DLVO interactions of tungsten oxide and cobalt oxide surfaces measured with the colloidal probe technique

We have investigated the DLVO surface forces of oxidized tungsten and cobalt surfaces using the atomic force microscope (AFM) colloidal probe technique. It was shown by X-ray photoelectron spectroscopy (XPS) and electrokinetic measurements that this model system is representative of industrial tungsten carbide (WC) and cobalt powders used in the production of hard metals. We found that the attractive van der Waals forces are well described by Hamaker constants, calculated from optical data for WO(3) and CoOOH. The repulsive electrostatic double layer forces between WO(3) surfaces increase with increasing pH due to an increasingly negative surface potential. This surface potential decreases with increasing ionic strength at pH 7.5. The electrostatic interaction between WO(3) and CoOOH is attractive at pH 10, suggesting a positively charged CoOOH surface.     

Applications of silica-based monolithic HPLC columns

The recent invention and successive commercial introduction of monolithic silica columns has motivated many scientists from both academia and industry to study their use in HPLC. The first paper on monolithic silica columns appeared in 1996. Currently about 200 papers have been published relating to applications and characterization of monolithic silica columns, including monolithic capillaries. This review attempts to give an overview covering various aspects of this new column type in the field of high throughput analysis of drugs and metabolites, chiral separations, analysis of pollutants and food-relevant compounds, as well as in bioanalytical separations such as in proteomics. Some of the applications are described in greater detail. The numerous publications dealing with the physicochemical and chromatographic characterization of monolithic silica columns are briefly summarized.     

Novel polyamine coating providing non-covalent deactivation and reversed electroosmotic flow of fused-silica capillaries for capillary electrophoresis

A new polycationic coating for use in capillary electrophoresis has been developed that enables chemical modification of fused-silica capillary surfaces for analysis of compounds like basic proteins. The cationic polyamine, containing short aliphatic blocks of combined 2 and 3-carbon length, was physically adsorbed onto the negatively charged fused-silica surface through ionic interaction by flushing the capillary with a polyamine solution, followed by a self-stabilization step. The polyamine coated capillaries generated an anodal electroosmotic flow that was independent of pH in the investigated range of pH 4-8. The capillary performance was demonstrated by fast separations of basic proteins with peak efficiencies in the range of 265,000-584,000 plates.     

Small-angle X-ray scattering, light scattering, and NMR study of PEO-PPO-PEO triblock copolymer/cationic surfactant complexes in aqueous solution

The formation of triblock copolymer/surfactant complexes upon mixing a nonionic Pluronic polymer (PEO-PPO-PEO) with a cationic surfactant, hexadecyltrimethylammonium chloride (CTAC), has been studied in dilute aqueous solutions using small-angle X-ray scattering, static and dynamic light scattering, and self-diffusion NMR. The studied copolymer (denoted P123, EO(20)PO(68)EO(20)) forms micelles with a radius of 10 nm and a molecular weight of 7.5 x 10(5), composed of a hydrophobic PPO-rich core of radius 4 nm and a water swollen PEO corona. The P123/CTAC system has been investigated between 1 and 5 wt % P123 and with varying surfactant concentration up to approximately 170 mM CTAC (or a molar ratio n(CTAC)/n(P123) = 19.3). When CTAC is mixed with micellar P123 solutions, two different types of complexes are observed at various CTAC concentrations. At low molar ratios (>/=0.5) a "P123 micelle-CTAC" complex is obtained as the CTAC monomers associate noncooperatively with the P123 micelle, forming a spherical complex. Here, an increased interaction between the complexes with increasing CTAC concentration is observed. The interaction has been investigated by determining the structure factor obtained by using the generalized indirect Fourier transformation (GIFT) method. The interaction between the P123 micelle-CTAC complexes was modeled using the Percus-Yevick closure. For the low molar ratios a small decrease in the apparent molecular weight of the complex was obtained, whereas the major effect was the increase in electrostatic repulsion between the complexes. Between molar ratios 1.9 and 9 two coexisting complexes were found, one P123 micelle-CTAC complex and one "CTAC-P123" complex. The latter one consists of one or a few P123 unimers and a few CTAC monomers. As the CTAC concentration increases above a molar ratio of 9, the P123 micelles are broken up and only the CTAC-P123 complex that is slightly smaller than a CTAC micelle exists. The interaction between the P123/CTAC complexes was modeled with the hypernetted-chain closure using a Yukawa type potential in the GIFT analysis, due to the stronger electrostatic repulsion.     

