title: The Structure of Glycine Dihydrate: Implications for the Crystallization of Glycine from Solution and Its Structure in Outer Space.
abstract: Glycine, the simplest amino acid, is also the most polymorphous. Herein, we report the structure determination of a long unknown phase of glycine, which was first reported by Pyne and Suryanarayanan in 2001. To date, this phase has only been prepared at 208 K as nanocrystals within ice. Through computational crystal-structure prediction and powder X-ray diffraction methods, we identified this elusive phase as glycine dihydrate (GDH), representing the first report on the structure of a hydrated glycine structure. The structure of GDH has important implications for the state of glycine in aqueous solution and the mechanisms of glycine crystallization. GDH may also be the form of glycine that comes to Earth from extraterrestrial sources.
authors.affiliation: X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, IL, 60439, USA.
authors.forename: Wenqian
authors.identifier: 0000-0002-4815-6253
authors.initials: W
authors.lastname: Xu
authors.affiliation: Department of Physics and Astronomy, High Pressure Science and Engineering Center, University of Nevada Las Vegas, Las Vegas, NV, 89154, USA.|Department of Geosciences, Stony Brook University, Stony Brook, NY, 11794, USA.
authors.forename: Qiang
authors.identifier: 0000-0002-9892-0344
authors.initials: Q
authors.lastname: Zhu
authors.affiliation: Department of Chemistry, New York University, 100 Washington Square East, New York, NY, 10003, USA.
authors.forename: Chunhua Tony
authors.identifier: 0000-0002-8172-2202
authors.initials: CT
authors.lastname: Hu
keywords: X-ray diffraction; amino acids; crystal structures; glycine; phase transitions