Reducing End Groups Research Articles

Structural characterization and anti-inflammatory activities of novel polysaccharides obtained from Pleurotus eryngii

Natural polysaccharides named PEP-0.1-1, PEP-0-1 and PEP-0-2 from edible mushroom species Pleurotus eryngii were obtained in the present study. Results showed that molecular weights of these polysaccharides were 3235, 2041 and 23933 Da, respectively. Further, structural characterization revealed that PEP-0.1-1 had a →4-α-D-Glcp-1→ backbone and contained →4)-α-D-Glcp and →4)-β-D-Glcp reducing end groups. PEP-0-1 backbone contained →4-α-D-Glcp-1→ and →6-α-3-O-Me-D-Galp-1→, and the side chains contained α-D-Glcp, β-D-Manp-1→ and α-D-Glcp-3→. However, PEP-0-2 backbone consisted of →4-α-D-Glcp-1→ and →6-α-3-O-Me-D-Galp-(1→6)-α-D-Galp-1→ while the side chains contained α-D-Glcp and β-D-Manp-1→. Biological activity analysis was then carried out and found that all these polysaccharides could significantly suppress the relative mRNA expression of toll-like receptor 4, nitric oxide, tumor necrosis factor-α, interleukin (IL)-1β and IL-6 in lipopolysaccharide (LPS)-induced inflammation of RAW264.7 cells, as well as the over secretion of the above cell cytokines. Moreover, Western blotting analysis revealed that all these purified fractions displayed significant inhibition effects on the expression of c-Jun N-terminal kinases protein protein induced by LPS in mitogen activated protein kinase pathway, along with the relieving on the inhibition effect of LPS on IκB-α protein expression. In summary, the information generated by the present study could provide a theoretical basis for the exploration of novel healthy food materials from edible mushroom with anti-inflammation activities.

Pyrolysis mechanistic study on sulfated polysaccharide from marine algal biomass with density functional theory method

Sulfated polysaccharide (SPS) derived from marine algae represents a promising renewable carbon biomass source. Through pyrolysis, SPS can be converted into C5 platform chemicals, including furfural (FF) and 5-methylfurura (5-MF). Understanding the fundamental reaction mechanisms during pyrolysis is essential for the advancing pyrolysis techniques. This work presents a detailed reaction mechanism that reveal new pathways leading to the most important products and intermediates. Simulations focusing on the initial steps in SPS pyrolysis showed that the unimolecular degradation of SPS is dominated by SO3 elimination, with a barrier height of 157.2 kJ/mol; ring-opening and glycosidic bond fission were identified as important competitive reactions, both of which have a barrier height of 207.6 kJ/mol and 260.1 kJ/mol, respectively. The 4,5-unsaturated acyclic rhamnose derived from the glycosidic bond fission of acyclic reducing end group can transform into 5-MF with high selectivity. In addition, the acyclic reducing end group is readily dehydrated to form a 2,3-unsaturated acyclic reducing end group, a reactive unsaturated intermediate. Its decomposition involves an 8-membered ring transition state that requires a low barrier height and results in the formation of a C5 fragment, which can be cyclized directly and dehydrated to form 5-MF. The majority of CO2 is mostly formed by the synergistic breakage of C-Ccarboxyl bonds and glycosidic bonds, with a barrier height of 197.9 kJ/mol. Moreover, a mechanism is uncovered for the formation of formic acid (FA) from a 4,5-unsaturated no-reducing end group. The major pyrolysis channel is initiated by a retro Diels-Alder reaction and followed by a retro-ene reaction to produce a 3,4-unsaturated non-reducing end group, which further decomposes into FA and a new 4,5-unsaturated non-reducing end group.

