was explained based on the structural differences for the monomeric zwitterionic species of AABA and GABA. Such structural differences are supported by both 1H and 13C NMR spectroscopy and theoretical calculations, which indicate that the predominant species of AABA in these solutions is the extended zwitterionic form in contrast with the curled one of GABA.

Finite-Size Effects of Binary Mutual Diffusion Coefficients from Molecular Dynamics.

Molecular dynamics simulations were performed for the prediction of the finite-size effects of Maxwell-Stefan diffusion coefficients of molecular mixtures and a wide variety of binary Lennard–Jones systems. A strong dependency of computed diffusivities on the system size was observed. Computed diffusivities were found to increase with the number of molecules. We propose a correction for the extrapolation of Maxwell–Stefan diffusion coefficients to the thermodynamic limit, based on the study by Yeh and Hummer (J. Phys. Chem. B, 2004, 108, 15873−15879). The proposed correction is a function of the viscosity of the system, the size of the simulation box, and the thermodynamic factor, which is a measure for the nonideality of the mixture. Verification is carried out for more than 200 distinct binary Lennard–Jones systems, as well as 9 binary systems of methanol, water, ethanol, acetone, methylamine, and carbon tetrachloride. Significant deviations between finite-size Maxwell–Stefan diffusivities and the corresponding diffusivities at the thermodynamic limit were found for mixtures close to demixing. In these cases, the finite-size correction can be even larger than the simulated (finite-size) Maxwell–Stefan diffusivity. Our results show that considering these finite-size effects is crucial and that the suggested correction allows for reliable computations.

Diffusion in ternary aqueous {L-dopa + (NaSO3) -β-cyclodextrin} solutions using the pseudo-binary approximation

Mass transport in (drug + cyclodextrin) solutions is investigated by using Taylor dispersion technique, monitored by differential refractometry, to measure ternary mutual diffusion in aqueous solutions of {L-dopa + (NaSO3)n-β-CD} (the sodium salt of sulfated β-cyclodextrin). The values of the binary mutual diffusion coefficients of both aqueous L-dopa and aqueous (NaSO3)n-β-CD solutions are close to each other differing only by a few per cent units. As a result, the eigenvalues for the matrix of the ternary Dik diffusion coefficients for aqueous {L-dopa(1) + (NaSO3)n-β-CD(2)} solutions are nearly identical, and the numerical analysis of the Taylor dispersion data may be ill-conditioned in view of the unreliable data obtained from their analysis. To overcome these difficulties, the pseudo-binary diffusion approximation is used to evaluate in a simple way this ternary system. The pseudo-binary diffusion coefficient values found, Dp1 and Dp2, are very close to the binary diffusion ones, being the cross-coefficients approached zero, within the experimental error. From the obtained results, and under the circumstances of this study, we may deduct that no interaction between L-dopa and NaSO3ßCD was determined.

Limiting values of diffusion coefficients of glycine, alanine, $\alpha$ α -amino butyric acid, norvaline and norleucine in a relevant physiological aqueous medium

The side chain effect on transport in ionic aqueous salt solutions was investigated for [Formula: see text]-amino acids glycine, alanine, [Formula: see text]-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.

Optimization of Taylor Dispersion Technique for Measurement of Mutual Diffusion in Benchmark Mixtures

The Taylor dispersion technique has been used for measuring binary mutual diffusion coefficients for mixtures of 1,2,3,4-tetrahydronaphthalene (THN), isobutylbenzene (IBB) and dodecane (C12H26) at 0.5:0.5 mass fraction symmetric points, and for 0.9:0.1 mass fraction in IBB- C12H26. From the Stokes–Einstein equation and our experimental results, the limiting diffusion coefficients, D0, and the equivalent solvated radii, Rs, have been estimated at infinitesimal concentration of these species (TNH, IBB and C12H26). The measured diffusion coefficients are used to estimate activity coefficients of the components in the mixture, contributing to a better understanding of the structure of such systems and of their thermodynamic behaviour at different concentrations. We have also investigated the diffusion properties for a ternary system containing equal mass fractions of all the components (0.33THN: 0.33IBB: 0.33C12H26) and at 298.15 K.

Binary Mutual Diffusion Coefficients of Polymer/Solvent Systems Using Compressible Regular Solutions Theory and Free Volume Theory

AbstractThe free volume theory has found practical application for prediction of diffusional behavior of polymer/solvent systems. In this paper, reviewing free volume theory, binary mutual diffusion coefficients in some polymer/solvent systems have been systematically presented through chemical thermodynamic modeling in terms of both activity coefficients and fugacity coefficients models. Here chemical thermodynamic model of compressible regular solution (CRS) was used for evaluation of diffusion coefficients calculations as the pure component properties would be required only. Four binary polymeric solutions of cyclohexane/polyisobutylene,

Limiting diffusion coefficients of sodium octanoate, and octanoic acid in aqueous solutions without and with α-cyclodextrin

The Taylor dispersion technique has been used for measuring limiting binary mutual diffusion coefficients of octanoic acid and sodium octanoate at T=298.15K (D0), respectively, using water as carrier solution, and different injections solutions from (0.75 to 100)·10−3mol⋅dm−3. These D0 values, together with the Stokes–Einstein equation, were used to determine the equivalent hydrodynamic radii, Rh, at infinitesimal concentration of these species (octanoic acid and sodium octanoate). In addition, the limiting diffusion coefficients of the molecular (D0m) and dissociated (D0±) forms of the octanoic acid were estimated.We have also investigated the diffusion properties for a system containing octanoic acid, α-cyclodextrin (α-CD) and water. From these results, we have estimated the percentages of free (C7COOH) and associated forms of octanoic acid (α-CD/C7COOH) and the equilibrium constant, K, for a supramolecular host–guest complex between octanoic acid and α-CD.

