Ternary Mutual Diffusion Coefficients Research Articles

Transport Properties in Multicomponent Systems Containing Cyclodextrins and Nickel Ions.

In this work, we propose a comprehensive experimental study of the diffusion of nickel ions in combination with different cyclodextrins as carrier molecules for enhanced solubility and facilitated transport. For this, ternary mutual diffusion coefficients measured by Taylor dispersion method are reported for aqueous solutions containing nickel salts and different cyclodextrins (that is, α-CD, β-CD, and γ-CD) at 298.15 K. A combination of Taylor dispersion and other methods, such as UV-vis spectroscopy, will be used to obtain complementary information on these systems. The determination of the physicochemical properties of these salts with CDs in aqueous solution provides information that allows us to understand solute-solvent interactions, and gives a significant contribution to understanding the mechanisms underlying diffusional transport in aqueous solutions, and, consequently, to mitigating the potential toxicity associated with these metal ions. For example, using mutual diffusion data, it is possible to estimate the number of moles of each ion transported per mole of the cyclodextrin driven by its own concentration gradient.

Effect of Caffeine in the Diffusion Behaviour of Analgesic Drugs in Aqueous Solutions

The aim of the study was to examine the effect of caffeine on the diffusion of two pain-relieving drugs, namely paracetamol and sodium salicylate, in aqueous solutions at a temperature of 25.00ºC, using the Taylor dispersion method to determine the mutual diffusion coefficients for these ternary aqueous solutions. Ternary mutual diffusion coefficients are reported for aqueous solutions of paracetamol + caffeine, and sodium salicylate + caffeine, at 25.00ºC, and concentrations up to 0.050mol·dm-3. The data indicate that the presence of caffeine affects the diffusion of analgesic drugs. For example, a coupled diffusion of these drugs with caffeine was observed through the non-zero values of the cross-diffusion coefficients. Support for this came from the good agreement between our data and the predicted by a model of the diffusion that includes 1:1 complex, being obtained the association constants for systems [(caffeine and paracetamol) and (caffeine and salicylate sodium)], K=70mol-1·dm3 and K=80, respectively. These data provide us with a better understanding of the mechanisms of mass transport through diffusion in biological systems, as well as the structure of these systems.

Interactions of Sodium Salicylate with β-Cyclodextrin and an Anionic Resorcin[4]arene: Mutual Diffusion Coefficients and Computational Study.

The interaction between sodium salicylate (NaSal) and the two macrocycles 5,11,17,23-tetrakissulfonatomethylene-2,8,14,20-tetra(ethyl)resorcinarene (Na4EtRA) and β-cyclodextrin (β-CD) has been studied by the determination of ternary mutual diffusion coefficients, and spectroscopic and computational techniques. The results obtained by the Job method suggest that the complex formation is given in a 1:1 ratio for all systems. The mutual diffusion coefficients and the computational experiments have shown that the β-CD-NaSal system presents an inclusion process, whereas the Na4EtRA-NaSal system forms an outer-side complex. This fact is also in line with the results obtained from the computational experiments, where the calculated solvation free energy has been found to be more negative for the Na4EtRA-NaSal complex because of the partial entry of the drug inside the Na4EtRA cavity.

Effect of potassium dihydrogen citrate on the diffusion behaviour of citric acid

Ternary mutual diffusion coefficients (D11, D22, D12, and D21) in aqueous solutions of citric acid (H3Cit) (component 1) plus potassium dihydrogen citrate (KH2Cit) (component 2) at 298.15 K and concentrations up to 0.040 mol dm−3 were measured using a Taylor scattering method. The obtaining of the negative values for D12 and D21 cross coefficients, mainly in dilute solutions and for the first ones, indicates that there is a strongly coupled diffusion of these components. In fact, the concentration gradients of KH2Cit drive substantial counter current coupled flows of H3Cit citric acid, indicating that each mol of diffusing potassium dihydrogen citrate can counteract the transport of up to 0.74 mol of citric acid, approximately. A better interpretation of the electrostatic mechanism for the coupled diffusion of KH2Cit and H3Cit was achieved based on the values predicted by the Nernst-Planck equations, having been verified as a good agreement between them and experimental data.

Diffusion of Vanadium Ions in Artificial Saliva and Its Elimination from the Oral Cavity by Pharmacological Compounds Present in Mouthwashes.

