Taylor Dispersion Technique Research Articles

On Interactions of Sulfamerazine with Cyclodextrins from Coupled Diffusometry and Toxicity Tests.

This scientific study employs the Taylor dispersion technique for diffusion measurements to investigate the interaction between sulfamerazine (NaSMR) and macromolecular cyclodextrins (β-CD and HP-β-CD). The results reveal that the presence of β-CD influences the diffusion of the solution component, NaSMR, indicating a counterflow of this drug due to solute interaction. However, diffusion data indicate no inclusion of NaSMR within the sterically hindered HP-β-CD cavity. Additionally, toxicity tests were conducted, including pollen germination (Actinidia deliciosa) and growth curve assays in BY-2 cells. The pollen germination tests demonstrate a reduction in sulfamerazine toxicity, suggesting potential applications for this antimicrobial agent with diminished adverse effects. This comprehensive investigation contributes to a deeper understanding of sulfamerazine-cyclodextrin interactions and their implications for pharmaceutical and biological systems.

Measurement of Diffusion Coefficients in Binary Mixtures and Solutions by the Taylor Dispersion Method

The theory and application of the Taylor Dispersion technique for measuring diffusion coefficients in binary systems is reviewed. The theory discussed in this paper includes both the ideal Taylor–Aris model and the estimation of corrections required to account for small deviations from this ideal associated with a practical apparatus. Based on the theoretical treatment, recommendations are given for the design of practical instruments together with suggestions for calibration, data acquisition and reduction, and the rigorous estimation of uncertainties. The analysis indicates that relative uncertainties on the order of 1% are achievable in practice.

Binary Diffusion Coefficients for Short Chain Alcohols in Supercritical Carbon Dioxide—Experimental and Predictive Correlations

Experimental binary diffusion coefficients for short-chain alcohols in supercritical carbon dioxide were measured using the Taylor dispersion technique in a temperature range of 306.15 K to 331.15 K and along the 10.5 MPa isobar. The obtained diffusion coefficients were in the order of 10-8 m2 s-1. The dependence of D on temperature and solvent density was examined together with the influence of molecular size. Some classic correlation models based on the hydrodynamic and free volume theory were used to estimate the diffusion coefficients in supercritical carbon dioxide. Predicted values were generally overestimated in comparison with experimental ones and correlations were shown to be valid only in high-density regions.

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.

Diffusion of Ethanol in Supercritical Carbon Dioxide—Investigation of scCO2-Cosolvent Mixtures Used in Pharmaceutical Applications

Diffusion coefficients, D, for ethanol in supercritical carbon dioxide (scCO2) were measured in the temperature range 306.15–331.15 K and along the 10.5 MPa isobar, using the Taylor dispersion technique. The obtained diffusivities ranged from 1.49 × 10−8 to 2.98 × 10−8 m2 s−1, an order of magnitude higher than in usual liquids. The dependence of D on temperature and solvent density was examined. Various correlation models based in the hydrodynamic theory were assessed to estimate the diffusion coefficients, with reasonable results obtained for the Wilke–Chang and Lai–Tan models.

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.

Effect of Hofmeister Ions on Transport Properties of Aqueous Solutions of Sodium Hyaluronate.

Tracer diffusion coefficients obtained from the Taylor dispersion technique at 25.0 °C were measured to study the influence of sodium, ammonium and magnesium salts at 0.01 and 0.1 mol dm−3 on the transport behavior of sodium hyaluronate (NaHy, 0.1%). The selection of these salts was based on their position in Hofmeister series, which describe the specific influence of different ions (cations and anions) on some physicochemical properties of a system that can be interpreted as a salting-in or salting-out effect. In our case, in general, an increase in the ionic strength (i.e., concentrations at 0.01 mol dm−3) led to a significant decrease in the limiting diffusion coefficient of the NaHy 0.1%, indicating, in those circumstances, the presence of salting-in effects. However, the opposite effect (salting-out) was verified with the increase in concentration of some salts, mainly for NH4SCN at 0.1 mol dm−3. In this particular salt, the cation is weakly hydrated and, consequently, its presence does not favor interactions between NaHy and water molecules, promoting, in those circumstances, less resistance to the movement of NaHy and thus to the increase of its diffusion (19%). These data, complemented by viscosity measurements, permit us to have a better understanding about the effect of these salts on the transport behaviour of NaHy.

