title: A phase transition from monoclinic C2 with Z' = 1 to triclinic P1 with Z' = 4 for the quasiracemate L-2-aminobutyric acid-D-methionine (1/1).
abstract: Racemates of hydrophobic amino acids with linear side chains are known to undergo a unique series of solid-state phase transitions that involve sliding of molecular bilayers upon heating or cooling. Recently, this behaviour was shown to extend also to quasiracemates of two different amino acids with opposite handedness [Görbitz & Karen (2015). J. Phys. Chem. B, 119, 4975-4984]. Previous investigations are here extended to an L-2-aminobutyric acid-D-methionine (1/1) co-crystal, C4H9NO2·C5H11NO2S. The significant difference in size between the -CH2CH3 and -CH2CH2SCH3 side chains leads to extensive disorder at room temperature, which is essentially resolved after a phase transition at 229 K to an unprecedented triclinic form where all four D-methionine molecules in the asymmetric unit have different side-chain conformations and all three side-chain rotamers are used for the four partner L-2-aminobutyric acid molecules.
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: Carl Henrik
authors.initials: CH
authors.lastname: Görbitz
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: David S
authors.initials: DS
authors.lastname: Wragg
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: Ingrid Marie Bergh
authors.initials: IM
authors.lastname: Bakke
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: Christian
authors.initials: C
authors.lastname: Fleischer
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: Gaute
authors.initials: G
authors.lastname: Grønnevik
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: Maria
authors.initials: M
authors.lastname: Mykland
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: Yoomin
authors.initials: Y
authors.lastname: Park
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: Kristian Wiedicke
authors.initials: KW
authors.lastname: Trovik
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: Halvard
authors.initials: H
authors.lastname: Serigstad
authors.affiliation: Department of Chemistry, University of Oslo, PO Box 1033 Blindern, N-0315 Oslo, Norway.
authors.forename: Bård Edgar Vestheim
authors.initials: BE
authors.lastname: Sundsli
keywords: crystal structure; d-methionine; disorder; l-2-aminobutyric acid; phase transition; quasiracemate; steric conflict