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Alginates consist of distinct blocks with different physical properties. This short review focuses on research carried out in Trondheim related to the early discovery of the block structure, their isolation, their different chemical and physical properties, and how they recently are utilized in diblock polysaccharides to obtain new nanostructuring properties.

Renewable resources can provide a range of different polysaccharide blocks that can be used to prepare new types of stimuli-responsive polysaccharide-based block copolymers. Alginates are natural polysaccharides widely used as biomaterials. Functional properties depend on the content and distribution of the two 4-linked monomers (β-D-mannuronate (M) and α-L-guluronate (G)). Blocks of L-guluronate (Gn) are responsible for cooperative binding of calcium ions and hydrogel formation. Incorporation of such blocks in block polysaccharide copolymers would represent a new class of engineered, Ca-sensitive biomacromolecules. Dioxyamines and dihydrazides have recently been shown to be well suited for preparation of block polysaccharide structures. Here we first show that when applied to alginate blocks (Gn and Mn) the two types are both very reactive, but the detailed distribution of acyclic (E)- and (Z)-forms and cyclic N-pyranosides, reaction kinetics, conjugate stability, and the rate of Schiff base reduction with α-picoline borane differ considerably, also compared to other polysaccharides. Hence, alginate specific protocols were developed. The linkers introduce a highly flexible joint in otherwise semiflexible Gn-based diblocks. This was demonstrated by SEC-MALS using a symmetrical Gn-b-Gn diblock, which in solution can best be described according to a broken rod model. Ca-Induced self-assembly of Gn-b-dextran diblocks was studied by dynamic light scattering, demonstrating that well defined nanoparticles could be prepared for certain combinations of chain lengths. Taken together, this approach provides a new class of engineered, stimuli-responsive block polysaccharide copolymers solely based on natural resources.

Schizophyllan, a triple helical polysaccharide, exhibits cooperative order-disorder transition (CODT) in aqueous solutions. The transition transforms the ordered structure (triple helix I) formed between the branched side chains and solvent molecules into the disordered structure (triple helix II) without dissociation of the triple helix. The CODT behaviors in H

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.

Injectable, self-setting calcium phosphate cements (CPCs) are synthetic bone substitutes considered favorable for the repair and regeneration of bone due to their osteocompatibility and unique handling properties. However, their clinical applicability can be compromised due to insufficient cohesion upon injection into the body coupled with poor degradation rates that restricts new bone formation. Consequently, carboxymethyl cellulose (CMC) was incorporated into CPC formulations to improve their cohesion and injectability while poly (D,L -lactic-co-glycolic acid) (PLGA) porogens were added to introduce macroporosity and improve their biodegradation rate. Like most biomaterials, CPCs are gamma irradiated before clinical use to ensure sufficient sterilization. However, it is well known that gamma irradiation also reduces the molecular weight of CMC and PLGA via chain scission, which affects their material properties. Therefore, the aim of this study is to measure the effect that gamma irradiation has on the molecular weight of CMC at varying doses of 15, 40, or 80 kGy and investigate how this affects the handling (i.e., injectability, cohesion, washout, and setting times) and in vitro degradation behavior of CPC formulations. Results reveal that the molecular weight of CMC decreases with increasing gamma irradiation dose, thereby reducing the viscosifying capabilities of CMC, which causes CPCs to deteriorate more readily. Further, the addition of CMC seems to inhibit the degree of phase transformation during cement setting while the subsequent reduction in molecular weight of PLGA after gamma irradiation improves the in vitro degradation rate of CPCs due to the faster degradation rate of low molecular weight PLGA. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2216-2228, 2019.

Most polysaccharides used in polysaccharide-based block copolymers are attached to the second block through the reducing end, due to the few and highly polysaccharide specific non-reducing end (NRE) functionalisation methods available. Chitin oligomers, prepared by nitrous acid degradation of chitosan (AnM) can, however, be selectively oxidised by periodate since they only possess a single vicinal diol in the NRE residue. Here, we show that both aldehydes formed after oxidation are highly reactive towards bifunctional oxyamines and hydrazide linkers. Sub-stochiometric amounts of linkers resulted in conjugation of AnM oligomers through both chain termini to yield a discrete distribution of 'polymerised' oligomers. Such chitin-based block polymers were, in contrast to chitins of the same chain lengths, water-soluble. Oxidised AnM oligomers, functionalised at both termini can also enable the preparation of more complex block polysaccharides such as ABA- or ABC-type.

