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Sökning: WFRF:(Orädd Greger)

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1.
  • Adebahr, J, et al. (författare)
  • Ion and solvent dynamics in gel electrolytes based on ethylene oxide grafted acrylate polymers
  • 2002
  • Ingår i: The Journal of Physical Chemistry Part B. - : The American Chemical Society (ACS). - 1520-5207 .- 1089-5647. ; 106:47, s. 12119-12123
  • Tidskriftsartikel (refereegranskat)abstract
    • Multinuclear pulsed field gradient NMR measurements and theological viscosity measurements were performed on three series of polymer gel electrolytes. The gels were based on a lithium salt electrolyte swollen into a copolymer matrix comprising an acrylate backbone and ethylene oxide side chains. In each series the side chains differed in length and number, but the acrylate-to-ethylene oxide ratio was kept constant. It was found that the self-diffusion coefficient of the cations was much lower than that of the anions, and that it decreased rapidly when the side chains got longer. In contrast, the self-diffusion coefficient of the anions was found to be independent of chain length. In the gel electrolytes, the diffusion coefficients of the solvent molecules are relatively constant despite an increased viscosity with increasing length of the side chains. However, in saltfree gels made for comparison, the diffusion coefficients of the solvent molecules decreased with, increasing length of the side chains, which is consistent with an increased viscosity.
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2.
  • Oradd, Greger, et al. (författare)
  • Effects of peptide hydrophobicity on its incorporation in phospholipid membranes - an NMR and ellipsometry study
  • 2011
  • Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier. - 0005-2736 .- 1879-2642. ; 1808:1, s. 244-252
  • Tidskriftsartikel (refereegranskat)abstract
    • Effects of peptide hydrophobicity on lipid membrane binding, incorporation, and defect formation was investigated for variants of the complement-derived antimicrobial peptide CNY21 (CNYITELRRQHARASHLGLAR), in anionic 1-palmitoyl-2-oleoylphosphatidylethanolamine (POPE)/1-palmitoyl-2-oleoylphosphatidylglycerol (POPG) and zwitterionic 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) membranes. Using a method combination of, e.g., ellipsometry, CD, and fluorescence spectroscopy, it was shown that peptide adsorption, as well as peptide-induced liposome leakage and bactericidal potency against Escherichia coli and Pseudomonas aeruginosa, was promoted by increasing the hydrophobicity of CNY21 through either substituting the two histidines (H) in CNY21 with more hydrophobic leucine (L) residues, or end-tagging with tritryptophan (WWW). Fluorescence spectroscopy revealed that both CNY21WWW and the WWW tripeptide localized to the polar headgroup region of these phospholipid membranes. Deuterium NMR experiments on macroscopically oriented membranes containing fully (palmitoyl) deuterated POPC (POPC-d(31)) demonstrated that both CNY21L and CNY21WWW induced disordering of the lipid membrane. In contrast, for cholesterol-supplemented POPC-d(31) bilayers, peptide-induced disordering was less pronounced in the case of CNY21L, indicating that the peptide is unable to partition to the interior of the lipid membrane in the presence of cholesterol. CNY21WWW, on the other hand, retained its membrane-disordering effect also for cholesterol-supplemented POPC-d(31). These findings were supported by pulsed field gradient NMR experiments where the lateral lipid diffusion was determined in the absence and presence of peptides. Overall, the results provide some mechanistic understanding to previously observed effects of peptide hydrophobization through point mutations and end-tagging, particularly so for complement-based antimicrobial peptides. (C) 2010 Elsevier B.V. All rights reserved.
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3.
