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Engineered block polysaccharides is a relatively new class of biomacromolecules consisting of chemical assembly of separate block structures at the chain termini. In contrast to conventional, laterally substituted polysaccharide derivatives, the block arrangement allows for much higher preservation of inherent chain properties such as biodegradability and stimuli-responsive self-assembly, while at the same time inducing new macromolecular properties. Abundant, carbon neutral, and even recalcitrant biomass is an excellent source of blocks, opening for numerous new uses of biomass for a wide range of novel biomaterials. Among a limited range of methodologies available for block conjugation, bifunctional linkers allowing for oxyamine and hydrazide 'click' reactions have recently proven useful additions to the repertoire. This article focuses the chemistry and kinetics of these reactions. It also presents some new data with the aim to provide useful protocols and methods for general use towards new block polysaccharides.

Sequential periodate-chlorite oxidation of sodium hyaluronate to 2,3-dicarboxylated hyaluronate (DCH), a novel biocompatible and highly functionalized derivative bearing additional pair of COOH groups at C2 and C3 carbons of oxidized ᴅ-glucuronic acid units, is investigated. The impact of various reaction parameters (time, oxidizer concentration, and molar amount) on DCH's composition, molecular weight, degree of oxidation, and cytotoxicity are investigated to guide the synthesis of DCH derivatives of desired properties. Subsequently, fully (99%) and partially (70%) oxidized DCH derivatives were compared to untreated sodium hyaluronate in terms of anticancer drug cisplatin loading efficacy, carrier capacity, drug release rates, and cytotoxicity towards healthy and cancerous cell lines. DCH derivatives were found to be superior in every aspect, having nearly twice the carrier capacity, significantly slower release rates, and higher efficacy. DCH is thus a highly interesting hyaluronate derivative with an adjustable degree of oxidation, molecular weight, and great potential for further modifications.

Engineered block polysaccharides is a relatively new class of biomacromolecules consisting of chemical assembly of separate block structures at the chain termini. In contrast to conventional, laterally substituted polysaccharide derivatives, the block arrangement allows for much higher preservation of inherent chain properties such as biodegradability and stimuli-responsive self-assembly, while at the same time inducing new macromolecular properties. Abundant, carbon neutral, and even recalcitrant biomass is an excellent source of blocks, opening for numerous new uses of biomass for a wide range of novel biomaterials. Among a limited range of methodologies available for block conjugation, bifunctional linkers allowing for oxyamine and hydrazide ‘click’ reactions have recently proven useful additions to the repertoire. This article focuses the chemistry and kinetics of these reactions. It also presents some new data with the aim to provide useful protocols and methods for general use towards new block polysaccharides.

Schizophyllan and scleroglucan are water-soluble polysaccharides having repeating units consisting of three β-1,3-linked glucose residues in the main chain and a single β-1,6-linked glucose residue as the side chain. This polysaccharide dissolves as a triple helix in an aqueous solution and shows a cooperative order-disorder transition between the side chain and solvent molecules while retaining the triple helical conformation. Periodate and subsequent chlorite oxidations selectively modify the side chain glucose to provide the corresponding dicarboxylate units. Optical rotation measurements and differential scanning calorimetry were performed on carboxylated schizophyllan/scleroglucan (‘sclerox’) samples to investigate the effects of the degree of carboxylation on the order-disorder transition in deuterium oxide with 0.1 M NaCl. The transition curves for the sclerox samples are strongly dependent on the degree of carboxylation. The modified side chains cannot take the ordered structure, resulting in a reduction of the transition enthalpy. The transition temperature for carboxylated schizophyllan becomes lowered and the transition curve broadens with increasing the degree of carboxylation. The permanent disordered units are included in a trimer by the carboxylation to inhibit a long sequence of the ordered units. © 2017. This is the authors’ accepted and refereed manuscript to the article. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