This study reports a green, inexpensive, and highly versatile procedure to synthesize well-dispersed transition-metal nanoparticles anchored on carbon supports. The resulting metal loadings are 26 wt % or above. Achieving both these properties simultaneously has been difficult with established synthesis methods of carbon-supported metal catalysts, such as impregnation and deposition-precipitation. Herein, low-molar-mass sodium alginate with high guluronate content was ion-exchanged with transition-metal ions, followed by a pyrolysis step at 500 °C. The investigated transition-metal ions were Fe3+, Co2+, Ni2+, and Cu2+. The alginate’s properties and interaction with the transition-metal ions greatly influenced the pyrolyzed material’s characteristics, whereas the observed metal particle size was found to negatively correlate with the metal’s melting point. The pyrolyzed Fe-alginate was tested as a catalyst for the Fischer−Tropsch synthesis and exhibited an iron time yield of 885 μmolCO h−1 g−1 , which is among the highest activities reported in the literature. The activity is mainly attributed to the iron nanoparticle size achieved by the reported synthesis procedure, and the improved olefin selectivity is ascribed to the sodium and sulfur that originates from the alginate and iron precursor, respectively.

International audience; Diblock oligosaccharides based on renewable resources allow for a range of new but, so far, little explored biomaterials. Coupling of blocks through their reducing ends ensures retention of many of their intrinsic properties that otherwise are perturbed in classical lateral modifications. Chitin is an abundant, biodegradable, bioactive, and self-assembling polysaccharide. However, most coupling protocols relevant for chitin blocks have shortcomings. Here we exploit the highly reactive 2,5-anhydro-D-mannose residue at the reducing end of chitin oligomers obtained by nitrous acid depolymerization. Subsequent activation by dihydrazides or dioxyamines provides precursors for chitin-based diblock oligosaccharides. These reactions are much faster than for other carbohydrates, and only acyclic imines (hydrazones or oximes) are formed (no cyclic N-glycosides). α-Picoline borane and cyanoborohydride are effective reductants of imines, but in contrast to most other carbohydrates, they are not selective for the imines in the present case. This could be circumvented by a simple two-step procedure. Attachment of a second block to hydrazide- or aminooxy-functionalized chitin oligomers turned out to be even faster than the attachment of the first block. The study provides simple protocols for the preparation of chitin-b-chitin and chitin-b-dextran diblock oligosaccharides without involving protection/deprotection strategies.

Xanthan belongs to a special class of bacterial polysaccharides by having on one hand a oligosaccharide repeating unit and on the other higher order structures resulting in an unusually large chain rigidity. It is further characterized with an ionic strength, pH, and solvent-dependent cooperative conformational (order-disorder) transition. The ordered state is predominantly double-stranded, but partially denatured, fully or aggregated forms may coexist, depending on the sample history. In this chapter, we have reviewed the literature on chemical modifications of xanthan, and the resulting physical properties resulting from the modifications. It appears that research has been carried out without fully recognizing the complex conformational issues and possible degradations (depolymerizations) accompanying the modifications of xanthan. However, in recent years this issue has been more systematically dealt with, including studies on hydrophobization in both the ordered and disordered state.

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.

