44 research outputs found
Neutron powder-diffraction study of phase transitions in strontium-doped bismuth ferrite: 1. Variation with chemical composition
We report results from a study of the crystal structure of strontium-doped BiFeO3 using neutron powder diffraction and the Rietveld method. Measurements were obtained over a wide range of temperatures from 300–800 K for compositions between 10–16% replacement of bismuth by strontium. The results show a clear variation of the two main structural deformations – symmetry-breaking rotations of the FeO6 octahedra and polar ionic displacements that give ferroelectricity – with chemical composition, but relatively little variation with temperature. On the other hand, the antiferromagnetic order shows a variation with temperature and a second order phase transition consistent with the classical Heisenberg model. There is, however, very little variation in the behaviour of the antiferromagnetism with chemical composition, and hence with the degree of the structural symmetry-breaking distortions. We therefore conclude that there is no significant coupling between antiferromagnetism and ferroelectricity in Sr-doped BiFeO3 and, by extension, in pure BiFeO3
Kdm3a lysine demethylase is an Hsp90 client required for cytoskeletal rearrangements during spermatogenesis
The lysine demethylase Kdm3a (Jhdm2a, Jmjd1a) is required for male fertility, sex determination, and metabolic homeostasis through its nuclear role in chromatin remodeling. Many histone-modifying enzymes have additional nonhistone substrates, as well as nonenzymatic functions, contributing to the full spectrum of events underlying their biological roles. We present two Kdm3a mouse models that exhibit cytoplasmic defects that may account in part for the globozoospermia phenotype reported previously. Electron microscopy revealed abnormal acrosome and manchette and the absence of implantation fossa at the caudal end of the nucleus in mice without Kdm3a demethylase activity, which affected cytoplasmic structures required to elongate the sperm head. We describe an enzymatically active new Kdm3a isoform and show that subcellular distribution, protein levels, and lysine demethylation activity of Kdm3a depended on Hsp90. We show that Kdm3a localizes to cytoplasmic structures of maturing spermatids affected in Kdm3a mutant mice, which in turn display altered fractionation of beta-actin and gamma-tubulin. Kdm3a is therefore a multifunctional Hsp90 client protein that participates directly in the regulation of cytoskeletal components.Publisher PDFPeer reviewe
Ion Association in Aqueous Solutions Probed through Vibrational Energy Transfers among Cation, Anion, and Water Molecules
KSCN and NH<sub>4</sub>SCN aqueous solutions were investigated
with intermolecular vibrational energy transfer methods. In a KSCN/H<sub>2</sub>O (1/10 molar ratio) solution, 90% of the initial excitation
of the CN stretch (∼2066 cm<sup>–1</sup>) of the SCN<sup>–</sup> anion is transferred to the HOH bending mode (∼1636
cm<sup>–1</sup>) of water molecules with an energy transfer
time constant 3.1 ps. In a NH<sub>4</sub>SCN/H<sub>2</sub>O (1/10
molar ratio) solution, only 49% of the CN excitation flows to the
water HOH bending mode with a time constant 6.3 ps. Most of the remaining
CN excitation goes to the NH bending mode (∼1460 cm<sup>–1</sup>) of the NH<sup>+</sup> cation with a time constant of 7.0 ps. The
results indicate that about 50% of the energy transfer channel from
the CN stretch to the HOH bending observed in the KSCN solution is
overpowered by the NH<sub>4</sub><sup>+</sup> cations in the NH<sub>4</sub>SCN/H<sub>2</sub>O solution. Ion concentration dependent measurements
support this argument. According to the dipole/dipole approximation,
the CN/OH energy transfer occurs most efficiently between SCN<sup>–</sup> anions and the water molecules closest to them. The
experimental results therefore suggest that more than 50% of the water
molecules closest to the SCN<sup>–</sup> anions are replaced
by the NH<sub>4</sub><sup>+</sup> cations in the NH<sub>4</sub>SCN/H<sub>2</sub>O (1/10 molar ratio) solution. The percentage is much larger
than the NH<sub>4</sub><sup>+</sup>/water ratio of 10%, indicating
that the ion association between NH<sub>4</sub><sup>+</sup> and SCN<sup>–</sup> is caused by the chemical nature of the solution rather
than the statistical “forced contact” because of the
high ion concentration