Vacuum ultraviolet photobiology with synchrotron radiation.

Abstract

The vacuum-ultraviolet (VUV) region of the electromagnetic spectrum is situated between the far-UV and X-ray regions. It covers a vast range of photon energy from 6.20 eV (200 nm) to 41.3 eV (30 nm). In a broader sense, it covers several hundred eV. The spectral regions on both sides of the VUV are relatively easy in biological experimentations since atmospheric conditions pose no obstacles. In contrast, VUV experiments are difficult to perform with living systems because of the necessity of maintaining the target in a vacuum. Besides, photon sources available for VUV experiments have been limited. In the work by Boyle (1916) we see what seems to be the earliest work on biological experiments with VUV radiation. He irradiated microorganisms with VUV radiation through a fluorite crystal plate. Blank and Arnold (1935) reported the killing of Bacillus spores by 110–130 nm photons. Heinmets and Taylor (1952) treated bacterial cells by passing them in aqueous suspension through an electrical arc. More recently, Jagger et al., (1967) studied VUV effects on Streptomyces conidia by successive use of cutoff filters down to 155 nm. These experiments avoided the vacuum problem either by using vacuum-resistant spores or by special innovations for the VUV irradiation. Apart from living materials, biomolecules, like proteins, can be dried in vacuum and thus become suitable for VUV irradiation. Setlow et al., (1959) were probably the first to perform inactivation experiments with enzymes using monochromatic light in the VUV region. Wirths and Jung (1972) and Sontag and Dertinger (1975) irradiated DNA and bacteriophages in vacuum with dispersed VUV radiation using a conventional light source. Although these biological effects, for which a sensitive assay technique is available, could be investigated by conventional VUV light sources, precise product analysis in the chemical sense is almost unthinkable with them due to the lack of intensity after monochromatization. Rare gas discharge lamps such as the one using bromine (Ito and Kobayashi, 1976) or an excimer laser (Green et al., 1987) could provide intense monochromatic VUV radiation but are greatly limited in the number of wavelengths that are available. Synchrotron radiation (SR) is a breakthrough as a VUV radiation source.