Interval Sorption of Alkyl Acetates and Benzenes in Poly(methyl acrylate)

We describe a simple, low-cost, gas flow vapor sorption/desorption apparatus that enables “interval” or “differential” experiments on supported polymer films, with control of small step changes in diffusant weight fraction, ω1, to intervals as small as 0.1%. The apparatus permits accurate determination of the binary mutual diffusion coefficient D12(ω1) for ω1 up to at least 3% for “condensable” organic species that typically exhibit very sharp increases in D12 with the diffusant’s weight fraction. We report results for two homologous series of diffusants, n-alkyl acetates and alkyl benzenes, in monodisperse poly(methyl acrylate) (PMA). The Vrentas–Duda free volume theory adequately accounts for the strong concentration dependence of D12 seen in all cases. Nearly constant values of the jump-unit size ratio, ξ, for the homologous set of n-alkyl acetates in the range ξ = 0.61–0.67 closely match those reported previously. For the alkyl benzenes, ξ for benzene (ξ = 0.78 ± 0.04) was higher than those for the larger homologues toluene, ethylbenzene, and cumene (ξ = 0.58–0.60). The ξ values for both homologous series are well-predicted by a free volume based estimate for eccentric diffusants, which jump as a single unit in a mixture whose components contribute different amounts of free volume per jump unit, according to their geometries.

Diffusion coefficients of paracetamol in aqueous solutions

Binary mutual diffusion coefficients measured by the Taylor dispersion method, for aqueous solutions of paracetamol (PA) at concentrations from (0.001 to 0.050)mol·dm−3 at T=298.15K, are reported. From the Nernst–Hartley equation and our experimental results, the limiting diffusion coefficient of this drug and its thermodynamic factors are estimated, thereby contributing in this way to a better understanding of the structure of such systems and of their thermodynamic behaviour in aqueous solution at different concentrations.

Diffusion of calcium gluconate in aqueous solutions of lactose at 298.15 K

Binary mutual diffusion coefficients (interdiffusion coefficients) of calcium gluconate (C12H22CaO14) in water at 298.15K and at concentrations between 0.001 and 0.0500moldm−3 have been measured, using a Taylor dispersion method. These data are discussed on the basis of the Onsager-Fuoss model. Based on these data, the equivalent conductance at infinitesimal concentration of the gluconate ion in the studied solutions has been estimated. Through the same technique, ternary mutual diffusion coefficients (D11, D22, D12 and D21) for aqueous solutions containing calcium gluconate and lactose, at T=298.15K, and at different carrier concentrations, were also measured. These data permit us to have a better understanding of the structure of these systems and the thermodynamic behaviour of calcium gluconate in different media.

Diffusion coefficients of nickel chloride in aqueous solutions of lactose at T = 298.15 K and T = 310.15 K

Binary mutual diffusion coefficients (interdiffusion coefficients) of nickel chloride in water at T = 298.15 K and T = 310.15 K, and at concentrations between (0.000 and 0.100) mol · dm −3, using a Taylor dispersion method have been measured. These data are discussed on the basis of the Onsager–Fuoss and Pikal models. The equivalent conductance at infinitesimal concentration of the nickel ion in these solutions at T = 310.15 K has been estimated using these results. Through the same technique, ternary mutual diffusion coefficients ( D 11, D 22, D 12, and D 21) for aqueous solutions containing NiCl 2 and lactose, at T = 298.15 K and T = 310.15 K, and at different carrier concentrations were also measured. These data permit us to have a better understanding of the structure of these systems and the thermodynamic behaviour of NiCl 2 in different media.

Binary mutual diffusion coefficient of aqueous solutions of propylene glycol and dipropylene glycol

Binary mutual diffusion coefficient data for aqueous solutions of propylene and dipropylene glycols were measured using the Taylor dispersion technique for each aqueous binary system at different concentrations ( x 1 = 0.2–0.80) and temperatures (303.2–323.2 K). The measured data were fit to different empirical and semi-theoretical models and compared with the values predicted from such models. The measured mutual diffusion coefficient data are well represented by either rough hard-sphere or UNIDIF model. On the side, the infinite dilution diffusion coefficient has been found greater at lower glycol molecular weight, an observation that corroborates with the property's dependence on free volume.

Binary Mutual Diffusion Coefficients of Isoniazid Aqueous Solutions at (298.15 and 310.15) K

Binary mutual diffusion coefficients measured by the Taylor dispersion method in two different laboratories (University of Naples, Federico II, Italy, and University of Coimbra, Portugal) are reported for aqueous solutions of isoniazid at concentrations from (0.000 to 0.100) mol·dm−3 and at two temperatures (298.15 and 310.15) K. The hydrodynamic radii for the isoniazid in aqueous solution are calculated from the experimental results. In addition, the Hartley equation and the experimental diffusion coefficients are used to estimate activity coefficients for aqueous isoniazid at both temperatures.

Some Transport Properties of γ-Cyclodextrin Aqueous Solutions at (298.15 and 310.15) K

Values of binary mutual diffusion (interdiffusion) coefficients, obtained by using the Taylor dispersion method, for aqueous solutions of γ-cyclodextrin in the concentration range from (0.002 to 0.010) mol·dm−3 and temperatures (298.15 and 310.15) K are reported. From these experimental results, the hydrodynamic radius values for the γ-cyclodextrin are estimated. Also, the measured diffusion coefficients are used with both Hartley’s and Gordon’s equations to estimate activity coefficients for aqueous γ-cyclodextrin. These studies are complemented by some density and viscosity measurements, carried out at the same range of concentrations and temperatures. The effect of both the viscosity of the medium and the formation of γ-cyclodextrin dimers on the estimated hydrodynamic radius is discussed.