Effects of background electrolyte composition and addition of selectors on separation selectivity in nonaqueous capillary electrophoresis

This review gives a survey of the approaches employed to obtain, enhance and tune selectivity in nonaqueous capillary electrophoresis (NACE). Recent developments in NACE are described and the effects of background electrolyte composition and addition of selectors on separation selectivity are discussed. The use of one organic solvent, a mixture of several organic solvents or the use of additives to tune separation selectivity in NACE is presented and a list of relevant applications is included.     

Dealing with a local heating effect when measuring catalytic solids in a reactor with Raman spectroscopy

In continuation of our previous work on the applicability of the G(R(infinity)) correction factor for the quantification of Raman spectra of coke during propane dehydrogenation experiments (Phys. Chem. Chem. Phys., 2005, 7, 211), research has been carried out on the potential of this correction factor for the quantification of supported metal oxides during reduction experiments. For this purpose, supported chromium oxide catalysts have been studied by combined in situ Raman and UV-Vis spectroscopy during temperature programmed reduction experiments with hydrogen as reducing agent. The goal was to quantify on-line the amount of Cr(6+) in a reactor based on the measured in situ Raman spectra. During these experiments, a significant temperature effect was observed, which has been investigated in more detail with a thermal imaging technique. The results revealed a temperature 'on the spot' that can exceed 100 degrees C. It implies that Raman spectroscopy can have a considerable effect on the local reaction conditions and explains observed inconsistencies between the in situ UV-Vis and Raman data. In order to minimize this heating effect, reduction of the laser power, mathematical matching of the spectroscopic data, a different cell design and a change in reaction conditions has been evaluated. It is demonstrated that increasing the reactor temperature is the most feasible method to solve the heating problem. Next, it allows the application of in situ Raman spectroscopy in a reliable quantitative way without the need of an internal standard.     

High‐Resolution Separation of Oligo(acrylic acid) by Capillary Zone Electrophoresis

Summary: Oligo(acrylic acid)s, produced by RAFT polymerization, have been separated and analyzed for the first time by capillary zone electrophoresis. The resolution obtained by capillary electrophoresis in borate buffers is far higher than that currently achieved using size exclusion chromatography. This work demonstrates that capillary electrophoresis is the technique of choice for the characterization of oligomers of acrylic acid and of other water‐soluble monomers involved in emulsion polymerization processes.

Electropherograms of different acrylic acid (AA) oligomers obtained by CZE.     

Catalytic Synthesis of 8-Membered Ring Compounds via Cobalt(III)-Carbene Radicals

The metalloradical activation of o-aryl aldehydes with tosylhydrazide and a cobalt(II) porphyrin catalyst produces cobalt(III)-carbene radical intermediates, providing a new and powerful strategy for the synthesis of medium-sized ring structures. Herein we make use of the intrinsic radical-type reactivity of cobalt(III)-carbene radical intermediates in the [Co^II(TPP)]-catalyzed (TPP=tetraphenylporphyrin) synthesis of two types of 8-membered ring compounds; novel dibenzocyclooctenes and unprecedented monobenzocyclooctadienes. The method was successfully applied to afford a variety of 8-membered ring compounds in good yields and with excellent substituent tolerance. Density functional theory (DFT) calculations and experimental results suggest that the reactions proceed via hydrogen atom transfer from the bis-allylic/benzallylic C−H bond to the carbene radical, followed by two divergent processes for ring-closure to the two different types of 8-membered ring products. While the dibenzocyclooctenes are most likely formed by dissociation of o-quinodimethanes (o-QDMs) which undergo a non-catalyzed 8π-cyclization, DFT calculations suggest that ring-closure to the monobenzocyclooctadienes involves a radical-rebound step in the coordination sphere of cobalt. The latter mechanism implies that unprecedented enantioselective ring-closure reactions to chiral monobenzocyclooctadienes should be possible, as was confirmed for reactions mediated by a chiral cobalt-porphyrin catalyst.     

