Water-Induced Chiral Separation on a Au(111) Surface.

Facing the scientific question of the origin of chirality in life, water is considered to play a crucial role in driving many biologically relevant processes in vivo. Water has been demonstrated in vitro to be related to chiral generation, amplification, and inversion, while the underlying mechanism is still not fully understood. Real-space evidence at the single-molecule level is thus urgently required to understand the role of water molecules in biomolecular chirality related issues. Herein, we choose one of the RNA bases, the biomolecule uracil (U), which self-assembles into racemic hydrogen-bonded structures. Upon water exposure, surprisingly, racemic structures could be transformed to homochiral water-involved structures, resulting in an unexpected chiral separation on the surface. The origin of chiral separation is due to preferential binding between water and the specific site of U molecules, which leads to the formation of the energetically most favorable homochiral (U-H2O-U)2 cluster as seed for subsequent chiral amplification. Such a water-driven self-assembly process may also be extended to other biologically relevant systems such as amino acids and sugars, which would provide general insights into the role that water molecules may play in the origin of homochirality in vivo.

Development of Hot-Extruded Mg-RE-Zn Alloy Bar with High Mechanical Properties.

A new elevated-temperature high-strength Mg-4Er-2Y-3Zn-0.4Mn (wt %) alloy was developed by semi-continuous casting, solid solution treatment, and hot extrusion. W phase (Mg3(Er,Y)2Zn3) with fcc structure, long period stacking ordered phases with 18R (Mg10(Er,Y)1Zn1) and 14H (Mg12(Er,Y)1Zn1) structures, and basal plane stacking faults (SFs) was formed in the as-cast alloy, mainly due to the alloy component of (Er + Y)/Zn = 1:1 and Er/Y = 1:1 (at %). After solid solution treatment and hot extrusion, the novel microstructure feature formed in as-extruded alloy is the high number-density nanospaced basal plane SFs throughout all the dynamically recrystallized (DRXed) and un-DRXed grains, which has not been previously reported. The as-extruded alloy exhibits superior tensile properties from room temperature to 300 °C. The tensile yield strength can be maintained above 250 MPa at 300 °C. The excellent elevated-temperature strength is mainly ascribed to the formation of nanospaced basal plane SFs throughout the whole Mg matrix, fine DRXed grains ~2 µm in size, and strongly basal-textured un-DRXed grains with profuse substructures. The results provide new opportunities for the development of deformed Mg alloys with satisfactory mechanical properties for high-temperature services.