  • Andersson, Gustav, et al. (författare)
  • In vivo Diffusion Tensor Imaging, Diffusion Kurtosis Imaging, and Tractography of a Sciatic Nerve Injury Model in Rat at 9.4T
  • 2018
  • Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
  • Tidskriftsartikel (refereegranskat)abstract
    • Peripheral nerve injuries result in severe loss of sensory and motor functions in the afflicted limb. There is a lack of standardised models to non-invasively study degeneration, regeneration, and normalisation of neuronal microstructure in peripheral nerves. This study aimed to develop a non-invasive evaluation of peripheral nerve injuries, using diffusion tensor imaging (DTI), diffusion kurtosis imaging (DKI), and tractography on a rat model of sciatic nerve injury. 10 female Sprague Dawley rats were exposed to sciatic nerve neurotmesis and studied using a 9.4 T magnet, by performing DTI and DKI of the sciatic nerve before and 4 weeks after injury. The distal nerve stump showed a decrease in fractional anisotropy (FA), mean kurtosis (MK), axonal water fraction (AWF), and radial and axonal kurtosis (RK, AK) after injury. The proximal stump showed a significant decrease in axial diffusivity (AD) and increase of MK and AK as compared with the uninjured nerve. Both mean diffusivity (MD) and radial diffusivity (RD) increased in the distal stump after injury. Tractography visualised the sciatic nerve and the site of injury, as well as local variations of the diffusion parameters following injury. In summary, the described method detects changes both proximal and distal to the nerve injury.
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4.
  • Chermenina, Maria, et al. (författare)
  • GDNF is important for striatal organization and maintenance of dopamine neurons grown in the presence of the striatum
  • 2014
  • Ingår i: Neuroscience. - 0306-4522 .- 1873-7544. ; 270, s. 1-11
  • Tidskriftsartikel (refereegranskat)abstract
    • Glial cell-derived neurotrophic factor (GDNF) exerts neuroprotective and neurorestorative effects on neurons and GDNF plays a significant role in maintenance of the dopamine neurons utilizing grafting to create a nigrostriatal microcircuit of Gdnf knockout (Gdnf(-/-)) tissue. To further evaluate the role of GDNF on organization of the nigrostriatal system, single or double grafts of ventral mesencephalon (VM) and lateral ganglionic eminence (LGE) with mismatches in Gdnf genotypes were performed. The survival of single grafts was monitored utilizing magnetic resonance imaging (MRI) and cell survival and graft organization were evaluated with immunohistochemistry. The results revealed that the size of VM single grafts did not change over time independent of genotype, while the size of the LGE transplants was significantly reduced already at 2weeks postgrafting when lacking GDNF. Lack of GDNF did not significantly affect the survival of tyrosine hydroxylase (TH)-positive neurons in single VM grafts. However, the survival of TH-positive neurons was significantly reduced in VM derived from Gdnf(+/+) when co-grafted with LGE from the Gdnf(-/-) tissue. In contrast, lack of GDNF in the VM portion of co-grafts had no effect on the survival of TH-positive neurons when co-grafted with LGE from Gdnf(+/+) mice. The TH-positive innervation of co-grafts was sparse when the striatal co-grafts were derived from the Gdnf(-/-) tissue while dense and patchy when innervating LGE producing GDNF. The TH-positive innervation overlapped with the organization of dopamine and cyclic AMP-regulated phosphoprotein-relative molecular mass 32,000 (DARPP-32)-positive neurons, that was disorganized in LGE lacking GDNF production. In conclusion, GDNF is important for a proper striatal organization and for survival of TH-positive neurons in the presence of the striatal tissue.
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5.
  • Danino, Dganit, et al. (författare)
  • Microstructures in the aqueous solutions of a hybrid anionic fluorocarbon/hydrocarbon surfactant
  • 2003
  • Ingår i: Journal of Colloid and Interface Science. ; 259:2, s. 382-90
  • Tidskriftsartikel (refereegranskat)abstract
    • The aqueous solutions of the anionic hybrid fluorocarbon/hydrocarbon surfactant sodium 1-oxo-1[4-(tridecafluorohexyl)phenyl]-2-hexanesulfate (FC6HC4) shows peculiar rheological behavior. At 25 °C the viscosity vs concentration curve goes successively through a maximum and a minimum, while the viscosity vs temperature curve of the 10 wt% aqueous FC6HC4 solution goes through a marked maximum at 36 °C [Tobita et al., Langmuir 13 (1997) 5054]. In an attempt to explain these properties the microstructure of aqueous solutions of FC6HC4 has been investigated by means of digital light microscopy, transmission electron microscopy at cryogenic temperature (cryo-TEM), rheology, and self-diffusion NMR. At 20 °C, the increase of the FC6HC4 concentration was found to result in a progressive change of structure of the surfactant assemblies from mainly spherical micelles at 0.5 wt% to mainly cylindrical micelles at 10 wt%. At intermediate concentrations small disklike micelles and small complete and incomplete vesicles coexisting with cylindrical micelles were visualized. The occurrence of stretched cylindrical micelles is responsible for the effect of the surfactant concentration on the solution viscosity. Cryo-TEM, rheology, and self-diffusion NMR all suggest that an increase of the temperature brings about a growth of the assemblies present in the 10 wt% solution of FC6HC4. The structure of the assemblies present at the temperature where the viscosity is a maximum could not be elucidated by cryo-TEM because of the probable occurrence of an on-the-grid phase transformation, the result of blotting during specimen preparation. Nevertheless, the results show that the observed large assemblies break up at higher temperature to give rise to a more labile bicontinuous structure that consists of multiconnected disordered lamellae, with many folds and creases, and that may well be the L3 phase.
