Mechanisms of interaction of radiation with matter. Progress report, July 1, 1992--June 30, 1993

Abstract

This project is concerned with the mechanisms by which polynuclear aromatic (PNA) compounds on the one hand, and ionizing radiation on the other, cause damage to DNA. PNA compounds constitute an important class of environmental pollutants derived from energy-related sources which, upon metabolic activation to diolepoxide derivatives, produce bulky PNA-DNA lesions interfere with the normal DNA replication and transcription processes, and give rise to mutations and the initiation of tumors. Chiral and other stereochemical effects play a key role in determining the biological effects of a given PNA diol epoxide and the potentially mutagenic lesions which are formed. New and efficient methods for synthesizing stereochemically pure and precisely positioned PNA diol epoxide-DNA lesions in small DNA fragments are reported here. We have elucidated the structures of three stereoisomeric benzo[a]pyrene diol epoxide-DNA adducts. How these adducts affect on DNA polymerase fidelity, transcription, and DNA repair are currently being investigated with respect to detailed structure-biological activity correlations. Spectroscopic techniques such as circular dichroism, fluorescence, and photoionization play an important role in the characterizations of the PNA adducts. A new method was developed for measuring the lifetimes as well as the energies of picosecond duration electronically excited states. Using this technique, it ismore » proposed that short-lived (15 ps) charge-transfer (CT) states in the PNA compound tetracene are activated by a 20 ps laser pulse; an unusual external photoemission echo do to the recombination of CT states is observed 85 ps after the pulse.« less