Functionalization of Graphene Oxide with Low Molecular Weight Poly (Lactic Acid)

In this paper, the hydroxyl groups on the surface of graphene oxide (GO) were used to initiate the ring-opening polymerization of a lactic acid O-carboxyanhydride. GO grafted with poly (l-lactic acid) molecular chains (GO-g-PLLA) was prepared. Lactic acid O-carboxyanhydride has a higher polymerization activity under mild polymerization conditions. Thus, the functionalization of the polymer chains and obtaining poly (lactic acid) (PLLA) was easily achieved by ring-opening polymerization with 4-dimethylaminopyridine (DMAP) as the catalyst. The results showed that with this method, PLLA can be rapidly grafted to the surface of GO in one step. As a result, the chemical structure of the GO surface was altered, improving its dispersion in organic solvents and in a PLLA matrix, as well as its bonding strength with the PLLA interface. We then prepared GO/PLLA and PLLA/GO-g-PLLA composite materials and investigated the differences in their interfacial properties and mechanical properties. GO-g-PLLA exhibited excellent dispersion in the PLLA matrix and formed excellent interfacial bonds with PLLA through mechanical interlocking, demonstrating a significant enhancement effect compared to PLLA. The water vapor and oxygen permeabilities of the GO-g-PLLA/PLLA composite decreased by 19% and 29%, respectively

Sungeidines from a non-canonical enediyne biosynthetic pathway

We report the genome-guided discovery of sungeidines, a class of microbial secondary metabolites with unique structural features. Despite evolutionary relationships with dynemicin-type enediynes, the sungeidines are produced by a biosynthetic gene cluster (BGC) that exhibits distinct differences from known enediyne BGCs. Our studies suggest that the sungeidines are assembled from two octaketide chains that are processed differently than those of the dynemicin-type enediynes. The biosynthesis also involves a unique activating sulfotransferase that promotes a dehydration reaction. The loss of genes, including a putative epoxidase gene, is likely to be the main cause of the divergence of the sungeidine pathway from other canonical enediyne pathways. The findings disclose the surprising evolvability of enediyne pathways and set the stage for characterizing the intriguing enzymatic steps in sungeidine biosynthesis.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)Accepted versio

Leonuketal, a Spiroketal Diterpenoid from <i>Leonurus japonicus</i>

An architecturally complex spiroketal diterpenoid, leonuketal (<b>1</b>), was isolated from the aerial parts of the plant <i>Leonurus japonicus</i>. This compound possessed an unprecedented tetracyclic skeleton that comprised a bridged spiroketal moiety fused with a ketal-γ-lactone unit. The structure and absolute configuration were determined by spectroscopic analyses, a modified Mosher’s method, and ECD (electronic circular dichroism) calculations. Leonuketal (<b>1</b>) showed significant vasorelaxant activity against KCl-induced contraction of rat aorta, with the EC₅₀ value of 2.32 μM