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  • 1. Cervin, Nicholas T.
    et al.
    Andersson, Linnea
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ng, Jovice Boon Sing
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Olin, Pontus
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wågberg, Lars
    Lightweight and Strong Cellulose Materials Made from Aqueous Foams Stabilized by Nanofibrillated Cellulose2013In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 14, no 2, p. 503-511Article in journal (Refereed)
    Abstract [en]

    A lightweight and strong porous cellulose material has been prepared by drying aqueous foams stabilized with surface-modified nanofibrillated cellulose (NFC). This material differs from other dry, particle stabilized foams in that renewable cellulose is used as stabilizing particles. Confocal microscopy and high speed video imaging show that the octylamine-coated, rod-shaped NFC nanoparticles residing at the air-liquid interface prevent the air bubbles from collapsing or coalescing. Stable wet foams can be achieved at solids content around 1% by weight. Careful removal of the water results in a cellulose-based material with a porosity of 98% and a density of 30 mg cm(-3). These porous cellulose materials have a higher Young's modulus than porous cellulose materials made from freeze-drying, at comparable densities, and have a compressive energy absorption of 56 kJ m(-3) at 80% strain. Measurement with the aid of an autoporosimeter revealed that most pores are in the range of 300 to 500 mu m.

  • 2.
    Kumar, Sugam
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Bhabha Atomic Research Centre, India.
    Yadav, Indresh
    Ray, Debes
    Abbas, Sohrab
    Saha, Debasish
    Aswal, Vinod K.
    Kohlbrecher, Joachim
    Evolution of Interactions in the Protein Solution As Induced by Mono and Multivalent Ions2019In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 20, no 5, p. 2123-2134Article in journal (Refereed)
    Abstract [en]

    The evolution of interactions in the bovine serum albumin (BSA) protein solution on addition of mono and multivalent (di, tri and tetra) counterions has been studied using small-angle neutron scattering (SANS), dynamic light scattering (DLS) and zeta-potential measurements. It is found that in the presence of mono and divalent counterions, protein behavior can be well explained by DLVO theory, combining the contributions of screened Coulomb repulsion with the van der Waals attraction. The addition of mono or divalent salts in protein solution reduces the repulsive barrier and hence the overall interaction becomes attractive, but the system remains in one-phase for the entire concentration range of the salts, added in the system. However, contrary to DLVO theory, the protein solution undergoes a reentrant phase transition from one-phase to a two-phase system and then back to the one-phase system in the presence of tri and tetravalent counterions. The results show that tri and tetravalent (unlike mono and divalent) counterions induce short-range attraction between the protein molecules, leading to the transformation from one-phase to two-phase system. The two-phase is characterized by the fractal structure of protein aggregates. The excess condensation of these higher-valent counterions in the double layer around the BSA causes the reversal of charge of the protein molecules resulting into reentrant of the one-phase, at higher salt concentrations. The complete phase behavior with mono and multivalent ions has been explained in terms of the interplay of electrostatic repulsion and ion induced short-range attraction between the protein molecules.

  • 3.
    Lundborg, Magnus
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Automatic structure determination of regular polysaccharides based solely on NMR spectroscopy2011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 11, p. 3851-3855Article in journal (Refereed)
    Abstract [en]

    The structural analysis of polysaccharides requires that the sugar components and their absolute configurations are determined. We here show that this can be performed based on NMR spectroscopy by utilizing butanolysis with (+)- and (-)-2-butanol that gives the corresponding 2-butyl glycosides with characteristic 1H and 13C NMR chemical shifts. The subsequent computer-assisted structural determination by CASPER can then be based solely on NMR data in a fully automatic way as shown and implemented herein. The method is additionally advantageous in that reference data only have to be prepared once and from a user's point of view only the unknown sample has to be derivatized for use in CASPER.

  • 4. Luo, Jinghui
    et al.
    Mohammed, Inayathulla
    Wärmländer, Sebastian K. T. S.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Hiruma, Yoshitaka
    Gräslund, Astrid
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Abrahams, Jan Pieter
    Endogenous Polyamines Reduce the Toxicity of Soluble A beta Peptide Aggregates Associated with Alzheimer's Disease2014In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 15, no 6, p. 1985-1991Article in journal (Refereed)
    Abstract [en]

    Polyamines promote the formation of the A beta peptide amyloid fibers that are a hallmark of Alzheimer's disease. Here we show that polyamines interact with nonaggregated A beta peptides, thereby reducing the peptide's hydrophobic surface. We characterized the associated conformational change through NMR titrations and molecular dynamics simulations. We found that even low concentrations of spermine, sperimidine, and putrescine fully protected SH-SY5Y (a neuronal cell model) against the most toxic conformational species of AA even at an A beta oligomer concentration that would otherwise kill half of the cells or even more. These observations lead us to conclude that polyamines interfere with the more toxic prefibrillar conformations and might protect cells by promoting the structural transition of A beta toward its less toxic fibrillar state that we reported previously. Since polyamines are present in brain fluid at the concentrations where we observed all these effects, their activity needs to be taken into account in understanding the molecular processes related to the development of Alzheimer's disease.