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6.
  • de la Serna, Jorge Bernardino, et al. (författare)
  • Segregated Phases in Pulmonary Surfactant Membranes Do Not Show Coexistence of Lipid Populations with Differentiated Dynamic Properties
  • 2009
  • Ingår i: Biophysical Journal. - : Elsevier Inc. ; 97:5, s. 1381-1389
  • Tidskriftsartikel (refereegranskat)abstract
    • The composition of pulmonary surfactant membranes and films has evolved to support a complex lateral structure, including segregation of ordered/disordered phases maintained up to physiological temperatures. In this study, we have analyzed the temperature-dependent dynamic properties of native surfactant membranes and membranes reconstituted from two surfactant hydrophobic fractions (i.e., all the lipids plus the hydrophobic proteins SP-B and SP-C, or only the total lipid fraction). These preparations show micrometer-sized fluid ordered/disordered phase coexistence, associated with a broad endothermic transition ending close to 37°C. However, both types of membrane exhibit uniform lipid mobility when analyzed by electron paramagnetic resonance with different spin-labeled phospholipids. A similar feature is observed with pulse-field gradient NMR experiments on oriented membranes reconstituted from the two types of surfactant hydrophobic extract. These latter results suggest that lipid dynamics are similar in the coexisting fluid phases observed by fluorescence microscopy. Additionally, it is found that surfactant proteins significantly reduce the average intramolecular lipid mobility and translational diffusion of phospholipids in the membranes, and that removal of cholesterol has a profound impact on both the lateral structure and dynamics of surfactant lipid membranes. We believe that the particular lipid composition of surfactant imposes a highly dynamic framework on the membrane structure, as well as maintains a lateral organization that is poised at the edge of critical transitions occurring under physiological conditions.
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7.
  • Edman, Ludvig, et al. (författare)
  • Analysis of diffusion in a solid polymer electrolyte in the context of a phase-separated system
  • 2002
  • Ingår i: Physical Review E 65, 042803. ; :4, s. 1-4
  • Tidskriftsartikel (refereegranskat)abstract
    • The salt and ionic diffusion coefficients of the salt LiN(CF3SO2)2 (LiTFSI) dissolved in high-molecular-weight poly(ethylene oxide) [PEO] have been measured over a broad concentration range, and the interrelationship of the measured values is demonstrated to be in good agreement with basic electrochemical theory. In the light of recently published structural findings, we propose a biphasic model for the conducting amorphous state, consisting of a stoichiometric P(EO)6LiTFSI phase dispersed into a salt-containing disordered phase, and analyze the ionic diffusion data within the framework of the Bruggeman-Landauer theory. The agreement between experimental and fitted data is shown to be excellent. We conclude by pointing out and discussing potential weaknesses of our analysis.
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8.
