scholarly journals Pathological transitions in myelin membranes driven by environmental and multiple sclerosis conditions

2018 ◽  
Vol 115 (44) ◽  
pp. 11156-11161 ◽  
Author(s):  
Rona Shaharabani ◽  
Maor Ram-On ◽  
Yeshayahu Talmon ◽  
Roy Beck
Keyword(s):  
Multiple Sclerosis ◽  
Phase Transition ◽  
Lipid Composition ◽  
Environmental Conditions ◽  
Structural Changes ◽  
Environmental Changes ◽  
Hexagonal Phase ◽  
Structural Phase ◽  
Structural Modifications ◽  
Transition Points

Multiple sclerosis (MS) is an autoimmune disease, leading to the destruction of the myelin sheaths, the protective layers surrounding the axons. The etiology of the disease is unknown, although there are several postulated environmental factors that may contribute to it. Recently, myelin damage was correlated to structural phase transition from a healthy stack of lamellas to a diseased inverted hexagonal phase as a result of the altered lipid stoichiometry and low myelin basic protein (MBP) content. In this work, we show that environmental conditions, such as buffer salinity and temperature, induce the same pathological phase transition as in the case of the lipid composition in the absence of MBP. These phase transitions have different transition points, which depend on the lipid’s compositions, and are ion specific. In extreme environmental conditions, we find an additional dense lamellar phase and that the native lipid composition results in similar pathology as the diseased composition. These findings demonstrate that several local environmental changes can trigger pathological structural changes. We postulate that these structural modifications result in myelin membrane vulnerability to the immune system attacks and thus can help explain MS etiology.

scholarly journals Crystal structures of 2D coordination networks in [M(bbtr)3](ClO4)2(M=Mn, Cd)

2014 ◽  
Vol 70 (a1) ◽  
pp. C1361-C1361
Author(s):  
Joachim Kusz ◽  
Maria Nowak ◽  
Robert Bronisz ◽  
Grzegorz Szklarz
Keyword(s):  
Phase Transition ◽  
Structural Phase Transition ◽  
Structural Changes ◽  
Structural Phase ◽  
Cooling Mode ◽  
Structural Modifications ◽  
Polymeric Networks ◽  
Polymeric Layer ◽  
Higher Temperature

[Fe(bbtr)3](ClO4)2 (bbtr=1,4-di(1,2,3-triazol-1-yl)butane) represents a spin crossover (SCO) system where the first coordination sphere consists of 1,2,3-triazole rings coordinated by exodentate nitrogen atoms [1]. Iron(II) ion is linked to six other iron(II) ions by bbtr ligands. This creates two dimensional (2D) polymeric layers. SCO is abrupt, accompanied by hysteresis loop. In the cooling mode P-3 -> P-1 structural phase transition precedes SCO. The non-magnetic structural transformation is accompanied by reorganization of weak intermolecular interactions and shift of 2D layers with respect to each other. Surprisingly, an analog [Fe(bbtr)3](BF4)2, does not exhibit in cooling mode neither thermally SCO nor structural phase transition [2]. To clarify the role of structural phase transition on SCO we have performed structural modifications by exchanging the kind of anions and/or metal ions. An exchange of perchlorate on triflate anion involves deeper structural changes. A topology of the polymeric layer remains the same, but the SCO is shifted to higher temperature and structural phase transition is not observed. The studies of isostructural zinc(II) analogs confirmed the crucial role of anion in the occurrence of non-magnetic structural phase transition. The [Zn(bbtr)3](ClO4)2 exhibites P-3 -> P-1 structural phase transition which is not present in tetrafluoroborate analog [2]. We expand studies on other hexacoordinating metal(II) ions. Reactions between manganese(II) or cadmium(II) perchlorates and bbtr in acetonitrile lead to [M(bbtr)3](ClO4)2 (M=Mn, Cd) complexes. Single crystal X-ray diffraction studies revealed that both compounds create a 2D polymeric networks. The temperature dependence of lattice parameters for these complexes showed that, in contrast to [Fe(bbtr)3](ClO4)2 and [Zn(bbtr)3](ClO4)2 systems, the structural phase transition is not present. This work was funded by the Polish National Science Centre Grant No. DEC-2011/01/B/ST5/06311.

