We report a novel nanoparticle that is promising for photodynamic therapy applications, which consists of a π-conjugated polymer doped with a singlet oxygen photosensitizer. The nanoparticles exhibit highly efficient collection of excitation light due to the large excitation cross-section of the polymer. A quantum efficiency of singlet oxygen production of 0.5 was determined. Extraordinarily large two-photon excitation cross-sections were determined, indicating promise for near infrared multiphoton photodynamic therapy. Gel electrophoresis of DNA after near-UV irradiation in the presence of nanoparticles indicated both purine base and backbone DNA damage.

Copper and iron are two widely studied transition metals associated with hydroxyl radical (˙OH) generation, oxidative damage, and disease development. Because antioxidants ameliorate metal-mediated DNA damage, DNA gel electrophoresis assays were used to quantify the ability of ten selenium-containing compounds to inhibit metal-mediated DNA damage by hydroxyl radical. In the Cu(I)/H(2)O(2) system, selenocystine, selenomethionine, and methyl-selenocysteine inhibit DNA damage with IC(50) values ranging from 3.34 to 25.1 μM. Four selenium compounds also prevent DNA damage from Fe(II) and H(2)O(2). Additional gel electrophoresis experiments indicate that Cu(I) or Fe(II) coordination is responsible for the selenium antioxidant activity. Mass spectrometry studies show that a 1 : 1 stoichiometry is the most common for iron and copper complexes of the tested compounds, even if no antioxidant activity is observed, suggesting that metal coordination is necessary but not sufficient for selenium antioxidant activity. A majority of the selenium compounds are electroactive, regardless of antioxidant activity, and the glutathione peroxidase activities of the selenium compounds show no correlation to DNA damage inhibition. Thus, metal binding is a primary mechanism of selenium antioxidant activity, and both the chemical functionality of the selenium compound and the metal ion generating damaging hydroxyl radical significantly affect selenium antioxidant behavior.

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Inorganic selenium and oxo-sulfur compounds are widely available in dietary supplements and have been extensively studied for their antioxidant and anticancer properties. Although many in vivo and clinical trials have been conducted using these compounds, their biochemical and chemical mechanisms of efficacy are the focus of much current research. This review discusses the ability of inorganic selenium compounds, such as selenite, and selenate, to prevent damage from reactive oxygen species as well as their ability to promote cell death by reactive oxygen species generation. Oxo-sulfur and selenium compounds, such as allicin, dimethyl sulfone, methionine sulfoxide, and methylselenenic acid also have similar abilities to act as both antioxidants and pro-oxidants, but the mechanisms for these behaviors are distinctly different from those of the inorganic selenium compounds. The antioxidant and pro-oxidant properties of these small-molecule sulfur and selenium compounds are extremely complex and often greatly depend on experimental conditions, which may explain contradictory literature reports of their efficacy.