Feedback-controlled electro-kinetic traps for single-molecule spectroscopy

A principal limitation of single-molecule spectroscopy in solution is the diffusion-limited residence time of a given molecule within the detection volume. A common solution to this problem is to immobilize molecules of interest on a passivated glass surface for extending the observation time to obtain reliable data statistics. However, surface tethering of molecules often introduces artifacts, particularly when studying the structural dynamics of biomolecules. To circumvent this limitation, we investigated alternative ways to extend single-molecule observation times in solution without surface immobilization. Among various possibilities, the so-called anti-Brownian electro-kinetic trap (or ABEL trap) seems best suited to achieve this goal. The essential part of that trap is a feedback-controlled electro-kinetic steering of a molecule’s position in reaction to its diffusive Brownian motion which is monitored by fluorescence, thus keeping the molecule within a sub-micron sized detection volume. Fluorescence trace recordings of over thousands of milliseconds duration on individual dye molecules within an ABEL trap have been reported. In this short review, we shall briefly discuss the principle and some results of ABEL trapping of individual molecules with possible extensions to future works.     

An algebraic loop theorem and the decomposition of PD3-pairs

Let (Y, X) denote a three-dimensional Poincaré pair (PD³-pair).By the work of Eckmann, Müller and Linnell we may suppose,up to a homotopy equivalence, that the boundary X is a closed2-manifold. We show that if a component of X fails to be ₁-injectivein Y, then there is an essential simple loop in X which is nullhomotopicin Y. It follows that there is a finite process of attaching2-disks along essential simple loops on X, and filling sphericalcomponents of X, which transforms (Y, X) into a PD³-pair (Y',X') with aspherical incompressible boundary X' and such that₁(Y) = ₁(Y'). The PD³-pair (Y', X') then admits a canonicaldecomposition as a connected sum of a finite number of asphericalPD³-pairs with incompressible boundary, together with a PD³-pairhaving virtually free (possibly finite) fundamental group andboundary a (possibly empty) disjoint union of projective planes.     

Synthesis of 5-Aryluridines and 5-Aryl-2′-deoxyuridines

The palladium-catalysed coupling of both 5-iodouridine and 5-iodo-2′-deoxyuridine derivatives with functionalized and non-functionalized arylboronic acids and aryltrimethylstannanes gave moderate to good yields of the corresponding 5-aryluridines and 5-aryl-2′-deoxyuridines.     

Relative hyperbolicity and Artin groups

This paper considers the question of relative hyperbolicity of an Artin group with regard to the geometry of its associated Deligne complex. We prove that an Artin group is weakly hyperbolic relative to its finite (or spherical) type parabolic subgroups if and only if its Deligne complex is a Gromov hyperbolic space. For a two-dimensional Artin group the Deligne complex is Gromov hyperbolic precisely when the corresponding Davis complex is Gromov hyperbolic, that is, precisely when the underlying Coxeter group is a hyperbolic group. For Artin groups of FC type we give a sufficient condition for hyperbolicity of the Deligne complex which applies to a large class of these groups for which the underlying Coxeter group is hyperbolic. The key tool in the proof is an extension of the Milnor-Svarc Lemma which states that if a group G admits a discontinuous, co-compact action by isometries on a Gromov hyperbolic metric space, then G is weakly hyperbolic relative to the isotropy subgroups of the action.      

A magnetically polarized He-Ne laser

The performance of an internal mirror He-Ne laser that has a fraction of its capillary immersed in a strong transverse magnetic field will be described. The field is produced by permanent magnets which are built into the laser's housing. The laser produces a light output which has less than 0.1% of its power in the modes polarized orthogonal to the magnetic field. The attainment of such a high degree of polarization requires that the magnetic field be oriented relative to naturally occuring anisotropies of the laser cavity. Misalignment not only lowers the degree of polarization, but also decreases the laser's output.     

An extraction—spectrophotometmc method for the determination of non-ionic surfactants

The surfactant is extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozincate(II), and zinc(II) in the extract is determined spectrophotometrically after addition of l-(2-pyridylazo)-2-naphthol and triethanolamine. With a 150-ml water sample, the limit of detection is 15 μg l^-1 (as Triton X-100). The method requires only one extraction and is applicable, without modification, to fresh, estuarine and sea-water samples.     

A spectrophotometric method for the determination of anionic surfactants at μg l-1 levels

The anionic surfactant is extracted into chloroform as a neutral complex with the bis(ethylenediamine)copper(II) cation, and copper(II) is determined spectrophotometrically after addition of 1-(2-pyridylazo)-2-naphthol and diethylamine. With a 200-ml water sample, the limit of detection is 5 μg l^-1 (as linear alkyl sulphonic acids). The method is simple and is directly applicable to fresh, estuarine and marine waters.