90,247 research outputs found
Reversible pressure-induced amorphization of a zeolitic imidazolate framework (ZIF-4).
No full textWe report the reversible pressure-induced amorphization of a zeolitic imidazolate framework (ZIF-4, [Zn(Im)(2)]). This occurs irrespective of pore occupancy and takes place via a novel high pressure phase (ZIF-4-I) when solvent molecules are present in the pores. A significant reduction in bulk modulus upon framework evacuation is also observed for both ZIF-4 and ZIF-4-I
Modeling and Rescue of RP2 Retinitis Pigmentosa Using iPSC-Derived Retinal Organoids
Get PDFCheetham and colleagues show that 3D retinal organoids lacking the RP2 protein develop rod photoreceptor degeneration that can be prevented with AAV gene augmentation for RP2
Charge ordering in manganates
No full textSeveral compounds are known to exhibit magnetoresistance, a change in electrical resistivity in the presence of magnetic field. Such materials are of interest both for technology and basic science. In their perspective, Rao and Cheetham discuss recent results on magnetoresistance in rare-earth manganate materials, which exhibit especially interesting fundamental physical phenomena
On the Nature of Water Bound to a Solid Acid Catalyst
No full textThe nature of the species formed when water interacts with Brønsted acid sites in a microporous solid acid catalyst, HSAPO-34, was studied by powder neutron diffraction and infrared spectroscopy. Previous infrared and computational studies had failed to unambiguously establish whether water is protonated to form hydronium (H3O+) ions or is merely hydrogen-bonded to acid sites inside the zeolite. Our experiments clearly showed that both species are present: An H3O+ ion is found in the eight-ring channel of the zeolite and a second water molecule is hydrogen-bonded to an acid site on the six-ring.</p
A tale of two siblings: two cases of AML arising from a single pre-leukemic DNMT3A mutant clone
Get PDFLetters to the EditorC N Hahn, D M Ross, J Feng, A Beligaswatte, D K Hiwase, W T Parker, M Ho, M Zawitkowski, K L Ambler, G D Cheetham, Y K Lee, M Babic, C M Butcher, G A Engler, A L Brown, R J D'Andrea, I D Lewis, A W Schreiber, L B To and H S Scot
Giant magnetoresistance in transition metal oxides
No full textSome materials exhibit large changes in electrical resistance in the presence of a magnetic field, and this change can be used in applications from sensor technology to magnetic data storage. In their perspective, Rao and Cheetham discuss magnetoresistance in perovskite manganates, where the effect is unusually strong. Much has been learned about these materials, and this understanding is driving the search for new materials with even more impressive properties
A density functional study of the high-pressure chemistry of MSiN2(M = Be,Mg, Ca)
Get PDFNormal pressure modifications and tentative high-pressure phases of the nitridosilicates MSiN2 with M = Be, Mg, or Ca have been thoroughly studied by density functional methods. At ambient pressure, BeSiN2 and MgSiN2 exhibit an ordered wurtzite variant derived from idealized filled β-cristobalite by a C1-type distortion. At ambient pressure, the structure of CaSiN2 can also be derived from idealized filled β-cristobalite by a different type of distortion (D1-type). Energy–volume calculations for all three compounds reveal transition into an NaCl superstructure under pressure, affording sixfold coordination for Si. At 76 GPa BeSiN2 forms an LiFeO2-type structure, corresponding to the stable ambient-pressure modification of LiFeO2, while MgSiN2 and CaSiN2 adopt an LiFeO2-type structure, corresponding to a metastable modification (24 and 60 GPa, respectively). For both BeSiN2 and CaSiN2 intermediate phases appear (for BeSiN2 a chalcopyrite-type structure and for CaSiN2 a CaGeN2-type structure). These two tetragonal intermediate structures are closely related, differing mainly in their c/a ratio. As a consequence, chalcopyrite-type structures exhibit tetrahedral coordination for both cations (M and Si), whereas in CaGeN2-type structures one cation is tetrahedrally (Si) and one bisdisphenoidally (M) coordinated. Both structure types, chalcopyrite and CaGeN2, can also be derived from idealized filled β-cristobalite through a B1-type distortion. The group–subgroup relation of the BeSiN2/MgSiN2, the CaSiN2, the chalcopyrite, the CaGeN2 and the idealized filled β-cristobalite structure is discussed and the displacive phase transformation pathways are illustrated. The zero-pressure bulk moduli were calculated for all phases and have been found to be comparable to compounds such as α- Si3N4, CaIrO3 and Al4C3. Furthermore, the thermodynamic stability of BeSiN2, MgSiN2 and CaSiN2 against phase agglomerates of the binary nitrides M3N2 and Si3N4 under pressure are examined
Magnetic and structural studies of some mixed metal oxides
