1.
Nilsson, Peter, et al.
(författare)
Effect of salt and surfactant concentration on the structure of polyacrylate gel/sutrfactant complexes
2007
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 111:37, s. 10959-10964
Tidskriftsartikel (refereegranskat) abstract
Small-angle X-ray scattering was used to elucidate the structure of crosslinked polyacrylate gel/ dodecyltrimethylammonium bromide complexes equilibrated in solutions of varying concentrations of surfactant and sodium bromide (NaBr). Samples were swollen with no ordering (micelle free), or they were collapsed with either several distinct peaks (cubic Pm3n) or one broad correlation peak (disordered micellar). The main factor determining the structure of the collapsed complexes was found to be the NaBr concentration, with the cubic structure existing up to similar to 150 mM NaBr and above which only the disordered micellar structure was found. Increasing the salt concentration decreases the polyion mediated attractive forces holding the micelles together causing swelling of the gel. At sufficiently high salt concentration the micelle-micelle distance in the gel becomes too large for the cubic structure to be retained, and it melts into a disordered micellar structure. As most samples were above the critical micelle concentration, the bulk of the surfactant was in the form of miscelles in the solution and the surfactant concentration thereby had only a minor influence on the structure. However, in the region around 150 mM Nal3r, increasing the surfactant concentration, at constant NaBr concentration, was found to change the structure from disordered micellar to ordered cubic and back to disordered again.
2.
Bäck, Marcus, et al.
(författare)
Anionic Oligothiophenes Compete for Binding of X-34 but not PIB to Recombinant A beta Amyloid Fibrils and Alzheimers Disease Brain-Derived A beta
2016
Ingår i: CHEMISTRY-A EUROPEAN JOURNAL. - : WILEY-V C H VERLAG GMBH. - 0947-6539. ; 22:51, s. 18335-18338
Tidskriftsartikel (refereegranskat) abstract
Deposits comprised of amyloid- (A) are one of the pathological hallmarks of Alzheimers disease (AD) and small hydrophobic ligands targeting these aggregated species are used clinically for the diagnosis of AD. Herein, we observed that anionic oligothiophenes efficiently displaced X-34, a Congo Red analogue, but not Pittsburgh compoundB (PIB) from recombinant A amyloid fibrils and Alzheimers disease brain-derived A. Overall, we foresee that the oligothiophene scaffold offers the possibility to develop novel high-affinity ligands for A pathology only found in human AD brain, targeting a different site than PIB.
3.
4.
Enquist, Per-Anders, et al.
(författare)
ESI-MS Detection of Proposed Reaction Intermediates in the Air-Promoted and Ligand-Modulated Oxidative Heck Reaction
2006
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 71:23, s. 8779-8786
Tidskriftsartikel (refereegranskat) abstract
Electrospray ionization mass spectrometry (ESI-MS) and subsequent MS/MS analyses were used to directly detect palladium-containing cationic reaction intermediates in a ligand controlled palladium(II)-catalyzed oxidative Heck arylation. All potential intermediates were observed as dmphen-ligated palladium(II) species, suggesting that the dmphen bidentate ligand is attached to the metal center during the entire catalytic cycle. The study supports previous mechanistic propositions and provides new information regarding the composition of aryl-containing Pd(II) complexes in an ongoing oxidative Heck reaction. In addition, sodium acetate was found to be a useful base alternative to previously used tertiary amines.
5.
Lindh, Jonas, et al.
(författare)
Convenient Stille carbonylative cross-couplings using molybdenum hexacarbonyl
2010
Ingår i: Tetrahedron Letters. - : Elsevier BV. - 0040-4039 .- 1359-8562. ; 51:18, s. 2470-2472
Tidskriftsartikel (refereegranskat) abstract
Palladium catalysis was used in Stille-type carbonylative cross-couplings employing Mo(CO)(6) as the carbon monoxide source. Robust and convenient transformations were carried out in closed vessels at 100 degrees C, providing a set of diaryl ketones in good yields. Aryl triflates and bromides were used as coupling partners with aryl stannanes. Inclusion of the Mo(CO)(6) destabilizing agent DBU made this protocol operationally simple and suppressed side-product formation. (C) 2010 Elsevier Ltd. All rights reserved.
6.
Lindh, Jonas, et al.
(författare)
Efficient palladium(II) catalysis under air. Base-free oxidative heck reactions at room temperature or with microwave heating
2007
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 72:21, s. 7957-7962
Tidskriftsartikel (refereegranskat) abstract
Scope and limitations of the base-free oxidative Heck reaction with arylboronic acids have been explored. Under our conditions, the dmphen−palladium(II)-catalyzed arylation proceeded with air or p-benzoquinone as reoxidants of palladium(0). We found that ambient temperature and mild aerobic conditions allow for the use of substrates sensitive to palladium(II)-catalyzed oxidation. Oxidative Heck couplings, employing different arylboronic acids, were smoothly and regioselectively conducted with both electron-rich and electron-poor olefins, providing high yields even with disubstituted butyl methacrylate, sensitive acrolein, and a vinylboronate ester. Controlled microwave processing was used to reduce reaction times from hours to minutes both in small scale and in 50 mmol scale batch processes.
7.
Nilsson, Peter, et al.