International audience; Reducing end activation of poly-and oligosaccharides by bifunctional dioxyamines and dihydrazides enables aniline-free and cyanoborohydride-free conjugation to aldehyde-containing molecules, particles and surfaces without compromising the chain structure. Chitosans are due to their polycationic character, biodegradability, and bioactivity important candidates for conjugation. Here, we present a kinetic and structural study of the conjugation of a dioxyamine and a dihydrazide to enzymatically produced chitooligosaccharides ranging from N,N'-diacetylchitobiose to a decamer, all having N-acetyl D-glucosamine at the reducing end. Conjugation of the dioxyamine resulted in mixtures of (E)-and (Z)-oximes and β-N-pyranoside, whereas the dihydrazide yielded cyclic N-glycosides. Reaction kinetics was essentially independent of DP. Stable secondary amines were in both cases obtained by reduction with α-picoline borane, but higher temperatures were needed to obtain acceptable reduction rate. Comparison to dextran oligomers shows that the nature of the reducing end strongly influences the kinetics of both the conjugation and reduction.

Water-soluble (1→3)-β- d -glucans with 1,6-linked branches (SBG), originally isolated from the cell walls of Saccharomyces cerevisiae and partially depolymerised to a weight average degree of polymerisation (DP w ) in the range 120–160 for optimal performance in wound healing applications, were studied by dynamic light scattering (DLS), SEC MALLS and AFM. Results indicate that dilute aqueous SBG solutions (1 μg/ml to 3 mg/ml) contain higher order structures with a very wide size distribution in water (10–500 nm), corresponding to a mixture of single chains, multi-chain aggregates including triple-stranded motifs, and particulate materials. The latter were enriched in longer chains compared to non-particulate fractions. The size distribution of SBG aggregates shifted to slightly lower values upon heating, but showed hysteresis upon cooling. AFM images prepared from very dilute aqueous solution (1–5 μg/ml) analysis showed by comparison to other (1→3)-β- d -glucans that some of the structures were the triple helical species coexisting with larger aggregates and single chains, in contrast to carboxymethylated SBG, which contained predominantly single chains. The ability to control the aggregation behaviour of SBG enables tailoring of the physical, and possibly bioactive, properties of SBG preparations.

Water-soluble (1→3)-β-D-glucans with 1,6-linked branches (SBG), originally isolated from the cell walls of Saccharomyces cerevisiae and partially depolymerised for optimal performance in wound healing applications, were studied by size exclusion chromatography (SEC) with multi-angle laser light scattering (MALLS) detector and a viscosity detector at both high and ambient column temperatures. The strongly aggregating materials could be dispersed as single chains in water following partial carboxymethylation (degree of substitution (DS) 0.51 or higher). Lower DS (0.23) also dispersed as single chains provided a column temperature of 80 °C was applied. Reduction of reducing ends prior to carboxymethylation was required to avoid alkaline peeling and hence to obtain correct molecular weight distributions of the native material. DS was determined using (13)C NMR and potentiometric titration (range 0.23-0.91). Further analysis of CM-SBG in the single chain state suggested a randomly coiled behaviour with marginal influence of the branches in terms of macromolecular dimensions, which were close to those of CM-curdlan. The result of the investigation is a simple and reliable protocol for preparing undegraded and un-aggregated SBG derivatives, which are well suited as a standard analysis of the molecular weight distribution of SBG-like molecules.

The localisation of pectin in Sphagnum moss leaves and its role in preservation has been investigated. Light microscopy using ruthenium red to detect pectin in whole and sectioned Sphagnum papillosum leaves revealed it is abundant in hyaline cell walls, fibrils, papillae, chlorophyllous cell walls and thickenings around hyaline cell pores. Transmission electron microscopy of ultrathin cell walls labelled with poly- l -lysine colloidal gold revealed pectin was distributed throughout the cell wall. The preservative/microbiocidal properties of these pectins are explained by the acid-dissociation properties of galacturonic acid carboxyls and their incorporation in the unique cell arrangement of the Sphagnum leaf. Liquid from a salmon fillet absorbed into S. papillosum leaves and incubated at room temperature for 22 h had a pH around 4.85, was dominated by Lactobacillus sp. and smelled fresh compared to experimental controls. Chlorite-treated Sphagnum leaves could have a potential as a food tray pad that absorbs liquid and prevents the growth of spoilage bacteria inside it.

