Tuning a Schottky barrier in a photoexcited topological insulator with transient Dirac cone electron-hole asymmetry.

The advent of Dirac materials has made it possible to realize two-dimensional gases of relativistic fermions with unprecedented transport properties in condensed matter. Their photoconductive control with ultrafast light pulses is opening new perspectives for the transmission of current and information. Here we show that the interplay of surface and bulk transient carrier dynamics in a photoexcited topological insulator can control an essential parameter for photoconductivity-the balance between excess electrons and holes in the Dirac cone. This can result in a strongly out of equilibrium gas of hot relativistic fermions, characterized by a surprisingly long lifetime of more than 50 ps, and a simultaneous transient shift of chemical potential by as much as 100 meV. The unique properties of this transient Dirac cone make it possible to tune with ultrafast light pulses a relativistic nanoscale Schottky barrier, in a way that is impossible with conventional optoelectronic materials.

Coexpression of interleukin-6 and -2 from giant panda in Escherichia coli and the biological activity of the fusion protein.

To construct a fusion cytokine protein with more and stronger bioactivities to enhance the immunity of the cytokine alone, we expressed interleukin (IL)-6/(IL)-2 from giant panda (Ailuropoda melanoleuca) in Escherichia coli as a 59.4-kDa fusion protein. Subsequently, the inclusion bodies were solubilized with 8 M urea and applied onto a Ni-nitrilotriacetic acid column. The final production of IL-6/IL-2 reached 6 mg/L in soluble form, and the purified final product was >96% pure. In Western blot assays, the recombinant IL-6/IL-2 was recognized by polyclonal antibodies against IL-6 and IL-2 of giant panda. The results demonstrated that the protein mixture contained correctly folded IL-2 and IL-6 proteins. A 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyltetrazolium bromide assay demonstrated that IL-6/IL-2 can promote lymphocyte proliferation and differentiation. These data suggest that the fusion protein could be used to develop a novel immunoadjuvant to enhance the immunity of animals against infectious diseases.

[Screening of steroidal saponins from the bulbs of Lilium brownii var. colchesteri by combination of high performance liquid chromatography-electrospray ionization mass spectrometry and electron impact mass spectrometry].

With the combination of high performance liquid chromatography-electrospray ionization mass spectrometry (HPLC/ESI-MS) and electron impact mass spectrometry (EI-MS), two steroidal saponins, one compound containing three glycosyls and tigogenin and the other one containing three glycosyls and diosgenin, from the bulbs of Lilium brownii var. calchesteri in China have been screened. In the method, on-line HPLC/ESI-MS allows us to obtain rapidly useful information about the molecular weight and the glycosyl chain of glycoside without the necessity of isolating individual compounds, but little information about steroidal sapogenins. Just with 1 mg to 2 mg of pure sample, off-line EI-MS allows us to acquire useful information about a steroidal sapogenin of saponins, but it is difficult to obtain the molecular ion peak. The combination of HPLC/ESI-MS and EI-MS is well suitable for rapidly screening steroidal saponins from plants.