Catalytic destruction of brominated aromatic compounds studied in a catalyst microbed coupled to gas chromatography/mass spectrometry

The capability of solid porous catalysts has been studied for the destruction or modification of halogenated aromatic compounds contaminating the pyrolysis oil of recycled plastics from electronic waste. A fast and simple experimental procedure is carried out using a micropyrolyser coupled to GC-MS in such a way that catalyst microbed was placed in the sample tube of the pyrolyser. The pyrolysis products of polycarbonate blended with a frequently applied flame retardant tetrabromobisphenol A (TBBPA) and epoxy resin containing TBBPA monomer units have been analysed, and the brominated components were compared with the thermal decomposition products of TBBPA and its diallyl ether. When TBBPA vapour passes through molecular sieve 4A a slight debromination and a partial cleavage of bisphenol A into phenols occur. Over molecular sieves of larger pore size (13X and NaY zeolite) an important decrease of TBBPA amount is observed indicating effective trapping ability of these catalysts of basic character for brominated aromatic compounds. A total chemical modification of the vapour was achieved by Al-MCM-41 catalyst that split TBBPA into bromophenols. Analogous results were obtained by carrying out similar experiments on diallyl ether of TBBPA. Moreover, it was revealed that brominated bisphenol A compounds are modified essentially the same way, either evaporated or evolved from a polycarbonate blend or produced by pyrolysis from an epoxy resin.     

Direct experimental evidence for an enamine radical cation in SOMO catalysis

SOMO catalysis has lately obtained large interest as a new and powerful version of enantioselective organocatalysis which includes radical steps initiated by a one-electron oxidation. The intermediate enamine radical cation has been postulated, but has not been observed directly so far. This communication now reports the direct detection of this key intermediate.     

Studies on pectin coating of liposomes for drug delivery

The present study investigated the surface coating of charged liposomes by three different types of pectin (LM, HM and amidated pectin) by particle size determinations and zeta potential measurements. The pectins and the pectin coated liposomes were visualized by atomic force microscopy. The adsorption of pectin onto positive liposomes yielded a reproducible increase in particle size and a shift of the zeta potential from positive to negative side for all three pectin types, whereas the adsorption of pectin onto negative liposomes did not render any significant changes probably due to electrostatic repulsion. The positive liposomes coated with HM-pectin gave the largest pectin coated particles with the least negative zeta potential, while the opposite was observed for the LM-pectin coated positive liposomes. Furthermore, results from dynamic light scattering revealed narrow size distributions, indicating that the degree of aggregation was low for the pectin coated liposomes. As liposomes are able to encapsulate drugs and pectin has been found to be mucoadhesive, these pectin coated liposomes may be potential drug delivery systems.     

Rational redesign of Candida antarctica lipase B for the ring opening polymerization of D,D-lactide

Based on molecular modelling, the enzyme Candida antarctica lipase B was redesigned as a catalyst for the ring opening polymerization of D,D-lactide. Two mutants with 90-fold increased activity as compared to the wild-type enzyme were created. In a preparative synthesis of poly(D,D-lactide) the mutants greatly improved the rate and the degree of polymerization.     

Improving the reproducibility of chemical reactions on the surface of cellulose nanocrystals: ROP of ε-caprolactone as a case study

In our group, we work on the surface modification of cellulose nanocrystals. During this work, we have encountered reproducibility issues when the same reactions were performed on nanocrystals from different hydrolysis batches, indicating a variable surface composition. Given the inherent purity of the nanoparticles themselves, this issue was believed to be due to the presence of adsorbed species at the surface of the nanocrystals blocking reactive sites. To investigate this in detail, nanocrystals from several batches were extracted with different solvents. The effect of these extractions on the surface composition of the nanowhiskers was investigated, followed by its effect on the Surface-Initiated Ring-Opening Polymerization (SI-ROP) of ε-caprolactone. The extracted impurities were analysed by NMR (¹H and ¹³C) and MS, showing a variety of adsorbed species which can be removed by solvent extraction. A Soxhlet extraction using ethanol before the reaction was shown to be the most effective in removing adsorbed low molecular weight organic compounds produced during the hydrolysis, resulting in improved reproducibility between reactions using nanocrystals from different batches, as confirmed by FTIR, elemental analysis and XPS. Extraction with ethanol should thus be performed before all reaction as these adsorbed species can be expected to interfere with all surface modification reactions.