2-amidopyrroles and 2,5-diamidopyrroles as simple anion binding agents.

Four new 2-amidopyrroles and 2,5-diamidopyrroles have been synthesized and their anion complexation properties investigated. The crystal structures of these receptors have been elucidated and reveal hydrogen bonding in the solid state leading to dimer and network formation. Selectivity for oxo-anions has been demonstrated by (1)H NMR titration techniques.     

Characterization of the Chemical Structure of Sulphur Vulcanizates of Natural Rubber Using 1H NMR Spectroscopy

Abstract

Vulcanizates containing only di- and poly-suiphidic crosslinks can be transformed into soluble rubber by treatment with hexane-1-thiol/piperidine, enabling examination of the crosslink sites by ¹H NMR spectroscopy in solution.     

Determination of Lead and Cadmium in Sea‐ and Freshwater by Anodic Stripping Voltammetry with a Vibrating Bismuth Electrode

A solid, bismuth (Bi), disk, electrode is used to determine lead (Pb) in natural waters including seawater. The diffusion layer thickness was lowered from 93 to 29 µm by stirring, and to 18 µm by using the vibrated version of the Bi electrode. The Bi electrode does not require removal of dissolved oxygen, which facilitates in situ detection. The electrode was tested for the determination of Pb in coastal seawater samples. The detection limit for Pb was 0.15 nM in acetate buffer and 0.5 nM in seawater using a 2 min deposition time. Cadmium can be determined together with Pb but the sensitivity is about 10×lower. The Bi electrode compares unfavourably to a mercury electrode in terms of sensitivity.     

Square-central elements and standard generators for biquaternion algebras

Analyzing square-central elements in central simple algebras of degree 4, we show that every two elementary abelian Galois maximal subfields are connected by a chain of nontrivially-intersecting pairs. Similar results are proved for non-central quaternion subalgebras, and for central quaternion subalgebras when they exist. Along these lines we classify the maximal square-central subspaces. We also show that every two standard quadruples of generators of a biquaternion algebra are connected by a chain of basic steps, in each of which at most two generators are being changed.     

Direct evidence for enzyme persulfide and disulfide intermediates during 4-thiouridine biosynthesis

Two proposed mechanisms for 4-thiouridine generation share key cysteine persulfide and disulfide intermediates, and indirect evidence of their existence has been previously reported; chemical trapping and mass spectrometry have now provided direct and definitive evidence of these key intermediates.     

Asymptotics of large bound states of localized structures

We analyze stationary fronts connecting uniform and periodic states emerging from a pattern-forming instability. The size of the resulting periodic domains cannot be predicted with weakly nonlinear methods. We show that what determine this size are exponentially small (but exponentially growing in space) terms. These can only be computed by going beyond all orders of the usual multiple-scale expansion. We apply the method to the Swift-Hohenberg equation and derive analytically a snaking bifurcation curve. At each fold of this bifurcation curve, a new pair of peaks is added to the periodic domain, which can thus be seen as a bound state of localized structures. Such scenarios have been reported with optical localized structures in nonlinear cavities and localized buckling.     

K isomers in 254No: probing single-particle energies and pairing strengths in the heaviest nuclei

We have identified two isomers in 254No, built on two- and four-quasiparticle excitations, with quantum numbers K pi = 8- and (14+), as well as a low-energy 2-quasiparticle Kpi = 3+ state. The occurrence of isomers establishes that K is a good quantum number and therefore that the nucleus has an axial prolate shape. The 2-quasiparticle states probe the energies of the proton levels that govern the stability of superheavy nuclei, test 2-quasiparticle energies from theory, and thereby check their predictions of magic gaps.