| 1. |
- da Silva, Fernando L B, et al.
(författare)
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Titration of fatty acids solubilized in catonic, nonionic and anionic micelles: Theory and experiment.
- 2002
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 106:13, s. 3515-3522
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Tidskriftsartikel (refereegranskat)abstract
- The titration properties of a fatty acid solubilized in different types of micelles, cationic, anionic and nonionic, have been investigated experimentally and theoretically. The solution containing micelles, counterions, and added salt was treated as a dielectric continuum in the Monte Carlo simulations. The dielectric permittivity of the interior of the micelle can have a profound effect on the calculated pK shifts depending on how the dielectric discontinuity is chosen in the model. The simulated results are compared to data from Poisson-Boltzmann calculations and from experiments. The experimentally observed apparent pKa value changes from 7.6 to 4.9 when solubilizing lauric acid in anionic (SDS) and cationic (DoTAC) micelles, respectively. For the nonionic micelle it is found to be approximately 6.6. A significant ion specificity in the pKa value is observed for the DoTAC and DoTAB systems and surprisingly enough both systems show an upward pK shift.
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| 2. |
- Kanai, Noriko, et al.
(författare)
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Self-diffusion coefficients of heavy water in low n-alkanes
- 2023
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Ingår i: Journal of Molecular Liquids. - 0167-7322. ; 388
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Tidskriftsartikel (refereegranskat)abstract
- The self-diffusion coefficients of D2O (i.e., heavy water or 2H2O) in eight n-alkanes at 298 K were investigated using 2H NMR diffusometry. D tended to decrease in the n-alkanes with increasing carbon number and be inversely proportional to the n-alkane viscosity to a fractional power. The hydrodynamic radius of D2O in the n-alkanes, calculated from Stokes-Einstein-Sutherland equation with stick boundary conditions, decreased with increasing n-alkane size and was smaller in the n-alkanes than in the bulk phase due to the absence of hydrogen bonds. This study provides fundamental data on the diffusion properties of water molecules dissolved in n-alkanes with applications to, for instance, molecular dynamics simulations or interpretation of Ostwald ripening.
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| 3. |
- Kocherbitov, Vitaly, et al.
(författare)
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Hydration of trimethylamine-N-oxide and of dimethyldodecylamine-N-oxide: An ab initio study
- 2007
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Ingår i: Journal of molecular structure. Theochem. - : Elsevier BV. - 0166-1280. ; 808:1-3, s. 111-118
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Tidskriftsartikel (refereegranskat)abstract
- Density functional theory (B3LYP) calculations of the hydration of trimethylamine-N-oxide (TMAO) and a surfactant dimethyldodecylamine-N-oxide (DDAO) are reported. Hydrogen-bonded complexes of DDAO with up to three water molecules and of TMAO with up to five water molecules are studied. Interactions of both TMAO and DDAO with water give rise to the binding energies that are much higher than that in the water dimer. A significant charge transfer from amine oxide to water is observed. Energies of water-water interactions increase in the presence of amine oxides. The hydration number of TMAO in the hydrogen bonded complexes is shown to be three. The energies of amine oxide-water interactions in the hydrogen bonded complexes have been analyzed using differential energetic parameters analogous to the parameters measured in calorimetric experiments.
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| 4. |
- Söderman, Olle, et al.
