Ion Exchange Effects on the Electrical Conductivity of Acidified (HCl) Sodium Dodecyl Sulfate Solutions

Pazo‐Llorente, Roman; Bravo‐Díaz, Carlos; González-Romero, Elisa

doi:10.1021/la035793s

Cited by 11 publications

(12 citation statements)

References 27 publications

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“…80% of the total 4NBD is incorporated in the micellar aggregate, thus decreasing the effective concentration in the aqueous pseudophase, which is the region where the amino acids are mainly located. The obtained CMC value is lower than that in pure aqueous solution, CMC ¼ 8 · 10 À3 m at 258, consistent with the well-known effects of electrolyte concentration on CMC values [1] [48].…”

Section: à5supporting

confidence: 84%

Effects of Micellar Aggregates on the Kinetics and Mechanism of the Reaction between 4‐Nitrobenzenediazonium Ions and Some Amino Acids

Fernández-Alonso

Bravo‐Díaz

2007

Helvetica Chimica Acta

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We have explored the kinetics and mechanism of the reaction between 4-nitrobenzenediazonium ions (4NBD), and the hydrophilic amino acids (AA) glycine and serine in the presence and absence of sodium dodecyl sulfate (SDS) micellar aggregates by means of UV/VIS spectroscopy. The observed rate constants k obs were obtained by monitoring the disappearance of 4NBD with time at a suitable wavelength under pseudo-first-order conditions. In aqueous acid (buffer-controlled) solution, in the absence of SDS, the dependence of k obs on [AA] was obtained from the linear relationship found between the experimental rate constant and [AA]. At a fixed amino acid concentration, k obs values show an inverse dependence on acidity in the range of pH 5 -6, suggesting that the reaction takes place through the nonprotonated amino group of the amino acid. All kinetic evidence is consistent with an irreversible bimolecular reaction with k ¼ 2390 AE 16 and 376 AE 7 m À1 s À1 for glycine and serine, respectively. Addition of SDS inhibits the reaction because of the micellar-induced separation of reactants originated by the electrical barrier imposed by the SDS micelles; k obs values are depressed by factors of 10 (glycine) and 6 (serine) on going from [SDS] ¼ 0 up to [SDS] ¼ 0.05m. The hypothesis of a micellar-induced separation of the reactants was confirmed by 1 H-NMR spectroscopy, which was employed to investigate the location of 4NBD in the micellar aggregate: the results showed that the aromatic ring of the arenediazonium ion is predominantly located in the vicinity of the C(b) atom of the surfactant chain, and hence the reactive ÀN þ 2 group is located in the Stern layer of the micellar aggregate. The kinetic results can be quantitatively interpreted in terms of the pseudophase kinetic model, allowing estimations of the association constant of 4NBD to the SDS micelles.

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Section: à5supporting

confidence: 84%

Effects of Micellar Aggregates on the Kinetics and Mechanism of the Reaction between 4‐Nitrobenzenediazonium Ions and Some Amino Acids

Fernández-Alonso

Bravo‐Díaz

2007

Helvetica Chimica Acta

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“…1). The obtained cmc values are lower than that in pure aqueous solution (8 mm at 258), which is consistent with the well-known effects of electrolyte concentration on cmc [51] [52]. The solubility of OG in H 2 O is extremely low [55], and because of its hydrophobic tail, it is likely to behave as a surfactant.…”

supporting

confidence: 86%

“…According to the pseudophase-ion-exchange (PIE) model [45], which is commonly used to interpret micellar effects on chemical reactivity [30] [45] [51], shifts of pK a values in micellar media compared to the values in the absence of surfactant may be caused primarily due to the transfer of the indicator (in both neutral and ionic form) and H 3 O þ from the large bulk volume of H 2 O into the much smaller volume of the micellar interface. When the indicator is significantly incorporated into the aggregate, then addition of HCl may increase the apparent pK a of the indicator probe, because addition of HCl into an SDS micellar solution results in the displacement of Na þ ions from the micellar surface by H þ ions [52]. The results obtained may, thus, be suggestive of insignificant incorporation of GA into the micellar aggregate, which is consistent with the high water-solubility of GA.…”

supporting

confidence: 54%

Micellar Effects on the Reaction between an Arenediazonium Ion and the Antioxidants Gallic Acid and Octyl Gallate

Losada‐Barreiro

Sánchez-Paz

Pastoriza-Gallego

et al. 2008

Helvetica Chimica Acta

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The effect of sodium dodecyl sulfate (SDS) micelles on the reaction between the 3-methylbenzenediazonium (3MBD) ion and either the hydrophilic antioxidant gallic acid (GA) or the hydrophobic analogue octyl gallate (OG) have been investigated as a function of pH. Titration of GA in the absence and presence of SDS micelles showed that the micelles do not alter the first ionization equilibrium of GA. Analysis of the dependence of the observed rate constant (k obs ) with pH shows that the reactive species are GA 2À and OG À. Kinetics results in the absence and presence of SDS micelles suggest that SDS aggregates do not alter the expected reaction pathway. SDS Micelles inhibit the spontaneous decomposition of 3MBD as well as the reaction between 3MBD and either GA or OG, and upon increasing the SDS concentration, with k obs approaching the value for the thermal decomposition of 3MBD in the presence of SDS. Our results are consistent with the prediction of the pseudophase model and show that the origin of the inhibition for the reaction with GA is different to that for the reaction with OG; in the former case, the observed inhibition can be rationalized in terms of the micelle-induced electrostatic separation of reactants in the micellar Stern layer, whereas the observed inhibition in the reaction with OG is a consequence of the dilution effect caused by increasing SDS concentration, decreasing the local OG À concentration in the Stern layer.

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“…Therefore, the task of the DLS study was to reveal the correlation between the particle size and the CP phenomenon in mixed DS-[H 4 L] 4− micellar solutions at various counter ion conditions. Electric conductivity method is known to be a powerful tool, sensitive to all changes in counterion binding, accompanied by micellar size and shape transitions [40], which are caused by concentration or ion exchange effects [6,41]. That is why conductivity data were used to confirm the regularities obtained from DLS and CP data.…”

Section: Cp Dls and Conductivity Data In Sds-[h 4 L] 4− -Tba Micellamentioning

confidence: 99%

Counterion effect in SDS–calix[4]resorcinarene micelles

Mustafina

Zakharova

Elistratova

et al. 2009

Journal of Colloid and Interface Science

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Ion Exchange Effects on the Electrical Conductivity of Acidified (HCl) Sodium Dodecyl Sulfate Solutions

Cited by 11 publications

References 27 publications

Effects of Micellar Aggregates on the Kinetics and Mechanism of the Reaction between 4‐Nitrobenzenediazonium Ions and Some Amino Acids

Effects of Micellar Aggregates on the Kinetics and Mechanism of the Reaction between 4‐Nitrobenzenediazonium Ions and Some Amino Acids

Micellar Effects on the Reaction between an Arenediazonium Ion and the Antioxidants Gallic Acid and Octyl Gallate

Counterion effect in SDS–calix[4]resorcinarene micelles

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