Due to their unique electronic and optoelectronic properties, tin selenide nanostructures show great promise for applications in energy storage and photovoltaic devices. Despite the great progress that has been achieved, the phase-controlled synthesis of two-dimensional (2D) tin selenide nanostructures remains a challenge, and their use in supercapacitors has not been explored. In this paper, 2D tin selenide nanostructures, including pure SnSe2 nanodisks (NDs), mixed-phase SnSe-SnSe2 NDs, and pure SnSe nanosheets (NSs), have been synthesized by reacting SnCl2 and trioctylphosphine (TOP)-Se with borane-tert-butylamine complex (BTBC) and 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone. Utilizing the interplay of TOP and BTBC and changing only the amount of BTBC, the phase-controlled synthesis of 2D tin selenide nanostructures is realized for the first time. Phase-dependent pseudocapacitive behavior is observed for the resulting 2D nanostructures. The specific capacitances of pure SnSe2 NDs (168 F g(-1)) and SnSe NSs (228 F g(-1)) are much higher than those of other reported materials (e.g., graphene-Mn3O4 nanorods and TiN mesoporous spheres); thus, these tin selenide materials were used to fabricate flexible, all-solid-state supercapacitors. Devices fabricated with these two tin selenide materials exhibited high areal capacitances, good cycling stabilities, excellent flexibilities, and desirable mechanical stabilities, which were comparable to or better than those reported recently for other solid-state devices based on graphene and 3D GeSe2 nanostructures. Additionally, the rate capability of the SnSe2 NDs device was much better than that of the SnSe NS device, indicating that SnSe2 NDs are promising active materials for use in high-performance, flexible, all-solid-state supercapacitors.

Magnetotactic bacteria (MTB) are a diverse group of microorganisms with the ability to orient and migrate along geomagnetic field lines. This unique feat is based on specific intracellular organelles, the magnetosomes, which, in most MTB, comprise nanometer-sized, membrane bound crystals of magnetic iron minerals and organized into chains via a dedicated cytoskeleton. Because of the special properties of the magnetosomes, MTB are of great interest for paleomagnetism, environmental magnetism, biomarkers in rocks, magnetic materials and biomineralization in organisms, and bacterial magnetites have been exploited for a variety of applications in modern biological and medical sciences. In this paper, we describe general characteristics of MTB and their magnetic mineral inclusions, but focus mainly on the magnetosome formation and the magnetisms of MTB and bacterial magnetosomes, as well as on the significances and applications of MTB and their intracellular magnetic mineral crystals.

Alcohol dehydrogenases (ADHs), which belong to the oxidoreductase superfamily, catalyze the interconversion between alcohols and aldehydes or ketones with high stereoselectivity under mild conditions. ADHs are widely employed as biocatalysts for the dynamic kinetic resolution of racemic substrates and for the preparation of enantiomerically pure chemicals. This review provides an overview of biotechnological applications for ADHs in the production of chiral pharmaceuticals and fine chemicals.

L-methionine has attracted a great deal of attention for its nutritional, pharmaceutical, and clinical applications. In this study, Escherichia coli W3110 was engineered via deletion of a negative transcriptional regulator MetJ and over-expression of homoserine O-succinyltransferase MetA together with efflux transporter YjeH, resulting in L-methionine overproduction which is up to 413.16 mg/L. The partial inactivation of the L-methionine import system MetD via disruption of metI made the engineered E. coli ΔmetJ ΔmetI/pTrcA*H more tolerant to high L-ethionine concentration and accumulated L-methionine to a level 43.65% higher than that of E. coli W3110 ΔmetJ/pTrcA*H. Furthermore, deletion of lysA, which blocks the lysine biosynthesis pathway, led to a further 8.5-fold increase in L-methionine titer of E. coli ΔmetJ ΔmetI ΔlysA/pTrcA*H. Finally, addition of Na S O to the media led to an increase of fermentation titer of 11.45%. After optimization, constructed E. coli ΔmetJ ΔmetI ΔlysA/pTrcA*H was able to produce 9.75 g/L L-methionine with productivity of 0.20 g/L/h in a 5 L bioreactor. This novel metabolically tailored strain of E. coli provides an efficient platform for microbial production of L-methionine. Biotechnol. Bioeng. 2017;114: 843-851. © 2016 Wiley Periodicals, Inc.

Exploring low-cost, high-activity, and long-durability hybrid electrocatalysts for cathodic oxygen reduction reaction (ORR) is vital to advance fuel cells technologies. In this paper, a series of graphene (G)-CuxPdy (Cu4Pd, Cu3Pd, CuPd, CuPd3, CuPd4) nanocomposites (G-CuxPdy NCPs) is obtained by assembly of CuxPdy alloy nanocrystals (NCs) with controlled component ratios on G nanosheets using the "dispersing-mixing-vaporizing solvent" strategy and used as electrocatalysts for ORR. Compared with pure CuxPdy NCs, greatly enhanced interfacial electron transfer dynamics are observed in G-CuxPdy NCPs, which show a strong correlation with the alloy compositions of the NCPs. The electrocatalytic experiments in alkaline solution reveal that the ORR activities of those G-CuxPdy NCPs are also strongly dependent on alloy components and exhibit a double-volcano feature with variations of alloy components. Among them, G-Cu3Pd NCPs possess the highest electrocatalytic activity, which is much better than some reported electrocatalysts and commercial Pd/C catalyst and close to Pt/C catalyst. By correlating the Pd 3d binding energies and the sizes of CuxPdy NCs with the mass-specific activities of G-CuxPdy NCPs and considering the interfacial electron transfer dynamics, the best catalytic activity of G-Cu3Pd NCPs may result from the unique electronic structure and the smallest size of Cu3Pd NCs as well as the strong synergistic effect between G and Cu3Pd NCs. Moreover, the durability of G-Cu3Pd NCPs is superior to that of Pt/C catalyst, indicating that they are promising cathodic electrocatalysts for using in alkaline fuel cells.