Electronic Structure of Sulfur Compounds and Their Protecting Action against Ionizing Radiation

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Abstract
The mechanism of the protecting action of sulfur compounds against ionizing radiation from the electronic structural point of view was studied. The extremely high reactivity of sulfur compounds with hydroxyl radicals, which was considered to be related to their indirect protecting action, is explained by the significantly low energy of the lowest unoccupied molecular orbital (LUMO) and the relatively high energy of the highest occupied molecular orbital (HOMO) of these compounds in comparison with others. Intermolecular and intramolecular energy transfers which were considered to be intimately correlated with the direct protecting action of sulfur compounds were explained on the basis of electronic structure, and sulfur groups may act as sinks of irradiation energy due to the extremely low values of LUMO of sulfur compounds. Besides the special feature of energy values of HOMO and LUMO, sulfur compounds were characterized by having large electron density at the pz orbital which was concerned with chemical reactivity and energy transfer. The contribution of d-orbitals was considered to make sulfur compounds more reactive than other compounds which lack contributions from d-orbitals.