Quantification, characterization and biofunctional studies of N-glycans on proteins remain challenging tasks due to the complexity, diversity and low abundance of these glycans. The availability of structurally defined N-glycan (especially isomer) libraries is essential to help solve these tasks. We report herein an efficient chemoenzymatic strategy, namely Core Synthesis/Enzymatic Extension (CSEE), for rapid production of diverse N-glycans. Starting with 5 chemically prepared building blocks, 8 N-glycan core structures containing one or two terminal N-acetyl-d-glucosamine (GlcNAc) residue(s) were chemically synthesized via consistent use of oligosaccharyl thioethers as glycosylation donors in a convergent fragment coupling strategy. Each of these core structures was then extended to 5 to 15 N-glycan sequences by enzymatic reactions catalyzed by 4 robust glycosyltransferases. Success in synthesizing N-glycans with Neu5Gc and core-fucosylation further expanded the ability of the enzymatic extension. Meanwhile, high performance liquid chromatography with an amide column enabled rapid and efficient purification (>98% purity) of N-glycans in milligram scales. A total of 73 N-glycans (63 isomers) were successfully prepared and characterized by MS2 and NMR. In summary, the CSEE strategy provides a practical approach for “mass production” of structurally defined N-glycans, which are important standards and probes for glycoscience. 相似文献
We report on an electrochemical method for the determination of the activity of trypsin. A multi-functional substrate peptide (HHHAKSSATGGC-HS) is designed and immobilized on a gold electrode. The three His residues in the N-terminal are able to recruit thionine-loaded graphene oxide (GO/thionine), a nanocover adopted for signal amplification. Once the peptide is cleaved under enzymatic catalysis by trypsin (cleavage site: Lys residue), the His residues leave the electrode, and the GO/thionine cannot cover the peptide-modified electrode anymore. Thus, the changes of the electrochemical signal of thionine, typically acquired at a voltage of -0.35 V, can be used to determine the activity of trypsin. A detection range of 1 × 10−4 to 1 U, with a detection limit of 3.3 × 10−5 U, can be achieved, which is better than some currently available methods. In addition, the method is highly specific, facile, and has the potential for the detection of trypsin-like proteases.
Graphene oxide was adopted as a nanocover for the development of a sensitive electrochemical method to detect the activity of trypsin.
Single crystals of [Cr(H2O)6]2[B12H12]3 · 15H2O and [In(H2O)6]2[B12H12]3 · 15H2O were obtained by reactions of aqueous solutions of the acid (H3O)2[B12H12] with chromium(III) hydroxide and indium metal shot, respectively. The title compounds crystallize isotypically in the trigonal system with space group R$\bar{3}$ c (a = 1157.62(3), c = 6730.48(9) pm for the chromium, a = 1171.71(3), c = 6740.04(9) pm for the indium compound, Z = 6). The arrangement of the quasi‐icosahedral [B12H12]2– dianions can be considered as stacking of two times nine layers with the sequence …ABCCABBCA… and the metal trications arrange in a cubic closest packed …abc… stacking sequence. The metal trications are octahedrally coordinated by six water molecules of hydration, while another fifteen H2O molecules fill up the structures as zeolitic crystal water or second‐sphere hydrating species. Between these free and the metal‐bonded water molecules, bridging hydrogen bonds are found. Furthermore, there is also evidence of hydrogen bonding between the anionic [B12H12]2– clusters and the free zeolitic water molecules according to B–Hδ– ··· δ+H–O interactions. Vibrational spectroscopy studies prove the presence of these hydrogen bonds and also show slight distortions of the dodecahydro‐closo‐dodecaborate anions from their ideal icosahedral symmetry (Ih). Thermal decomposition studies for the example of [Cr(H2O)6]2[B12H12]3 · 15H2O gave no hints for just a simple multi‐stepwise dehydration process. 相似文献
The use of polyanion and polycation-sensitive membrane electrodes to detect five different preparations of fucoidan is described. Unlike linear polyanionic molecules previously measured with polymer membrane-based electrochemical sensors, fucoidans from marine brown algae are all highly branched, sulfated polysaccharides with varying charge densities and structures, depending on the species of seaweed, method of extraction used and extent of purification. When tridodecylmethylammonium (TDMA) was used as the ion-exchanger, a large, non-equilibrium EMF response was observed over a concentration range of 0.5–50 μg mL−1 fucoidan. Fucoidan was also measured by titration with polycationic protamine, using a dinonylnaphthalene sulfonate (DNNS)-doped membrane electrode as the potentiometric endpoint detector. Potentiometric titration was used to determine the binding ratio between protamine and fucoidan at the neutralization endpoint for each fucoidan preparation. This binding ratio was then used to successfully determine the fucoidan content of commercially available nutritional supplements. Fucoidan was also measured in undiluted blood serum, demonstrating that this method may be applicable for measuring fucoidan for clinical applications. 相似文献
Two new steroidal alkaloids, 23‐methoxycyclopamine 3‐O‐β‐D ‐glucopyranoside ( 1 ) and isoecliptalbine ( 2 ), were isolated from the root and rhizoma of Veratrum maackii Regel , together with five known compounds, i.e., verussurine ( 3 ), verabenzoamine ( 4 ), verazine ( 5 ), isoverazine ( 6 ), and verazinine ( 7 ). Their structures were established by extensive analysis of spectroscopic data, as well as by comparison with literature data. Compounds 1 – 7 could cause DNA damage in the cerebellum and cerebral cortex of mice in a dose‐dependent manner by using single‐cell gel electrophoresis (comet assay). 相似文献