(författare)
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NMR in colloid science with special emphasis on self-aggregating systems
- 2002
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Ingår i: Magnetic Resonance in Colloids and Interface Science. Proceedings of the NATO Advanced Research Workshop. - 1402007876 ; , s. 123-138
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Konferensbidrag (refereegranskat)abstract
- The purpose of this paper has been to show how NMR diffusometry can be used to convey information about structure and dynamics of complex fluids. The information can be obtained without the need to invoke complicated models. In fact, simple reasoning pertaining to how a molecule may diffuse through the studied systems allows one to chose between different conceivable solution structures and to obtain non-trivial information about solution structure
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| 5. |
- Söderman, Olle
(författare)
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Nuclear Magnetic Resonance Studies of Bicontinuous Liquid Crystalline Phases of Cubic Symmetry : Transport Properties from 2H Nuclear Magnetic Resonance Relaxation Rates
- 2023
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Ingår i: Langmuir. - 0743-7463. ; 39:26, s. 9085-9093
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Tidskriftsartikel (refereegranskat)abstract
- The ternary system didodecyltrimethylammonium bromide, 1-decanol, and water forms an extended reversed continuous phase of cubic symmetry at 25 °C. The cubic phase belongs to the space group Im3m, as shown by small-angle X-ray experiments. We present extensive deuterium NMR relaxation data from this cubic phase for 1-decanol, deuterated at the carbon adjacent to the hydroxyl carbon position. 2H spin-lattice (R1) and spin-spin (R2) relaxation rates were measured over the existence region of the cubic phase, which extends from 0.2 to 0.6 in volume fraction of the dividing bilayer surface of the cubic phase. The data are interpreted with an existing theoretical framework for NMR spin relaxation in bicontinuous cubic phases, which takes its starting point in the description of bicontinuous phases using periodic minimal surfaces. Specifically, we obtain the self-diffusion coefficient over the minimal surface in one unit cell for 1-decanol. We also present pulsed field gradient NMR-derived self-diffusion data for didodecyltrimethylammonium bromide and compare the two sets of data. The diffusion data for both components show a mild, if any, dependence on the volume fraction of the bilayer surface. Furthermore, we present diffusion data for the water component in the cubic phase. Finally, we discuss the influences of the choice of the value of the product of the deuterium quadrupole constant and the order parameter S. Within the framework of the model used to analyze the relaxation data, a value for this parameter is required. As an initial value, we rely on measurements of deuterium quadrupolar splittings from deuterated decanol in an anisotropic phase.
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| 6. |
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| 7. |
- Gavelin, Patrik, et al.
(författare)
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Amphiphilic polymer gel electrolytes. 4. Ion transport and dynamics as studied by multinuclear pulsed field gradient spin-echo NMR
- 2002
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:13, s. 5097-5104
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Tidskriftsartikel (refereegranskat)abstract
- The transport dynamics in gel electrolytes based on amphiphilic polymers was found to be faster than in gel electrolytes based on corresponding nonamphiphilic polymers. The amphiphilic polymer studied was a polymethacrylate grafted with fluorocarbon and (EO)(9) side chains, and the nonamphiphilic one was a polymethacrylate carrying only (EO)(9) side chains. Self-diffusion coefficients of gel electrolytes based on the two polymers with different contents of 1 M lithium bis(trifluoromethylsulfonyl) imide (LiTFSI) salt in gamma-butyrolactone were determined by H-1, F-19, and Li-7 pulsed field gradient spin-echo NMR spectroscopy. The polymer self-diffusion coefficients showed that the amphiphilic polymer molecules diffused faster than the nonamphiphilic ones and seemed more intramolecularly aggregated than intermolecularly. At electrolyte contents above 43 wt %, the ion conductivity of the amphiphilic polymer gel electrolytes was higher than for the corresponding gel based on the nonamphiphilic polymer under identical conditions, as measured by impedance spectroscopy. Moreover, the lithium ion diffusion coefficient in the amphiphilic gel electrolytes was found to be significantly higher than that for corresponding gels based on the nonamphiphilic polymer, The higher ethylene oxide content of the nonamphiphilic polymer decreased the mobility of the lithium ions due to cooperative coordination of lithium ions by ether oxygens in comparison with gamma-BL. The TFSI anion diffusion was however approximately the same in the two gel systems. Consequently, the apparent lithium transference number (taudivided by) of the amphiphilic gels was higher by almost a factor of 3 as compared to that of the gels based on the nonamphiphilic polymer. A splitting of the TFSI signal in the F-19 NMR spectra suggested that the TFSI anions in the amphiphilic polymer gels were partly present in a solvent-rich environment and partly associated with the aggregates formed by the fluorinated side chains. This kind of splitting was not observed in the spectra of the gels based on the nonamphiphilic polymer. The association of TFSI anions to the aggregated fluorinated side chains may thus also play a role in increasing the value of taudivided by for the amphiphilic polymer gels.
