Less than perfect divorces: dysregulated mitochondrial fission and neurodegeneration

Research efforts during the last decade have deciphered the basic molecular mechanisms governing mitochondrial fusion and fission. We now know that in mammalian cells mitochondrial fission is mediated by the large GTPase dynamin-related protein 1 (Drp1) acting in concert with outer mitochondrial membrane (OMM) proteins such as Fis1, Mff, and Mief1. It is also generally accepted that organelle fusion depends on the action of three large GTPases: mitofusins (Mfn1, Mfn2) mediating membrane fusion on the OMM level, and Opa1 which is essential for inner mitochondrial membrane fusion. Significantly, mutations in Drp1, Mfn2, and Opa1 have causally been linked to neurodegenerative conditions. Despite this knowledge, crucial questions such as to how fission of the inner and outer mitochondrial membranes are coordinated and how these processes are integrated into basic physiological processes such as apoptosis and autophagy remain to be answered in detail. In this review, we will focus on what is currently known about the mechanism of mitochondrial fission and explore the pathophysiological consequences of dysregulated organelle fission with a special focus on neurodegenerative conditions, including Alzheimer's, Huntington's and Parkinson's disease, as well as ischemic brain damag

Film deposition, X-ray diffraction and optical absorption of novel (R-NH3)2ZnCl4 hybrid perovskites

Organic-inorganic (CnH2n+1NH3)2MX4 hybrid perovskites (where M is a divalent metal and X a halide) are presently attracting much attention, due to their unique electronic properties and excellent film processability [1]. These self-assembling structures contain 2D semiconductor layers ((MX6)=) alternately stacked with organic ammonium layers. Excitons resulting from the low dimensionality of the semiconductor sheets have binding energy of several tenths eV, and are expected to have interesting potentialities for optoelectronic and electronic applications [2]. In this communication we report on the preparation and the basic X-ray and optical characterization of the novel (CnH2n+1NH3)2ZnCl4 (1<n<6) compounds, deposited as thin films by spin-coating alcoholic solutions of stoichiometric precursors on glass and quartz substrates. X-ray diffraction data prove that the as-prepared films are single phase, well crystallized and with a dominant in-plane grain orientation. The distance between the inorganic sheets, as measured through the "d" parameters, linearly increases with the amine chain length ("n" value) (Fig.1a), thus suggesting that the organic chains are ordered perpendicularly to the film surface. The diffraction pattern refinement is presently in progress, in order to assign the appropriate space group and to determine the in-plane lattice parameters. Room temperature optical absorption spectra exhibit a maximum at about 240 nm, which is almost independent on "n" (Fig.1b). Such finding is consistent with the results we obtained in the homologous series of Cu-based hybrids [3] and suggests that also in the Zn-compounds the optical absorption phenomena are related to the inorganic cluster of the structure. References. [1] D.B.Mitzi, K.Chondroudis, C.R. Kagan, IBM J.Res.Dev. 45, 29-45, 2001; [2] M.Era, S.Morimoto, T.Tsutsui, S.Saito, Appl.Phys.Lett 65, 676-678, 1994; [3] F.Chiarella, A.Zappettini, T.Besagni, F.Licci, A.Cassinese, M.Barra, R.Vaglio, C.Aruta, Cryst.Res.Technol. 40, 1028-1032, 2005

ab-plane resistivity and possible charge stripe ordering in strongly underdoped La2−x_{2-x}Srx_{x}CuO4_{4} single crystals

We have measured the ab-plane resistivity of La$_{2-x}$Sr$_x$CuO$_4$ single crystals with small Sr content (x=0.052 $\div$ 0.075) between 4.2 and 300 K by using the AC Van der Pauw technique. As recently suggested by Ichikawa et al., the deviation from the linearity of the $\rho_{\mathrm{ab}}(T)$ curve starting at a temperature T$_{\mathrm{ch}}$ can be interpreted as due to a progressive slowing down of the fluctuations of pre-formed charge stripes. An electronic transition of the stripes to a more ordered phase could instead be responsible for some very sharp anomalies present in the $\rho_{\mathrm{ab}}(T)$ of superconducting samples just above $T_{\mathrm{c}}$.Comment: M2S-HTSC-VI Conference paper (2 pages, 2 figures), using Elsevier style espcrc2.st

Dielectric versus magnetic pairing mechanisms in high-temperature cuprate superconductors investigated using Raman scattering