  • 5.
    Munier, Pierre
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Chimie ParisTech, France.
    Gordeyeva, Korneliya
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fall, Andreas B.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Directional Freezing of Nanocellulose Dispersions Aligns the Rod-Like Particles and Produces Low-Density and Robust Particle Networks2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 5, p. 1875-1881Article in journal (Refereed)
    Abstract [en]

    We show that unidirectional freezing of nanocellulose dispersions produces cellular foams with high alignment of the rod-like nanoparticles in the freezing direction. Quantification of the alignment in the long direction of the tubular pores with X-ray diffraction shows high orientation of cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) at particle concentrations above 0.2 wt % (CNC) and 0.08 wt % (CNF). Aggregation of CNF by pH decrease or addition of salt significantly reduces the particle orientation; in contrast, exceeding the concentration where particles gel by mobility constraints had a relatively small effect on the orientation. The dense nanocellulose network formed by directional freezing was sufficiently strong to resist melting. The formed hydrogels were birefringent and displayed anisotropic laser diffraction patterns, suggesting preserved nanocellulose alignment and cellular structure. Nondirectional freezing of the hydrogels followed by sublimation generates foams with a pore structure and nanocellulose alignment resembling the structure of the initial directional freezing.

  • 6.
    Naseri, Narges
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Deepa, B.
    Mathew, Aji P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Luleå University of Technology, Sweden.
    Oksman, Kristiina
    Girandon, Lenart
    Nanocellulose-Based Interpenetrating Polymer Network (IPN) Hydrogels for Cartilage Applications2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 11, p. 3714-3723Article in journal (Refereed)
    Abstract [en]

    Double cross-linked interpenetrating polymer network (IPN) hydrogels of sodium alginate and gelatin (SA/G) reinforced with 50 wt % cellulose nanocrystals (CNC) have been prepared via the freeze-drying process. The IPNs were designed to incorporate CNC with carboxyl surface groups as a part of the network contribute to the structural integrity and mechanical stability of the hydrogel. Structural morphology studies of the hydrogels showed a three-dimensional (3D) network of interconnected pores with diameters in the range of 10-192 mu m and hierarchical pores with a nanostructured pore wall roughness, which has potential benefits for cell adhesion. Significant improvements in the tensile strength and strain were achieved in 98% RH at 37 degrees C for CNC cross-linked IPNs. The high porosity of the scaffolds (>93%), high phosphate buffered saline (PBS) uptake, and cytocompatibility toward mesenchymal stem cells (MSCs) are confirmed and considered beneficial for use as a substitute for cartilage.

  • 7.
    Navarro, Julien R. G.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Conzatti, Guillaume
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yu, Yang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Fall, Andreas B.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mathew, Renny
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Multicolor Fluorescent Labeling of Cellulose Nanofibrils by Click Chemistry2015In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 16, no 4, p. 1293-1300Article in journal (Refereed)
    Abstract [en]

    We have chemically modified cellulose nanofibrils (CNF) with furan and maleimide groups, and selectively labeled the modified CNF with fluorescent probes; 7-mercapto-4-methylcoumarin and fluorescein diacetate 5-maleimide, through two specific click chemistry reactions: Diels-Alder cycloaddition and the thiol-Michael reaction. Characterization by solid-state C-13 NMR and infrared spectroscopy was used to follow the surface modification and estimate the substitution degrees. We demonstrate that the two luminescent dyes could be selectively labeled onto CNF, yielding a multicolor CNF that was characterized by UV/visible and fluorescence spectroscopies. It was demonstrated that the multicolor CNF could be imaged using a confocal laser scanning microscope.

  • 8. Navarro, Julien R. G.
    et al.
    Wennmalm, Stefan
    Godfrey, Jamie
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Edlund, Ulrica
    Luminescent Nanocellulose Platform: From Controlled Graft Block Copolymerization to Biomarker Sensing2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 3, p. 1101-1109Article in journal (Refereed)
    Abstract [en]

    A strategy is devised for the conversion of cellulose nanofibrils (CNF) into fluorescently labeled probes involving the synthesis of CNF-based macroinitiators that initiate radical polymerilation of methyl acrylate and acrylic acid N-hydroxysuccinimide ester producing a graft block copolymer modified CNF. Finally, a luminescent probe (Lucifer yellow derivative) was labeled onto the modified CNF through an amidation reaction. The surface modification steps were :verified with solid-state C-13 nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy. Fluorescence correlation spectroscopy (FCS) confirmed the successful labeling of the CNF; the CNF have a hydrodynamic radius of about 700 nm with an average number of dye molecules per fibril of at least 6600. The modified CNF was also imaged with confocal laser scanning microscopy. Luminescent CNF proved to be viable biomarkers and allow for fluorescence-based optical detection of CNF uptake and distribution in organisms such as crustaceans. The luminescent CNF were exposed to live juvenile daphnids and microscopy analysis revealed the presence of the luminescent CNF all over D. magna's alimentary canal tissues without any toxicity effect leading to the death of the specimen.

