Dielectric Constants of Some Organic Solvent-Water Mixtures at Various Temperatures

Åkerlöf, Gösta

doi:10.1021/ja01350a001

Cited by 1,233 publications

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“…Z = 0.1 M was adjusted with a salt ( K N 0 3 , N a N 0 3 or NaCI04). The dielcctric constants E for the ethanol/water mixtures are interpolated rrom the data given in Tabk XI1 of [26]; those for the dioxanc/water mixtures are from [27]. A dash (-) indicates values not determined but, if needed, these values may be interpolated with great precision (see Fig.…”

Section: Resultsmentioning

confidence: 99%

An estimation of the equivalent solution dielectric constant in the active-site cavity of metalloenzymes. Dependence of carboxylate - metal-ion complex stabilities on the polarity of mixed aqueous/organic solvents

et al. 1985

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The stability constants of the 1:l complexes between Cu2+ and Zn2+ with formate, acetate and several phenylalkanecarboxylates, i.e. C6H5-(CH2)n-C00-with n = 0 to 5, are summarized for water, 50% aqueous ethanol and 50% aqueous dioxane ( I = 0.1 M; 25°C): Complex stability depends upon carboxylate group basicity. The influence of varying amounts of ethanol or dioxane (up to 90%) on the stability of the Cu2' and Zn2+ (M") complexes with formate and acetate (CA) was measured by potentiometric pH titrations. The values for pf(,(,., and log K&-.) increase, as expected, with increasing amounts of the organic solvents, i.e. with decreasing solvent polarity. The changes in the equilibrium constants are also evaluated with regard to the mole fractions of the organic solvents and the corresponding dielectric constants. These results may be used to estimate for low dielectric cavities in proteins the equivalent solution dielectric constant on the basis of enhanced carboxylate basicity or metal ion binding capability (method 1). Furthermore, the measured stability constants are used for comparisons of the coordination tendency of carboxylate ligands towards zinc(I1)-metalloenzymes (method 2) ; in this way the equivalent solution dielectric constants in the active-site cavities of bovine carbonic anhydrase and carboxypeptidase A are estimated: the values are of the order of 35 and 70, respectively. This method seems to be generally applicable to metalloproteins.Among the prominent binding sites for metal ions in biological systems are the carboxylate, imidazole and amino groups [l -31. They are not only part of the low-molecularmass ligands [4], but occur also as side chains in proteins, sometimes located in low dielectric cavities.The acidity constants of N and 0 ligands are clearly dependent upon the polarity of the solvent [l, 51: the basicity of N ligands (with no charge) usually decreases as the polarity of the solvent decreases, while the basicity of 0 ligands (with a negative charge) increases markedly as the dielectric constant decreases. The change in the stability of complexes [l] is in accord with the change in basicity, but with N ligands the stability decreases usually only slightly, as the polarity of the solvent decreases, while with 0 ligands the increase in stability may be quite pronounced. This means that the affinity towards metal ions of an imidazole moiety is expected to change little with a change in solvent polarity, while the change Correspondence to H . Sigel, Institut fur Anorganische Chemie der Universitat Basel, Spitalstrasse 51, CH-4056 Basel, SwitzerlandAhhreviutions. Ac-, acetate; CA-, carboxylate ligand; M 2 + , general divalent metal ion. Additionally, in the Supplement: Bz-, benzoate; PAC-, 2-phenylacetate; PBu-, 4-phenylbutyrate; PCa-, 6-phenylcapronate; PPr -, 3-phenylpropionate; PVa-, 5-phenylvalerate.Miniprint supplement. Some parts of this work, including Materials and Measurements, and further details on Results and Discussion, are given in a miniprint supplement a t the end of the p...

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Section: Resultsmentioning

confidence: 99%

An estimation of the equivalent solution dielectric constant in the active-site cavity of metalloenzymes. Dependence of carboxylate - metal-ion complex stabilities on the polarity of mixed aqueous/organic solvents

et al. 1985

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“…The above expression gives the temperature-dependent pore dielectric constant as a function of the temperature-dependent pore radius and dielectric constant of the annulus of water lining the pore inner surface. According to Bowen et al [21], the dielectric constant of the ordered layer of water forming the annulus, *  was found to be 31 from their experiments at 25 o C. Since the extensive experimentation to determine the exact variation of this quantity as a function of temperature is beyond the scope of the current work, the dielectric constant of the oriented water molecules is assumed to change similarly to that of bulk water over the given temperature range and thus to decrease by 10.87% from 22 o C to 50 o C [43]. Equation 9 is thus used to estimate the pore dielectric constant at 50 o C, by using fitted values of pore radius from Amar et al [10], assuming the size of the water molecule does not change with temperature.…”

Section: Variation Of Pore Dielectric Constant With Temperaturementioning

confidence: 99%

Effect of temperature on ion transport in nanofiltration membranes: Diffusion, convection and electromigration

