Chlorin p(6) as a fluorescent probe for the investigation of surfactant-cyclodextrin interactions - art. no. 609708

Abstract

Cyclodextrins (CD) are often projected as potential vehicles in targeted drug delivery. However, if the membrane structure is disrupted by CD, then it cannot be considered to be a good drug delivery vehicle. When an extrinsic fluorescence probe is used to monitor such interactions, there are no less than three possible equilibria that can operate simultaneously: surfactant-cyclodextrin, surfactant-fluorophore and cyclodextrin-fluorophore. The fluorescence intensity / lifetime might be affected by all these and so, the results depend strongly on the fluorophore used as well as the nature of the surfactant. This aspect highlights the importance of the suitability of the fluorescence probe to be used to study complicated systems and interaction. In the present work, chlorin p(6), prepared from chlorophyll from spinach leaves, has been used as the fluorescence probe to investigate the interaction between alpha-CD and beta-CD with the neutral surfactants TX 100 and CTAB. The fluorophore is found to be a sensitive one for the study of the interaction of alpha- and beta-CD with the surfactants Tritron X 100 (TX 100) and cetyl trimethyl ammonium bromide (CTAB). It is found that contrary to earlier reports, a complex between alpha-CD and TX 100 is formed, even though the binding constant is not very high. This observation can be obtained with chlorin p6, which does not bind to the CDs, but not with a fluorophore like TNS, which binds to the CD as well and thus complicates the situation as the binding with CID is stronger than that between TX 100 and alpha-CD as compared to that between TNS and CD.