| 1. |
- Baks, Tim, et al.
(författare)
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Schrödinger's capsule : a (micro) capsulate that is open and closed, almost, at the same time
- 2010
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Ingår i: Proceedings of the Physics with Industry 2010, 11-15 October 2010, Leiden, The Netherlands. - : Lorentz Center Leiden.
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Konferensbidrag (refereegranskat)abstract
- We exploit different routes for encapsulation of food additives, such as minerals or vitamins, in a polymeric capsule. The added active ingredients should remain inside the capsule for at least a year in an aqueous environment (e.g. a dairy product), since sensory properties or functionality of the ingredients may otherwise be affected. However, after intake the active compound should readily (within 1 h) be released due to the acidic environment in the stomach. First, we propose a phenomenological model in order to study how a polymeric matrix may limit the diffusion of incorporated active molecules. The relation between the release rate of the active compound and its molecular weight is elucidated. Second, the desired capsules may be obtained by specific binding between subunits within the capsule and the active ingredient. We show two examples that rely on this mechanism: amylose-lipid complexes and mixed metal hydroxides. Amylose is able to form inclusion complexes with various types of ligands, including iodine, monoglycerides, fatty acids and alcohols, where the hydrophobic parts of the ligands are entrapped in the hydrophobic helical cavity of amylose. Mixed metal hydroxides are a versatile class of inorganic solids that consist of sheets of metal cations that are octahedrally surrounded by hydroxide molecules. In between these layers anionic species compensate for charge neutrality. In this way, various metal cations (minerals) may be incorporated with a high loading, and negatively charged actives may be placed between the layers. Upon digestion the particles dissolve and the ingredients are digested. Finally, we show that nature has already developed many intriguing capsules.
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| 2. |
- Li, Feng, et al.
(författare)
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Formation of nanotapes by co-assembly of triblock peptide copolymers and polythiophenes in aqueous solution
- 2009
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Ingår i: SOFT MATTER. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 5:8, s. 1668-1673
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Tidskriftsartikel (refereegranskat)abstract
- Nanotapes are formed by the co-assembly of triblock peptide copolymers with an amino acid-substituted polythiophene derivative (PTT). The driving force for the assembly is ionic interaction (complex coacervation). These nanotapes were visualized by atomic force microscopy and confocal laser scanning microscopy. The interactions between the triblock peptide copolymers and the PTT are also expressed in the steady state and time resolved fluorescence spectra. The steady-state spectra indicate that upon interaction with the peptide copolymer, the backbone of the PTT adopts a rather twisted, and definitely less, aggregated conformation. The time-resolved fluorescence decay studies further confirm this interpretation. The structure of these nanotapes at the mesoscopic scale depends, among other physical chemical parameters, on the concentrations of its constituents.
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| 3. |
- Li, Feng, et al.
(författare)
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Nanowires Formed by the Co-Assembly of a Negatively Charged Low-Molecular Weight Gelator and a Zwitterionic Polythiophene
- 2010
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Ingår i: ChemPhysChem. - : John Wiley and Sons, Ltd. - 1439-4235 .- 1439-7641. ; 11:9, s. 1956-1960
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Tidskriftsartikel (refereegranskat)abstract
- Conjugated organic nanowires have been prepared by co-assembling a carboxylate containing low-molecular weight gelator (LMWG) and an amino acid substituted polythiophene derivative (PTT). Upon introducing the zwitterionic polyelectrolyte PTT to a basic molecular solution of the organogelator, the negative charges on the LMWG are compensated by the positive charges of the PTT. As a result, nanowires form through co-assembly. These nanowires are visualized by both transmission electron microscopy (TEM) and atomic force microscopy (AFM). Depending on the concentration and ratio of the components these nanowires can be micrometers long. These measurements further suggest that the aggregates adopt a helical conformation. The morphology of these nanowires are studied with fluorescent confocal laser scanning microscopy (CLSM). The interactions between LMWG and PTT are characterized by steady-state and time-resolved fluorescence spectroscopy studies. The steady-state spectra indicate that the backbone of the PTT adopts a more planar and more aggregated conformation when interacting with LMWG. The time-resolved fluorescence decay studies confirm this interpretation.
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| 4. |
- Lützenkirchen, Johannes, et al.
(författare)
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Comparison of various models to describe the charge−pH dependence of Poly(acrylic acid)
- 2011
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Ingår i: Journal of Chemical and Engineering Data. - : American Chemical Society. - 0021-9568 .- 1520-5134. ; 56:4, s. 1602-1612
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Tidskriftsartikel (refereegranskat)abstract
- The charge of poly(acrylic acid) (PAA) in dilute aqueous solutions depends on pH and ionic strength. We report new experimental data and test various models to describe the deprotonation of PAA in three different NaCl concentrations. A simple surface complexation approach is found to be very successful: the constant capacitance model requires one pKa value and one capacitance for excellent fits to the data, with both parameters depending on ionic strength. The use of a self-consistent set of diffuse double layer parameters with one pKa for flat, spherical, and cylindrical geometry does not result in a satisfactory description of the data, and a number of adjustments to that model were tested to improve the fit. The basic Stern model (BSM) was tested with both plate and cylinder geometry. The cylinder geometry along with strong electrolyte binding was found to be superior to a similar approach involving weak electrolyte binding both in terms of goodness of fit and self-consistency of the parameters. The third approach, the non-ideal competitive consistent adsorption-Donnan (NICCA-Donnan) model, involving one functional group, allows an excellent description of the experimental data. Finally, the polyacid chain was modeled using a mechanistically more realistic self-consistent field (SCF) approach, which allows for radially inhomogeneous distributions of the charges and radial variations in the polymer density and electrostatic potential, while the functional groups can be in protonated, deprotonated, or complexed states. One functional group was insufficient for a satisfactory description of the data. With two segments (one monoprotic, the other diprotic) a reasonable description of the data, including the ionic strength dependence, is achieved, and the tendency of the size of the macro-ion with pH and ionic strength is as expected. This model has the fewest adjustable parameters and is considered the most realistic and comprehensive among the models tested.
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