Cleavage Of Glycosidic Linkages Research Articles

Surface analysis and thermal behavior of the functionalized cellulose by glutaric anhydride through a solvent-free and catalyst-free process

According to the 12 principles of green chemistry, surface functionalization was performed using glutaric anhydride under solvent-free and catalyst-free conditions. FTIR spectra and DS analyses demonstrated the functionalization of HCl-hydrolyzed cellulose. The influence of two parameters, i.e., the glutaric anhydride concentration and the reaction time, on the functionalization of HCl-hydrolyzed cellulose was investigated. Protocol efficiency was studied by a degree of substitution (DS). It was found that higher concentrations of glutaric anhydride cause an enhancement of DS to 0.75 and 0.87 for GA3–12 and GA9–12, respectively. In addition, the longer reaction time increased zeta potential from −12.2 ± 1.7 for G9–6 to −34.57 ± 2.2 for GA9–12. Morphology analysis by SEM showed a decrease in fiber length for the functionalized cellulose. DSC profiles confirmed dehydration at a range of 17 to 134 °C. A glass transition was revealed at −30 to −20 °C for all studied samples. The fusion, the depolymerization of cellulose chains, the cleavage of glycosidic linkages, and the decomposition of the crystalline parts of cellulose occur at 195 to 374 °C. Therefore, an efficient and greener process was developed to functionalize the HCl-hydrolyzed cellulose by glutaric anhydride, a safe and non-toxic anhydride, in the absence of the solvent and catalyst.

Processive binding mechanism of Cel9G from Clostridium cellulovorans: molecular dynamics and free energy landscape investigations.

The degradation of recalcitrant polysaccharides such as cellulose and chitin requires the synergistic functionality of processive glycosidase (GH) cocktails. Understanding the fundamental phenomenon of processivity is of biological and economic importance for the conversion of biomass into biofuel. In this work, cellulase family 9 from Clostridium cellulovorans (Cel9G), which is a processive endoglucanase, was used to elucidate the processive binding mechanism with respect to polysaccharides, since it exhibits a multimodular crystallographic structure. Metadynamics and molecular dynamics simulations were performed to explore the dynamics of cellulose chain binding to Cel9G via processive motion. The processive movement of the cellulose chain towards the catalytic domain may exhibit several local minima, which are related to strong CH/π interactions between the sugar rings and the aromatic residues distributed at the active site. For the binding of the G6 and G12 molecules, the energy barriers were determined to be 4.8 and 7.4 kcal mol-1, respectively. Based on the site-directed mutagenesis simulations of Y520A, it was found that the existence of Y520 is critical for processive binding. It is likely that Y520 and H125/Y416 form two anchor points to facilitate processive binding to polysaccharides. More importantly, the straight-line morphology of the substrate could be observed after the formation of the so-called slide mode, which is different from the V-shaped Michaelis complex structure revealed by quantum mechanics/molecular mechanics simulations. This indicates that an additional step, namely, catalytic activation, probably exists between processive binding and the hydrolysis reaction. Finally, a four-step catalytic cycle was proposed for Cel9G. Our work provides novel molecular-level insights into the structure-function relationship for the processive enzyme Cel9G and should aid the development of improved GH cocktails for the efficient cleavage of glycosidic linkages.

Re-understanding of structure and anticoagulation: Fucosylated chondroitin sulfate from sea cucumber Ludwigothurea grisea

Fucosylated chondroitin sulfate (FCS) from sea cucumber Ludwigothurea grisea (FCSLg) is the first one that reported to bear the di-fucosyl branches. Here we deciphered it by analyzing the physicochemical properties and its derivatives. Oligosaccharides prepared by selective cleavage of glycosidic linkages presented the mono-fucose and heterodisaccharide branches in FCSLg. The disaccharide branch was determined as d-GalNAcR1-(α1,2)-l-FucR2 rather than the di-fucosyl branch, where R1 was 4-mono-O- or 4,6-di-O-sulfation, and R2 was 3-mono-O- or 3,4-di-O-sulfation, respectively. The diversity of sulfation patterns in branches complicated the structure. These results give us a new understanding of FCSLg and provided a reliable method to decipher the FCS with complex branches. Bioanalysis of chemically modified derivatives showed that modulating the molecular mass could enhance the Xase target selectivity. Side chains conferred the Xase complex inhibition by binding to FIXa with a high affinity. Whether monosaccharide and disaccharide branches have differential effects needs to be further explored.

