Fast immobilization of probe beads by dielectrophoresis-controlled adhesion in a versatile microfluidic platform for affinity assay

The use of probe beads for lab-on-chip affinity assays is very interesting from a practical point of view. It is easier to handle and trap beads than molecules in microfluidic systems. We present a method for the immobilization of probe beads at defined areas on a chip using dielectrophoresis (DEP)-controlled adhesion. The method is fast, i.e., it takes between 10 and 120 s--depending on the protocol--to functionalize a chip surface at defined areas. The method is versatile, i.e., it works for beads with different types of probe molecule coatings. The immobilization is irreversible, i.e., the retained beads are able to withstand high flow velocities in a flow-through device even after the DEP voltage is turned off, thus allowing the use of conventional high-conductivity analyte buffers in the following assay procedure. We demonstrate the on-chip immobilization of fluorescent beads coated with biotin, protein A, and goat-antimouse immunoglobulin G (IgG). The number of immobilized beads at an electrode array can be determined from their fluorescence signal. Further, we use this method to demonstrate the detection of streptavidin and mouse IgG. Finally, we demonstrate the feasibility of the parallel detection of different analyte molecules on the same chip.     

Reaction of Hydroxymethyl- and Alkyl-Substituted Azulenes with Manganese Dioxide

It is shown that the 2-(hydroxymethyl)-1-methylazulenes 6 are being oxidized by activated MnO₂ in CH₂Cl₂ at room temperature to the corresponding azulene-1,2-dicarbaldehydes 7 (Scheme 2). Extension of the MnO₂ oxidation reaction to 1-methyl- and/or 3-methyl-substituted azulenes led to the formation of the corresponding azulene-1-carbaldehydes in excellent yields (Scheme 3). The reaction of unsymmetrically substituted 1,3-dimethyl-azulenes (cf. 15 in Scheme 4) with MnO₂ shows only little chemoselectivity. However, the observed ratio of the formed constitutionally isometric azulene-1-carbaldehydes is in agreement with the size of the orbital coefficients in the HOMO of the azulenes. The reaction of guaiazulene ( 18 ) with MnO₂ in dioxane/H₂O at room temperature gave mainly the expected carbaldehyde 19 . However, it was accompanied by the azulene-diones 20 and 21 (Scheme 5). The precursor of the demethylated compound 20 is the carbaldehyde 19 . Similarly, the MnO₂ reaction of 7-isopropyl-4-methyalazulene ( 22 ) as well as of 4,6,8-trimethylazulene ( 24 ) led to the formation of a mixture of the corresponding azulene-1,5-diones and azulene-1,7-diones 20 / 23 and 25 / 26 , respectively, in decent yields (Schemes 6 and 7). No MnO₂ reaction was observed with 5,7-dimethylazulene.     

[ReF6]2−: A Robust Module for the Design of Molecule‐Based Magnetic Materials

A facile synthesis of the [ReF₆]^2? ion and its use as a building block to synthesize magnetic systems are reported. Using dc and ac magnetic susceptibility measurements, INS and EPR spectroscopies, the magnetic properties of the isolated [ReF₆]^2? unit in (PPh₄)₂[ReF₆]?2 H₂O ( 1 ) have been fully studied including the slow relaxation of the magnetization observed below ca. 4 K. This slow dynamic is preserved for the one‐dimensional coordination polymer [Zn(viz)₄(ReF₆)]_∞ ( 2 , viz=1‐vinylimidazole), demonstrating the irrelevance of low symmetry for such magnetization dynamics in systems with easy‐plane‐type anisotropy. The ability of fluoride to mediate significant exchange interactions is exemplified by the isostructural [Ni(viz)₄(ReF₆)]_∞ ( 3 ) analogue in which the ferromagnetic Ni^II–Re^IV interaction (+10.8 cm^?1) dwarfs the coupling present in related cyanide‐bridged systems. These results reveal [ReF₆]^2? to be an unique new module for the design of molecule‐based magnetic materials.     

