Thermal Deformations of Crystal Structures in the L-Aspartic Acid/L-Glutamic Acid System and DL-Aspartic Acid

Roman Sadovnichii,Heike Lorenz,Elena Kotelnikova

doi:10.3390/cryst11091102

Roman Sadovnichii, Heike Lorenz + Show 1 more

Open Access

https://doi.org/10.3390/cryst11091102

Copy DOI

Abstract

The method of temperature-resolved powder X-ray diffraction (TRPXRD) was used to determine the elevated temperature behavior of L-aspartic acid (L-asp), DL-aspartic acid (DL-asp), L-glutamic acid (L-glu), and an L-asp0.25,L-glu0.75 solid solution. These amino acids were not found to undergo any solid-phase (polymorph) transformations. When heated, they all experienced only thermal deformations. The corresponding parameters of the monoclinic cells of L-asp and DL-asp, and the orthorhombic cells of L-glu and L-asp0.25,L-glu0.75, were calculated for the entire range of studied temperatures (up to 220 °C). The data obtained were used to calculate the parameters of the thermal deformation tensors, and to plot the figures of their thermal expansion coefficients. A correlation between the maximum and minimum values of thermal expansion coefficients and the length, type, direction, and number of hydrogen bonds in the crystal structures of the investigated amino acids was established. The observed negative thermal expansion (contraction) of crystal structures of L-asp and DL-asp along the ac plane can be explained as a result of shear deformations occurring in monoclinic crystals with a non-fixed angle β. The studies were related to the presence of amino acids in various natural and technological processes occurring at different temperatures.

Highlights

Amino acids of the general formula NH2 -CHR-COOH play an important role in natural biochemical processes
The mode of the thermal deformations observed in all of the above crystal structures was consistent with the distance, type, geometry, and concentration of the intermolecular hydrogen bonds
Thermal deformations of L-aspartic acid (L-asp) and DL-aspartic acid (DL-asp) are characterized by the manifestation of negative thermal expansion—i.e., contraction—of their crystal structures in the monoclinicity plane ac

Summary

Introduction

Amino acids of the general formula NH2 -CHR-COOH play an important role in natural biochemical processes. They are typical representatives of organic crystals composed of chiral molecules. Chirality is the ability of a substance to occur in two or more configurations of molecules, which are referred to as enantiomers and diastereomers. Molecules of enantiomers are mirror images of one another. Relative configurations of enantiomers are designated as L (levorotary) and D (dextrorotary). All of the naturally occurring protein molecules are composed of L-enantiomers of amino acids.

Methods

Discussion

Conclusion