On the stacking disorder of DL-norleucine

Abstract

dl-Norleucine (2-aminohexanoic acid, C 6 H 13 NO 2 ) forms a double-layer structure in all known phases (, , ). The crystal structure of the -phase was redetermined at 173 K. Diffraction patterns of theand -phases frequently show diffuse streaks parallel to c*, which indicates a stacking disorder of the layers. A symmetry analysis was carried out to derive possible stacking sequences. Lattice-energy minimizations by force fields and by dispersioncorrected density functional theory (DFT-D) were performed on a set of ordered model structures with Z = 4, 8 and 16 with different stacking sequences. The calculated energies depend not only on the arrangement of neighbouring double layers, but also of next-neighbouring double layers. Stacking probabilities were calculated from the DFT-D energies. According to the calculated stacking probabilities large models containing 100 double layers were constructed. Their simulated diffraction patterns show sharp reflections for h + k = 2n and diffuse streaks parallel to c* through all reflections with h + k = 2n + 1. Experimental single-crystal X-ray diffraction revealed that at 173 K norleucine exists in the -phase with stacking disorder. After reheating to room temperature, the investigated crystal showed a diffraction pattern with strong diffuse scattering parallel to c* through all reflections with h + k = 2n + 1, which is in good agreement with the simulated disordered structure.

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.…”

Try Another Crystal: Crystal-Dependent Disorder of Pentaphosphaferrocene within the Same Crystallization

“…The crystal structure of the β-form of d , l -norleucine (2-aminohexanoic acid, C 6 H 13 NO 2 ) was determined three times in 1996 at T = 120 K (CSD: DLNLUA02, crystal 4A ), in 2009 at T = 198 K (CSD: DLNLUA04, crystal 4B ), and in 2017 at T = 173 K (CSD: DLNLUA06, crystal 4C ) by different groups . Besides, the streaking was observed along with c * for both crystals 4A and 4C , indicating the faults in the stacking sequence of the double-layer units.…”

Study of stacking interactions between two neutral tetrathiafulvalene molecules in Cambridge Structural Database crystal structures and by quantum chemical calculations

“…Stacking interactions of all these moieties are comparable in energy with stacking interactions of aromatic molecules and some of them are significantly stronger. Stacking arrangements of entire blocks of non-aromatic molecules (Mora et al, 2017) and even non-cyclic molecules (Czech et al, 2017) can also be found in crystal structures.…”