Human sphingomyelin synthase 1 generates diacylglycerol in the presence and absence of ceramide via multiple enzymatic activities.

Sphingomyelin (SM) synthase 1 (SMS1), which is involved in lipodystrophy, deafness, and thrombasthenia, generates diacylglycerol (DG) and SM using phosphatidylcholine (PC) and ceramide as substrates. Here, we found that SMS1 possesses DG-generating activities via hydrolysis of PC and phosphatidylethanolamine (PE) in the absence of ceramide and ceramide phosphoethanolamine synthase (CPES) activity. In the presence of the same concentration (4.7 mol%) of PC and ceramide, the amounts of DG produced by SMS and PC-phospholipase C (PLC) activities of SMS1 were approximately 65% and 35% of total DG production, respectively. PC-PLC activity showed substrate selectivity for saturated and/or monounsaturated fatty acid-containing PC species. A PC-PLC/SMS inhibitor, D609, inhibited only SMS activity. Mn2+ inhibited only PC-PLC activity. Intriguingly, DG attenuated SMS/CPES activities. Our study indicates that SMS1 is a unique enzyme with PC-PLC/PE-PLC/SMS/CPES activities.

Pressure-induced transitions inRCo5(R=Y, La) studied by x-ray emission spectroscopy, x-ray diffraction and density functional theory.

The hydrostatic pressure dependent evolution of the electronic and magnetic structure of LaCo5and YCo5was investigated by means of x-ray emission spectroscopy, x-ray diffraction, and spin-polarized density functional theory (DFT) calculations. Using experimental lattice parameters the DFT correctly predicts the pressure of the magnetic transition in both compounds to be 26 GPa (La) and 22-23 GPa (Y). The transition was experimentally resolved in the changes of the electronic structure via the integrated absolute difference of the CoKßemission spectra. Comparison of theory and experiment confirm for the first time a common feature in both LaCo5and YCo5to be the source of the transition; the Fermi-level crossing of an up-spin polarized flat band driving the systems into a low spin configuration via a Lifshitz type transition of the Fermi surface. Another phase transition observed around 12 GPa in LaCo5was clarified to be caused by the change in the down-spin density of states at the Fermi level.

Electronic and crystal structures ofLnFeAsO1-xHx(Ln= La, Sm) studied by x-ray absorption spectroscopy, x-ray emission spectroscopy, and x-ray diffraction: II pressure dependence.

We examine electronic and crystal structures of iron-based superconductorsLnFeAsO1-xHx(Ln= La, Sm) under pressure by means of x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), and x-ray diffraction. In LaFeAsO the pre-edge peak on high-resolution XAS at the Fe-Kabsorption edge gains in intensity on the application of pressure up to 5.7 GPa and it saturates in the higher pressure region. We found integrated-absolute difference values on XES forLn= La, corresponding to a spin state, decline on the application of pressure, and then it is minimized when theTcapproaches the maximum at around 5 GPa. In contrast, such the optimum value was not detected forLn= Sm. We reveal that the superconductivity is closely related to the lower spin state forLn= La unlike Sm case. We observed that As height from the Fe basal plane and As-Fe-As angle on the FeAs4tetrahedron forLn= La deviate from the optimum values of the regular tetrahedron in superconducting (SC) phase, which has been widely accepted structural guide to SC thus far. In contrast, the structural parameters were held near the optimum values up to ∼15 GPa forLn= Sm.

Electronic and crystal structures ofLnFeAsO1-xHx(Ln= La, Sm) studied by x-ray absorption spectroscopy, x-ray emission spectroscopy, and x-ray diffraction (part I: carrier-doping dependence).

A carrier doping by a hydrogen substitution in LaFeAsO1-xHxis known to cause two superconducting (SC) domes with the magnetic order at both end sides of the doping. In contrast, SmFeAsO1-xHxhas a similar phase diagram but shows single SC dome. Here, we investigated the electronic and crystal structures for iron oxynitrideLnFeAsO1-xHx(Ln= La, Sm) with the range ofx= 0-0.5 by using x-ray absorption spectroscopy, x-ray emission spectroscopy, and x-ray diffraction. For both compounds, we observed that the pre-edge peaks of x-ray absorption spectra near the Fe-Kedge were reduced in intensity on doping. The character arises from the weaker As-Fe hybridization with the longer As-Fe distance in the higher doped region. We can reproduce the spectra near the Fe-Kedge according to the Anderson impurity model with realistic valence structures using the local-density approximation (LDA) plus dynamical mean-field theory (DMFT). ForLn= Sm, the integrated-absolute difference (IAD) analysis from x-ray Fe-Kßemission spectra increases significantly. This is attributed to the enhancement of magnetic moment of Fe 3delectrons stemming from the localized picture in the higher doped region. A theoretical simulation implementing the self-consistent vertex-correction method reveals that the single dome superconducting phase forLn= Sm arises from a better nesting condition in comparison withLn= La.

Concomitant singularities of Yb-valence and magnetism at a critical lattice parameter of icosahedral quasicrystals and approximants.

Non-Fermi-liquid (NFL), a significant deviation from Fermi-liquid theory, usually emerges near an order-disorder phase transition at absolute zero. Recently, a diverging susceptibility toward zero temperature was observed in a quasicrystal (QC). Since an electronic long-range ordering is normally absent in QCs, this anomalous behaviour should be a new type of NFL. Here we study high-resolution partial-fluorescence-yield x-ray absorption spectroscopy on Yb-based intermediate-valence icosahedral QCs and cubic approximant crystals (ACs), some of which are new materials, to unveil the mechanism of the NFL. We find that for both forms of QCs and ACs, there is a critical lattice parameter where Yb-valence and magnetism concomitantly exhibit singularities, suggesting a critical-valence-fluctuation-induced NFL. The present result provides an intriguing structure-property relationship of matter; size of a Tsai-type cluster (that is a common local structure to both forms) tunes the NFL whereas translational symmetry (that is present in ACs but absent in QCs) determines the nature of the NFL against the external/chemical pressure.

Degenerate states, emergent dynamics and fluid mixing by magnetic rotors.

We investigate the collective motion of magnetic rotors suspended in a viscous fluid under a uniform rotating magnetic field. The rotors are positioned on a square lattice, and low Reynolds hydrodynamics is assumed. For a 3 × 3 array of magnets, we observe three characteristic dynamical patterns as the external field strength is varied: a synchronized pattern, an oscillating pattern, and a chessboard pattern. The relative stability of these depends on the competition between the energy due to the external magnetic field and the energy of the magnetic dipole-dipole interactions among the rotors. We argue that the chessboard pattern can be understood as an alternation in the stability of two degenerate states, characterized by striped and spin-ice configurations, as the applied magnetic field rotates. For larger arrays, we observe propagation of slip waves that are similar to metachronal waves. The rotor arrays have potential as microfluidic devices that can mix fluids and create vortices of different sizes.