Allgemeiner Zugang zu Polyaminen mit Ethan-1,2-diamin-Einheiten: Synthese von nicht natürlich vorkommenden homologen und isomeren N1,4-Di(4-cumaroyl)sperminen

█tl="American"█The synthesis of the three N,N′-di(4-coumaroyl)tetramines, i.e., of (E,E)-N-{3-[(2-aminoethyl)amino]propyl}-3,3′-bis(4-hydroxyphenyl)-N,N′-(ethane-1,2-diyl)bis[prop-2-enamide] ( 1a ), (E,E)-N-{4-[(2-aminoethyl)amino]butyl}-3,3′-bis(4-hydroxyphenyl)-N,N′-(ethane-1,2-diyl)bis[prop-2-enamide] ( 1b ), and (E,E)-N-{6-[(2-aminoethyl)amino]hexyl}-3,3′-bis(4-hydroxyphenyl)-N,N′-(ethane-1,2-diyl)bis[prop-2-enamide] ( 1c ), is described. It proceeds through stepwise construction of the symmetric polyamine backbone including protection and deprotection steps of the amino functions. Their behavior on TLC in comparison with that of 1,4-di(4-coumaroyl)spermine (=(E,E)-N-{4-[(3-aminopropyl)amino]butyl}-3,3′-bis(4-hydroxyphenyl)-N,N′-(propane-1,3-diyl)bis[prop-2-enamide]; 2 ) is discussed.     

Wavelength dependence of mycosporine-like amino acid synthesis in Gyrodinium dorsum

The synthesis or accumulation of mycosporine-like amino acids (MAAs) is an important UV tolerance mechanism in aquatic organisms. To investigate the wavelength dependence of MAA synthesis in the marine dinoflagellate Gyrodinium dorsum, the organism was exposed to polychromatic radiation (PAR and UV) from a solar simulator for up to 72 h. Different irradiance spectra were produced by inserting various cut-off filters between lamp and samples. A polychromatic action spectrum for the synthesis of MAA synthesis was constructed. PAR and long wavelength UV-A radiation showed almost no effect while the most effective wavelength range was around 310 nm. Shorter wavelengths where less effective in the induction of MAA synthesis. Wavelengths below 300 nm damaged the organisms severely as indicated by a decrease in chlorophyll a absorption.     

Single flexible hydrophobic polyelectrolyte molecules adsorbed on solid substrate: transition between a stretched chain, necklace-like conformation and a globule

Single flexible polyelectrolyte molecules of poly(2-vinylpyridine) undergo conformational transition from a stretched wormlike coil to a necklace-like globule, and to a compact globule depending on pH and ionic strength in aqueous solution in good agreement with recent theoretical reports. AFM investigations allow the visualization of details of the chain conformation on mica and the extraction of quantitative statistics of molecular dimensions.     

Weathering Phenomena on Naturally Weathered Potash-Lime-Silica-Glass with Medieval Composition Studied by Secondary Electron Microscopy and Energy Dispersive Microanalysis

 Samples of two model glasses with chemical compositions similar to medieval stained glass were exposed to the natural environment at 23 test sites for a period of 6 months, 1 and 2 years within an exposure programme of the “Working Group of Effects on Materials, Including Historic and Cultural Monuments” of the Economic Commission for Europe of the United Nations. During the exposure the environmental data were measured and collected at each test site in order to enable a correlation between the pollutant load in the ambient atmosphere and the weathering phenomena of the glass samples. After the exposure, which was performed in a sheltered as well as in an unsheltered mode for gaining information about the influence of dry and wet deposition of air pollutants, the glass samples were analysed in the scanning electron microscope with energy dispersive microanalysis (SEM/EDX). Model glass M1 – a potassium rich glass – was covered to a high amount with crystalline weathering products (above all syngenite), whereas glass M3 – a glass with a higher Ca and Si content – turned out to be more stable against weathering. This glass was covered with gypsum and arcanite crystals but in total to a less extent than glass M1. Received March 30, 1998. Revision February 8, 2000.     

