Metal-catalyzed oxidative damage and oligomerization of the amyloid-β peptide of Alzheimer’s disease

The most common form of dementia in old age is Alzheimer’s disease (AD). The presence in the brain of senile plaque is the major pathological marker of AD. The plaques are primarily composed of aggregated amyloid-β peptide (Aβ). Aβ is a 40–42 amino acid peptide that is a proteolytic product derived from the β-amyloid precursor protein. The function of Aβ and the exact mechanism of Aβ aggregation and neurotoxicity are unclear. However, metal coordination by Aβ plays an important role in inducing aggregation and the generation of reactive oxygen species, which appears to be at least partially responsible for Aβ neurotoxicity. In this review we examine the role of copper and zinc ions in Aβ neurotoxicity, especially with regards to the generation of free radicals. We discuss the role of copper or zinc ions in oxidative damage and Aβ conformational changes and the relationship of these metals to AD.

A 13C NMR study of the role of plasticizers in the conduction mechanism of solid polymer electrolytes

The addition of low molecular weight solvents such as dimethyl formamide (DMF) and propylene carbonate (PC) to urethane crosslinked polyethers results in enhancement of polymer segmental motion, as determined in this work from polymer ¹³C spin lattice relaxation measurements (T₁) and glass transition temperatures. The formation of salt-polyether complexes results in a decrease in T₁, even in the presence of the plasticizer, indicating that the polymer ether molecules are still involved in the alkali metal coordination. In a polymer electrolyte containing 1 mol kg⁻¹ LiClO₄ the addition of DMF and PC have significantly different affects on the polymer mobility, although they both enhance the conductivity. The conductivity enhancement therefore is not solely the result of an increased solvent mobility.

Rare earth 3-(4′-hydroxyphenyl)propionate complexes

The reaction of lanthanoid chlorides or nitrates with sodium 3-(4′-hydroxyphenyl)propionate (Na4hpp) in methanol or water has yielded complexes [La4(4hpp)12(H2O)6]·4H2O·MeOH (1), [Ce2(4hpp)6(H2O)3]·(H2O)·2.5(EtOH) (2a) (after crystallization from ethanol), [Ho(4hpp)3(H2O)2] (5), [Er(4hpp)3(H2O)2]·1.5(H2O) (6), and [Lu(4hpp)3]·H2O crystal composition (7), as well as heterobimetallics [NaCe2(4hpp)7(H2O)2]·3(H2O) (2b), [NaPr2(4hpp)7(H2O)2]·3(H2O) (3), and [NaNd2(4hpp)7(H2O)(MeOH)]·(H2O)·3(MeOH) (4). The structures of homometallic complexes 1, 2a, 6, and 7 reveal one-dimensional coordination polymers and vividly illustrate the effect of lanthanoid contraction with a decline in coordination numbers in the series from 9-11 (1), 9,10 (2a), 8 (6) to 7 (7) through variations in carboxylate coordination and ligation of water. Bimetallic complexes 2a and 4 each exhibit five different carboxylate binding modes as well as coordination of the 4-OH substituent of 4hpp to sodium thereby linking 1D polymer chains into a 2D network with both 9 and 10 coordinate Ln atoms and 6 coordinate sodium. Bulk products after drying lose solvent of crystallization in some cases (2a, 6), or exchange MeOH for water (4). X-ray powder diffraction indicates that bulk 2b and 3 are isotypic, as are bulk 5 and 6. In contrast to the excellent corrosion protection of lanthanum 4-hydroxycinnamate, compound 1 is ineffective in preventing the corrosion of mild steel, thereby establishing the importance of the -CHCH- structural unit of the former in its anti-corrosion properties. However the flexible -CH2-CH2- chain of the 4hpp ligand enables the crystal engineering of its lanthanoid complexes in a wide variety of structures as well as effective crystallization for structure determination, whereas the analogous 4-hydroxycinnamates have so far evaded structural characterization except for Ln = La, Ce owing to crystallization problems.

Patterned growth of carbon nanotubes on Si substrates without predeposition of metal catalysts

Aligned carbon nanotubes (CNTs) can be readily synthesized on quartz or silicon-oxide-coated Si substrates using a chemical vapor deposition method, but it is difficult to grow them on pure Si substrates without predeposition of metal catalysts. We report that aligned CNTs were grown by pyrolysis of iron phthalocyanine at 1000 °C on the templates created on Si substrates with simple mechanical scratching. Scanning electron microscopy and x-ray energy spectroscopy analysis revealed that the trenches and patterns created on the surface of Si substrates were preferred nucleation sites for nanotube growth due to a high surface energy, metastable surface structure, and possible capillarity effect. A two-step pyrolysis process maintained Fe as an active catalyst.

