ic201247v_si_001.pdf (48.89 kB)
Switching Off Electron Transfer Reactions in Confined Media: Reduction of [Co(dipic)2]− and [Co(edta)]− by Hexacyanoferrate(II)
journal contribution
posted on 2012-03-05, 00:00 authored by Michael D. Johnson, Bret B. Lorenz, Patricia
C. Wilkins, Brant G. Lemons, Bharat Baruah, Nathan Lamborn, Michelle Stahla, Pabitra B. Chatterjee, David T. Richens, Debbie C. CransThe kinetics of reduction of two cobalt(III) complexes
with similar
redox potentials by hexacyanoferrate(II) were investigated in water
and in reverse micelle (RM) microemulsions. The RMs were composed
of water, surfactant [(sodium(bis(2-ethylhexylsulfosuccinate)), NaAOT],
and isooctane. Compared to the reaction in water, the reduction rates
of (ethylenediaminetetraacetato)cobaltate(III) by hexacyanoferrate(II)
were dramatically suppressed in RM microemulsions whereas a slight
rate increase was observed for reduction of bis-(2,6-dipicolinato)cobaltate(III).
For example, the ferrocyanide reduction of [Co(dipic)2]− increased from 55 M–1 s–1in aqueous media to 85 M–1 s–1 in a wo = 20 RM. The one-dimensional
(1-D) and two-dimensional (2-D) 1H NMR and FT-IR studies
are consistent with the reduction rate constants of these two complexes
being affected by their location within the RM. Since reduction of
[Co(edta)]− is switched off, in contrast to [Co(dipic)2]−, these observations are attributed to
the penetration of the [Co(edta)]− into the interfacial
region of the RM whereas [Co(dipic)2]− is in a region highly accessible to the water pool and thus hexacyanoferrate(II).
These results demonstrated that compartmentalization completely turns
off a redox reaction in a dynamic microemulsion system by either reactant
separation or alteration of the redox potentials of the reactants.
