Sodium dodecyl sulfate micellar aggregation numbers in the presence of cyclodextrins

Micellar aggregation numbers, n, have been obtained for sodium dodecyl sulfate (SDS) micelles in cyclodextrin (CD) solutions through static fluorescence quenching. For α-cyclodextrin, β-cyclodextrin (hydroxylpropyl)-β-cyclodextrin, maltosyl-β-cyclodextrin, and γ-cyclodextrin solutions, n was found to be essentially unchanged from the 59 ± 5 value found in sodium dodecyl sulfate solutions without cyclodextrin present, even though the critical micelle concentrations as measured conductometrically had increased. The increases in critical micelle concentrations were consonant, with 1 :1 CD/SDS complexation predominating over other complexes in all CD systems except for α-CD solutions, where the 2 :1 α-CD/SDS complex prevailed. The association constants of the fluorescence quencher, 9-methylanthracene, with SDS and with each of the pure cyclodextrins were determined to ensure preferred binding of the quencher with SDS micelles rather than with CD. The substituted cyclodextrins, dimethyl-β-CD and trimethyl-β-CD, were not amenable to the fluorescence quenching method. The implications ofthese findings to drug delivery are examined.