tempo and curdlan

Curdlan is a bacterial polysaccharide that has been of significant recent interest due to its interesting and valuable rheological properties and its inherent bioactivity. The simple (1→3)-β-glucan homopolymeric, unbranched structure of curdlan is conducive to enhanced solubility relative to many other abundant natural polysaccharides, thus, providing alternatives for processing the polymer into desired shapes and formulations. At the same time, this relatively good solubility enables chemical modification under mild conditions, leading to a growing body of literature on derivative chemistry, structure-property relationships, and the potential for regioselective modification. Structure, properties, biosynthesis, modification chemistries, and key applications are the foci for this review of the curdlan literature.

Topics: beta-Glucans; Carbohydrate Sequence; Click Chemistry; Cyclic N-Oxides; Food Industry; Gels; Molecular Sequence Data; Phosphorylation; Polysaccharides, Bacterial; Solubility

A C6-carboxylated curdlan (C6-Cc) obtained from 4-acetamido-TEMPO-mediated oxidation of curdlan was used both as a reducing and stabilizing agent for green synthesis of pH-responsive AuNPs, which was carried out by controlling the pH of the C6-Cc solution at a high temperature (100°C). C6-Cc presented a semi-flexible random coil chain in the aqueous medium at pH 5.5 and became more expanded and rigid in alkaline conditions (pH 7.1-12.0), though the primary chemical structure of C6-Cc was virtually unchanged with the pH variation. The AuNPs prepared with C6-Cc at various pHs were characterized by various instrumental measurements. The shapes and sizes of AuNPs were found to be strongly dependent on the pH of the C6-Cc solution. The C6-Cc-decorated AuNPs exhibited a more well-dispersed spherical morphology with smaller particle sizes under alkaline conditions (pH 7.1-12.0). Through this study, a facile, simple, and green method has been demonstrated for preparation of stimuli-sensitive AuNPs using biocompatible polyanionic polysaccharides.

Topics: beta-Glucans; Cyclic N-Oxides; Gold; Green Chemistry Technology; Hot Temperature; Hydrogen-Ion Concentration; Metal Nanoparticles; Oxidation-Reduction; Particle Size

In this study, high-intensity ultrasound (20 kHz), a simple, effective and without any additive method, was used to the degradation of carboxylic curdlan (Cc) produced by 4-acetamido-TEMPO-mediated oxidation. The effects of ultrasound on molecular properties, structure and chain conformations of Cc were investigated by viscometry, size-exclusion chromatography with multiangle laser-light scattering (SEC-MALLS) analysis, as well as FTIR and NMR spectroscopies. The results indicated that the intrinsic viscosity [η] and the weight-average molecular weight (Mw) of Cc decreased obviously after ultrasound, and a uniform and narrow distribution of degradation product was obtained. The z-average radius of gyrations (Rg) firstly increased and then decreased as the sonication time prolonged. Ultrasound destroyed the hydrogen bonds resulting in the transition from compact random coil conformation to more flexible and even shorter extended chains. Ultrasonic treatment could not alter the primary chemical structure of Cc molecules according to the structural analysis by FTIR and NMR spectroscopies. Degradation kinetics based on Schmid model was applied to estimate the degradation rate constant k. It was found that the k value of Cc decreased with increasing the polymer concentration from 0.05 to 0.2% (w/v).

Topics: beta-Glucans; Carbohydrate Conformation; Cyclic N-Oxides; Kinetics; Molecular Weight; Oxidation-Reduction; Sonication; Viscosity

Regioselective oxidation was applied to commercial curdlan for the preparation of its water-soluble derivatives with improved antioxidant activities, using a 4-acetamido-2,2, 6,6-tetramethylpiperidine-1-oxyl radical/NaClO/NaClO2 system at pH 4.8 and 40°C. The structural features, molecular properties, and chain conformations of the oxidised curdlans were determined using Fourier transform (FT) infrared and FT Raman spectroscopy, carbon nuclear magnetic resonance, X-ray diffraction, and size-exclusion chromatography with multi-angle laser-light scattering analyses. The C6 primary hydroxyls of curdlan were successfully oxidised into carboxylate groups with less depolymerization, and no aldehyde groups were formed during oxidation. The crystalline region of curdlan was destroyed after oxidation. The oxidised curdlans formed random coils in aqueous solution, and the chain became more flexible and expanded with increasing carboxylate contents from 2.07mmol/g to 4.87mmol/g. The high polyglucuronic acid derivative (Cur-24) showed the best antioxidant activity in TEAC and FRAP assays, thus it could be explored as novel potential antioxidants for dietary and therapeutic applications.

Topics: Antioxidants; beta-Glucans; Carbohydrate Conformation; Cyclic N-Oxides; Multigene Family; Oxidation-Reduction; Spectroscopy, Fourier Transform Infrared; X-Ray Diffraction

Pure (1→3)-β-polyglucuronic acid sodium salt was prepared from curdlan by oxidation with 4-acetamido-TEMPO/NaClO/NaClO₂ in water at pH 4.7 and 35°C. The oxidation conditions, including the reaction time and amounts of reagents added, were optimized for the preparation of (1→3)-β-polyglucuronic acids with high molecular weights. The primary C6 hydroxyl groups of curdlan were completely oxidized to the corresponding C6-carboxylates using a one- or two-step reaction process by controlling the oxidation conditions, thus providing pure (1→3)-β-polyglucuronic acids consisting only of D-glucuronosyl units. Unfortunately, however, the increased amounts of reagents and long reaction time led to significant depolymerization of the curdlan during the oxidation process, and the resulting (1→3)-β-polyglucuronic acids had weight-average degrees of polymerization of 340-360. The (13)C and (1)H NMR chemical shifts of the products were successfully assigned using pure (1→3)-β-polyglucuronic acid.

