Structural Isotopic Effects in the Smallest Chiral Amino Acid:  Observation of a Structural Phase Transition in Fully Deuterated Alanine

• Published in: The journal of physical chemistry. B Vol. 111; no. 19; pp. 5034 - 5039
• Main Authors: de Souza, Joelma M, Freire, Bordallo, Heloisa N, Argyriou, Dimitri N
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17-05-2007
• Subjects: Alanine - chemistry; Deuterium; Molecular Structure; Neutron Diffraction; Phase Transition; Spectrum Analysis, Raman
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp070366z

A first study of possible changes instigated by deuteration in amino acids was carried out using neutron diffraction, inelastic neutron scattering, and Raman scattering in l-alanine, C2H4(NH2)COOH. Careful analysis of the structural parameters shows that deuteration of l-alanine engenders significant geometric changes as a function of temperature, which can be directly related to the observation of new lattice vibration modes in the Raman spectra. The combination of the experimental data suggests that C2D4(ND2)COOD undergoes a structural phase transition (or a structural rearrangement) at about 170 K. Considering that this particular amino acid is a hydrogen-bonded system with short hydrogen bonds (O···H ∼ 1.8 Å), we evoke the Ubbelohde effect to conclude that substitution of hydrogen for deuterium gives rise to changes in the hydrogen-bonding interactions. The structural differences suggest distinct relative stabilities for the hydrogenous and deuterated l-alanine.