| 2. |
- Jóhannesson, Haukur
(författare)
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Nuclear Magnetic Relaxation Dispersion and Pulsed-Gradient Spin Echo Studies of Biomolecular Solutions and Amphiphilic Liquid Crystals.
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomolecular solutions and amphiphilic liquid crystals are studied by Nuclear Magnetic Resonance Dispersion (NMRD) and Pulsed-Gradient Spin Echo (PGSE) respectively. A random-flight simulation is performed to obtain the obstructing factors for self-diffusion of small molecules in macrofluids. The accuracy of existing mean-field approximations for the obstruction factors is analyzed. The orientational order and the size of the discoidal micelles in the nematic phase of the binary system CsPFO/water is studied by water self-diffusion measurements using the 2H PGSE NMR technique. The results challenge the theoretical predictions based on hard-particle models, and indicate that soft potentials, such as the anisotropic double-layer repulsion, are important. The 2H NMRD technique is used to characterize interactions of DMSO with globular proteins. The importance of specific binding sites for a stable DMSO-protein complex is demonstrated. The observed NMRD for DMSO/lysozyme solution is found to be due to a single DMSO molecule in the active site of the protein. A quantitative analysis yields information about orientational order and residence time of this DMSO molecule. The hydration of six B-DNA dodecamers with A-tracts of variable length and sequence is investigated via the NMRD of the water 2H and 17O resonances. Highly ordered long-lived water molecules are found in the minor groove of the duplex, with an occupancy which is correlated with the width of the groove. An essentially invariant residence time is found for all long-lived water molecules, suggesting that water exchange occurs from an open state with a uniformly wide minor groove. A model-free approach for analyzing stretched dispersion profiles is proposed. The method is validated with the aid of synthetic relaxation data, and is then applied to water 1H NMRD data from solutions of BPTI. It is demonstrated that a widely used empirical dispersion function for stretched NMRDs, known as ”the Cole-Cole expression”, is unphysical and gives qualitatively different results, as compared to the model-free approach, when used in the analysis of the BPTI data.
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| 3. |
- Stefánsson, Andri, et al.
(författare)
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Quantifying mixing, boiling, degassing, oxidation and reactivity of thermal waters at Vonarskard, Iceland
- 2016
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Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 309, s. 53-62
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Tidskriftsartikel (refereegranskat)abstract
- The chemical composition of geothermal fluids may be altered upon ascent from the reservoir to surface by processes including boiling, degassing, mixing, oxidation and water-rock interaction. In an attempt to quantify these processes, a three step model was developed that includes: (1) defining the composition of the end-member fluid types present in the system, (2) quantifying mixing between the end-members using non-reactive elemental concentrations and enthalpy and (3) quantifying the changes of reactive elements including degassing, oxidation and water-rock interaction. The model was applied to geothermal water at Vonarskard, Iceland, for demonstration having temperatures of 3-98°C, pH of 2.15-9.95 and TDS of 323-2250ppm, and was thought to be produced from boiled reservoir water, condensed steam and non-thermal water. Most geothermal water represented mixture of non-thermal water and condensed steam whereas the boiled reservoir water was insignificantly mixed. CO2 and H2S degassing was found to be quantitative in steam-heated water, with oxidation of H2S to SO4 also occurred. In contrast, major rock forming elements are enriched in steam-heated water relative to their mixing ratios, suggesting water-rock interaction in the surface zone. Boiled reservoir water observed in alkaline hot springs have, however, undergone less geochemical changes upon ascent to surface and within the surface zone.
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