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  • 1.
    Andersson, Magnus
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Almqvist, Fredrik
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Uhlin, Bernt Eric
    Umeå universitet, Medicinsk fakultet, Molekylärbiologi (Medicinska fakulteten).
    Fällman, Erik
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Fysik.
    Physical Properties of Biopolymers Assessed by Optical Tweezers: Analysis of folding and refolding of bacterial pili2008Ingår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 9, nr 2, s. 221-235Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bacterial adhesion to surfaces mediated by specific adhesion organelles that promote infections, as exemplified by the pili of uropathogenic E. coli, is studied mostly at the level of cell-cell interactions and thereby reflects the averaged behavior of multiple pili. The role of pilus rod structure has therefore only been estimated from the outcome of experiments involving large numbers of organelles at the same time. It has, however, lately become clear that the biomechanical behavior of the pilus shafts play an important, albeit hitherto rather unrecognized, role in the adhesion process. For example, it has been observed that shafts from two different strains, even though they are similar in structure, result in large differences in the ability of the bacteria to adhere to their host tissue. However, in order to identify all properties of pilus structures that are of importance in the adhesion process, the biomechanical properties of pili must be assessed at the single-molecule level. Due to the low range of forces of these structures, until recently it was not possible to obtain such information. However, with the development of force-measuring optical tweezers (FMOT) with force resolution in the low piconewton range, it has lately become possible to assess forces mediated by individual pili on single living bacteria in real time. FMOT allows for a more or less detailed mapping of the biomechanical properties of individual pilus shafts, in particular those that are associated with their elongation and contraction under stress. This Mi- nireview presents the FMOT technique, the biological model system, and results from assessment of the biomechanical properties of bacterial pili. The information retrieved is also compared with that obtained by atomic force microscopy.

  • 2. Anoshkin, Ilya
    et al.
    Talyzin, Alexandr
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Nasibulin, Nasibulin
    Krasheninnikov, Arkady
    Jiang, Hua
    Nieminen, Risto
    Kauppinen, Esko
    Coronene Encapsulation in Single-Walled Carbon Nanotubes: Stacked Columns, Peapods, and Nanoribbons2014Ingår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, nr 8, s. 1660-1665Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Encapsulation of coronene inside single-walled carbon nanotubes (SWNTs) was studied under various conditions. Under high vacuum, two main types of molecular encapsulation were observed by using transmission electron microscopy: coronene dimers and molecular stacking columns perpendicular or tilted (45-608) with regard to the axis of the SWNTs. A relatively small number of short nanoribbons or polymerized coronene molecular chains were observed. However, experiments performed under an argon atmosphere (0.17 MPa) revealed reactions between the coronene molecules and the formation of hydrogen-terminated graphene nanoribbons. It was also observed that the morphology of the encapsulated products depend on the diameter of the SWNTs. The experimental results are explained by using density functional theory calculations through the energies of the coronene molecules inside the SWNTs, which depend on the orientation of the molecules and the diameter of the tubes.

