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Zhu C.,Lulea University of Technology | Dobryden I.,Lulea University of Technology | Ryden J.,Lulea University of Technology | Oberg S.,Lulea University of Technology | And 3 more authors.
Langmuir | Year: 2015

The aim of this study was to develop a fundamental understanding of the adsorption behavior of metal ions on cellulose surfaces using experimental techniques supported by computational modeling, taking Ag(I) as an example. Force interactions among three types of cellulose microspheres (native cellulose and its derivatives with sulfate and phosphate groups) and the silica surface in AgNO3 solution were studied with atomic force microscopy (AFM) using the colloidal probe technique. The adhesion force between phosphate cellulose microspheres (PCM) and the silica surface in the aqueous AgNO3 medium increased significantly with increasing pH while the adhesion force slightly decreased for sulfate cellulose microspheres (SCM), and no clear adhesion force was observed for native cellulose microspheres (CM). The stronger adhesion enhancement for the PCM system is mainly attributed to the electrostatic attraction between Ag(I) and the negative silica surface. The observed force trends were in good agreement with the measured zeta potentials. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analyses confirmed the presence of silver on the surface of cellulose microspheres after adsorption. This study showed that PCM with a high content of phosphate groups exhibited a larger amount of adsorbed Ag(I) than CM and SCM and possible clustering of Ag(I) to nanoparticles. The presence of the phosphate group and a wavenumber shift of the P-OH vibration caused by the adsorption of silver ions on the phosphate groups were further confirmed with computational studies using density functional theory (DFT), which gives support to the above findings regarding the adsorption and clustering of Ag(I) on the cellulose surface decorated with phosphate groups as well as IR spectra. © 2015 American Chemical Society.

Dabrowska-Kloda K.,County Hospital of Varmland | Kloda T.,Stockholm UniversityStockholm | Boudiaf S.,County Hospital of Varmland | Jakobsson G.,Sahlgren University Hospital | Stenevi U.,Sahlgren University Hospital
Journal of Cataract and Refractive Surgery | Year: 2015

Purpose To identify risk factors for late in-the-bag intraocular lens (IOL) dislocation and estimate the incidence of this condition over a 21-year period. Setting Department of Ophthalmology, County Hospital of Värmland, Karlstad, Sweden. Design Retrospective cohort study and nested case-control study. Methods The medical records of eyes operated on for late in-the-bag IOL dislocation between 1992 and 2012 were reviewed. The annual incidence and cumulative risk were calculated. Results Of 140 eyes whose records were reviewed, 123 qualified for comparison (24 variables) with an equal number in a control group. The annual incidence varied between 0.00% and 0.08%. An increasing trend was found (P <.001). The cumulative risk 5, 10, 15, and 20 years after cataract extraction was 0.09%, 0.55%, 1.00%, and 1.00%, respectively, and was significantly higher (P < .001) in eyes that had cataract surgery between 2002 and 2012 than in those operated on between 1992 and 2001 (0.89% versus 0.39% at 10 years postoperatively) (P <.001). Calendar time (date) of dislocation was positively correlated with the duration of preceding pseudophakia (P = .005). Phacoemulsification time was longer in eyes with dislocation than in control eyes (P <.001). Other identified risk factors were pseudoexfoliation, zonular dehiscence, pseudophacodonesis, and increased axial length. Conclusions The increasing number of late in-the-bag IOL dislocations cannot be explained by the growing pseudophakic population only. The increase in the incidence was due primarily to the longer duration of pseudophakia in the population and to a greater dislocation risk with recent cataract surgery. The increase in life expectancy played a minor role. Long phacoemulsification time was a risk factor for dislocation. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned. © 2015 ASCRS and ESCRS.

Helmfors H.,Stockholm UniversityStockholm | Eriksson J.,Stockholm UniversityStockholm | Langel U.,Stockholm UniversityStockholm
Analytical Biochemistry | Year: 2015

Abstract An improved assay for screening for the intracellular delivery efficacy of short oligonucleotides using cell-penetrating peptides is suggested. This assay is an improvement over previous assays that use luciferase reporters for cell-penetrating peptides because it has been scaled up from a 24-well format to a 96-well format and no longer relies on a luciferin reagent that has been commercially sourced. In addition, the homemade luciferin reagent is useful in multiple cell lines and in different assays that rely on altering the expression of luciferase. To establish a new protocol, the composition of the luciferin reagent was optimized for both signal strength and longevity by multiple two-factorial experiments varying the concentrations of adenosine triphosphate, luciferin, coenzyme A, and dithiothreitol. In addition, the optimal conditions with respect to cell number and time of transfection for both short interfering RNA (siRNA) and splice-correcting oligonucleotides (SCOs) are established. Optimal transfection of siRNA and SCOs was achieved using the reverse transfection method where the oligonucleotide complexes are already present in the wells before the cells are plated. Z′ scores were 0.73 for the siRNA assay and 0.71 for the SCO assay, indicating that both assays are suitable for high-throughput screening. © 2015 Elsevier Inc.

