The effects of further irradiation of the radiation products of ergosterol

Abstract

The effects of ultra-violet radiation upon ergosterol have been studied by many workers, but the results have been difficult to interpret owing to the fact that certain of the products of radiation are themselves changed by further exposure, at a rate greater than the velocity of change of ergosterol itself.Windaus, Westphal, Werder and Rygh (1929) have carried out some experi ments in which the irradiation products of ergosterol were freed from unchanged ergosterol, and then re-radiated. They used the same source of energy (a magnesium spark) for both first and second irradiations, and obtained results of some interest, but still difficult to interpret.We have carried out a series of experiments on re-radiation, by exposing ergosterol to radiation of long wave-lengths only, removing the unchanged ergosterol, and then exposing the product to radiation of either short or long wave-lengths. These tests have been supplemented by the further irradiation of such isolated fractions of the mixed irradiation products of ergosterol as we have been able to separate from the mixture by precipitation or distillation. The absorption spectra and antirachitic activity of the products were measured both before and after the second irradiation.* Technique of Measurement and of Irradiation.The measurements of absorption spectra, and of antirachitic activity were made by the methods described in our paper on the Distillation of Vitamin D (Askew et al., 1930).The initial irradiations of ergosterol were carried out on alcoholic or ethereal solutions of highly purified ergosterol. These solutions were irradiated by a mercury vapour lamp, through light filters of different substances, as shown in the second column of Table I. During irradiation the solution was either contained in silica cells in a layer 1 cm. thick and stirred by nitrogen, or was passed in a rapid stream through a spiral silica tube of 2 mm. bore, which * A preliminary account of certain of these experiments was published in 4 Nature ' (1930).