1973 年 19 巻 2 号 p. 123-128
In the irradiation of ergosterol, the effect of wavelength on the forma-tion of potential vitamin D2 (the sum of pre-D2 and vitamin D2) was investigated. Monochromatic UV rays obtained from a spectroirradiator were used for the irradiations and the yield of potential vitamin D2 was estimated by the GLC method as described previously (1). When an ergosterol solution in ethanol (1.0 mg/ml) was irradiated by mono-chromatic UV ray in the range 230-400mμ with the quantum of 4.0×108 erg/cm2, the figure of the relationship between yield of potential vitamin D2 and wavelengths of irradiating UV rays showed a mountain shape with a maximum at 295mμ. Ultraviolet rays in the range 285-310mμ were more effective than the other rays for the formation of potential vitamin D2 (yield: higher than 22%), whereas those either below 230mμ or above 330mμ were less effective (yield: lower than 3.5%). The gas chromatograms of TMS ethers of all the irradiated solutions showed the presence of peaks due to gyro- and isopyro-D2 (thermal cyclized products of pre-D2 and vitamin D2), lumisterol2, ergosterol and tachy-sterol2, although their peak area ratios were very different. The irradiations by various monochromatic UV rays with different quanta of energy were also examined, and the ray of 295mμ with quanta of 2.1-6.4×108 erg/cm2 was found to give the best yields of potential vitamin D2, between 31.5 and 33%. Further irradiations beyond the maxima effected a decrease in the yield.