Limited periodate oxidation (0–8%) of alginates results in enhanced degradability, extending the range of applications of alginates as biomaterials, e.g. in tissue engineering. Oxidation produces dialdehydes that are highly sensitive to alkaline β-elimination, even under physiological conditions (pH 7.4, 37 °C). Although all periodate is consumed during limited oxidation, not all of the resulting dialdehydes are equally degradable, leading to a characteristic level off in molecular weight upon prolonged degradation. A significant fraction (20–50%) of the oxidized residues were resistant even at pH 10.4. We tentatively assign this finding to the presence of particularly stable intramolecular hemiacetals known to form in periodate oxidized alginates (POA). The enhanced degradation of POA persists into the gel state, allowing tailoring of more biodegradable alginate gels. The activation energy for β-elimination of dialdehydes was 88 kJ/mol compared to 113 kJ/mol for unoxidized residues, presumably reflecting the absence of strain in the non-cyclic transition state of the former.

Fully de-N-acetylated chito-oligomers were prepared by de-amination of chitosan using nitrous acid (HNO2). The dimer to hexamer fractions of chitosan oligomers were fractionated with preparative size-exclusion chromatography (SEC) and characterized using 1H NMR spectroscopy. The purified oligomers were polymerized by reductive N-alkylation by the action of NaCNBH3, in a reaction between the terminal 2,5-anhydro- d -mannofuranose (M-unit) and the primary amines of the repeating units (1 → 4) bound β- d -glucosamine (D-unit) resulting in a covalent bond and formation of secondary amines. The polymerized products were studied by SEC-RI and SEC-MALLS-RI and were confirmed to be branched reaching molecular weights of up to 10 000 g/mol. Analysis by 1H NMR spectroscopy confirmed that the chitosan oligomers had been branched by formation of secondary amines. Fully de-N-acetylated chitosan (FA

We studied the effect of the mole fraction ( F M ) of β- d -mannuronate residues in alginate chains and the weight-average molecular weight ( M w ) of alginates on intestinal immunological activity through Peyer's patch cells of C3H/HeJ mice. Over most of the range of M w (30,000–690,000), alginates with high mannuronate content (high-M alginates, F M 0.69–0.86) showed immunological activity, but alginates with F M lower than 0.31 did not. For high-M alginates with F M = 0.78 extracted from Laminaria japonica , those with M w lower than 200,000 showed the highest activity.

The paper presents a new investigation of a native and a hydrophobically modified hyaluronan (HMHA) C8NH-HA100 interactions with surfactants SDS, DTAB, and a dye polarity probe Coomassie Brilliant Blue (CBB), and their macromolecular properties in aqueous environment using isothermal titration calorimetry (ITC) and SEC-MALLS. A novel alkylated HA derivative was prepared by the introduction of octyl chains onto –OH groups of the HA d-glucuronic acid unit via carbamate bond at a high degree of substitution preserving the HA carboxylic groups. Large and abrupt endothermic enthalpy changes (ΔH) during the titration of HA by DTAB evidence a strong electrostatic interaction and a formation of complex aggregates between HA and DTAB micelles. Heat effects of HA–SDS titration are moderate and reveal a lowering of the surfactant CMC in the presence of HA. The C8NH-HA100 displays binding with CBB in terms of exothermic enthalpy changes, which is ascribed to hydrophobic interactions, while such binding is not observed for HA. The assessment of the polysaccharides backbone stiffness and the coefficient of the Mark–Houwink–Sakurada plot (MHS), a, by SEC-MALLS shows a little alternation of the HA backbone stiffness after its modification.

Novel alginates prepared by independent control of chain stiffness and distribution of G-residues : Structure and gelling properties

The carbonyl content of a pectic polysaccharide from Sphagnum papillosum (sphagnan) and periodate oxidised alginates was investigated using three different carbonyl labelling strategies combined with size-exclusion chromatography (SEC) with multi-angle laser light scattering (MALLS) and on-line fluorescence or off-line tritium detection. The labelling strategies were tritium incorporation via NaB3H4 reduction, and fluorescent labelling with carbazole carbonyl oxyamine (CCOA), or 2-aminobenzamide (2-AB), respectively. Carbonyl quantification was based on labelled pullulan, dextran and alginate standards possessing only the reducing end carbonyl group. As a result the carbonyl distribution in the polysaccharides could be determined. In sphagnan it was found that the carbonyl content increased with increasing molecular weight, whereas in periodate oxidised alginate the carbonyl content was as expected independent of the molecular weight. The methods proved useful for carbonyl detection in water soluble polysaccharides in general. The tritium incorporation method was preferred for alkali stable polysaccharides, while the CCOA method was most suitable for acid stable polysaccharides with low carbonyl content. The 2-AB method is applicable for all polysaccharides tested with varying carbonyl content; however, it lacks the ability to detect ketone functionalities.

