Sodium halide solid state electrolyte of Na3YBr6 with low activation energy.

Halide solid-state electrolytes (SSEs) are considered promising candidates for practical applications in all-solid-state batteries (ASSBs), due to their outstanding high voltage stability and compatibility with electrode materials. However, Na+ halide SSEs suffer from low ionic conductivity and high activation energy, which limit their applications in sodium all-solid-state batteries. Here, sodium yttrium bromide solid-state electrolytes (Na3YBr6) with a low activation energy of 0.15 eV is prepared via solid state reaction. Structure characterization using X-ray diffraction reveals a monoclinic structure (P21/c) of Na3YBr6. First principle calculations reveal that the low migration activation energy comes from the larger size and vibration of Br- anions, both of which expand the Na+ ion migration channel and reduce its activation energy. The electrochemical window of Na3YBr6 is determined to be 1.43 to 3.35 V vs. Na/Na+, which is slightly narrower than chlorides. This work indicates bromides are a good catholyte candidate for sodium all solid-state batteries, due to their low ion migration activation energy and relatively high oxidation stability.

[Flavonoids from Humulus lupulus].

Nine compounds were isolated and purified by column chromatographic techniques including macroporous resin, silica gel, ODS, Sephadex LH-20, and preparative reversed-phase HPLC. Their structures were elucidated as taxifolin (1), naringenin (2), chalconaringenin (3), acacetin (4), quercetin 3-O-beta-D-galactopyranoside (5), 6-prenylnaringenin (6) xanthohumol (7), desmethylxanthohumol (8), xanthohumol B (9) on the basis of MS and NMR spectroscopic data analysis. Compounds 1-5 were isolated from Humulus lupulus for the first time.

Characterization of SfmD as a Heme peroxidase that catalyzes the regioselective hydroxylation of 3-methyltyrosine to 3-hydroxy-5-methyltyrosine in saframycin A biosynthesis.

Saframycin A (SFM-A) is a potent antitumor antibiotic that belongs to the tetrahydroisoquinoline family. Biosynthetic studies have revealed that its unique pentacyclic core structure is derived from alanine, glycine, and non-proteinogenic amino acid 3-hydroxy-5-methyl-O-methyltyrosine (3-OH-5-Me-OMe-Tyr). SfmD, a hypothetical protein in the biosynthetic pathway of SFM-A, was hypothesized to be responsible for the generation of the 3-hydroxy group of 3-OH-5-Me-OMe-Tyr based on previously heterologous expression results. We now report the in vitro characterization of SfmD as a novel heme-containing peroxidase that catalyzes the hydroxylation of 3-methyltyrosine to 3-hydroxy-5-methyltyrosine using hydrogen peroxide as the oxidant. In addition, we elucidated the biosynthetic pathway of 3-OH-5-Me-OMe-Tyr by kinetic studies of SfmD in combination with biochemical assays of SfmM2, a methyltransferase within the same pathway. Furthermore, SacD, a counterpart of SfmD involved in safracin B biosynthesis, was also characterized as a heme-containing peroxidase, suggesting that SfmD-like heme-containing peroxidases may be commonly involved in the biosynthesis of SFM-A and its analogs. Finally, we found that the conserved motif HXXXC is crucial for heme binding using comparative UV-Vis and Magnetic Circular Dichroism (MCD) spectra studies of SfmD wild-type and mutants. Together, these findings expand the category of heme-containing peroxidases and set the stage for further mechanistic studies. In addition, this study has critical implications for delineating the biosynthetic pathway of other related tetrahydroisoquinoline family members.

Biosynthesis of 3-hydroxy-5-methyl-o-methyltyrosine in the saframycin/ safracin biosynthetic pathway.

The biosynthesis study of antibiotics saframycin (SFM) in Streptomyces lavendulae and safracin (SAC) in Pseudomonas fluorescens demonstrated that 3-hydroxy-5-methyl-Omethyltyrosine (3h5mOmTyr), a nonproteinogenic amino acid, is the precursor of the tetrahydroisoquinoline molecular core. In the biosynthetic gene cluster of SAC/SFM, sacD/ sfmD encodes a protein with high homology to each other but no sequence similarity to other known enzymes; sacF/ sfmM2 and sacG/sfmM3 encode methyltransferases for Cmethylation and O-methylation; and sacE/sfmF encodes a small protein with significant sequence similarity to the MbtH-like proteins, which are frequently found in the biosynthetic pathways of nonribosomal peptide antibiotics and siderophores. To address their function, the biosynthetic cassette of 3h5mOmTyr was heterologously expressed in S. coelicolor and P. putida, and an in-frame deletion and complementation in trans were carried out. The results revealed that (i) SfmD catalyzes the hydroxylation of aromatic rings;(ii) sacD/sacF/sacG in the SAC gene cluster and sfmD/sfmM2/sfmM3 in the SFM cluster are sufficient for the biosynthesis of 3h5mOmTyr; and (iii) the mbtH-like gene is not required for the biosynthesis of the 3h5mOmTyr precursor.