A Lanthipeptide‐like N‐Terminal Leader Region Guides Peptide Epimerization by Radical SAM Epimerases: Implications for RiPP Evolution

Ribosomally synthesized and posttranslationally modified peptide natural products (RiPPs) exhibit diverse structures and bioactivities and are classified into distinct biosynthetic families. A recently reported family is the proteusins, with the prototype members polytheonamides being generated by almost 50 maturation steps, including introduction of d ‐residues at multiple positions by an unusual radical SAM epimerase. A region in the protein‐like N‐terminal leader of proteusin precursors is identified that is crucial for epimerization. It resembles a precursor motif previously shown to mediate interaction in thioether bridge‐formation in class I lanthipeptide biosynthesis. Beyond this region, similarities were identified between proteusin and further RiPP families, including class I lanthipeptides. The data suggest that common leader features guide distinct maturation types and that nitrile hydratase‐like enzymes are ancestors of several RiPP classes.     

The effect of iron doping in La0.8Sr0.2Fe0.05Co0.95O3-δ perovskite

La0.8Sr0.257Fe0.05Co0.95O3- perovskite is investigated by 57Fe transmission and emission Mössbauer spectroscopy, X-ray diffraction, AC magnetic susceptibility and magnetotransport measurements. Temperature dependence of the 57Fe Mössbauer isomer shift, quadrupole splitting, magnetic hyperfine field, line broadening, and relative spectral area is presented in a detailed manner for La0.8Sr0.257Fe0.05Co0.95O3- . The oxidation state of iron is determined to be Fe3+, and the presence of preferential electronic charge compensation Fe3+ Fe4+ over that of Co3+ Co4+ is excluded. Relaxation of iron magnetic moments reflected by the 57Fe Mössbauer spectra of La0.8Sr0.257Fe0.05Co0.95O3- are interpreted as evidence for the existence of superparamagnetic like Co clusters and a corresponding cluster glass magnetic phase formed below T 65 K.     

A General Strategy for the Nickel‐Catalyzed C−H Alkylation of Anilines

The C?H alkylation of aniline derivatives with both primary and secondary alkyl halides was achieved with a versatile nickel catalyst of a vicinal diamine ligand. Step‐economic access to functionalized 2‐pyrimidyl anilines, key structural motifs in anticancer drugs, is thus provided. The C?H functionalization proceeded through facile C?H activation and SET‐type C?X bond cleavage with the assistance of a monodentate directing group, which could be removed in a traceless fashion.     

Copolymerizable initiator for improved polymer dispersed liquid crystal films

Abstract

The problems of photoinitiator contamination are addressed for the liquid crystal phase in polymer dispersed liquid crystal films formed by photopolymerization induced phase separation of liquid crystal from monomer solutions. Initiator contamination lowers the clearing point of the liquid crystal phase, and decreases the photostability and resistivity of the polymer dispersed liquid crystal. These problems are minimized by replacing the conventional photoinitiators with copolymerizable initiators which become incorporated in the polymer phase as it separates. Copolymerizable photoinitiators are studied and used to form polymer dispersed liquid crystals with higher clearing point liquid crystal phases, higher resistivity, and better photostability than polymer dispersed liquid crystals formed with conventional photoinitiators. These improvements provide very significant advantages for many polymer dispersed liquid crystal applications.