Gamma-Irradiated Bacterial Cellulose as a Three-Dimensional Scaffold for Osteogenic Differentiation of Rat Bone Marrow Stromal Cells

The effect of gamma-irradiation on bacterial cellulose (BC) was investigated in terms of improving its properties as scaffolds for tissue engineering. BC pellicles were exposed to 25, 50, and 75 kGy gamma-ray irradiation, and X-ray diffraction analyses showed that the crystallinity of the BC decreased as stronger irradiation accelerated BC’s degradation. Fourier transform infrared spectroscopy of the irradiated BC revealed the appearance of a new peak at 1724 cm–1, indicating the formation of a new carbonyl group due to the cleavage of glycosidic linkages of the BC. Rat bone marrow stromal cells seeded on the gamma-irradiated BC incubated in an osteogenic medium for 14 days produced calcium, a late marker for osteogenic differentiation, as shown by Alizarin Red S (ARS) staining. Gamma-irradiated BC with higher irradiation doses showed intense ARS staining indicating higher calcium deposition. These findings demonstrate the feasibility of using gamma-irradiated BC as a cytocompatible 3D scaffold for bone tissue regeneration.

Charge-reversible and biodegradable chitosan-based microgels for lysozyme-triggered release of vancomycin

IntroductionHigh-dose drug administration for the conventional treatment of inflammatory bowel disease induces cumulative toxicity and serious side effects. Currently, few reports have introduced smart carriers for intestinal inflammation targeting toward the treatment of inflammatory bowel disease. ObjectivesFor the unique lysozyme secretory microenvironment of the inflamed intestine, vancomycin-loaded chitosan-polyaniline microgels (CH-PANI MGs) were constructed for lysozyme-triggered VM release. MethodsAniline was first grafted to chitosan to form polymers that were crosslinked by glutaraldehyde to achieve CH-PANI MGs using the inverse (water-in-oil) miniemulsion method. Interestingly, CH-PANI MGs exhibit polyampholyte behaviour and display charge-reversible behaviour (positive to negative charges) after treatment with a NaCl solution. ResultsThe formed negatively charged N-CH-PANI MG aqueous solution is employed to load cationic vancomycin with a satisfactory loading efficiency of 91.3%, which is significantly higher than that of chitosan-based MGs. Moreover, N-CH-PANI MGs present lysozyme-triggered biodegradation and controllable vancomycin release upon the cleavage of glycosidic linkages of chitosan. In the simulated inflammatory intestinal microenvironment, vancomycin is rapidly released, and the cumulative release reaches approximately 76.9%. Remarkably, N-CH-PANI@VM MGs not only exhibit high resistance to harsh gastric acidity but also prevent the premature leakage of vancomycin in the healthy gastrointestinal tract. Encouragingly, the N-CH-PANI@VM MGs show obvious antibacterial activity against Staphylococcus aureus at a relatively low concentration of 20 μg/mL. ConclusionCompared to other pH-responsive carriers used to treat inflammatory bowel disease, the key advantage of lysozyme-responsive MGs is that they further specifically identify healthy and inflammatory intestines, achieving efficient inflammatory bowel disease treatment with few side effects. With this excellent performance, the developed smart MGs might be employed as a potential oral delivery system for inflammatory bowel disease treatment.

Glycoside phosphorylases for carbohydrate synthesis: An insight into the diversity and potentiality

