| 1. |
- Acke, Filip, et al.
(author)
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Effects of O-2 on the reduction of NO over prereduced CaO surfaces: A mechanistic understanding
- 1999
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In: Journal of Physical Chemistry B Materials. - 1089-5647. ; 110:12, s. 2195-2201
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Journal article (peer-reviewed)abstract
- The effect of O-2 on the reduction of NO over prereduced CaO surfaces is investigated. The experimental results suggest the existence of at least three different reaction channels, of which two are related to the high-temperature reduction of the CaO surfaces and involve the use of extra electrons in breaking the NO bond. The third reaction channel does not employ extra electrons for bond breaking, but the activity is affected by the amount of adsorbed surface oxygens. The difference between the former two reaction channels is found in the temperature needed for an observable activity. The reaction channel which is already active at low temperatures is described by a model based on F-centers, whereas the one which needs elevated temperatures involves a hole transport through the bulk. The activation energy for this transport is determined experimentally using a temperature-programmed reaction technique as well as theoretically by means of ab initio quantum chemistry calculations. Room-temperature exposure to O-2 is suggested to result in a poisoning of the F-centers, but has only a minor effect on the reaction channel proposed for high temperatures. Effects on the reduction of NO of time as well as temperature for the O-2 exposure step are also investigated and found to be consistent with an understanding based on the coexistence of different reaction channels.
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| 2. |
- Acke, Filip, et al.
(author)
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Kinetic study of heterogeneous oxygen-exchange reactions and bulk self-diffusion of oxygen
- 1998
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In: Journal of Physical Chemistry B Materials. - 1089-5647. ; 102:26, s. 5158-5164
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Journal article (peer-reviewed)abstract
- Apparent activation energies are determined for oxygen-isotope exchange reactions between O2, CO, or NO and preoxidized or prereduced CaO surfaces. Oxygen exchange between N16O or C16O and isotope labeled Ca18O surfaces produced an apparent activation energy of 2 kcal/mol. Similar values are obtained for single- isotope-exchange between 18O18O and prereduced Ca16O surfaces. Apparent activation energies of 15−18 kcal/mol are found for single and double exchange between 18O18O and preoxidized Ca16O surfaces, as well as for double exchange between 18O18O and prereduced Ca16O surfaces. The low apparent activation energies are believed to result from adsorbed intermediates, whereas the high values may involve the formation of a singlet O2 transient. It is shown that eventually the self-diffusion of oxygen ions in the bulk becomes the rate-determining step in the isotope-exchange reaction. Apparent activation energies are determined, and the values are found to depend on surface treatment, (i.e., 44 kcal/mol under reducing and 78 kcal/mol under oxidizing conditions). The involvement of oxygen vacancies under reducing conditions is discussed.
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| 3. |
- Acke, Filip, et al.
(author)
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Promoting effects of Na and Fe impurities on the catalytic activity of CaO in the reduction of NO by CO and H-2
- 1998
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In: Journal of Physical Chemistry B Materials. - 1089-5647. ; 102:26, s. 5127-5134
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Journal article (peer-reviewed)abstract
- The heterogeneous reduction of NO by H-2 and CO over different CaO materials is investigated. The dependence of the specific NO reduction rate on the impurity content is demonstrated for both reducing species. The roles of two specific impurities, i.e., Na and Fe, as well as their combined effect are investigated. The apparent activation energies for the NO + CO and NO + Hz reactions are determined for three different calcium oxides. Values between 26 and 28 kcal/mol are obtained. The influence of impurity content is found in the preexponential factor of the Arrhenius equation. A reaction mechanism based on a rate-determining surface-oxygen-abstraction step is suggested. This mechanistic understanding is explored to compare the activities of other alkaline-earth oxides. Particularly, a linear correlation between the apparent activation energy and the lattice parameter is observed.
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| 4. |
- Acke, Filip, 1968, et al.
