A low-temperature (23 K) study of L-alanine

Abstract

From a spherical crystal of L-alanine an extensive set (20Mo < 100°) of X-ray diffraction data has been measured at 23 (1) K. No phase transition has been observed on cooling, and the cell parameters of the orthorhomt ic crystals (space group />2,2121) are, at the temperature of data collection, a = 5.928 (1) k, b = 12.260 (2) A, c = 5.794 (1) A. The contraction of the cell volume, with respect to the room temperature value, amounts to 2.2%. Intensity data, carefully corrected for scan-truncation losses, have been analyzed with various models. The best fit was reached by interpreting the electron density function in terms of pseudoatoms (multipoles). The analysis of the correlation coefficients has shown that the quality and quantity of the data set allowed a reliable deconvolution of thermal motion from the charge density. Precise and accurate geometry, as well as experimental deformation maps of both charge density and electrostatic potential, has been obtained. Ab initio calculations of atomic populations and group charges for the zwitterionic amino acid have been performed with various basis sets, up to the 6-31G** level. Derived results are compared with those of the multipole analysis of the X-ray diffraction data.

Low-temperature Fourier transform infrared spectra and hydrogen bonding in polycrystalline l-alanine

“…Using these values in the above described empirical relationship yields OÁ Á ÁHN ' distances of 0.189, 0.181 and 0.165 nm, respectively. These values are in a reasonable agreement with the experimental data obtained from X-ray and neutron diffraction structural studies [10,11]. For Table 1 Peak frequencies, widths (in parentheses) and relative intensities (qualitative) of bands in pure and isotopically diluted L-alanine polycrystals at 10 K in the 3400 Á/2000 cm (1 range …”

“…1:1:1), these observations agree with the suggested assignment of each one of these bands to the n 1 mode originated in one of the three individual NH or ND bonds in NH 3 ' or ND 3 ' groups. These were found to be involved in three different H-bonds in the L-alanine crystal, with associated NÃ/H bond lengths of 0.1047, 0.1031 and 0.1031 nm [10] (0.1082, 0.1044, 0.1018 nm [11]). The analysis of the structured band of pure NH(ND) L-alanine crystal, especially at room temperature, cannot be done on the basis of such an easy interpretation, due to the above-mentioned complexity due to intermode and intermolecular couplings and thermal broadening.…”

“…However, no studies have been reported until now describing an approach based on this vibration, in particular for crystalline L-alanine. Nevertheless, structural data unambiguously show that three different types of H-bonds exist in the crystal of L-alanine [10,11], and these should give rise to different NH stretching frequencies. The first attempt to identify in the IR spectra of crystalline L-alanine bands which can be assigned to the structurally sensitive vibrational modes of individual protons and to correlate them with both H-bond distances and energies is made in this paper.…”

Neutron Scattering

“…L-alanine, the simplest chiral amino acid, is an example where surprising aspects of the vibrational properties stand. Among these aspects it is possible to cite some: the intriguing step-wise evolution of the wavenumber of some bands [13], the unconventional increasing of the c lattice parameter when L-alanine is cooled [14], and the localization of vibrational states as revealed by the variation of intensities of the low wavenumber modes at 41 and 49 cm -1 [15]. Simultaneously to the increasing of the c lattice parameter a progressive conformational change of the NH 3 + zwitterion, as well as a strong dynamic JahnTeller-like effect due the coupling between NH 3 + charge and the lattice were observed [13].…”

A Study on Structural, Optical, Electrical and Etching Characteristics of Pure and L-Alanine Doped Potassium Dihydrogen Phosphate Crystals

“…It belongs to the orthorhombic crystal system and the unit cell parameters are; a = 6.320 Å, b = 12.343 Å, c = 5.784 Å, α = β = γ = 90˚. Recently, several new complexes incorporating the amino acid L-alanine have been crystallized and their structural, optical and thermal properties have also been investigated [15][16][17][18]. The growth of pure L-alanine crystals was reported [19] and found higher damage threshold than Potassium dihydrogen phosphate (KDP).…”