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.
Highlights
It is well known that chirality plays a fundamental role in the bioactivity of molecules taking part in vital functions of living organisms
We will discuss the Raman spectra of d-Ala between 30 and 180 cmÀ1 for six different scattering geometries [zðxxÞz, xðyyÞx, yðzzÞy, xðyzÞx, yðxzÞy, zðxyÞz] and between 200 and 600 cmÀ1 in the xðyyÞx, yðzzÞy geometries as a function of temperature
We have investigated the influence of temperature in the structure of d-Ala combining polarized Raman spectroscopy (RS), neutron powder diffraction (NPD) and DFTbased methods
Summary
It is well known that chirality plays a fundamental role in the bioactivity of molecules taking part in vital functions of living organisms. Sullivan et al (2003) have reexamined these measurements, and as well carried out X-ray diffraction and 13C solid-state NMR in both enantiomers of alanine between room temperature and about 250 K, and found no anomalous behaviour Along these lines Wilson et al (2005) have further investigated the crystal structures of hydrogenated l-Ala (at 295 and 60 K) and d-Ala (at 300, 295, 260, 250, 240 and 60 K) using single-crystal neutron diffraction. We report on a number of differences in the dynamical behaviour of d-Ala compared with l-Ala, the most remarkable being the observation of new Raman active modes in the A- and B-irreducible representations of the factor group D2 below 160 and 260 K, respectively These findings together with the neutron powder diffraction and density-functionaltheory-based methods (DFT) results show that small differ-. We note that the macroscopic symmetry of the crystal is preserved
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