Brandt E.G.,Stockholm UniversityStockholm | Lyubartsev A.P.,Stockholm UniversityStockholm
Journal of Physical Chemistry C | Year: 2015

Atomistic force field parameters were developed for the TiO2-water interface by systematic optimization with respect to experimentally determined crystal structures (lattice parameters) and surface thermodynamics (water adsorption enthalpy). Optimized force field parameters were determined for the two cases where TiO2 was modeled with or without covalent bonding. The nonbonded TiO2 model can be used to simulate different TiO2 phases, while the bonded TiO2 model is particularly useful for simulations of nanosized TiO2 and biomatter, including protein-surface and nanoparticle-biomembrane simulations. The procedure is easily generalized to parametrize interactions between other inorganic surfaces and biomolecules. © 2015 American Chemical Society.

Brandt E.G.,Stockholm UniversityStockholm | Lyubartsev A.P.,Stockholm UniversityStockholm
Journal of Physical Chemistry C | Year: 2015

Abstract Adsorption profiles and adsorption free energies were determined for the side chain analogues of the 20 naturally occurring amino acids and a titanium binding peptide on the TiO2 (100) surface. Microsecond simulations with umbrella sampling and metadynamics were used to sample the free energy barriers associated with desolvation of strongly bound water molecules at the TiO2 surface. Polar and aromatic side chain analogues that hydrogen bond either to surface waters or directly to the metal oxide surface were found to be the strongest binders. Further, adsorption simulations of a 6-residue titanium binding peptide identified two binding modes on TiO2 (100). The peptide structure with lowest free energy was shown to be stabilized by a salt bridge between the end termini. A comparison between the free energies of the side chain analogues of the peptide sequence and the peptide itself shows that the free energy contributions are not additive. The simulations emphasize that tightly bound surface waters play a key role for peptide and protein structures when bound to inorganic surfaces in biological environments. © 2015 American Chemical Society.

Heydari H.,Stockholm UniversityStockholm | Andersson O.,Stockholm UniversityStockholm
Physica Scripta | Year: 2015

Geometrical structures of quantum mechanics provide us with new insightful results about the nature of quantum theory. In this work we consider mixed quantum states represented by finite rank density operators. We review our geometrical framework that provide the space of density operators with Riemannian and symplectic structures, and we derive a geometric uncertainty relation for observables acting on mixed quantum states. We also give an example that visualizes the geometric uncertainty relation for spin-1/2 particles. © 2015 The Royal Swedish Academy of Sciences.

Liao R.-Z.,Stockholm UniversityStockholm | Siegbahn P.E.M.,Stockholm UniversityStockholm
Journal of Photochemistry and Photobiology B: Biology | Year: 2015

Density functional theory calculations have been used to study the reaction mechanism of water oxidation catalyzed by a tetranuclear Mn-oxo cluster Mn4O4L6 (L = (C6H4)2PO4 -). It is proposed that the O-O bond formation mechanism is different in the gas phase and in a water solution. In the gas phase, upon phosphate ligand dissociation triggered by light absorption, the O-O bond formation starting with both the Mn4(III,III,IV,IV) and Mn4(III,IV,IV,IV) oxidation states has to take place via direct coupling of two bridging oxo groups. The calculated barriers are 42.3 and 37.1 kcal/mol, respectively, and there is an endergonicity of more than 10 kcal/mol. Additional photons are needed to overcome these large barriers. In water solution, water binding to the two vacant sites of the Mn ions, again after phosphate dissociation triggered by light absorption, is thermodynamically and kinetically very favorable. The catalytic cycle is suggested to start from the Mn4(III,III,III,IV) oxidation state. The removal of three electrons and three protons leads to the formation of a Mn4(III,IV,IV,IV)-oxyl radical complex. The O-O bond formation then proceeds via a nucleophilic attack of water on the MnIV-oxyl radical assisted by a Mn-bound hydroxide that abstracts a proton during the attack. This step was calculated to be rate-limiting with a total barrier of 29.2 kcal/mol. This is followed by proton-coupled electron transfer, O2 release, and water binding to start the next catalytic cycle. © 2014 Elsevier B.V.

