On the stereochemistry of 2-hydroxyethylphosphonate dioxygenase

Stereochemical investigations have shown that the conversion of 2-hydroxyethylphosphonate to hydroxymethylphosphonate by the enzyme HEPD involves removal of the pro-S hydrogen at C2 and, surprisingly, the loss of stereochemical information at C1. As a result, the mechanisms previously proposed for HEPD must be re-evaluated.     

Tail-labelling of DNA probes using modified deoxynucleotide triphosphates and terminal deoxynucleotidyl transferase. Application in electrochemical DNA hybridization and protein-DNA binding assays

A simple approach to DNA tail-labelling using terminal deoxynucleotidyl transferase and modified deoxynucleoside triphosphates is presented. Amino- and nitrophenyl-modified dNTPs were found to be good substrates for this enzyme giving 3'-end stretches of different lengths depending on the nucleotide and concentration. 3-Nitrophenyl-7-deazaG was selected as the most useful label because its dNTP was efficiently incorporated by the transferase to form long tail-labels at any oligonucleotide. Accumulation of many nitrophenyl tags per oligonucleotide resulted in a considerable enhancement of voltammetric signals due to the nitro group reduction, thus improving the sensitivity of electrochemical detection of the tail-labelled probes. We demonstrate a perfect discrimination between complementary and non-complementary target DNAs sequences by tail-labelled hybridization probes as well as the ability of tumour suppressor p53 protein to recognize a specific binding site within tail-labelled DNA substrates, making the methodology useful in electrochemical DNA hybridization and DNA-protein interaction assays.     

Influence of calcium-induced aggregation on the sensitivity of aminobis(methylenephosphonate)-containing potential MRI contrast agents

A novel class of 1,4,7,10-tetraazacyclododecane-1,4,7-tris(methylenecarboxylic) acid (DO3A)-based lanthanide complexes with relaxometric response to Ca(2+) was synthesized, and their physicochemical properties were investigated. Four macrocyclic ligands containing an alkyl-aminobis(methylenephosphonate) side chain for Ca(2+)-chelation have been studied (alkyl is propyl, butyl, pentyl, and hexyl for L(1), L(2), L(3), and L(4), respectively). Upon addition of Ca(2+), the r(1) relaxivity of their Gd(3+) complexes decreased up to 61% of the initial value for the best compounds GdL(3) and GdL(4). The relaxivity of the complexes was concentration dependent (it decreases with increasing concentration). Diffusion NMR studies on the Y(3+) analogues evidenced the formation of agglomerates at higher concentrations; the aggregation becomes even more important in the presence of Ca(2+). (31)P NMR experiments on EuL(1) and EuL(4) indicated the coordination of a phosphonate to the Ln(3+) for the ligand with a propyl chain, while phosphonate coordination was not observed for the analogue bearing a hexyl linker. Potentiometric titrations yielded protonation constants of the Gd(3+) complexes. log K(H1) values for all complexes lie between 6.12 and 7.11 whereas log K(H2) values are between 4.61 and 5.87. Luminescence emission spectra recorded on the Eu(3+) complexes confirmed the coordination of a phosphonate group to the Ln(3+) center in EuL(1). Luminescence lifetime measurements showed that Ca-induced agglomeration reduces the hydration number which is the main cause for the change in r(1). Variable temperature (17)O NMR experiments evidenced high water exchange rates on GdL(1), GdL(2), and GdL(3) comparable to that of the aqua ion.     

Controlling the length and location of in situ formed nanowires by means of microfluidic tools

Progress in microelectronics, sensors and optics is strongly dependent on the miniaturization of components, and the integration of nanoscale structures into applicable systems. In this regard, conventional top-down technologies such as lithography have limits concerning the dimensions and the choice of material. Therefore, several bottom-up approaches have been investigated to satisfy the need for structures with large aspect ratios in the nanometre regime. For further implementation, however, it is crucial to find methods to define position, orientation and length of the nanowires. In this study, we present a microchip to trap in situ formed bundles of nanowires in microsized cages and clamps, thereby enabling immobilisation, positioning and cutting-out of desired lengths. The microchip consists of two layers, one of which enables the formation of metal-organic nanowires at the interface of two co-flowing laminar streams. The other layer, separated by a thin and deflectable PDMS membrane, serves as the pneumatic control layer to impress microsized features ("donuts") onto the nanowires. In this way, a piece of the nanowire bundle with a prescribed length is immobilised inside the donut. Furthermore, partly open ring-shaped structures enabled trapping of hybrid wires and subsequent functionalisation with fluorescent beads. We believe that the method is a versatile approach to form and modify nanoscale structures via microscale tools, thereby enabling the construction of fully functional nanowire-based systems.     

Switching preconditioners using a hybrid approach for linear systems arising from interior point methods for linear programming

Numerical Algorithms - In general, interior point methods are successful in solving large-scale linear programming problems. Their effectiveness is determined by how fast they calculate each...     

An Improved Method for Site‐Specific End Modification of Zeolite L for the Formation of Zeolite L and Gold Nanoparticle Self‐Assembled Structures

The ability to site‐selectively modify micro‐ and nanosized particles has allowed for directed self‐assembly in two and three dimensions. Site‐selective modification of particles can be a complicated task requiring the pre‐organization of particles or enhanced particle fabrication methods. The aluminum silicate, zeolite L has been reported to undergo site‐specific modification at the zeolite channel entrances, post‐fabrication in a solution‐based method. The process by which the channel entrances are site selectively modified is explored here. The preliminary step of charging the zeolite channels with aqueous acid allows for catalysis of covalent bond formation at the channel entrances. Three new end‐specific modification reagents are described based on silanol and silyl ether functional groups. These reagents are purified by column chromatography and characterized by¹H NMR spectroscopy and high resolution mass spectrometry (HRMS); they provide for reliable end modification of zeolites L. Preferential reactivity at the channel entrances is also observed. The utility of the approach is demonstrated by modifying zeolite L with adamantane at the channel entrances. Site‐specific self‐assembly with β‐cyclodextrin coated gold nanoparticles can be triggered with a chemical stimulus. The resulting multivalent host‐guest interactions give gold clustered nanoparticles at the ends of the micrometer‐sized zeolites.     

Determination of Ground State Vibrational Frequencies of Jet-Cooled Resorcinol by Means of Dispersed Fluorescence Spectroscopy and ab Initio Calculations

The vibrational frequencies of the electronic ground state of resorcinol have been determined via laser-induced dispersed fluorescence spectroscopy. An assignment based on comparison with ab initio calculations on the MP2 and B3LYP (6-311 G (d,p)) level is presented.