Investigation of cyclomaltooligosaccharide-bound 6-(4-methoxyphenyl)imidazo[1,2-a]pyrazin-3(7H)-one for enhanced...

The chemiluminescence compound 2-methyl-6-(4-methoxyphenyl)imidazo[1, 2-a]pyrazin-3(7H)-one (MCLA) was attached to cyclomaltooligosaccharides (cyclodextrins) through a single spacer by the formation of an amide bond. The properties of oxygen-induced chemiluminescence of the synthesized cyclodextrin-bound MCLA were investigated in an aqueous phosphate buffer, pH 8.0. The light-emitting efficiency was remarkably dependent on the kind of bound cyclodextrin, spacer length between the MCLA and cyclodextrin, and the binding site in cyclodextrin. The light-emitting efficiencies of cyclomaltooctaose (gamma-cyclodextrin)-bound compounds were higher than those of cyclomaltohexaose- or cyclomaltoheptaose-bound compounds. Especially, compounds in which MCLA attached to the secondary side of gamma-cyclodextrin through a short chain showed an up to 44-fold enhancement over that of a non-cyclodextrin compound. In the current case, the efficiency of single excited-state formation was 23 times greater than that of the non-cyclodextrin compound and significantly responsible for greater light-emitting efficiency. The chemiluminescence spectra indicated the wide entrance of the secondary side of gamma-cyclodextrin, and the short spacer allowed suitable intramolecular affinity between the singlet excited-state chromophore moiety and the cyclodextrin.