1.
2.
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.
3.
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.
4.
Trejos, Alejandro, et al.
(författare)
Stereoselective Heck arylation of a functionalized cyclopentenyl ether using (S)-N-methyl-pyrrolidine as the stereochemical controller
2008
Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 64:37, s. 8746-8751
Tidskriftsartikel (refereegranskat) abstract
The study of a series of palladium(0)-catalyzed C2-arylations of a 1-cyclopentenyl ether equipped with a chiral (S)-N-methyl-pyrrolidine auxiliary is reported. Stereoselective Heck monoarylations were performed using aryl iodides under classical heating conditions for 1.7-3.0 h at 80 degrees C and in one case using 30 min of microwave irradiation at 110 degrees C. To further explore the scope and nature of this stereoselective methodology, aryl bromides were also utilized as arylating agents, using 20 min of microwave processing at 120-130 degrees C. High to excellent diastereopurities (90-98% de) were obtained according to H-1 NMR and GC-MS analyses. The prolinol fragment apparently controlled the chastereoselectivity of the Heck reaction by presenting the arylpalladium species from the preferred side of the double bond. By X-ray structure diffraction analysis of an N-quaternized Heck product, the absolute configuration of the new stereocenter was established as (R), Supporting a Si-face migratory insertion.
