Photocatalytic production of hydrogen from methanol and saccharides using carbon nanotube-TiO2 catalysts
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Silva, Cláudia G. (ORCID:0000000164694871)↗
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Influence of length and conformation of saccharide head groups on the mechanics of glycolipid membranes: Unraveled by off-specular neutron scattering
The mechanical properties of multilayer stacks of Gb3 glycolipid that play key roles in metabolic disorders (Fabry disease) were determined quantitatively by using specular and off-specular neutron scattering. Because of the geometry of membrane stacks deposited on planar substrates, the scattered intensity profile was analyzed in a 2D reciprocal space map as a function of in-plane and out-of-plane scattering vector components. The two principal mechanical parameters of the membranes, namely, bending rigidity and compression modulus, can be quantified by full calculation of scattering functions with the aid of an effective cut-off radius that takes the finite sample size into consideration. The bulkier “bent” Gb3 trisaccharide group makes the membrane mechanics distinctly different from cylindrical disaccharide (lactose) head groups and shorter “bent” disaccharide (gentiobiose) head groups. The mechanical characterization of membranes enriched with complex glycolipids has high importance in understanding the mechanisms of diseases such as sphingolipidoses caused by the accumulation of non-degenerated glycosphingolipids in lysosomes or inhibition of protein synthesis triggered by the specific binding of Shiga toxin to Gb3.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Catalytic Activation of Pyran Ethers in Self-Solvating Saccharides with Alkaline Earth Metals (Final Report)
Catalytic activation of cellulose ethers occurs via hydroxyl-stabilized cleavage of inter-monomer glycosidic bonds. Cooperativity between two hydroxyl groups lowers the ether cleavage transition state necessary to break apart long carbohydrate chains to initiate small molecule formation as fuel precursors. Metals existing with lignocellulosic materials including alkaline earth metals (Ca 2+ , Mg 2+ ) or alkali (Na + , K + ) also can catalyze ether scission cooperatively. By bonding with carbohydrate hydroxyl groups, a metal cation disrupt the hydrogen bonding network and free carbohydrate functional groups to react; a second metal cation stabilizes the carbohydrate ether transition state and enhances the rate of polymer scission. In this work, we expanded our initial understanding of metal-catalyzed glycoside ether scission. Within polysaccharides such as cellulose, two ether groups exist: one between monomers (glycosidic linkages) and one within a pyran ring. The hydroxyl-group hydrogen bonding network and bound metal ions form low energy binding states that interact with both ether oxygens simultaneously. Based on this interaction, our primary hypothesis was that the competition between stabilizing the two ether scission transition states determines the extent of the major pathways. Metals that disrupt the hydrogen bonding network of the C6 of sugars and stabilize the glycosidic ether promote transglycosylation to levoglucosan; in contrast, metals that stabilize the pyran ether oxygen promote sugar ring fragmentation to furans such as furfural. Varying characteristics of metal cation catalysts and configurations of bound polysaccharide chains dictate the relative rates of ether scission.
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Oligomer Saccharide Reduction During Dilute Acid Pretreatment Co-Catalyzed with Lewis Acids on Corn Stover Biomass
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Saccharide antifreeze compositions
The invention provides an antifreeze glycolipid compounds and composition comprising a polysaccharide moiety of Formula I; ##STR00001## wherein D-Manp represents a D-mannopyranose moiety, D-Xylp represents a D-xylopyranose moiety, and n is about 5 to about 70; and one or more lipid moieties covalently linked to the polysaccharide moiety of Formula I or electrostatically associated with the polysaccaride moiety for Formula I. The antifreeze glycolipid compounds and compositions can be used for a variety of industrial, agricultural, medical, and cosmetic applications where recrystallization-inhibition, cyroprotection, or cryopreservation is desired. The antifreeze glycolipid compounds or compositions can be used as, for example, as cryoprotectants for tissue preservation and transplantation, improving the texture of processed frozen food and frozen meats, frostbit protection, crop protection, and green alternatives for land vehicle antifreeze and aircraft de-icing.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Systems and methods for continuously fermenting C5 and C6 saccharides
This invention provides optimized fermentation of cellulosic and hemicellulosic sugars. Biomass-derived hemicellulosic and cellulosic sugars are independently conditioned and separately fermented, utilizing reuse and recycle of microorganisms, metabolic intermediates, and nutrients. Conditioned sugars can be fermented in separate vessels, where excess cells from glucose fermentation are conveyed to hemicellulose sugar fermentation along with raffinate from solvent recovery, to enhance productivity and product yield. Some variations provide a method of fermenting C5 and C6 sugars to fermentation products, the method comprising: fermenting a C6-rich sugar feed to a first fermentation product; fermenting a C5-rich sugar feed to a second fermentation product; removing microorganism cells from the first fermentor, to maintain a cell concentration within a selected range; conveying microorganism cells to a second fermentor; and removing microorganism cells from the second fermentor, to maintain a microorganism cell concentration that is greater than that in the C6-rich fermentor.
