C(6)-Oxidation Followed by C(5)-Epimerization of Guar Gum Studied by High Field NMR

Double Photocrosslinked Responsive Hydrogels Based on Hydroxypropyl Guar

Double crosslinked hydrogels based on a biodegradable polymer were prepared by photocopolymerization of methacrylated hydroxypropyl guar (HPG-MA) and 3-acrylamidophenylboronic acid. Along with irreversible strong covalent crosslinks by methacrylic groups, these hydrogels contained labile boronate crosslinks formed as a result of the interaction of boronic acid with cis-diol moieties of HPG. These hydrogels demonstrated higher elasticity than HPG-MA hydrogels with only irreversible covalent crosslinks. Labile boronate crosslinks not only strengthened the hydrogels but also imparted to them pronounced responsive properties. It was demonstrated that the mechanical properties, the swelling behavior, as well as the uptake and release of some substances from the double crosslinked hydrogel were pH controlled. For instance, the hydrogels could release cationic disinfectant at a rate regulated by pH. Such photocrosslinkable in situ forming hydrogels are very promising for the production of smart coatings that release targeted substances at the desired rate.

Dual Transient Networks of Polymer and Micellar Chains: Structure and Viscoelastic Synergy

Dual transient networks were prepared by mixing highly charged long wormlike micelles of surfactants with polysaccharide chains of hydroxypropyl guar above the entanglement concentration for each of the components. The wormlike micelles were composed of two oppositely charged surfactants potassium oleate and n-octyltrimethylammonium bromide with a large excess of anionic surfactant. The system is macroscopically homogeneous over a wide range of polymer and surfactant concentrations, which is attributed to a stabilizing effect of surfactants counterions that try to occupy as much volume as possible in order to gain in translational entropy. At the same time, by small-angle neutron scattering (SANS) combined with ultrasmall-angle neutron scattering (USANS), a microphase separation with the formation of polymer-rich and surfactant-rich domains was detected. Rheological studies in the linear viscoelastic regime revealed a synergistic 180-fold enhancement of viscosity and 65-fold increase of the longest relaxation time in comparison with the individual components. This effect was attributed to the local increase in concentration of both components trying to avoid contact with each other, which makes the micelles longer and increases the number of intermicellar and interpolymer entanglements. The enhanced rheological properties of this novel system based on industrially important polymer hold great potential for applications in personal care products, oil recovery and many other fields.

Effect of γ-irradiation on the structure and antioxidant activity of polysaccharide isolated from the fruiting bodies of Morchella sextelata

The molecular weight of the polysaccharide and the chemical groups it contains has an important influence on its biological activity, relatively low molecular weight polysaccharides may have better antioxidant activity. Polysaccharides isolated from the fruiting bodies of Morchella sextelata (MSP) were treated by γ-irradiation at 10, 100 and 1000 kGy doses, and the physicochemical properties and antioxidant activity of irradiated MSP were investigated. Microscopic observation under a scanning electron microscope (SEM) showed that breakage and pores appeared on the surface of the irradiated polysaccharide. As the irradiation dose increased, the average molecular weight of MSP decreased significantly, while the particle size and thermal stability of MSP first increased at 10 and 100 kGy doses and then decreased at 1000 kGy doses. The antioxidant activities, measured by free radical scavenging tests and protective effect on PC12 cells injured by H₂O₂, were all increased after irradiation, especially when the concentration of MSP was low (50 and 100 μg/ml). Therefore, irradiation treatment was an effective method to enhance the activity of polysaccharides.

Properties and potential applications of mannuronan C5-epimerase: A biotechnological tool for modifying alginate

Given the excellent characteristics of alginate, it is an industrially important polysaccharide. Mannuronan C5-epimerase (MC5E) is an alginate-modifying enzyme that catalyzes the conversion of β-D-mannuronate (M) to its C5 epimer α-L-guluronate (G) in alginate. Both the biological activities and physical properties of alginate are determined by M/G ratios and distribution patterns. Therefore, MC5E is regarded as a biotechnological tool for modifying and processing alginate. Various MC5Es derived from brown algae, Pseudomonas and Azotobacter have been isolated and characterized. With the rapid development of structural biology, the crystal structures and catalytic mechanisms of several MC5Es have been elucidated. It is necessary to comprehensively understand the research status of this alginate-modifying enzyme. In this review, the properties and potential applications of MC5Es isolated from different kinds of organisms are summarized and reviewed. Moreover, future research directions of MC5Es as well as strategies to enhance their properties are elucidated, highlighted, and prospected.

Synthesis of guar gum-g-(acrylic acid-co-acrylamide-co-3-acrylamido propanoic acid) IPN via in situ attachment of acrylamido propanoic acid for analyzing superadsorption mechanism of Pb(ii)/Cd(ii)/Cu(ii)/MB/MV

GG-g-(AA-co-AM-co-APA) IPN superadsorbent, characterization of loaded microstructures and individual/synergistic adsorption mechanism of MB/SF/Pb(ii)/Cd(ii)/Cu(ii) are reported.

