Cytosine, molecular orbitals, energy

Length of the bridge containing adenine-cytosine base pairs only Lowest unoccupied molecular orbital Marcus reorganization energy Mass of the tunneling particle... 

The energies of the molecular orbitals of the guanine-cytosine base... 

Energies op the Lowest Empty (LEMO) and Three Highest (HOMO) Molecular Orbitals of Cytosine Calculated by Different All-Valence or All-Electron Methods... 

The Energies of Highest Occupied (HOMO) and Lowest Empty (LEMO) Molecular Orbitals of Guanine, Cytosine, and their Pair Calculated by w-SCF MO (Closed-Shell)0... 

Hayon s suggestion 44, 45) and species 50 in alkaline solution (Hayon s suggestion 46). The calculation (the spectra as well as the INDO calculation446 of electron densities of uracil and cytosine radical anion) suggested that the solvated electron reacts with uracil and cytosine by addition to the lowest unoccupied molecular orbital, followed at neutral pH by protonation to form the C-4 ketyl radical of uracil and the C-2 ketyl radical of cytosine. The calculation on transition energies presented in ref. 446 cannot be treated as evidence that the species above is the one formed on pulse rediolysis of aqueous solutions of the pyrimidines. 

Table 24. Orbital energies for the highest occupied molecular orbital (HOMO) and the lowest unoccupied moler cular orbital (LUMO) for the hydrogen-bonded pai-guanine-cytosine a...

In two papers, the energies of the molecular orbitals of the guanine-cytosine pair have not been given. The evaluation could be made only from the correlation diagram of the molecular orbitals. 

From ETS experiments (Aflatooni et al. 1998), Aflatooni et al. showed that energies required to attach an electron into the lowest empty valence molecular orbitals of all the bases are positive. This means that all the bases have negative valence vertical electron affinity (<0). The vertically formed anions of pyrimidines bases (C, T, and U) were found to be more stable than the purines (G and A) by ca. 0.2 eV. The ETS spectra of U, T, C, G, and A are shown in O Fig. 34-7. The spectra in O Fig. 34-7 arise due to the occupation of the lowest empty 7t -MOs of the parent molecules by the electron. The vertical lines on the spectra (O Fig. 34-7) show the position of the vertical attachment energies. For guanine anion, the ETS (shown in O Fig. 34-7) was observed for its enol tautomer (for details see Aflatooni et al. [1998]). For each of these molecules, three VAEs, associated with the three lowest vacant tTi, tT2, and 7T3 MOs, were determined. The VAEs 0.22,1.58, and 3.83 eV for uracil 0.29,1.71, and 4.05 eV for thymine 0.32,1.53, and 4.50 eV for cytosine 0.54,1.36, and 2.17 eV for adenine and 0.46,1.37, and 2.36 eV for guanine(enol) tautomer were determined by ETS. 

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