Electrolytic preconcentration in instrumental analysis

The use of electrolytic deposition as a separation and preconcentration step in trace metal analysis is reviewed. Both the principles and applications of the technique are dealt with in some detail. Electrolytic preconcentration can be combined with a variety of instrumental techniques. Special attention is given to stripping voltammetry, potentiometric stripping analysis, different combinations with atomic-absorption spectrometry, and the use of flow-through porous electrodes. It is pointed out that the electrolytic preconcentration technique deserves more extensive use as well as fundamental investigation.     

Dendrimers in drug research

Dendrimers are versatile, derivatisable, well-defined, compartmentalised chemical polymers with sizes and physicochemical properties resembling those of biomolecules e.g. proteins. The present critical review (citing 158 references) briefly describes dendrimer design, nomenclature and divergent/convergent dendrimer synthesis. The characteristic physicochemical features of dendrimers are highlighted, showing the effect of solvent pH and polarity on their spatial structure. The use of dendrimers in biological systems are reviewed, with emphasis on the biocompatibility of dendrimers, such as in vitro and in vivo cytotoxicity, as well as biopermeability, biostability and immunogenicity. The review deals with numerous applications of dendrimers as tools for efficient multivalent presentation of biological ligands in biospecific recognition, inhibition and targeting. Dendrimers may be used as drugs for antibacterial and antiviral treatment and have found use as antitumor agents. The review highlights the use of dendrimers as drug or gene delivery devices in e.g. anticancer therapy, and the design of different host-guest binding motifs directed towards medical applications is described. Other specific examples are the use of dendrimers as 'glycocarriers' for the controlled multimeric presentation of biologically relevant carbohydrate moieties which are useful for targeting modified tissue in malignant diseases for diagnostic and therapeutic purposes. Finally, the use of specific types of dendrimers as scaffolds for presenting vaccine antigens, especially peptides, for use in vaccines is presented.     

Acoustic Wave Mass Sensors

The application of acoustic wave microsensors for mass sensing will be reviewed with focus on the quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices. The use of QCM and SAW devices in chemical sensing as well as in the determination of solid and liquid properties will be described. In chemical sensing, it is unlikely that a single sensor with a single coating will display a selective and reversible response to a given analyte in a mixture. Alternative strategies such as the use of sensor arrays and the use of sampling devices can be used to improve performance. QCM sensors (QCMs) will oscillate under liquids; their use in under-liquid sensing will be discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intramolecular Anodic Olefin Coupling Reactions and the Use of Electron-Rich Aryl Rings(1)

The utility of intramolecular anodic olefin coupling reactions involving electron-rich aromatic rings for constructing fused, bicyclic ring skeletons has been examined. Reactions involving alkoxy-substituted phenyl rings were found to benefit strongly from a 3-methoxy substituent on the phenyl ring. Although overoxidation of the bicyclic product was observed in these reactions, this problem could be minimized with the use of controlled potential electrolysis conditions when a monomethoxy phenyl ring was used and avoided entirely with the use of a vinyl sulfide moiety as the initiator when a more electron-rich phenyl ring was used. Reactions involving 4-alkoxy-substituted phenyl rings as substrates did not lead to good yields of fused products. Furan rings were found to be excellent coupling partners for the reactions and afforded products having fused, bicyclic furan ring skeletons. Cyclizations involving furans were shown to be compatible with the formation of both six- and seven-membered rings, the generation of a quaternary carbon, and the use of a variety of electron-rich olefins as the other coupling partner. It appears that the furan can serve as either the initiating group or the terminating group for the cyclizations. Finally, the reactions were shown to be compatible with the use of a pyrrole ring as one of the participants.     