Diffusion of Quinine with Ethanol as a Co-Solvent in Supercritical CO2.

This study aims at contributing to quinine extraction using supercritical CO2 and ethanol as a co-solvent. The diffusion coefficients of quinine in supercritical CO2 are measured using the Taylor dispersion technique when quinine is pre-dissolved in ethanol. First, the diffusion coefficients of pure ethanol in the supercritical state of CO2 were investigated in order to get a basis for seeing a relative change in the diffusion coefficient with the addition of quinine. We report measurements of the diffusion coefficients of ethanol in scCO2 in the temperature range from 304.3 to 343 K and pressures of 9.5, 10 and 12 MPa. Next, the diffusion coefficients of different amounts of quinine dissolved in ethanol and injected into supercritical CO2 were measured in the same range of temperatures at p = 12 Mpa. At the pressure p = 9.5 MPa, which is close to the critical pressure, the diffusion coefficients were measured at the temperature, T = 343 K, far from the critical value. It was found that the diffusion coefficients are significantly dependent on the amount of quinine in a small range of its content, less than 0.1%. It is quite likely that this behavior is associated with a change in the spatial structure, that is, the formation of clusters or compounds, and a subsequent increase in the molecular weight of the diffusive substance.

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.

The effects of sodium chloride on the diffusion of sulfonated resorcinarenes in aqueous solutions

The effect of sodium chloride on the diffusion of aqueous Na4ETRA (tetrasodium 5,11,17,23-tetrakissulfonatemethylen-2,8,14,20-tetra(ethyl)resorcin[4]arene) and Na4PRRA (tetrasodium 5,11,17,23-tetrakissulfonatemethylen-2,8,14,20-tetra(propyl)resorcin[4]arene) are investigated by using the Taylor dispersion technique to measure diffusion in aqueous resorcinarene solutions with and without added NaCl. In binary solutions of Na4ETRA or Na4PRRA (no added NaCl), the ETRA4− and PRRA4− ions diffuse at the same speed as the Na+ counterions to maintain electroneutrality. As a result, the binary diffusion coefficients of the resorcinarenes are weighted averages of the diffusion coefficients of the ETRA4− or PRRA4− ions and the relatively mobile Na+ ions. As the NaCl concentration is raised, the diffusion coefficients of Na4ETRA and Na4PRRA drop to the tracer diffusion coefficients of ETRA4− or PRRA4− ions in a supporting NaCl electrolyte solution. Coupled diffusion of Na4ETRA and Na4PRRA with NaCl is significant, driven primarily by the electric field (diffusion potential) generated by concentration gradients in Na4ETRA, Na4PRRA and NaCl.

Effect of sodium salts on diffusion of poly(vinyl alcohol) in aqueous solutions

Abstract The Taylor dispersion technique has been used for measuring the tracer diffusion coefficients, D0Tracer, for poly (vinyl alcohol) (PVA) in aqueous systems containing two specific electrolytes (i.e., NaCl and Na2SO4) at three different concentrations (0.020, 0.050 and 0.10 mol dm−3), and at 25 °C. The selection of these salts has been based on the Hofmeister series of cations and anions, which order the ions with respect to the behavior of some macroscopic properties (such as, surface tension) and that can be interpreted as an effect salting-out or salting-in, depending if the target ions are strongly (kosmotropic) or a weakly hydrated (chaotropic). In this work, we have been used the combination of two kosmotropic ions (Na2SO4) and another one with a kosmotropic cation and a chaotropic anion (NaCl). These data, complemented by NMR measurements, permit us to have a better understanding about the effect of these sodium salts on transport and thermodynamic behaviour of PVA.

Developing a new correlation for the aliphatic and aromatic hydrocarbon diffusion coefficients at infinite dilution in ionic liquids