Glycoside phosphorylases (GPs) are a major group of enzymes which catalyze the reversible formation and cleavage of glycosidic linkages, thus combining a dual functionality of both glycoside hydrolases (GHs) and glycosyltransferases (GTs). This unique advantage of reversibility, alongside with the strict regioselectivity, and the use of simple sugar phosphate donors, makes phosphorylases valuable catalysts in the synthesis of various carbohydrate structures, such as the synthesis of low-calorie sweeteners and valuable disaccharides, the synthesis of prebiotic compounds linked to health benefits, synthetic drug delivery systems and other physiological related structures, including, core components of N-linked glycans, O-linked mucin glycoproteins. Although these types of enzymes are still under-explored compared to the glycoside hydrolases and the glycosyltransferases, recently more discovered phosphorylases had been reported leading to more possibilities of synthesizing difficult glycosides. Herein we provide an overview of the distribution of GPs within the carbohydrate-active enzymes (CAZy) database, and the recent utilization of these enzymes for synthetic approaches of di- and oligosaccharides. • Glycoside phosphorylases (GPs) catalyze the reversible formation and cleavage of glycosidic linkages. • Glycoside phosphorylases have distinctive strict regioselectivity. • The reverse phosphorylsis functionality of GPs can be exploited to synthesize high value carbohydrate structures.

Chemical profiling and characterization of phenolic acids, flavonoids, terpene glycosides from Vangueria agrestis using ultra-high-performance liquid chromatography/ion mobility quadrupole time-of-flight mass spectrometry and metabolomics approach.

Vangueria agrestis is a shrub indigenous to tropical Africa, belonging to family Rubiaceae and is traditionally used as a decoction for treatment of fever, pain, and malaria. This study was undertaken to investigate the chemical constituents based on precursor exact mass and fragment ion information. The chemical profiling and structural characteristics of chemical constituents from methanolic extracts of dried aerial parts and roots of V. agrestis and dietary supplements were analyzed using ultra-high-performance liquid chromatography/ion mobility quadrupole time-of-flight mass spectrometry coupled with UNIFI platform and multivariate analysis in both negative and positive ion modes. A non-targeted ultra-high-performance liquid chromatography-mass spectrometry analysis was carried out to profile the chemical constituents of crude extracts of V. agrestis, and 73 compounds, including reference compounds, were identified. The fragments of flavonoids, monoterpene, and triterpene glycosides revealed the characteristic cleavage of glycosidic linkages, and the fragmentation pattern provided the identity of the sugars. This analytical method provides a quick method for quality assessment of dietary supplements. Finally, a chemometrics approach with multivariate statistical tools was used to visualize the differences between root and aerial parts of plant samples and to find the potential chemical markers that differentiate among these parts of V. agrestis samples and dietary supplements.

Effects of alkali and alkaline earth metals on the co-pyrolysis of cellulose and high density polyethylene using TGA and Py-GC/MS

The effects of the type and content of alkali/alkaline earth metals (AAEMs) on the co-pyrolysis of cellulose/high density polyethylene (HDPE) were studied using TGA and Py-GC/MS. AAEMs showed different effects on the decomposition characteristics of cellulose/HDPE mixtures. During cellulose/HDPE co-pyrolysis, AAEMs present in char could act as a base catalyst, with different catalytic effect on products distribution depending on the types of AAEMs. Na showed stronger catalytic cracking effect to promote alkenes formation compared to the use of K, Ca, and Mg. The comparison of experimental and calculated products distributions of raw cellulose/HDPE confirmed the existence of synergistic effect, which facilitated the cleavage of glycosidic linkages to form anhydrosugars and promoted the scission of HDPE chains to produce hydrocarbons. The effect of potassium on this synergy was also investigated. With increased potassium content, the yields of anhydrosugars and hydrocarbons decreased while the yields of furans and ketones increased, suggesting that potassium inhibited the cleavage of glycosidic bonds and promoted ring-opening reactions. This indicated that addition of potassium inhibited the synergy between cellulose and HDPE.

Char Reduction for Pyrolysis of Lignocellulosic Biomass

Thermal decomposition of biomass in controlled environment produces bio-oil, which can serve as an alternative to diesel and gasoline. Alongwith bio-oil, the by-product char is also produced which affects the yield of bio-oil. Hence the present work is focused to the control the amount of char by varying the heat regulation rate and different chemical and microwave pretreatments of the biomass (rice husk). Extract of the treated biomass, biomass samples and the char was studied in different characterization techniques, such as Thermo Gravimetry (TGA), Thermal Differential Analysis (DTA), Fourier Transform Infrared Spectroscopy (FT-IR), Elemental Analyser (CHNS), Inductively Coupled Argon Plasma (ICP). Thermal analysis showed the rate of weight loss was high at higher heating rates. Two different degradation temperatures were observed for Cellulose and lignin in biomass which was not disturbed by acid treatment, representing no significant loss in cellulose and hemicellulose structure, while alkali treated sample approached to a unique temperature representing significant loss/removal of lignin and some portion of hemicellulose/cellulose. Microwave treatment resulted in the cleavage of glycosidic linkage of cellulose resulting in monosaccharides, xylose, and other sugar forms.