  • 9.
    Nordmark, Eva-Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Zhennai
    Huttunen, Eine
    Widmalm, Göran
    Structural studies of an exopolysaccharide produced by Streptococcus thermophilus THS2005In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 1, p. 105-108Article in journal (Refereed)
    Abstract [en]

    The structure of an extracellular polysaccharide (EPS) from Streptococcus thermophilus THS has been determined. A combination of component analysis, methylation analysis and NMR spectroscopy shows that the polysaccharide is composed of pentasaccharide repeating units. Sequential information was obtained by two-dimensional 1H,1H−NOESY and 1H,13C−HMBC NMR experiments. NMR data indicate different mobility within the EPS with a stiffer backbone and a more flexible side-chain.

  • 10.
    Nordmark, Eva-Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Yang, Zhennai
    Huttunen, Eine
    Widmalm, Göran
    Structural studies of the exopolysaccharide produced by Propionibacterium freudenreichii ssp. shermanii JS2005In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 6, no 1, p. 521-523Article in journal (Refereed)
  • 11. Sarkar, Anita
    et al.
    Fontana, Carolina
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Imberty, Anne
    Perez, Serge
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Conformational Preferences of the O-Antigen Polysaccharides of Escherichia coli O5ac and O5ab Using NMR Spectroscopy and Molecular Modeling2013In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 14, no 7, p. 2215-2224Article in journal (Refereed)
    Abstract [en]

    Escherichia coli serogroup O5 comprises two different subgroups (O5ab and O5ac), which are indiscernible from the point of view of standard immunological serotyping. The structural similarities between the O-antigen polysaccharides (PSs) of these two strains are remarkable, with the only difference being the glycosidic linkage connecting the biological tetrasaccharide repeating units. In the present study, a combination of NMR spectroscopy and molecular modeling methods were used to elucidate the conformational preferences of these two PSs. The NMR study was based on the analysis of intra- and inter-residue proton-proton distances using NOE build-up curves. Molecular models of the repeating units and their extension to polysaccharides were obtained, taking into account the conformational flexibility as assessed by the force field applied and a genetic algorithm. The agreements between experimentally measured and calculated distances could only be obtained by considering an averaging of several low energy conformations observed in the molecular models.

  • 12.
    Svensson, Mona V.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Zhang, Xue
    Huttunen, Eine
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structural studies of the capsular polysaccharide produced by Leuconostoc mesenteroides ssp. cremoris PIA22011In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 12, no 7, p. 2496-2501Article in journal (Refereed)
    Abstract [en]

    The structure of the capsular polysaccharide (CPS) produced by Leuconostoc mesenteroides ssp. cremoris PIA2 has been determined using component analysis and NMR spectroscopy. 1H and 13C resonances were assigned using 2D NMR experiments, and sequential information was obtained by 1H,1H-NOESY and 1H,13C-HMBC experiments. The CPS consists of linear pentasaccharide repeating units with the following structure: →3)-β-d-Galf-(1→6)-β-d-Galf-(1→2)-β-d-Galf-(1→6)-β-d-Galf-(1→3)-β-d-Galp-(1→, in which four out of the five sugar residues have the furanoid ring form, a structural entity found in bacteria but not in mammals. The analysis of the magnitude of the homonuclear three-bond coupling constants of the anomeric protons for the five-membered sugar rings indicates that the sugar residues substituted at a primary carbon atom show one kind of conformational preferences, whereas those substituted at a secondary carbon atom show another kind of conformational preferences.

  • 13. Zhou, Yaxin
    et al.
    Saito, Tsuguyuki
    Bergstrom, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). The University of Tokyo, Japan.
    Isogai, Akira
    Acid-Free Preparation of Cellulose Nanocrystals by TEMPO Oxidation and Subsequent Cavitation2018In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 19, no 2, p. 633-639Article in journal (Refereed)
    Abstract [en]

    Softwood bleached kraft pulp (SBKP) and microcrystalline cellulose (MCC) were oxidized using a 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated system. The TEMPO-oxidized SBKP prepared with 10 mmol/g NaClO (SBKP-10) had a higher mass recovery ratio and higher carboxylate content than the other prepared celluloses including the TEMPO-oxidized MCCs. The SBKP-10 was then exposed to cavitation-induced forces through sonication in water for 10-120 min to prepare aqueous dispersions of needle-like TEMPO-oxidized cellulose nanocrystals (TEMPO-CNCs) with homogeneous width of 3.5 to 3.6 nm and average lengths of similar to 200 nm. The average chain lengths of the cellulose molecules that make up the TEMPO-CNCs were less than half the average lengths of the TEMPO-CNCs. Compared with conventional CNCs prepared by acid hydrolysis, the TEMPO-CNCs prepared by the acid-free and dialysis-free process exhibited higher mass recovery ratios, significantly higher amounts of surface anionic groups, and smaller and more homogeneous widths.

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