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| 8. |
- Pettersson, Erik, et al.
(författare)
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Surfactant/nonionic polymer interaction. a NMR diffusometry and NMR electrophoretic investigation
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:4, s. 1138-1143
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between the nonionic polymer poly(ethylene oxide) (PEO) of molecular weight 20 000 and surfactants of various types [sodium dodecyl sulfate (SDS), dodecyl trimethylammonium bromide, octyl beta-D-glucoside, and potassium laurate] has been investigated in an aqueous solution at 25 degreesC by H-1 NMR pulsed-gradient spin-echo self-diffusion techniques. The SDS/PEO study was further complemented by component-resolved H-1 NMR-based studies of the electrophoretic mobility of PEO and the alkyl part of SDS under the same measurement conditions. Through such combined studies, a much more complete picture of the binding and aggregation processes becomes accessible.
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| 9. |
- Söderman, Olle, et al.
(författare)
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NMR studies of surfactants
- 2004
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Ingår i: Concepts in magnetic resonance. Bridging education and research. - : Wiley. - 1546-6086 .- 1552-5023. ; 23A:2, s. 121-135
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Tidskriftsartikel (refereegranskat)abstract
- Surfactant molecules are amphipathic and posses complicated solution chemistry and self-assembly properties. In addition to being of enormous practical significance, the physical characterization of surfactant systems presents a rich area of condensed matter physics. This article focuses on the application and interpretation of the commonly used NMR approaches for probing these systems. In particular, the use of NMR relaxation, diffusometry and, more briefly, electrophoretic NMR to determine characteristics such as micellar size and structure, ion-binding and solubilization are considered. The application of these NMR techniques is illustrated by a number of pertinent examples.
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| 10. |
- Thoren, Per, 1972, et al.
(författare)
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Interactions of novel, nonhemolytic surfactants with phospholipid vesicles.
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1751-6668 .- 0743-7463 .- 1520-5827. ; 23:13, s. 6956-6965
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Tidskriftsartikel (refereegranskat)abstract
- PEG-12-acyloxystearates constitute a novel class of pharmaceutical solubilizers and are synthesized from polyethylene glycol and 12-hydroxystearic acid, which has been esterified with a second acyl chain. The hemolytic activity of these surfactants decreases drastically with increasing pendant acyloxy chain length, and surfactants with an acyloxy chain of 14 carbon atoms or more are essentially nonhemolytic. In this paper, the interactions of PEG-12-acyloxystearates (acyloxy chain lengths ranging from 8 to 16 carbon atoms) with phosphatidylcholine vesicles, used as a model system for erythrocyte membranes, were studied in search of an explanation for the large variations in hemolytic activity. Surfactant-induced alterations of membrane permeability were investigated by studying the leakage of vesicle-entrapped calcein. It was found that all of the surfactants within the series interact with the vesicle membranes and cause slow leakage at elevated surfactant concentrations, but with large variations in leakage kinetics. The initial leakage rate decreases rapidly with increasing pendant acyloxy chain length. After prolonged incubation, on the other hand, the leakage is not a simple function of acyloxy chain length. The effect of the surfactants on membrane integrity was also investigated by turbidity measurements and cryo-transmission electron microscopy. At a surfactant/lipid molar ratio of 0.4, the vesicle membranes are saturated with surfactant. When the surfactant/lipid molar ratio is further increased, the vesicle membranes are progressively solubilized into mixed micelles. The rate of this process decreases strongly with increasing acyloxy chain length. When comparing the results of the different experiments, it can be concluded that there is no membrane permeabilization below saturation of the vesicle membranes. The large variations in the kinetics suggest that several steps are involved in the mechanism of leakage induced by PEG-12-acyloxystearates and that their relative rates vary with acyloxy chain length. The slow kinetics may in part be explained by the low critical micelle concentrations (CMCs) exhibited by the surfactants. The CMCs were found to be in the range of 0.003-0.025 microM.
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