5‐Amino‐2,4,6‐tribromoisophthalic acid: the MAD triangle for experimental phasing

The title compound, C₈H₄Br₃NO₄, shows an extensive hydrogen‐bond network. In the crystal structure, molecules are linked into chains by COO—H...O bonds, and pairs of chains are connected by additional COO—H...O bonds. This chain bundle shows stacking interactions and weak N—H...O hydrogen bonds with adjacent chain bundles. The three Br atoms present in the molecule form an equilateral triangle. This can be easily identified in the heavy‐atom substructure when this compound is used as a heavy‐atom derivative for experimental phasing of macromolecules. The title compound crystallizes as a nonmerohedral twin.     

Treatment of Silylene–Phosphinidene with Chalcogens Resulted Exclusively in the Formation of Silicon-Bonded Chalcogens

Chalcogen-bonded silicon phosphinidenes LSi(E)−P−^MecAAC (E=S ( 1 ); Se ( 2 ); Te ( 3 ); L=PhC(NtBu)₂; ^MecAAC=C(CH₂)(CMe₂)₂N-2,6-iPr₂C₆H₃)) were synthesized from the reactions of silylene–phosphinidene LSi−P−^MecAAC ( A ) with elemental chalcogens. All the compounds reported herein have been characterized by multinuclear NMR, elemental analyses, LIFDI-MS, and single-crystal X-ray diffraction techniques. Furthermore, the regeneration of silylene–phosphinidene ( A ) was achieved from the reactions of 2 – 3 with L′Al (L′=HC{(CMe)(2,6-iPr₂C₆H₃N)}₂). Theoretical studies on chalcogen-bonded silicon phosphinidenes indicate that the Si−E (E=S, Se, Te) bond can be best represented as charge-separated electron-sharing σ-bonding interaction between [LSi−P−^MecAAC]⁺ and E⁻. The partial double-bond character of Si−E is attributed to significant hyperconjugative donation from the lone pair on E⁻ to the Si−N and Si−P σ*-molecular orbitals.     

Analysis of methylisothiazolones by ion pair high-performance liquid chromatography after pre-column derivatisation

Summary 2-Methyl-3(2H)-isothiazolone resp. 5-chloro-2-methyl-3(2H)-isothiazolone were isolated from a commercial methylisothiazolone formulation (Kathon CG) by flash chromatography and subsequently converted into the respective-thio-substituted acrylamide derivative with the help of the nucleophilic reagent hydrogensulfite. UV spectra and absorption characteristics, for both the derivates as well as the original methylisothiazolones are given and represented in comparison. The derivatives differ clearly in their absorption characteristics from the reactants. Especially in case of the non-chlorinated constituent, derivatisation leads to a distinct increase of its UV activity. For separation and quantification of the derivates an ion pair high-performance liquid Chromatographic method had been developed. With this method an independent system for verification of the content of methylisothiazolones, determined in conventional analysis, is available.

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Analytik von Methylisothiazolonen durch Ionenpaar-HPLC nach Vorsäulen-DerivatisierungTeil I. Derivatisierung von 2-Methyl-3(2H)-isothiazolon und 5-Chlor-2-methyl-3(2H)-isothiazolon