Hydrogen bonds in crystalline D-alanine: diffraction and spectroscopic evidence for differences between enantiomers

Abstract

Enantiomeric amino acids have specific physiological functions in complex biological systems. Systematic studies focusing on the solid-state properties of d-amino acids are, however, still limited. To shed light on this field, structural and spectroscopic studies of d-alanine using neutron powder diffraction, polarized Raman scattering and ab initio calculations of harmonic vibrational frequencies were carried out. Clear changes in the number of vibrational modes are observed as a function of temperature, which can be directly connected to variations of the N-D bond lengths. These results reveal dissimilarities in the structural properties of d-alanine compared with l-alanine.

Response to comment on `Hydrogen bonds in crystalline D-alanine: diffraction and spectroscopic evidence for differences between enantiomers'

“…We note that the results of Belo et al (2018) do not provide, or claim to provide, evidence for, or against, the Salam hypothesis, which predicted that quantum mechanical cooperative and condensation phenomena may give rise to a second-order phase transition below a critical temperature linking the transformation of d-amino acids to l-amino acids. An order of magnitude estimate by Salam (1992) indicated a transition temperature of~250 K. The work of Belo et al (2018) does not support the idea of the d-alanine (d-ala) ! l-alanine (l-ala) transformation, but instead provides a microscopic picture of the alanine solids consistent with the other experimental measurements.…”

“…In the preceding comment on our paper Bü rgi & Macchi (2018) stated 'The recent paper by Belo, Pereira, Freire, Argyriou, Eckert & Bordallo [(2018), IUCrJ, 5, 6-12] reports observations that may lead one to think of very strong and visible consequences of the parity-violation energy difference between enantiomers of a molecule, namely alanine' and 'Therefore, the conclusions drawn by Belo et al (2018) are deemed inappropriate as the data presented do not contain sufficient information to reach such a conclusion'. In response to this comment we would like to stress the point that we did not in fact draw any conclusions at all in our paper concerning the parity-violating energy difference (PVED) hypothesis of Salam [Salam (1992), see also Laerdahl et al (2000) and Berger & Quack (2000) for discussion] and therefore find it difficult to see how they could therefore be 'deemed inappropriate'.…”

“…At temperatures where the structural information from the reported neutron powder diffraction measurements can be compared with previous single-crystal X-ray diffraction in l-alanine (Lehmann et al, 1972;Destro et al, 2008) and single-crystal neutron diffraction in l-and d-alanine (Wilson et al, 2005), there is good agreement when the difference between hydrogenated and deuterated samples is taken into account. The results reported by Belo et al (2018), however, provide a continuous picture of the temperature evolution of the bonds in d-alanine from 280 K down to 4 K, which shows that while the average structure is kept the same (no changes in space group) in d-alanine, as opposed to l-alanine, local symmetry changes are seen at lower temperatures. Furthermore, below 250 K, both l-alanine and d-alanine appear to undergo microconformational transitions resulting from a subtle rearrangement of the hydrogen-bond network.…”

Theoretical Characterization of the Hydrogen Bonding Interaction Sites of Mycolactone C Using the ONIOM Method

“…Etter and Reutzel 11 have been among the first research teams to classify the acceptor power of H binding (ALH) of different organic functionalities. More recently, some works were focused on the competition between nitrogen and oxygen atoms [12][13][14][15][16] or between amino and nitrile nitrogen atoms 17 in different structural units. This work, which is part of the Buruli ulcer control program, is interested in mycolactone C. It aims to determine, by the methods of Quantum Chemistry, some physicochemical properties of mycolactone C, particularly the geometric, energetic, and spectroscopic parameters of hydrogen bonding established on heteroatoms, the probable site of intermolecular interaction of the toxin.…”

Nanoscale hydrogen bound network revealed by neutron scattering

“…In this talk I will discuss on this promising approach by presenting a couple of specific examples. The first is related to a number of differences in the structural and dynamical behavior of D-alanine when compared to L-alanine [1] and the second to the interplay of molecular flexibility and hydrogen bonding manifested in the polymorphs of paracetamol.[2] Finally I will give a brief overview in how this approach can extend to the study of highly intricate pore structures. …”