Tracer diffusion in aqueous sucrose and urea solutions

Easteal, Allan J.

doi:10.1139/v90-248

Cited by 33 publications

(16 citation statements)

References 14 publications

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“…Figure 5 shows that the logarithm of diffusion coefficients of water, ethanol and TPA decreases linearly with the logarithm of the viscosity of the corresponding clear sol. This means that the diffusion coefficients are dependent on the viscosity of the medium following a relationship of the form [72]:…”

Section: H Nmr Dosymentioning

confidence: 99%

Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

et al. 2016

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Abstract:The dynamic behavior of tetrapropylammonium (TPA) cations in the clear precursor sols for silicalite synthesis has been investigated by 1 H diffusion ordered spectroscopy (DOSY), T 1 , T 2 , and T 1ρ 1 H relaxation, as well as 1 HÑ 13 C cross polarization (CP) nuclear magnetic resonance. The DOSY NMR experiments showed the presence of strong solute-solvent interactions in concentrated sols, which are decreasing upon dilution. Similarities in dependence of diffusion coefficients with fractional power of the viscosity constant observed for nanoparticles, TPA cations and water led to the conclusion that they aggregate as anisotropic silicate-TPA particles. Relaxation studies as well as 1 HÑ 13 C CP experiments provide information on dynamic properties of ethanol, water and TPA cations, which are function of silicate aggregates. The general tendency showed that the presence of silicate as oligomers and particles decreases the relaxation times, in particular T 2 and T 1ρH , as a consequence of involvement of these latter in ion-pairing interactions with water-solvated TPA molecules slowing down their mobility. Furthermore, from the 1 HÑ 13 C CP dynamics curve profiles a change in the CP transfer regime was observed from fast (T CH << T 1ρH ) for solutions without silicates to moderate (T CH~T1ρH ) when silicates are interacting with the TPA cations that may reflect the occlusion of TPA into flexible silicate hydrate aggregates.

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Section: H Nmr Dosymentioning

confidence: 99%

Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

et al. 2016

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“…The values of diffusion coefficients are 2.28, 0.40, 1.45, and 0.06 (10 −5 cm 2 s −1 ) in water, water−GB, water−urea, and water−urea−GB mixtures, respectively, which are found to be in reasonable agreement with available reported values. 47,88 The diffusion of water molecules is less in the mixtures of these osmolytes, suggesting that they strengthen the water−water interaction. The lower values of D in water−GB and water− urea−GB suggest strong association of GB with water molecules ( Figure S5, Supporting Information).…”

Section: The Journal Of Physical Chemistry Bmentioning

confidence: 99%

Salting-Out of Methane in the Aqueous Solutions of Urea and Glycine–Betaine

2015

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We have studied the hydrophobic association and solvation of methane molecules in aqueous solutions of urea and glycine betaine (GB). We have calculated the potentials of mean force (PMFs) between methane molecules in water, aqueous GB, aqueous urea and aqueous urea-GB mixtures. The PMFs and equilibrium constants indicate that both urea and GB increase the hydrophobic association of methane. Calculation of thermodynamic parameters shows that the association of methane is stabilized by entropy whereas solvation is favored by enthalpy. In the case of the water-urea-GB mixture, both hydrophobic association and solvation are stabilized by entropy. From the investigation of radial distribution functions, running coordination numbers and excess coordination numbers, we infer that both urea and GB are preferentially excluded from methane surface in the mixtures of osmolytes and methane is preferentially solvated by water molecules in all the mixtures. The favorable exclusion of both urea and GB from the methane surface suggests that both urea and GB increase the interaction between methane molecules, i.e., salting-out of methane. We observe that addition of both urea and GB to water enhances local water structure. The calculated values of diffusion constants of water also suggest enhanced water-water interactions in the presence of urea and GB. The calculated free energies of methane in these mixtures show that methane is less soluble in the mixtures of urea and GB than in water. The data on solvation free energies support the observations obtained from the PMFs of methane molecules.

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“…12,14,15 During 0.75 V anodal dc iontophoresis with the Nuclepore membranes, water and urea fluxes were essentially the same at the same donor concentration (permeability coefficients of urea and water ) 1.1 ( 0.4 × 10 -5 and 1.2 ( 0.3 × 10 -5 cm/s, respectively, average ( SD, n ) 3), demonstrating that the water velocity was essentially the same as the average velocity for urea and that the electroosmotic transport was at the convection limit. 2 Tritiated water has been used to study the barrier properties of skin [16][17][18] and the electroosmosis behavior of skin.…”

Section: Analysis Of the Water/urea Dual-permeant Datasmentioning

confidence: 99%

Pore charge distribution considerations in human epidermal membrane electroosmosis

Ghanem

Higuchi

1999

Journal of Pharmaceutical Sciences

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The aim of this study was to assess the extent to which a model with pores having only net negative charges would adequately describe transdermal electroosmosis in human epidermal membrane (HEM) at neutral pH. Such information would enhance the predictive value of the modified Nernst-Planck model for transdermal iontophoresis, in addition to providing insights regarding the likelihood of significant pore charge distribution in HEM. Baseline results (the control) obtained from 0.1 to 0.4 V anodal and cathodal electroosmosis experiments with synthetic polycarbonate membranes (Nuclepore membranes), using radiolabeled urea and mannitol as the model permeants, demonstrated that such a membrane system can be modeled by the electrokinetic (electroosmosis) theory with the assumption of the pores possessing only negative charges. The studies with HEM were carried out at low voltage (/approximately = 1.0 V) where significant field-induced pore formation in HEM occurred. In both the low and high voltage studies, radiolabeled urea, mannitol, and water were employed as permeants in cathodal and anodal iontophoresis experiments. The results of the low voltage iontophoresis experiments suggest significant pore charge distribution in HEM (a significant deviation between the predictions from the single pore charge type assumption and the experimental data). Under the higher applied voltage conditions (>/approximately = 1.0 V), results from anodal and cathodal electroosmosis studies were consistent with the model in which the HEM has only pores that are net negatively charged.

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Tracer diffusion in aqueous sucrose and urea solutions

Cited by 33 publications

References 14 publications

Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

Tetrapropylammonium Occlusion in Nanoaggregates of Precursor of Silicalite-1 Zeolite Studied by 1H and 13C NMR

Salting-Out of Methane in the Aqueous Solutions of Urea and Glycine–Betaine

Pore charge distribution considerations in human epidermal membrane electroosmosis

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