A phase transition from monoclinicC2 withZ′ = 1 to triclinicP1 withZ′ = 4 for the quasiracemateL-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.

The Rich Solid-State Phase Behavior of l-Phenylalanine: Disappearing Polymorphs and High Temperature Forms

“…The phase transitions involve relative shifts between these bilayers, in some cases accompanied by a conformational change. We and others have recently reviewed the phase transitions in this class of materials − comparing a range of macroscopic quantities such as the enthalpy of transition, volume change, the amount of hysteresis in the transition temperature, and cyclability of the transition, and found distinctly different behavior for the transitions involving only shifts as compared to the phase transitions that involved a large conformational change. Although all phase transitions in aliphatic amino acid crystals are first-order and proceed through nucleation-and-growth, the shifts probably do not occur in a molecule-by-molecule fashion, but cooperatively with many molecules shifting at the same time. ,− Conformational changes, on the other hand, are more likely to proceed one molecule at a time.…”

A large anisotropic plasticity of L-leucinium hydrogen maleate preserved at cryogenic temperatures

“…Relative shifts and re-orientations of the hydrophobic alkyl side chains in the interlayer space of layered amino acids (Coles et al, 2009;Ende & Cuppen, 2014;Ende et al, 2015;Gö rbitz, 2015;Gö rbitz & Karen, 2015;Smets et al, 2015;Gö rbitz, Karen et al, 2016;Smets et al, 2016;Gö rbitz, Wragg et al, 2016;Czech et al, 2017;Smets, Pitak et al, 2017;Smets, 2018), as well as in other organic compounds (Kolesov et al, 2008;Minkov et al, 2008;Minkov et al, 2009;Bordallo et al, 2010;Minkov et al, 2010;Drebushchak et al, 2011;Minkov et al, 2012;Braun et al, 2017;Smets, Kalkman et al, 2017) often account for structural rearrangements related to phase transitions. To visualize the changes in (l-LeuH + )ÁM À on cooling, the free space was compared at 293 K and 100 K (using the void function in Mercury) (Fig.…”

Polymorphism of the quasiracemate d-2-aminobutyric acid:l-norvaline

“…[2][3][4] In the case of amino acids, many quasiracemates have been found by Görbitz et al over the past 18 years. 1,[5][6][7][8][9][10] Most of the linear aliphatic chain quasiracemates consist of bilayers interconnected by an LD-LD hydrogen bonding pattern. Since racemic amino acids with a linear aliphatic chain are known for their single-crystal-to-single-crystal phase transitions, see ref.…”

“…A previous attempt by Dalhus and Görbitz to determine the structure of the mirrorimage quasiracemate L-Abu:D-Nva has been reported as an 'incomplete structural model with a high R factor at 150 K', but indicated an LD-LD hydrogen bonding pattern. 10 Both racemic counterparts DL-Abu and DL-Nva, as well as the enantiopure counterparts L-Abu and L-Nva, are known for their single-crystal-to-single-crystal phase transitions and most of their crystal structures show severe disorder in the conformations of the aliphatic chains. 11,12,16 The racemic compounds DL-Abu and DL-Nva both have the LD-LD hydrogen bonding pattern, which is typical for amino acid racemates.…”