The binding of human carbonic anhydrase II by functionalized folded polypeptide receptors

Several receptors for human carbonic anhydrase II (HCAII) have been prepared by covalently attaching benzenesulfonamide carboxylates via aliphatic aminocarboxylic acid spacers of variable length to the side chain of a lysine residue in a designed 42 residue helix-loop-helix motif. The sulfonamide group binds to the active site zinc ion of human carbonic anhydrase II located in a 15 A deep cleft. The dissociation constants of the receptor-HCAII complexes were found to be in the range from low micromolar to better than 20 nM, with the lowest affinities found for spacers with less than five methylene groups and the highest affinity found for the spacer with seven methylene groups. The results suggest that the binding is a cooperative event in which both the sulfonamide residue and the helix-loop-helix motif contribute to the overall affinity.     

Quasi‐classical fluctuation–dissipation description of dielectric loss in oxides with implications for quantum information processing

One of the most important problems in developing devices for quantum computation is the coupling and dissipation of states by thermal noise. We present a study of a two‐state electric dipole in a crystal coupling to noise from a reservoir. As a realization of such an energy‐dissipating dipole, we report and analyze dielectric loss measurements in single crystal and polycrystalline Al₂O₃ over the temperature range 70–300 K. We are able to model the dielectric loss in terms of a quasi‐classical model that uses the fluctuation–dissipation theorem. Two key parameters in this model are the crystal oscillator energy and reservoir–lattice coupling constant. In polycrystalline samples, it is assumed that the main effect of structural disorder is a modification of the spectrum of the thermal phonons, so that acoustical vibrations acquire some optical mode character. The temperature dependence of the linewidth of the high dielectric strength infrared (IR) mode at 438 cm^?1 and the quasi‐degenerate Raman mode of the k = 0 (418 cm^?1) transition are also investigated and are shown to be related simply to the dielectric loss. The model reproduces the unusual temperature dependence of the dielectric loss observed experimentally. The implications for the coupling of quantum mechanical objects to noise and quantum information processing are discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Diaminopyridazine aus diaminocyclopropenyliumsalzen und (diazomethyl)- verbindungen

Diaminocyclopropenylium salts 14a,b react specifically with the phosphorylated diazomethanes 15a-e in dichloromethane in the presence of ethyl diisopropylamine and 1,5-diazabicyclo[4.3.0]non-5-ene respectively to the 4,5-diaminopyridazines 16a-f. In contrast to that the 3,4-diaminopyridazines 17a-i are formed in the reaction of the salt 14c with the diazomethyl compounds 15a,c,d such as f-k in dichloromethane in the presence of the bicyclic base. With regard to the reaction mechanism the formation of the intermediate diazomethyl cyclopropenes ( 14a,b + 15 → 18 or 14c + 15 → 19 ) has to be interpreted in the sense of an electrophilic diazoalkane substitution reaction; neither 18 nor 19 can be isolated but undergo a fast [1,5]-cyclization to the betaines 20 or 21 , which finally isomerize to the pyridazines 16 or 17 by opening of the bridge bond.     

Photoaktivierte selective hydrierung von butindiol zu butendiol mit dem katalysator IrCl(CO)(PPh3)2

Under a weak UV irradiation butynediol is selectively hydrogenated to butenediol with IrCl(CO)(PPh₃)₂ as the catalyst in toluene/trifluroethanol ($\text{1}\text{1}$) at 60 °C.     

Monitoring dioxins in food and feedstuffs using accelerated solvent extraction with a novel integrated carbon fractionation cell in combination with a CAFLUX bioassay

The concentrations of dioxins in fish oil and fish meal were determined with accelerated solvent extraction, using a novel integrated carbon fractionation extraction cell followed by a miniturized multilayer silica column and bioanalysis on a recently-developed chemically-activated fluorescent gene expression cell bioassay. The developed method allows for simultaneous gravimetric lipid weight determination, which was shown for both matrices under study (about 100% lipid recovery of each sample). Initial results practically meet the quality criteria on screening methods for control of dioxins in food and feedstuffs laid down in the EU Commission Directives 2002/69/EC (food) and 2002/70/EC (feed). This demonstrates that the developed method can be used as a screening tool for monitoring dioxins in food and feed after some additional improvements and testing on a greater number of matrices.     

Process monitoring of polymers by in-line ATR-IR, NIR and Raman spectroscopy and ultrasonic measurements

The aim of the present work is to show that spectroscopic and ultrasonic methods are powerful in situ methods for monitoring polymerization processes and for the determination of the composition of polymer blends and additives during extrusion. Quantitative analysis carried out with chemometric methods can determine the composition of multicomponent polymer mixtures and predict real world samples in real-time during extrusion. Examples are the modification of hyperbranched poly(urea-urethane)s, the polymerization of MMA, the real-time determination of flame retardants in PA, and the determination of the composition of the blend PE/PS. To cite this article: D. Fischer et al., C. R. Chimie 9 (2006).