The mechanism of the reaction between Au(III) and PADA in sodium dodecylsulphate

Abstract

HIGHLIGHTS  Au(III) reacts with PADA on SDS surface; the Au-PADA complex is fully retained.  The reaction rate is modulated by suitable changes of pH and NaCl concentration.  The reaction at high pH is much faster owing to the high reactivity of the Au(OH)3(H2O) species  LM-MEUF of the Au(III)-PADA system in SDS provides high extraction yields.

Influence of Microheterogeneous Environments of Sodium Dodecyl Sulfate on the Kinetics of Oxidation of l-Serine by Chloro and Chlorohydroxo Complexes of Gold(III)

“…In aqueous solution, the long chain amphiphilic surfactant molecules agglomerate to form organized dynamic assemblies called “micelles” which owing to their anisotropic interfacial regions between polar aqueous and nonpolar hydrocarbon phases generate an inhomogeneous microreaction environment. , As a consequence, the organized assemblies influence the physical and chemical properties of a system by enveloping the reactant molecules through the noncovalent-like hydrophobic and electrostatic interactions. , A micelle catalyzed reaction is known to be similar to an enzyme catalyzed reaction in many aspects for which a micelle catalyzed reaction model may be employed to study the complex reactions occurring in biological systems. ,, There are a number of surfactant-mediated reactions where micelles influence the reaction rates. − Micelles of different anionic and cationic surfactants are also found to accelerate or inhibit the oxidation rates of different amino acids. ,,− In the present study, since the reactants hold either charged groups and/or polar hydroxyl groups, it may be expected that cationic or anionic surfactants may interact with the reactant species through electrostatic or H-bonding that in turn may play an instrumental role in the reaction kinetics.…”

Quantitative Analysis of the Interactions of Metal Complexes and Amphiphilic Systems: Calorimetric, Spectroscopic and Theoretical Aspects

“…The latter option is needed when we seek to unveil the speciation for metal ions that may contain, for instance, chloride-coordinated forms. Fastreaction kinetic experiments (using the stopped-flow technique) [80,81] are also precious to discern the detailed reaction mechanisms, such as those in the examples reported in Figure 7. Figure 6 shows that at a low pH, the ligand is 100% retained and thus that data will refer to a system reacting at this phase only, whilst this is no longer true at a higher pH.…”

“…The latter option is needed when we seek to unveil the speciation for metal ions that may contain, for instance, chloride-coordinated forms. Fast-reaction kinetic experiments (using the stopped-flow technique) [80,81] Figure 6 shows that at a low pH, the ligand is 100% retained and thus that data will refer to a system reacting at this phase only, whilst this is no longer true at a higher pH. On the whole, the pH-range conditions for mechanistic studies on the solution equilibria have to be carefully tuned to possibly avoid intricate deconvolution problems from different contributions.…”

“…The latter option is needed when we seek to unveil the speciation for metal ions that may contain, for instance, chloride-coordinated forms. Fast-reaction kinetic experiments (using the stopped-flow technique) [80,81] The particular case of pressure dependence needs peculiar apparatuses, which enable us to make changes over a quite wide range (until 1500 atm) [82]. The value of the activation volume (∆V # ) can be obtained from the slope of a plot of the natural logarithm of the rate constant over pressure; these values are crucial to unveil the fine details of the metal/ligand interaction in the different media and decide between an associative or dissociative metal ion-binding mechanism (for Ni 2+ /PADA system, see, for instance, reference [83]).…”

“…The latter option is needed when we seek to unveil the speciation for metal ions that may contain, for instance, chloride-coordinated forms. Fast-reaction kinetic experiments (using the stopped-flow technique)[80,81] are also precious to discern the detailed reaction mechanisms, such as those in the examples reported in Figure 7.…”