Mechanism of Ni2+ and NiOH+ interaction with hydroxamic acids in SDS: evaluation of the contributions to the equilibrium and rate parameters in the aqueous and micellar phase

Abstract

The equilibria and kinetics (stopped-flow) of the binding of Ni(II) to salicylhydroxamic acid (SHA) and phenylbenzohydroxamic acid (PBHA) have been investigated in aqueous solutions containing SDS micelles. The two ligands are fairly distributed between the two pseudophases present, so the binding reaction occurs in both phases. The contributions to the total reaction from each phase has been evaluated, following a procedure where use is made of the experimentally determined partition coefficients of the reactants involved. The mechanism of the reaction occurring on the micelle surface has been derived and comparison with the mechanism in water shows that the step Ni(2+) + HL ⇄ NiHL(2+) is operative in both pseudophases, whereas the step Ni(2+) + L(-)⇄ NiL(+), which is operative in water, is replaced in SDS by the step NiOH(+) + HL ⇄ NiL(+). The analysis of the equilibrium and of the kinetic data enabled the evaluation of the equilibrium and the rate constants of the individual steps taking part in the binding process over the micelle surface. Interestingly, the first hydrolysis constant of the Ni(H(2)O)(6)(2+) ion in SDS is more than two orders of magnitude higher than in water. The agreement between the equilibrium constants derived from kinetics and those obtained by static measurements confirms the validity of the proposed mechanism.

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

“…Acceleration (or deceleration) of reaction rates by about a 10-100 fold have been observed [3][4][5][6][7][8][9].…”

“…However, in order to optimize the conditions of the extraction process it is very important to know the kinetic and thermodynamic features of the reaction of metal binding to the extractor in the aqueous and in the micellar phase. Hence, in the framework of our studies on complex formation reactions in micellar media [3][4][5][6][7] we have performed a kinetic study of the reaction between AuCl4and PADA, in water and in the presence of dodecyltrimethylammonium chloride (DTAC). This surfactant has been chosen because it has been employed in a previous study of the effect of micelles on the pKAs of PADA.…”

Purification of proteins with native terminal sequences using a Ni(II)-cleavable C-terminal hexahistidine affinity tag

“…2A shows, a new band appeared on the SDS-PAGE at slightly smaller molecular mass, suggesting that the SRHSEFELVDKLAAALEHHHHHH C-terminal affinity tag was successfully removed. SDS as it was outlined earlier [52]. Because of the possible coordinative interaction, we also applied imidazole as a competing agent.…”

“…The detergent or imidazole containing elution buffer was then removed in a buffer exchange step by ultrafiltration. Efficient removal of the detergent can be achieved by diluting the solution below the critical micellar concentration (being ~ 0.23 % of SDS [52]) prior to ultrafiltration.…”

Thermodynamic and FTIR studies of the interactions between sodium dodecyl sulphate and strong acids – atypical conductivity pattern

“…Among the salts of long-chain primary alkyl sulphates, sodium dodecyl sulphate (SDS) is a very important surfactant in research and development and it is probably the most widely researched anionic surfactant [1][2][3][4][5]. It is well established that the micellisation behaviour of surfactants plays a significant role in their various fields of applications such as cosmetics, detergency, pharmaceuticals etc.…”