Facile, efficient, and enantiospecific syntheses of 1,1'-N-linked pseudodisaccharides as a new class of glycosidase inhibitors

This article describes an efficient synthesis of a potent trehalase inhibitor, 1,1'-N-linked pseudodisaccharide 1 (consisting of two valienamines), in 14 steps with an overall yield of 12% and a first synthesis of 2 (consisting of two 2-epi-valienamines) in 15 steps with an overall yield of 24% from (-)-quinic acid. The synthesis involves a stereospecific palladium-catalyzed coupling reaction between an allylic amine and an allylic chloride as the crucial step. The acetonide blocking groups were shown to be the best hydroxyl protecting groups, compatible with the palladium-catalyzed allylic amination reaction that afforded high yields of the 1,1'-N-linked pseudodisaccharides with a minimum amount of an elimination diene side product.     

Characterization of polyethylene glycols and polypropylene glycols by capillary zone electrophoresis and micellar electrokinetic chromatography

Methods based on capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) have been developed and optimized for the separation of polyethylene glycols (PEGs) and polypropylene glycols (PPGs). To provide for charge and detectability both types of polymeric compounds were derivatized with phthalic anhydride (PhAH) or 1,2,4-benzenetricarboxylic anhydride (BTA) before the separation. Derivatization with BTA yielded more complex electropherograms, due to the occurrence of different isomeric reaction products for every PEG or PPG species. Effective mobilities of the PhAH derivatives were related to the number of monomer units in the polymers in a straightforward way. The CZE method could also be used to determine the monomer-number distribution of random and block PEG-PPG copolymers. For an MEKC analysis the PEGs and PPGs were derivatized with phenyl isocyanate. Oligomers of PEGs could be separated up to molecular masses of 5,000, while for the more hydrophobic PPGs oligomeric separation was only accomplished for molecular masses of up to 1,500. Due to a strongly different separation mechanism for the PEG and PPG derivatives in the MEKC system. a complete group separation of the two types of polymer molecules could be obtained.     

New detection modes for the determination of cephalosporins and their decomposition products

Summary The feasibility of using fluorescence and electrochemical detection after high performance liquid chromatography separation is investigated for a sensitive and selective determination of cephalosporins and their decomposition products. The sensitivity and detectability of fluorescence and electrochemical detection are compared to those of UV absorption detection. The methods have been validated for the determination of cephalosporins in biological fluids and for stability studiesin vitro.     

An electrochemical detector cell for open tubular liquid chromatography and capillary electrophoresis

Summary An electrochemical detector cell has been developed for micro-flow separation systems (OTLC, CE). The cell contains two electrodes, a disk-shaped working electrode made from a carbon fiber bundle, and a tubular Ag/AgCl quasi-reference electrode. The effective cell volume and the coulometric yield have been determined, for different electrode diameters and at different flow rates, in an OTLC system. An effective cell volume of less than 1 nl was observed. The applicability of the cell was demonstrated with the detection of OPA-derivatized amino acids. For use in CE, the cell was equipped with an additional compartment, housing a semi-permeable joint for the decoupling of the high electric field used for the electrophoretic separation. Results are shown on the determination of catecholamines by CE with electrochemical detection. Detection limits with both OTLC and CE were well below 1 fmole.     

Comparison of on-line flow-cell and off-line solvent-elimination interfaces for size-exclusion chromatography and Fourier-transform infrared spectroscopy in polymer analysis

Two commercial liquid chromatography-Fourier-transform infrared spectroscopy interfaces (LC-FTIR), viz. a flow cell and a solvent-elimination interface have been assessed for use in size-exclusion chromatography (SEC) with respect to their chromatographic integrity (i.e. peak asymmetry, chromatographic resolution), quantitative and qualitative aspects. A polycarbonate/aliphatic polyester (PC/APE) blend and a polycarbonate-co-polydimethylsiloxane (PC-co-PDMS) copolymer were selected for the assessment. Both samples were successfully and selectively analyzed. The relatively large volume of the flow cell and the inherent deposition characteristics of the solvent-elimination interface led to a comparable decrease in the chromatographic resolution. The separation of oligomers was diminished in comparison with SEC-ultra-violet (UV). However, the peak asymmetry was not significantly affected by either interface. For both interfaces, a linear relationship was obtained for the FTIR response versus the injected concentration. The sensitivity was found to be higher for the solvent-elimination interface. For the current model compounds, the flow-cell interface detection limits are worse. However, the repeatability of flow-cell SEC-FTIR, evaluated by means of four SEC-FTIR analyses of polycarbonate, was considerably better than for solvent-elimination SEC-FTIR. This is probably due to the well-defined optical path length of the sample in the flow cell. By spectral subtraction, it was very well possible to obtain qualitative (functional group) information for compound identification also with flow-cell SEC-FTIR.     

Influence of the carrier composition on thermal field-flow fractionation for the characterisation of sub-micron polystyrene latex particles

A study on the influence of the carrier composition in a ThFFF system on the retention and thermal diffusion of sub-micron polystyrene latex particles has been carried out. Various factors that may influence retention were studied. These include: the type of electrolyte and surfactant, their respective concentrations, and the addition of an organic modifier. Particle retention is highly sensitive to small changes in the carrier composition. It is demonstrated that under the conditions applied, secondary effects, such as particle-wall and particle-particle interactions, are negligible. Addition of surfactants is required to minimise particle-wall interactions. Generally, retention increases at higher electrolyte concentration. Furthermore, the addition of acetonitrile (ACN) to an aqueous carrier leads also to an increased retention. The type of surfactant as well as its concentration is of influence on the retention time. The three surfactants that were studied, i.e., sodium dodecyl sulfate, Brij 35 and cetyltrimethylammonium bromide, showed significant differences in particle retention behaviour. The observed differences in retention in the carriers can be attributed to actual changes in thermal diffusion. D(T) appears to be mainly determined by the interaction between the particle's surface and the carrier liquid, and is therefore highly sensitive to changes in the chemical composition of the particle surface and the carrier. Strong differences in size selectivity were found for different carrier compositions. This allows a relatively easy optimisation of the separation. On the other hand, it complicates the size and composition analysis of particles.     

The effect of sodium sulfite and cobalt chloride on the oxygen transfer coefficient

An experiment was conducted in an aeration system made from 2000 mL Erlenmeyer Flask to investigate the effect of sodium sulfite with cobalt chloride and the sparging nitrogen gas on the measurement of the oxygen transfer coefficient. Twice the theoretical quantity of sodium sulfite that is required to react with dissolved oxygen, or nitrogen sparging at a rate equivalent to that of air used during the aeration process, was used to deoxygenate the water. The results obtained from the study were consistent and repeatable and showed no significant differences in the values of the oxygen transfer coefficient obtained by the two methods.