(författare)
Deswelling Kinetics of Polyacrylate Gels in Solutions of Cetyltrimethylammonium Bromide
2007
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 111:33, s. 9770-9778
Tidskriftsartikel (refereegranskat) abstract
The deswelling kinetics of single sodium polyacrylate gel beads (radius 40−160 μm) in aqueous solutions of cetyltrimethylammonium bromide under conditions of forced convection are investigated using micromanipulator assisted light microscopy. The purpose of the study is to further evaluate a previously published model (J. Phys. Chem. B 2003, 107, 9203) using a higher homolog surfactant. For gels with expected fast deswelling (small gel size/low surfactant concentration) and/or in low electrolyte concentration, the model is found to correctly predict the deswelling characteristics of the gel beads. However, for some gels with expected slow deswelling, especially in high electrolyte concentration (10 mM NaBr), the model widely underestimates the required deswelling time. The reason for this is argued to be the longer time frame and high bromide concentration allowing the formation of a denser, more ordered structure in the surface phase, which resists the deformation and reorganization of material necessary for deswelling. Unexpectedly long lag times before the start of deswelling are also found for gels in low surfactant concentration, indicating that a relatively high surfactant concentration in the gel, greatly exceeding the critical aggregation concentration, is needed to start formation of a collapsed surface phase. This critical surfactant concentration is found to be dependent on initial gel radius, as small gels require a relatively higher concentration to initiate collapse.
8.
Nilsson, Peter, et al.
(författare)
Regular and Irregular Deswelling of Polyacrylate and Hyaluronate Gels Induced by Oppositely Charged Surfactants
2008
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 325:2, s. 316-323
Tidskriftsartikel (refereegranskat) abstract
The deswelling kinetics of macroscopic polyacrylate (PA) gels in solutions of dodecyltrimethylammonium bromide (C(12)TAB) and cetyltrimethylammonium bromide (C(16)TAB), with and without added sodium bromide, as well as hyaluronate (HA) gels in solutions of cetylpyridinium chloride (CPC) are investigated. Additional data are also provided by small-angle X-ray scattering and microgel experiments. The purpose is to study the deswelling behavior of (1) regularly deswelling gels, for which the deswelling is successfully described using a core/shell model earlier employed for microgels, and (2) irregularly deswelling gels, where the gel turns into a balloon-like structure with a dense outer layer surrounding a liquid-filled core. For regularly deswelling gets, the deswelling of PA/C(12)TAB is found to be controlled by diffusion through both stagnant layer and collapsed surface phase, while for PA/C(16)TAB it is found to be controlled mainly by the latter. The difference in deswelling rate between the two is found to correspond to the difference in surfactant diffusion coefficient in the surface phase. Factors found to promote irregular deswelling, described as balloon formation, are rapid surfactant binding, high bromide and surfactant concentration, longer surfactant chain length, and macroscopic gel size. Scattering data indicating a cubic structure for HA/CPC complexes are reported.
9.
Psonka-Antonczyk, Katarzyna M., et al.
(författare)
Nanoscale Structure and Spectroscopic Probing of A beta 1-40 Fibril Bundle Formation
2016
Ingår i: Frontiers in Chemistry. - : Frontiers Research Foundation. - 2296-2646. ; 4
Tidskriftsartikel (refereegranskat) abstract
Amyloid plaques composed of fibrillar Amyloid-beta (A beta) are hallmarks of Alzheimers disease. However, A beta fibrils are morphologically heterogeneous. Conformation sensitive luminescent conjugated oligothiophenes (LCOs) are versatile tools for monitoring such fibril polymorphism in vivo and in vitro. Biophysical methods applied on in vitro generated A beta fibrils, stained with LCOs with different binding and fluorescence properties, can be used to characterize the A beta fibrillation in depth, far beyond that possible for in vivo generated amyloid plaques. In this study, in vitro fibrillation of the A beta 1-40 peptide was monitored by time-lapse transmission electron microscopy, LCO fluorescence, and atomic force microscopy. Differences in the LCO binding in combination with nanoscale imaging revealed that spectral variation correlated with fibrils transforming from solitary filaments (empty set similar to 2.5 nm) into higher order bundled structures (empty set similar to 5 nm). These detailed in vitro experiments can be used to derive data that reflects the heterogeneity of in vivo generated A beta plaques observed by LCO fluorescence. Our work provides new structural basis for targeted drug design and molecular probe development for amyloid imaging.
10.
Svennebring, Andreas, et al.
(författare)
A mechanistic study on modern palladium catalyst precursors as new gateways to Pd(0) in cationic Heck reactions
2008
Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 64:8, s. 1808-1812
Tidskriftsartikel (refereegranskat) abstract
Electrospray ionization mass spectrometry (ESI-MS) was used as a means to directly identify catalytic cationic organopalladium species in ligand-controlled Heck reactions involving electron-rich olefins and different Pd-sources. In these high-temperature Heck arylations, the oxidative addition intermediates were observed as bidentate ligand chelated cationic aryl palladium species, suggesting that the used ligand attaches to the metal center at the very beginning of the catalytic cycle. This was also in agreement with the obtained regioisomeric profile of the isolated products. The investigation supports the standard Pd(0)/Pd(II) Heck mechanism and provides further insight regarding the conceivable composition of fundamental Pd(II) intermediates in an ongoing Heck reaction.
