A multiplanet system of super-Earths orbiting the brightest red dwarf star GJ 887

The closet exoplanets to the Sun provide opportunities for detailed characterization of planets outside the Solar System. We report the discovery, using radial velocity measurements, of a compact multiplanet system of super-Earth exoplanets orbiting the nearby red dwarf star GJ 887. The two planets have orbital periods of 9.3 and 21.8 days. Assuming an Earth-like albedo, the equilibrium temperature of the 21.8-day planet is ~350 kelvin. The planets are interior to, but close to the inner edge of, the liquid-water habitable zone. We also detect an unconfirmed signal with a period of ~50 days, which could correspond to a third super-Earth in a more temperate orbit. Our observations show that GJ 887 has photometric variability below 500 parts per million, which is unusually quiet for a red dwarf.

Cinoxacin complexes with divalent metal ions. Spectroscopic characterization. Crystal structure of a new dinuclear Cd(II) complex having two chelate-bridging carboxylate groups. Antibacterial studies

Several cinoxacin (HCx) complexes with divalent metal ions have been prepared and characterized by spectroscopic techniques. The crystal structure of [Cd2(Cx)4(H2O)2].10H2O has been determined by X-ray diffraction. The complex is triclinic, space group P1 with unit-cell dimensions: a = 10.412(2), b = 11.119(2), c = 13.143(6)A, chi== 76.78(4) degrees, beta = 74.59(3) degrees, gamma = 77.12(3) degrees, V = 1406.0(8) A3. In this complex each cadmium atom is heptacoordinated: the metal environment is formed by two Oketo and two Ocarbox atoms from two different cinoxacinate monoanions, two carboxylate oxygen atoms from a third cinoxacinate ligand and by one water oxygen atom on the seventh position. Two of the cinoxacinate ions act as tridentate chelate and bridging ligands and the other one as a bidentate chelate ligand. In the bridging monoanions the carboxylate group is behaving as a chelate ligand. All the complexes were screened for their activity against several bacteria, showing activity similar to that of cinoxacin. Additionally, the number of bacteria killed after 3 h of incubation with cinoxacin, [Cu(Cx)2].2H2O and [Co(Cx)3]Na.10H2O complexes was determined against E. coli ATCC 25922; the copper compound presents paradoxical effect which has been described and related to the mechanism of action of quinolones.

Villamaninite, a case of noncubic pyrite-type structure

This paper reports the results obtained in a study of the crystal structure of two villamaninite samples from Villamanín (León, Spain), labeled (1) and (2). Villamaninite, (Cu,Ni,Co,Fe)(S,Se)2, is a pyrite-type disulfide. Different long-period elements, including Au, in ionic substitution are also observed. Previous authors have assumed a cubic Pa{\bar 3} symmetry for this mineral. The result of our single-crystal study shows a deviation from the cubic symmetry Pa{\bar 3} pyrite-type to a pseudocubic symmetry, which is in agreement with the observed optical anisotropy shown by both samples. The structural refinement process leads to a monoclinic model, space group P1211, with a = 5.709 (2), b = 5.707 (2), c = 5.708 (2) Å, β = 90.01 (1)° for sample (1),° and a = 5.704 (3), b = 5.703 (3), c = 5.704 (3) Å, β = 89.99 (2)° for sample (2), with Z = 4. Previous Mössbauer spectroscopic studies stating two different cation sites for Au support the monoclinic model.