| 11. |
- Hellberg, D, et al.
(författare)
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Kinetics of liposome adhesion on a mercury electrode
- 2005
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 109, s. 14715-14726
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Tidskriftsartikel (refereegranskat)abstract
- The adhesion of liposomes on a mercury electrode leads to capacitive signals due to the formation of islands of lecithin monolayers. Integration of the current-time transients gives charge-time transients that can be fitted by the empirical equation Q(t) = Q(0) + Q(1)(1 - exp(-t/tau(1))) + Q(2)(1 - exp(-t/tau(2))), where the first term on the right side is caused by the docking of the liposome on the mercury surface, the second term is caused by the opening of the liposome, and the third term is caused by the spreading of the lecithin island on the mercury surface. The temperature dependence of the two time constants tau(1) and tau(2) and the temperature dependence of the overall adhesion rate allow determination of the activation energies of the opening, the spreading, and the overall adhesion process both for gel-phase 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and for liquid-crystalline-phase DMPC liposomes. In all cases, the spreading is the rate-determining process. Negative apparent activation energies for the spreading and overall adhesion process of liquid-crystalline-phase DMPC liposomes can be explained by taking into account the weak adsorption equilibria of the intact liposomes and the opened but not yet spread liposomes. A formal kinetic analysis of the reaction scheme supports the empirical equation used for fitting the charge-time transients. The developed kinetic model of liposome adhesion on mercury is similar to kinetic models published earlier to describe the fusion of liposomes. The new approach can be used to probe the stability of liposome membranes.
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| 12. |
- Hellberg, F, et al.
(författare)
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Investigating the breakup dynamics of dihydrogen sulfide ions recombining with electrons
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:22, s. 224314-
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents results concerning measurements of the dissociative recombination (DR) of dihydrogen sulfide ions. In combination with the ion storage ring CRYRING an imaging technique was used to investigate the breakup dynamics of the three-body channel in the DR of (SD2+)-S-32. The two energetically available product channels S(P-3)+2D(S-2) and S(D-1)+2D(S-2) were both populated, with a branching fraction of the ground-state channel of 0.6(0.1). Information about the angle between the two deuterium atoms upon dissociation was obtained together with information about how the available kinetic energy was distributed between the two light fragments. The recombination cross sections as functions of energy in the interval of 1 meV to 0.3 eV in the center-of-mass frame are presented for (SH2+)-S-34. The thermal rate coefficient for the DR of (SH2+)-S-34 was determined to be (4.8 +/- 1.0)x10(-7)(T/300)(-0.72 +/- 0.1) cm(3) s(-1) over this interval.
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| 13. |
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| 14. |
- Montaigne, Helen, et al.
(författare)
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Dissociative recombination of the thioformyl (HCS+) and carbonyl sulfide (OCS+) cations
- 2005
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 631:1, s. 653-659
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Tidskriftsartikel (refereegranskat)abstract
- Branching ratios and absolute cross sections have been measured for the dissociative recombination of HCS+ and OCS+ at the CRYRING ion storage ring. In the case of OCS+, the channel leading to CO + S ( 83%) dominates, whereas the other exoergic pathways leading to CS + O (14%) and C + SO (3%) are of lesser importance. In the case of HCS+, fracture of the C - S bond is predominant (81%), with the production of H + CS accounting for the remainder (19%). The cross section of the reaction could be fitted by the expressions sigma = 1.41 x 10(-15)E(eV)(-1.11) and 4.47 x 10(-16)E(eV) (-1.14) cm(2) for HCS+ and OCS+, respectively. The derived energy dependences of the thermal reaction rate coefficients can be fitted by k(T) 9.7 x 10(-7)(T/300)(-0.57) and 3.5 x 10(-7)(T/300)(-0.62) cm(3) s(-1) for HCS+ and OCS+, respectively. We use these data to perform model calculations on the HCS+/CS abundance ratio in dark clouds and find that the models using the UMIST and Ohio State University databases have even more difficulty in accounting for the large observed ratio.
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| 15. |
- Novotny, O, et al.
(författare)
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The dissociative recombination of fluorocarbon ions : II. CF
- 2005
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 38:10, s. 1471-1482
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Tidskriftsartikel (refereegranskat)abstract
- The dissociative recombination and excitation of CF+ have been measured at the ASTRID and CRYRING storage rings. Though examination of the available potential energy curves would suggest that the recombination rate would be large for this ion, in fact a rate constant of 5.2 +/- 1.0 x 10(-8) (T-e/300)(-0.8) cm(3) s(-1) was found. The recombination cross section at low energies falls off to a minimum at 0.5 eV centre-of-mass collision energy but exhibits resonances at energies above this. The dissociative excitation cross section leading to C+ + F was also measured and this displays an onset beginning at about 7 eV.
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| 16. |
- Viggiano, A. A., et al.
(författare)
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Rate constants and branching ratios for the dissociative recombination of CO2
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:22, s. 226101-
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Tidskriftsartikel (refereegranskat)abstract
- The calculation of rate constants and branching ratios was carried out to study the dissociative recombination of CO2+. The recombination of CO2+ is significant in the atmospheres of Venus and Mars. Rate constants and cross sections were studied by ramping the electron beam around a center-of-mass energy of 0 eV. The results of the study confirms that all the recombination of CO2+ results in a simple bondbreaking to form CO plus O. The rate constants show good agreement with measurements at 300 K and the electron energy dependence is identical to storage ring results.
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| 17. |
- Österdahl, Fabian, et al.
(författare)
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Position- and time-sensitive coincident detection of fragments from the dissociative recombination of O-2(+) using a single hexanode delay-line detector
- 2005
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Ingår i: DR2004. - BRISTOL : IOP PUBLISHING LTD. ; , s. 286-289
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This contribution describes the use of the RoentDek hexanode delay line detector to detect fragments from the dissociative recombination of O-2(+) in an experiment at the ion storage ring CRYRING, Manne Siegbahn Laboratory, Stockholm. In this experiment, the fragments have a maximum time- and position-separation of 20ns and 40 mm, respectively. The position resolution obtained was 0.16mm (FWHM) on the 67 rum diameter detector. The time resolution obtained from the time-of-arrival difference between the product fragments was about 1 ns. The detector system handles event rates as large as 30 kHz. Techniques for the calibration of the absolute position of particles on the detector are discussed.
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