Oxidized reducing ends in celluloses: Quantitative profiling relative to molar mass distribution by fluorescence labeling

Fluorescence labeling with N-(1-naphthyl)ethylenediamine is highly effective for quantifying oxidized reducing end groups (REGs) in cellulosic materials. When combined with size exclusion chromatography in DMAc/LiCl, along with fluorescence / multiple-angle laser light scattering / refractive index detection, a detailed profile of C1-oxidized REGs relative to the molecular weight distribution of the cellulosic material can be obtained. In this work, the derivatization process was extensively optimized, to be carried out heterogeneously in the solvent N-methyl-2-pyrrolidone. Furthermore, we show that to achieve high selectivity for carboxyl groups at the C1 position, keto and aldehyde groups need to be selectively reduced (e.g., by NaBH4), and carboxyl groups other than at C1 need to be blocked (e.g., by methylation with (trimethylsilyl)diazomethane) prior to fluorescence labeling of carboxyl groups at C1 position. Finally, we demonstrate the practical value of the analytical method by measuring the content of the C1-oxidized REGs in cellulose samples after chemical (by Pinnick oxidation) or enzymatic (by treatment with C1-oxidizing LPMO enzymes) oxidation of various pulp samples.

A Review of Modified Cellulose Nanocrystals and their Applications

Abstract: Cellulose is one of the most abundant natural polymers developed in the ecosystem and has been used in many applications for industrial products since ancient times. Although the main sources of cellulose are wood plant, fibers and, additional sources can also be discovered, such as algae, fungi, bacteria, and even some marine organisms (such as tunicates). Mechanical or chemical processes are used to transform cellulosic materials into cellulose nanocrystals due to their efficacy, high aspect ratio, low density, renewability, and non-toxicity. They have drawn a lot of attention in a variety of industries. Here, we discuss various applications and properties in particular mechanical, rheological, liquid crystalline nature, and adhesives to introduce cellulose nanocrystals hydrophilic, colloidal stable, and rigid rod-shaped bio-based nanomaterial with high strength and high surface area. Under various circumstances, it improves the characteristics of various compounds. The grafting of polymers on the surface of cellulose nanocrystals has attracted significant interest in both academia and industry due to the rapidly expanding number of potential applications of surface-modified cellulose nanocrystals, which range from building blocks in nanocomposites and responsive nanomaterials to antimicrobial agents. Furthermore, we explore the most popular polymerization methods, such as surface-initiated ring-opening polymerization, surface-initiated free radical polymerization, surface-initiated atom transferred radical polymerization and surface-initiated controlled radical polymerization that are employed to graft polymers from the surface and reducing end groups of cellulose nanocrystals. In this review, we examine the available literature and provide a summary of recent applications of cellulose nanocrystals, including biomedical application, drug delivery, biosensor, tissue engineering, antibacterial activity, wound healings, etc.

Stable glycosylamines at the reducing ends of cellulose nanocrystals.

The reaction of reducing end groups in cellulose nanocrystals with dodecylamine was examined. Using a direct-dissolution solution-state NMR protocol, the regioselective formation of glucosylamines was shown. This provides an elegant approach to sustainably functionalize these bio-based nanomaterials, that may not require further reduction to more stable secondary amines.

Microstructural feature of cellulose fibre in cement-based composites at different curing temperature

Thermal stability, chemical structure and microstructure of cellulose fibre under cement paste and dry conditions at different temperature were tested to investigate its temperature adaptability in cement-based composites. Results demonstrated that after curing for 60 days at 60 and 90 °C, the compressive strength of cement paste containing 0.4 wt% cellulose fibre increased 16.16% and 22.79%, respectively. However, the compressive strength of the paste curing at 120 and 150 °C had no enhancement effect. Compared with the dry condition, cement paste filtrate had a significant influence on chemical structure and microstructure at 120 and 150 °C. In filtrate cured at 120 °C, β-1,4-polyglucose in cellulose fibre underwent alkaline hydrolysis, fragmenting cellulose fibre to smaller pieces, which converted the “fibrous structure” to “cluster structure”. However, in filtrate cured at 150 °C, reducing end group in cellulose fibre underwent peeling reaction, which decreased its thermal stability and changed its crystallinity from 0.69 to 0, whereby microstructure transformed into “agglomeration structure”.

