| 1. |
- Hedlund, Artur, et al.
(författare)
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Microstructures of cellulose coagulated in water and alcohols from 1-ethyl-3-methylimidazolium acetate : contrasting coagulation mechanisms
- 2019
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 26:3, s. 1545-1563
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Coagulation of cellulose solutions is a process whereby many useful materials with variable microstructures and properties can be produced. This study investigates the complexity of the phase separation that generates the structural heterogeneity of such materials. The ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]), and a co-solvent, dimethylsulfoxide (DMSO), are used to dissolve microcrystalline cellulose in concentrations from 5 to 25 wt%. The solutions are coagulated in water or 2-propanol (2PrOH). The coagulated material is then washed and solvent exchanged (water → 2PrOH → butanone → cyclohexane) in order to preserve the generated microstructures upon subsequent drying before analysis. Sweep electron microscopy images of 50 k magnification reveal open-pore fibrillar structures. The crystalline constituents of those fibrils are estimated using wide-angle X-ray spectroscopy and specific surface area data. It is found that the crystalline order or crystallite size is reduced by an increase in cellulose concentration, by the use of the co-solvent DMSO, or by the use of 2PrOH instead of water as the coagulant. Because previous theories cannot explain these trends, an alternative explanation is presented here focused on solid–liquid versus liquid–liquid phase separations. Graphical abstract: [Figure not available: see fulltext.].
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| 2. |
- Andersson, Erika, et al.
(författare)
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Generation and properties of organic colloids extracted by water from the organic horizon of a boreal forest soil
- 2023
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Ingår i: Geoderma. - : Elsevier BV. - 0016-7061. ; 432
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Tidskriftsartikel (refereegranskat)abstract
- Organic colloids are an important part of dissolved organic matter (DOM) yet many of their properties remain elusive. The main aims of this study were to assess how the colloidal properties of DOM extracted with water from an organic boreal soil horizon varied with the extraction protocol, and thereby provide insight into the nature of the DOM colloids and develop a mechanistic understanding of how the colloids were generated from the parent soil aggregates. This was accomplished by systematic variations of extraction temperature (4 °C–100 °C), time, mechanical agitation, and pH, together with a combination of chemical analyses, and light and X-ray scattering. Our results agreed with the previous identification of two main colloidal DOM species, one fractal cluster and a second, smaller colloidal DOM species described as chains or coils. Fractal clusters completely dominated the colloidal DOM in extracts from our soil at room temperature and below. Colloidal coils only existed in DOM extracted above room temperature, and their amount increased significantly between 50 °C–100 °C. Moreover, the temperature variation indicated that the fractal clusters partly dissolved into colloidal coils at elevated temperatures. Mechanical agitation at 4 °C significantly increased the amount of DOM extracted, increasing the concentrations of both fractal clusters and low-molecular weight organic compounds. While the clusters were extracted from agitated and non-agitated soil suspensions, the low molecular weight organics were mainly released by agitation. Based on the experimental observations, we propose a conceptual model where parent soil aggregates contain the fractal clusters in mobile and occluded forms, and that the occluded clusters co-exist with occluded low molecular weight organics. These occluded forms may be released by mechanical forces, increasing pH and temperature. At higher temperatures, the soil aggregates and the fractal clusters start to break up, and subsequently individual colloidal coils, presumably carbohydrates, disperse in the water phase. The model explains the origin and properties of the fractal clusters that completely dominate the colloidal DOM extracted from our soil at room temperature and below.
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| 3. |
- Lecerof, David, et al.
(författare)
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Metal binding to Bacillus subtilis ferrochelatase and interaction between metal sites.
- 2003
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Ingår i: Journal of Biological Inorganic Chemistry. - : Springer Science and Business Media LLC. - 1432-1327 .- 0949-8257. ; 8:4, s. 452-458
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Tidskriftsartikel (refereegranskat)abstract
- Ferrochelatase, the terminal enzyme in heme biosynthesis, catalyses metal insertion into protoporphyrin IX. The location of the metal binding site with respect to the bound porphyrin substrate and the mode of metal binding are of central importance for understanding the mechanism of porphyrin metallation. In this work we demonstrate that Zn2+, which is commonly used as substrate in assays of the ferrochelatase reaction, and Cd2+, an inhibitor of the enzyme, bind to the invariant amino acids His183 and Glu264 and water molecules, all located within the porphyrin binding cleft. On the other hand, Mg2+, which has been shown to bind close to the surface at 7 Å from His183, was largely absent from its site. Activity measurements demonstrate that Mg2+ has a stimulatory effect on the enzyme, lowering KM for Zn2+ from 55 to 24 µM. Changing one of the Mg2+ binding residues, Glu272, to serine abolishes the effect of Mg2+. It is proposed that prior to metal insertion the metal may form a sitting-atop (SAT) complex with the invariant His-Glu couple and the porphyrin. Metal binding to the Mg2+ site may stimulate metal release from the protein ligands and its insertion into the porphyrin.