(author)
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Role of adsorbed surface oxygen in the adsorption of NO on alkaline earth oxides and Pt-promoted CaO surfaces
- 1999
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In: Journal of Physical Chemistry B Materials. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 103:6, s. 972-978
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Journal article (peer-reviewed)abstract
- Adsorbed surface oxygens are formed on CaO, SrO, and BaO during exposure to N2O, and their presence is shown to affect the room-temperature NO adsorption. Information about the adsorbed intermediates is contained in the desorption products and in the desorption temperatures during the subsequent heating ramp in Ar. The presence of adsorbed oxygen species increases the total amount of adsorbed NO for CaO and BaO substrates, whereas for SrO the adsorbed intermediate is stabilized. Two NO desorption peaks are found for CaO and SrO, one at low and one at high temperature. The former is assigned to adsorbed NO, whereas the latter is assigned to adsorbed -NO2 and/or -NO3 species. NO adsorption as -NO2 and/or -NO3 species finds evidence in the corresponding O2 desorption. Only one NO desorption peak is found for BaO. This NO desorption peak disappears in the absence of preadsorbed surface oxygens. O2 desorption is observed, even in the absence of any preadsorbed surface oxygens, for CaO and SrO substrates. This suggests NO bond dissociation upon NO adsorption. The effect of the promotion of CaO by Pt has also been investigated. The respective desorption profiles are similar to those for the unpromoted CaO with preadsorbed surface oxygens, although the amounts are significantly increased.
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| 5. |
- Adebahr, J, et al.
(author)
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Ion and solvent dynamics in gel electrolytes based on ethylene oxide grafted acrylate polymers
- 2002
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In: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106 .- 1089-5647. ; 106:47, s. 12119-12123
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Journal article (peer-reviewed)abstract
- Multinuclear pulsed field gradient NMR measurements and theological viscosity measurements were performed on three series of polymer gel electrolytes. The gels were based on a lithium salt electrolyte swollen into a copolymer matrix comprising an acrylate backbone and ethylene oxide side chains. In each series the side chains differed in length and number, but the acrylate-to-ethylene oxide ratio was kept constant. It was found that the self-diffusion coefficient of the cations was much lower than that of the anions, and that it decreased rapidly when the side chains got longer. In contrast, the self-diffusion coefficient of the anions was found to be independent of chain length. In the gel electrolytes, the diffusion coefficients of the solvent molecules are relatively constant despite an increased viscosity with increasing length of the side chains. However, in saltfree gels made for comparison, the diffusion coefficients of the solvent molecules decreased with, increasing length of the side chains, which is consistent with an increased viscosity.
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| 6. |
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Bales, BL, et al.
(author)
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Time-resolved fluorescence quenching and electron paramagnetic resonance studies of the hydration of lithium dodecyl sulfate micelles
- 2000
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In: JOURNAL OF PHYSICAL CHEMISTRY B. - : AMER CHEMICAL SOC. - 1089-5647. ; 104:2, s. 256-263
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Journal article (peer-reviewed)abstract
- A spin-probe method to study the surface hydration of sodium dodecyl sulfate (SDS) micelles (Bales, B. L.; Messina, L.; Vidal, A.; Peric, M.; Nascimento, O. R. J. Phys. Chem. 1998, 102, 10347; referred to as I) is applied to lithium dodecyl sulfate (LiDS)
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| 11. |
- Bauer, C., et al.
(author)
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Electron injection and recombination in Ru(dcbpy)(2)(NCS)(2) sensitized nanostructured ZnO
- 2001
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:24, s. 5585-5588
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Journal article (peer-reviewed)abstract
- The dynamics of electron-transfer processes between bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2'-bypiridine-4,4'-dicarboxylato)ruthenium(II) (called N719) and nanostructured ZnO films have been investigated by femtosecond and nanosecond spectroscopy. The incident photon to current conversion efficiency (IPCE) for these dye-sensitized electrodes was 36% in the maximum of 530 nm, corresponding to a quantum efficiency of 80%. The highest: IPCE values were obtained when the electrodes were prepared under conditions where formation of dye aggregates in the pores of the nanostructured films is avoided. For such films, the electron injection time was in the subpicosecond regime (< 300 fs), which is comparable to the N719-TiO2 system. The back electron-transfer kinetics between conduction band electrons and oxidized dye molecules were biexponential with time constants of 300 mus and 2.6 us. Variation of the light intensity did not affect the time constants, but only their relative weights. The kinetics of back electron transfer in the N719-ZnO and N719-TiO2 systems were found to be identical.
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| 12. |
- Bauer, Christophe, et al.
(author)
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Electron injection and recombination in Ru(dcbpy)(2)(NCS)(2) sensitized nanostructured ZnO
- 2001
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In: JOURNAL OF PHYSICAL CHEMISTRY B. - : AMER CHEMICAL SOC. - 1089-5647. ; 105:24, s. 5585-5588
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Journal article (peer-reviewed)abstract
- The dynamics of electron-transfer processes between bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2'-bypiridine-4,4'-dicarboxylato)ruthenium(II) (called N719) and nanostructured ZnO films have been investigated by femtosecond and nanosecond spectrosco
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| 13. |
- Bergström, Lars Magnus, et al.