The sensitivity of microorganisms to low pH can be utilized in food protection by preparing coatings based on macromolecular acids. Due to limited diffusivity of macromolecules low pH occurs primarily at the surface, while the interior parts of the food remain unaffected. This principle is demonstrated using food approved alginic acid in various types of coatings (aqueous, emulsions, dispersions, dry coating) on a wide range of foods including meat, fish, chicken, shrimp and boiled rice. Significant delay or inhibition of the natural flora is generally demonstrated, particularly when exposed to ‘temperature abuse’. Specifically, we show that the coatings reduce or inhibit regrowth of pathogens (Bacillus cereus, B. weihenstephanensis, Listeria monocytogenes serotype 1 and Staphylococcus aureus). In special cases like boiled rice, alginic acid may largely replace acetic acid for acidification and preservation, as demonstrated studying regrowth of added spores of B. cereus. Most formulations allow easy removal prior to further processing (cooking, frying). Temporary side effects such as ‘acid cooking’ obtained for high acid concentrations on sensitive surfaces (e.g. salmon) disappear during processing, recovering the normal taste and texture. The coating is hence suitable for a large variety of foods. © 2018. This is the authors’ accepted and refereed manuscript to the article. Locked until 16.8.2019 due to copyright restrictions. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

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.

β‐1,3‐d‐glucan with different degrees of branching were obtained by selectively and gradually removing side chains from schizophyllan, a water‐soluble triple helical polysaccharide, using the Smith degradation. Size exclusion chromatography combined with a multi‐angle light scattering detection was performed in aqueous 0.1 M NaCl. The degree of branching decreased after the Smith degradation, while the molar mass distributions were almost unchanged. The molecular conformation of the Smith‐degraded β‐1,3‐d‐glucan was analyzed on the basis of the molar mass dependency of the radius gyration, and found to be comparable to the original triple helix of schizophyllan. Differential scanning calorimetry in deuterium oxide–hexadeuterodimethylsulfoxide mixtures was performed to investigate the effects of the degree of branching on the cooperative order‐disorder transition. Removal of side chains affects both the transition temperature and transition enthalpy. The ordered structure is formed by the residual side chains in the triplex unit, so that the linear cooperative system of the triplex is maintained after the Smith degradation. Locked until 12.06.2020 due to copyright restrictions. This is the peer reviewed version of an article, which has been published in final form at [DOI:10.1002/bip.23315 ]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.

Alginate is a linear polysaccharide from brown algae consisting of 1,4-linked β-D-mannuronic acid (M) and α-L-guluronic acid (G) arranged in M, G, and mixed MG blocks. Alginate was assumed to be indigestible in humans, but bacteria isolated from fecal samples can utilize alginate. Moreover, genomes of some human gut microbiome–associated bacteria encode putative alginate-degrading enzymes. Here, we genome-mined a polysaccharide lyase family 6 alginate lyase from the gut bacterium Bacteroides cellulosilyticus (BcelPL6). The structure of recombinant BcelPL6 was solved by X-ray crystallography to 1.3 Å resolution, revealing a single-domain, monomeric parallel β-helix containing a 10-step asparagine ladder characteristic of alginate-converting parallel β-helix enzymes. Substitutions of the conserved catalytic site residues Lys-249, Arg-270, and His-271 resulted in activity loss. However, imidazole restored the activity of BcelPL6-H271N to 2.5% that of the native enzyme. Molecular docking oriented tetra-mannuronic acid for syn attack correlated with M specificity. Using biochemical analyses, we found that BcelPL6 initially releases unsaturated oligosaccharides of a degree of polymerization of 2–7 from alginate and polyM, which were further degraded to di- and trisaccharides. Unlike other PL6 members, BcelPL6 had low activity on polyMG and none on polyG. Surprisingly, polyG increased BcelPL6 activity on alginate 7-fold. LC–electrospray ionization–MS quantification of products and lack of activity on NaBH4-reduced octa-mannuronic acid indicated that BcelPL6 is an endolyase that further degrades the oligosaccharide products with an intact reducing end. We anticipate that our results advance predictions of the specificity and mode of action of PL6 enzymes. Author’s Choice—Final version open access under the terms of the Creative Commons CC-BY license

Injectable, self-setting calcium phosphate cements (CPCs) are synthetic bone substitutes considered favorable for the repair and regeneration of bone due to their osteocompatibility and unique handling properties. However, their clinical applicability can be compromised due to insufficient cohesion upon injection into the body coupled with poor degradation rates that restricts new bone formation. Consequently, carboxymethyl cellulose (CMC) was incorporated into CPC formulations to improve their cohesion and injectability while poly (

