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 NH₄SCN aqueous solutions were investigated with intermolecular vibrational energy transfer methods. In a KSCN/H₂O (1/10 molar ratio) solution, 90% of the initial excitation of the CN stretch (∼2066 cm^–1) of the SCN^– anion is transferred to the HOH bending mode (∼1636 cm^–1) of water molecules with an energy transfer time constant 3.1 ps. In a NH₄SCN/H₂O (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^–1) of the NH⁺ 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 NH₄⁺ cations in the NH₄SCN/H₂O solution. Ion concentration dependent measurements support this argument. According to the dipole/dipole approximation, the CN/OH energy transfer occurs most efficiently between SCN^– 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^– anions are replaced by the NH₄⁺ cations in the NH₄SCN/H₂O (1/10 molar ratio) solution. The percentage is much larger than the NH₄⁺/water ratio of 10%, indicating that the ion association between NH₄⁺ and SCN^– is caused by the chemical nature of the solution rather than the statistical “forced contact” because of the high ion concentration