Nonaqueous capillary zone electrophoresis of synthetic organic polypeptides

Poly(Nε-trifluoroacetyl-l-lysine) was used as a model solute to investigate the potential of nonaqueous capillary electrophoresis (NACE) for the characterization of synthetic organic polymers. The information obtained by NACE was compared to that derived from size exclusion chromatography (SEC) experiments, and the two techniques were found to be complimentary for polymer characterization. On one hand, NACE permitted (i) the separation of oligomers according to their molar mass and (ii) the separation of the polymers according to the nature of the end groups. On the other hand, SEC experiments were used for the characterization of the molar mass distribution for higher molar masses. Due to the tendency of the solutes (polypeptides) to adsorb onto the fused-silica capillary wall, careful attention was paid to the rinsing procedure of the capillary between runs in order to keep the capillary surface clean. For that purpose, the use of electrophoretic desorption under denaturating conditions was very effective. Optimization of the separation was performed by studying (i) the influence of the proportion of methanol in a methanol/acetonitrile mixture and (ii) the influence of acetic acid concentration in the background electrolyte. Highly resolved separation of the oligomers (up to a degree of polymerization n of ∼50) was obtained by adding trifluoroacetic acid to the electrolyte. Important information concerning the polymer conformations could be obtained from the mobility data. Two different plots relating the effective mobility data to the degree of polymerization were proposed for monitoring the changes in polymer conformations as a function of the number of monomers.

Oxidative degradation and stabilisation of polymers

The aim of this review is to present a coherent treatment of the fundamental aspects of the science that underpins current technological practices, and future advances, in the stabilisation of synthetic organic polymers. Aspects of polymer oxidation are introduced first before discussing the role of antioxidants, with numerous examples, to illustrate their basic mechanisms of action. The state of the art is discussed with particular emphasis on recent development and progress.

Pd/C catalysts based on synthetic carbons with bi- and tri-modal pore-size distribution:applications in flow chemistry

Two new types of phenolic resin-derived synthetic carbons with bi-modal and tri-modal pore-size distributions were used as supports for Pd catalysts. The catalysts were tested in chemoselective hydrogenation and hydrodehalogenation reactions in a compact multichannel flow reactor. Bi-modal and tri-modal micro-mesoporous structures of the synthetic carbons were characterised by N2 adsorption. HR-TEM, PXRD and XPS analyses were performed for characterising the synthesised catalysts. N2 adsorption revealed that tri-modal synthetic carbon possesses a well-developed hierarchical mesoporous structure (with 6.5 nm and 42 nm pores), contributing to a larger mesopore volume than the bi-modal carbon (1.57 cm3 g-1versus 1.23 cm3 g-1). It was found that the tri-modal carbon promotes a better size distribution of Pd nanoparticles than the bi-modal carbon due to presence of hierarchical mesopore limitting the growth of Pd nanoparticles. For all the model reactions investigated, the Pd catalyst based on tri-modal synthetic carbon (Pd/triC) show high activity as well as high stability and reproducibility. The trend in reactivities of different functional groups over the Pd/triC catalyst follows a general order alkyne ≫ nitro > bromo ≫ aldehyde.