Redox processes acidify and decarboxylate steam-pretreated lignocellulosic biomass and are modulated by LPMO and catalase

BackgroundThe bioconversion of lignocellulosic feedstocks to ethanol is being commercialised, but further process development is required to improve their economic feasibility. Efficient saccharification of lignocellulose to fermentable sugars requires oxidative cleavage of glycosidic linkages by lytic polysaccharide monooxygenases (LPMOs). However, a proper understanding of the catalytic mechanism of this enzyme class and the interaction with other redox processes associated with the saccharification of lignocellulose is still lacking. The in-use stability of LPMO-containing enzyme cocktails is increased by the addition of catalase implying that hydrogen peroxide (H2O2) is generated in the slurry during incubation. Therefore, we sought to characterize the effects of enzymatic and abiotic sources of H2O2 on lignocellulose hydrolysis to identify parameters that could improve this process. Moreover, we studied the abiotic redox reactions of steam-pretreated wheat straw as a function of temperature and dry-matter (DM) content.ResultsAbiotic reactions in pretreated wheat straw consume oxygen, release carbon dioxide (CO2) to the slurry, and decrease the pH. The magnitude of these reactions increased with temperature and with DM content. The presence of LPMO during saccharification reduced the amount of CO2 liberated, while the effect on pH was insignificant. Catalase led to increased decarboxylation through an unknown mechanism. Both in situ-generated and added H2O2 caused a decrease in pH.ConclusionsAbiotic redox processes similar to those that occur in natural water-logged environments also affect the saccharification of pretreated lignocellulose. Heating of the lignocellulosic material and adjustment of pH trigger rapid oxygen consumption and acidification of the slurry. In industrial settings, it will be of utmost importance to control these processes. LPMOs interact with the surrounding redox compounds and redirect abiotic electron flow from decarboxylating reactions to fuel the oxidative cleavage of glycosidic bonds in cellulose.

Digestive behavior of Dendrobium huoshanense polysaccharides in the gastrointestinal tracts of mice

With fluorescent end-labeling method, a homogenous Dendrobium huoshanense polysaccharide (GXG) that was orally administrated to mice was found to be degraded into a stable fragment (dGXG) in the stomach, where dGXG was propelled into the small intestine and absorbed into the systemic circulation. The residual GXG in the stomach could pass through the gastrointestinal tract and was excreted into faeces with a very slow fermentation in the large intestine. The simulated digestion of GXG indicated that the acidic pH condition in the gastric fluid was responsible for GXG degradation, which was supported by the oral digestion of dGXG. Chemical analysis not only showed a change in the molar ratio of monosaccharide compositions and glycosidic linkage types, but also found the loss of the sugar residue (1→4)-linked Galp after the acid treatment of GXG, suggesting that the cleavage of glycosidic linkage, especially (1→4)-linked Galp linkage, resulted in GXG degradation in the gastrointestinal tract.

Gamma-irradiation of cellulose nanocrystals (CNCs): investigation of physicochemical and antioxidant properties

Gamma irradiation is a common process mostly used for sterilization against bacteria growth. However, when the process is applied to a material, physical and chemical changes may alter its integrity and behaviour. The aim of this study was to observe the effect of γ-irradiation on the surface chemistry of CNCs. The carbonyl content (both carboxylic acid and aldehyde functionalities) was followed to investigate the influence of the irradiation dose. Thermal stability, wettability and antioxidant properties were also measured. Conductometric titration showed that the carboxylic acid groups content (COOH) was increased from 43 mmol COOH kg−1 CNCs for native CNCs to 631 mmol COOH kg−1 CNCs when a dose of 80 kGy was applied. These changes were confirmed by FTIR and fluorescence spectroscopy. At high irradiation doses, a significant decrease of approximately 30% was observed in the cellulose degree of polymerization while the aldehyde groups content was increased to 379 mmol CHO kg−1 CNCs due to the cleavage of glycosidic linkages. These physicochemical changes led to enhanced antioxidant properties of CNCs.