Liquid Crystalline Properties of Symmetric and Asymmetric End-Grafted Cellulose Nanocrystals.

The hydrophilic polymer poly[2-(2-(2-methoxy ethoxy)ethoxy)ethylacrylate] (POEG3A) was grafted onto the reducing end-groups (REGs) of cellulose nanocrystal (CNC) allomorphs, and their liquid crystalline properties were investigated. The REGs on CNCs extracted from cellulose I (CNC-I) are exclusively located at one end of the crystallite, whereas CNCs extracted from cellulose II (CNC-II) feature REGs at both ends of the crystallite, so that grafting from the REGs affords asymmetrically and symmetrically decorated CNCs, respectively. To confirm the REG modification, several complementary analytical techniques were applied. The grafting of POEG3A onto the CNC REGs was evidenced by Fourier transform infrared spectroscopy, atomic force microscopy, and the coil-globule conformational transition of this polymer above 60 °C, i.e., its lower critical solution temperature. Furthermore, we investigated the self-assembly of end-tethered CNC-hybrids into chiral nematic liquid crystalline phases. Above a critical concentration, both end-grafted CNC allomorphs form chiral nematic tactoids. The introduction of POEG3A to CNC-I does not disturb the surface of the CNCs along the rods, allowing the modified CNCs to approach each other and form helicoidal textures. End-grafted CNC-II formed chiral nematic tactoids with a pitch observable by polarized optical microscopy. This is likely due to their increase in hydrodynamic radius or the introduced steric stabilization of the end-grafted polymer.

Challenges in Synthesis and Analysis of Asymmetrically Grafted Cellulose Nanocrystals via Atom Transfer Radical Polymerization.

When cellulose nanocrystals (CNCs) are isolated from cellulose microfibrils, the parallel arrangement of the cellulose chains in the crystalline domains is retained so that all reducing end-groups (REGs) point to one crystallite end. This permits the selective chemical modification of one end of the CNCs. In this study, two reaction pathways are compared to selectively attach atom-transfer radical polymerization (ATRP) initiators to the REGs of CNCs, using reductive amination. This modification further enabled the site-specific grafting of the anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS) from the CNCs. Different analytical methods, including colorimetry and solution-state NMR analysis, were combined to confirm the REG-modification with ATRP-initiators and PSS. The achieved grafting yield was low due to either a limited conversion of the CNC REGs or side reactions on the polymerization initiator during the reductive amination. The end-tethered CNCs were easy to redisperse in water after freeze-drying, and the shear birefringence of colloidal suspensions is maintained after this process.

Revisiting Alkaline Pretreatment of Lignocellulose: Understanding the Structural Evolution of Three Components

AbstractHerein, sodium hydroxide (NaOH) pretreatment of lignocellulose is performed to investigate the structural evolution of lignin, cellulose, and hemicellulose. It is found that most of hemicellulose and part of cellulose are hydrolyzed/converted to monosaccharide, alcohols, and carboxylic acids. Over half of cellulose is stabilized because the reducing end groups of cellulose convert to stable carboxylic groups. In addition, lignin is converted to aromatic monomers (predominately vanillin and acetovanillone) with a highest yield of 6.1 wt%, along with dimers and oligomers with Mw less than 10 000 Da. According to heteronuclear single quantum coherence analysis, no common interlinkages (β‐O‐4, β‐β, β‐5, etc.) appear in lignin oligomers due to lignin fragments condensed during the alkaline pretreatment. Notably, the acidification process is also the cause of lignin condensation since high aromatic monomers yield of 15 wt% (based on original lignin in pine) is achieved by a postoxidation of alkaline solution, while few no aromatic monomers generated by using the isolated lignin oligomers. The direct oxidation of lignocellulose in alkaline solutions to aromatic monomers demonstrates the potential application of lignocellulose alkaline pretreatment for high‐value chemicals production.

One-step synthesis of cellooligomer-conjugated gold nanoparticles in a water-in-oil emulsion system and their application in biological sensing.

