Vinylic MIDA Boronates: New Building Blocks for the Synthesis of Aza‐Heterocycles

A two‐step synthesis of structurally diverse pyrrole‐containing bicyclic systems is reported. ortho‐Nitro‐haloarenes coupled with vinylic N‐methyliminodiacetic acid (MIDA) boronates generate ortho‐vinyl‐nitroarenes, which undergo a “metal‐free” nitrene insertion, resulting in a new pyrrole ring. This novel synthetic approach has a wide substrate tolerance and it is applicable in the preparation of more complex “drug‐like” molecules. Interestingly, an ortho‐nitro‐allylarene derivative furnished a cyclic β‐aminophosphonate motif.     

Sodium trichloro­methane­sulfonate monohydrate

Sodium trichloro­methane­sulfonate monohydrate, Na⁺·CCl₃SO₃⁻·H₂O, crystallizes in P2₁/a with all the atoms located in general positions. The trichloro­methane­sulfonate (trichlate) anion consists of pyramidal SO₃ and CCl₃ groups connected via an S—C bond in a staggered conformation with approximate C_3v symmetry. The water mol­ecule is hydrogen bonded to the sulfonate O atoms, with one water H atom forming weak bifurcated O—H⋯O hydrogen bonds to two different trichlate ions. Two water O atoms and three O atoms from different SO₃ groups form a square‐pyramidal arrangement around the sodium ion.     

Pure-silica optical waveguides, fiber couplers, and high-aspect ratio submicrometer channels for electrokinetic separation devices

A new fabrication procedure for integration of ultraviolet transparent pure-silica planar waveguides, fiber couplers and high-aspect ratio submicrometer channels is presented. Only a single photolithographic mask step is required. The channels are 80-90 microm deep and the width can be reduced to about 0.5 microm, corresponding to a height-to-width ratio of more than 150. The core of the waveguides consists of pure silicon dioxide, which is favorable over doped silica, due to the absence of absorption centers associated with the dopants. This furthermore improves the long-term stability of the waveguides, because of an increased radiation resistance of the glass. The propagation loss decreases from 1.0 dB/cm at 200 nm to 0.2 dB/cm at 800 nm, which, to our knowledge, is the lowest propagation loss reported for integrated planar waveguides in the ultraviolet wavelength region to date. The effective optical path length is 1.2 mm for an absorbance cell with a nominal length of 1.0 mm, indicating effective suppression of stray light. The limit of detection for paracetamol when present in the entire channel network was determined to 3 microg/mL. Finally, the applicability of the fabricated devices for capillary electrophoresis was evaluated by separation of caffein, paracetamol and ketoprofone using absorbance detection at 254 nm.     

Thermal Oxidative Stability of Heat-Stabilised Polyamide 66 by Differential Scanning Calorimetry

The thermal stability of heat-stabilised polyamide 66 in an oxidative environment is evaluated by DSC. The oxidative stability of the polyamide decreases as a result of repeated injection moulding. The results also indicate that the presence of glass fibres in the polyamide has a negative influence on the oxidative stability. Both isothermal and dynamic DSC measurements seem to be useful tools for assessing the stability of polyamides and there is a relationship between data determined using both procedures. This revised version was published online in July 2006 with corrections to the Cover Date.     

The s-p bonded representatives of the prominent BaAl4 structure type: a case study on structural stability of polar intermetallic network structures

This work presents a detailed, combined experimental and theoretical study on the structural stability of s-p bonded compounds with the BaAl4 structure type (space group I4/mmm, Z = 2) as part of a broad program to investigate the complex questions of structure formation and atomic arrangements in polar intermetallics. From ab initio calculations employing pseudopotentials and a plane wave basis set, we extracted optimized structural parameters, binding energies, and the electronic structure of the systems AeX(III)4, AeX(II)2X(IV)2, AeX(II)2X(III)2 (Ae = Ca, Sr, Ba; X(II) = Mg, Zn; X(III) = Al, Ga; X(IV) = Si, Ge). For all systems we found a pronounced pseudo-gap in the density of states separating network X42- bonding from antibonding electronic states that coincides with the Fermi level for an electron count of 14 electrons per formula unit, the optimum value for stable BaAl4-type polar intermetallics. However, the synthesis and structural characterization (from X-ray single crystal and powder diffraction data) of the new compounds AeZn2-Al2+, AeZn2-deltaGa2+delta (Ae = Ca, Sr, Ba; delta = 0-0.2) and AeMg0.9Al3.1, AeMg1.7Ga2.3 (Ae = Sr, Ba) manifested that electron deficiency is rather frequent for BaAl4-type polar intermetallics. The site preference for different "X" elements in the ternary systems was quantified by calculating "coloring energies", which, for some systems, was strongly dependent on the size of the electropositive Ae component. The Ae2+ cations decisively influence the nearest neighbor distances in the encapsulating polyanionic networks X4(2-) and the structures of these networks are surprisingly flexible to the size of the Ae component without changing the overall bonding picture. A monoclinically distorted variant of the BaAl4 structure occurs when the cations become too small for matching the size of encapsulating X4(2-) cages. An even larger size mismatch leads to the formation of the EuIn4 structure type.     

Solvating,manipulating, damaging,and repairing DNA in a computer

This work highlights four different topics in modeling of DNA: (i) the importance of water and ions together with the structure and function of DNA; the hydration structure around the ions appears to be the determining factor in the ion coordination to DNA, as demonstrated in the results of our MD simulations; (ii) how MD simulations can be used to simulate single molecule manipulation experiments as a complement to reveal the structural dynamics of the studied biomolecules; (iii) how damaged DNA can be studied in computer simulations; and (iv) how repair of damaged DNA can be studied theoretically. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007