Assembly of 2D MXene sheets into a 3D macroscopic architecture is highly desirable to overcome the severe restacking problem of 2D MXene sheets and develop MXene-based functional materials. However, unlike graphene, 3D MXene macroassembly directly from the individual 2D sheets is hard to achieve for the intrinsic property of MXene. Here a new gelation method is reported to prepare a 3D structured hydrogel from 2D MXene sheets that is assisted by graphene oxide and a suitable reductant. As a supercapacitor electrode, the hydrogel delivers a superb capacitance up to 370 F g −1 at 5 A g −1 , and more promisingly, demonstrates an exceptionally high rate performance with the capacitance of 165 F g −1 even at 1000 A g −1 . Moreover, using controllable drying processes, MXene hydrogels are transformed into different monoliths with structures ranging from a loosely organized porous aerogel to a dense solid. As a result, a 3D porous MXene aerogel shows excellent adsorption capacity to simultaneously remove various classes of organic liquids and heavy metal ions while the dense solid has excellent mechanical performance with a high Young's modulus and hardness.
Pif1 is a conserved SF1B DNA helicase involved in maintaining genome stability through unwinding double-stranded DNAs (dsDNAs), DNA/RNA hybrids, and G quadruplex (G4) structures. Here, we report the structures of the helicase domain of human Pif1 and Bacteroides sp Pif1 (BaPif1) in complex with ADP-AlF4(-) and two different single-stranded DNAs (ssDNAs). The wedge region equivalent to the β hairpin in other SF1B DNA helicases folds into an extended loop followed by an α helix. The Pif1 signature motif of BaPif1 interacts with the wedge region and a short helix in order to stabilize these ssDNA binding elements, therefore indirectly exerting its functional role. Domain 2B of BaPif1 undergoes a large conformational change upon concomitant binding of ATP and ssDNA, which is critical for Pif1's activities. BaPif1 cocrystallized with a tailed dsDNA and ADP-AlF4(-), resulting in a bound ssDNA bent nearly 90° at the ssDNA/dsDNA junction. The conformational snapshots of BaPif1 provide insights into the mechanism governing the helicase activity of Pif1.
To elevate the iodine level in edible plants has been shown to be an excellent approach to correct iodine deficiency. We have proposed an innovative approach to produce iodine supplementation by growing vegetables on soils with algal-based iodized organic fertilizer. Ten species of vegetables were tested. The biological absorption and migration of the iodine within the vegetable plants were revealed using microscopy with silver iodide precipitation technique. The results show that the absorption of iodine by the vegetable increases with increasing amount of the algal-based iodized organic fertilizer in general. And the uptake of iodine by leaf vegetable is significantly greater than that by fruit vegetable. Distribution of iodine in various plant organs shows a trend of decreasing iodine concentration from root, leaf, stalk, to fruit. A similar of decreasing concentration can also be found in various cells (cytoplasm>cytoderm>organelles). The exploration of the iodine uptake and biogeochemistry migration mechanisms provides an important scientific foundation for establishing a new method of producing a natural iodine supplementation by iodine biofortification of vegetables.
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