Monodisperse gold nanoparticles (GNPs) were synthesized in a water-in-oil emulsion system (reverse micelles) composed of 80% N-methylmorpholine N-oxide (NMMO)/20% H2O and dodecane, stabilized with an anionic surfactant: bis(2-ethylhexyl)sulfosuccinate sodium salt. Cellooligomers with a degree of polymerization of 6 or 15 (βGlc6 or βGlc15, respectively), which were labeled at each reducing end group with thiosemicarbazide (TSC) and dissolved in the aqueous NMMO phase, were successfully conjugated to the surfaces of GNPs in situ during spontaneous NMMO-mediated gold reduction. As-synthesized βGlc6-GNPs and βGlc15-GNPs had average diameters of 11.3 ± 2.1 and 10.5 ± 0.7 nm, respectively, while their surface sugar densities were 0.21 and 0.51 chains nm-2, respectively. Concanavalin A (ConA), a lectin that recognizes non-reducing end groups of glucose residues, aggregated with βGlc15-GNPs with higher sensitivity than it did with βGlc6-GNPs, possibly as a result of the sugar density on the GNP surfaces. The aggregates were rapidly re-suspended by adding methyl-β-d-glucopyranoside as a binding inhibitor. Other lectins and proteins showed no interaction with βGlc-GNPs. Therefore, clustering of glucose non-reducing ends on the GNP surfaces via strong intermolecular association of cellooligomers, possibly led to high affinity for ConA. This facile synthesis route to structural carbohydrate-decorated GNPs has potential applications in carbohydrate-nanometal conjugate nano-biosensor development.

A novel method for preparing microcrystalline cellulose from bleached chemical pulp using transition metal ions enhanced high temperature liquid water process

A novel method for preparing microcrystalline cellulose (MCC) from bleached chemical pulp based on the transition metal ion-enhanced high temperature liquid water (HTLW) process was established in this study. Transition metal ions (Fe3+, Cu2+ or Cr3+) were used to enhance the depolymerization effect of HTLW treatment on fibers. Hemicelluloses are selectively removed, resulting in an increase in the α-cellulose content; cellulose undergoes hydrolytic degradation, causing a significant decrease in the average degree of polymerization (DP). SEM images indicated that the as-prepared MCC had granular or rod-like shape. The repose angle results showed a desirable fluidity of obtained MCC. The copper number results showed an increase in the reducing end groups of the obtained MCC. The XRD analysis indicated that the cellulose crystallite exhibited negligible changes, and the crystallization index (CI) increased. However, a very high concentration of transition metal ions lowered the CI. The transition metal ion-enhanced HTLW treatment provides an acid free method for preparing MCC.

Synthesis of pyridine-free xylan sulfates

The usual sulfation of polysaccharides applying chlorosulfuric acid and pyridine may form products containing pyridine-based impurities, which may yield toxic side effects. The synthesis of pyridine-free polysaccharide sulfates could be realized simply by using xylan that was treated with a reducing agent (NaBH4) prior to the sulfation reaction. The reduced xylan possess same reactivity compared to untreated xylan. The purity of the alternatively synthesized xylan sulfate is proofed by NMR spectroscopic studies. Thus, the simple reduction of the reducing end groups of the polysaccharide prior the sulfation is an efficient tool to get pure products, which may be scaled up easily.

Synthesis and characterization of nano fibrillated cellulose/Cu2O films; micro and nano particle nucleation effects

Cubic, truncated cubic and spherical nano and micro particles of Cu2O, can be selectively deposited onto nano fibrilated cellulose gels by the modulated alkaline reduction of Cu2+ ions aided by the cellulose’s reducing end groups. The role of the cellulose’s reducing end groups and that of externally added carbohydrate reducing agents, towards inducing various Cu2O morphologies, is discussed with respect to the detailed nucleation effects leading to micro and nano Cu2O particle deposition on NFC. When the reducing end groups are provided only by the cellulose’s chain ends, supersaturation effects seem to be affecting the Cu2O nucleation mechanism. However, the Cu2O nucleation considerations were altered when mobile reducing end groups were provided by adding dextrose in the system, promoting additional particle nucleation sites. Furthermore, the effort offered the possibility to quantitatively determine the number of accessible reducing end groups (-CHO) present in NFC, expressed in mmol/g. The optical properties of the created NFC/Cu2O films were examined by UV–vis absorption measurements, revealing band gaps ranging between 2.02–2.25 eV. The accumulated understanding expands the utility window and opens new directions for the novel utilization of nano-fibrillated cellulose, and more specifically toward semiconductor applications.