In this study, diffusion coefficients of ammonium vanadate at tracer concentrations in artificial saliva with and without sodium fluoride, at different pH values, were measured using an experimental model based on the Taylor dispersion technique. Ternary mutual diffusion coefficients (D11, D22, D12, and D21) for four aqueous systems {NH4VO3 (component 1) + β-cyclodextrin (β-CD) (component 2),} {NH4VO3 (component 1) + β-cyclodextrin (HP-β-CD) (component 2)}, {NH4VO3 (component 1) + sodium dodecyl sulphate (SDS) (component 2)} and {NH4VO3 (component 1) + sodium hyaluronate (NaHy) (component 2)} at 25.00 °C were also measured by using the same technique. These data showed that diffusion of ammonium vanadate was strongly affected in all aqueous media studied. Furthermore, a significant coupled diffusion of this salt and β-CD was observed through the non-zero values of the cross-diffusion coefficients, D12, allowing us to conclude that there is a strong interaction between these two components. This finding is very promising considering the removal, from the oral cavity, of vanadium resulting from tribocorrosion of Ti-6Al-4V prosthetic devices.

Ternary diffusion in aqueous sodium salicylate + sodium dodecyl sulfate solutions

A Taylor dispersion method has been used to measure ternary mutual diffusion coefficients (D11, D22, D12 and D21) in aqueous sodium salicylate (NaSal) (component 1) + sodium dodecyl sulfate (NaDS) (component 2) solutions at 25.00 °C and concentrations up to 0.050 mol dm−3. In general, the data show that diffusion of NaDS drives co-current flow of NaSal, and that diffusion of NaSal drives also co-current flows of NaDS. The experimental ternary diffusion coefficients are compared with Nernst-Planck coefficients allowing a better interpretation of the electrostatic mechanism for the coupled diffusion of NaSal and SDS. From these equations, at compositions below the critical micelle concentration (cmc) of NaDS, small positive values of D12 and D21 are obtained resulting from fully dissociation of NaDS; however, at compositions above the cmc, the coupled diffusion of NaSal and NaDS becomes significant, as indicated by the experimental and predicted large positive cross-diffusion coefficients, D21. There is a good agreement between our data and those predicted by the Nernst-Planck equations for NaDS concentrations below and above the cmc.

Complexation of 5-Fluorouracil with β-Cyclodextrin and Sodium Dodecyl Sulfate: A Useful Tool for Encapsulating and Removing This Polluting Drug.

The formation of complexes of the drug 5-fluorouracil (5-FU) with β-cyclodextrin (β-CD) and sodium dodecyl sulphate (SDS) was studied through experimental measurements of the ternary mutual diffusion coefficients (D11, D22, D12, and D21) for the systems {5-FU (component 1) + β-CD (component 2) + water} and {5-FU (component 1) + SDS (component 2) + water} at 298.15 K and at concentrations up to 0.05 mol dm−3 by using the Taylor dispersion method, with the objective of removing this polluting drug from the residual systems in which it was present. The results found showed that a coupled diffusion of 5-FU occurred with both β-CD and SDS, as indicated by the nonzero values of the cross-diffusion coefficients, D12 and D21, as a consequence of the complex formation between 5-FU and the β-CD or SDS species. That is, 5-FU was solubilized (encapsulated) by both carriers, although to a greater extent with SDS (K = 20.0 (±0.5) mol−1 dm3) than with β-CD (K = 10.0 (±0.5) mol−1 dm3). Values of 0.107 and 0.190 were determined for the maximum fraction of 5-FU solubilized with β-CD and SDS (at concentrations above its CMC), respectively. This meant that SDS was more efficient at encapsulating and thus removing the 5-FU drug.

Effect of Cobalt and Chromium Ions on the Chlorhexidine Digluconate as Seen by Intermolecular Diffusion

Metal ions such as cobalt (II) and chromium (III) might be present in the oral cavity, as a consequence of the corrosion of Co-Cr dental alloys. The diffusion of such metal ions into the organism, carried by saliva, can cause health problems as a consequence of their toxicity, enhanced by a cumulative effect in the body. The effect of the chlorhexidine digluconate, which is commonly used in mouthwash formulations, on the transport of these salts is evaluated in this paper by using the Taylor dispersion technique, which will allow an assessment of how the presence of chlorhexidine digluconate (either in aqueous solution or in a commercial formulation) may affect the diffusion of metal ions. The ternary mutual diffusion coefficients of metal ions (Co and Cr) in the presence of chlorhexidine digluconate, in an artificial saliva media, were measured. Significant coupled diffusion of CoCl2 (and CrCl3) and chlorhexidine digluconate is observed by analysis of the non-zero values of the cross-diffusion coefficients, D12 and D21. The observed interactions between metal ions and chlorhexidine digluconate suggest that the latter might be considered as an advantageous therapeutic agent, once they contribute to the reduction of the concentration of those ions inside the mouth.

