Crystal structure and properties of l-tryptophanium hydrogen selenite

l-Tryptophanium hydrogen selenite was synthesised and structurally characterised at room and low temperature. The aminoacid is positively charged with the amine and carboxylic group protonated. It adopts a staggered conformation with the N1 gauche to C4 that is gauche to C1. The anion displays a pyramidal conformation with three different Se–O bond lengths, one characteristic of a double bond, another of a single bond and the third with an intermediate character. At room temperature there is a disordered hydrogen atom between the carboxylic group of the cation and the O atom of the anion with the intermediate Se–O bond length. At low temperature this hydrogen atom orders and attaches to the carboxylic group. This ordering is most likely related to the transition seen in DSC measurements occurring at −82.5 °C.

Structure characterisation of l-tryptophanium hydrogen selenite at low and room temperature. A disordered hydrogen atom shared between the carboxylic group of the cation and one of the oxygen atoms of the anion is found to order at low temperature.Figure optionsDownload as PowerPoint slide