  • 3.
    Castelain, Mickaël
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Koutris, Efstratios
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Andersson, Magnus
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Wiklund, Krister
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Björnham, Oscar
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Schedin, Staffan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Axner, Ove
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Characterization of the Biomechanical Properties of T4 Pili Expressed by Streptococcus pneumoniae – A Comparison between Helix-like and Open Coil-like Pili2009Ingår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 10, nr 9-10, s. 1533-1540Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bacterial adhesion organelles, known as fimbria or pili, are expressed by Gram–positive as well as Gram–negative bacteria families. These appendages play a key role in the first steps of the invasion and infection processes, and they therefore provide bacteria with pathogenic abilities. To improve the knowledge of pili-mediated bacterial adhesion to host cells and how these pili behave under the presence of an external force, we first characterize, using force measuring optical tweezers, open coil-like T4 pili expressed by Gram–positive Streptococcus pneumoniae with respect to their biomechanicalproperties. It is shown that their elongation behavior can be well described by the worm-like chain model and that they possess a large degree of flexibility. Their properties are then compared with those of helix-like pili expressed by Gram–negative uropathogenic Escherichia coli (UPEC), which have different pili architecture. The differences suggest that these two types of pili have distinctly dissimilar mechanisms to adhere and sustain external forces. Helix-like pili expressed by UPEC bacteria adhere to host cells by single adhesins located at the distal end of the pili while their helix-like structures act as shock absorbers to dampen the irregularly shear forces induced by urine flow and to increase the cooperativity of the pili ensemble. Open coil-like pili expressed by S. pneumoniae adhere to cells by a multitude of adhesins distributed along the pili. It is hypothesized that these two types of pili represent different strategies of adhering to host cells in the presence of external forces. When exposed to significant forces, bacteria expressing helix-like pili remain attached bydistributing the external force among a multitude of pili, whereas bacteria expressing open coil-like pili sustain large forces primarily by their multitude of binding adhesins.

  • 4.
    Driver, Gordon W
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Aqueous Brønsted–Lowry Chemistry of Ionic Liquid Ions2015Ingår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 16, nr 11, s. 2432-2439Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ionic liquids have become commonplace materials found in research laboratories the world over, and are increasingly utilised in studies featuring water as co-solvent. It is reported herein that proton activities, aH+, originating from auto-protolysis of H2O molecules, are significantly altered in mixtures with common ionic liquids comprised of Cl, [HSO4], [CH3SO4], [CH3COO], [BF4], relative to pure water. paH+ values, recorded in partially aqueous media as −log(aH+), are observed over a wide range (∼0–13) as a result of hydrolysis (or acid dissociation) of liquid salt ions to their associated parent molecules (or conjugate bases). Brønsted–Lowry acid–base character of ionic liquid ions observed is rooted in equilibria known to govern the highly developed aqueous chemistry of classical organic and inorganic salts, as their well-known aqueous pKs dictate. Classical salt behaviour observed for both protic and aprotic ions in the presence of water suggests appropriate attention need be given to relevant chemical systems in order to exploit, or avoid, the nature of the medium formed.

  • 5.
    Driver, Gordon W
    et al.
    Department of Chemical Engineering.
    Ingman, Petri
    Non-spherical ion dynamics and rotational diffusion for imidazolium based ionic liquids2011Ingår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 12, nr 4, s. 757-60Artikel i tidskrift (Refereegranskat)
  • 6. Johnson, Rene L.
    et al.
    Harley, Stephen J.
    Ohlin, C. Andre
    Panasci, Adele F.
    Casey, William H.
    Multinuclear NMR Study of the Pressure Dependence for Carbonate Exchange in the UO2(CO3)34-(aq) Ion2011Ingår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 12, nr 16, s. 2903-2906Artikel i tidskrift (Refereegranskat)
  • 7. Mihichuk, Lynn M
    et al.
    Driver, Gordon W
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Johnson, Keith E
    Brønsted acidity and the medium: fundamentals with a focus on ionic liquids2011Ingår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 12, nr 9, s. 1622-1632Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fundamental aspects of Brønsted acidity in ionic liquid systems, in relation to those of simple protic molecules in the gas phase, pure protic molecules in the condensed phase and solutions of protic molecules in molecular systems, are presented. The variety of acidities possible, beyond those observed in aqueous systems, is emphasised and discussed in terms of differences of solvent levelling, ionisation, dissociation, homo-/hetero-conjugate ion speciation and the stabilisation of proton-transfer products from solvent to solvent. It is argued that data regarding aqueous systems do not necessarily explain acid/base behaviour in other liquids satisfactorily. Methods of measuring acidity are reviewed, particularly by spectrophotometry and electrochemistry and recommendations proffered for estimating speciation and acidity of ionic liquids of various complexities.

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