The Hexagonal ↔ Orthorhombic Structural Phase Transition in Claringbullite, Cu4FCl(OH)6

2021 ◽  
Author(s):  
Mark D. Welch ◽  
Jens Najorka ◽  
Michael S. Rumsey ◽  
John Spratt
Keyword(s):  
Phase Transition ◽  
Data Storage ◽  
Structural Phase Transition ◽  
Structural Changes ◽  
Structural Phase ◽  
Magnetic Behavior ◽  
Orthorhombic Phase ◽  
New Mineral ◽  
Storage Devices ◽  
Definition Of

ABSTRACT Frustrated magnetic phases have been a perennial interest to theoreticians wishing to understand the energetics and behavior of quasi-chaotic systems at the quantum level. This behavior also has potentially wide applications to developing quantum data-storage devices. Several minerals are examples of such phases. Since the definition of herbertsmithite, Cu3ZnCl2(OH)6, as a new mineral in 2004 and the rapid realization of the significance of its structure as a frustrated antiferromagnetic phase with a triangular magnetic lattice, there has been intense study of its magnetic properties and those of synthetic compositional variants. In the past five years it has been recognized that the layered copper hydroxyhalides barlowite, Cu4BrF(OH)6, and claringbullite, Cu4FCl(OH)6, are also the parent structures of a family of kagome phases, as they also have triangular magnetic lattices. This paper concerns the structural behavior of claringbullite that is a precursor to the novel frustrated antiferromagnetic states that occur below 30 K in these minerals. The reversible hexagonal (P63/mmc) ↔ orthorhombic (Pnma or Cmcm) structural phase transition in barlowite at 200−270 K has been known for several years, but the details of the structural changes that occur through the transition have been largely unexplored, with the focus instead being on quantifying the low-temperature magnetic behavior of the orthorhombic phase. This paper reports the details of the structural phase transition in natural claringbullite at 100−293 K as studied by single-crystal X-ray diffraction. The transition temperature has been determined to lie between 270 and 293 K. The progressive disordering of Cu at the unusual trigonal prismatic Cu(OH)6 site on heating is quantified through the phase transition for the first time, and a methodology for refining this disorder is presented. Key changes in the behavior of Cu(OH)4Cl2 octahedra in claringbullite have been identified that suggest why the Pnma structure is likely stabilized over an alternative Cmcm structure. It is proposed that the presence of a non-centrosymmetric octahedron in the Pnma structure allows more effective structural relaxation during the phase transition than can be achieved by the Cmcm structure, which has only centrosymmetric octahedra.

scholarly journals First Principles Study of Electronic Structure and Magnetic Properties of TMH (TM = Cr, Mn, Fe, Co)

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
S. Kanagaprabha ◽  
R. Rajeswarapalanichamy ◽  
K. Iyakutti
Keyword(s):  
Phase Transition ◽  
Magnetic Properties ◽  
Electronic Structure ◽  
First Principles ◽  
Local Density ◽  
Hexagonal Phase ◽  
Structural Phase ◽  
Tight Binding ◽  
Transition Metal Hydrides ◽  
Lmto Method

First principles calculations are performed using a tight-binding linear muffin-tin orbital (TB-LMTO) method with local density approximation (LDA) and atomic sphere approximation (ASA) to understand the electronic properties of transition metal hydrides (TMH) (TM = Cr, Mn, Fe, Co). The structural property, electronic structure, and magnetic properties are investigated. A pressure induced structural phase transition from cubic to hexagonal phase is predicted at the pressures of 50 GPa for CrH and 23 GPa for CoH. Also, magnetic phase transition is observed in FeH and CoH at the pressures of 10 GPa and 180 GPa, respectively.

TEM Analysis of Structural Phase Transition in MBE Grown Cubic InN on MgO (001) by MBE: Effect of Hexagonal Phase Inclusion in an C-Gan Nucleation Layer

2012 ◽  
Vol 229-231 ◽  
pp. 219-222
Author(s):  
Jamreonta Parinyataramas ◽  
Sakuntam Sanorpim ◽  
Chanchana Thanachayanont ◽  
Hiroyaki Yaguchi ◽  
Misao Orihara
Keyword(s):  
Phase Transition ◽  
Structural Phase Transition ◽  
High Power ◽  
Hexagonal Phase ◽  
Structural Phase ◽  
Low Latency ◽  
Tem Analysis ◽  
Nucleation Layer ◽  
Mesh Topology ◽  
Higher Power

In this paper, we introduced dbcube topology for Network-on Chips(NoC). We predicted the dbcube topology has high power and low latency comparing to other topologies, and in particular mesh topology. By using xmulator simulator,we compared power and latency of this topologyto mesh topology. Finally, it is demonstrated that the network has higher power and lower latency than the mesh topology.

