Structural effects of macrocyclic compounds and their partition in sodium dodecylsulphate aqueous solutions

The partition of 1,4,7,10,13,16-esaoxacyclooctadecane (18C6), 4,7,13,16-tetraoxa-1,10-diazacyclooctadecane (2.2), 2,5,8,11,14,17-esaoxabicyclo[16.4.0]dicosane (B18C6) and 2,5,8,15,18,21-esoxatricyclo[20.4.0.0^9.14]esacosane (Cy₂18C6) in sodium dodecyl sulfate (SDS) aqueous solutions and their effect on the structure of surfactant aggregates has been investigated by small-angle neutron scattering. Results from data analysis have shown that by increasing macrocycle concentration the SDS micelles dimensions reduce for all systems investigated. At the same time information on macrocycles partition between the micellar and the continuous phase have been obtained. It was found that an appreciable portion of macrocyclic compounds is located in micellar aggregates; in particular, the amount of B18C6 and Cy₂18C6 results larger than that of 18C6 and 2.2. It was found that 18C6 and 2.2 molecules interact with charged surface of SDS micelles only via complexes formation between the sodium ions and the macrocycles. B18C6 and Cy₂18C6 interact either via complexes formation with the charged surface or with hydrophobic region inside the micelle, as a consequence of the presence of hydrophobic substituents. It was concluded that Cy₂18C6 fraction present inside the micelles is located in the core, while the B18C6 fraction is located in the palisade.