Topics: beta-Glucans; Carboxylic Acids; Catalysis; Chlorides; Cyclic N-Oxides; Glucuronic Acid; Oxidation-Reduction; Polymerization; Sodium Hypochlorite

2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation was applied to curdlan to prepare water-soluble sodium (1→3)-β-polyglucuronate, and its biodegradation behavior was then investigated. A bacterial strain (EH621) having the ability to degrade (1→3)-β-polyglucuronate was isolated from soil, and identified as Paenibacillus sp. Strain EH621 cultured with (1→3)-β-polyglucuronate decreased the initial total carbon in the supernatant by approximately 60% within 3 days, showing that (1→3)-β-polyglucuronate can be readily degraded and metabolized by microorganisms present in the natural environment. Hydrolytic enzyme activity was detected in the cell-free extract of EH621, which was highly specific to (1→3)-β-polyglucuronate. Analyses of the enzymatic degradation products revealed that (1→3)-β-polyglucuronate was endolytically degraded to its monomeric unit, glucuronate, via some oligomers and dimers.

Topics: Base Sequence; beta-Glucans; Biodegradation, Environmental; Cyclic N-Oxides; DNA, Bacterial; Glucuronates; Molecular Sequence Data; Oxidation-Reduction; Paenibacillus; RNA, Ribosomal, 16S; Sequence Analysis, DNA; Soil Microbiology

A facile, simple, and eco-friendly method using 4-acetamido-2,2,6,6-tetramethypiperidine-1-oxyl radical-oxidized curdlan (Oc) as both reducing and stabilizing agents was developed for the fabrication of silver nanoparticles (AgNPs) from silver nitrate (AgNO₃). The structure, morphology, and particle size of the as-prepared AgNPs were investigated by ultraviolet-visible spectroscopy, transmission electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, and dynamic laser light scattering. The well-dispersed AgNPs were sphere like with a mean diameter of 15 nm. Their formation was dependent on reaction duration, reaction temperature, Oc concentration, and AgNO₃ concentration. Fourier transform-infrared and Raman spectra demonstrated that the as-prepared AgNPs can readily bind covalently with the carboxylate groups of Oc through the strong monodentate interaction in the reaction medium.

Topics: Acetamides; beta-Glucans; Chromatography, Gel; Cyclic N-Oxides; Green Chemistry Technology; Light; Metal Nanoparticles; Molecular Conformation; Particle Size; Scattering, Radiation; Silver; Silver Nitrate; Spectrometry, X-Ray Emission; Spectrophotometry, Ultraviolet; Spectroscopy, Fourier Transform Infrared; Spectrum Analysis, Raman; Temperature; X-Ray Diffraction

Curdlan, amylodextrin, and regenerated cellulose fiber were subjected to electromediated oxidation with a 4-acetamido-TEMPO catalyst in a buffer at pH 6.8 without NaClO or NaClO(2). More than 90% of the C6 primary hydroxyls of Curdlan and amylodextrin were converted to sodium carboxylate groups by this method. Molecular mass values of the oxidized products were much higher than those prepared by the TEMPO/NaBr/NaClO system at pH 10. When the regenerate cellulose fiber was treated by the TEMPO electromediated oxidation for 45 h, carboxylate and aldehyde groups of 1.1 and 0.6 mmol/g, respectively, were formed in the oxidized cellulose fiber. The original fibrous and fine surface morphologies were maintained, and nearly no weight losses by the oxidation were observed. Thus, the TEMPO electromediated oxidation is a characteristic and environmentally friendly chemical modification for regenerated cellulose fibers, films, and related forming materials, and ion-exchangeable carboxylate and reactive aldehyde groups can be efficiently introduced into regenerated celluloses.

Topics: beta-Glucans; Catalysis; Cellulose; Cyclic N-Oxides; Dextrins; Electrochemical Techniques; Hydrogen-Ion Concentration; Molecular Structure; Oxidation-Reduction

Curdlan from Agrobacterium sp. was oxidized using 2,2,6,6,-tetramethylpiperidine-1-oxyl radical (TEMPO)-NaBr-NaClO systems at pH 11. The effects of oxidation conditions on degrees of oxidation and polymerization of the products obtained were studied using SEC-MALLS, NMR and IR analyses. Different families of water-soluble beta-(1,3)-polyglucuronic and beta-(1,3)-polyglucoglucuronic acid sodium salts were quantitatively generated with a yield of 80% and without significant loss of their molecular weights. Given that beta-(1,3)-polyglucuronic acids prepared from the regioselective oxidation of curdlan by the TEMPO-NaBr-NaClO systems regularly consist of the glucuronic acid repeating unit; they may open new biotechnological fields for the utilizations of water soluble forms of curdlan.

Topics: beta-Glucans; Carbohydrates; Cyclic N-Oxides; Electrochemistry; Glucuronates; Hydrogen-Ion Concentration; Magnetic Resonance Spectroscopy; Models, Chemical; Molecular Weight; Oxygen; Rhizobium; Sodium Hypochlorite; Spectrophotometry, Infrared; Spectroscopy, Fourier Transform Infrared; Water