An unprecedented structural phase transition in struvite-type compounds: dimorphism of KMgAsO4(H2O)6

2019 ◽  
Vol 74 (1) ◽  
pp. 9-14
Author(s):  
Matthias Weil
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Diffraction Data ◽  
Structural Changes ◽  
Structural Phase ◽  
X Ray Diffraction ◽  
Hydrogen Atoms ◽  
X Ray ◽  
Continuous Type ◽  
Reversible Phase Transition

AbstractThe crystal structure of struvite-type KMgAsO4(H2O)6 has been redetermined from single crystal X-ray diffraction data at room temperature. The previous structure model based on powder X-ray diffraction data was confirmed with higher precision and accuracy and with all hydrogen atoms located. KMgAsO4(H2O)6 undergoes a reversible phase transition of the continuous type at 263(2) K, changing the symmetry from orthorhombic to monoclinic. The corresponding Pnm21→P1121 symmetry reduction is of a translationengleiche type with index 2 and was monitored by temperature-dependent powder X-ray diffraction measurements. Such a phase transition is unprecedented for struvite-type compounds. The crystal structure of the monoclinic polymorph was determined from a two-domain crystal at 100 K. Except for the motion of one of the water molecules towards stronger hydrogen-bonding interactions, structural changes between the two polymorphs are small.

Thermal Annealing Influence on Magnetic and Structural Properties of Cu56Ga28Mn16 Microwires

2009 ◽  
Vol 1200 ◽  
Author(s):  
Víctor Prida ◽  
Victor Vega ◽  
Jose Sanchez Llamazares ◽  
Maria L Sanchez ◽  
Jesus D Santos ◽  
...  
Keyword(s):  
Phase Transition ◽  
Structural Properties ◽  
Thermal Annealing ◽  
Hexagonal Phase ◽  
Structural Phase ◽  
Major Phase ◽  
Structure Morphology ◽  
B2 Phase ◽  
The One ◽  
Thermomagnetic Properties

AbstractWe report on the crystalline structure, morphology and thermomagnetic properties of glass-coated magnetic microwires with Cu56Ga28Mn16 composition, as well as the thermal annealing influence on its magneto-structural properties. As-cast CuMnGa microwires exhibit a majority cubic B2 phase, and upon annealing at temperatures up to 573 K a new hexagonal phase appears coexisting with the cubic B2 major phase. Thermal annealing treatments also shift the Curie temperature about 150 K with respect to the one for the as-cast microwire. Furthermore, the signature of a structural phase transition is observed for the microwire annealed at 523 K

Effect of lipid structural modifications on their intermolecular hydrogen bonding interactions and membrane functions

1986 ◽  
Vol 64 (1) ◽  
pp. 50-57 ◽  
Author(s):  
Joan M. Boggs
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Membrane Proteins ◽  
Lipid Composition ◽  
Hexagonal Phase ◽  
Ionization State ◽  
Hydrophobic Residues ◽  
Structural Modifications ◽  
Hydrogen Bonding Interactions ◽  
Head Groups

The large number of different membrane lipids with various structural modifications and properties and the characteristic lipid composition of different types of membranes suggest that different lipids have specific functions in the membrane. Many of the varying properties of lipids with different polar head groups and in different ionization states can be attributed to the presence of interactive or repulsive forces between the head groups in the bilayer. The interactive forces are hydrogen bonds between hydrogen bond donating groups such as —P—OH, —OH, and —NH3+ and hydrogen bond accepting groups such as —P—O− and —COO−. These interactions increase the lipid phase transition temperature and can account for the tendency of certain lipids to go into the hexagonal phase and the dependence of this tendency on the pH and ionization state of the lipid. The presence or absence of these interactions can also affect the penetration of hydrophobic substances into the bilayer, including hydrophobic residues of membrane proteins. Evidence for this suggestion has been gathered from studies of the myelin basic protein, a water-soluble protein with a number of hydrophobic residues. In this way the lipid composition can affect the conformation and activity of membrane proteins. Since hydrogen-bonding interactions depend on the ionization state of the lipid, they can be altered by changes in the environment which affect the pK of the ionizable groups. The formation of the hexagonal phase or inverted micelles, the conformation and activity of membrane proteins, and other functions mediated by lipids could thus be regulated in this way.

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