Photosnesitization of DNA by gold.

Au (III) reacts with DNA at pH 5.6 to form a complex which is sensitive to mid-UV radiation. Cyclobutane pyrimidine dimers are produced at some 15 to 30 times the rate that they are in untreated DNA. The mechanism of photosensitization appears to involve energy absorption by Au-urine and Au-cytosine adducts which can then transfer energy to thymine residues. There is no evidence for a "heavy atom" effect which enables metals such as Ag to mix excited states of DNA and to increase the quantum yields of some photoproducts. The use of mid-UV radiation as a probe for investigating the interaction between DNA and drugs such as sodium aurothiomalate is discussed.