Monomolecular films of pluronic-cyclodextrin inclusion complexes at the water-gas interface

This paper reports the synthesis and characteristics of inclusion type complexes between amphiphilic block copolymer of ethylene and propylene oxides (pluronic) and -, -, and heptakis-(2,6-di-O-methyl)--cyclodextrins. The process was investigated in monolayers at the water-gas interface according to Langmuir-Blodgett technique. Pluronic forms a monolayer, stable at the surface pressure 5 mN/m, which reacts with heptakis-(2,6-di-O-methyl)--cyclodextrin and does not react with - and -cyclodextrins. The absence of the reaction in the case of -cyclodextrin is explained by the fact that the polymer guest does not fit into a small cavity of the macrocyclic host, but for -cyclodextrin it may be explained by its low surface activity and, hence, its low local concentration in the vicinity of the pluronic monolayer. After introducing heptakis-(2,6-di-O-methyl)--cyclodextrin into the aqueous subphase under the pluronic monolayer an instant increase in the area is observed. An increase in the amount of heptakis-(2,6-di-O-methyl)--cyclodextrin in the aqueous phase causes first steep linear increase in the monolayer area, then its leveling off at the polymer-heptakis-(2,6-di-O-methyl)--cyclodextrin ratio equal to about 1:15. This value correlates well with a stoichiometric composition of the similar complex in solution.