In situ coupling of chitosan onto polypropylene foils by an Atmospheric Pressure Air Glow Discharge with a liquid cathode

Atmospheric air plasma treatment of chitosan solutions leads to degradation of chitosan molecules by OH radicals and is accompanied by a predominant cleavage of glycosidic linkages and by a decrease of the molecular weight. The degradation proceeds via first order kinetics with the rate constant of (5.73±0.22)×10−6s−1 and the energetic yield of chitosan bond scission of (2.4±0.2)×10−8mol/J. Products of degradation together with intact chitosan molecules adsorb and form coatings on polypropylene foils immersed into the solution that is being plasma treated. The plasma treatment results in strong binding of chitosan to polypropylene due to the formation of covalent bonds between the activated polymer surface and chitosan molecules. Plasma-driven crosslinking is responsible for the accumulation of compressive stress which leads to the development of buckling instabilities in the chitosan coatings.

Structure elucidation and gene cluster characterization of the O-antigen of Escherichia coli O80

Mild alkaline degradation of the lipopolysaccharide of Escherichia coli O80 afforded a polysaccharide, which was studied by sugar analysis, selective cleavage of glycosidic linkages, and 1H and 13C NMR spectroscopy. Solvolysis of the polysaccharide with CF3CO2H cleaved the linkages of α-Fuc and β-linked GlcNAc and GalNAc residues to give two disaccharides. The following structure of the hexasaccharide repeating unit of the O-polysaccharide was established: [Display omitted] The polysaccharide repeat also contains a minor O-acetyl group but its position was not determined. The O-antigen gene cluster of E. coli O80 between the conserved galF and gnd genes was analyzed and found to be consistent with the O-polysaccharide structure established.

Crosslinking of alginic acid/chitosan matrices using bis phenol-F-diglycidyl ether: mechanical, thermal and water absorption investigation

In this study, blends of alginic acid (AA) and chitosan (Cs) cross-linked with bis phenol-F-diglycidyl ether (BPFDGE) were prepared by solvent evaporation method. Chemical structure was analyzed by FTIR showing the existence of interaction between chitosan and sodium alginate. Three transition temperatures were observed for the AA/Cs/BPFDGE blend system in differential thermo-gravimetric analysis thermograms. The first transition showed weight loss due to elimination of absorbed moisture and second transition was due to cleavage of glycosidic linkage of chitosan and decarboxylation from polysaccharide backbone of alginic acid. In the third transition, decomposition temperature of blends (769 °C) was higher as compared to chitosan (580 °C) and alginic acid (620 °C). Investigation on mechanical properties of blends revealed a decreasing trend due to alginate addition that alters crystallization as well as molecular orientation in AA/Cs blend. Increased water uptake was observed owing to interaction between cationic (chitosan) and anionic (alginic acid) groups.

Structure elucidation and gene cluster annotation of the O-antigen of Escherichia coli O39; application of anhydrous trifluoroacetic acid for selective cleavage of glycosidic linkages

O-Polysaccharide (O-antigen) accompanied by a minor mannan was isolated from the lipopolysaccharide of Escherichia coli O39 and studied by component analyses, methylation, Smith degradation, mass spectrometry, and 1D and 2D NMR spectroscopy. In addition, a new approach, solvolysis with anhydrous trifluoroacetic acid, was applied to cleave selectively the rhamnosidic linkage. The following structure of the O-polysaccharide was established: [Display omitted] where d-Qui4N(R3Hb) indicates 4,6-dideoxy-4-[(R)-3-hydroxybutanoylamino]-d-glucose. The O-antigen gene cluster of E. coli O39 has been sequenced. The gene functions were tentatively assigned by a comparison with sequences in the available databases and found to be in agreement with the O-polysaccharide structure.

