Sign change in c-axis thermal expansion and lattice collapse by Ni substitution in Co1-xNixZr2 superconductors

We investigated the structural, electronic, and superconducting properties of Co1-xNixZr2, in which c-axis thermal expansion is systematically controlled. At x (smaller than) 0.3, c-axis negative thermal expansion (NTE) was observed, and the thermal expansion constant {\alpha}c approached zero with increasing x. At x = 0.4-0.6, zero thermal expansion was observed, and positive thermal expansion (PTE) appeared for x (greater than) 0.7. By analyzing the c/a ratio, we observed a possible collapsed transition in the tetragonal lattice at around x = 0.6-0.8. The lattice collapse results in c-axis PTE and the suppression of bulk superconductivity.Comment: 16 pages, 5 figures, 1 table, Supporting material

Dispersion of Graphene in an Aqueous Solution with Poly(sodium 4-styrenesulfonate) Monitored by Capillary Electrophoresis

Graphene was dispersed in an aqueous solution with poly(sodium 4-styrenesulfonate) as a dispersant. The charge of the graphene came to be apparently negative by the adsorption of poly(4-styrenesulfonate) ion (PSS). Two kinds of PSS were examined: the average molecular masses of 70,000 and 1,000,000 (PSS 70,000 and PSS 1,000,000, respectively). Capillary electrophoresis was used to evaluate the dispersion of the apparently anionic graphene in an aqueous solution. A broad signal corresponding to the dispersed graphene was detected in the electropherograms. The effective electrophoretic mobility of the dispersed graphene was somewhat larger at higher concentrations of PSS 70,000, suggesting that the adsorbed amount of PSS 70,000 increased. Even when the separation buffer did not contain PSS, the broad signal of the anionic graphene was still detected. The peak height and/or the peak area, as well as the effective electrophoretic mobility of the graphene decreased little at the reduced applied voltages, i.e., at longer separation/detection time. Therefore, the adsorption of PSS is irreversible or the desorption of PSS from the graphene surface is very slow. Accordingly, the dispersed graphene with PSS would be separated from the matrix PSS by the electrophoretic separation

Interaction between anti-Alzheimer and antipsychotic drugs in modulating extrapyramidal motor disorders in mice

AbstractAntipsychotics are often used in conjunction with anti-Alzheimer drugs to treat the behavioral and psychological symptoms of dementia (BPSD). Here, we examined the effects of cholinesterase inhibitors (ChEIs), donepezil and galantamine, on antipsychotic-induced extrapyramidal side effects (EPS) in mice. The effects of serotonergic agents on the EPS drug interaction were also evaluated. Donepezil (0.3–3 mg/kg) did not induce EPS signs by itself; however, it significantly potentiated bradykinesia induction with a low dose of haloperidol (0.5 mg/kg) in dose-dependent and synergistic manners. Galantamine (0.3–3 mg/kg) elicited mild bradykinesia at a high dose and dose-dependently augmented haloperidol-induced bradykinesia. The EPS potentiation by galantamine was blocked by trihexyphenidyl (a muscarinic antagonist), but not by mecamylamine (a nicotinic antagonist). In addition, the bradykinesia potentiation by galantamine was significantly reduced by (±)-8-hydroxy-2-(di-n-propylamino)-tetralin (a 5-HT1A agonist), ritanserin (a 5-HT2 antagonist), and SB-258585 (a 5-HT6 antagonist). The present results give us a caution for the antipsychotics and ChEIs interaction in inducing EPS in the treatment of BPSD. In addition, second generation antipsychotics, which can stimulate 5-HT1A receptors or antagonize 5-HT2 and 5-HT6 receptors, seem to be favorable as an adjunctive therapy for BPSD

