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.     

On the Lifetime of Quasi-Stationary States in Non-Relativistic QED

We consider resonances in the Pauli–Fierz model of non-relativistic QED. We use and slightly modify the analysis developed by Bach, Fr?hlich, and Sigal [3, 4] to obtain an upper and lower bound on the lifetime of quasistationary states. Submitted: September 30, 2007. Accepted: March 28, 2008.