pH-detachable polymer brushes formed using titanium−diol coordination chemistry and living radical polymerization (RAFT)

pH-detachable poly(styrene) brushes formed on indium−tin oxide (ITO) glass substrates using metal complex chemistry and reversible addition−fragmentation chain transfer (RAFT) polymerization was described. These pH-detachable polymeric brushes were generated using both “graft-from” and “graft-to” methodologies. The methodologies involved either the surface self-assembly of catechol-functional RAFT agents (graft-from) or catechol-terminal polymer chains (graft-to) onto the ITO substrate via titanium−diol coordination. The stepwise functionalization of the ITO glass surfaces was characterized successfully using X-ray photoelectron spectroscopy (XPS) and contact angle measurement. Poly(styrene) brushes generated using the “graft-from” method were denser than those generated using the “graft-to” method, as exemplified by atom force microscopy (AFM) and quantified using cyclic voltammetry. Poly(styrene) brushes assembled using both methods could be detached easily by manipulating the pH of the brush environment. Cyclic voltammetry was utilized to calculate precisely the surface coverage of the RAFT functionality and polymeric brush density.

Hydrogen evolution by a metal-free electrocatalyst

Electrocatalytic reduction of water to molecular hydrogen via the hydrogen evolution reaction may provide a sustainable energy supply for the future, but its commercial application is hampered by the use of precious platinum catalysts. All alternatives to platinum thus far are based on nonprecious metals, and, to our knowledge, there is no report about a catalyst for electrocatalytic hydrogen evolution beyond metals. Here we couple graphitic-carbon nitride with nitrogen-doped graphene to produce a metal-free hybrid catalyst, which shows an unexpected hydrogen evolution reaction activity with comparable overpotential and Tafel slope to some of well-developed metallic catalysts. Experimental observations in combination with density functional theory calculations reveal that its unusual electrocatalytic properties originate from an intrinsic chemical and electronic coupling that synergistically promotes the proton adsorption and reduction kinetics.

Physicochemical properties of N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide for sodium metal battery applications.

The physicochemical properties of a range of NaNTf2 (or NaTFSI) salt concentrations in N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (or C3mpyrFSI) ionic liquid were investigated by DSC, conductivity, cyclic voltammetry and diffusivity studies. Cyclic voltammetry indicated a stable sodium plating behavior with a current of 5 mA cm(-2) at 25 °C to 20 mA cm(-2) at 100 °C, along with high reversibility identifying this electrolyte as a possible candidate for sodium-ion or sodium metal battery applications. (23)Na NMR chemical shifts and spectral linewidths (FWHM) indicate a complex coordination of the Na(+) ion which is dependent on both temperature and salt concentration with an apparently stronger coordination to the NTf2 anion upon increasing the NaNTf2 concentration. Temperature dependent PFG-NMR diffusion measurements show that both FSI and NTf2 have a comparable behaviour although the smaller FSI anion is more diffusive.

Exploring zinc coordination in novel zinc battery electrolytes

The coordination of zinc ions by tetraglyme has been investigated here to support the development of novel electrolytes for rechargeable zinc batteries. Zn(2+) reduction is electrochemically reversible from tetraglyme. The spectroscopic data, molar conductivity and thermal behavior as a function of zinc composition, between mole ratios [80 : 20] and [50 : 50] [tetraglyme : zinc chloride], all suggest that strong interactions take place between chloro-zinc complexes and tetraglyme. Varying the concentration of zinc chloride produces a range of zinc-chloro species (ZnClx)(2-x) in solution, which hinder full interaction between the zinc ion and tetraglyme. Both the [70 : 30] and [50 : 50] mixtures are promising electrolyte candidates for reversible zinc batteries, such as the zinc-air device.

Sulfur-doped porous reduced graphene oxide hollow nanosphere frameworks as metal-free electrocatalysts for oxygen reduction reaction and as supercapacitor electrode materials.

Chemical doping with foreign atoms is an effective approach to significantly enhance the electrochemical performance of the carbon materials. Herein, sulfur-doped three-dimensional (3D) porous reduced graphene oxide (RGO) hollow nanosphere frameworks (S-PGHS) are fabricated by directly annealing graphene oxide (GO)-encapsulated amino-modified SiO2 nanoparticles with dibenzyl disulfide (DBDS), followed by hydrofluoric acid etching. The XPS and Raman spectra confirmed that sulfur atoms were successfully introduced into the PGHS framework via covalent bonds. The as-prepared S-PGHS has been demonstrated to be an efficient metal-free electrocatalyst for oxygen reduction reaction (ORR) with the activity comparable to that of commercial Pt/C (40%) and much better methanol tolerance and durability, and to be a supercapacitor electrode material with a high specific capacitance of 343 F g(-1), good rate capability and excellent cycling stability in aqueous electrolytes. The impressive performance for ORR and supercapacitors is believed to be due to the synergistic effect caused by sulfur-doping enhancing the electrochemical activity and 3D porous hollow nanosphere framework structures facilitating ion diffusion and electronic transfer.

Silver nanoparticles prepared by gamma irradiation across metal-organic framework templates

In this study, we demonstrate for the first time the successful fabrication of well-dispersed ultrafine silver nanoparticles inside metal-organic frameworks through a single step gamma irradiation at room temperature. HKUST-1 crystals are soaked in silver nitrate aqueous solution and irradiated with a Cobalt 60 source across a range of irradiation doses to synthesize highly uniformly distributed silver nano-particles. The average size of the silver nanoparticles across the Ag@HKUST-1 materials is found to vary between 1.4 and 3 nm for dose exposures between 1 and 200 kGy, respectively. The Ag@HKUST-1 hybrid crystals exhibit strong surface plasmon resonance and are highly durable and efficient catalytic materials for the reduction of 4-nitrophenol to 4-aminophenol (up to 14.46 × 10-3 s-1 for 1 kGy Ag@HKUST-1). The crystals can be easily recycled for at least five successive cycles of reaction with a conversion efficiency higher than 99.9%. The gamma irradiation is demonstrated to be an effective and environmental friendly process for the synthesis of nano-particles across confined metal-organic frameworks at room temperature with potential applications in environmental science.

Annihilation electrogenerated chemiluminescence of mixed metal chelates in solution : Modulating emission colour by manipulating the energetics

We demonstrate the mixed annihilation electrogenerated chemiluminescence of tris(2,2′-bipyridine)ruthenium(ii) with various cyclometalated iridium(iii) chelates. Compared to mixed ECL systems comprising organic luminophores, the absence of T-route pathways enables effective predictions of the observed ECL based on simple estimations of the exergonicity of the reactions leading to excited state production. Moreover, the multiple, closely spaced reductions and oxidations of the metal chelates provide the ability to finely tune the energetics and therefore the observed emission colour. Distinct emissions from multiple luminophores in the same solution are observed in numerous systems. The relative intensity of these emissions and the overall emission colour are dependent on the particular oxidized and reduced species selected by the applied electrochemical potentials. Finally, these studies offer insights into the importance of electronic factors in the question of whether the reduced or oxidized partner becomes excited in annihilation ECL. This journal is

Insights into the transport of alkali metal ions doped into a plastic crystal electrolyte

The application of organic ionic plastic crystals (OIPCs) as a new class of solid electrolyte for energy storage devices such as lithium batteries and, more recently, sodium batteries is attracting increasing attention. Key to this is achieving sufficient target ion transport through the material. This requires fundamental understanding of the structure and dynamics of OIPCs that have been doped with the necessary lithium or sodium salts. Here we report, for the first time, the atomic level structure and transport of both lithium and sodium ions in the plastic crystalline phases of an OIPC diethyl(methyl)(isobutyl)phosphonium hexafluorophosphate. These molecular dynamics simulations reveal two types of coordination geometries of the alkali metal ion first solvation shells, which cooperate closely with the metal ion hopping motion. The significantly different ion migration rates between two metal ion doped systems could also be related to the differences in solvation structures.

Elucidation of transport mechanism and enhanced alkali ion transference numbers in mixed alkali metal-organic ionic molten salts

Mixed salts of Ionic Liquids (ILs) and alkali metal salts, developed as electrolytes for lithium and sodium batteries, have shown a remarkable ability to facilitate high rate capability for lithium and sodium electrochemical cycling. It has been suggested that this may be due to a high alkali metal ion transference number at concentrations approaching 50 mol% Li(+) or Na(+), relative to lower concentrations. Computational investigations for two IL systems illustrate the formation of extended alkali-anion aggregates as the alkali metal ion concentration increases. This tends to favor the diffusion of alkali metal ions compared with other ionic species in electrolyte solutions; behavior that has recently been reported for Li(+) in a phosphonium ionic liquid, thus an increasing alkali transference number. The mechanism of alkali metal ion diffusion via this extended coordination environment present at high concentrations is explained and compared to the dynamics at lower concentrations. Heterogeneous alkali metal ion dynamics are also evident and, somewhat counter-intuitively, it appears that the faster ions are those that are generally found clustered with the anions. Furthermore these fast alkali metal ions appear to correlate with fastest ionic liquid solvent ions.

Desymmetrization of an octahedral coordination complex Inside a self-assembled exoskeleton

The synthesis of a centrally functionalized, ribbon-shaped [6]polynorbornane ligand L that self-assembles with PdII cations into a (Pd2L4) coordination cage is reported. The shape-persistent (Pd2L4) cage contains two axial cationic centers and an array of four equatorial H-bond donors pointing directly towards the center of the cavity. This precisely defined supramolecular environment is complementary to the geometry of classic octahedral complexes [M(XY)6] with six diatomic ligands. Very strong binding of [Pt(CN)6]2- to the cage was observed, with the structure of the host-guest complex ([Pt(CN)6]@Pd2L4) supported by NMR spectroscopy, MS, and X-ray data. The self-assembled shell imprints its geometry on the encapsulated guest, and desymmetrization of the octahedral platinum species by the influence of the D4h-symmetric second coordination sphere was evidenced by IR spectroscopy. [Fe(CN)6]3- and square-planar [Pt(CN)4]2- were strongly bound. Smaller octahedral anions such as [SiF6]2-, neutral carbonyl complexes ([M(CO)6]; M=Cr, Mo, W) and the linear [Ag(CN)2]- anion were only weakly bound, showing that both size and charge match are key factors for high-affinity binding.