Making Use of the δ Electrons in K4Mo2(SO4)4 for Visible-Light-Induced Photocatalytic Hydrogen Production.

Quadruply bonded dimolybdenum complexes with a σ2π4δ2 electronic configuration for the ground state have rich metal-centered photochemistry. An earlier study showed that stoichiometric or less amount of molecular hydrogen was produced upon irradiation by ultraviolet light (λ = 254 nm) of K4Mo2(SO4)4 in sulfuric acid solution, which was attributed to the reductive capability of the ππ* excited state. To make use of the δ electrons for visible-light-induced photocatalytic hydrogen evolution, a multicomponent heterogeneous photocatalytic system containing K4Mo2(SO4)4 photosensitizer, TiO2 electron relay, and MoS2 cocatalyst is designed and tested. With ascorbic acid added as a sacrificial reagent, irradiation by artificial sunlight (AM 1.5) on the reaction in 5 M H2SO4 has produced 13 400 µmol g-1 of molecular hydrogen (based on the Mo2 complex), which is 30 times higher than the hydrogen yield obtained from the reaction of bare K4Mo2(SO4)4 with H2SO4 under ultraviolet light irradiation. Further improvement of hydrogen evolution is achieved by addition of oxalic acid, along with an electron donor, which gives an additional 50% increase in H2 yield. Spectroscopic analyses indicate that, in this case, a junction between the Mo2 complex and TiO2 is built by the oxalate bridging ligand, which facilitates charge injection and separation from the Mo2 core. This Mo2-TiO2-MoS2 system has achieved a high hydrogen evolution rate up to 4570 µmol g-1 h-1. The efficiency of K4Mo2(SO4)4 as a metal-centered photosensitizer is also proved by parallel experiments with a dye chromophore, fluorescein, which presents comparable H2 yields and hydrogen evolution rates. Most importantly, in this study, detailed analyses illustrate that the photocatalytic cycle with hydrogen gas as an outcome of the reaction is established by involvement of the δδ* excited state generated by visible light irradiation. Therefore, this work shows the potential of quadruply bonded Mo2 complexes as photosensitizers for photocatalytic hydrogen evolution.

Synthesis and antiproliferative activity of some steroidal thiosemicarbazones, semicarbazones and hydrozones.

Steroidal thiosemicarbazones, semicarbazones and hydrazones have received extensive attention of scientists recently because they exhibit some biological activities such as antibacterial, antiviral and anticancer. Using different steroids as starting materials, through different chemical methods, 24 steroidal compounds with thiosemicarbazone, semicarbazone or hydrazone groups in their structures, were synthesized, characterized by IR, NMR and MS. The antiproliferative activity of the compounds was evaluated against human gastric cancer (SGC-7901) and human liver cancer (Bel-7404) cells. The structure-activity relationship of these compounds was discussed. The results showed that compound 3 and 12a-12c exhibited significant inhibitory activity to Bel-7404 cells, and IC50 values of them were 4.2, 11.0, 7.4 and 15.0µM respectively (Cisplatin, IC50: 11.6µM).