(author)
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A small-angle neutron scattering study of surfactant aggregates formed in aqueous mixtures of sodium dodecyl sulfate and didodecyldimethylammonium bromide
- 2000
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 104:17, s. 4155-4163
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Journal article (peer-reviewed)abstract
- The structure of aggregates formed in aqueous mixtures of a single-chain anionic surfactant, sodium dodecyl sulfate (SDS), and a double-chain cationic surfactant, didodecyldimethylammonium bromide (DDAB), has been investigated at 38 degrees C using small-angle neutron scattering (SANS). Several overall surfactant concentrations [SDS] + [DDAB] between 0.1 and 5 wt % were measured at the two SDS-rich compositions [SDS]:[DDAB] = 90:10 and 95:5. Samples with a concentration above about [SDS] + [DDAB] = 1 wt % at [SDS]:[DDAB] = 95:5 contained only somewhat elongated tablet-shaped micelles (triaxial ellipsoids) with typical values of the half-axes a (related to the thickness) = 14 Angstrom, b (related to the width) = 23 Angstrom, and c (related to the length) = 27 Angstrom. When a sample at [SDS]:[DDAB] = 95:5 is diluted below about [SDS] + [DDAB] = 1 wt %, an increasing amount of small unilamellar vesicles forms, and in the samples below about 0.2 wt %, only vesicles are observed. The average radius of the vesicles [R] increases from about 90 Angstrom at 0.3 wt % to 110 Angstrom at 0.1 wt %. The transition from micelles to vesicles with decreasing surfactant concentration was also observed in the samples at [SDS]:[DDAB] = 90:10 in which, however, an additional amount of bilayer sheets was seen to be always present. Compared with the micelles at [SDS]:[DDAB] = 95:5, the micelles formed at [SDS]:[DDAB] = 90:10 were considerably longer (c approximate to 40 Angstrom), but with similar cross section dimensions, and the vesicles formed were seen to be somewhat larger than the corresponding aggregates at 95:5. The relative standard deviation sigma(R)/[R] of the (number-weighted) vesicle size distributions was in the range 0.2 < sigma(R)/[R] < 0.3.
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| 14. |
- Bertilsson, L, et al.
(author)
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Adsorption of dimethyl methylphosphonate on self-assembled alkanethiolate monolayers
- 1998
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In: JOURNAL OF PHYSICAL CHEMISTRY B. - : AMER CHEMICAL SOC. - 1089-5647 .- 1520-6106 .- 1520-5207. ; 102:7, s. 1260-1269
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Journal article (peer-reviewed)abstract
- The adsorption of dimethyl methylphosphonate (DMMP), a model molecule for sarin, on three different organic interfaces, prepared by solution self-assembly of alkanethiols on gold, was followed by a surface acoustic wave mass sensor and infrared reflection-absorption spectroscopy at room temperature. The surfaces, characterized by the following tail groups (-OH, -CH3, -COOH), show both quantitative and qualitative differences concerning the interaction with DMMP, the acid surface giving rise to the strongest adsorption. Results obtained in UHV, at low temperatures using infrared spectroscopy and temperature-programmed desorption, support this observation and give complementary information about the nature of the interaction. The hydrogen-bond-accepting properties of the P=O part of DMMP and its impact on the design of sensing interfaces based on hydrogen bonding, as well as the use of self-assembled monolayers to study molecular interactions, are discussed.
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| 15. |
- Bertilsson, Lars, et al.
(author)
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Interaction of dimethyl methylphosphonate with alkanethiolate monolayers studied by temperature-programmed desorption and infrared spectroscopy
- 1997
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In: JOURNAL OF PHYSICAL CHEMISTRY B. - : AMER CHEMICAL SOC. - 1089-5647 .- 1520-6106 .- 1520-5207. ; 101:31, s. 6021-6027
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Journal article (peer-reviewed)abstract
- The adsorption of dimethyl methylphosphonate (DMMP) on well-defined organic surfaces consisting of self-assembled monolayers (SAMs) of omega-substituted alkanethiolates on gold has been studied. Three different surfaces were examined: one terminated with -OH groups (Au/S-(CH2)(16)-OH), one with -CH3 (Au/S-(CH2)(15)-CH3), and one mixed surface with approximately equal amounts of -OH and -CH3 terminated thiols. Detailed information about the nature and strength of the interaction was gathered by infrared reflection-absorption spectroscopy and temperature-programmed desorption under ultrahigh-vacuum conditions. It is found that the outermost functional groups of the thiol monolayer have a pronounced impact on the interaction with DMMP at low coverage. The -OH surface, allowing for hydrogen bonds with the P=O part of the DMMP molecule, increases the strength of interaction by approximately 3.8 kJ/mol as compared to the -CH3 surface. A preadsorbed layer of D2O leads to stronger interaction on all surfaces. This is explained by additional hydrogen bond formation between free O-D at the ice-vacuum interface and DMMP.
