Determination of twelve heparin- and heparan sulfate-derived disaccharides as 2-aminoacridone derivatives by capillary zone electrophoresis using ultraviolet and laser-induced fluorescence detection

In quest for high sensitivities, we developed an ultrahigh capillary electrophoresis (CE) method for the structural analysis of heparin and heparan sulfate (HS) in biologic samples. Heparin and HS were digested with an equi-unit mixture of heparin lyases I, II and III and the obtained Delta-disaccharides were derivatized with the fluorophore 2-aminoacridone. All known twelve non-, mono-, di- and trisulfated Delta-disaccharides were completely resolved in a single run, using 50 mM phosphate buffer, pH 3.5, and reversed polarity at 30 kV. Relative standard deviation in migration times and peak areas as well as day-to-day variance ranged from 0.9 to 2.4%, suggesting a reproducible and precise method. Detection of 2-aminoacridone (AMAC)-derivatives of Delta-disaccharides by UV at 255 nm showed 2.8 and 10 times higher sensitivity than that of derivatized and non-derivatized ones at 232 nm. Laser-induced fluorescence detection with an Ar-ion laser source showed an approximately 100 times higher sensitivity than that obtained at 232 nm of the non-derivatized species. Application of this method to quantitative analysis of Delta-disaccharides derived from porcine intestinal mucosa heparin and bovine kidney HS showed excellent agreement with previously published methods, suggesting an accurate method. The developed method can be easily applied for the disaccharide analysis of heparin/HS at the attomole level with high accuracy, for distinguishing between heparin and HS and may be of value for studying their interactions with matrix effective molecules.     

A Novel Dual Organocatalyst for the Asymmetric Pinder Reaction and a Mechanistic Proposal Consistent with the Isoinversion Effect Thereof

In general, the Pinder reaction concerns the reaction between an enolisable anhydride and an aldehyde proceeding initially through a Knoevenagel reaction followed by the ring closing process generating lactones with at least two chiral centers. These scaffolds are frequently present in natural products and synthetic bioactive molecules, hence it has attracted intense interest in organic synthesis and medicinal chemistry, particularly with respect to controlling the diastereo- and enantioselectivity. To the best of our knowledge, there has been only one attempt prior to this work towards the development of a catalytic enantioselective Pinder reaction. In our approach, we designed, synthesized, and tested dual chiral organocatalysts by combining BIMAH amines, (2-(α-(alkyl)methanamine)-1H-benzimidazoles, and a Lewis acid motif, such as squaramides, ureas and thioureas. The optimum catalyst was the derivative of isopropyl BIMAH bearing a bis(3,5-trifluoromethyl) thiourea, which afforded the Pinder products from various aromatic aldehydes with diastereomeric ratio >98:2 and enatioselectivity up to 92 ee%. Interestingly, the enantioselectivity of this catalyzed process is increased at higher concentrations and exhibits an isoinversion effect, namely an inverted "U" shaped dependency with respect to the temperature. Mechanistically, these features, point to a transition state involving an entropy-favored heterodimer interaction between a catalyst/anhydride and a catalyst/aldehyde complex when all other processes leading to this are much faster in comparison above the isoinversion temperature.     

Characteristics of composites based on PMMA modified gel silica glasses

Gel silica glass prepared by the sol-gel process can be modified by incorporating an organic phase into the intrinsically porous inorganic gel matrix, which results in a composite material with much improved mechanical and optical properties. Characterisation of PMMA modified gel silica glass prepared by the in situ polymerisation method using FT-Raman spectroscopy, gel permeation chromatography and the nitrogen adsorption technique are reported. Some essential problems encountered in the preparation are discussed.     

Turbulence Modeling for the Stable Atmospheric Boundary Layer and Implications for Wind Energy

The near-surface structure of atmospheric turbulence affects the design and operation of wind turbines and is especially difficult to predict under stably-stratified conditions. This study uses large-eddy simulation (LES) to explore properties of the stable boundary layer (SBL) using an explicit filtering and reconstruction turbulence modeling approach. Simulations of the atmospheric boundary layer over flat terrain, under both moderately and strongly stable conditions are performed. Results from high-resolution simulations are used to investigate SBL flow structures including mean profiles and turbulence statistics, which are relevant to wind energy applications. The applicability of power-law relations and empirical similarity formulations for predicting wind speed depend on the strength of stratification and are shown to be inadequate. Low-level jets form in the simulations. Under strong stability, vertical wind shear below the jet triggers intermittent turbulence. The associated sporadic “bursting” events are extremely energetic and last longer than the time scale of the largest eddies. Such phenomena can have adverse effects on turbine lifetime and performance.     