Dependence of Viscosity and Diffusion on β-Cyclodextrin and Chloroquine Diphosphate Interactions

Mutual diffusion coefficients of chloroquine diphosphate (CDP) in aqueous solutions both without and with β-cyclodextrin (β-CD) were measured at concentrations from (0.0000 to 0.0100) mol dm−3 and 298.15 K, using the Taylor dispersion technique. Ternary mutual diffusion coefficients (Dik) measured by the same technique are reported for aqueous CDP + β-CD solutions at 298.15 K. The presence of β CD led to relevant changes in the diffusion process, as showed by nonzero values of the cross-diffusion coefficients, D12 and D21. β-CD concentration gradients produced significant co-current coupled flows of CDP. In addition, the effects of β-CD on the transport of CDP are assessed by comparing the binary diffusion coefficient of aqueous CDP solutions with the main diffusion coefficient (D11) measured for ternary {CDP(1) + β-CD(2)} solutions. These observations are supported by viscosity analysis. All data allow to have a better interpretation on the effect of cyclodextrin on the transport behavior of CDP.

Host-guest paracetamol/cyclodextrin complex formation evaluated from coupled diffusion measurements

Ternary mutual diffusion coefficients (D11, D22, D12 and D21) measured by the Taylor dispersion method are reported for aqueous solutions of paracetamol (1) in the presence of β-cyclodextrin (β-CD) (2) at 298.15 K and solute concentrations up to 0.050 (mol dm−3). The diffusion of paracetamol and β-CD is coupled, as indicated by non-zero values of the cross-diffusion coefficients, D12 and D21 measuring interactions between the fluxes of the drug and the carbohydrate. The measured ternary diffusion coefficients are in close agreement with the diffusion coefficients predicted by a model assuming a 1:1 (paracetamol):(β-CD) complex. The association constant K = 27 (mol−1 dm3) for the formation of the complex was estimated from the diffusion data.

Coupled mutual diffusion in aqueous paracetamol + sodium hydroxide solutions

Ternary mutual diffusion coefficients (Dik) measured by the Taylor dispersion method are reported for aqueous paracetamol + NaOH solutions at 25.00 °C and concentrations up to 0.050 mol dm−3. The coupled diffusion of paracetamol (1) and NaOH (2) is significant, as indicated by the large negative cross-diffusion coefficients. In sodium hydroxide solutions, paracetamol, a weak acid, is partially converted to its sodium salt. To help interpret the results, the measured Dik coefficients are compared with predictions based on Nernst and Nernst-Planck equations for mixed electrolyte solutions. The analysis shows that the diffusion of the paracetamol and sodium hydroxide components is strongly coupled by the electric field (diffusion potential) generated by the ionic concentration gradients.

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.

Effect of sodium chloride on the behaviour of the lactose in aqueous solution studied from diffusion experiments and molecular dynamics simulations

Ternary mutual diffusion coefficients (D11, D22, D12 and D21) measured by the Taylor dispersion method are reported for aqueous solutions of (NaCl + lactose) at 298.15 K and NaCl concentrations up to 1.00 mol dm−3. The coupled diffusion of NaCl (1) and lactose (2) is significant, as indicated by the large negative cross-diffusion coefficients. In this sense, from the values of these cross-diffusion coefficients a counter-transport of 0.4 mol of NaCl per mol of diffusing lactose is inferred, whereas only 0.02 mol of lactose could be counter-transported by one diffusing mole of NaCl. The main diffusion coefficient data are compared with the binary ones of both pure solutes in water and discussed on the basis of Onsager-Fuoss and Pikal models. From these data and by performing molecular dynamics simulations, it is possible to obtain a better understanding of the effect of sodium chloride on the transport of lactose in aqueous solutions, as well as to assume the importance of the Na+-lactose short-range interaction, competing with the coulomb long-range interaction between the sodium and chloride ions, especially at low concentration of NaCl.

Interactions between glycyl-L-phenylalanine and β-cyclodextrin from diffusion, spectroscopic and computational studies

The transport and association of the dipeptide glycyl-L-phenylalanine (Gly-L-Phen) in solutions containing cyclodextrins are of prime importance given its relevance in different areas, from biochemistry to wastewater treatment. We have investigated the interaction between aqueous Gly-L-Phen and β-cyclodextrin (β-CD) by NMR, DFT calculations in parallel with UV/visible absorption, luminescence spectral measurements and diffusion experiments. Ternary mutual diffusion coefficients of aqueous {Gly-L-Phen + β-CD} solutions have been measured by using the Taylor dispersion technique. The results show that the association of Gly-L-Phen and β-CD has a significant effect on the diffusion coefficients, consistent with an association constant of about 50 to 100, assuming a 1:1 (Gly-L-Phen):(β-CD) stoichiometry. This stoichiometry has been assessed by the continuous variation (Job's plot) method and the association constant was determined by using the Hildebrand-Benesi equation modified for NMR applications. The association constant was estimated to be equal to 40. This association constant is in close agreement with that obtained by fluorescence measurements (K = 43). Additionally, from NMR, detailed structural information on the complex has been obtained. This has been complemented by DFT and TD-DFT studies.

