Complexation of single- and double-chain surfactants by cyclomalto-oligosaccharides

Use of Spectra Resolution Methodology to Investigate Surfactant/β-Cyclodextrin Mixed Systems

A study of the spectral behavior of crystal violet in mixed systems formed by hexadecyltrimethylammonium chloride (CTACl) and beta-cyclodextrin (beta-CD) has been carried out. The spectra resolution methodology was used to decompose the absorption spectra of crystal violet in the sum of constituent sub-bands centered at 17,953, 16,807, and 16,474 cm(-1). The sub-bands centered at upsilon = 17,953 and 16,807 cm(-1) correspond to planar and pyramidal isomers of the dye in water and the same isomers associated with the cyclodextrin and micelle. The sub-band centered at upsilon = 16,474 cm(-1) is due to the formation of an inclusion complex between the dye and the cyclodextrin, where solvation of the carbocation takes place through the hydroxyl groups of the cyclodextrin and the association of the crystal violet to micelles of CTACl through the formation of ion pairs in the Stern layer. The results obtained in the mixed systems are compatible with the results obtained in the previously studied simple systems, thus supporting the situation where interactions do not exist between cyclodextrins and micelles once these have formed.

In Search of Fully Uncomplexed Cyclodextrin in the Presence of Micellar Aggregates

The chemical behavior of beta-cyclodextrin/nonionic surfactant mixed systems has been investigated using the basic hydrolysis of N-methyl-N-nitroso-p-toluenesulfonamide as a chemical probe. The experimental results prove that at the cmc, there are significant quantities of uncomplexed beta-CD in equilibrium with the micellar aggregates. In contrast to the expected situation, the percentage of uncomplexed beta-CD in equilibrium with the micellar system increases on increasing the hydrophobicity of the surfactant molecule. This behavior is due to the existence of two simultaneous processes: complexation of surfactant monomers by cyclodextrin and the process of self-assembly to form micellar aggregates. The autoaggregation of surfactant monomers is expected to be more important than the complexation process in this mixed system. Varying the hydrophobicity of the surfactant monomer enabled us to determine that the percentages of uncomplexed cyclodextrin in equilibrium with the micellar system were in the range of 5-95%.

Mechanism of alpha-cyclodextrin-induced hemolysis. 1. The two-step extraction of phosphatidylinositol from the membrane

It has been suggested that the interaction of cyclodextrins with the lipid components of the erythrocyte membranes is the determining factor in the hemolysis induced by these cyclic oligosaccharides. In the case of alpha-cyclodextrin (cyclomaltohexose), phospholipids have been identified as the cell target. In our study, evidence for the interaction between alpha-cyclodextrin and different phospholipids has been obtained using synthetic membranes. Since phosphatidylinositol (PI) showed the strongest affinity for alpha-cyclodextrin, it has been selected to investigate the respective contributions of the polar head group and the aliphatic chains to the association process using 31P, 2H, and 1H NMR spectroscopy. In this work, we describe the two-step extraction of PI from the membrane following its association with alphaCD: a cyclodextrin molecule is first attracted to the membrane surface by electrostatic remote interactions and associates with the lipid head group. Then the whole PI molecule is extracted, and inclusion of its unsaturated sn-2 acyl chain into another alphaCD molecule occurs in the bulk.