Tomofuji Y., Yoshiba K., Christensen B., et al. Single-chain conformation of carboxylated schizophyllan, a triple helical polysaccharide, in dilute alkaline aqueous solution. Polymer, 185, 121944. © 2019 Elsevier Ltd https://doi.org/10.1016/j.polymer.2019.121944., Synchrotron-radiation small-angle X-ray scattering measurements were carried out for a schizophyllan (SPG) sample with the weight-average molar mass Mw of 340 kg mol−1 and five carboxylated SPG (sclerox) samples with different degrees of substitution (DS) ranging from 0.18 to 0.45 in 200 mM aqueous NaOH including 10 mM NaCl to determine Mw, the second virial coefficient A2, the particle scattering function P(q), and the radius of gyration ⟨S2⟩. Positive A2 values indicated that this alkaline solvent was a good solvent for all polysaccharide samples investigated. The resultant Mw values (~100 kg mol−1) were much smaller than that for the trimer in aqueous NaCl at neutral pH, indicating all SPG and sclerox samples dissolved as single chains in the alkaline solvent. Both P(q) and ⟨S2⟩ were consistently explained by the wormlike chain model. The obtained parameters were almost independent of DS. While the chain stiffness (12–18 nm) in terms of the Kuhn segment length or twice the persistence length was similar to those for the other single chain polysaccharides, the helix pitch per residue (0.1 nm) was quite smaller than the trimer state (0.3 nm). This shrunken main-chain helical structure is most likely due to hydrophobic interactions between helical main chain and side groups.

Carboxylated schizophyllan (“sclerox”) is a chemically modified polysaccharide obtained by partial periodate oxidation and subsequent chlorite oxidation of schizophyllan, a water-soluble neutral polysaccharide having a β-1,3-linked glucan backbone and a β-1,6-linked d-glucose residue side chain at every third residue of the main chain. The triple helix of schizophyllan in water has a cooperative order–disorder transition associated with the side chains. The transition is strongly affected by the presence (mole fraction) of dimethylsulfoxide (DMSO). In the present study, the solvent effects on the order–disorder transition of sclerox with different degrees of carboxylation (DS) in water–DMSO mixtures were investigated with differential scanning calorimetry and optical rotation. The transition temperature (Tr) and transition enthalpy (ΔHr) strongly depended on the mole fraction of DMSO (xD). Data were further analyzed with the statistical theory for the linear cooperative transition, taking into account the solvent effect, where DMSO molecules are selectively associated with the unmodified side chains. The modified side chain does not contribute to the transition; hence, ΔHr decreases with increasing DS. The dependence of Tr on the DMSO content becomes weaker than that for unmodified schizophyllan. The theoretical analyses indicated that the number of sites binding with the DMSO molecule and the successive ordered sequence of the ordered unit of the triple helix are changed by carboxylation. © American Chemical Society 2018. This is the authors accepted and refereed manuscript to the article. Locked until 3.6.2019 due to copyright restrictions.

The aim of this paper was to perform a comprehensive characterization of polysaccharides isolated from the interior (IOI) and exterior (IOE) parts of the fungus Inonotus obliquus. Pre-extraction with DCM and MeOH, followed by water and alkali extraction and ethanol precipitation gave two water extracts and two alkali extracts. Neutral and acidic polysaccharide fractions were obtained after anion-exchange chromatography of the water extracts. The neutral polysaccharides (60–73 kDa) were heterogeneous and branched and consisted of a (1 → 3)-linked β-Glc backbone with (1 → 6)-linked kinks in the chain at approximately every fifth residue, with branches of (1 → 6)-linked β-Glc in addition to substantial amounts of (1 → 6)-linked α-Gal with 3-O-methylation at about every third Gal residue. The acidic polysaccharide fractions (10–31 kDa) showed similar structural motifs as the neutral fractions differing mainly by the presence of (1 → 4)-linked α-GalA and α-GlcA. β-Xyl, α-Man and α-Rha were also present in varying amounts in all fractions. No major structural differences between the IOI and IOE fractions were observed. An alkaline polysaccharide fraction (>450 kDa) was obtained from the IOI alkali extract, and consisted mainly of (1 → 3)- and (1 → 6)-linked β-Glc and (1 → 4)-linked β-Xyl. Several of the fractions showed in vitro immunomodulatory effect by increasing NO production in the murine macrophage and dendritic cell lines J774.A1 and D2SC/1. Most fractions managed to increase NO production only at the highest concentration tested (100 μg/ml), while the neutral fraction IOE-WN activated potent NO production at 10 μg/ml and was considered the most promising immunomodulating fraction in this study.

