Adiabatically stable anions

Formation of Single Strand Breaks via Adiabatically Stable Anions of Pyrimidine Nucleotides... 

So far, two different mechanisms of single strand break formation based on adiabatically stable anions have been proposed. The first mechanism, suggested by the Leszczynski group, assumes the formation of stable anions of 3 - and 5 -phosphates of thymidine and cytidine in which the cleavage of the C-O bond take place via the SN2-type process. The second reaction sequence, proposed by us, starts from the electron induced BFPT process followed by the second electron attachment to the pyrimidine nucleobase radical, intramolecular proton transfer, and the C-O bond dissociation. In both mechanisms the bottleneck step is associated with very low kinetic barrier which enables the SSB formation to be completed in a time period much shorter than that required for the assay of damage. 

Schematic diagram showing the addition of LEE to DNA in gas phase (e ) and in liquid water via pre-hydrated electrons (e g) from the conduction band and by LEE addition. In the gas phase, LEE (e, ) can be captured into one of the UMOs of DNA (shown as SOMO after the e, capture) creati ng the TNI (DN A ). A TNI formed in the liquid water (DNA ) is quickly solvated resulting in the adiabatic DNA radical anion (DNA ). The energy of the adiabatic radical anion must be below the energy of the solvated electron (e ) to be stable to electron loss to water. For clarity, the MOs of DNA below the HDMO (highest doubly occupied MOs) and above the SOMO are not shown in the figure. (Figure based in part from Wang et al. 2009)...

As can be seen, generally all electron affinities predicted by ASCF are negative, indicating a more stable neutral system with respect to the anion. The inclusion of correlation via CCSD(T) and NOF approximates them to the available adiabatic experimental EAs, accordingly with the expected trend. The EAs tend to increase in moving from ACCSD(T) to ANOF and then from ANOF to the experiment. It should be noted that the NH anion is predicted to be unbound by CCSD(T), whereas the positive vertical EA value via NOE corresponds to the bound anionic state. 

Values of electron affinities of the neutral clusters are also an indication of the stability of the corresponding anionic clusters. In fact, it is important to check if the neutral system is able to attach an extra electron to form a stable species. The adiabatic electron affinity is given by the difference between the energy of the neutral system Lin, at its most stable geometry, and of the anionic Lin"... 

Adiabatic electron affinity, energy difference between the ground state of the anion and the most stable state of the neutral molecule. A particular semi-empirical self-consistent field calculation. It stands for Austin Model-1. 

It is worth mentioning that two electrons can be simultaneously attached to Au to form the dianion Au shown in Fig. 3. This dianion is stable relative to Au with a total energy difference of 65.6 kcal/mol (65.8 kcal/ mol after ZPVE) although it still remains unstable with respect to the corresponding anion Aus by 28.8 kcal/mol (28.6 kcal/mol after ZPVE). It is responsible for the second adiabatic electron affinity (see Ref. [68]). This first implies that such a dianion may exist in solvent or condensed phase (see Ref. [69] for current review) and second, that it does not exist in the gas phase and, therefore, there is no contradiction with the statement that the smallest stable dianion is Aui2 [70]. 

The TNI of DNA stabilized in solution over a TNI of DNA in the gas phase is shown in O Fig. 34-11. Once formed in solution, the TNI will undergo solvent reorganization, which liberates additional solvation energy. This occurs within a hundred picoseconds and results in stabilization by several electronvolts. For a stable (adiabatic) anion radical to be formed, the... 

The Most Stable Clusters, the Respective Energies (a.u.), Optimized Cation Energies, Anion Energies (in a.u.). Theoretical Adiabatic Ionization Potential, Electron Affinity, and Hardness (in eV) at B3LYP/6-31 + C(cO Level of Theory... 

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