Insights into the crystal structure, polymorphism and thermal behavior of menthol optical isomers and racemates

International audienceThe physico-chemical properties of the levo- and dextrorotatory menthol isomers as well as the corresponding racemic compound were studied using X-ray single-crystal or powder diffraction and differential scanning calorimetry experiments. As a result, the not yet determined crystal structure of DL-menthol was solved. Moreover, the stable and metastable experimental temperature-composition phase diagrams of the L-menthol/D-menthol binary system were determined. The thermodynamic relative stability of the different menthol polymorphs was also established. The present paper provides new physical, chemical and thermodynamic data of L-, D- and DL-menthol and offers new insight into their polymorphism as well as into the levorotatory-dextrorotatory menthol interactions. Both the thermodynamic and crystallographic approaches demonstrate unambiguously that racemic menthol is a racemate

High-pressure structural phase transitions in semiconducting niobium dioxide

Niobium dioxide was studied up to 47 GPa by angle-dispersive, x-ray powder diffraction. Semiconducting α − NbO 2 (space group I 4 1 / a , Z = 32 ) was found to transform to β − NbO 2 (space group I 4 1 , Z = 16 ) above 5 GPa. Both phases have distorted rutile-type structures and the transition involves a change in the long-range ordering of the metal-metal bonds. A further transition was observed above 8 GPa to a baddeleyite-related structure with a = 9.975 ( 1 ) , b = 9.963 ( 1 ) , c = 9.933 ( 1 ) Å , β = 104.023 ( 4 ) ° , and Z = 32 at 12.8 GPa. The doubling of the unit cell along a, b, and c and the larger monoclinic angle with respect to a baddeleyite-type cell are due to the presence of metal-metal bonds. The d 1 cation dioxide, NbO 2 , is thus shown to behave in a similar way to d 0 cation dioxides, which follow a phase transition sequence involving the baddeleyite-type structure

Hardness and elasticity in cubic ruthenium dioxide

The Knoop hardness of the highly incompressible cubic phase of ruthenium dioxide was found to be 19–20 GPa from indentation tests. This value scales well with the shear modulus approximated by the elastic constant C44 of 144 GPa obtained from Brillouin scattering measurements. This work provides evidence that the shear modulus is a better indicator of hardness than the bulk modulus for ionic and covalent materials

1-Allyl-3-phenyl­quinoxalin-2(1H)-one

The title compound, C17H14N2O, crystallizes with two mol­ecules in the asymmetric unit. The dihedral angles between the mean planes of the quinoxaline ring system and the phenyl ring in the two mol­ecules are 38.27 (10) and 37.14 (8)°. In the crystal, π-stacking along the b axis contributes to the crystal cohesion with an average distance between quinoxaline units of 3.397 (3) Å. Weak C—H⋯O interactions also occur

3-[2-(1H-Benzimidazol-2-ylsulfan­yl)eth­yl]-1,3-oxazolidin-2-one

In the title compound, C12H13N3O2S, the oxazolidin ring displays an envelope conformation. The dihedral angle between the benzimidazole ring and the 1,3-oxazolidin-2-one mean plane is 69.85 (13)°. In the crystal, mol­ecules are linked by inter­molecular N—H⋯N hydrogen bonds, forming a chain parallel to the b axis

Insight in the quorum sensing-driven lifestyle of the non-pathogenic Agrobacterium tumefaciens 6N2 and the interactions with the yeast Meyerozyma guilliermondii

Agrobacterium tumefaciens is considered a prominent phytopathogen, though most isolates are nonpathogenic. Agrobacteria can inhabit plant tissues interacting with other microorganisms. Yeasts are likewise part of these communities. We analyzed the quorum sensing (QS) systems of A. tumefaciens strain 6N2, and its relevance for the interaction with the yeast Meyerozyma guilliermondii, both sugarcane endophytes. We show that strain 6N2 is nonpathogenic, produces OHC8-HSL, OHC10-HSL, OC12-HSL and OHC12-HSL as QS signals, and possesses a complex QS architecture, with one truncated, two complete systems, and three additional QS-signal receptors. A proteomic approach showed differences in QS-regulated proteins between pure (64 proteins) and dual (33 proteins) cultures. Seven proteins were consistently regulated by quorum sensing in pure and dual cultures. M. guilliermondii proteins influenced by QS activity were also evaluated. Several up- and down- regulated proteins differed depending on the bacterial QS. These results show the importance of the QS regulation in the bacteria-yeast interactions.Fil: Bertini, Elisa Violeta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Torres, Mariela Analía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: Leger, Thibaut. Institut Jacues Monod; FranciaFil: Garcia, Camille. Institut Jacques Monod; FranciaFil: KarWai, Hong. University Of Malaya; MalasiaFil: Teik Min, Chong. University Of Malaya; MalasiaFil: Castellanos, Lucia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; ArgentinaFil: KokGan, Chan. University Of Malaya; MalasiaFil: Dessaux, Yves. Universite Paris-sud; FranciaFil: Camadro, Jean Michel. Institut Jacques Monod; FranciaFil: Nieto Peñalver, Carlos Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentin

The SARS algorithm: detrending CoRoT light curves with Sysrem using simultaneous external parameters

Surveys for exoplanetary transits are usually limited not by photon noise but rather by the amount of red noise in their data. In particular, although the CoRoT spacebased survey data are being carefully scrutinized, significant new sources of systematic noises are still being discovered. Recently, a magnitude-dependant systematic effect was discovered in the CoRoT data by Mazeh & Guterman et al. and a phenomenological correction was proposed. Here we tie the observed effect a particular type of effect, and in the process generalize the popular Sysrem algorithm to include external parameters in a simultaneous solution with the unknown effects. We show that a post-processing scheme based on this algorithm performs well and indeed allows for the detection of new transit-like signals that were not previously detected.Comment: MNRAS accepted. 5 pages, 3 figure