Study of surfactant-cyclodextrin complexation by cyclic voltammetry using polypyridyl metal complexes as electroactive probes

Abstract

Polypyridyl ruthenium(II) and cobalt(III) complexes were chosen as electroactive probes to study surfactant-cyclodextrin (CD) complexation. The complexation of sodium dodecyl sulfate (SDS) with CD and its influence on the electrochemistry of these metal complexes were studied. Complexation of SDS with CD released the metal complex from the SDS interaction. The ratio of K_red/K_ox (ratio of binding constants of reduced and oxidized forms of the metal complex) decreased upon the addition of CD and it confirmed the elimination of the interaction between SDS and metal complex and the inclusion of SDS into the cavity of CD. The insoluble precipitate formed at lower concentration of SDS with polypyridyl ruthenium(II) complex was solubilized by the addition of CD and is due to the inclusion of SDS into the cavity of CD. The SDS molecule prefers to bind with CD rather than with the metal complex. Geometric constraint forbid the inclusion of polypyridyl metal complex into the cavity of CDs. The critical micellar concentration (cmc) of SDS increased with increasing the concentration of β-CD. The electrochemistry of metal complexes has not been altered by the SDS-CD inclusion complex. The [CD] required to break the surfactant interaction has been determined by cyclic voltammetry. The emission spectral study also confirmed the release of metal complex from the surfactant interaction upon the addition of CD.