Valence electronic structure, nucleotides

Results from self-consistent field (SCF) molecular orbital calculations, in combination with gas-phase photoelectron data and results from post-SCF calculations have provided a basis for descriptions of the valence electronic structure of gas-phase nucleotides and of nucleotides in water-counterion clusters. These descriptions contain values for 11 to 14 of the lowest energy ionization events in the DNA nucleotides 5 -dGMP , 5 -dAMP, 5 -dCMP and 5 -dTMP . When used with an evaluation of the difference between the Gibbs free energies of hydration for the initial and final states associated with ionization, this approach also describes the influence of hydration on the energetic ordering of ionization events in nucleotides. 

The employment of photoelectronic spectroscopy in conjunction with results from ab initio MO calculations has provided a valence orbitals description of the structure of the neutral and anionic forms of the nucleotide (143), the simplest among all the common nucleotides occurring in DNA and RNA <90JA538>. The electronic structure enables conclusions to be drawn about the distribution of the products in the electrophilic attack of nucleotides. This is supported by alkylation patterns in methylation and ethylation of DNA and RNA. 

When described at the ab initio SCF level with a split-valence basis set the valence orbital electronic structure of 5 -dTMP" is localized like those of the previously examined nucleotides 5 -dCMP , 5 -dAMP and 5 -dGMP. This localized orbital structure of nucleotides makes it possible to employ PE data and results from post-SCF calculations on model anions to correct nucleotide valence IPs obtained from SCF... 

---