Effects of micelle nature and concentration on the acid dissociation constants of the metal extractor PADA

Aydınoğlu, Sabriye; Biver, Tarita; Secco, Fernando; Venturini, Marcella

doi:10.1016/j.colsurfa.2014.08.008

Cited by 11 publications

(8 citation statements)

References 35 publications

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“…This phenomenon can be explained by the change in the pKa value of the chromophore in the microenvironment inside the SDS micelle. Changes in the pKa inside micelles have been reported previously for other compounds (Aydinoglu, Biver, Secco, & Venturini, 2014). At pH 6 and high SDS concentrations, the visible-ultraviolet ratio decreases, showing folding of the chromophore.…”

Section: Effect Of Sds On Ph-dependent Colour Fluctuations Of Phycocysupporting

confidence: 71%

Stabilising phycocyanin by anionic micelles

et al. 2018

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Phycocyanins are pigment-protein complexes with potential application as natural food colourants. The perceived colour of phycocyanins varies with pH, and a method to stabilise the colour over a broad range of pH values is requested by the food industry. In this work, the stabilising effect of sodium dodecyl sulphate (SDS) micelles on pH-induced colour variations of phycocyanin was examined. SDS was shown to stabilise the blue conformation of phycocyanin, preventing formation of the green conformation, which is prevalent at low pH. The studies indicated that the stabilising effect occurred through interaction or entrapment of the non-protonated, circular helical (blue) structure of phycocyanin and the anionic SDS micelles. The interaction prevented conversion into protonated, partially unfolded (green) phycocyanin species. This information opens for new possibilities to stabilise the blue conformation of phycocyanin and to apply the stabilised form in food products as a natural blue food colourant.

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Section: Effect Of Sds On Ph-dependent Colour Fluctuations Of Phycocysupporting

confidence: 71%

Stabilising phycocyanin by anionic micelles

et al. 2018

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“…Concerning the position of the protons in the structure represented in Figure 1, it should be noted that the -N=N-group stays unprotonated whereas, in the case of dimethylamino azobenzene (indicator methyl yellow), this group is protonated at about pH 3 [12]. However, we favour the structure of Figure 1 on the basis of a previous contribution from our laboratory [13] where the effects of DTAC on the pKAs of PADA have been investigated. Our conclusions are corroborated by the results of Klotz et.…”

Section: Introductionmentioning

confidence: 90%

The kinetics of gold(III) extraction by pyridine-2-azo‑p‑dimethylaniline in water and in micellar systems

Aydınoğlu

Biver

Secco

et al. 2015

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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The kinetics of reaction between AuCl4-, and the azo-dye pyridine-2-azo-pdimethylaniline (PADA) have been investigated in water and in the presence of DTAC micelles, using classical spectrophotometry and the stopped-flow technique. PADA reacts with different chloro/hydroxo gold(III) complexes, in turn formed as the pH and Cl-concentration were changed, according to a network of parallel paths. In aqueous solution, at low pH values, a fast step is observed which is ascribed to the ligand induced expulsion of a labile water molecule from the reacting species Au(H2O)Cl3 which forms at low pH values. At higher values of pH, the reaction is much slower because in the key step PADA has to replace the more inert Clions in the gold coordination shell. In the presence of DTAC a remarkable catalytic effect is observed, owing to the absorption and attraction of the reactants on the micelle surface. Moreover, DTAC favors the formation of aquochloro aurates, thus inducing a change in the gold(III) speciation compared to that in water. The analysis of the data suggests that the aquo species Au(H2O)Cl3 and Au(H2O)2Cl2 + play a major role in the reaction mechanism.

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“…Hence, the hypothesis that PADA could be a triprotic acid, could not be excluded, in principle. However, our previous experiments [4] aimed to measure the proton dissociation constants of PADA in the pH range between 0.5 and 6, are perfectly fitted by two dissociation steps both in pure water and in micellar solution, and the relevant dissociation constants were found to be rather different. Moreover, it should be noted that protonation at the -N=N-group (where chelation occur) would entail a direct dependence on [H + ] in the kinetics of the complex dissociation step, which is not the case for the Au-PADA system here investigated.…”

Section: Kinetics Of the Fast Effectmentioning

confidence: 90%

“…The commercially available ligand PADA ( Figure 1) is totally adsorbed on a variety of surfactants, including SDS [4] and has proven to be an excellent metal extractor, being able to transfer metal ions from water to micellar phases with yields approaching 100% [5][6][7] Moreover, we have found that PADA is able to complex Au(III) with great affinity even if the coordination shell of the metal is occupied, as in AuCl4 - [8,9]. In this case, a molecule of PADA replaces two chloride ions forming a strong chelate.…”

Section: Introductionmentioning

confidence: 99%