Eklund L.,Stockholm UniversityStockholm
Computers in Human Behavior | Year: 2015

Studies of virtual worlds are often based on the dichotomous 'real world'/'virtual world', yet research has indicated that this division is far from unproblematic. The aim of this study is to examine empirically the link between online/offline using the example of social online gaming. The data consist of individual and group interviews with 33 adult gamers. The results explore three themes - sociability and design; group membership; norms and rules - and show how on-and offline are inexorably linked through the social organizational demands of Internet gaming. Individuals ground online group membership in offline relations and shared characteristics, aiming to maximize game-play gains and support sociability. Gaming with 'people like us' facilitates creation of norms and expectations, which aids in producing stable social groups. Thus the boundary between online and offline becomes contingent on links between people. The study shows how important offline connections are for online interaction. © 2015 Elsevier Ltd.

Mace A.,Stockholm UniversityStockholm | Leetmaa M.,Uppsala University | Laaksonen A.,Stockholm UniversityStockholm
Journal of Chemical Theory and Computation | Year: 2015

The kinetic CO2-over-N2 sieving capabilities in narrow pore zeolites are dependent on the free-energy barriers of diffusion between the zeolite pores, which can be fine-tuned by altering the framework composition. An ab initio level of theory is necessary to accurately compute the energy barriers, whereas it is desirable to predict the macroscopic scale diffusion for industrial applications. Using ab initio molecular dynamics on the picosecond time scale, the free-energy barriers of diffusion can be predicted for different local pore properties in order to identify those that are rate-determining for the pore-to-pore diffusion. Specifically, we investigate the effects of the Na+-to-K+ exchange at the different cation sites and the CO2 loading in Zeolite NaKA. These computed energy barriers are then used as input for the Kinetic Monte Carlo method, coarse graining the dynamic simulation steps to the pore-to-pore diffusion. With this approach, we simulate how the identified rate-determining properties as well as the application of skin-layer surface defects affect the diffusion driven uptake in a realistic Zeolite NaKA powder particle model on a macroscopic time scale. Lastly, we suggest a model by combining these effects, which provides an excellent agreement with the experimental CO2 and N2 uptake behaviors presented by Liu et al. (Chem. Commun. 2010, 46, 4502-4504). © 2015 American Chemical Society.

Liebau J.,Stockholm UniversityStockholm | Pettersson P.,Stockholm UniversityStockholm | Szpryngiel S.,Stockholm UniversityStockholm | Maler L.,Stockholm UniversityStockholm
Biophysical Journal | Year: 2015

The glycosyltransferase WaaG is involved in the synthesis of lipopolysaccharides that constitute the outer leaflet of the outer membrane in Gram-negative bacteria such as Escherichia coli. WaaG has been identified as a potential antibiotic target, and inhibitor scaffolds have previously been investigated. WaaG is located at the cytosolic side of the inner membrane, where the enzyme catalyzes the transfer of the first outer-core glucose to the inner core of nascent lipopolysaccharides. Here, we characterized the binding of WaaG to membrane models designed to mimic the inner membrane of E. coli. Based on the crystal structure, we identified an exposed and largely α-helical 30-residue sequence, with a net positive charge and several aromatic amino acids, as a putative membrane-interacting region of WaaG (MIR-WaaG). We studied the peptide corresponding to this sequence, along with its bilayer interactions, using circular dichroism, fluorescence quenching, fluorescence anisotropy, and NMR. In the presence of dodecylphosphocholine, MIR-WaaG was observed to adopt a three-dimensional structure remarkably similar to the segment in the crystal structure. We found that the membrane interaction of WaaG is conferred at least in part by MIR-WaaG and that electrostatic interactions play a key role in binding. Moreover, we propose a mechanism of anchoring WaaG to the inner membrane of E. coli, where the central part of MIR-WaaG inserts into one leaflet of the bilayer. In this model, electrostatic interactions as well as surface-exposed Tyr residues bind WaaG to the membrane. © 2015 The Authors.

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