Survase, Shrikant↗
Dissecting the substrate recognition of 3-O-sulfotransferase for the biosynthesis of anticoagulant heparin
Heparin is a polysaccharide-based natural product that is used clinically as an anticoagulant drug. Heparan sulfate 3-O-sulfotransferase (3-OST) is an enzyme that transfers a sulfo group to the 3-OH position of a glucosamine unit. 3-OST is present in multiple isoforms, and the polysaccharides modified by these different isoforms perform distinct biological functions. 3-OST isoform 1 (3-OST-1) is the key enzyme for the biosynthesis of anticoagulant heparin. Here, we report the crystal structure of the ternary complex of 3-OST-1, 3'-phosphoadenosine 5'-phosphate, and a heptasaccharide substrate. Comparisons to previously determined structures of 3-OST-3 reveal unique binding modes used by the different isoforms of 3-OST for distinguishing the fine structures of saccharide substrates. Our data demonstrate that the saccharide substrates display distinct conformations when interacting with the different 3-OST isoforms. Site-directed mutagenesis data suggest that several key amino residues, including Lys259, Thr256, and Trp283 in 3-OST-3 and Arg268 in 3-OST-1, play important roles in substrate binding and specificity between isoforms. These results deepen our understanding of the biosynthetic mechanism of heparan sulfate and provide structural information for engineering enzymes for an enhanced biosynthetic approach to heparin production.
60 APPLIED LIFE SCIENCES↗
Crystal Structures of GII.10 and GII.12 Norovirus Protruding Domains in Complex with Histo-Blood Group Antigens Reveal Details for a Potential Site of Vulnerability
Noroviruses are the dominant cause of outbreaks of gastroenteritis worldwide, and interactions with human histo-blood group antigens (HBGAs) are thought to play a critical role in their entry mechanism. Structures of noroviruses from genogroups GI and GII in complex with HBGAs, however, reveal different modes of interaction. To gain insight into norovirus recognition of HBGAs, we determined crystal structures of norovirus protruding domains from two rarely detected GII genotypes, GII.10 and GII.12, alone and in complex with a panel of HBGAs, and analyzed structure-function implications related to conservation of the HBGA binding pocket. The GII.10- and GII.12-apo structures as well as the previously solved GII.4-apo structure resembled each other more closely than the GI.1-derived structure, and all three GII structures showed similar modes of HBGA recognition. The primary GII norovirus-HBGA interaction involved six hydrogen bonds between a terminal {alpha}fucose1-2 of the HBGAs and a dimeric capsid interface, which was composed of elements from two protruding subdomains. Norovirus interactions with other saccharide units of the HBGAs were variable and involved fewer hydrogen bonds. Sequence analysis revealed a site of GII norovirus sequence conservation to reside under the critical {alpha}fucose1-2 and to be one of the few patches of conserved residues on the outer virion-capsid surface. The site was smaller than that involved in full HBGA recognition, a consequence of variable recognition of peripheral saccharides. Despite this evasion tactic, the HBGA site of viral vulnerability may provide a viable target for small molecule- and antibody-mediated neutralization of GII norovirus.
60 APPLIED LIFE SCIENCES↗
Sucrose‐Based Dense, Pure, and Highly‐Crystalline Graphitic Materials for Lithium‐Ion Batteries
At present, most synthetic graphite materials commonly used as anode active ingredients in lithium-ion cells are produced by graphitization of petroleum cokes. The carbon footprint associated with synthetic graphite production is significant. Thus, bio-derived and cheap precursors, such as saccharides, would be an attractive alternative for the sustainable production of graphitic carbons. However, they are non-graphitizing at temperatures as high as 3000 °C, preserving the curved, fullerene-like structure of graphene layers and microporosity. Consequently, many lithium ions are consumed during the formation of solid electrolyte interphase films and passivated in the nanovoids. Here, a method for the production of pure, crystalline, graphitic materials based on sucrose disposed of microporosity is presented, which also works with a variety of saccharides and other organic precursors of hard carbons—generally considered incapable of such transformation. This process employs catalytic graphitization by Si particles at high temperatures. Finally, the electrochemical response of such derived sucrose-based graphite in Li-ion half-cells demonstrated its feasibility to serve as an anode active material for rechargeable Li-ion batteries.
Si particles↗
Polyproline peptide targets Klebsiella pneumoniae polysaccharides to collapse biofilms
Hypervirulent Klebsiella pneumoniae is known for its increased extracellular polysaccharide production. Biofilm matrices of hyper- virulent K. pneumoniae have increased polysaccharide abundance and are uniquely susceptible to disruption by peptide bactenecin 7 (bac7 (1–35)). Here, using confocal microscopy, we show that poly- saccharides within the biofilm matrix collapse following bac7 (1–35) treatment. This collapse led to the release of cells from the biofilm, which were then killed by the peptide. Characterization of truncated peptide analogs revealed that their interactions with polysaccharide were responsible for the biofilm matrix changes that accompany bac7 (1–35) treatment. Ultraviolet photodissociation mass spec- trometry with the parental peptide or a truncated analog bac7 (10–35) reveal the important regions for bac7 (1–35) complexing with polysaccharides. Finally, we tested bac7 (1–35) using a murine skin abscess model and observed a significant decrease in the bacte- rial burden. These findings unveil the potential of bac7 (1–35) poly- saccharide interactions to collapse K. pneumoniae biofilms.
