| 39731. |
- Nordstierna, Lars, 1976, et al.
(författare)
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Comparison of release behaviour from microcapsules and microspheres
- 2010
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Ingår i: Progress in Organic Coatings. - : Elsevier BV. - 0300-9440. ; 69:1, s. 49-51
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Tidskriftsartikel (refereegranskat)abstract
- The plasticizing effect of core oil in the polymer shell of core shell particles, so-called microcapsules, was here examined. The study involved release measurements of 4-nitroanisole into aqueous solution from two types of microparticles. In the first study, a microcapsule with PMMA shell and hexadecane core was examined. The second type of particle was a homogeneous PMMA microsphere containing no oil. Experimental data were compared to models that describe release by a diffusion mechanism out from core shell particles as well as homogeneous spherical particles. Results clearly show that the alkane oil has a plasticizing effect on the PMMA shell, thereby generating a faster release of 4-nitroanisole. In both types of microparticles, the diffusion coefficients of 4-nitroanisole could be determined. The findings increase our understanding of important parameters in the microcapsule design with regard to tuning the release behaviour. Using microparticles, the ambition is to prolong the protection of paint and other coatings against fouling.
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| 39732. |
- Nordstierna, Lars, 1976, et al.
(författare)
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Molecular release from painted surfaces: Free and encapsulated biocides
- 2010
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Ingår i: Progress in Organic Coatings. - : Elsevier BV. - 0300-9440. ; 69:1, s. 45-48
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Tidskriftsartikel (refereegranskat)abstract
- The current standard way of using biocide in coatings for protection against micro-organic surface growth, so called biofouling, is insufficient as the biocide leaks out from the coating too fast. In this article, we investigate a method for prolongation of the coating protection by slowing down the release rate of biocides in a controlled way. The biocide is placed into micrometer-sized reservoirs, called microspheres, from where it is slowly distributed into the coating. By different microscopic techniques the microspheres were found to be compatible (i.e. no phase separation was observed) both with the coating material and the paint. Biocide release from the coating is recorded by liquid scintillation counting and it was clear that the release is considerably slower from coatings with microspheres compared to an ordinary formulation with freely dispersed biocides. Microspheres might thus be a beneficial tool for the development of coatings with a longer protection against biofouling. (C) 2010 Elsevier B.V. All rights reserved.
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| 39733. |
- Nordström, Fredrik, et al.
(författare)
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Analysis of solution nonideality of a pseudomorphic drug system through a comprehensive thermodynamic framework for the design of a crystallization process
- 2004
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 93:4, s. 995-1004
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Tidskriftsartikel (refereegranskat)abstract
- Solutions of a semipolar drug belonging to the alpha(v) beta(iii) integrin antagonist class of compounds were studied in a comprehensive thermodynamic framework. The solubility of two pseudomorphic forms (an anhydrate and a monohydrate) was measured at several temperatures and various solvent mixtures of acetonitrile and water. Both forms displayed a bell-shaped solubility behavior as a function of cosolvent composition. Thermodynamic framework used to analyze the data comprised van't Hoff and enthalpy-entropy compensation analyses. The two pseudomorphs exhibited linear temperature dependence from 25 to 65degreesC at all solvent compositions (i.e., ideal behavior with temperature for fixed solvent composition). Plots of enthalpy of solublization and Gibbs free energy showed two distinct regions with contrasting thermodynamic, and consequently, underlying structural properties (indicating non-deal behavior with solvent composition for a fixed temperature). Solubility increased due to entropy effects in the acetonitrile rich region, whereas enthalpy effects dominated solublization in the water-rich region. Quantification of this phenomenon by plotting DeltaH versus DeltaG showed considerable nonlinearity, and that the two regions were separated by a significant discontinuity-a trend rarely seen before in the literature. The reason behind this behavior is believed to be due to the complex interactions in the solution of the drug in water acetonitrile solvent system. A very significant aspect of the comprehensive thermodynamic analysis is that it helped explain the puzzling feature of the data, which showed that the free energy of phase transformation between the two pseudomorphic forms for a given temperature was not independent of the solvent composition. The resulting explanation has major consequences for crystallization process development.
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| 39734. |
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| 39735. |
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| 39736. |
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| 39737. |
- Norell, Jesper, et al.
