Preferred conformers of proteinogenic glutamic acid.

The molecular shape of proteinogenic glutamic acid has been determined for the first time. Vaporization of the solid amino acid by laser ablation in combination with Fourier transform microwave spectroscopy made possible the detection of five different structures in a supersonic jet. These structures have been identified through their rotational and (14)N quadrupole coupling constants. All conformers show hydrogen bonds linking the amino and alpha carboxylic group through N-H···O═C (type I) or N···H-O (type II) interactions. In three of them there are additional hydrogen bonds established between the amino group and the carboxylic group in the gamma position. Entropic effects related to the side chain have been found to be significant in determining the most populated conformations.