Observation of nonvolatile magneto-thermal switching in superconductors

Applying a magnetic field to a solid changes its thermal-transport properties. Although such magneto-thermal-transport phenomena are usually small effects, giant magneto-thermal resistance has recently been observed in spintronic materials1,2 and superconductors3,4, opening up new possibilities in thermal management technologies. However, the thermal conductivity conventionally changes only when a magnetic field is applied due to the absence of nonvolatility, which limits potential applications of thermal switching devices5,6. Here, we report the observation of nonvolatile thermal switching that changes the thermal conductivity when a magnetic field is applied and retains the value even when the field is turned off. This unconventional magneto-thermal switching, surprisingly, arises in commercial Sn-Pb solders and is realized by phase-separated superconducting states and resultant nonuniform magnetic flux distributions. This result confirms the versatility of the observed phenomenon and aids the development of active solid-state thermal management devices.Comment: 33 pages, 5 figures & 9 extended data figure

Pressure-induced volumetric negative thermal expansion in CoZr2 superconductor

We investigate the thermal expansion and superconducting properties of a CuAl2-type (tetragonal) superconductor CoZr2 under high pressures. We perform high-pressure synchrotron X-ray diffraction in a pressure range of 2.9 GPa < P < 10.4 GPa and discover that CoZr2 exhibits volumetric negative thermal expansion under high pressures. Although the uniaxial positive thermal expansion (PTE) along the a-axis is observed under ambient pressure, that is suppressed by pressure, while the large uniaxial negative thermal expansion (NTE) along the c-axis is maintained under the pressure regime. As a result of a combination of the suppressed uniaxial PTE along the a-axis and uniaxial NTE along the c-axis, volumetric negative thermal expansion is achieved under high pressure in CoZr2. The mechanisms of volumetric NTE would be based on the flexible crystal structure caused by the soft Co-Co bond as seen in the iso-structural compound FeZr2, which exhibits uniaxial NTE along the c-axis. We also perform high-pressure electrical resistance measurements of CoZr2 to confirm the presence of superconductivity under the examined pressure regime in the range of 0.03 GPa < P < 41.9 GPa. We confirm the presence of superconductivity under all pressures and observe dome-like shape pressure dependence of superconducting transition temperature. Because of the coexistence of two phenomena, which are volumetric NTE and superconductivity, in CoZr2 under high pressure, the coexistence would be achievable under ambient pressure by tuning chemical compositions after our present observation.Comment: 22 pages, 7 figures, supporting informatio

Sign change in c-axis thermal expansion constant and lattice collapse by Ni substitution in transition-metal zirconide superconductor Co1−x Ni x Zr2

Abstract Recently, c-axis negative thermal expansion (NTE) was observed in a CoZr2 superconductor and related transition-metal zirconides. Here, we investigated the structural, electronic, and superconducting properties of Co1−x Ni x Zr2 to achieve systematic control of c-axis NTE and switching from NTE to positive thermal expansion (PTE) by Ni substitution. At x ≤ 0.3, c-axis NTE was observed, and the thermal expansion constant α c approached zero with increasing x. At x = 0.4–0.6, c-axis thermal expansion close to zero thermal expansion (ZTE) was observed, and PTE appeared for x ≥ 0.7. On the superconducting properties, we observed bulk superconductivity for x ≤ 0.6, and bulk nature of superconductivity is suppressed by Ni heavy doping (x ≥ 0.7). For x ≤ 0.6, the evolution of the electronic density of states well explains the change in the superconducting transition temperature (T c), which suggests conventional phonon-mediated superconductivity in the system. By analyzing the c/a ratio, we observed a possible collapsed transition in the tetragonal lattice at around x = 0.6–0.8. The lattice collapse would be the cause of the suppression of superconductivity in Ni-rich Co1−x Ni x Zr2 and the switching from NTE to PTE

Observation of superconductivity and enhanced upper critical field of η-carbide-type oxide Zr4Pd2O