Chitosans with different chemical compositions ( F A = 0.05–0.65) and different molecular weights ( M w = 36.000–460.000) were studied by size-exclusion chromatography combined with multi-angle laser light scattering (MALS) and viscosity detectors to provide R G – M and [ η ]– M data as basis for further analysis using the wormlike chain model. In both cases intrinsic persistence lengths ( q 0 ) in the range 5.1–7.6 nm were obtained, with little or no detectable dependence on F A . These values are significantly lower than values obtained for alginates (12 nm), including homopolymeric mannuronan, using the same approach. This finding is also corroborated by differences in the Smidsrod B -parameter, confirming that chitosans are less extended than alginates, despite the similarity in basic chain geometry (cellulose type) and linear charge density. Partial periodate oxidation of chitosans led to a pronounced increase in the chain flexibility as shown by a gradual decrease in persistence length, approaching 2 nm for the most oxidised samples.

The purpose of this research was to evaluate if pectin-like polysaccharides, collectively known as sphagnan, extracted by acid hydrolysis from the leaves of Sphagnum moss have a unique ability to react with phenylhydrazine, o-phenylenediamine or collagen. A previous assay for determination of carbonyl groups in sphagnan by reaction with phenylhydrazine was disproved due to spectrophotometric interference from furans. The actual carbonyl content of sphagnan is estimated to be much less than previously thought. NMR spectroscopy showed that small amounts of o-phenylenediamine and/or its oxidation products bind to sphagnan probably via imine formation, but evidence of quinoxaline formation was inconclusive. Sphagnan-gelatin mixtures formed complex coacervates at pH 2.0-4.8 at low ionic strength, which is typical of electrostatic polyelectrolyte interactions, rather than covalent carbonyl-amine reactions. Measurements of hydrothermal stability and collagenase-degradation of sphagnan-treated hide powder collagen suggest that sphagnan is a poor tanning agent. The results indicate the suggested preservative properties of sphagnan are not related to tanning.

Mild acid hydrolysis was used to release polysaccharides from the chlorite-treated leaves of Sphagnum papillosum . These polysaccharides, collectively known as sphagnan, were physically and chemically characterised. No evidence was found of the presence of a previously described 5-keto- d -mannuronic acid (5-KMA) monomer in sphagnan, or in the chlorite-treated leaves from which sphagnan was extracted. After fractionation by anion-exchange chromatography the majority of polysaccharides were similar to rhamnogalacturonan I-type pectins. They were highly branched and had a weight average molecular weight of 3.9 × 10 g/mol.

Oat β-glucan was partially degraded with (1→4)-β- d -glucan 4-glucanohydrolase for different periods of time. Weight average molecular weight and weight average intrinsic viscosity were obtained from SEC-RI-RALLS-Visc and ranged from 2200 to 213,900 g/mol and 7 to 316 ml/g, respectively. The viscosity equation determined [ η ] w =1.06×10 −2 M w 0.86 indicated an extended random coil conformation. When the coil was modelled as a worm-like chain a persistent length of 3.65 nm was obtained. The hydrolysis products identified after extensive degradation were glucose, cellobiose, laminaribiose, 4-O-β-laminaribiosyl d -glucose, 4-O-β-laminaribiosyl d -cellobiose and 3-O-β-cellobiosyl d -cellobiose showing that other enzyme activities were present. The depolymerization kinetics suggested that longer sequences of consecutive (1→4)-linkages represent fast hydrolysable sites and the presence of higher relative proportions of (1→3)-linkages restricts the affinity of the enzyme.

