A doubly substituted form of the nitrogenase MoFe protein (α-70 ^{Val →Ala} , α-195 ^His→Gln ) has the capacity to catalyze the reduction of carbon dioxide (CO ₂ ) to yield methane (CH ₄ ). Under optimized conditions, 1 nmol of the substituted MoFe protein catalyzes the formation of 21 nmol of CH ₄ within 20 min. The catalytic rate depends on the partial pressure of CO ₂ (or concentration of HCO ₃ ⁻ ) and the electron flux through nitrogenase. The doubly substituted MoFe protein also has the capacity to catalyze the unprecedented formation of propylene (H ₂ C = CH-CH ₃ ) through the reductive coupling of CO ₂ and acetylene (HC≡CH). In light of these observations, we suggest that an emerging understanding of the mechanistic features of nitrogenase could be relevant to the design of synthetic catalysts for CO ₂ sequestration and formation of olefins.

The ATP-binding cassette transporter ABCG2 mediates the efflux of several chemotherapeutic drugs, contributing to the development of multidrug resistance (MDR) in many cancers. The most promising strategy to overcome ABCG2-mediated MDR is the use of specific inhibitors. Despite many efforts, the identification of new potent and specific ABCG2 inhibitors remains urgent. In this study, a structural optimization of indeno[1,2-b]indole was performed and a new generation of 18 compounds was synthesized and tested as ABCG2 inhibitors. Most compounds showed ABCG2 inhibition with IC₅₀ values below 0.5 µM. The ratio between cytotoxicity (IG₅₀) and ABCG2 inhibition potency (IC₅₀) was used to identify the best inhibitors. In addition, it was observed that some indeno[1,2-b]indole derivatives produced complete inhibition, while others only partially inhibited the transport function of ABCG2. All indeno[1,2-b]indole derivatives are not transported by ABCG2, and even the partial inhibitors are able to fully chemosensitize cancer cells overexpressing ABCG2. The high affinity of these indeno[1,2-b]indole derivatives was confirmed by the strong stimulatory effect on ABCG2 ATPase activity. These compounds did not affect the binding of conformation-sensitive antibody 5D3 binding, but stabilized the protein structure, as revealed by the thermostabilization assay. Finally, a docking study showed the indeno[1,2-b]indole derivatives share the same binding site as the substrate estrone-3-sulfate.