Identification of a new metabolite of macrolide immunosuppressant, like rapamycin and SDZ RAD, using high performance liquid chromatography and electrospray tandem mass spectrometry

Previously unknown metabolites from the two macrolide immunosuppressants rapamycin (sirolimus) and SDZ RAD [40-O-(2-hydroxyethyl)rapamycin] obtained after in vitro incubation with human liver microsomes have been purified. Structure elucidation was performed by nanoelectrospray ionization tandem mass spectrometry applying low energy collision activated dissociation. This ionization method is, as shown here, a powerful tool to determine metabolic pathways by analysis of even low abundance products. Product ion spectra of the isolated metabolites indicate a new kind of biotransformation reaction for rapamycin and SDZ RAD. The proposed metabolic pathway starts with an ester hydrolysis which leads to a ring-opened structure. A dehydration on C33-C34 and a supplementary hydrogenation at C33-C34 result in a structure similar to the ring-opened isomer with an single bond at C33-C34.     

Polyacrolein-isonicotinic acid hydrazone and polyacrylic acid-thiohydrazide resins-synthesis and sorption properties for precious and base metals

This investigation carries on previous studies on polyacrolein-styrene resins. Further attempts were made to convert the reactive aldehyde groups of the polymeric support to functional acrolein-isonicotinic acid hydrazone (P-NHZ) or acrylic acid-thiohydrazide derivatives (P-THZD). The conditions of synthesis and the basic sorption and desorption properties of the polymers synthesized are described. For gold and platinum group metals the resins show differences in loading capacities, rates of simultaneous sorption in static conditions and efficiencies in column tests. The elution by thiourea solution was utilized to separate Au, Pd and Pt from an excess of base metals. The P-NHZ resin seems to be more advantageous than the sulfur containing P-THZD resin.     

The trifluoromethoxy group: a long-range electron-withdrawing substituent

Judged by its capacity to promote a hydrogen/metal permutation at an ortho position, the trifluoromethoxy group is superior to both the methoxy and trifluoromethyl groups. Moreover, like CF(3) and unlike OCH(3), OCF(3) exerts a long-range effect that still considerably lowers the basicity of arylmetal compounds when located in a more remote meta or even para position. As a consequence, 4-(trifluoromethoxy)anisole is deprotonated by sec-butyllithium mainly, and by tert-butyllithium exclusively, at a position adjacent to the OCH(3) group rather than next to the strongly electron-withdrawing CF(3)O group. 1,3-Benzodioxole undergoes ortho lithiation only six times faster than anisole, whereas 2,2-difluoro-1,3-benzodioxole reacts about 5000 times faster, as evidenced by competition experiments. The structure and distance dependence of substituent effects can be rationalized by assuming superposing sigma- and pi-polarizing interactions.     

Fast H/D exchange of B,B',B'-tribromoborazine in C6D6 in the presence of aluminum tribromide: first evidence for an electrophilic substitution reaction of borazines in solution

A solution of B,B',B'-tribromoborazine (BrBNH)(3) in excess C(6)D(6) in a sealed NMR tube shows no changes for over 14 months at room temperature but undergoes fast (within minutes) H/D exchange in the presence of AlBr(3) as a Lewis acid, as evidenced by (1)H, (2)H, (11)B, and (27)Al NMR spectroscopy. The proposed electrophilic exchange mechanism is in agreement with the results of DFT computations. To our knowledge, this is the first example of the electrophilic substitution reaction of borazines in solution.     

Recent advances in hydrophilic interaction liquid chromatography (HILIC) for structural glycomics

This review presents recent progress in employing hydrophilic interaction liquid chromatography (HILIC) for glycan and glycopeptides analysis. After an introduction of this technique, the following themes are addressed: (i) implementation of HILIC in large-scale studies for analyzing the human plasma N-glycome; (ii) the use of HILIC UPLC (ultrahigh pressure liquid chromatography) for fast high-resolution runs and its successful application with online MS for glycan and glycopeptide analysis; (iii) high-throughput profiling using HILIC solid-phase extraction in combination with MS detection; (iv) HILIC sample preparation for CE and CGE; (v) the latest glycoproteomic approaches implementing HILIC separation; (vi) future perspectives of HILIC including its use in large-scale glycoproteomics studies such as the analysis of entire glycoproteomes at the glycopeptide level.