2017

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Nanofiltration performance as a function of feed temperature is relevant to several industrial settings including pretreatment for scale control in thermal desalination. Understanding of solute transport as a function of temperature is critical for effective membrane and system design. In this study, nanofiltration is modeled at 22, 40 and 50 o C using the Donnan Steric Pore Model with dielectric exclusion (DSPM-DE).This modeling includes the temperature dependence of the three modes of solute transport, namely the convective, electromigrative, and diffusive modes, and the three mechanisms of solute exclusion, namely Donnan, steric, and dielectric exclusion. The effect of temperature is captured through the variation of membrane parameters and solvent and ionic mobilities with temperature. We compare the most abundant ionic compound in natural water, sodium-chloride with magnesium-chloride to portray how the salt passage and rejection change for a 1:1 salt compared to a 2:1 salt, and we analyze Arabian Gulf seawater to understand how rejection of scale-forming ions, such as Mg 2+ and Ca 2+ , is affected by feed temperature.In all cases, solute transport increases with temperature, attributed predominantly to the cumulative effect of membrane parameters and only to a small extent (up to 5%) to the solvent viscosity and ion diffusivity together.Keywords: Nanofiltration, Temperature, Ion transport, Desalination

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“…The effect of ionic strength on the rate constant, ki, has, in the case of many simple ionic reactions, been found to obey the theoretical relationship Using a value of 4.72 x iO-3 K-l for L [16] and the data in Fig.6 the electrostatic contributions to the free energy, enthalpy and entropy of activation for unfolding a t 20 "C have been calculated and are listed in Table 1. A standard state of infinite ionic strength was chosen in these calculations as this represents the state where the ionic contribution is effectively absent.…”

Section: Ionic-strength Dependence Of Unfoldingmentioning

confidence: 93%

Acid Denaturation of Human Carbonic Anhydrase B

Flanagan

Hesketh

1974

European Journal of Biochemistry

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1.The acid denaturation of human carbonic anhydrase B has been followed using fluorescence spectroscopy. On lowering the pH of the protein solution through the acid unfolding transition region the quantum yield was increased and the wavelength of maximum fluorescence emission red shifted.2. The rate of unfolding of the protein, as measured fluorimetrically, was shown to obey firstorder kinetics. Arrhenius plots a t two ionic strengths were linear between 7 "C and 35 "C. I n the pH range 3.0 to 3.8 the rate constant was second order with respect to hydrogen ion concentration. Approximately 30°/, of the free energy of activation for unfolding was shown to be an electrostatic contribution.3. Circular dichroism spectra showed that the first, reversible unfolding step is followed by a slower irreversible step, the rate of which is reduced by the presence of Zn2+.4. The irreversibly unfolded protein aggregated on increasing the pH, the onset of aggregation occurring sharply a t pH 3.6.Human erythrocyte carbonic anhydrase is present as two isozymes, B and C. They are both single polypeptide proteins of molecular weight 30 000. They contain no disulphide bridges, possess one free thiol group and contain a zinc ion in a coordination complex a t the active site [l].The denaturation of this enzyme has been studied extensively in urea and guanidine hydrochloride [Z-41 and to a lesser extent at acid pH [5-91. The denaturation in urea and guanidine hydrochloride has been shown to be complex, involving intermediate conformations, and to be substantially reversible. The ultraviolet spectra of the denatured proteins are blueshifted relative to those of the active enzymes and optical rotatory dispersion measurements show that the strong Cotton effects associated with the asymmetric interactions of the aromatic side chains disappear as the protein unfolds. A similar effect on the circular dichroism spectra of the isozymes due to acid denaturation was observed by Beychok et al. [5].Earlier studies by Keller and Gottwald [6] had shown acid denaturation of carbonic anhydrase to involve both reversible and irreversible steps and they found that the reversibility was a function of the time, temperature, nature of the anion and the Enzymes. Carbonic anhydrase, carbonate hydro-lyase (EC 4.2.1.1).hydrogen ion concentration. They also showed that acidic conditions weaken the protein-zinc ion bond, a finding which has subsequently been confirmed and utilized in the preparation of the apoenzyme [lo, 111.Extensive studies by Riddiford [7 -91 have shown both isozymes to exhibit similar titration characteristics ; most of the histidyl and tyrosyl residues are masked in the active protein and only become reactive after denaturation. The acid difference spectra of Riddiford indicate a timedependent conformational transition having its mid-point in the pH range 3.6 to 4.3; the C isozyme mid-point is higher than that of the B by approximately 0.18 pH unit. Increase in ionic strength from 0.05 to 0.15 increases the p H mid-point by approximately 0.4...

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Dielectric Constants of Some Organic Solvent-Water Mixtures at Various Temperatures

Cited by 1,233 publications

References 0 publications

An estimation of the equivalent solution dielectric constant in the active-site cavity of metalloenzymes. Dependence of carboxylate - metal-ion complex stabilities on the polarity of mixed aqueous/organic solvents

An estimation of the equivalent solution dielectric constant in the active-site cavity of metalloenzymes. Dependence of carboxylate - metal-ion complex stabilities on the polarity of mixed aqueous/organic solvents

Effect of temperature on ion transport in nanofiltration membranes: Diffusion, convection and electromigration

Acid Denaturation of Human Carbonic Anhydrase B

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