Chromatographic methods and techniques used in studies of coals, their progenitors and coal-derived materials

The use of chromatography in studies of coals, their progenitors and coal-related products was reviewed. The specificity of the coal structure was discussed. The use of extraction in preparing study samples was discussed paying special attention to the occurrence of undesirable phenomena such as aggregation of coal derivate molecules, resulting from the formation of their dimers and trimers, and degradation of polar solvents at temperatures above 350 °C. The following ways of fractionating samples of coal materials were considered: thermal, solvent, column with the use of preparative size exclusive chromatography and preparative thin layer chromatography as well as membrane separation. The use of chromatography coupled with experimental techniques such as mass spectrometry, infrared spectroscopy, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and pyrolysis was analysed.     

“HFM”, the universal sputter method in SNMS analytics

For the analysis of surfaces with poor conductivity the use of the “direct current sputter process”, usual in SNMS, produces unreproducible depth profiles with often widened transition widths. An efficient method for eliminating static charging in the case of non-coducting samples is the use of a high-frequency discharge. By comparison of the direct current mode with high frequency mode it is shown, that the use of SNMS with HF sputtering is the universal analysis method for most matrices, technical surfaces as well as oxidic materials. For non-conducting or poorly conducting samples, however, matrix-adjusted factors are to be used.     

Creating a pseudometallic state of K+ by intercalation into 18-crown-6 grafted on polyfluorene as electron injection layer for high performance PLEDs with oxygen- and moisture-stable Al cathode

Polymer light-emitting diodes (PLEDs) suffer from inadequate lifetimes because of the use of environmentally sensitive metals as the cathodes. We present the use of water/methanol-soluble polyfluorene grafted with 18-crown-6 chelating to K(+) as the electron-injection layer (EIL) for deep-blue-emission PLEDs, allowing the use of environmentally stable Al as the cathode since electron donation from the 18-crown-6 can reduce K(+) to a stable "pseudometallic state", enabling it to act as an intermediate step for electron injection. Furthermore, when poly(ethylene oxide) was blended into the EIL to provide hole blocking (HB), the device exhibited the highest performance reported to date for a deep-blue-emission PLED based on a conjugated polymer as the emitting layer, with a brightness of 54,800 cd/m(2) and an external quantum efficiency of 5.42%. The use of such an EI-HB layer opens a broad avenue leading toward industrialization of PLEDs.     

De novo asymmetric synthesis of all-D-, all-L-, and D-/L-oligosaccharides using atom-less protecting groups

Oligosaccharide synthesis is hindered by the need for multiple steps as well as numerous selective protections and deprotections. Herein we report a highly efficient de novo route to various oligosaccharide motifs, of use for biological and medicinal structure activity studies. The key to the overall efficiency is the judicious use of asymmetric catalysis and synthetic design. These green principles include the bidirectional use of highly stereoselective catalysis (Pd(0)-catalyzed glycosylation/post-glycosylation). In addition, the chemoselective use of C-C and C-O π-bond functionality, as atom-less protecting groups as well as an anomeric directing group (via a Pd-π-allyl), highlights the atom-economical aspects of the route to a divergent set of natural and unnatural oligosaccharides (i.e., various d-/l-diastereomers of oligosaccharides as well as deoxysugars which lack C-2 anomeric directing groups). For example, in only 12 steps, the construction of a highly branched heptasaccharide with 35 stereocenters was accomplished from an achiral acylfuran.     

Metals and coordination compounds as modifiers for epoxy resins

This review concentrates on the use of metals in the formulation of epoxy resin systems and the effect that this has on the physical and mechanical properties of the polymer system. Epoxy resins are one of the most important higher performance polymer systems in use today, ranging from simple two-part adhesives and sports equipment to high-tech applications such as formula one racing cars and the aerospace industry. Epoxy resins are capable of undergoing homopolymerisation, although this process generally yields products with inadequate properties for high-tech applications. Consequently, in many cases catalysts, additives and co-curing-agents are formulated with the epoxy resin to significantly increase the storage stability, decrease the cure time and improve the final properties. The use of metals to formulate resin systems with excellent storage stability is discussed, along with the use of coordination compounds to improve cured resin properties such as fracture toughness, thermal stability and water absorption, etc.     