Novel insight in carbohydrate degradation during alkaline treatment

Abstract A mathematical model is presented, in which the yield loss (YL) and the decline in polymerization of carbohydrates is comprehended. The model is applicable to the treatment of cellulose and hemicelluloses in alkaline media, and it features the actions of peeling, stopping, and alkaline hydrolysis of the polymer chains. The peeling reaction is further subdivided into primary and secondary peeling depending on whether it originates from an initial reducing end-group (REG) or from an REG created by alkaline hydrolysis. Fitting the model to experimental data provides estimates of the various reaction rate constants. When available, simultaneous observations of the YL and the decrease in chain length contribute to the evaluation of the parameters. Alternatively, if the data are limited to the YL, the obtained parameter estimates allow for a projection of the time development of chain length. The model has been applied on data from two types of experiments: soda-anthraquinone treatment of cotton linters and kraft treatment of Scots pine. It was possible to evaluate the impact of the different processes on degradation as well as the portions of polymer chains possessing active or stabilized REGs.

Asymmetric cellulose nanocrystals: thiolation of reducing end groups via NHS–EDC coupling

Cellulose nanocrystals (CNC) were functionalized in aqueous media at the reducing, aldehyde ends of cellulose. CNC oxidation to produce carboxyl groups was followed by carbodiimide-mediated reaction to install thiol groups. The selectivity and extent of thiolation at the reducing ends was qualitatively confirmed by imaging (transmission electron microscopy) silver nanoparticles that tagged the CNC termini and by X-ray photoelectron spectroscopy, respectively. The adsorption of thiolated CNC onto gold surfaces as well as the viscoelastic property of the formed adlayer was investigated by using quartz crystal microgravimetry. The thiolated CNC chemisorbed on the surfaces were further analyzed for surface density and distribution by using atomic force microscopy. Overall we introduce a facile, mild asymmetric thiolation procedure as an efficient alternative to conventional reductive amination.

Thermal stability of cellulose and their nanoparticles: Effect of incremental increases in carboxyl and aldehyde groups

Oxidized cellulose containing carboxyl and aldehyde functional groups represent an important class of cellulose derivatives. In this study effect of incrementally increasing COOH and CHO groups at C2, C3, and C6 positions of cellulose and nanocellulose has been investigated, with a view to understanding their effect on thermal treatment of cellulose. The results show that 2,3-dialdehyde cellulose (DAC) is the most thermally stable oxidized product of cellulose while the most unstable derivatives contain carboxyl group at the C6 position (6CC). Carboxymethylcellulose (CMC), with carboxymethyl group on C6 position, is more stable than 6CC. Multi-functionalized celluloses 2,3,6-tricarboxycellulose and 6-carboxy-2,3-dialdehyde, have the same level of thermal stability as 6CC, showing that the presence of carboxyl at the C6 is a key destabilizing factor in the thermal stability of oxidized cellulose products. More the number of reducing end groups on the polymer chain, lower the thermal stability of the cellulose, as proved by comparing the TGA/DTG of monomeric analogs dextrose, cellobiose and glucuronic acid with the oxidized celluloses. The thermal stability trend observed for oxidized celluloses was DAC>DCC>nanoparticles>dextrose>glucuronic acid, caused by extent of reducing ends and COOH groups.

