A multi-enzymatic cascade reaction for the stereoselective production of γ\gamma-oxyfunctionalyzed amino acids

A stereoselective three-enzyme cascade for synthesis of diasteromerically pure $\gamma$-oxyfunctionalized $\alpha$-amino acids was developed. By coupling a dynamic kinetic resolution (DKR) using an $\it N$-acylamino acid racemase (NAAAR) and an L-selective aminoacylase from $\textit {Geobacillus thermoglucosidasius}$ with a stereoselective isoleucine dioxygenase from $\textit {Bacillus thuringiensis,}$ diastereomerically pure oxidized amino acids were produced from racemic $\it N$-acetylamino acids. The three enzymes differed in their optimal temperature and pH-spectra. Their different metal cofactor dependencies led to inhibitory effects. Under optimized conditions, racemic $\it N$-acetylmethionine was quantitatively converted into L-methionine-$\textit {(S)}$-sulfoxide with 97% yield and 95% $\textit {de.}$ The combination of these three different biocatalysts allowed the direct synthesis of diastereopure oxyfunctionalized amino acids from inexpensive racemic starting material

Aerosol‐based synthesis of multi‐metal electrocatalysts for oxygen evolution and glycerol oxidation

Discovery of new catalysts is crucial for future growth and development of environmentally friendly energy conversion processes e. g. the production of hydrogen by water electrolysis. We developed an aerosol-based synthesis technique as a comparatively fast and facile method to prepare multi-metal catalysts. 22 different quinary metal compositions were synthesized and investigated with respect to their activity for the oxygen evolution (OER) and the glycerol oxidation (GOR) reactions. The impact of the element composition and the homogeneous distribution of the elements in the particles on catalytic performance were evaluated. The highest activity for OER was found for $Co_{20}Cu_{20}Ni_{20}Fe_{20}Zn_{20}$. For GOR, Ag-containing catalysts were the most active, however, in most cases Ag was locally enriched and not homogeneously mixed with the other metals in the particles. Ag-based catalysts outperformed similar compositions containing one or more noble metals. The GOR selectivity of selected catalysts during long-term electrolysis was also investigated and it was shown that varying the catalyst composition via aerosol-based synthesis is a potential way to modulate the GOR selectivity

Splicing the active phases of copper/cobalt-based catalysts achieves high-rate tandem electroreduction of nitrate to ammonia

Electrocatalytic recycling of waste nitrate ($NO_{3}$$^-$) to valuable ammonia ($NH_3$) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate $NH_3$ synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade $NO_{3}$$^-$-to-$NH_3$ conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell $Cu/CuO_x$ and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner $Cu/CuO_x$ phases preferentially catalyze $NO_{3}$$^-$ reduction to $NO_{2}$$^-$, which is rapidly reduced to $NH_3$ at the nearby Co/CoO shell. This unique tandem catalyst system leads to a $NO_{3}$$^-$-to-$NH_3$ Faradaic efficiency of 93.3 $\pm$ 2.1% in a wide range of $NO_{3}$$^-$ concentrations at pH 13, a high $NH_3$ yield rate of 1.17 mmol $cm^{−2} h^{−1}$ in 0.1 M $NO_{3}$$^-$ at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports

Concentrated aqueous peroxodicarbonate

Peroxodicarbonates are of substantial interest as potentially powerful and sustainable oxidizers but have so far been accessible only in low concentrations with unsatisfactory energy efficiency. Concentrated (> 0.9 mol $L^{−1}$) peroxodicarbonate solutions have now been made accessible by the electrolysis of aqueous $K_{2}CO_{3}/Na_{2}CO_{3}/KHCO_{3}$ solutions at high current density of 3.33 A $cm^{−2}$ in an efficiently cooled circular flow reactor equipped with a boron-doped diamond anode and a stainless-steel cathode. Their synthetic potential as platform oxidizers was clearly demonstrated in transformations including sulfoxidation, $\it N$-oxidation, and epoxidation

Blood serum stimulates p38-mediated proliferation and changes in global gene expression of adult human cardiac stem cells

During aging, senescent cells accumulate in various tissues accompanied by decreased regenerative capacities of quiescent stem cells, resulting in deteriorated organ function and overall degeneration. In this regard, the adult human heart with a generally low regenerative potential is of extreme interest as a target for rejuvenating strategies with blood borne factors that might be able to activate endogenous stem cell populations. Here, we investigated for the first time the effects of human blood plasma and serum on adult human cardiac stem cells (hCSCs) and showed significantly increased proliferation capacities and metabolism accompanied by a significant decrease of senescent cells, demonstrating a beneficial serum-mediated effect that seemed to be independent of age and sex. However, RNA-seq analysis of serum-treated hCSCs revealed profound effects on gene expression depending on the age and sex of the plasma donor. We further successfully identified key pathways that are affected by serum treatment with p38-MAPK playing a regulatory role in protection from senescence and in the promotion of proliferation in a serum-dependent manner. Inhibition of p38-MAPK resulted in a decline of these serum-mediated beneficial effects on hCSCs in terms of decreased proliferation and accelerated senescence. In summary, we provide new insights in the regulatory networks behind serum-mediated protective effects on adult human cardiac stem cells