In this work the Taylor dispersion technique has been used to measure the diffusion coefficients of n-heptane and toluene at infinite dilution in four ionic liquids, namely 1-ethyl-3-methylimidazolium thiocyanate ([emim][SCN]), 1-ethyl-3-methylimidazolium tricyanomethanide ([emim][TCM]), 1-butyl-3-methylimidazolium tricyanomethanide ([bmim][TCM]), and 1-butyl-4-methylpyridinium tricyanomethanide ([4bmpy][TCM]), at the range temperatures from (298.2–333.2) K. The hydrocarbon diffusion is faster at higher temperatures because of the lower ionic liquid viscosity, and toluene diffuses faster than n-heptane due to its smaller molecular volume. In addition, it is seen that the values of the n-heptane diffusion coefficients decrease with an increase in the molecular weight and molar volume of the ionic liquid. The same is observed for the diffusion coefficients of toluene in the most viscous ionic liquids ([bmim][TCM], [4bmpy][TCM] and [4empy][Tf2N]), but, conversely, they increase for the least viscous ionic liquids ([emim][SCN], [emim][DCA], and [emim][TCM]). This behavior suggests that the strength of the toluene-ionic liquid chemical interactions have a significant effect on diffusion. A new empirical correlation has been proposed as a variation of the Wilke-Chang equation. Two additional variables have been introduced in this correlation; the molar fraction of the maximum hydrocarbon solubility, to take into account the toluene-ionic liquid interactions, as well as the molar volume of the ionic liquid, because of the huge difference between them and the solute. This new correlation satisfactorily fits the experimental data with an average deviation of 9.6%.

Near-Critical Behavior of Fick Diffusion Coefficient in Taylor Dispersion Experiments

This paper is addressing the challenge related to understanding the experimental results obtained by Taylor dispersion technique when working under high pressure with supercritical carbon dioxide (CO2). We discuss typical experimental problems that arise when using the Taylor dispersion method for measuring diffusion coefficients in the supercritical fluids. The diffusion coefficients of the two samples in supercritical carbon dioxide were measured along the isobars at different temperatures. The diffusion coefficients of ethanol in supercritical CO2 have been measured in the temperature range from 304.15 to 343 K along the isobar p = 12.0 MPa. Experiments with the gaseous CH4/CO2 mixture with a mole fraction of CH4 = 0.2052 mol mol− 1 have been conducted in the temperature range from 317.85K to 343.15 K along the isobar p = 12.5 MPa. A comparative analysis of a diffusion behavior of these very different mixtures is presented.

Limiting diffusion coefficients of glufosinate ammonium, cymoxanil and imidacloprid in aqueous solutions

We have measured the limiting diffusion coefficients of three different pesticides in aqueous solutions: glufosinate ammonium, cymoxanil and imidacloprid, highly used for tomato production. The experiments were carried in aqueous solutions, at 25 °C, at concentrations below 3 mmol dm−3 (depending on the solubility of pesticides). Mutual diffusion coefficients (D) obtained by using the Taylor dispersion technique, and by using pure water and different solutions of concentration c, as carrier stream and injection solutions, respectively, show that the systems can be analyzed as binary ones. The hydrodynamic radii and the respective limiting diffusion coefficients of the glufosinate anion, cymoxanil and imidacloprid have also been estimated. For the electrolyte glufosinate ammonium, by using the Nernst equation, it is also possible to estimate the limiting molar conductivity of the glufosinate anion.In order to mimic field conditions, we have measured the tracer diffusion coefficients of glufosinate ammonium in aqueous solutions of ammonium nitrate at different concentrations, permitting us to analysis the salting-in effects on the diffusion of this pesticide.From these measurements useful information on the thermodynamic, transport and structural parameters can be obtained, allowing a better understanding of the behaviour of these compounds in aqueous solution.These studies have been complemented with 1H and 31P NMR spectroscopy in order to obtain more additional structural information on the interaction of ammonium nitrate with glufosinate-ammonium in aqueous solution. The results obtained support the hypothesis of salting-in effects on the diffusion of this pesticide in aqueous solution.

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.

Diffusion of methane in supercritical carbon dioxide across the Widom line

Diffusion of methane diluted in supercritical carbon dioxide is studied by experiment and molecular simulation in the temperature range from 292.55 to 332.85 K along the isobars 9.0, 12.5 and 14.7 MPa. Measurements of the Fick diffusion coefficient are carried out with the Taylor dispersion technique. Molecular dynamics simulation and the Green-Kubo formalism are employed to obtain Fick, Maxwell-Stefan and intradiffusion coefficients as well as shear viscosity. The obtained diffusion coefficients are on the order of 10−8 m2/s. The composition, temperature and density dependence of diffusion is analyzed. The Fick diffusion coefficient of methane in carbon dioxide shows an anomaly in the near-critical region. This behavior can be attributed to the crossing of the so-called Widom line, where the supercritical fluid goes through a transition between liquid-like and gas-like states. Further, several classical equations are tested on their ability to predict this behavior and it is found that equations that explicitly include the density are better suited to predict the sharp variation of the diffusion coefficient near the critical region predicted by molecular simulation.

