Enhanced chemiluminescence of 6-(4-methoxyphenyl)imidazo[1,2-a]pyrazin-3(7H)-one by attachment of a cyclomaltooligosaccharide (cyclodextrin). Attachment of cyclomaltononaose (δ-cyclodextrin) Original Research Article

2-Methyl-6-(4-methoxyphenyl)imidazo[1,2-a]pyrazin-3(7H)-one (MCLA) is an oxygen-induced chemiluminescent compound. It has been shown that the chemiluminescence can be enhanced by forming a cyclomaltooligosaccharide (cyclodextrin)-bound MCLA, and therefore, in continuation of the survey of the types of cyclodextrins, in this study, MCLA was attached to the secondary hydroxyl face of δ-cyclodextrin, which consists of nine d-glucose units. Although the oxygen-induced chemiluminescence efficiency of δ-cyclodextrin-bound MCLA in a pH 8.0 aqueous phosphate buffer was 12 times greater than that of MCLA, the efficiency was markedly lower than that of γ-cyclodextrin-bound MCLA, which exhibited the highest chemiluminescence efficiency in the previous investigation. Although fluorescence efficiency and light-emitter formation efficiency for δ-cyclodextrin-bound MCLA were similar to those for γ-cyclodextrin-bound MCLA, singlet-excited state formation efficiency for δ-cyclodextrin-bound MCLA was lower than that for γ-cyclodextrin-bound MCLA. This study distinctly indicated the optimum cyclodextrin for construction of greatly luminescent cyclodextrin-bound MCLA is γ-cyclodextrin.