Research of complexes of pyrene-cyclodextrins using fluorescent methods
Supramolecular “host-guest” inclusion complexes on the basis of cyclic oligosaccharides - β- and γ-cyclodextrins. Highlight the major unresolved issues in the study of systems of this type, in particular complexes using pyrene as a “guest” are specified as an object of this article. The aim is to study the spectral properties of fluorescent complexes of pyrene-cyclodextrins, and cyclodextrins aggregation influence on it. Investigation results of spectral and kinetic fluorescence properties of aqueous pyrene complexes with β- and γ-cyclodextrin are described in the main part of the article. A significant weakening of the fluorescence quenching of probe by oxygen and ionic quenchers during formation process of complexes, and the absence of influence of cyclodextrins on pyrene fluorescence quenching processes in the medium (DMSO) that prevents the formation of cyclodextrins aggregates are determined. An author shows that the addition of β- or γ-cyclodextrin in an aqueous solution of pyrene gives a similar effect as well as the removal of oxygen from the solution. At a solution filtration intensity and decay kinetics of pyrene fluorescence as a fact of removing cyclic oligosaccharide aggregates with the built in pyrene probe molecules are modified. Based on the experimental results the author shows that pyrene without additional activation does not form inclusion complexes with considered cyclodextrins. As a result of researches an another model of the complex, which take account of aggregation of cyclodextrins in water is proposed. Observed changes of the spectra and decay kinetics of fluorescence of pyrene during pyrene adding to a cyclodextrins solution are the result of probe insertion into cyclic oligosaccharides aggregates but not into their internal cavity, as previously it was thought. The new model provides more correct interpret the results of fluorescence quenching of pyrene by oxygen, anionic quenchers, aliphatic and aromatic amines and points to the need to consider the cyclodextrins aggregation in the formation of complexes with ligands.