The role of spin in biological processes: O₂, NO, nucleobases, nucleosides, nucleotides and Watson–Crick base pairs

Abstract

The experimental electron affinities of adenine, guanine, cytosine, thymine and uracil have been determined from reduction potentials and negative ion photoelectron spectra. Updated values for purine, pyrimidine and other nitrogen heterocyclics, which have not been measured in the gas phase, are presented. The electron affinity of Watson -Crick guanine -cytosine is estimated empirically. The experimental values are consistent with quantum mechanical semi-empirical multiconfiguration configuration interaction calculations. The bulk hydration energies of the nucleobase anions, 2.34 eV, determined from the experimental data and sequential anion hydration energy difference of about 0.20(5) eV suggest that 10 -15 water molecules complete the hydration shell. The electron affinities for the formation of doublet and quartet anions of the nucleobases, nucleosides, nucleotides and Watson -Crick base pairs are calculated. We postulate that low-lying quartet anion states and their spin distribution can and will participate in electron conduction, radiation damage, oxidation damage and repair, strand breakage and protein synthesis.

The Electronic Behavior of Zinc-Finger Protein Binding Sites in the Context of the DNA Extended Ladder Model

“…4, are respectively 0.25eV, 0.44eV, 0.33eV and 0.45eV. The DFT analysis, supported by experimental anion photoelectron spectra, also suggests that a A , a T , a C and a G in the Morse potential are correspondingly around 3.0 Å−1 , 3.0 Å−1 , 3.0 Å−1 and 2.5 Å−1 [38,39]. The k v comes from DNA vibrational spectra using Raman spectroscopy [69] and we fix this to 0.0125eV.…”

“…Unfortunately the findings in this section cannot be compared with accurate quantum chemistry calculations, because the literature reports results just for few nucleotides [37][38][39][40][41]. Systematic analysis at least 26 nucleotides is usually avoided, because this demands huge processing time to include hydrogen bonds and sugar residues for the description of DNA-protein interactions.…”

“…The lost electron is usually in the highest occupied molecular orbital valence band (HOMO) and it may easily jump to the lowest unoccupied molecular orbital in the conductor band (LUMO). But, the literature also suggests electronic affinity models, where the energy is described by the gain of electrons in neutral molecules [37][38][39][40][41]. These theoretical results usually combine density functional theory and molecular dynamic simulation.…”