Polysaccharides such as scleroglucan and schizophyllan contain periodate-resistant β-1,3-linked d -glucan backbones with regularly distributed side chains consisting primarily of single β-1,6-linked d -glucose residues that are susceptible to periodate oxidation. Side chain oxidation results in the formation of dialdehyde groups and the production of formic acid. During the initial periodate oxidation an increase in the storage modulus (G′) associated with the formation of gels, was observed when the reduced concentration, Cp [η] was above 3. These gels appeared to be physically stable, whereas aldehyde reduction (e.g. with NaBH4) or oxidation to carboxyl (e.g. with NaClO2 in acetic acid) dissolved the gels. The mechanism of cross-linking can be explained by the formation of intermolecular hemiacetal linkages. The gels were further characterised rheologically in terms of the initial increase in the storage modulus and the stability when stored in seawater at 55 and 90°C, respectively.

Six (1→3)(1→4)-β- d -glucan standards (A–F) isolated from barley were analysed by size-exclusion chromatography (SEC) in five different laboratories with varying columns, solvent conditions and detector systems (low- and multi-angle light scattering and viscometry). Static (batch) measurements by capillary viscometry and laser light scattering were included. Fairly consistent results were obtained for the weight average molecular weights (Mw), radii of gyration (RG) and intrinsic viscosities [η], demonstrating that the β-glucans may serve as useful standards or reference materials in the study of cereal β-glucans. Average values for Mw were: A,E: 114,000 (±11%); B,C: 374,000 (±9%), D,F: 228,000 (±13%). Some inconsistencies regarding the polydispersity (Mw/Mn) could be ascribed to the influence of peak broadening in certain column/solvent systems. The study further demonstrated that individual researchers tended to use different processing parameters, especially refractive index increments (dn/dc), due to ambiguities in the literature or to differing experimental values. The need for consistent parameters and processing methods is clearly demonstrated.

The triple-stranded polysaccharide scleroglucan was subjected to free-radical depolymerisation with Fenton's reagent (H2O2/Fe2+), and partially degraded samples in the molecular weight (Mw) range from 8 200 000 to 5200 were studied. Analyses of the chemical composition of partially degraded samples by 13C nuclear magnetic resonance spectroscopy and by determination of reducing end-groups suggested that the degradation was random. The decrease in Mw followed the kinetics expected for a multiple-stranded polymer. Following an apparently initial stable regime, degradation occurred with an exponential decrease (exponent (ν) ∼3.6) in Mw. Partially degraded samples displayed bimodal molecular weight distributions. This was attributed to the release of single-stranded oligomers having a degree of polymerisation (DP) too low to remain incorporated in the triplex structure (DP

Defatted leaves from the medicinal tree Cola cordifolia were extracted with 50% EtOH, 50 °C and 100 °C water. The polysaccharide rich extracts were fractionated and the structure of the polysaccharides elucidated. Linkage analysis of the polysaccharides indicates a rhamnogalacturonan type I backbone where both Rha and parts of GalA are substituted in position 3, indicating a highly branched polymer with short side chains. The purified fractions were tested for complement fixation, macrophage stimulating activity and anti-adhesion activity towards Helicobacter pylori. Here we report on complex and polydisperse types of pectins (Mw: 3-1300 kDa) as well as the presence of low Mw (3 kDa) acidic oligosaccharides. The fractions showed a moderate complement fixing activity and no macrophage activating effects after LPS removal. Anti-adhesion activity towards H. pylori was not found.

A new and flexible method for preparation of dry macroporous alginate foams with the capability of absorbing physiological solutions has been developed, which may find use within areas such as wound healing, cell culture, drug delivery and tissue engineering. The present study demonstrates how the gelation rate of the alginate and degree of ionic crosslinking can be utilized to control the physical foam properties. The rate of released Ca(2+)/Sr(2+) gelling ions available for interaction with the alginate was influenced by the concentration and physical characteristics of CaCO₃/SrCO₃ particles. The method of preparation of such foams allows, as described herein, tailoring of the pore structure, hydration properties and mechanical integrity in a manner not possible by other techniques.