Temperature-dependent photoacoustic spectroscopy with a Helmholtz resonator

We describe and example the Beam Propagation Method (BPM) used to model and simulate nonlinear refractive and absorptive effects in materials with applications to optical limiting and switching. Various scenarios including laser-beam trapping and laser-beam division are investigated, in order to demonstrate the power of the BPM. A novel technique is also described for efficiently modelling the external far-field propagation from nonlinear media, including the propagation of non-Gaussian-shaped spatial profiles. The methods are finally combined with the phenomenon of nonlinear absorption to demonstrate enhanced power limiting in the presence of self-refraction. Optimal parameters for high-fluence power-limiting are subsequently discussed.     

Restricted Liapunov stability and stabilization of ordinary differential equations

Summary For the solutions of a system of ordinary differential equations restricted Liapunov stability and the notion of Liapunov stable sets are discussed, in particular for separable and almost separable Hamiltonian systems. We consider stabilization procedures, i.e. modifications of the original differential equations such that the solutions of the modified are Liapunov stable and thus the new system is better suited for numerical integration. In this paper some theoretical aspects rather than numerical methods are pointed out.

---

Zusammenfassung Wir diskutieren die eingeschränkte Liapunov-Stabilität von Lösungen eines Systems von gewöhnlichen Differentialgleichungen und den Begriff der Liapunov-stabilen Menge, insbesondere für separable und fastseparable Hamilton'sche Systeme. Dann betrachten wir Stabilisierungs-methoden, d.h. Abänderungen der Differentialgleichungen, die bewirken, dass die Lösungen des modifizierten Systems Liapunov-stabil sind und die numerische Integration dadurch verbessert wird. Das Gewicht liegt auf der Klärung von einigen theoretischen Zusammenhängen und nicht auf der Erläuterung von numerischen Methoden.

     

Benzo[a]azulenediones and 10,10′‐Bibenzo[a]azulene

The oxidation of benzo[a]azulene ( 4 ) with commercial MnO₂ in dioxane/H₂O leads to a number of products in low yield (Table 1). Treatment of 4 with ‘mild’ MnO₂ (MnO₂/C) in dioxane/5% H₂O results in the formation of 10,10′‐bibenzo[a]azulene ( 18 ) in yields of up to 59% of isolated and purified material. Compound 18 exhibits atropisomerism and can be separated by HPLC on a Chiralcel column at room temperature into its stable antipodes (Fig.).     

电感耦合等离子体原子发射光谱法测定钛酸钡纳米粉体中7种杂质元素

钛酸钡纳米粉体样品用盐酸溶解,在所得样品溶液中用电感耦合等离子体原子发射光谱法测定了以氧化物存在于样品中的7种杂质元素(包括镁、锶、钾、钠、铝、硅及铁),对测定的光谱条件进行了试验并优化达到上述各元素的测定上限为0.1%(质量分数).测得方法的检出限(3S/b)为(单位μg·L-1):2.0(铝),1.0(铁),20.0(钾),0.2(镁),4.0(钠),3.0(硅)及0.5(锶).应用此方法分析了两件实样,所得结果的相对标准偏差(n=6)小于等于2.0%,对其中4种杂质元素(镁、钾、钠和锶)同时用HG/T 3587-1999标准中的方法作分析校核,所得结果与此方法结果一致.     

Theoretical insights into the magnetostructural correlations in Mn3-based single-molecule magnets

Density functional theory (DFT) and the valence bond configuration interaction (VBCI) model have been applied to the oximato-based Mn(III)(3)O single-molecule magnets (SMMs), allowing one to correlate the Mn(III)-Mn(III) exchange coupling energy (J) with the bridging geometry in terms of two structural angles: the Mn-O-N-Mn torsion angle (γ) and the Mn(3) out-of-plane shift of O (angle δθ). Using DFT, a two-dimensional (γ, δθ) energy surface of J is derived and shown to yield essentially good agreement with the reported J values deduced from magnetic susceptibility data on trigonal oximato-bridged Mn(3) SMMs. VBCI is used to understand and analyze the DFT results. It is shown that the exchange coupling in these systems is governed by a spin-polarization mechanism inducing a pronounced and dominating ferromagnetic exchange via the oximato bridge as opposed to kinetic exchange, which favors a weaker and antiferromagnetic exchange via the bridging oxide. In the light of these results, a discussion of the exchange coupling in the Mn(6) family of the SMM with a record demagnetization barrier is given.