Y. Barrans

The prediction of protein domains

The ab initio prediction of the domain boundaries and types remains one of the most important problems which makes a possible description of protein tertiary structure from its amino-acid sequence elusive. The present paper describes new methods to predict both of them. The predictions of domain boundaries and types in proteins of known X-ray structures are reported in order to check the efficiency of these new algorithms.

Structure and non-linear optical properties of phosphine oxide derivatives

The crystal structures of three different phosphine oxides derivatives possessing high quadratic susceptibilities, β, in solution have been investigated by X-ray diffraction. Slight modification of the transmitter chain leads to an acentric molecule; however, it is shown that these polar molecules have specific arrangements in the crystalline state, leading to a weak non-linear optical (NLO) response. The crystallographic data were entered into the MOPAC program to calculate the quadratic hyperpolarizability of each structure. The results were compared to those obtained by the use of standard internal data of the MOPAC program.

Structural aspects of the phase transitions in (BEDO-TTF)2ReO4·H2O

The effect of the first-order phase transition occurring around 220K on the crystal and electronic structure of the molecular superconductor (BEDO-TTF)2ReO4·H2O has been studied. The crystal structure at 170K has been determined and it is found that the main structural change resulting from the phase transition is connected with a rotation of the ReO4− anions. This rotation leads to changes in the S…S and S…O intermolecular contacts within the BEDO-TTF donor layers, nevertheless the band structure is remained practically unchanged. Possible changes in the crystal structure which can occur at room temperature depending on the experimental conditions are considered. It seems very likely that the (BEDO-TTF)2ReO4·H2O crystal loses its water molecules in the vacuum and hence changes its crystal structure.

Laboratory high-pressure single-crystal x-ray diffraction: recent improvements and examples of studies

Some recent improvements made to the high-pressure single-crystal x-ray diffraction (XRD) experiments in use in our laboratory are reviewed. In particular a set-up to perform high-pressure (0–3.0 GPa)–low-temperature (300–9 K) investigations as well as a protocol for high-pressure XRD data collection using a CCD detector are shown. Examples of studies are also presented.

Crystal structures at 10 K (1 bar), 7 kbar (295 K), and 7 kbar (7 K) of the molecular metal (TSeT)2Cl

Abstract The low temperature crystal packing of (TSeT) 2 Cl is similar to that obtained at room temperature, no structural transition occuring. Only small changes in the atomic parameters are observed. On the contrary, the high pressure and the high pressure-low temperature crystal structures show a change in the symmetry which leads to a difference in the network of the chloride anions and in their environment.

Low temperature structural properties of the (TMTSF)2NO3 salt

Abstract The ordering of the anion in the molecular conductor salt (TMTSF) 2 NO 3 at low temperature depends on the rate of cooling and corresponds to the doubling of the a cell parameter. This order-disorder transition does not affect the crystal packing as the TMTSF chains in the ordered and in the disordered crystal structures at 12K can not be distinguished. This salt is strongly 1D at low temperature.

Influence of the pressure on the low temperature (7K) crystal structure of the superconducting molecular salt (TMTSF)2ClO4

Abstract The anion ordering which occurs in (TMTSF) 2 ClO 4 at 24 K is characterized by the appearance of b * /2 superlattice reflections, without any important change in the basic crystal structure. The intensities of these superlattice reflections have been measured at 7 K (ambient pressure). At the same temperature, these reflections do not appear under pressure (5 kbar). Thus, in the latter case, the anions remain disordered.