Date of this Version
In a recent report (1) from this laboratory, an improved fluorometric assay for coumarin in sweetclover is described. Briefly, the method consists of opening the lactone ring of coumarin by treatment with alkali, after which the resulting non-fluorescent cis-o-hydroxycinnamic acid is partially converted, by means of ultraviolet irradiation, to the fluorescent trans isomer. Measurements of fluorescence are then made. In the interval between ultraviolet treatment and measurement of fluorescence, the solutions to be assayed must be protected from the usual light of the laboratory, since exposure to such light results in loss of fluorescence, indicating a reconversion of some of the trans isomer to the cis form. The experiments reported here were designed to investigate, by fluorometric and spectrophotometric determinations, the influence of quality of light upon interconversion of the cis and trans isomers of o-hydroxycinnamic acid. Careful studies [e.g., (2-4)] have been made of the influence of ultraviolet irradiation upon cis-trans interconversion of various compounds, including o-hydroxycinnamic acid. A limited amount of information also is available concerning the influence of sunlight upon this compound (3), but no reports were found in the literature which deal specifically with the influence of quality of visible light upon the interconversion.