  • Every, Hayley A, et al. (författare)
  • Room temperature fast-ion conduction in imidazolium halide salts
  • 2001
  • Ingår i: Journal of Materials Chemistry Articles. ; 11:3031-6
  • Tidskriftsartikel (refereegranskat)abstract
    • Fast-ion conduction has been observed in the iodide and bromide salts of 1-methyl-3-ethylimidazolium at ambient temperatures. The melting point of these two compounds is above 350 K and even at 273 K the ionic conductivity in the solid-state is greater than 10–3S cm–1. Cation diffusion coefficients have been measured using fringe field gradient and/or pulse field gradient 1H NMR techniques, which indicated cation diffusion coefficients of the order of 10–10 m2 s–1 in the solid-state. Remarkably, these values are up to an order of magnitude higher than the cation diffusion coefficient in the supercooled liquid at 293 K. The activation energy for diffusion in the solid-state is extremely small, as is typical of solid-state fast-ion conductors and indicates a change in transport mechanism from the melt to the crystal. The inability to detect an 127I signal together with the modelling of the conductivity using the Nernst–Einstein equation suggests that the solid-state conduction is primarily due to cation diffusion. The solid-state fast-ion conduction is most likely related to vacancy diffusion along the cation layers in the crystal. The temperature dependence of the NMR signal intensity indicates that the number of mobile species is increasing with increasing temperature with an activation energy of approximately 20–30 kJ mol–1.
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9.
  • Every, HA, et al. (författare)
  • Transport properties in a family of dialkylimidazolium ionic liquids
  • 2004
  • Ingår i: PHYSICAL CHEMISTRY CHEMICAL PHYSICS. - 1463-9076. ; 6:8, s. 1758-65
  • Tidskriftsartikel (refereegranskat)abstract
    • The transport properties of 1,3-methylalkylimidazolium based ionic liquids are sensitive to their chemical structure. In this work, two key features of the chemical structure were investigated: the role of the anion and the length of the alkyl chain. Four different anions were examined for the 1,3-methylethylimidazolium salt (MeEtlmX): bromide (Br-), iodide (I-), trifluoromethanesulfonate (Tf-) and bis(trifluoromethanesulfonyt)-amide (NTf2-) anions. Increasing the size of the anion resulted in a decrease of the melting point and a slight increase in the cation diffusion coefficient. The differences in cation diffusion behaviour reflect the differences in viscosity, with much higher viscosities expected for the halide salts. In contrast to this diffusion behaviour, the melt conductivities are all very similar. The inconsistency between the calculated conductivity (based on diffusion measurements) and the conductivity measured, however, is attributed to correlated ion motions and/or the diffusion of neutral species that do not contribute to the conductivity. The effect of the length of the alkyl substituent was also studied for 1,3-methylalkylimidazolium iodide (MeRImI). Increasing the length of the alkyl chain, from methyl to a linear heptyl chain, suppresses the melting point and decreases both the conductivity and cation diffusion coefficients. In this case, the viscosity, as well as the size of the cation, influence ion transport in these materials.
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10.
  • Filippov, Andrey, et al. (författare)
  • Domain Formation in Model Membranes Studied by Pulsed-Field Gradient-NMR: The Role of Lipid Polyunsaturation
  • 2007
  • Ingår i: Biophysical Journal. ; 93, s. 3182-90
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of increased unsaturation in the sn-2 fatty acyl chain of phosphatidylcholines (PCs) on the lipid lateral diffusion have been investigated by pulsed-field gradient NMR. Macroscopically oriented bilayers containing a monosaturated PC, egg sphingomyelin, and cholesterol (CHOL) have been studied at temperatures between 0°C and 60°C, and the number of double bonds in the PC was one, two, four, or six. For PC bilayers, with and without the incorporation of egg sphingomyelin and CHOL, the lateral diffusion increased with increasing number of double bonds, as a consequence of the increased headgroup area caused by the unsaturation. Addition of CHOL caused a decrease in lipid diffusion due to the condensing effect of CHOL on the headgroup area. Phase separation into large domains of liquid-disordered and liquid-ordered phases were observed in the ternary systems with PCs containing four and six double bonds, as evidenced by the occurrence of two lipid diffusion coefficients. PC bilayers with one or two double bonds appear homogeneous on the length scales probed by the experiment, but the temperature dependence of the diffusion suggests that small domains may be present also in these ternary systems.
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  • Resultat 1-10 av 58
  • [1]23456Nästa

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