BackgroundChemotherapeutic agents (anti-cancer drugs) are small cytostatic or cytotoxic molecules that often bind to double-stranded DNA (dsDNA) resulting in modifications of their structural and nanomechanical properties and thus interfering with the cell proliferation process.MethodsWe investigated the anthraquinone compound mitoxantrone that is used for treating certain cancer types like leukemia and lymphoma with magnetic tweezers as a single molecule nanosensor. In order to study the association of mitoxantrone with dsDNA, we conducted force-extension and mechanical overwinding experiments with a sensitivity of 10−14 N.ResultsUsing this method, we were able to estimate an equilibrium constant of association Ka ≈ 1 × 105 M−1 as well as a binding site size of n ≈ 2.5 base pairs for mitoxantrone. An unwinding angle of mitoxantrone-intercalation of ϑ ≈ 16° was determined.ConclusionMoreover, we observed a complex concentration-dependent bimodal binding behavior, where mitoxantrone associates to dsDNA as an intercalator and groove binder simultaneously at low concentrations and as a mere intercalator at high concentrations.Electronic supplementary materialThe online version of this article (10.1186/s12951-018-0381-y) contains supplementary material, which is available to authorized users.

The reaction of octacarbonyldicobalt with octahydridosilsesquioxane (4:1 stoichiometry) in hexane leads to octakis(tetracarbonylcobaltio)octasilsesquioxane (1), the first octasilsesquioxane in which eight metals are directly bound to the silicon atoms of the siloxane cage. The product has been characterized by 29Si CP-MAS NMR, IR, and Raman spectroscopy as well as elemental analysis and MALDI TOF spectrometry. The molecular structure of 1 has been determined by single-crystal X-ray diffraction. In combination with triphenylphosphine, 1 shows catalytic activity in the hydroformylation of 1-hexene.

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