Kinetic Model for Carbohydrate Degradation and Dissolution during Kraft Pulping

The time development of the polysaccharide content in the wood residue and the black liquor during kraft pulping for softwood is the focus of this study. The degradation process falls into two distinct categories: the chain element type and the chain fragment type. In the chain element reactions, a single element in the polymer chain can be removed, whereas in the chain fragment reaction a longer piece of the polymer is dissolved into the black liquor. The element-wise process consists of the subreactions peeling, stopping, and alkaline hydrolysis. A mathematical model considering peeling, stopping, and alkaline hydrolysis of the polymer chains as well as the dissolution of the wood components into the black liquor is presented and tested for the experimental data obtained from kraft cooking of Scots pine wood meal. As a novelty, the model distinguishes between primary peeling originating in the initial reducing end groups and secondary peeling following alkaline hydrolysis. Four series of cooking at high...

What is active cellulose in pyrolysis? An approach based on reactivity of cellulose reducing end

The idea of active cellulose is based on the initial induction period that is observed during thermogravimetric analysis of cellulose. The role of the reducing ends of cellulose samples (Avicel PH-101 and Whatman No. 42) was studied in relation to active cellulose formation, because our previous studies suggested that these end groups have lower thermal stabilities. Elimination of the reducing ends from Avicel PH-101 by reduction with NaBH4 substantially prolonged the induction period. These features were only characteristic of Avicel PH-101, with a leveling-off degree of polymerization (DP) of DP¯n 218. Formation of water-soluble oligosaccharides was also lower (240°C/60min). For Whatman No. 42 cellulose with a higher DP (DP¯n 2170), similar elimination of the reducing ends had almost no effect on the weight-loss behavior. The reducing group analysis data showed that a large number of new reducing ends were formed in Whatman cellulose during DP reduction as the initial pyrolysis process. Based on these differences arising from the initial DP of cellulose, a mechanism for active cellulose was proposed: thermal decomposition of reducing end groups, which are originally present or are formed during pyrolysis in crystalline cellulose, activates the following pyrolysis reactions. The molecular mechanism for activation is also discussed; we propose that it includes hydrogen-bond rearrangement in the initiation of pyrolytic reactions such as depolymerization (transglycosylation) and dehydration, based on our previous proposal that proton donation (acting as an acid catalyst) through hydrogen bonding is a fundamental mechanism for these pyrolytic reactions.

Cellulose degradation in alkaline media upon acidic pretreatment and stabilisation

The present study reports on a revised kinetic model for alkaline degradation of cellulose accounting for primary peeling/stopping reactions as well as for alkaline hydrolysis followed by secondary peeling. Oxalic acid pretreated cotton linters was utilised as the model substrate for the prehydrolysis-soda anthraquinone process. The main emphasis was investigating the effect of end-group stabilising additives such as sodium borohydride (BH), anthraquinone (AQ), and anthraquinone-2-sulphonic acid sodium salt (AQS) on the rates of the yield loss reactions. BH and AQS ensured a cellulose yield gain of 13% and 11%, respectively, compared to the reference. Both stabilisation agents decreased the content of the reducing end groups in the samples, while in the case of AQS stabilisation a 25% increase in carboxyl group content compared to the reference was also observed. As expected, the addition of end group stabilisers resulted in a significant decrease in the peeling-to-stopping rate constants ratio.

Irradiation of Cellulosic Pulps: Understanding Its Impact on Cellulose Oxidation

Different pulp samples were irradiated by three energy sources: plasma, electron beaming, and γ radiation. The effect of increased exposure to irradiation was studied by multidetector gel permeation chromatography with fluorescence labeling of carbonyl groups to quantify changes of the cellulose. Whereas plasma treatment had no effect, for gamma and electron beam the degradation primarily affects the high molar mass area. Kinetic calculations based on DPw were performed. They show close-to-linear relations with slopes in the same order of magnitude, suggesting that wood-derived pulps degrade slower than pulps from annual plants. The rise in carbonyl group content is linear with increasing dose. In particular, in pulps from annual plants, most detected carbonyl structures originate from the new reducing end groups. Therefore, oxidative modification of cellulose molecules by means of radiation appears to be viable for pulps produced from wood. Here the increase in oxidized functionalities is partially disconnected from chain scission.