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| 16. |
- Biesuz, R., et al.
(author)
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Estimation of deprotonation coefficients for chelating ion exchange resins. Comparison of different thermodynamic model
- 2001
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:20, s. 4721-4726
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Journal article (peer-reviewed)abstract
- The deprotonation of quinolic resin P-127 and iminodiacetic resin Amberlite IRC-718 has been studied. The process of salt transfer into the resin phase is considered to be an important contributor to the deprotonation process. Estimation of the salt transfer was based on the principle of equal activity of the salt in both phases at equilibrium. Two assumptions were made: sorbed alkali metal ions are not associated with functional groups, while all hydrogen ions are associated with functional groups. The associated hydrogen ions and functional groups do not contribute to the internal ionic strength value. Two thermodynamic models, describing the deprotonation of ion-exchange resin, were used and compared: the Gibbs-Donnan-based model of Bukata and Marinsky and the model proposed by Erik Hogfeldt. Thermodynamic characteristics of the resins' deprotonation are obtained using two different thermodynamic approaches. Hogfeldt's three-parameter model provides a better agreement with experimental data. The fitting of the data to Marinsky's method can be improved by taking into account the influence of the resins' macroporosity; however, this requires an additional empirical parameter to describe the resin.
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| 17. |
- Boschloo, Gerrit, et al.
(author)
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Spectroelectrochemical investigation of surface states in nanostructured TiO2 electrodes
- 1999
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In: JOURNAL OF PHYSICAL CHEMISTRY B. - : AMER CHEMICAL SOC. - 1089-5647. ; 103:12, s. 2228-2231
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Journal article (other academic/artistic)abstract
- Surface states at the nanostructured TiO2 (anatase)/aqueous electrolyte interface have been investigated using spectroelectrochemical methods. It is found that electrons trapped in these states have an absorption spectrum that differs significantly from t
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| 18. |
- Boschloo, Gerrit, et al.
(author)
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Spectroelectrochemistry of nanostructured NiO
- 2001
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:15, s. 3039-3044
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Journal article (peer-reviewed)abstract
- Transparent nanostructured NiO electrodes have been prepared by heating Ni(OH)(2) sol-gel films at a temperature of 300-320 degreesC. Nanostructured NiO (bunsenite) behaves as a p-type semiconductor and has an indirect band gap of 3.55 eV. It shows a strong anodic electrochromic effect, as it changes color from transparent to brown-black upon application of positive potentials. This effect is caused by oxidation of Ni atoms located at the NiO/electrolyte interface. Electrochemical oxidation reactions are highly reversible in both aqueous and nonaqueous electrolytes. In aqueous electrolyte, the half-potentials show a Nernstian pH dependence, whereas in nonaqueous electrolytes, the type of cation present determines the shape and position of the cyclic voltammogram.
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| 19. |
- Boschloo, Gerrit, et al.
(author)
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Spectroelectrochemistry of nanostructured NiO
- 2001
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In: JOURNAL OF PHYSICAL CHEMISTRY B. - : AMER CHEMICAL SOC. - 1089-5647. ; 105:15, s. 3039-3044
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Journal article (peer-reviewed)abstract
- Transparent nanostructured NiO electrodes have been prepared by heating Ni(OH)(2) sol-gel films at a temperature of 300-320 degreesC. Nanostructured NiO (bunsenite) behaves as a p-type semiconductor and has an indirect band gap of 3.55 eV. It shows a stro
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| 20. |
- Brinck, Tore, et al.