Biomaterials based on peptide-coupled alginates must provide both optimal biological environments and tuneable stability/degradation profiles. The present work investigates the degradation pattern and kinetics of peptide-coupled alginates prepared via the periodate oxidation reductive amination route. Alginates degrade slowly (non-enzymatically) under physiological conditions by acid-catalysed hydrolysis and alkali-catalysed β-elimination, both operating simultaneously but dominated by the latter. While periodate oxidation alone largely increases the rate of β-elimination, substitution restores the susceptibility towards β-elimination to that of the parent alginate. For acid hydrolysis the rate of depolymerization is proportional to the degree of substitution, being approximately one order of magnitude larger than the parent alginate, but still lower than for the corresponding materials with fully reduced dialdehydes. Results also suggest a composition-dependent preference for substitution at C2 or C3. These results demonstrate how the various chemistries introduced by the coupling provide useful means to tune the biodegradability profiles. © 2016. 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/

Alginate-based biomaterials and medical devices are commonly subjected to γ-irradiation as a means of sterilization, either in the dry state or the gel (hydrated) state. In this process the alginate chains degrade randomly in a dose-dependent manner, altering alginates’ material properties. The addition of free radical scavenging amino acids such as histidine and phenylalanine protects the alginate significantly against degradation, as shown by monitoring changes in the molecular weight distributions using SEC-MALLS and determining the pseudo first order rate constants of degradation. Tris buffer (0.5 M), but not acetate, citrate, or phosphate buffers had a similar effect on the degradation rate. Changes in pH itself had only marginal effects on the rate of alginate degradation and on the protective effect of amino acids. Contrary to previous reports, the chemical composition (M/G profile) of the alginates, including homopolymeric mannuronan, was unaltered following irradiation up to 10 kGy. © American Chemical Society 2014. This is the authors accepted and refereed manuscript to the article.

Degradation of alginate remains a critical issue to allow predictable biological performance upon implantation of alginate-based materials. Therefore, the objective of the current study is to compare the effects of gamma-irradiation (dry state, 20-80 kGy), partial (1 and 4%) periodate oxidation (aqueous solution), and autoclaving (dry state) on the molecular weight of alginate, as well as the degradation behavior of alginate-based composites. The results show that gamma-irradiation is by far the most destructive technique characterized by strongly reduced molecular weights and rapid loss of composite integrity upon soaking in simulated body fluid. Partial periodate oxidation is less destructive as characterized by more moderate decreases in molecular weight, but the production of hydrolytically labile bonds compromises the integrity of the resulting composites. Autoclaving is shown to be a powerful tool to reduce the molecular weight of alginate in a controllable and mild manner without compromising the integrity of the resulting alginate-hydroxyapatite composites, simply by increasing the number of repetitive autoclaving cycles.

The molecular weight distributions of artificially aged transformer papers were studied using SEC–MALLS with 0.5 % DMAc/LiCl as solvent, providing chain length distributions and averages. The slow dissolution and presence of non-cellulosic contaminants tend in some cases to introduce errors in the DPw estimates, and a modified data processing procedure was developed to correct for extraneous scattering. Data were compared to the intrinsic viscosities obtained in 0.5 M Cuen and the ‘viscosimetric DP’ calculated thereof according to ISO 5351. DPvisc was 2–3 times lower than the weight average DP (DPw), but closer to or slightly above the number average DP (DPn) obtained by SEC–MALLS in the case of pure cellulose. Ageing of transformer papers were in some cases associated with changes in the polydispersity (DPw/DPn). The apparent degradation rate (defined as δ(1/DP)/δt) gradually decreased with time, resulting in a tendency for a ‘level-off’ DP in the range 200–300 for DPvisc and DPn, and roughly 1,000 for DPw.

