Fluorescence studies on the reduction of quinone by cyanide in aqueous 2-hydroxypropyl-β-cyclodextrin solutions

Water-soluble 2-hydroxypropyl-β-cyclodextrin was used to enclose 1,4-dibenzoquinone, 1,4-naphthoquinone, and 9,10-anthraquinone to form inclusion complexes. The inclusion complex of 1,4-dibenzoquinone was the most reactive of the three complexes in the presence of cyanide anion. The 1,4-dibenzoquinone inclusion complex reacted with cyanide anion to form a fluorescent product with stable excitation and emission maxima at 410 and 480 nm, respectively. Assuming one to one stoichiometry the formation constant for 2-hydroxypropyl-β-cyclodextrin and 1,4-dibenzoquinone was estimated to be 4 M^-1. Formation of the inclusion complex did not enhance fluorescence yield but increased the rate of product formation in aqueous solutions. In the presence of excess cyanide the limit of detection for 1,4-dibenzoquinone was 0.006 mM with a linear range of 0.01 to 0.04 mM. For cyanide detection the linear range of the assay was 2 to 10 mM with a detection limit of 0.041 mM. Rate assays for cyanide possessed linear ranges from 0.041 to 12 mM. The reaction was used to detect cyanide in beverages, acetaminophen preparations and brass plating solutions.