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| 4. |
- Segad, Mo, et al.
(författare)
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Microstructural and Swelling Properties of Ca and Na Montmorillonite: (In Situ) Observations with Cryo-TEM and SAXS
- 2012
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:13, s. 7596-7601
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous dispersions of pure sodium and calcium smectite clays with platelet sizes on the order of a few hundred nanometers were characterized using a combination of cryo-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS). With monovalent sodium counterions the clay is dispersed as individual platelets, as seen by cryo-TEM, that order into a nematic phase. From SAXS a one-dimensional swelling of the day in water is observed with the characteristic spacing h(s) = delta/phi(c), where h(s) is the separation between the platelets, delta = 1 nm is the effective platelet thickness, and phi(c) is the clay volume fraction in the sample. In calcium montmorillonite, on the other hand, cryo-TEM images dearly show the presence of tactoids, where the platelets have aggregated into stacks with a periodic spacing of 2 nm. From imaging a large number of tactoids the distribution function f(N) far the number of platelets per tactoid was estimated, and the average number (N) approximate to 10. The characteristic 2 nm spacing as well as the small number of platelets per tactoid was also confirmed by SAXS. The present study demonstrates that cryo-TEM, with carefully prepared specimen, is a very useful technique to characterize clay dispersions, particularly in aggregated systems.
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| 5. |
- Kuczera, Stefan, et al.
(författare)
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Two dimensional oblique molecular packing within a model peptide ribbon aggregate
- 2020
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Ingår i: Chemphyschem. - : Wiley. - 1439-4235 .- 1439-7641. ; 21:14, s. 1519-1523
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Tidskriftsartikel (refereegranskat)abstract
- A(10)K (A=alanine, K=lysine) model peptides self-assemble into ribbon-like beta-sheet aggregates. Here, we report an X-ray diffraction investigation on a flow-aligned dispersion of these self-assembly structures. The two-dimensional wide-angle X-ray scattering pattern suggests that peptide pack in a two-dimensional oblique lattice, essentially identical to the crystalline packing of polyalanine, A(n)(forn>4). One side of the oblique unit cell, corresponding to the anti-parallel beta-sheet, is oriented along the ribbon's axis. Together with recently published small angle X-ray scattering data of the same system, this work thus yields a detailed description of the self-assembled ribbon aggregates, down to the molecular length scale. Notably, our results highlight the importance of the crystalline peptide packing within its self-assembly aggregates, which is often neglected.
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| 6. |
- Bernin, Diana, 1979, et al.
(författare)
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Real time MRI to elucidate the functionality of coating films intended for modified release
- 2019
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Ingår i: Journal of Controlled Release. - : Elsevier BV. - 0168-3659 .- 1873-4995. ; 311-312, s. 117-124
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Tidskriftsartikel (refereegranskat)abstract
- Polymer films based on mixtures of ethyl cellulose (EC) and hydroxypropyl cellulose (HPC) have been widely used to coat pellets and tablets to modify the release profile of drugs. For three different EC/HPC films we used 1H and 19F MRI in combination with a designed release cell to monitor the drug, polymer and water in 5 dimensional (5D) datasets; three spatial, one diffusion or relaxation and a temporal dimension, in real time. We observed that the water inflow through the films correlated with the initiation of the dissolution of the drug in the tablet beneath the film. Leaching of the pore forming HPC further accelerated water penetration and resulted in a drug release onset after a hydrostatic pressure was generated below the film indicated by positional changes of the film. For the more permeable film, both water ingress and drug egress showed a large variability of release over the film surface indicating the heterogeneity of the system. Furthermore, the 1H diffusion dataset revealed the formation of a gel layer of HPC at the film surface. We conclude that the setup presented provides a significant level of details, which are not achieved with traditional methods.
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| 7. |
- Viitala, Lauri, et al.
(författare)
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Shape and Phase Transitions in a PEGylated Phospholipid System
- 2019
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 35:11, s. 3999-4010
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Tidskriftsartikel (refereegranskat)abstract
- Poly(ethylene glycol) (PEG) polymers and PEG-conjugated lipids are widely used in bioengineering and drug transport applications. A PEG layer in a drug carrier increases hydrophilic repulsion, inhibits membrane fusion and serum opsonin interactions, and prolongs the storage and circulation time. It can also change the carrier shape and have an influence on many properties related to the content release of the carrier. In this paper, we focus on the physicochemical effects of PEGylation in the lipid bilayer. We introduce laurdanC as a fluorophore for shape recognition and phase transition detection. Together with laurdanC, cryogenic transmission electron microscopy, differential scanning calorimetry, molecular dynamics simulations, and small-angle X-ray scattering/wide-angle X-ray scattering, we acquire information of the particle/bilayer morphology and phase behavior in systems containing 1,2-dipalmitoyl-sn-glycero-3-phosphocholine:1,2-distearoyl-sn-glycero-3-phosphoethanolamine-PEG(2000) with different fractions. We find that PEGylation leads to two important and potentially usable features of the system. (1) Spherical vesicles present a window of elevated chain-melting temperatures and (2) lipid packing shape-controlled liposome-to-bicelle transition. The first finding is significant for targets requiring multiple release sequences and the second enables tuning the release by composition and the PEG polymer length. Besides drug delivery systems, the findings can be used in other smart soft materials with trigger-polymers as well.