59 BASIC BIOLOGICAL SCIENCES↗
Investigation of the Amide Proton Solvent Exchange Properties of Glycosaminoglycan Oligosaccharides
One-dimensional 1 H NMR experiments were conducted for aqueous solutions of glycosaminoglycan oligosaccharides to measure the amide proton temperature coefficients, activation energy barriers for solvent exchange, and evaluate the effect of pH on the solvent exchange properties. A library of mono- and oligosaccharides was prepared by enzymatic depolymerization of amide-containing polysaccharides and by chemical modification of heparin and heparan sulfate saccharides including members that contain a 3- O -sulfated glucosamine residue. The systematic evaluation of this saccharide library facilitated assessment of the effects of structural characteristics, such as size, sulfation number and site, and glycosidic linkage, on amide proton solvent exchange rates. Charge repulsion by neighboring negatively charged sulfate and carboxylate groups was found to have a significant impact on the catalysis of amide proton solvent exchange by hydroxide. Furthermore, this observation leads to the conclusion that solvent exchange rates must be interpreted within the context of a given chemical environment. On their own, slow exchange rates do not conclusively establish the involvement of a labile proton in a hydrogen bond and additional supporting experimental evidence such as reduced temperature coefficients is required.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Glycosylated Peptoid Nanosheets as a Multivalent Scaffold for Protein Recognition
Glycoproteins adhered on the cellular membrane play an important role in a wide range of cellular functions. Their significance is particularly relevant in the recognition process between infectious pathogens (such as viruses, bacteria, toxins) and their host cells. Multivalent interactions at the pathogen-cell interfaces govern binding events and can result in a strong and specific interaction. Here in this paper, we report an approach to mimic the cell surface presentation of carbohydrate ligands by the multivalent display of sugars on the surface of peptoid nanosheets. The constructs provide a highly organized 2D platform for recognition of carbohydrate-binding proteins. The sugars were displayed using different linker lengths or within loops containing 2-6 hydrophilic peptoid monomers. Both the linkers and the loops contained one alkyne-bearing monomer, to which different saccharides were attached by copper-catalyzed azide-alkyne cycloaddition reactions. Peptoid nanosheets functionalized with different saccharide groups were able to selectively bind multivalent lectins, Concanavalin A and Wheat Germ Agglutinin, as observed by fluorescence microscopy and a homogeneous Förster resonance energy transfer (FRET)-based binding assay. To evaluate the potential of this system as sensor for threat agents, the ability of functionalized peptoid nanosheets to bind Shiga toxin was also studied. Peptoid nanosheets were functionalized with globotriose, the natural ligand of Shiga toxin, and the effective binding of the nanomaterial was verified by the FRET-based binding assay. In all cases, evidence for multivalent binding was observed by systematic variation of the ligand display density on the nanosheet surface. These cell surface mimetic nanomaterials may find utility in the inactivation of pathogens or as selective molecular recognition elements.
bioinspired polymers↗
Protocols for isolating and characterizing polysaccharides from plant cell walls: a case study using rhamnogalacturonan-II
Abstract Background In plants, a large diversity of polysaccharides comprise the cell wall. Each major type of plant cell wall polysaccharide, including cellulose, hemicellulose, and pectin, has distinct structures and functions that contribute to wall mechanics and influence plant morphogenesis. In recent years, pectin valorization has attracted much attention due to its expanding roles in biomass deconstruction, food and material science, and environmental remediation. However, pectin utilization has been limited by our incomplete knowledge of its structure. Herein, we present a workflow of principles relevant for the characterization of polysaccharide primary structure using nature’s most complex polysaccharide, rhamnogalacturonan-II (RG-II), as a model. Results We outline how to isolate RG-II from celery and duckweed cell walls and from red wine using chemical or enzymatic treatments coupled with size-exclusion chromatography. From there, we applied mass spectrometry (MS)-based techniques to determine the glycosyl residue and linkage compositions of the intact RG-II and derived oligosaccharides including special considerations for labile monosaccharides. In doing so, we demonstrated that in the duckweed Wolffiella repanda the arabinopyranosyl (Ara p ) residue of side chain B is substituted at O- 2 with rhamnose. We used electrospray-MS techniques to identify non-glycosyl modifications including methyl-ethers, methyl-esters, and acetyl-esters on RG-II-derived oligosaccharides. We then showed the utility of proton nuclear magnetic resonance spectroscopy ( 1 H-NMR) to investigate the structure of intact RG-II and to complement the RG-II dimerization studies performed using size-exclusion chromatography. Conclusions The complexity of pectic polysaccharide structures has hampered efforts aimed at their valorization. In this work, we used RG-II as a model to demonstrate the steps necessary to isolate and characterize polysaccharides using chromatographic, MS, and NMR techniques. The principles can be applied to the characterization of other saccharide structures and will help inform researchers on how saccharide structure relates to functional properties in the future.
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