Temporary anion states of radiosensitive halopyrimidines: Shape and core-excited resonances

Abstract

Halopyrimidines are known to be important radiosensitizers in the radiation treatment of cancer. The characterization of their temporary anion states (TASs) is important in the understanding of bond dissociation during such treatment. TASs, in general, can be categorized as shape resonances (SRs) and core-excited resonances (CERs). In this paper, the SRs of example compounds 2-chloro, 2-bromo, and 5-bromopyrimidine are studied via “stabilized Koopmans theorem in the framework of long range corrected density functional theory” and the CERs and possible mixture with SRs are studied via “stabilized long range corrected time-dependent density functional theory”. For each of the molecules, π∗, σ∗, and several with strong Cl/Br “d” character SRs are identified below 10eV. In addition, several π–π∗, π–σ∗, n–π∗, n–σ∗, σ–π∗, and σ–σ∗ CERs are also revealed. Moreover, when interpreted as mixture of π∗3 SR with π–π∗ CERs, the discrepancy between the calculated π∗3 SR and electron transmission spectroscopy experimental values can be very much reduced. Finally, to have a better understanding of these TASs in human bodies during cancer therapy, the solvent effect of water is also considered via the self-consistent reaction field method using polarized continuum model. Results indicate the TASs of these molecules are more stabilized in water but with different degrees. Our study provides a more detailed analysis of the CERs especially in the 5–10eV energy range. It will definitely help us in understanding the dissociative electron attachment process of the nucleobases.