Two chitosan samples (fraction of acetylated units (FA) 0.15 and 0.52) were fractionated by preparative size exclusion chromatography (SEC). The molecular weights and molecular weight distributions of the fractions were analyzed by analytical size exclusion chromatography coupled to an on-line low angle laser light scattering detector and a differential refractive index detector (SEC-LALLS-DRI), and their intrinsic viscosities were determined. The exponent (a) of the Mark-Houwink-Kuhn-Sakurada (MHKS) equation was found to be 0.92 ± 0.07 and 1.1 ± 0.1, respectively, at I = 0.1 and pH 4.5. No variation in FA related to molecular weight was found. Reversible interaction between chitosans and different column packings strongly influenced the log M-V relationships. This interaction was generally most pronounced for the low-FA chitosan, suggesting that the protonated amino groups are involved. Ammonium acetate buffer reduced this effect and the use of a new type of SEC-packing seemed to eliminate it. The more highly acetylated chitosan also had a more pronounced tendency towards concentration dependent self-association, which most probably involve intermolecular hydrophobic interactions between the acetyl groups.

Three different types of 15μm macroporous polymer particles (MP) based on poly(styrene- co -divinylbenzene), all with an extreme degree of monodispersity, were prepared by the method of ‘activated swelling’. The type and relative content of low molecular weight compounds used as pore-forming agents (porogens) ensured that the total pore volume was confined to large pores with radii larger than 300 A, and with an increasingly larger fraction of the pore volume shifted towards very large pores (> 2000A). A hydrophilic layer was covalently linked to the particles to eliminate their Hydrophobic character, and they were subsequently tested in aqueous size exclusion chromatography (SEC). Favourable Chromatographic properties generally associated with monosized particles were obtained, and column packing as well as the separations were performed with very low back pressures. The particles were found to be suitable for SEC of a series of high molecular weight polysaccharides, irrespective of their charge (anionic, cationic and neutral). The shift in pore size distribution towards very large pores resulted in a corresponding shift in the range of molecular weights (strictly, hydrodynamic volumes) where separation took place. For particles with 70% of the pore volume confined to pores with radii larger than 2000A, it was estimated that the molecular weight range of polysaccharides of the pullulan type accessible to SEC was extended up to ca. 10 8 . The corresponding value for an extended, rod-like, triple-helical polysaccharide (scleroglucan) was 10 7 .

Swelling behaviour of alginic acid gel beads with different chemical composition, molecular weight and size was studied in acetate buffer at pH4. A correlation was observed between the swelling behaviour in this buffer and the equilibrium properties of alginic acid gels. High contents of long l -guluronic acid blocks (G-blocks), known to give a high acid gel strength, reduced the rate of swelling and also the amount of solubilized alginate molecules leaching out of the gel beads. Compared to the original alginate, the leaching molecules had a lower average molecular weight, higher content of mannuronic acid residues and a reduced average length of G-blocks. Swelling capacity, rate of swelling and solubility of alginic acid seemed to depend on a balance between the tendency of homopolymeric blocks to form intermolecular junction zones, and the tendency of alginate to reduce the chemical potential of water. As expected, swelling rate increased with increasing temperature and decreasing bead size.

Samples of carboxylated scleroglucan, sclerox, with a degree of carboxylation in the side-chains varying from 10 to 50% were made in order to investigate the potential of using carboxylation as a means to control subsequent gelation by heavy metal ions. The storage and loss moduli of aqueous solutions of sclerox samples as a function of time were determined at T = 20 °C and 30 °C after addition of trivalent chromium ions. The rheological characterization showed a transition from a viscoelastic liquid to a gel with a characteristic time depending on the chromium concentration and the degree of carboxylation. For 20% carboxylation, the rate of change in the storage modulus could be controlled within nearly three orders of magnitude from 10 −3 to 1 Pa min −1 , using total chromium concentrations ranging from 0.3 to 6 m m . This rate was decreased by a factor of 2–5 by reducing the degree of carboxylation to 10%. The present study indicates that carboxylation of scleroglucan can be used to control the rate of gelation mediated by heavy metal ion complexation. This finding suggests that extension of the application range of this polysaccharide from an efficient viscosifer for polymer flooding to profile modification of high temperature oil reservoirs is attainable.

