Electrons play a large role in DNA reactions with carcinogens; however, little is accurately known about the details of these electronic influences. UV photoelectron (PE) spectroscopy in conjunction with quantum mechanical calculations currently provides the most detailed and accurate information available about valence electron ionization potentials (IPs) and electron distributions in nucleotides. Because of the large size of nucleotides, IPs of individual orbitals cannot be directly measured in PE experiments, nor can they be accurately calculated. We have developed a procedure, which exploits the localized valence electronic structure in nucleotides, and which employs PE data and quantum calculations on small nucleotide components. With this procedures, orbitals from the nucleotide components, for which accurate IPs are available, can be correlated with nucleotide orbitals. This correlation permits orbital IPs, calculated for the intact nucleotide, to be individually corrected. The method has also been applied to small clusters of 5'-dGMP- with Na+ and four H2O molecules and most recently to 5'-dGMP-with Na+ in bulk water. The goal of this project is to employ the experience gained in earlier investigations to examine the electronic properties of transition states for reactions of nucleotides with carcinogenic methylating and ethylating agents.
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