Light‐Induced Reversible Reconfiguration of DNA‐Based Constitutional Dynamic Networks: Application to Switchable Catalysis

The light‐induced reversible and cyclic reconfiguration of constitutional dynamic networks, consisting of supramolecular nucleic acid structures as constituents and a photoisomerizable trans/cis‐azobenzene‐functionalized nucleic acid as the trigger is demonstrated. In addition, the cyclic photochemical reconfiguration of the constitutional dynamic networks guides the switchable on/off operation of an emerging hemin/G‐quadruplex DNAzyme.     

Label-free and reagentless aptamer-based sensors for small molecules

A label free, reagentless aptasensor for adenosine is developed on an ISFET device. The separation of an aptamer/nucleic acid duplex by adenosine leads to the aptamer/adenosine complex that alters the gate potential of the ISFET. The sensitivity limit of the device is 5 x 10-5 M. Also, the immobilization of the aptamer/nucleic acid duplex on an Au-electrode and the separation of the duplex by adenosine mono-phosphate (AMP) enable the electrochemical detection of adenosine by faradaic impedance spectroscopy. The separation of the aptamer/nucleic acid duplex by adenosine and the formation of the aptamer/adenosine complex results in a decrease in the interfacial electron-transfer resistance in the presence of [Fe(CN)6]3-/4- as redox active substrate.     

Magnetic field effects on cytochrome c-mediated bioelectrocatalytic transformations

Constant magnetic fields affect many biological transformations, but we lack mechanistic understanding of the processes. The magnetohydrodynamic effect may account for the enhancement of bioelectrocatalytic transformations at interfaces. This is exemplified by the bioelectrocatalyzed cytochrome c-mediated reduction of oxygen and oxidation of lactate in the presence of cytochrome oxidase and lactate dehydrogenase, respectively. We observe significant magnetic field effects on the rates of bioelectrochemical transformations (ca. 3-fold increase) at the functionalized interfaces at field strengths, B, up to 1 T. We show that the limiting current is proportional to the B(1/3)C*(4/3), where C is the concentration of electroactive species. The results may have important implications on the understanding of the magnetic field effects on natural biocatalytic processes at membranes and on the enhancement of biotransformations in biotechnology.     

Rearrangement reactions of the transient lewis acids (CF(3))(3)B and (CF(3))(3)BCF(2): an experimental and theoretical study

Short-lived (CF(3))(3)B and (CF(3))(3)BCF(2) are generated as intermediates by thermal dissociation of (CF(3))(3)BCO and F(-) abstraction from the weak coordinating anion [B(CF(3))(4)](-), respectively. Both Lewis acids cannot be detected because of their instability with respect to rearrangement reactions at the B-C-F moiety. A cascade of 1,2-fluorine shifts to boron followed by perfluoroalkyl group migrations and also difluorocarbene transfer reactions occur. In the gas phase, (CF(3))(3)B rearranges to a mixture of linear perfluoroalkyldifluoroboranes C(n)()F(2)(n)()(+1)BF(2) (n = 2-7), while the respective reactions of (CF(3))(3)BCF(2) result in a mixture of linear (n = 2-4) and branched monoperfluoroalkyldifluoroboranes, e.g., (C(2)F(5))(CF(3))FCBF(2). For comparison, the reactions of [CF(3)BF(3)](-) and [C(2)F(5)BF(3)](-) with AsF(5) are studied, and the products in the case of [CF(3)BF(3)](-) are BF(3) and C(2)F(5)BF(2) whereas in the case of [C(2)F(5)BF(3)](-), C(2)F(5)BF(2) is the sole product. In contrast to reports in the literature, it is found that CF(3)BF(2) is too unstable at room temperature to be detected. The decomposition of (CF(3))(3)BCO in anhydrous HF leads to a mixture of the new conjugate Br?nsted-Lewis acids [H(2)F][(CF(3))(3)BF] and [H(2)F][C(2)F(5)BF(3)]. All reactions are modeled by density functional calculations. The energy barriers of the transition states are low in agreement with the experimental results that (CF(3))(3)B and (CF(3))(3)BCF(2) are short-lived intermediates. Since CF(2) complexes are key intermediates in the rearrangement reactions of (CF(3))(3)B and (CF(3))(3)BCF(2), CF(2) affinities of some perfluoroalkylfluoroboranes are presented. CF(2) affinities are compared to CO and F(-) affinities of selected boranes showing a trend in Lewis acidity, and its influence on the stability of the complexes is discussed. Fluoride ion affinities are calculated for a variety of different fluoroboranes, including perfluorocarboranes, and compared to those of the title compounds.     

Fluorisocyanat (F?NCO) – eine reaktive Zwischenstufe

Fluorine Isocyanate (F? NCO) – a Reactive Intermediate Fluorine isocyanate, produced in four different ways, reacts to the compounds NF₂C(O)NCO, FC(O)NCO, NF₂C(O)F, and COF₂in various molar ratios. Even in the gas phase at p <0.1 mbar and 20°C FNCO is not stable. So, in the family of covalent isocyanates, the fluorine compound is the most reactive one. In contrast to other isocyanates, FNCO dimerizes to NF₂C(O)NCO exclusively. The properties of NF₂C(O)NCO have been reinvestigated.     

Magnetic control of chemical transformations: application for programmed electrocatalysis and surface patterning

Lateral translocation of electrocatalyst-modified magnetic particles was achieved upon application of an external magnetic field. Programmed electrocatalytic reactions at different electrodes or different areas of an electrode were performed. The spatially controlled electrocatalytic reactions were exemplified with NADH electrocatalytic oxidation and with bioelectrocatalytic electrode patterning. The method will be particularly useful for programmed electrochemical reactions at interdigitated electrodes.     

Dynamics of Finger Formation in Laplacian Growth Without Surface Tension

We study the dynamics of “finger” formation in Laplacian growth without surface tension in a channel geometry (the Saffman–Taylor problem). We present a pedagogical derivation of the dynamics of the conformal map from a strip in the complex plane to the physical channel. In doing so we pay attention to the boundary conditions (no flux rather than periodic) and derive a field equation of motion for the conformal map. We first consider an explicit analytic class of conformal maps that form a basis for solutions in infinitely long channels, characterized by meromorphic derivatives. The great bulk of these solutions can lose conformality due to finite time singularities. By considerations of the nature of the analyticity of these solutions, we show that those solutions which are free of such singularities inevitably result in a single asymptotic “finger” whose width is determined by initial conditions. This is in contradiction with the experimental results that indicate selection of a finger of width 1/2. In the last part of this paper we show that such a solution might be determined by the boundary conditions of a finite body of fluid, e.g. finiteness can lead to pattern selection.