The effect of the length and chemical composition of the side-chains in comb-like branched polysaccharides on gelation with trivalent metal ions has been studied using xanthan and xylinan (acetan) with intact and truncated side-chains. Partial or complete removal of the terminal β-d-mannose, or removal of up to 22% of the trisaccharide side-chains of xanthan using partial acid hydrolysis, has only small effects on the Cr3+-induced gelation. In contrast, replacement of β-d-mannose by the trisaccharide α-l-Rhap-(1 → 6)-α-d-Glcp-(1 → 6)-α-d-Glcp-(1 → 4)- to yield the polysaccharide xylinan totally inhibits the gelation with Cr3+ ions. Removal of the trisaccharide by partial acid hydrolysis, which leads to a series of polymers with structures converging towards the partially hydrolysed xanthans, restores the gelling ability with Cr3+ ions. These observations seem to support the gelation model where Cr3+-glucuronic acid interactions are involved in the cross-linking of chains. It is further suggested that this interaction can be suppressed due to steric hindrance caused by the bulky side-chains in xylinan.

Degradation of single- and multiple-stranded polysaccharides by acid hydrolysis or free radical depolymerisation with H 2 O 2 Fe 2+ was monitored by viscosity measurements. Single-stranded polysaccharides (alginate, hydroxyethyl cellulose, carboxymethyl cellulose and κ-carrageenan in its disordered conformation) gave the expected linear relationship between 1 η sp ( 1 a ) and the degradation time, where a is the Mark-Houwink-Sakurada exponent. Double-stranded xanthan and triple-stranded scleroglucan showed a different pattern. Following an initial period with apparently slow degradation, a second regime was entered where the apparent degradation rate was much higher, and where ηsp followed the power law, ηsp ∼ t−va. However, the estimated values of the parameter v differed from those calculated by a Monte Carlo method for double- (xanthan) and triple-(scleroglucan) stranded polymers. κ-Carrageenan in its iodide-induced ordered conformation was very stable in acid as compared to the disordered conformation. In the ordered state the apparent degradation rate was initially constant, but increased in later stages. However, the double-logarithmic plot of ηsp versus time showed that there was neither a pronounced stable regime nor a regime following the power law. The degradation of gellan resulted in a rapid and linear increase in 1 η sp with degradation time, both in the ordered and disordered conformation. The same type of degradation kinetics was obtained for welan.

The bark of Cola cordifolia used in Malian traditional medicine contains unusual types of polysaccharides with immunomodulating activities. We report for the first time on the structure of a polymer designated CC1P1 having the repeating structure [2→)[α-D-Gal(1→3)]α-L-Rha(1→4)α-d-GalA(1→] as determined by NMR and GC/MS. α-Linked Gal is unusual in pectins. The Mw of 135 kDa was determined by SEC-MALLS. CC1P2 (1400 kDa), another polymer, having the same backbone, but this was substituted with α-4-OMe-GlcA, α-2-OMe-Gal and α-Gal as terminal units. CC1P1 shows a high complement-fixing activity, IC₅₀ being 2.2 times lower than the positive pectin control PMII (IC₅₀ appr. 71 μg/mL) while IC₅₀ of CC1P2 is 1.8 times lower. The simple structure of CC1P1 did not activate macrophages, while CC1P2 (100 μg/mL) showed the same potency as the positive controls PMII (100 μg/mL) and LPS (500 ng/mL). No cytotoxicity was detected.

Current research on polysaccharides in Trondheim is summarized, with emphasis on the interests and activities of the individuals concerned. The present research activity has evolved mainly from early work on seaweeds and polysaccharides derived from them. Polysaccharides produced by unicellular and other planktonic algae were later added to the list of interests, and this has now expanded to include bacterial exopolysaccharides of special industrial significance, capsular proteoglycans of edaphic algae, and polysaccharides from mosses. The emphasis ranges from fundamental aspects of aquatic and edaphic ecology to practical problems such as biofilm formation. The preparation and use of well defined samples and development of new or improved instrumental methods of characterization of polysaccharides are other special features. The Norwegian Biopolymer Laboratory (NOBIPOL) is a new organization which functions within the University, initiating and coordinating multidisciplinary research programmes centred on polysaccharides.