(författare)
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Ab initio simulations of complementary K-edges and solvatization effects for detection of proton transfer in aqueous 2-thiopyridone
- 2019
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:11
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Tidskriftsartikel (refereegranskat)abstract
- The nitrogen and sulfur K-edge X-ray absorption spectra of aqueous 2-thiopyridone, a model system for excited-state proton transfer in several recent time-resolved measurements, have been simulated from ab initio molecular dynamics. Spectral signatures of the local intra- and inter-molecular structure are identified and rationalized, which facilitates experimental interpretation and optimization. In particular, comparison of aqueous and gas phase spectrum simulations assesses the previously unquantified solvatization effects, where hydrogen bonding is found to yield solvatochromatic shifts up to nearly 1 eV of the main peak positions. Thereby, while each K-edge can still decisively determine the local protonation of its core-excited site, only their combined, complementary fingerprints allow separating all of the three relevant molecular forms, giving a complete picture of the proton transfer.
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| 39738. |
- Norell, Jesper, et al.
(författare)
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Interdependent Electronic Structure, Protonation, and Solvatization of Aqueous 2-Thiopyridone
- 2019
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 123:26, s. 5555-5567
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Tidskriftsartikel (refereegranskat)abstract
- 2-Thiopyridone (2-TP), a common model system for excited-state proton transfer, has been simulated in aqueous solution with ab initio molecular dynamics. The interplay of electronic structure, protonation, and solvatization is investigated by comparison of three differently protonated molecular forms and between the lowest singlet and triplet electronic states. An interdependence clearly manifests in the mixed-character T-1 state for the 2-TP form, systematic structural distortions of the 2-mercaptopyridine (2-MP) form, and photobase protolysis of the 2-TP- form, in the aqueous phase. In comparison, simplified continuum models for the solvatization are found to be significantly inaccurate for several of the species. To facilitate future computational studies, we therefore present a minimal representative solvatization complex for each stable form and electronic state. Our findings demonstrate the importance of explicit solvatization of the compound and sets the studies. stage for including it also in future studies.
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| 39739. |
- Norell, Jesper, et al.
(författare)
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Photoelectron shake-ups as a probe of molecular symmetry : 4d XPS analysis of I-3(-) in solution
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:30, s. 19916-19921
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Tidskriftsartikel (refereegranskat)abstract
- A combination of multi-configurational restricted active space calculations with a Dyson orbital formalism has been applied for accurate simulations of 4d photo-electron spectra of the I-3(-) molecular ion. The analysis based on the occupation numbers of natural orbitals allowed to predict and rationalize the spectral fingerprints of solvent-induced nuclear asymmetry. In particular, it demonstrates how the nuclear asymmetry directly causes an increase of shake-up intensity. The relative intensity of shake-up and main features of the I 4d XPS spectrum could therefore serve as a simplified experimental observable of structural asymmetry, complementary to changes in the shape of the main spectral features.
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| 39740. |
- Norén, Katarina, et al.
(författare)
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Adsorption mechanisms of EDTA at the water−iron oxide interface : implications for dissolution
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : ACS Publications. - 1932-7447 .- 1932-7455. ; 113:18, s. 7762-7771
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between chelating agents and metal oxide particles play important roles for the distribution and availability of metal ions in aquatic environments. In this work, the adsorption of ethylenediaminetetraacetate (EDTA) onto goethite (α-FeOOH) was studied as a function of pH, time, and background electrolyte concentration at 25.0 °C, and the molecular structures of the surface complexes formed were analyzed by means of infrared spectroscopy using the attenuated total reflectance sampling technique. The collective infrared spectroscopic results of this study show that two surface complexes consisting of HEDTA3− and H2EDTA2− predominate at the water−goethite interface within the pH range of 3−9. No direct interactions of these complexes with surface Fe(III) ions were detected; hence, most likely the surface complexes are stabilized at the interface by electrostatic and hydrogen-bonding forces. The formation of the EDTA surface complexes is fast (time scale of minutes), but a slower (time scale of hours to days) dissolution reaction also occurs. The dissolved iron in solution is in the form of the highly stable FeEDTA− solution complex, and the experimental evidence presented indicates that this complex can readsorb to the mineral surface. As dissolution proceeds, the concentration of FeEDTA− in the solution phase increases, and this in turn leads to a buildup of readsorbed FeEDTA− onto goethite. In the pH range of 4−7, this dissolution and readsorption process increases the total EDTA concentration at the surface. Under the experimental conditions in the present study, it is primarily the presence of uncomplexed EDTA in solution that drives the dissolution of goethite resulting in the subsequent readsorption of FeEDTA−, while the HEDTA3− and H2EDTA2− surface complexes are stable during this process.
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