First principles investigation of electronic structures and associated energy and wave-function dependent properties of biological systems: --Deoxyribonucleic acid (DNA) --Oxy-haemoglobin.

摘要

The Hartree-Fock procedure combined with many body perturbation theory has been used to investigate the electronic structures and associated properties of DNA systems and their corresponding muonium (Mu) adducts, as well as oxyhaemoglobin (HbO2).;For the DNA systems, we have performed two types of studies. The first is an investigation of the nuclear quadrupole interaction (NQI) parameters in DNA and related systems. The nuclear quadrupole interactions of 17O, 14N and 2H nuclei have been studied for free nucleobases and nucleobases in single strand and double strand DNA as well as in solid nucleobases. Our results provide the conclusion that for any property dependent on the electronic structures of the nucleic acids, the effects of the bonding between the nucleobases and the nucleic acid backbones have to be included. Furthermore, care must be taken to preserve the initial symmetry of the system when representative clusters are constructed.;The second study is that of muonium (mu+e-) adducts in the free nucleobases, the nucleobases in single and double strand DNA, and in solid nucleobases. Results for the muon (mu) magnetic contact and dipolar hyperfine interactions (HFI) are presented for the various environments. The trends among the different environments are rather different from those for the nuclear quadrupole interactions in the corresponding systems because of the differences in geometry of the Mu trapping sites in the various systems. Quantitative comparison is made between our theoretical results and experimentally measured muon HFI properties in the solid nucleobases.;The other biological system that we have studied is the oxyhaemoglobin system for which we have attempted to resolve the spin state (diamagnetic or paramagnetic). To test this we have studied the energies of the singlet and triplet states of the system at both the Hartree-Fock (HF) level and the Hartree-Fock with many body perturbation theory (HF+MP2) level. Our results indicate that the singlet state lies above the triplet state at the HF level of calculation. Incorporation of many-body effects by the perturbation method reverses this order, with the triplet state above the singlet state. Physical explanations for these relative orderings of the singlet and triplet states will be discussed. The question of possibility of making the ground state paramagnetic by attaching a muon to HbO2 will be analyzed.