Electron transfer reactions of transition metal aminocarboxylates in the presence of micelle-forming surfactants. Catalysis by cetyltrimethylammonium bromide of the reduction of Mn(cydta)- by Co(edta)2- and Co(cydta)2-

Abstract

The reduction of Mncydtaby Co(edta)2-and Co(cydta)2-is catalyzed by aqueous micellar cetyltrimethylammonium bromide (CTAB). The maximum rate enhancements are ca. 600X and 160X, respectively. The binding between Co-(cydta)-and CTAB micelles was investigated by gel filtration chromatography using a Sephadex G-25 gel. The binding constant of Co(cydta)-, defined in terms of partitioning between bulk aqueous phase and micellar pseudophase, is 325 M-1 (25 °C) and incorporates contributions from electrostatic as well as hydrophobic interactions. The kinetic data have been interpreted in terms of Berezin's theory (assuming similar binding constants for Co(cydta)-and Mn(cydta)-) and current theories about the mechanism of electron transfer processes. This reveals that the rate constant for the bimolecular reaction in the micellar pseudophase (km) is smaller than the rate constant in aqueous solution, whereas the rate constant for the interphase reaction (£m0 involving Co(edta)2on the micellar surface and Mn(cydta)-in bulk aqueous phase is higher than ku and the rate constant in aqueous solution. Various factors which affect &m and ku are discussed taking into account the micellar surface solvent properties.

Potential-Driven Electron Transfer Lowers the Dissociation Energy of the C–F Bond and Facilitates Reductive Defluorination of Perfluorooctane Sulfonate (PFOS)

“…CTAB and PFOS can form complexes/micelles (either in solution or possibly on the surface of the CNT/CTAB electrode), where the positively charged quaternary ammonium group of CTAB interacts with the negatively charged PFOS sulfonate group (Figure 5). Micelle catalysis has been suggested as an efficient way to enhance ET due to the lowered dielectric constant in the vicinity of the micelle surface and outer-sphere solvent reorganization, 57,58 which can contribute to the large electrontransfer reaction rate increase. 59 A similar observation was made by a study investigating ET between an electrode surface and biomolecules, where CTAB-modified CNT electrodes exhibited elevated ET.…”

Inhibition effect of {surfactant–substrate} aggregation on the rate of oxidation of reducing sugars by alkaline hexacyanoferrate(III)

“…The binding constant ( K s ) of the substrate with surfactant can be related 24–27 to the partition coefficient ( P ) by relation where is the partial molar volume of the surfactant monomer and the partition coefficient P = [substrate] micelle /[substrate] water .…”

Hydrotropic Enhancement of Rate of Ninhydrin‐α‐Amino Acid Reaction: A Kinetic Study

“…The mechanism of a-amino acid-ninhydrin reaction in aqueous medium has been reported (McCaldin, 1960;Bhaleker and Engberts, 1978;Friedman and Williams, 1974;Khan, 1989, 1990;Khan and Ali, 1997;Kabir-UdDin, 2000a). The loan pair of electrons of amino nitrogen attack on the carbonyl-carbon of ninhydrin in the primary step to give a Schiff base.…”

“…The kinetics of the reaction in aqueous organic solvents (McCaldin, 1960;Bhaleker and Engberts, 1978;Friedman and Williams, 1974;Khan, 1989, 1990) and in the presence of surfactants (Khan and Ali, 1997;Kabir-Ud-Din et al, 2000a, b) have been studied extensively. The inhibition effect of cationic or anionic micelles on the rate of reaction of ninhydrin with some amino acids has been accounted for the distribution of substrate into both micellar and aqueous pseudo-phase and on the association of the substrate with surfactant (Kabir- UdDin et al, 2000a).…”