Effect of additives on the proline-catalyzed ketone–aldehyde aldol reactions

The effect of bases, acids, and water as additives in proline-catalyzed ketone–aldehyde aldol reactions has been studied. While the reaction appears to be relatively tolerant to small amounts of tertiary amine bases or weak acids, it stops completely with strong acids. The use of water as an additive had a highly beneficial effect on reactions that were conducted with a stoichiometric ratio of ketone to aldehyde, especially with cyclic ketones. This allows the efficient use of more precious ketones such as 4-thianone as donors in the direct enantioselective aldol and facilitates purification.     

Separation of metal ions and metal-containing species by micellar electrokinetic capillary chromatography, including utilisation of metal ions in separations of other species

The use of micellar electrokinetic capillary chromatography (MEKC) for the separation of metal ions and metal-containing species is reviewed, together with the use of metal ions as a means to separate other species. Topics covered include the manipulation of separation selectivity through the use of complexation reactions induced by addition of a metal ion to the background electrolyte, enantiomeric separations facilitated through metal-analyte interactions, separation of organometallic species, separation of stable metal complexes in which the entire complex is the analyte and the separation of metal ions as analytes using pre-capillary or on-capillary complexation reactions with a suitable ligand.     

Unconventional TLC systems in lipophilicity determination: A review

ABSTRACT

This review focuses on four unusual thin-layer chromatography (TLC) approaches for the determination of lipophilicity: (1) the use of medium-polar stationary phases: CN, NH₂, and DIOL instead of RP plates, together with water-based mobile phase; (2) the use of silica gel in a typical normal-phase manner and treating extrapolated retention indices as the “reversed lipophilicity”; (3) the use of oil impregnated silica gel in the reversed-phase manner; and (4) the use of salting-out mobile phases. The chromatographic indices obtained in these systems are numerously reported as well correlated with lipophilicity and they are an interesting alternative to classical RP systems approaches.     

A Review of Ionic Liquids in Chromatographic and Electromigration Techniques

Although there have been numerous studies on the use of ionic liquids (IL) as solvents for synthesis and catalysis, there are many potential new fields for their application. The number of studies dealing with the use of ILs as additives to the mobile phase in LC and CZE and as a stationary phases in GC is constantly increasing. The main goal of the present paper is to gather together studies concerning the use of ILs in chromatographic techniques. The application of these substances as stationary phases, mobile phase additives and electroosmotic flow modifiers is discussed. Conversely, the application of separation methods in the analysis of ILs is also the subject of this review.     

Evaluation of the enantioselectivity of carbon nanoparticles‐modified chiral separation systems using dextrin as chiral selector by capillary electrokinetic chromatography

Nanoparticles (NPs) can be used as pseudostationary phases (PSPs) in EKC, which is similar to the use of micelle additives as applied in MEKC. To date, the use of NPs to enhance enantiomeric separation by EKC with β‐CD or its derivative as chiral selector has been reported only in two papers. However, to the best of our knowledge, there has been no prior effort to use NPs for achieving enantioseparation with polysaccharides as chiral selector. This paper describes for the first time the use of carbon nanoparticles (CNPs) as PSPs to modify chiral separation system employing dextrin as chiral selector for the enantioseparations of several basic drugs in capillary EKC. Three different types of CNPs, including carbogenic nanoparticles (NPs), carboxylated single‐walled carbon nanotubes, and carboxylated multiwalled carbon nanotubes, were used as running buffer additives, respectively. The potential of the PSPs and the effects of dextrin concentration, buffer pH, and buffer concentration on the enantioseparations were evaluated. Four pairs of tested enantiomers were successfully resolved in less than 15 min with the resolution values in the range of 1.41–4.52 under optimized conditions. Compared to the buffer without NPs, the introduction of NPs into the buffer enhanced the separation of the enantiomers.     

