Chromophores in cellulosics, VI. First isolation and identification of residual chromophores from aged cotton linters

In the present work, aged cotton linters have been analyzed for their chromophore content according to the CRI (“chromophore release & identification”) method. Despite the very low contents in the ppb range, nine chromophores have been unambiguously identified, which makes this account the first one on defined chromophoric structures isolated from cotton. A common feature of the chromophores are 2-hydroxy-[1,4]benzoquinone, 2-hydroxyacetophenone and 5,8-dihydroxynaphthoquinone moieties, which resemble chromophoric structures found in other cellulosic substrates, such as bleached pulps or fibers. The finding of these compounds in lignin-free cotton linters confirms the previous hypothesis that those chromophores are formed from (oxidized) carbohydrate structures rather than from lignin fragments.     

Development of a microfluidic biosensor module for pathogen detection

The development of a microfluidic biosensor module with fluorescence detection for the identification of pathogenic organisms and viruses is presented in this article. The microfluidic biosensor consists of a network of microchannels fabricated in polydimethylsiloxane (PDMS) substrate. The microchannels are sealed with a glass substrate and packed in a Plexiglas housing to provide connection to the macro-world and ensure leakage-free flow operation. Reversible sealing permits easy disassembly for cleaning and replacing the microfluidic channels. The fluidic flow is generated by an applied positive pressure gradient, and the module can be operated under continuous solution flow of up to 80 microL min(-1). The biosensor recognition principle is based on DNA/RNA hybridization and liposome signal amplification. Superparamagnetic beads are incorporated into the system as a mobile solid support and are an essential part of the analysis scheme. In this study, the design, fabrication and the optimization of concentrations and amounts of the different biosensor components are carried out. The total time required for an assay is only 15 min including sample incubation time. The biosensor module is designed so that it can be easily integrated with a micro total analysis system, which will combine sample preparation and detection steps onto a single chip.     

Solution-state conformational study of the hevamine inhibitor allosamidin and six potential inhibitor analogues by NMR spectroscopy and molecular modeling

The solution-state conformations of the hevamine inhibitor allosamidin and six potential inhibitor analogues were studied by various NMR spectroscopic techniques and molecular modeling using force field calculations. Determination solely of the global energy minimum conformation was found to be insufficient for consensus with the NMR results, and agreement between the NMR experimental data and the theoretical calculations was only reached by assessing the structures as population-weighted average conformers on the basis of Boltzmann distributions derived from the calculated relative energies. The conformations of the glycosidic linkages in the compounds were found to be similar when the sugar residues were the same, but differences were markedly evident otherwise and also for the various heterocyclic group linkages. The binding of the compounds to hevamine, which may also complex to chitinases in general, was assessed using HMQC, transfer-NOESY, and both 1-D and 2-D saturation transfer difference NMR experiments. Under the conditions employed, only allosamidin was implicated to be bound to hevamine, and then only by HMQC with the dipolar coupling-based experiments failing to substantiate the formation of the complex. However, the results are consistent with the biochemical activities of the compounds whereby only allosamidin has been shown to act as a competitive inhibitor.     

Total Synthesis of the Hypermodified RNA Bases Wybutosine and Hydroxywybutosine and Their Quantification Together with Other Modified RNA Bases in Plant Materials

We report an efficient synthesis of the hypermodified natural tRNA modifications wybutosine (yW) and hydroxywybutosine (OHyW). We also describe the preparation of isotopically labeled analogues for precise quantification of yW and OHyW in different tissues including plant materials. The synthesis involved the formation of the unusual tricyclic ring structure of the bases by using a catalytic, intramolecular hydroamination reaction. The basis for the synthesis is also a stereoselective coupling reaction that allows the introduction of the fully substituted side chains to the tricyclic core structure. The isotopologues of yW and OHyW, together with other isotopically labeled tRNA modifications, were ultimately used in LC‐MS quantification experiments to investigate the role of the modified bases in the translational process. Quantification was performed in the plant species Arabidopsis thaliana.     