Study on the thermal degradation of chitosan-Cu/Ni/Mn complexes

AbstractThe thermal degradation of chitosan-Cu/ Ni/ Mn complexes at different heating rates in nitrogen was studied by thermogravimetric analysis (TGA) in the temperature range 30-500 °C. Fourier transform-infrared (FTIR) was utilized to determine the microstructure of chitosan-metal complexes. The results of FTIR show that there are coordinating bonds between chitosan and cupric, manganese, nickel ions. The results of thermal analysis indicate that the thermal degradation of chitosan-Cu/ Mn/Ni complexes is a two-step reaction, which is related to water loss from the material, the deacetylation of the main chain and the cleavage of glycosidic linkages of chitosan, respectively. Characteristic temperature increases with the increment of heating rate and the impact of coordination of metal ion on the thermal degradation of chitosan is very significant. The kinetic parameters were determined by using Flynn-Wall-Ozawa method. The results show that the activation energy of the complexes is different but the variable tendency is similar

Revealing pyrolysis chemistry for biofuels production: Conversion of cellulose to furans and small oxygenates

Biomass pyrolysis utilizes high temperatures to produce an economically renewable intermediate (pyrolysis oil) that can be integrated with the existing petroleum infrastructure to produce biofuels. The initial chemical reactions in pyrolysis convert solid biopolymers, such as cellulose (up to 60% of biomass), to a short-lived (less than 0.1 s) liquid phase, which subsequently reacts to produce volatile products. In this work, we develop a novel thin-film pyrolysis technique to overcome typical experimental limitations in biopolymer pyrolysis and identify α-cyclodextrin as an appropriate small-molecule surrogate of cellulose. Ab initio molecular dynamics simulations are performed with this surrogate to reveal the long-debated pathways of cellulose pyrolysis and indicate homolytic cleavage of glycosidic linkages and furan formation directly from cellulose without any small-molecule (e.g., glucose) intermediates. Our strategy combines novel experiments and first-principles simulations to allow detailed chemical mechanisms to be constructed for biomass pyrolysis and enable the optimization of next-generation biorefineries.

Asparagine 405 of heparin lyase II prevents the cleavage of glycosidic linkages proximate to a 3-O-sulfoglucosamine residue

Heparin and heparan sulfate contain a rare 3-O-sulfoglucosamine residue critical for anticoagulation and virus recognition, respectively. The glycosidic linkage proximate to this 3-O-sulfoglucosamine is resistant to cleavage by all heparin lyases (Heps). HepII has a broad specificity. The crystal structure of the wild type HepII identified its active site and showed a close spatial proximity between Asn405 and the 3-OH group of the bound glucosamine residue. In this study, we mutated Asn405 to the less sterically demanding Ala405 or Gly405, which broadened the substrate specificity of HepII and caused it to cleave the resistant linkage proximate to the 3-O-sulfoglucosamine residue.

ChemInform Abstract: First Application of Triflic Acid for Selective Cleavage of Glycosidic Linkages in Structural Studies of a Bacterial Polysaccharide from Pseudoalteromonas sp. KMM 634.

A marine bacterium Pseudoalteromonas sp. KMM 634 produces a highly acidic, regular O-specific polysaccharide, containing D-glucuronic acid (D-GlcA), 2,3-diacetamido-2,3-dideoxy-D-glucuronic acid (D-GlcNAc3NAcA), 2,3-diacetamido-2,3-dideoxy-D-mannuronoyl-L-alanine (D-ManNAc3NAcA6Ala) and 2-acetamido-2,4,6-trideoxy-4-[(S)-3-hydroxybutyramido]-D-glucose (D-QuiNAc4NAcyl). The polysaccharide was stable towards solvolysis with anhydrous HF but could be partially depolymerised by triflic acid. This new reagent for selective cleavage of carbohydrates split primarily 1,2-trans-β-glycosidic linkages and did not affect amide-linked substituents. As a result, a disaccharide and a trisaccharide with a GlcNAc3NAcA residue at the reducing end were obtained. Based on these data and studies of the initial polysaccharide and derived oligosaccharides by two-dimensional NMR spectroscopy, the following structure of the tetrasaccharide repeating unit was established: →3)-α-D-QuipNAc4NAcyl-(1→4)-β-D-ManpNAc3NAcA6Ala-(1→4)-β-D-GlcpNAc3NAcA-(1→4)-β-D-GlcpA-(1→