Get PDFPowder neutron diffraction and magnetic susceptibility measurements of the antiferromagnetic phases of MnxNi1-xO,MnxCo1-xO, (MnxFe1-x)zO and (CoxFe1-x)zO reveal that the magnetic moments of unlike ions are always effectively collinear, despite the presence of competing anisotropies. The magnetic moments of MnxNi1-xO (x = 0.24,0.48 and 0.77) at 5K are confined to (111) planes by dipole-dipole forces, and the small trigonal exchangestrictions are the products of opposed antiferromagnetic Mn2+-Mn2+ and ferromagnetic Ni2+-Mn2+ nearest neighbour interactions. In MnxCo1-xO (x = 0.05, 0.10, 0.25,0.36) at 5K, the orbital degener- acy of Co2+ is removed by both Jahn-Teller (J.T) and spin-orbit coupling (S.O) mechanisms, leading to orthorhombic or triclinic symmetries and partially quenched Co2+ moments. Monoclinic symmetry is observed for 0.512+ moments are evident. The cobalt concentration is too small to support a cooperative J.T stabilisation in Mn0.83Co0.17O, where a magnetostriction (c/a MnO»FezO≈NiO. The weak trigonal anisotropy of Fe2+ correlates with the near-cubic symmetries of (CoxFe1-x)z( (x = 0.04,0.12) and (MnxFe1-x)zO (0.11) magnetostriction of Fe2+ is observed in (CoxFe1-x)zO with x > 0.5. Measurements of vacancy-ferric interstitial ratios for (MnxFe1-x)zO and (CoxFe1-x)zO suggest that non-stoichiometry is accommodated by 6:2 or 8:3 defect clusters in the former, and by larger units in the latter. The observed magnetic moments of defective samples are normally larger than those calculated according to a previous model for FezO, and require the postulation of partial antiferromagnetic order around the clusters. The room temperature Mossbauer effect parameters of (MnxFe1-x)zO (02+ and Mn2+ ions are randomly distributed over octahedral sites, ferric ions are localised around defect clusters
Depolarization and decreased surface expression of K+ channels contribute to NSAID-inhibition of intestinal restitution
No full textNon-steroidal anti-inflammatory drugs (NSAIDs) contribute to gastrointestinal ulcer formation by inhibiting epithelial cell migration and mucosal restitution; however, the drug-affected signaling pathways are poorly defined. We investigated whether NSAID inhibition of intestinal epithelial migration is associated with depletion of intracellular polyamines, depolarization of membrane potential (Em) and altered surface expression of K+ channels. Epithelial cell migration in response to the wounding of confluent IEC-6 and IEC-Cdx2 monolayers was reduced by indomethacin (100μM), phenylbutazone (100μM) and NS-398 (100μM) but not by SC-560 (1μM). NSAID-inhibition of intestinal cell migration was not associated with depletion of intracellular polyamines. Treatment of IEC-6 and IEC-Cdx2 cells with indomethacin, phenylbutazone and NS-398 induced significant depolarization of Em, whereas treatment with SC-560 had no effect on Em. The Em of IEC-Cdx2 cells was: −38.5±1.8mV under control conditions; −35.9±1.6mV after treatment with SC-560; −18.8±1.2mV after treatment with indomethacin; and −23.7±1.4mV after treatment with NS-398. Whereas SC-560 had no significant effects on the total cellular expression of Kv1.4 channel protein, indomethacin and NS-398 decreased not only the total cellular expression of Kv1.4, but also the cell surface expression of both Kv1.4 and Kv1.6 channel subunits in IEC-Cdx2. Both Kv1.4 and Kv1.6 channel proteins were immunoprecipitated by Kv1.4 antibody from IEC-Cdx2 lysates, indicating that these subunits co-assemble to form heteromeric Kv channels. These results suggest that NSAID inhibition of epithelial cell migration is independent of polyamine-depletion, and is associated with depolarization of Em and decreased surface expression of heteromeric Kv1 channels.ID: S0006295207001931; M3: Article; Accession Number: S0006295207001931; Author: L.C. Freeman (b); Author: D.F. Narvaez (a); Author: A. McCoy (a); Author: F.B. von Stein (c); Author: S. Young (b); Author: K. Silver (a); Author: S. Ganta (b); Author: D. Koch (b); Author: R. Hunter (b); Author: R.F. Gilmour (c); Author: J.D. Lillich (a, ⁎); Affiliation: Department of Clinical Sciences, Kansas State University, Manhattan, KS 66506, United States; Affiliation: Department of Anatomy and Physiology, Kansas State University, Manhattan, KS 66506, United States; Affiliation: Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, United States; Keyword: Non-steroidal anti-inflammatory drugs; Keyword: Intestinal epithelial cells; Keyword: Membrane potential; Keyword: Potassium channels; Number of Pages: 12; Language: English;Source type: Electronic(1)http://search.ebscohost.com/login.aspx?direct=true&db=edselp&AN=S0006295207001931&site=eds-live&scope=sit
A Quantitative Description of the Active Sites in the Dehydrated Acid Catalyst HSAPO34 for the Conversion of Methanol to Olefins
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