| 31. |
- Andersson, Magnus, et al.
(författare)
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Force measuring optical tweezers system for long time measurements of P pili stability
- 2006
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Ingår i: Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues IV. - : SPIE. - 081946130X - 9780819461308 ; , s. 608810-
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Konferensbidrag (refereegranskat)abstract
- A force-measuring optical tweezers instrumentation and long time measurements of the elongation and retraction of bacterial fimbriae from Uropathogenic E. coli (UPEC) under strain are presented. The instrumentation is presented in some detail. Special emphasis is given to measures taken to reduce the influence of noise and drifts in the system and from the surrounding, which makes long term force measurements possible. Individual P pili from UPEC bacteria were used as a biological model system for repetitive unfolding and refolding cycles of bacterial fimbriae under equilibrium conditions. P pili have evolved into a three-dimensional helix-like structure, the PapA rod, that can be successively and significantly elongated and/or unfolded when exposed to external forces. The instrumentation is used for characterization of the force-vs.-elongation response of the PapA rod of individual P pili, with emphasis on the long time stability of the forced unfolding and refolding of the helical structure of the PapA rod. The results show that the PapA rod is capable of withstanding extensive strain, leading to a complete unfolding of the helical structure, repetitive times during the life cycle of a bacterium without any noticeable alteration of the mechanical properties of the P pili. This function is believed to be importance for UPEC bacteria in vivo since it provides a close contact to a host cell (which is an initial step of invasion) despite urine cleaning attempts.
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| 32. |
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| 33. |
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| 34. |
- Andersson, Magnus, et al.
(författare)
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Physical Properties of Biopolymers Assessed by Optical Tweezers : Analysis of folding and refolding of bacterial pili
- 2008
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Ingår i: ChemPhysChem. - : Wiley-VCH Verlagsgesellschaft. - 1439-4235 .- 1439-7641. ; 9:2, s. 221-235
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 35. |
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| 36. |
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| 37. |
- Andersson, Ove, et al.
(författare)
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A high-pressure study of PMMA-based gels with and without TiO2 nano-particle filler: a filler induced change in the activation volume
- 2005
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 50:16-17, s. 3217-3223
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Tidskriftsartikel (refereegranskat)abstract
- The ionic conductivity σ of PMMA-based gels with and without nano-particle filler has been investigated at elevated pressure up to 0.9 GPa and in the temperature range 220-330 K to determine the effect of pressure and to obtain the activation volume. Both gels had molar ratios: EC:PC:LiClO 4 :PMMA 53.9:22:5.2:18.9, and one gel contained 8 wt.% TiO 2 nano-particles. At room temperature and atmospheric pressure, the conductivity of the gel with filler is almost the same as that for the gel without filler. At increasing pressure p, σ(p) for both gels exhibits an abrupt change, which is associated with a transition, and consequently there is a pressure induced change in the activation volume for both gels. The activation volume ΔV * in low-pressure state is the same for the gels with and without filler and about 14 cm 3 mol -1 at room temperature, which is typical liquid-like behaviour. In the high-pressure state, ΔV * = 42 and 45.3 cm 3 mol -1 at 294 K for the gels with and without filler, respectively. The results show that the ionic movements are restricted by the rigid environment of the high-pressure state and that the filler affects ΔV * under this condition. In particular, the filler appears to improve the cation transport number as a results of a decreased mobility of large-sized ions in the rigid environment of the high-pressure state. © 2004 Elsevier Ltd. All rights reserved.
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| 38. |
- Andersson, Ove, et al.
(författare)
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A low-temperature high-pressure apparatus with a temperature control system
- 1992
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 10:4, s. 599-606
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Tidskriftsartikel (refereegranskat)abstract
- A low-temperature high-pressure apparatus was designed using commercial cryogenic equipment. Pressures up to 1 GPa and temperatures down to 40 K can be obtained in a volume of up to 30 cm3. The apparatus is of the piston-cylinder type with a piston diameter of 45 mm, and the pressure can be varied at all temperatures, An adaptive temperature control system keeps the temperature inside the pressure cylinder constant to within ±0.1 K.
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| 39. |
- Andersson, Ove, et al.
(författare)
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A Second Glass Transition in Pressure Collapsed Type II Clathrate Hydrates
- 2018
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 122:15, s. 4376-4384
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Tidskriftsartikel (refereegranskat)abstract
- Type II clathrate hydrates (CHs) M-17 H2O, with M = tetrahydrofuran (THF) or 1,3-dioxolane, are known to collapse, or amorphize, on pressurization to similar to 1.3 GPa in the temperature range 77-140 K. On heating at 1 GPa, these pressure-amorphized CH states show a weak, stretched sigmoid-shaped, heat-capacity increase because of a glass transition. Here we use thermal conductivity and heat capacity measurements to show that also type II CH with M = cyclobutanone (CB) collapses on isothermal pressurization and undergoes a similar, weak, glass transition upon heating at 1 GPa. Furthermore, we reveal for both THF CH and CB CH a second, much more pronounced, glass transition at temperatures above the thermally weak glass transition on heating in the 0.2-0.7 GPa range. This result suggests the general occurrence of two glass transitions in water-rich (94 mol %) pressure-collapsed CHs. Because of a large increase in dielectric permittivity concurrently as the weak heat capacity increase, the first glass transition must be due to kinetic unfreezing of water molecules. The thermal features of the second glass transition, measured on isobaric temperature cycling, are typical of a glass liquid glass transition, which suggests that pressure-amorphized CHs transform reversibly to liquids.
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| 40. |
- Andersson, Ove, et al.
(författare)
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Amorphous-like thermal conductivity and high mechanical stability of cyclopentane clathrate hydrate
- 2024
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 26:22, s. 16017-16025
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity κ of cyclopentane clathrate hydrate (CP CH) of type II was measured at temperatures down to 100 K and at pressures up to 1.3 GPa. The results show that CP CH displays amorphous-like κ characteristic of many crystalline clathrate hydrates, e.g., tetrahydrofuran (THF) CH. The magnitude of κ is 0.47 W m−1 K−1 near the melting point of 280 K at atmospheric pressure, and it is almost independent of pressure and temperature T: ln κ = −0.621−40.1/T at atmospheric pressure (in SI-units). This is slightly less than κ of type II CHs of water-miscible solvents such as THF. Intriguingly, unlike other water-rich type II clathrate hydrates of water-miscible molecules M (M·17 H2O), CP CH does not amorphize at pressures up to 1.3 GPa at 130 K and also remains stable up to 0.5 GPa at 240 K. This shows that CP CH is mechanically more stable than the previously studied water-rich type II CHs, and suggests that repulsive forces between CP and the H2O cages increase the mechanical stability of crystalline CP CH. Moreover, we show that κ of an ice-CH mixture, which often arises for CHs that form naturally, is described by the average of the parallel and series heat conduction models to within 5% for ice contents up to 22 wt%. The findings provide a better understanding of the thermal and stability properties of clathrate hydrates for their applications such as gas storage compounds.
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