Shape and core‐excited resonances of thionucleobases

Abstract

Thionucleobases can be used in chemoradiation therapy of cancer. Shape resonances (SRs) and core-excited resonances (CERs) can lead to fragmentation and eventually result in strand breaks of DNA. In particular, the more energetic CERs are believed to cause double-strand breaks that can hardly be repaired. In this work, both the SRs and CERs of exemplary 2-thiouracil, 4-thiouracil, 2thiothymine, 4-thiothymine, and 6-aza-2-thiothymine are investigated using stabilization method in conjunction with long range corrected time-dependent density functional theory. Results indicate that the energies of (1) p* 1 and p* 2 SRs, (2) n-p* CERs, and (3) mixed resonances of p-p* CERs with p* SRs can be significantly stabilized due to thionation of uracil or thymine. It is noteworthy that the resonant cases of (2) and (3) can be accessed by electrons even at energies below 4 eV.Consequently, the increased decay of temporary anions can enhance strand breaks of DNA.chemoradiation therapy, density functional theory, shape and core-excited resonances, stabilization method, thionucleobases

Multi-Basis-Set (TD-)DFT Methods for Predicting Electron Attachment Energies

“…16,18,22 Electronic calculations can be performed at EOM-MP2, EOM-CCSD, MRCI, ADC, or TDDFT level, while the simulation box is represented implicitly through a localized basis set whom diffuse exponents of Gaussian functions are scaled with a parameter α to increase or decrease the box size. 16,18,[23][24][25] In figure 1, we give a stabilization graph for CCl 2 F 2 calculated at TDDFT level. Most of the calculated low-energy states are found to be DC states.…”

“…The coupling of a discrete state of the molecule with a DC state leads to an avoided crossing in a so-called stabilization graph (plot of the electronic energies vs simulation box size). The resonance energy and the lifetime of the temporary anion can be extracted from the plateau. ,, Electronic calculations can be performed at EOM-MP2, EOM-CCSD, MRCI, ADC, or TDDFT level, while the simulation box is represented implicitly through a localized basis set for which diffuse exponents of Gaussian functions are scaled with a parameter α to increase or decrease the box size. ,,− …”