A number of methods can be used to improve the stability of the protein crystal-growth environment, including growth in microgravity without an air-liquid phase boundary, growth in gels and growth under oil ('microbatch'). In this study, X-ray data has been collected from and structures refined for crystals of hen egg-white lysozyme (HEWL) grown using four different methods, liquid-liquid dialysis on Earth and in microgravity using the European Space Agency's (ESA) Advanced Protein Crystallization Facility (APCF) on board the NASA Space Shuttle Life and Microgravity Spacelab (LMS) mission (STS-78), crystallization in agarose gel using a tube liquid-gel diffusion method and crystallization in microbatch under oil. A comparison of the overall quality of the X-ray data, the protein structures and especially the bound-water structures has been carried out at 1.8 A. The lysozyme protein structures corresponding to these four different crystallization methods remain similar. A small improvement in the bound-solvent structure is seen in lysozyme crystals grown in microgravity by liquid-liquid dialysis, which has a more stable fluid physics state in microgravity, and is consistent with a better formed protein crystal in microgravity.
Tuning physical properties of transition metal dichalcogenide (TMD) monolayers by strain engineering have most widely studied, and recently Janus TMD monolayer MoSSe has been synthesized. In this work, we systematically study biaxial strain dependence of electronic structures and transport properties of Janus TMD MXY (M = Mo or W, X/Y = S, Se, or Te) monolayer by using generalized gradient approximation (GGA) plus spin-orbit coupling (SOC). It is found that SOC has a noteworthy detrimental influence on power factor in p-type MoSSe, WSSe, n-type WSTe, p-type MoSeTe and WSeTe, and has a negligible influence on one in n-type MoSSe, MoSTe, p-type WSTe and n-type MoSeTe. These can be understood by considering SOC effects on their valence and conduction bands. For all six monolayers, the energy band gap firstly increases, and then decreases, when strain changes from compressive one to tensile one. It is found that strain can tune strength of bands convergence of both valence and conduction bands by changing the numbers and relative position of valence band extrema (VBE) or conduction band extrema (CBE), which can produce very important effects on their electronic transport properties. By applying appropriate compressive or tensile strain, both n-or p-type Seebeck coefficient can be enhanced by strain-induced band convergence, and then the power factor can be improved. Our works further enrich studies on strain dependence of electronic structures and transport properties of new-style TMD monolayers, and motivate farther experimental works.
Acrylamide and acrylic acid are grafted on graphene by free-radical polymerization to produce a series of graphene-poly(acrylamide-co-acrylic acid) hybrid materials with different contents of graphene. The materials demonstrate shape memory effect and self-healing ability when the content of graphene is in the range of 10%-30% even though poly(acrylamide-co-acrylic acid) itself had poor shape memory ability. The permanent shape of the materials can be recovered well after 20 cycles of cut and self-healing. The result is attributed to the hard-soft design that can combine nonreversible "cross-link" by grafting copolymer on graphene and reversible "cross-link" utilizing the "zipper effect" of poly(acrylamide-co-acrylic acid) to form or dissociate the hydrogen-bond network stimulated by external heating.
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