Antifungal ouzo nanoparticles from guar gum propionate

Synthesis of high DS guar gum propionate esters and the formation of self-assembly nanoparticles for fungus contact killing.

New water resistant biomaterial biocide film based on guar gum

This work was aimed to develop water resistant biocide film from renewable resources for applications in food and water technology. Guar gum, a polymeric galactomannan, was intrinsically modified to a new guar gum benzamide. Benzoylation was carried out by benzoyl chloride reaction in water medium and a propyl amine spacer was used to impart a high degree of hydrophobicity. The new guar gum benzamide was resistant to water and soluble in non aqueous solvent like dimethyl sulfoxide. Cast films of thickness 0.162 mm had a breaking point tensile strength of 21.95 Mpa. The water vapor permeability of biomaterial film was 0.28 g mm kPa(-1)h(-1)m(-2) and water contact angle on evaporative surface was 90.35 degree. Qualitative and quantitative biocide activity of film was established against Salmonella enterica, Escherichia coli, Staphylococcus aureus and Bacillus subtilis. The new guar gum benzamide absorbed strongly in UV region.

Cancer chemopreventive and anti-inflammatory activities of chemically modified guar gum

Guar gum (G) is a simple characterized branched polysaccharide, which is frequently used in food industries. We prepared the gum C-glycosylated derivative (GG), and its sulphated derivative (SGG), aiming to characterize their cancer chemopreventive, and anti-inflammatory properties. Estimation of cancer chemopreventive activity, specifically anti-initiation, including the modulation of carcinogen metabolism and the antioxidant capacity, revealed that GG was a potent anti-initiator, where it inhibited not only the carcinogen activator enzyme, cytochrome P450 1A (CYP1A), but also induced the carcinogen detoxification enzymes glutathione-S-transferases (GSTs), while SGG inhibited both CYP1A and GSTs. SGG was an effective radical scavenger than GG against hydroxyl, peroxyl, and superoxide anion radicals. GG and SGG were found to modulate the macrophage functions into an anti-inflammatory pattern. Thus, both enhanced the macrophage proliferation and phagocytosis of fluorescein isothiocyanate (FITC)-zymosan; however, they also inhibited strongly the nitric oxide generation and tumor necrosis factor-alpha secretion in lipopolysaccharide (LPS)-stimulated RAW macrophage 264.7. Unexpectedly, both GG and SGG dramatically inhibited the binding affinity of FITC-LPS to RAW 264.7, as indicated by flow cytometry analysis. GG and SGG exhibited a significant anti-proliferative activity against human hepatocellular carcinoma cells (Hep G2), and only SGG was specifically cytotoxic for human breast carcinoma cells (MCF-7), but neither was significantly cytotoxic for human lymphoblastic leukemia cells (1301). SGG led to a major disturbance in cell cycle phases of Hep G2 cells as indicated by concomitant arrest in S- and G2/M-phases, a disturbance that was associated with an induced cell death as a result of necrosis, but not apoptosis in both GG- and SGG-treated cells. Taken together, the modified gums could be used as an alternative of G in health food industries to provide cancer prevention in risk populations.

Versatile Grafting of Polysaccharides in Homogeneous Mild Conditions by Using Atom Transfer Radical Polymerization

A versatile atom transfer radical polymerization (ATRP) method for polysaccharide grafting in homogeneous mild conditions without using protecting group chemistry is presented. Water/DMF mixtures with different compositions were used as the solvent. The "grafting-from" approach was used in order to prepare suitable pullulan and dextran ATRP macroinitiators with a well controlled degree of functionalization. Methacrylate and acrylamide monomers were grafted obtaining good control over the number, molecular weight and polydispersity of the grafted chains without homopolymer formation and polysaccharide degradation. The versatility of this method allowed us to prepare comblike derivatives with a wide range of properties (amphiphilic, ionic, and thermoresponsive) by simply changing the solvent composition and the catalyst. This could make possible the synthesis of new interesting biomaterials starting from a wide range of polysaccharides.

C(6)-Oxidation and C(5)-Epimerization of Locust Bean Galactomannan Studied by High Field NMR and Circular Dichroism

Galactose depleted locust bean gum was selectively oxidized in C(6) position and epimerized with mannuronan C(5)-epimerases to obtain the corresponding artificial uronanes. These new pseudo-alginates were characterized by NMR spectroscopy and circular dichroism (CD). Specifically, 1D and 2D NMR techniques allowed the degree of epimerization, the distribution of mannuronic and guluronic acid residues in the polysaccharidic chain, and the average G block length to be determined. In addition, NMR diffusion experiments showed that the epimerization reaction did not significantly degrade the polysaccharidic chains. Circular dichroism was used to investigate the kinetics of the epimerization reaction and to evidence the specific interaction between the epimerized locust bean samples with Ca(II) ions in dilute solution. All of the samples considered in this study form wall to wall gels in concentrated polymer solutions.