| 1. |
- Berglund, Johan, et al.
(författare)
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Reaction of Peroxomonosulfate Radical with Manganese(II) in Acidic Aqueous Solution. A Pulse Radiolysis Study
- 1994
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Ingår i: Journal of the Chemical Society - Faraday Transactions. - : Royal Society of Chemistry (RSC). - 0956-5000 .- 1364-5455. ; 90:21, s. 3309-3313
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Tidskriftsartikel (refereegranskat)abstract
- The reaction between the SO5– radical and MnII has been proposed to be the most important process for regeneration of MnIII in the MnIII/II-catalysed autoxidation of SIV in acidic aqueous solution. In the present study, the second-order rate constant for this reaction has been determined at pH 3. 0 and 10 mmol dm–3 ionic strength by use of pulse radiolysis. The study was performed in the presence of excess SIV. Under these conditions MnII is distributed among the complexes Mn2+(aq), [Mn(HSO3)]+ and [Mn(SO3)Mn]2+. The rate of reaction decreases as a function of increasing [MnII]total which is rationalized qualitatively by a mechanism involving three parallel reactions between SO5– and the MnII complexes, with rate constants k16, k17 and k18, respectively. Mn2++ SO5– [graphic omitted] Mn3++ HSO5–(16), [Mn(HSO3)]++ SO5– [graphic omitted] [Mn(HSO3)]2+ HSO5–(17), [Mn(SO3)Mn]2++ SO5– [graphic omitted] [Mn(SO3)Mn]3++ HSO5–(18), For increasing total concentrations of MnII, formation of the sulfito-bridged complex is favoured which implies that k18 < k16, k17. Values of the second-order rate constant in the range 2 × 10 108–2 × 1010 dm3 mol–1 s–1 have been determined, depending on which MnII species is predominant. Subsequent slow processes are observed following the formation of MnIII. These reactions have been attributed to the disproportionation of MnIII and reactions between the MnIII species and excess SIV. The implications of the present results for the MnIII/II catalysed autoxidation of SIV are discussed.
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| 2. |
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| 3. |
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| 4. |
- Geppert, W.D., et al.
(författare)
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Dissociative recombination of protonated methanol
- 2006
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Ingår i: Faraday discussions. - Cambridge : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 133, s. 177-190
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Tidskriftsartikel (refereegranskat)abstract
- The branching ratios of the different reaction pathways and the overall rate coefficients of the dissociative recombination reactions of CH3OH2+ and CD3OD2+ have been measured at the CRYRING storage ring located in Stockholm, Sweden. Analysis of the data yielded the result that formation of methanol or deuterated methanol accounted for only 3 and 6% of the total rate in CH3OH2+ and CD3OD2+, respectively. Dissociative recombination of both isotopomeres mainly involves fragmentation of the C - O bond, the major process being the three-body break-up forming CH3, OH and H (CD3, OD and D). The overall cross sections are best fitted by sigma = 1.2 +/- 0.1 x 10(-15) E-1.15 +/- 0.02 cm(2) and sigma = 9.6 +/- 0.9 x 10(-16) E-1.20 +/- 0.02 cm(2) for CH3OH2+ and CD3OD2+, respectively. From these values thermal reaction rate coefficients of k(T) = 8.9 +/- 0.9 x 10(-7) (T/300) (- 0.59 +/- 0.02) cm(3) s(-1) (CH3OH2+) and k( T) = 9.1 +/- 0.9 x 10(-7) (T/ 300) (- 0.63 +/- 0.02) cm(3) s(-1)(CD3OD2+) can be calculated. A non-negligible formation of interstellar methanol by the previously proposed mechanism via radiative association of CH3+ and H2O and subsequent dissociative recombination of the resulting CH3OH2+ ion to yield methanol and hydrogen atoms is therefore very unlikely.
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| 7. |
- Jonsson, Mats, 1939, et al.
(författare)
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ORIENTATION OF LARGE DNA DURING FREE SOLUTION ELECTROPHORESIS STUDIED BY LINEAR DICHROISM
- 1993
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Ingår i: Journal of the Chemical Society - Faraday Transactions. - : Royal Society of Chemistry (RSC). - 0956-5000. ; 89:15, s. 2791-2798
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Tidskriftsartikel (refereegranskat)abstract
- DNA T7 (40 kbp(double dagger)), T5 (120 kbp) and T2 (170 kbp) have been studied under electrophoretic conditions in free solution (25 mmol dm-3 ionic strength) regarding chain orientation and field-free decay using phase-modulation detected linear dichroism. The steady-state orientation does not show Kerr-law behaviour for the larger T5 and T2 DNAs but increases roughly linearly with field strength, the orientation factor being around 3 x 10(-3) at 100 V cm-1. When subjected to the electric field DNA displays within 0.1-5 s an orientation overshoot which increases strongly with DNA size and comes faster the higher the field strength. When the field is switched off a major portion of the DNA orientation has relaxed within 10 ms while a smaller portion decays more slowly: 0.3 s for T2, comparable with the slowest relaxation of a Zimm-Rouse chain. The observed orientation phenomena could be important in free-solution capillary electrophoresis of DNA. The question of the mechanism by which the DNA is aligned (dipole or electrophoretic orientation?) cannot be addressed adequately within existing theories for chain-like macromolecules. Awaiting results from simulations it is speculated that the overshoot phenomenon and the slow decay component of large DNA may represent reptative deformations of the DNA coil similar to those recently observed for large DNA during gel electrophoresis. Rapid field reversal did not lead to any dip in steady-state orientation for the pure DNA; however, in a complex with the recombinase protein RecA which stacks outside DNA, apparently in a polar way to form a large permanent dipole, a pronounced dip suggests that there is a 180-degrees rotation of the particle upon field reversal. The electro-optical cell was designed to give minimal influence from electro-osmosis and convection. The experiments on T2 and T7 DNA (on the ground) were replicated under microgravity conditions during a sounding-rocket flight without any noticeable differences in orientation dynamics.