Development of an Improved Rhodium Catalyst for Z‐Selective Anti‐Markovnikov Addition of Carboxylic Acids to Terminal Alkynes

To develop more active catalysts for the rhodium‐catalyzed addition of carboxylic acids to terminal alkynes furnishing anti‐Markovnikov Z enol esters, a thorough study of the rhodium complexes involved was performed. A number of rhodium complexes were characterized by NMR, ESI‐MS, and X‐ray analysis and applied as catalysts for the title reaction. The systematic investigations revealed that the presence of chloride ions decreased the catalyst activity. Conversely, generating and applying a mixture of two rhodium species, namely, [Rh(DPPMP)₂][H(benzoate)₂] (DPPMP=diphenylphosphinomethylpyridine) and [{Rh(COD)(μ₂‐benzoate)}₂], provided a significantly more active catalyst. Furthermore, the addition of a catalytic amount of base (Cs₂CO₃) had an additional accelerating effect. This higher catalyst activity allowed the reaction time to be reduced from 16 to 1–4 h while maintaining high selectivity. Studies on the substrate scope revealed that the new catalysts have greater functional‐group compatibility.     

Interactions of ionic liquids with polysaccharides 9. Hydroxyalkylation of cellulose without additional inorganic bases

Water-soluble hydroxyalkyl cellulose with a molar degree of substitution of up to 2.79 was prepared under completely homogeneous reaction conditions in various ionic liquids without addition of inorganic bases. In acetate containing solvents the IL acts as a catalyst. The substitution patterns of the cellulose ethers were analyzed by ¹³C NMR spectroscopy, ¹H NMR spectroscopy after peracetylation and GLC/MS after permethylation and depolymerization. A diminished tendency towards the formation of side chains compared to heterogeneously prepared hydroxyalkyl celluloses in the presence of inorganic bases was found.     

Synthesis of Block Copolymers Modified with Phosphonate Ester Groups Using Nitroxide‐Mediated Radical Polymerization

Summary: Phosphonate groups were introduced into block copolymers of styrene derivatives either as single end‐groups or as small blocks using nitroxide‐mediated radical polymerization. In order to combine the hydrophobic and hydrophilic segments, block copolymers with N,N‐dimethyl acrylamide were synthesized. After hydrolysis to phosphonic acid groups, adsorption of the polymer onto metal oxides was possible.

Conversion of the phosphonate groups by transesterification with trimethylbromosilane (TMBS), followed by hydrolysis of the silylester group.     

Hydrogen bond catalyzed direct reductive amination of ketones

[reaction: see text] A novel, biomimetic concept for the direct reductive amination of ketones is described that relies on selective imine activation by hydrogen bond formation. The mild, acid- and metal-free process requires only catalytic amounts of thiourea as hydrogen bond donor and utilizes the Hantzsch ester for transfer hydrogenation. The method allows the efficient synthesis of structurally diverse amines.     

Capillary electrophoresis of ANTS labelled oligosaccharide ladders and complex carbohydrates

The detection limits of the ANTS (8-aminonaphthalene-1,3,6-trisulfonic acid) label and ANTS maltose as a model carbohydrate conjugate were investigated with on-column UV and laser induced fluorescence detection. Under capillary electrophoresis conditions, the concentration and mass detection limits were found to be 5×10^–7 mol/l or 8 femtomole with UV and 5×10^–8 mol/l or 400 attomole with laser induced fluorescence detection, respectively. Including the derivatization reaction, the best concentration detection limit increases to 1×10^–6 mol/l carbohydrate. A model calculation shows that these detection levels are still insufficient to match those of current protein sequencing protocols.Derivatization conditions for dextran and polygalacturonic acid ladders are described with subsequent fast separation in a capillary electrophoresis system under acidic pH buffer conditions. Up to 30 oligomers could be separated in less than 10 min. The application of ANTS labelled carbohydrate analysis in the food industry is demonstrated with the carbohydrate fraction of sweets and the kinetic monitoring of the hydrolysis of polygalacturonic acid.The described ANTS derivitization protocol works with as little as 5 g carbohydrate as demonstrated with a complex oligosaccharide labelled in a reaction volume as little as 2 l. To demonstrate the applicability of this approach to complex carbohydrate analysis, an oligosaccharide mixture derived from human Immunoglobuline G was labelled and separated within 5 min. Separation efficiency and speed are superior to state-of-the-art chromatographic methods. Both electrophoretic and chromatographic methods are complementary because of their different separation mechanism. The implications of using capillary electrophoresis with laser induced fluorescence and appropriate labelling strategies for structural and compositional analysis of complex carbohydrates are discussed.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday