Organic ferroelectrics, in which the constituent molecules retain remanent polarization, represent an important topic in condensed-matter science, and their attractive properties, which include ...lightness, flexibility, and non-toxicity, are of potential use in state-of-the-art ferroelectric devices. However, the mechanisms for the generation of ferroelectricity in such organic compounds remain limited to a few representative concepts, which has hitherto severely hampered progress in this area. Here, we demonstrate that a bowl-to-bowl inversion of a relatively small organic molecule with a bowl-shaped π-aromatic core generates ferroelectric dipole relaxation. The present results thus reveal an unprecedented concept to produce ferroelectricity in small organic molecules, which can be expected to strongly impact materials science.
Ferroelectrics are used in a wide range of applications, including memory elements, capacitors and sensors. Recently, molecular ferroelectric crystals have attracted interest as viable alternatives ...to conventional ceramic ferroelectrics because of their solution processability and lack of toxicity. Here we show that a class of molecular compounds-known as plastic crystals-can exhibit ferroelectricity if the constituents are judiciously chosen from polar ionic molecules. The intrinsic features of plastic crystals, for example, the rotational motion of molecules and phase transitions with lattice-symmetry changes, provide the crystals with unique ferroelectric properties relative to those of conventional molecular crystals. This allows a flexible alteration of the polarization axis direction in a grown crystal by applying an electric field. Owing to the tunable nature of the crystal orientation, together with mechanical deformability, this type of molecular crystal represents an attractive functional material that could find use in a diverse range of applications.
Both of the two most common neurodegenerative disorders, namely Alzheimer's disease (AD) and Parkinson's disease (PD), have multiple lines of evidence from molecular and cellular to epidemiological, ...that nicotinic transmission is implicated in their pathogenesis. This review article presents evidence of nicotinic acetylcholine receptor (nAChR)-mediated protection against neurotoxicity induced by amyloid-β (Aβ), glutamate, rotenone, and 6-hydroxydopamine (6-OHDA) and the signal transduction involved in this mechanism. Our studies clarified that survival signal transduction, α7 nAChR-Src family-PI3 K-AKT pathway, and subsequent upregulation of Bcl-2 and Bcl-x, would lead to neuroprotection. In addition to the PI3 K-AKT pathway, two other survival pathways, JAK2/STAT3 and MEK/ERK, are proposed by other groups. These three survival pathways are related to each other through intracellular signal transductions in neurons. The JAK2/STAT3 pathway is cholinergic anti-inflammation pathway mediated by α7 nAChR on macrophage and microglia as well as neuron. Recently analyzing the properties of galantamine, we clarify the 4th independent neuroprotective pathway, which is mediated by enhancement of microglial α7 nAChR resulting in upregulation of Aβ phagocytosis. Galantamine sensitizes microglial α7 nAChRs to choline and induce Ca2+ influx into microglia. The Ca2+-induced intracellular signaling cascades may then stimulate Aβ phagocytosis through actin reorganization. The discovery of the 4th pathway would facilitate further investigation of possible nAChRs enhancing drugs targeting not only neuronal but also microglial nAChRs.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
We report the development of a molecular ferroelectric material inspired by the hexamethylenetetramine (hmta) non‐centrosymmetric molecular rotator. The bromide salt of diprotonated hmta (hmtaH2) ...crystalized as (hmtaH2)(NH4)Br3 in a metal‐free ABX3 perovskite‐type structure, in which the A and B sites are occupied by hmtaH22+ and ammonium cations, respectively. The compound crystallized in the Pma2 polar space group. A distorted polar perovskite structure formed owing to the distortion of {(NH4)Br6} octahedrons that are stabilized through the formation of NH⋅⋅⋅Br hydrogen bonds and the orientational ordering of positive charges on the non‐centrosymmetric hmtaH2 molecules. This spontaneous polarization exhibited ferroelectric behavior with a nominally high Curie temperature (>400 K), in which the electrical switching of polarization originates from the rotation of the hmtaH2 unit.
Perovskite ferroelectrics: A molecular ferroelectric material with a non‐centrosymmetric hexamethylenetetramine molecular rotator was developed through the fabrication of a metal‐free perovskite‐type structure.
Preparation of single-layer manganese oxide nanosheets (monosheets) comprised of edge-shared MnO6 octahedra has relied on multistep processing involving a high-temperature solid-state synthesis of ...bulk templates, and ion-exchange and exfoliation reactions in solutions, requiring high cost and long processing time. Here we demonstrate the first single-step approach to directly access the MnO2 monosheets, by the chemical oxidation of Mn2+ ions in the presence of tetramethylammonium cations in an aqueous solution. Of importance is that this template-free reaction readily proceeds within a day at room temperature. The ability of the MnO2 monosheets to self-assemble allows aggregation, to form layered structures with potassium cations and cationic tetrathiafulvalene analogues as intercalants. Furthermore, Langmuir−Blodgett (LB) films composed of the MnO2 monosheets were successfully fabricated by the LB deposition method, in which about one layer of the monosheets was deposited for each process.
High‐speed two‐photon microscopy can be used to analyze vascular dynamics in living animals and is essential for the understanding of brain diseases. Recent advances in fluorescent probes/optical ...systems have allowed successful imaging of the hippocampal vasculature in the deep brain of mice (1 mm from the brain surface) under low‐speed conditions (1–2 fps); however, using high‐speed techniques (>30 fps), observation of the deep‐brain vasculature is still challenging. Here, a new nanoemulsion that encapsulates thousands of red‐emissive pyrene dye molecules while maintaining their high two‐photon brightness 1.5 × 102 GM (GM = 10−50 cm4·s·photon−1·molecule−1) at 960 nm excitation and delivers a large amount of such pyrene dyes (65 nmol) into the blood vessels of mice is developed. Remarkably, the nanoprobe is found to exploit the inherent performance of a commonly used Ti:sapphire excitation laser and a sensitive gallium arsenide phosphide nondescanned fluorescence detector to the limit, enabling visualization of the brain vasculature under the cortex region of mice (up to 1.5 mm) under very low‐speed conditions. As a highlight, such a nanoprobe is successfully used to directly observe the blood flow in the hippocampal CA1 region (1.1 mm) through high‐speed resonant scanning (120 fps).
A novel dye‐loaded nanoemulsion is developed for high‐speed two‐photon microscopic imaging of the deep‐brain vasculature in mice. The nanoprobe delivers numerous bright pyrene dyes into the blood vessels of mice, fully exploiting the performance of a Ti:sapphire laser and a gallium arsenide phosphide detector. This approach allows the visualization of hippocampal blood flow in mice at above the video rate.
Optical properties of porphyrin derivatives were used to fabricate an artificial light-harvesting system. The introduction of a N–H···O hydrogen-bonding alkylamide chain (−CONHC n H2n+1) into a ...functional π-system is among the useful approaches to design multifunctional supramolecular assemblies. The tetraphenylporphyrin derivative bearing four −CONHC14H29 chains (1) shows the successive and reversible phase transition behavior of S1–S2 at 338 K, S2–Colr at 444 K, and Colr–I (isotropic liquid) at 564 K, where a fluidic discotic rectangular columnar (Colr) liquid crystal phase was observed in a wide temperature range of 444–564 K before melting. The one-dimensional columnar molecular assembly of (1)∞ was constructed using a simultaneous operation of N–H···O hydrogen-bonding and π-stacking interactions. Temperature (T)- and frequency (f)-dependent dielectric constants of 1 indicated characteristic dielectric enhancement at higher-T and lower-f conditions above 500 K because of the thermally activated motional freedom of the polar N–H···O hydrogen-bonding unit in the Colr phase. The polarization–electric field (P–E) curves at f = 0.1 Hz clearly indicated ferroelectric hysteresis behavior with a remanent polarization (P r) of 1 μC cm–2 and a coercive electric field (E c) of 2 V μm–1 at 503 K. The stable operation of the high-T ferroelectrics at approximately 500 K facilitates the potential application of a memory device in a high-T environment.
Optically induced rotation of an exfoliated fluorohectorite (FHT) in colloidal dispersion has been demonstrated. By illuminating a tightly focused circularly polarized laser beam of which power was ...higher than 5 mW with the wavelength at 532 nm, FHT with the in-plane area of 100 µm2 was rotated. While the rotational motion, FHT was optically trapped with maintaining its center of gravity position at the focal point. As the illuminated laser power increased, the rotation speed accelerated. The direction of rotation of the FHT could be switched by alternating the handedness of polarized light.
Alzheimer's disease (AD) is a common neurodegenerative disease that progressively impairs memory and cognition. Deposition of amyloid-β (Aβ) peptides is the most important pathophysiological hallmark ...of AD. Oxidative stress induced by generation of reactive oxygen species (ROS) is a prominent phenomenon in AD and known to occur early in the course of AD. Several reports suggest a relationship between change in redox status and AD pathology including progressive Aβ deposition, glial cell activation, and inflammation. Galantamine is an acetylcholinesterase inhibitor and has been reported to have an oxidative stress inhibitory function. In the present study, galantamine was administered orally to AD model mice from before the appearance of Aβ plaques (preplaque phase), and in vivo change in redox status of the brain was measured using electron paramagnetic resonance (EPR) imaging. Administration of galantamine from the preplaque phase ameliorated memory decline in Morris water maze test and novel object recognition test. Monitoring of the redox status of the brain using EPR imaging showed that galantamine treatment improved the unbalanced redox state. Additionally, galantamine administration enhanced microglial function to promote Aβ clearance, reducing the Aβ-positive area in the cortex and amount of insoluble Aβ in the brain. In contrast, galantamine treatment from the preplaque phase suppressed the production of proinflammatory cytokines through neurotoxic microglial activity. Therefore, galantamine administration from the preplaque phase may have the potential of clinical application for the prevention of AD. In addition, our results demonstrate the usefulness of EPR imaging for speedy and quantitative evaluation of the efficacy of disease-modifying drugs for AD.
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•Administration of galantamine from the preplaque phase ameliorated the cognitive decline of APPswe/PS1dE9 (APdE9) mice.•EPR imaging demonstrated improvement of redox state in APdE9 mice treated with galantamine from the preplaque phase.•Administration of galantamine from the preplaque phase reduced accumulation of amyloid-β peptides.•Administration of galantamine from the preplaque phase suppressed microglial activation and production of proinflammatory cytokines.
Guanidinium ( G + ) and benzene-1,4-disulfonate ( BDS 2− ) form a rigid electrostatic cation–anion crystal lattice, which undergoes an interesting dynamic structural reconstruction through guest ...adsorption–desorption processes with H 2 O, pyrrole (Pyrr), pyrazine (Pyz), thiophene (TP), pyridine (Py), 1,4-dioxane (Diox), or aniline (Ani). The host lattice of bis(guanidinium)benzene-1,4-disulfonate, ( G + ) 2 ( BDS 2− ), which does not contain void spaces initially, changed to host–guest crystals of ( G + ) 2 ( BDS 2− )·(guest) x upon guest adsorption ( x = 1, 2, and 3). The cation–anion electrostatic N–H + ⋯ − O 3 S– hydrogen bonds between the G + cation and BDS 2− dianion formed tightly bound two-dimensional (2D) structures. These layers are connected by perpendicular BDS 2− dianions, forming the guest adsorption crystalline pores. The adsorption–desorption isotherm for Diox at 298 K indicated the formation of ( G + ) 2 ( BDS 2− )·(Diox) 3 , which was consistent with the single-crystal X-ray structural analysis. Single crystals of ( G + ) 2 ( BDS 2− )·(Py–H 2 O) 2 consist of two hydrogen-bonded ( G + ) 2 ( BDS 2− ) 2 bilayers connected by the BDS 2− dianions, forming crystalline pores that accommodate 2 Py guest molecules. The H 2 O molecules in ( G + ) 2 ( BDS 2− )·(Py–H 2 O) 2 are lodged in the intralayer, leading to the ( G + ) 2 ( BDS 2− )⋯(H 2 O) 2 ⋯( G + ) 2 ( BDS 2− ) hydrogen-bonded bilayer. The electrostatic cation–anion host lattice of ( G + ) 2 ( BDS 2− ) responded to the guest adsorption–desorption cycle by a dynamic structural reconstruction. A guest adsorption of polar Ani into ( G + ) 2 ( BDS 2− ) host changed the crystal symmetry from centric P 1̄ to acentric P 2 1 of ( G + ) 2 ( BDS 2− )·(Ani) 3 .
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