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Cover Picture: Photostability of Isolated and Paired Nucleobases: N-H Dissociation of Adenine and Hydrogen Transfer in its Base Pairs Examined by Laser Spectroscopy (ChemPhysChem 9/2004)
The cover picture shows an artist's view of the interaction of the DNA α helix with light. Prebiotic chemistry supposedly happened under conditions of intense short wavelength radiation without UV-absorbing oxygen or ozone layer. UV photostability may have been an important factor for the evolutionary selection of the DNA bases besides their capability to form strong hydrogen bonds. The apparent photostability of the genetic code has been ascribed to fast internal conversion of the electronically excited DNA bases to the electronic ground state via doorway states. The results presented on page 1427 by Hünig et al. point to N-H dislocation as important pathway to convert photoexcitation of DNA to innoxious heat in the condensed phase.