Abstract We report the first observation of bulk superconductivity of a η-carbide-type oxide Zr4Pd2O. The crystal structure and the superconducting properties were studied through synchrotron X-ray diffraction, magnetization, electrical resistivity, and specific heat measurement. The superconducting transition was observed at T c = 2.73 K. Our measurement revealed that the η-carbide-type oxide superconductor Zr4Pd2O shows an enhanced upper critical field μ 0 H c2(0) = 6.72 T, which violates the Pauli-Clogston limit μ 0 H P = 5.29 T. On the other hand, we found that the enhanced upper critical field is absent in a Rh analogue Zr4Rh2O. The large μ 0 H c2(0) of Zr4Pd2O would be raised from strong spin–orbit coupling with Pd-4d electrons. The discovery of new superconducting properties for Zr4Pd2O would shed light on the further development of η-carbide-type oxide superconductors

Crystal Structures of Human Transthyretin Complexed with Glabridin

Transthyretin (TTR) is a plasma protein implicated in human amyloid diseases. Several small molecules that bind to the thyroxine-binding site of TTR have been shown to stabilize the TTR tetramer and to inhibit amyloid fibril formation of TTR. Herein, we demonstrated that glabridin (Glab), a prenylated isoflavan isolated from Glycyrrhiza glabra L., inhibited aggregation of TTR in a thioflavin assay. The TTR–Glab complex structure revealed a novel binding mode including a CH−π interaction with A108 and a hydrogen bond with K15. A structural comparison with the wild type-apo structure revealed that the CH−π interaction with A108 was strengthened by the induced-fit conformational change upon Glab binding. Furthermore, the binding of Glab induced a rotation of the T119 side chain, and the inclusion of a water molecule, leading to stabilization of the dimer–dimer interface. These results demonstrate that Glab is a novel inhibitor of TTR fibrillization and suggest the molecular mechanism by which Glab binding stabilizes the tetramer

Inhibitory Activities of Propolis and Its Promising Component, Caffeic Acid Phenethyl Ester, against Amyloidogenesis of Human Transthyretin

Transthyretin (TTR) is a homotetrameric serum protein associated with amyloidoses such as familial amyloid polyneuropathy and senile systemic amyloidosis. The amyloid fibril formation of TTR can be inhibited through stabilization of the TTR tetramer by the binding of small molecules. In this study, we examined the inhibitory potency of caffeic acid phenethyl ester (CAPE) and its derivatives. Thioflavin T assay showed that CAPE suppressed the amyloid fibril formation of TTR. Comparative analysis of the inhibitory potencies revealed that phenethyl ferulate was the most potent among the CAPE derivatives. The binding of phenethyl ferulate and the selected compounds to TTR were confirmed by the 8-anilino-1-naphthalenesulfonic acid displacement and X-ray crystallography. It was also demonstrated that Bio 30, which is a CAPE-rich commercially available New Zealand propolis, inhibited TTR amyloidogenesis and stabilized the TTR tetramer. These results suggested that a propolis may be efficient for preventing TTR amyloidosis

Structural Insight into the Interactions between Death-Associated Protein Kinase 1 and Natural Flavonoids

Death-associated protein kinase 1 (DAPK1) is a 160 kDa serine/threonine protein kinase that belongs to the Ca²⁺/calmodulin-dependent protein kinase subfamily. DAPK1 is a possible target for the treatment of acute ischemic stroke and endometrial adenocarcinomas. In the present study, we investigated the binding characteristics of 17 natural flavonoids to DAPK1 using a 1-anilinonaphthalene-8-sulfonic acid competitive binding assay and revealed that morin was the strongest binder among the selected compounds. The crystallographic analysis of DAPK1 and 7 selected flavonoid complexes revealed the structure–binding affinity relationship in atomic-level detail. It was suggested that the high affinity of morin could be accounted for by the ionic interaction between 2′-OH and K42 and that such an interaction would not take place with either cyclin-dependent protein kinases or PIM kinases because of their broader entrance regions. Thus, morin would be a more selective inhibitor of DAPK1 than either of these other types of kinases. In addition, we found that the binding of kaempferol to DAPK1 was associated with a chloride ion. The present study provides a better understanding of the molecular properties of the ATP site of DAPK1 and may be useful for the design of specific DAPK1 inhibitors