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| 8. |
- Andersson, Erika, et al.
(författare)
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A contrast variation SANS and SAXS study of soil derived dissolved organic matter, and its interactions with hematite nanoparticles
- 2023
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Ingår i: JCIS Open. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Soil derived dissolved organic matter (DOM) is an important component of the carbon cycle and influences numerous biogeochemical processes, including the formation of mineral-organic associations. DOM ranges in size from small organic molecules to macromolecules and colloidal aggregates. In this study we have used small angle neutron (SANS) and X-ray (SAXS) scattering to characterize the colloidal DOM fraction from the organic layer of a boreal forest soil, and its interactions with hematite (α-Fe2O3) mineral nanoparticles. Comparison between SAXS and contrast variation SANS patterns revealed that the scattering form factor of the colloidal DOM aggregates was essentially independent of the scattering contrast, implying that the colloidal aggregates have an essentially homogeneous chemical composition, down to the nanometre length scale. Variation of the D2O/H2O ratio of the solvent yielded a SANS intensity minimum at ca. 40 vol % D2O, which was consistent with colloids composed of mainly polysaccharides. At pH 5.5 the pure hematite nanoparticles were colloidally stable in water and characterized by a ζ-potential of +25 mV and a hydrodynamic radius of ca. 70 nm. In the presence of DOM, the hematite nanoparticles lost the colloidal stability and aggregated into larger clusters, displaying a negative ζ-potential of ca. −25 mV. The charge reversal suggested that negatively charged polyanions of DOM adsorbed onto the hematite particles, possibly leading to bridging flocculation. Our results suggested that mainly low molecular weight components induced hematite aggregation because no or very limited interactions between DOM colloids and hematite were detected.
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| 9. |
- Angelico, Ruggero, et al.
(författare)
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Anomalous surfactant diffusion in a living polymer system
- 2006
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Ingår i: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 74:3
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Tidskriftsartikel (refereegranskat)abstract
- Random processes are generally described by Gaussian statistics as formulated by the central limit theorem. However, there exists a large number of exceptions to this rule that can be found in a variety of fields. Diffusion processes are often analyzed by the scaling law < r(2)>similar to t(2 beta), where the second moment of the diffusion propagator or molecular mean square displacement, < r(2)>, in the case of Gaussian diffusion is proportional to t, i.e., beta=1/2. A deviation from Gaussian behavior may be either superdiffusion (beta > 1/2) or subdiffusion (beta < 1/2). In this paper we demonstrate that all three diffusion regimes may be observed for the surfactant self-diffusion, on the length scale of 10(-6) m and the time scale of 0.02-0.8 s. in a system of wormlike micelles, depending on small variations in the sample composition. The self-diffusion is followed by pulsed gradient NMR where one not only measures the second moment of the diffusion propagator, but actually measures the Fourier transform of the full diffusion propagator itself. A generalized diffusion equation in terms of fractional time derivatives provides a general description of all the different diffusion regimes, and where 1/beta can be interpreted as a dynamic fractal dimension. Experimentally, we find beta=1/4 and 3/4, in the regimes of sub- and superdiffusion, respectively. The physical interpretation of the subdiffusion behavior is that the dominating diffusion mechanism corresponds to a lateral diffusion along the contour of the wormlike micelles. Superdiffusion is obtained near the overlap concentration where the average micellar size is smaller so that the center of mass diffusion of the micelles contributes to the transport of surfactant molecules.
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| 10. |
- Angelico, R, et al.
(författare)
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Biocompatible lecithin organogels: Structure and phase equilibria
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:1, s. 140-148
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure of organogels formed upon the addition of tiny amounts of water to a solution of lecithin in fatty acid esters (viz. isopropylpalmitate and ethyloleate) was investigated by means of molecular self-diffusion measurements. In both systems lecithin and water form disconnected cylindrical reverse micelles. The ternary phase map for the lecithin/water/isopropylpalmitate has been investigated in detail. The organogel exists in a narrow region close to the lecithin-oil binary axis; for higher water content equilibrium between lamellae and reverse micelles is found. Lamellar phase occupies the lecithin-rich region, close to the lecithin corner (with the exception of a small island of hexagonal phase) and coexists with neat water close to the water-lecithin axis. The remaining part of the phase map shows the three-phase coexistence of water, oil, and lamellar phase.
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