Efficient electroreduction of nitrate via enriched active phases on copper-cobalt oxides

Electrochemical conversion of nitrate(NO_(3)~-) to ammonia(NH_(3)) can target two birds with one stone well, in NO_(3)^(-)-containing sewage remediation and sustainable NH_(3) production. However, single metalbased catalysts are difficult to drive high-efficient NO_(3)~- removal due to the multi-electron transfer steps.Herein, we present a tandem catalyst with simple structure, Cu-Co binary metal oxides(Cu-Co-O), by engineering intermediate phases as catalytic active species for NO_(3)~- conversion. Electrochemical evaluation,X-ray photoelectron spectroscopy, and in situ Raman spectra together suggest that the newly-generated Cu-based phases was prone to NO_(3)~- to NO_(2)~- conversion, then NO_(2)~- was reduced to NH_(3) on Co-based species. At an applied potential of -1.1 V vs. saturated calomel electrode, the Cu-Co-O catalyst achieved NO_(3)~- -N removal of 90% and NH_(3) faradaic efficiency of 81% for 120 min in 100 m L of 50 mg/L NO_(3)~- -N,consuming only 0.69 k Wh/mol in a two-electrode system. This study provides a facile and efficient engineering strategy for developing high-performance catalysts for electrocatalytic nitrate conversion.

Nanozymes for regulation of reactive oxygen species and disease therapy

With high catalytic activity and stability,nanozymes have huge advantage in generating or eliminating the reactive oxygen species(ROS)due to their intrinsic enzyme-mimicking abilities,therefore attracting wide attention in ROS-related disease therapy.To better design nanozyme-based platforms for ROSrelated biological application,we firstly illustrate the catalytic mechanism of different activities,and then introduce different strategies for using nanozymes to augment or reduce ROS level for the applications in cancer therapy,pathogen infection,neurodegeneration,etc.Finally,the challenges and future opportunities are proposed for the development and application of nanozymes.

Mutagenesis and selective breeding of a high producing ε-poly-L-lysine strain

ε-Poly-L-lysine （ε-PL） is an L-lysine linear homopolymer, which is produced by bacteria belonging to the Streptomycetaceae family and by ergot fungi. How- ever, the production of ε-PL by the wild bacteria strain is very low, which limits its utilization. In most bacteria including the Streptomyces genus, L-lysine is a precursor of ε-PL and is biosynthesized by the L-aspartate pathway. Aspartokinase （Ask） is the first key enzyme in this pathway and is subject to complex regulation such as the feedback inhibition by the end product amino acids. In addition, phosphoenolpyruvate carboxykinase is feedback- regulated by L-aspartate. To reduce these feedback inhibitions and to improve e-PL productivity, resistant mutants were produced using sulfaguanidine （SG） ＋ glycine ＋ L-lysine ＋ DL-3-hydroxynorvaline （AHV） as selective markers. Using the interaction between e-PL and the charged dye in the solid culture medium, hundreds of colonies were simultaneously screened in a quick and effective manner. Finally, one ε-PL-producing strain, Streptomyces diastatochromogenes L9, was selected. The productivity of this strain during flask fermentation was 0.77 g/L, which was 15% higher than that of the original strain. Moreover, its fermentation performance and genetic characteristics were very stable.