| 1. |
- Frise, Anton, et al.
(author)
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Adsorption isotherms of cationic surfactants on silica particles measured by NMR spectroscopy
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Other publication (other academic/artistic)abstract
- We present here a new method that employs NMR spectroscopy to quantify the adsorbed amount of surfactant on the surface of particles and thereby provide the adsorption isotherm. As demonstration, the adsorption isotherms for a series of cationic surfactants on silica particles are obtained. Those results are in general agreement with previous observations and the overall appearances of adsorption isotherms exemplify the interplay between electrostatic and hydrophobic interactions. Compared to other available methods, the experimental error is comparable or smaller in a very wide range of surfactant concentrations and there exist other potential advantages.
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| 2. |
- Frise, Anton, et al.
(author)
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Anisotropic Ion Mobility in an Ionic Liquid Crystal Complex of a Rodlike Mesogen Containing an Oxyethylene Moiety and Lithium Triflate
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Other publication (other academic/artistic)abstract
- A liquid-crystalline (LC) complex of a rodlike mesogen containing an oxyethylene moiety and lithium triflate has been synthesized and its mesophases have been characterized by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). The ion conductive behaviour was investigated in isotropic and LC phases and related to the ionic mobility, as observed by 7Li and 19F NMR diffusometry. The observed two-dimensional ion mobilities show that planes conducting both lithium and triflate ions are formed in the smectic mesophases. The conductivity of the lithium ions is large in the smectic C phase where conductive planes rich in ethylene oxide chains exist.
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| 3. |
- Frise, Anton E., et al.
(author)
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Ion Channels and Anisotropic Ion Mobility in a Liquid-Crystalline Columnar Phase As Observed by Multinuclear NMR Diffusometry
- 2010
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:47, s. 15477-15482
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Journal article (peer-reviewed)abstract
- The anisotropic diffusion of anions and cations in the columnar and isotropic phases of a fan-shaped imidazolium hexafluorophosphate salt is measured by H-1 and F-19 diffusion NMR experiments. The macroscopic orientation of the columnar phase is investigated by H-2 NMR spectroscopy. We find that the anions, confined by the cations, diffuse faster than the cations along the columns but slowly across them, which exemplifies the ion channel model of these materials. The cations and anions are dissociated in the columnar phase but are paired or clustered in the isotropic phase.
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| 4. |
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| 5. |
- Frise, Anton E., et al.
(author)
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Protein Dispersant Binding on Nanotubes Studied by NMR Self-Diffusion and Cryo-TEM Techniques
- 2010
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 1:9, s. 1414-1419
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Journal article (peer-reviewed)abstract
- Carbon nanotubes can be dispersed by a variety of molecules. We investigate the dynamics of protein-assisted carbon nanotube dispersion in water. We find that in equilibrium only a small fraction of the dispersants is indeed adsorbed to the nanotube Surface, while there is a fast exchange process between the adsorbed and free protein molecules. Self-diffusion NMR spectroscopy in combination with cryo-transmission electron microscopy imaging are employed.
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| 6. |
- Frise, Anton, 1982-
(author)
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Nano-segregated soft materials observed by NMR spectroscopy
- 2011
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Doctoral thesis (other academic/artistic)abstract
- This thesis is about using nuclear magnetic resonance (NMR) spectroscopy for studying soft materials. Soft materials may be encountered everyday by most readers of this thesis, for example when taking a shower or watching TV. The usefulness of these materials originates from them being soft yet, at the same time, having some kind of a structure. The characteristic length scale of those structures is often on the order of nanometers (10-9 m) and the structure can respond to various external stimuli such as temperature, electric and magnetic fields, or the presence of interfaces. NMR spectroscopy excels when studying soft materials because it is a non-invasive technique with a large spectral resolution. Moreover, different NMR methods allow us to study local molecular dynamics or longer-range translational diffusion. Understanding those latter aspects is very important for the development of dynamic and responsive materials. Papers I-III present our work on assessing molecular adsorption on interfaces in colloidal dispersions. Here, carbon nanotubes (CNTs) or silica particles were the colloidal substrates to which proteins, polymers or surfactants adsorbed. Papers IV-VI concern ionic mobility in liquid crystals (LCs). The influence of material structure on, for example, the anisotropy of diffusion or on the association/dissociation of ions was studied in several LC phases.
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| 7. |
- Frise, Anton, et al.
(author)
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Polymer binding to carbon nanotubes in aqueous dispersions : Residence time on the nanotube surface As Obtained by NMR diffusometry
- 2012
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 116:9, s. 2635-2642
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Journal article (peer-reviewed)abstract
- The binding of block copolymer Pluronic F-127 in aqueous dispersions of single- (SWCNT) and multiwalled (MWCNT) carbon nanotubes has been studied by pulsed-field-gradient (PFG) 1H NMR spectroscopy. We show that a major fraction of polymers exist as a free species while a minor fraction is bound to the carbon nanotubes (CNT). The polymers exchange between these two states with residence times on the nanotube surface of 24 ± 5 ms for SWCNT and of 54 ± 11 ms for MWCNT. The CNT concentration in the solution was determined by improved thermal gravimetric analysis (TGA) indicating that the concentration of SWCNT dispersed by F-127 was significantly higher than that for MWCNT. For SWCNT, the area per adsorbed Pluronic F-127 molecule is estimated to be about 40 nm 2.
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| 8. |
- Frise, Anton, et al.
(author)
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Polymer Binding to Carbon Nanotubes in Aqueous DispersionsStudied by NMR Diffusometry
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Other publication (other academic/artistic)abstract
- The diffusion behavior of block copolymer Pluronic F-127 in aqueous dispersions of single-walled (SW) and multi-walled (MW) carbon nanotubes (CNT) has been studied by pulsed-field-gradient (PFG) 1H NMR spectroscopy. We show that the polymers are either free monomers or bound to the CNT and exchange between these two states. The residence times and relative populations in those states could also be obtained. For both classes of CNT, the residence time in the bound state was found to be similar and in the order of 10-100 milliseconds. Thermal gravimetric analysis (TGA) showed that the SWCNT concentration dispersed by F-127 was higher than that for MWCNT.
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| 9. |
- Svedendahl, Maria, 1975-, et al.
(author)
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Direct Epoxidation in Candida antarctica Lipase B Studied by Experiment and Theory
- 2008
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In: ChemBioChem. - : Wiley. - 1439-4227 .- 1439-7633. ; 9:15, s. 2443-2451
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Journal article (peer-reviewed)abstract
- Candida antarctica lipase B (CALB) is a promiscuous serine hydrolase that, besides its native function, catalyzes different side reactions, such as direct epoxidation. A single-point mutant of CALB demonstrated a direct epoxidation reaction mechanism for the epoxidation of alpha,beta-unsaturated aldehydes by hydrogen peroxide in aqueous and organic solution. Mutation of the catalytically active Ser105 to alanine made the previously assumed indirect epoxidation reaction mechanism impossible. Gibbs free energies, activation parameters, and substrate selectivities were determined both computationally and experimentally. The energetics and mechanism for the direct epoxidation in CALB Ser105Ala were investigated that the reaction proceeds through a two step-mechanism with formation of an oxyanionic intermediate. The active-site residue His224 functions as a general acid-base catalyst with support from Asp187. Oxyanion stabilization is facilitated by two hydrogen bonds from Thr40.
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