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.

Three water-soluble, non-ionic extracellular polysaccharides (EPS) obtained from lactic acid bacteria (S. thermophilus THS, L. helveticus K16 and S. thermophilus ST1) were subjected to a comparative study by means of multidetector size-exclusion chromatography, providing distributions and averages of molar masses, radii of gyration and intrinsic viscosities. All polysaccharides displayed random coil character. Further analysis of the data reveals differences in chain stiffness and extension that could be well correlated to structural features. The calculated persistence lengths ranged from 5 to 10 nm and fall within the range typical for many single-stranded bacterial or plant polysaccharides. The ST1 polysaccharide had the highest molar mass but the lowest persistence length, which is attributed to the presence of the flexible (1→6)-linkage in the main chain.

Alginates in the format of scaffolds provide important functions as materials for cell encapsulation, drug delivery, tissue engineering and wound healing among others. The method for preparation of alginate-based foams presented here is based on homogeneous, ionotropic gelation of aerated alginate solutions, followed by air drying. The method allows higher flexibility and better control of the pore structure, hydration properties and mechanical integrity compared to foams prepared by other techniques. The main variables for tailoring hydrogel properties include operational parameters such as degree of aeration and mixing times and concentration of alginate, as well as macromolecular properties such as the type of alginate (chemical composition and molecular weight distribution). Exposure of foams to γ-irradiation resulted in a dose-dependent (0-30 kGy) reduction in molecular weight of the alginate and a corresponding reduction in tensile strength of the foams.

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.

An isothermal microcalorimeter has been used to study ageing of oil impregnated kraft paper. Under the assumption that the heat flow is proportional to the ageing rate of paper it is found that activation energy seems to be lower for oxidation than for hydrolysis. This observation corresponds well with results obtained by traditional ageing methods. The results have also been confirmed by measuring the changes in DP of the samples used in the calorimetric measurements. Comparing degradation of aged and unaged oil impregnated paper in air gave a higher heat flow for the unaged paper, but the activation energy for the processes remained the same. The process was also studied with another cellulosic material and in addition varying size of the sample holder of the calorimeter, giving similar results. Hence, since the microcalorimeter appears to give the same qualitative ageing characteristics for oxidation and hydrolysis as more time consuming methods, calorimeter could be a useful tool for quick ageing investigations.

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.

A limited degree (typically 1-20%) of periodate oxidation of polysaccharides may give rise to derivatives with entirely altered chemical and physical properties. Notably, the ring opening caused by periodate leads to the formation of highly flexible 'hinges' in otherwise rather semiflexible or rigid structures. This review highlights selected examples with the main focus on periodate oxidation of alginates, chitosans, hyaluronan, scleroglucan/schizophyllan, and cellulose.

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.

Summary The industrially widely used polysaccharide alginate is a co-polymer of β-d-mannuronic acid and α-l-guluronic acid (G), and the G residues originate from a polymer-level epimerization process catalysed by mannuronan C-5-epimerases. In the genome of the alginate-producing bacterium Azotobacter vinelandii genes encoding one periplasmic (AlgG) and seven secreted such epimerases (AlgE1–7) have been identified. Here we report the generation of a strain (MS163171) in which all the algE genes were inactivated by deletion (algE1–4 and algE6–7) or interruption (algE5). Shake flask-grown MS163171 produced a polymer containing less than 2% G (algG still active), while wild-type alginates contained 25% G. Interestingly, addition of proteases to the MS163171 growth medium resulted in a strong increase in the chain lengths of the alginates produced. MS163171 was found to be unable to form functional cysts, which is a desiccation-resistant differentiated form developed by A. vinelandii under certain environmental conditions. We also generated mutants carrying interruptions in each separate algE gene, and a strain containing algE5 only. Studies of these mutants indicated that single algE gene inactivations, with the exception of algE3, did not affect the fractional G content much. However, for all strains tested the alginate composition varied somewhat as a response to the growth conditions.

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.