A comparative study between the behavior diffusion of α-aminobutyric acid and γ-aminobutyric acid in sodium chloride aqueous solutions

Ternary mutual diffusion coefficients measured by the Taylor dispersion method are reported for two aqueous systems, that is, DL-2-aminobutyric acid (AABA) + sodium chloride, and DL-4-aminobutyric acid (GABA) + sodium chloride at 298.15 K, and at different carrier concentrations (from 0 to 0.010 mol dm−3). These data, complemented by NMR measurements, permit us to have a better understanding of the structure of these ternary systems, and their thermodynamic and transport behaviour. The effect of the ionic strength on the transport properties of both amino acids has been assessed. Contrary to AABA, the presence of sodium chloride does not affect the structure of GABA and its diffusion properties. This has been justified by the preferential intramolecular electrostatic interaction between ammonium and carboxylate groups.

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.

Uncommon temperature effect on the interaction between levodopa and β-cyclodextrin seen by diffusometry and NMR spectroscopy

Experimental ternary mutual diffusion coefficients (D11, D22, D12 and D21, obtained by the Taylor dispersion method, are reported for aqueous solutions of levodopa (L-dopa)+β-cyclodextrin (β-CD) solutions at 310.15K and concentrations up to 0.007moldm−3. Comparison of these experimental results with data predicted by a model of the diffusion that includes inclusion complexes, it is possible to conclude that the association equilibrium at 310.15K has little effect on the diffusion properties. Support for this comes from 1H NMR spectroscopy, which shows that there are no interactions, which may be related to the reduced L-dopa/cavity interactions resulting from both the amine and carboxylate groups on L-dopa being charged.

Isothermal molecular diffusion in mixtures containing toluene, cyclohexane and methanol

The Taylor dispersion technique has been used for measuring ternary mutual diffusion coefficients for mixtures of cyclohexane-toluene-methanol, corresponding to the mixtures under study on the International Space Station (ISS) within the scope of the project DCMIX2 (second series of the experiment Diffusion Coefficients in Mixtures). Five ternary systems with different composition of cyclohexane-toluene-methanol were investigated in order to accurately obtain the mass diffusion coefficients, contributing to a better understanding of the isothermal molecular diffusion in conjunction with the coupled flows of solutes occurring in such fluid systems. Current standardized protocols for carrying out an experience are also examined to understand if the experimental conditions may be ill conditioning the final results.

Effect of pH in the structure and mass transport by diffusion of theophylline

The influence of hydrochloric acid and sodium hydroxide on the diffusion of aqueous solutions of theophylline (TPh) has been investigated by using Taylor dispersion method to measure ternary mutual diffusion coefficients for aqueous solutions of (TPh+HCl) and (TPh+NaOH) at 25°C. The goal of this research is to have an assessment on the effect of the pH on the transport of this drug and thus giving a better understanding on the mechanisms behind the mass transport by diffusion. This has been complemented with 1H and 13C NMR spectroscopy combined with DFT calculations allowing to confirm the presence of different species depending on the local pH, corresponding to the doubly protonated TPh (pH 2.0), singly protonated TPh (pH 3.0), and the neutral TPh base, above pH 8.8.

Effect of 2-Hydroxypropyl-β-cyclodextrin on the diffusion behaviour of L-dopa in aqueous solutions

Ternary mutual diffusion coefficients (D11, D22, D12 and D21) measured by the Taylor dispersion method are reported for aqueous solutions of levodopa (L-dopa) (1) in the presence of 2-Hydroxypropyl-β-cyclodextrin (HP-β-CD) (2) at 25°C and 37°C and concentrations up to 0.005mol·dm−3. The effects of HP-β-CD (HP-β-CD) on the transport of L-dopa are assessed by comparing the binary diffusion coefficient of aqueous L-dopa solutions with the main diffusion coefficient (D11) measured for ternary {L-dopa (1)+HP-β-CD (2)} solutions. 1H NMR spectroscopy suggests no significant complexation between HP-β-CD and L-dopa. However, coupled diffusion of L-dopa and HP-β-CD occurs, as indicated by non-zero values of the cross-diffusion coefficients, D12 and D21. HP-β-CD concentration gradients produce significant co-current coupled flows of L-dopa.