Aliphatic and aromatic hydrocarbon diffusion coefficients at infinite dilution in [emim][DCA] and [4empy][Tf2N] ionic liquids

In this work the diffusion coefficients at infinite dilution of eight aromatic and aliphatic hydrocarbons (n-hexane, n-heptane, n-octane, n-nonane, benzene, toluene, p-xylene, and ethylbenzene) in 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) and 1-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4empy][Tf2N]) ionic liquids (ILs) at (298.2–333.2) K have been measured using the Taylor dispersion technique. First, three well-known systems, namely n-hexane, n-octane, and toluene at infinite dilution in n-heptane, have been studied to assure the reliability of the experimental equipment and to set the operational conditions which comply with the requirements for the Taylor dispersion technique. From the data obtained, it has been shown that the hydrocarbon diffusion is slower in ILs than in hydrocarbons because of the higher solvent viscosity. In the same way, hydrocarbon diffusion coefficients in [emim][DCA] presented a high value than in [4empy][Tf2N]. Given the large deviation in the coefficient diffusion predicted by the Wilke-Chang correlation, a different correlation has been proposed to estimate them at the studied temperature interval. The modified Wilke-Chang equation satisfactorily represented the present experimental data.

Drug Delivery Systems: Study of Inclusion Complex Formation between Methylxanthines and Cyclodextrins and Their Thermodynamic and Transport Properties

This paper presents an analysis of the molecular mechanisms involved in the formation of inclusion complexes together with some structural interpretation of drug–carrier molecule interactions in aqueous multicomponent systems comprising methylxanthines and cyclodextrins. The determination of apparent partial molar volumes () from experimental density measurements, both for binary and ternary aqueous solutions of cyclodextrins and methylxanthines, was performed at low concentration range to be consistent with their therapeutic uses in the drug-releasing field. The estimation of the equilibrium constant for inclusion complexes of 1:1 stoichiometry was done through the mathematical modelling of this apparent molar property. The examination of the volume changes offered information about the driving forces for the insertion of the xanthine into the cyclodextrin molecule. The analysis on the volumes of transfer, Δ, and the viscosity B-coefficients of transfer, ΔB, for the xanthine from water to the different aqueous solutions of cyclodextrin allowed evaluating the possible interactions between aqueous solutes and/or solute–solvent interactions occurring in the solution. Mutual diffusion coefficients for binary, and ternary mixtures composed by xanthine, cyclodextrin, and water were measured with the Taylor dispersion technique. The behavior diffusion of these multicomponent systems and the coupled flows occurring in the solution were analyzed in order to understand the probable interactions between cyclodextrin–xanthine by estimating their association constants and leading to clearer insight of these systems structure. The measurements were performed at the standard (298.15 ± 0.01) K and physiological (310.15 ± 0.01) K temperatures.

Effects of Hydrogen Bonding on Diffusion of Aromatic Compounds in Acetone: An Experimental Investigation from 268.2 to 328.2 K.

Diffusion coefficients of pseudoplanar aromatic compounds at infinite dilution in acetone have been measured at different temperatures by the Taylor dispersion technique. The data of the polar solutes that can form hydrogen bonds with acetone are compared with those of the nonpolar ones incapable of hydrogen bonding to quantify the effects of hydrogen-bonded association on diffusion. The effects are further found to correlate strongly with the overall hydrogen-bonded acidity of the polar solutes containing proton-donating groups. For the nonpolar solutes in this study, the diffusivities at different temperatures can be expressed very well by the recently developed molecular-modified fractional Stokes-Einstein relation with only two constants. An innovative model for solute diffusion in liquid solutions, which is constructed by combining the molecular-hydrodynamic relation for nonpolar solutes with the overall hydrogen-bonded acidity scale for polar solutes, is introduced for representing the diffusivities of different types of disc-shaped molecules at various temperatures. An equation developed from this model is demonstrated to be capable of calculating a total of 191 diffusion data of both the hydrogen-bonded and the nonassociated aromatic solutes in acetone from 268.2 to 328.2 K to a standard deviation of 2.7%.