(author)
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Solvation of carbanions in organic solvents : A test of the polarizable continuum model
- 2000
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 104:42, s. 9887-9893
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Journal article (peer-reviewed)abstract
- The solvation of carbanions in the solvents N,N-dimethylformamide (DMF) and tetrahydrofuran (THF) has been analyzed on the basis of experimental and theoretical data. Experimental solvation energies are obtained from present and previously reported electrochemical measurements of reduction potentials of the corresponding radicals. Theoretical solvation energies are obtained from quantum chemical calculations using the polarizable continuum model (PCM). It is found that the solvation energy is relatively independent of molecular size and structure for the saturated carbanions. This indicates that the negative charge is strongly localized to the anionic carbon. The conjugated carbanions have considerably lower absolute solvation energies (\ DeltaG degrees (sol)\) than the saturated carbanions. This is a consequence of the strong delocalization of the negative charge in the former group. The propargyl anion is also found to have a surprisingly low absolute solvation energy. However, high-level quantum chemical calculations show that the electronic structure has large contributions from two different resonance structures, CH=CCH2- and -CH=C=CH2, which results in a significant charge delocalization. There is good agreement between calculated and experimental solvation energies for both the conjugated and nonconjugated primary anions. However, the PCM method consistently underestimates the absolute solvation energies of the secondary and tertiary carbanions. This is attributed to an insufficient treatment of first-layer solvation effects in the method. According to the experimental measurements, the absolute solvation energies are on average 2-3 kcal mol(-1) lower in THF than in DMF. The theoretical data indicate a considerably larger solvent effect, 7-10 kcal mol(-1). The discrepancy between theory and experiment may partly be attributed to the use of a supporting electrolyte in the measurements, but the main cause seems to be that the short-range interaction tendencies of the solvent cannot be Fully characterized by its dielectric constant.
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| 21. |
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| 22. |
- Cho, K. B., et al.
(author)
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The substrate reaction mechanism of class III anaerobic ribonucleotide reductase
- 2001
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:27, s. 6445-6452
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Journal article (peer-reviewed)abstract
- The substrate mechanism of class III anaerobic ribonucleotide reductase has been studied using quantum chemical methods. The study is based on the previously suggested mechanism for the aerobic class I enzyme, together with the recently determined X-ray structure of the anaerobic enzyme. The initial steps are similar in the mechanisms of these enzymes, but for the suggested rate-limiting steps there are key differences. In the class I enzyme, the 3 ' -keto group of the substrate is protonated in a step involving formation of a sulfur-sulfur bond between two cysteines, One of these cysteines is not present in the anaerobic enzyme. Instead, carbon dioxide is formed in this step from formate, which is present as a cofactor. In line with previous suggestions from experimental observations, the formate first forms a formyl radical. The next step, where the formyl radical protonates the 3 ' -keto group of the substrate, is suggested to be rate limiting with a calculated total barrier of 19.9 kcal/mol, in reasonable agreement with the experimental rate-limiting barrier of 17 kcal/mol. Zero-point and entropy effects are found to be quite significant in lowering the barrier. The mechanism for the entire cycle is discussed in relation to known experimental facts.
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| 23. |
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| 24. |
- Claesson, Per M., et al.
(author)
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Mixtures of cationic polyelectrolyte and anionic surfactant studied with small-angle neutron scattering
- 2000
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 104:49, s. 11689-11694
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Journal article (peer-reviewed)abstract
- Small-angle neutron scattering (SANS) data for solutions containing a highly charged cationic polyelectrolyte and an anionic surfactant are presented. The scattering data were obtained in pure D2O, emphasizing the scattering from the polyelectrolyte, and in a H2O/D2O mixture that contrast matches the polyelectrolyte. In the absence of surfactant, a broad scattering peak due to the mesh size of the polyelectrolyte solution is the most characteristic feature. This peak moves to larger q-values (smaller distances) as the polyelectrolyte concentration is increased, as expected for a semidilute polyelectrolyte solution. Addition of a small amount of surfactant reduces and finally removes this peak. Instead a sharp diffraction peak appears at high q-values. This Bragg peak corresponds to a characteristic distance of 37-39 Angstrom, and it is observed when either the polyelectrolyte or the surfactant is contrast matched by the solvent. Once this peak has appeared, its position does not change when the surfactant concentration is increased. The intensity of the peak grows, however, until a stoichiometric polyelectrolyte-surfactant complex has been formed. The Bragg peak remains in excess surfactant solution. These results are discussed in relation to the structure of the polyelectrolyte-surfactant aggregates and in connection with recent results from surface force and turbidity measurements using the same polyelectrolyte-surfactant pair.
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| 25. |
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