We suggest, and demonstrate, a systematic approach to the study of cuprate superconductors, namely, progressive change of ion size in order to systematically alter the interaction strength and other key parameters. R(Ba,Sr)$_2$Cu$_3$O$_y$ (R={La, ... Lu,Y}) is such a system where potentially obscuring structural changes are minimal. We thereby systematically alter both dielectric and magnetic properties. Dielectric fluctuation is characterized by ionic polarizability while magnetic fluctuation is characterized by exchange interactions measurable by Raman scattering. The range of transition temperatures is 70 to 107 K and we find that these correlate only with the dielectric properties, a behavior which persists with external pressure. The ultimate significance may remain to be proven but it highlights the role of dielectric screening in the cuprates and adds support to a previously proposed novel pairing mechanism involving exchange of quantized waves of electronic polarization.Comment: Manuscript: 5 pages, 4 figures. Supplemental material included (9 pages, 5 figures

Influence of Ambient Humidityon The Conductivity of CH3NH3SnCl3 Hybrid Films

Organic-inorganic (CnH2n+1NH3)2MX4 hybrid perovskites (M=divalent metal, X=halide) are attracting much attention, due to their unique electronic properties and excellent film processability [1]. The Sn based CH3NH3MX3 compounds are a subclass of that hybrid family, with cubic structure, where the organic component is included in the extended three-dimensional inorganic cage. Studies concerning the structural properties of these compounds [2] prove that methylammonium ions are orientationally disordered due to their polar character. On cooling the disorder is removed through one or more phase transitions, that usually determine large conductivity variations. However, the chemical instability is a major problem for accurate transport measurements on Sn hybrids. Furthermore, most of reported conductivity results refer to iodine-based hybrids, that are conductive, while Br- and Cl- compounds are semiconducting or insulating. In this communication we study the influence of ambient humidity on the electrical properties of thermally ablated CH3NH3SnCl3 films. In particular we show that conductivity increases by more than four orders of magnitude when relative humidity increases from 0 to 80%. Measurements performed in sequence give reproducible results, thus indicating that conductivity increase does not originate from irreversible reactions between hybrid and water vapour. We investigate the mechanisms responsible for the conductivity increase by studying the DC and AC characteristics of two contact planar devices as a function of the relative humidity. The results of impedance spectroscopy measurements are interpreted by suitable equivalent circuits that allow us to study the dipendence of the different circuit components on relative humidity. On this base we discuss the device characteristics and suggest novel insights into humidity sensing properties of CH3NH3SnCl3 films

Photocatalytic activity of ZnO nanostructures grown by vapour and solution

Zinc oxide (ZnO) is one of the most studied functional materials in the last years because it matches the opportunity to be easily synthesized in nanocrystalline form (with different morphologies and by different growth techniques) with a very large number of possible applications in different fields (optoelectronics, photovoltaics, piezoelectric devices, gas-sensing and bio-sensing, photocatalysis, spintronics, nano power generators, cantilever production, etc.). In the present contribution we report on ZnO nanocrystalline structures, with the same wurtzite structure but different morphologies, synthesized by vapour-phase and by solution growth techniques. More in detail, ZnO nanotetrapods and nanopowders with different size have been obtained by a combination of metallic Zn thermal evaporation and controlled oxidation in a non-standard CVD (chemical vapour deposition) reactor where temperature have been set in the 450?C-650?C range. Other ZnO multi-branched nanostructures, resulting from aggregation or twinning of nanosized crystals, have been grown in aqueous solution of zinc salts and hexamine, in slightly alkaline medium below 100?C. Moreover, ZnO nanopowders have been obtained by thermal decomposition of a metallorganic gel precursor, resulting from dehydration of a zinc citrate solution. Different nanopowders samples have been prepared with different decomposition processes (time, temperature). ZnO nanostructures have been later on deposited on a photocatalysis-inert substrate (glass) from an alcoholic suspension at room temperature by forcing solvent evaporation and surface cleaning for a few minutes at 200?C in low vacuum. The obtained specimens are about 50 cm2 in size. All the ZnO nanostructure films are characterized by high porosity and high surface-to-volume ratios, which are generally basic requirements for the application in photocatalysis of gaseous species. The samples have been characterised by scanning electron microscopy and tested for photocatalytic degradation activity of airborne pollutant using a stirred flow photoreactor irradiated with UV-A. The measurements were carried out using ethylbenzene as organic target pollutant at concentration level typically found in ambient conditions. The samples demonstrated a good photocatalytic activity in the degradation of ethylbenzene in air

Sensitization of Metal Oxide Nanostructures by CH3NH3SnCl3 Hybrid Perovskite

Metal oxide nanostructures (NS) are attracting great interest due to the large variety of physical properties they present. Control of size, shape, surface, and assembly properties of nanoscale oxides are prerequisites to their implementation in technological devices as well as to the development of nanostructures modelled and designed to match the physical requirements of their applications. The achievement o