Design, synthesis, and miniemulsion polymerization of new phosphonate surfmers and application studies of the resulting nanoparticles as model systems for biomimetic mineralization and cellular uptake

Heterophase polymerizations have gained increasing attention in the past decades, especially as the decoration and functionalization of the particle surface for further applications gets more and more into focus. One promising approach for the functionalization exclusively on the particle surface is the use of surfmers (surfactant and monomer). Herein, we present the synthesis of a new family of surfmers and their use for decorating nanoparticles with phosphonate groups through miniemulsion polymerization. Furthermore the synthesis of a dye-labeled functional surfmer provided an elegant manner to evaluate and get deeper insights about its copolymerization. Additionally, potential applications of the synthesized particles in biological studies as well as their use as template for biomimetic mineralization are presented.     

Nucleic acid encoding to program self-assembly in chemical biology

This tutorial review serves as an introduction to the use of oligonucleotides and in particular peptide nucleic acids (PNAs) to encode function beyond heredity. Applications in chemical biology are reviewed starting with the use of nucleic acid tags to program self-assembled microarrays of small and macromolecules, followed by the use of nucleic acid templated reactions for the purpose of DNA or RNA sensing and finally, the use of nucleic acid templates to display ligands.     

Calibration in solid-sample spectrometry: statistical routine or a complex of problems?

The analytical calibration in atomic spectrometry similar to other indirect analytical methods has been for many years basically a routine procedure. While the calibration is based on the use of the solution standards, it is only a chemometrical routine in which the by IUPAC recommended complex procedure could be used. In the last two decades the solid-sampling methods have been spread out, their interactivity is connected with their use in analysis of the non-oxide ceramics as well as samples of the environmental relevancy (e.g. sediments, sludge, dust sediments, etc.). This wide use of the solid sampling methods has pointed to more specific problems, as lack of suitable CRM-s, homogeneity problems and with those connected problems of the useable sample amounts. Some of the mentioned problems as well as their elimination possibilities are the aim of this work.     

Polyethyleneimine coating renders polycarbonate resistant to organic solvents

We propose a method for the modification of surfaces of microchannels in chips fabricated in polycarbonate (PC) that makes the devices resistant to a range of organic solvents. Coating of PC with branched polyethyleneimine (BPEI) with the use of trimethylpropane triglycidyl ether (TTE) as a linker renders the devices resistant to toluene, benzene, acetonitrile, tetrahydrofuran, dioxane and ethylene dichloride. The optimized procedure of modification allows for continuous operation of the chips for several hours without dissolution of PC. Additional modification with the use of Krytox? allows for the use of Fluorinert (FC-40) as the continuous phase and for generation and handling of droplets of organic solvents that are miscible with water.     

Asymmetric activation of tropos species in the achievement of chiral inducers for enantioselective catalysis

The use of chiral derivatives embedding flexible chiral moieties in enantioselective catalysis is reported and the compounds are classified as chiral ligands for metal catalysis, on the basis of the coordinating atom and phase transfer catalysts. The use of phosphorus, nitrogen, and oxygen ligands as well as the development of organocatalysts, with these structural features, outlines the wide applicability of this approach to asymmetric catalysis.     

Chromatographic Properties of Ethanol/Water Mobile Phases on Silica Based Monolithic C18

For almost 10 years, silica-based monolithic stationary phases have been used in numerous fields of analytical chemistry, especially when high flow rate is required or for the separation of high molecular weight compounds such as peptides. In comparison with particulate stationary phases, the macroporous structure of the silica rod induces low pressure drops, which allows the use of high flow rates, leading to a dramatic reduction of the analysis duration. We suggest another use of this type of phases with mobile phases having a high viscosity, such as ethanol–water mixtures. These mobile phases are environmentally friendly, avoiding the use of toxic solvents such as methanol and acetonitrile, and consequently the necessary cleaning of waste is reduced. In this paper, the eluting strength of different hydro-organic mobile phases and their efficiencies are compared on Chromolith RP-18e. Due to higher eluting strength, the use of ethanol–water mixtures also allows decreasing the amount of organic solvent required to achieve a separation, whereas, despite a higher viscosity, the chromatographic efficiencies are as good as those obtained with classical mobile phases. Finally, separation of pesticides (triazines) and sunscreen molecules are presented.