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Electrochemical estimation of diffusion anisotropy of N,N,N′,N′-tetramethyl-para-phenylenediamine within the normal hexagonal lyotropic mesophase of triton X 100/light water: when can the effects of cross-pseudophase electron transfer be neglected for par

Halls, Jonathan E.; Lawrence, Nathan S.; Wadhawan, Jay D.

Authors

Jonathan E. Halls

Nathan S. Lawrence



Abstract

The H1 lyotropic liquid crystalline phase of Triton X 100 with aqueous 0.1 M potassium chloride is examined as a medium in which to determine the axiosymmetric anisotropy in the diffusion flux of N,N,N′,N′-tetramethyl-para-phenylenediamine using electrochemical methods (voltammetry and potential step chronoamperometry) at both planar electrodes and two-dimensional flux microdisk electrodes. Comparison of experiment with theory suggests the ratio of anisotropic diffusion coefficients in the directions tangential and perpendicular to the electrode surface varies over two orders of magnitude (from 0.04 to 3.3) with increasing concentration of the redox analyte. This is understood through the occurrence of a long-range charge transfer across the pseudophase | pseudophase boundary interface, occurring as a result of differential diffusivities of the redox probe within the surfactant and aqueous subphases. These data and their dependence on the analyte concentration empower, in a proof-of-concept, the estimation of the partition equilibrium constant (KP); the value estimated for the small electroactive-drug mimetic considered is log KP = 2.01 ± 0.05 (at 294 ± 2 K) and is in agreement with that envisaged for its partition between n-octanol and water. It is suggested that only measurements at low analyte loadings allow for interphase electron transfers to be neglected, since then percolation effects appear to dominate the Faradaic current.

Journal Article Type Article
Publication Date May 26, 2011
Journal JOURNAL OF PHYSICAL CHEMISTRY B
Print ISSN 1520-6106
Electronic ISSN 1520-5207
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 115
Issue 20
Pages 6509-6523
APA6 Citation Halls, J. E., Lawrence, N. S., & Wadhawan, J. D. (2011). Electrochemical estimation of diffusion anisotropy of N,N,N′,N′-tetramethyl-para-phenylenediamine within the normal hexagonal lyotropic mesophase of triton X 100/light water: when can the effects of cross-pseudophase electron transfer be neglected for partitioned reagents?. Journal of Physical Chemistry B, 115(20), 6509-6523. doi:10.1021/jp201806f
DOI https://doi.org/10.1021/jp201806f
Keywords Physical and Theoretical Chemistry; Materials Chemistry; Surfaces, Coatings and Films
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