Soluble rigid–flexible polyethers containing bis(biphenyl)anthracene or bis(styryl)anthracene units in the main chain for light-emitting applications

New rigid–flexible polyethers containing bis(biphenyl)anthracene or bis(styryl)anthracene units in the main chain were synthesized and characterized by viscosimetry, thermal and mechanical analysis, NMR, UV-vis, and luminescence spectroscopy. The polyethers containing bis(styryl)anthracene units in the main chain form free-standing films either from solution casting or after melt pressing at temperatures where they are thermally stable. The length of the flexible spacer influences the thermal and mechanical behavior of these polymers. The isotropization temperature as well as the glass transition temperature show an odd–even effect depending on the spacer segment length. Films with high modulus at room temperature and glass transition temperatures in the range 74–103°C were obtained using dynamic mechanical analysis. These polymers show bright-yellow photoluminescence with maximum at 580 nm in solution. In the solid state, the luminescence maximum is either red or blue shifted depending on the number of the methylene units in the aliphatic segment. The polyethers containing bis(biphenyl)anthracene units in the main chain are blue-light-emitting polymers with photoluminescence maxima at 435 and 455 nm in solution. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3826–3837, 1999     

A new rhodium complex with a nitrogen‐containing bis(phosphine oxide) ligand as an efficient catalyst for the hydroformylation of styrene

A new rhodium complex with a nitrogen‐containing bis(phosphine oxide) ligand has been synthesized. The complex was applied to hydroformylation of styrene and displayed high activity and regioselectivity towards the branched aldehyde, which was found to be higher than those of the tertiary bis(phosphine) analogue. Copyright © 2006 John Wiley & Sons, Ltd.     

Tear analysis of ascorbic acid,uric acid and malondialdehyde with capillary electrophoresis

Tears have a significant role in antioxidant defense in ocular tissues and since their collection is quick and noninvasive, their analysis would facilitate monitoring of pathophysiological changes. However, their low volume and low content of antioxidants makes analysis difficult; methods of high sensitivity are needed. In this paper, we present a method for tear analysis of two antioxidant molecules (ascorbic and uric acid) and of a lipid peroxidation indicator (malondialdehyde) with capillary electrophoresis. Tears were collected with Schirmer strips, extracted with a low‐pH phosphate buffer, centrifuged through membrane filters and an antioxidant was added. They were stable at ?70°C for 15 days. After pilot experiments, optimum electrophoretic separation was achieved in a 25 mm borate buffer, pH 10.0, containing 100 mm sodium dodecyl sulfate at 25°C and 20 kV. The developed method has good repeatability (<5% RSD), precision (<15% relative error values) and high sensitivity (LLOQ values of 20, 2.3 and 2.5 μM for ascorbate, urate and malondialdehyde, respectively). It was applied to the analysis of tears from healthy individuals and the antioxidant levels are in agreement with those obtained with other techniques. This method might serve as a tool to clarify the role of endogenous antioxidants in the pathophysiology of ocular diseases. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of the Mg-Concentration Profile in Near-Surface Layers of Materials Using the 24Mg(α,p)27Al Nuclear Reaction

 The ²⁴Mg(α, p)²⁷ Al nuclear reaction was applied for the determination of the magnesium distribution in near-surface layers of materials. The cross sections of this reaction were determined in the energy region between 4.5 and 5.5 MeV in steps of 5 to 10 KeV (θ_lab : 158°) using thin magnesium films. The investigated projectile energy region included five main resonances allowing the determination of magnesium. The uncertainty of the cross-section determination was of the order of 7%. The applicability of the technique was tested using Mg-implanted AISI 321 steel samples. Depth resolution of 100 nm and detection limits of the order of 0.1 ppm were achieved for the determination of magnesium in steel samples using the 4805 keV resonance of the ²⁴Mg(α, p)²⁷ Al nuclear reaction. The shape and height of the magnesium depth-profile in the Mg-implanted steel samples were compared with corresponding values obtained by X-ray photoelectron spectroscopy. Received July 15, 1999. Revision March 30, 2000.