Phase Transitions in the Crystals of l- and dl-Cysteine on Cooling: Intermolecular Hydrogen Bonds Distortions and the Side-Chain Motions of Thiol-Groups. 1. l-Cysteine

Abstract

The role of the distortion of the hydrogen bond network and of the motions of the -CH 2SH side chains in the phase transition in the orthorhombic L-cysteine ( (+)NH 3-CH(CH 2SH)-COO (-)) on cooling and the reverse transformation on heating is discussed. The extended character of the phase transition, which was recently discovered by adiabatic calorimetry [ J. Phys. Chem. B 2007, 111, 9186 ], and its very high sensitivity to the thermal prehistory of the sample could be interpreted based on the changes in the polarized Raman spectra measured for the single-crystals in several orientations in the temperature range 3-300 K and precise diffraction data on the changes in intramolecular conformations and intermolecular hydrogen bonding. In the low-temperature phase the SH...S hydrogen bonds dominate as compared to the weaker SH...O contacts, and at ambient temperature the situation is inverse. The transition from one phase to another goes via a series of states differing in conformations of the cysteine zwitterions and the intermolecular contacts of the thiol-group. Motions of different molecular fragments (NH 3 (+), CH 2, CH, SH) are activated at different temperatures. Structural strain on cooling involves several dynamic processes, such as a rigid rotation of the molecule in the lattice, a rigid rotation of the NH 3 group with respect to NH 3-CH bond, and the rotation of the thiol side chain resulting in the switching of S-H hydrogen bonding from one type to another. Different NH...O hydrogen bonds forming the framework in the L-cysteine crystal structure are distorted to a different extent, and this provokes the rotation of the -CH 2SH side chains within the cavities of this framework resulting in a change in the coordination from SH...O to SH...S at low temperatures. The results are interesting for understanding the polymorphism of molecular crystals and the factors determining their dynamics and structural instability, and also for biophysical chemistry, since the properties of the hydrogen bonded thiole-groups in biomolecules can be mimicked using L-cysteine in the crystalline state, variations in temperature and pressure serving as powerful tools, to modify the intramolecular conformations and the intermolecular hydrogen bonding.

Anharmonic transitions in nearly dry l-cysteine I

“…Above ∼ 200 K a tendency to change was observed for G3, which presented smaller slope than the G2 one. It is important to notice that recent reports on literature claimed for the occurrence of signatures of subtle phase transitions at ∼ 70 K in L-cysteine by specific heat, Raman spectroscopy, X-ray diffraction, and neutron scattering [21][22][23].This kind of behavior can be understood by considering phonon-phonon interactions. Balkanski, Wallis, and Haro [10] developed a detailed theory of the higher order phonon anharmonic decay in order to explain the temperature dependence of the frequency and linewidth of the optical phonons probed by Raman scattering.…”

Thermal behavior and polymorphism in medium–high temperature range of the sulfur containing amino acids l-cysteine and l-cystine

“…L-Cysteine crystallizes in the monoclinic and orthorhombic forms and has been structurally characterized by X-ray [8][9][10] and neutron [11] diffraction methods at ambient and low temperatures [12][13][14] as well as at ambient and higher pressures [15]. Phase transitions have been detected when lowering the temperature (ca.…”

“…Phase transitions have been detected when lowering the temperature (ca. 70 K) [14] and also when increasing pressures up to 4.2 GPa and decreasing to 1.7 GPa [15]. L-Cystine crystallizes in the tetragonal and hexagonal forms and has also been studied at ambient [16,17] and at low temperature [18] and at high pressures [19]; however, no solid-solid phase transition has been detected.…”

Contribution of weak S—H...Xhydrogen bonds to phase transitions in crystals of cysteine, its salts and derivatives under high pressures and low temperatures

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Spin crossover (SCO) phenomenon is connected with the switching process of electronic configuration of iron(II) ion by a change of temperature [1], pressure [2], magnetic field [3] or after light irradiation [4]. The result of such transition is not only the change of metal -ligand bond lengths but also cooperative interactions with other SCO centers.

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“…In crystals cysteine can adopt different conformations since its side chain may easily rotate along C-C bond providing three general types of its orientation characterized by the value of N-C-C-S torsion angle: gauche+ , gauche-and trans. Investigations of L-and DL-cysteine on variation of temperature and pressure have revealed many phase transitions [1][2][3][4][5][6] . On cooling the orthorhombic L-cysteine its side chain becomes ordered, in monoclinic L-cysteine a subtle phase transition is detected.…”