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| 8. |
- Larsson, Karin M., et al.
(författare)
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Enzyme catalysis in uni- and bi-continuous microemulsions : Dependence of kinetics on substrate partitioning
- 1991
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Ingår i: Journal of the Chemical Society, Faraday Transactions. - 0956-5000. ; 87:3, s. 465-471
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of enzymatic conversion in a microemulsion have been investigated. Racemic 3-methylcyclohexanone was oxidized by horse-liver alcohol dehydrogenase (HLADH, E.C. 1.1.1.1.) using a coupled substrate-coenzyme regenerating cycle in a sodium bis-(2-ethylhexyl) sulphosuccinate (AOT)-isooctane-buffer microemulsion. Initial enzyme activity was measured as a function of the oil volume fraction in the range 0 ≤ Φ ≤ 0.83 for a constant surfactant concentration. The change in composition is followed by a change in microstructure from oil-in-water (O/W) to water-in-oil (W/O) via a bicontinuous structure as determined by self-diffusion measurements using the pulsed-gradient NMR technique. The variation of the initial rate with composition is well described by modifying the rate equation, valid in pure buffer, by simply taking into account the partitioning of the substrates between the polar and apolar microdomains in the structured solvent. Also the enzyme stability was investigated at various compositions of the microemulsion. The stability was found to increase with increasing Φ.
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| 9. |
- Larsson, Karin, et al.
(författare)
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REORIENTATION OF WATER-MOLECULES IN SOLID HYDRATES - CORRELATION WITH SPECTROSCOPIC AND STRUCTURAL DATA
- 1991
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Ingår i: Journal of the Chemical Society, Faraday Transactions. - : Royal Society of Chemistry (RSC). - 0956-5000 .- 1364-5455. ; 87:8, s. 1193-1200
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Tidskriftsartikel (refereegranskat)abstract
- A review is presented of experimentally known activation energies, E(a), for the 180-degrees flip motion of the H2O molecule about its two-fold axis in 30 different solid hydrates. The relationship between E(a) and other parameters characterizing a hydrogen bond is discussed. Diagrams correlating E(a) with the hydrogen-bond length, R(o ... x, stretching frequency, nu-OH, librational twist frequency, nu-tw, and deuterium quadrupole coupling constant, e2qQ/h, are presented. The dependence of these correlations on the coordination of the water molecule is discussed, and it is clear that the number of atoms coordinating the water molecule is one of the main factors determining the flip activation energy E(a). The activation energy and the librational twist frequency display a strong correlation, with an associated correlation coefficient of 0.90.
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| 10. |
- Otamiri, JC, et al.
(författare)
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Effect of Zn Substitutions in YBa2Cu3O6 + x Phases on Reactivity during the Ammoxidation of Toluene
- 1991
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Ingår i: Journal of the Chemical Society, Faraday Transactions. - : Royal Society of Chemistry (RSC). - 0956-5000 .- 1364-5455. ; 87:8, s. 1265-1271
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Tidskriftsartikel (refereegranskat)abstract
- Zn substitution in Y-Ba-Cu-O phases influences the catalytic ammoxidation of toluene. The activity for formation of both benzonitrile and CO2 at low and high O2 pressures, respectively, decreases strongly with increasing Zn content up to 4%. Above this substitution level, the activity, however, increases slightly. Characterisations of the surface by XPS and of the bulk by XRD analysis, indicate the presence of overlayers on the catalysts. In these overlayers, irrespective of the Zn content of catalysts, Cu1 states predominate at low O2 pressure and Cu11 at high pressure. These states are associated with selective and non-selective properties, respectively. The activity of the catalysts shows a general tendency to increase with surface copper concentrations as found from XPS studies. However, strong deviations from linearity indicate that the activity of the overlayer is greatly influenced by the bulk acting as a support.
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| 11. |
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| 12. |
- Abellan-Flos, Marta, et al.
(författare)
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QCM sensing of multivalent interactions between lectins and well-defined glycosylated nanoplatforms
- 2019
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Ingår i: Biosensors & bioelectronics. - : Elsevier. - 0956-5663 .- 1873-4235. ; 139
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Tidskriftsartikel (refereegranskat)abstract
- Quartz crystal microbalance (QCM) methodology has been adopted to unravel important factors contributing to the "cluster glycoside effect" observed in carbohydrate-lectin interactions. Well-defined, glycosylated nanostructures of precise sizes, geometries and functionalization patterns were designed and synthesized, and applied to analysis of the interaction kinetics and thermodynamics with immobilized lectins. The nanostructures were based on Borromean rings, dodecaamine cages, and fullerenes, each of which carrying a defined number of carbohydrate ligands at precise locations. The synthesis of the Borromeates and dodecaamine cages was easily adjustable due to the modular assembly of the structures, resulting in variations in presentation mode. The binding properties of the glycosylated nanoplatforms were evaluated using flow-through QCM technology, as well as hemagglutination inhibition assays, and compared with dodecaglycosylated fullerenes and a monovalent reference. With the QCM setup, the association and dissociation rate constants and the associated equilibrium constants of the interactions could be estimated, and the results used to delineate the multivalency effects of the lectin-nanostructure interactions.
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