Seiichiro Higashiya

Genetic engineering combined with deep UV resonance Raman spectroscopy for structural characterization of amyloid-like fibrils.

Elucidating the structure of the cross-beta core in large amyloid fibrils is a challenging problem in modern structural biology. For the first time, a set of de novo polypeptides was genetically engineered to form amyloid-like fibrils with similar morphology and yet different strand length. Differential ultraviolet Raman spectroscopy allowed for separation of the spectroscopic signatures of the highly ordered beta-sheet strands and turns of the fibril core. The relationship between Raman frequencies and Ramachandran dihedral angles of the polypeptide backbone indicates the nature of the beta-sheet and turn structural elements.

Structural investigations of copper(II) complexes containing fluorine-substituted β-diketonate ligands

Abstract The crystal structures of the β-diketonate complexes Cu(pta)2, Cu(pta)2·EtOH, and Cu(F6-thd)2 (where pta is the anion of 1,1,1-trifluoro-5,5-dimethylhexane-2,4-dione and F6-thd is the anion of 2,2-bis(trifluoromethyl)-6,6-dimethylheptane-3,5-dione) were determined. The solid-state structures of Cu(pta)2 and Cu(F6-thd)2 are square planar, while Cu(pta)2·EtOH is approximately square pyramidal with the EtOH ligand occupying the apical position. In each case, only one geometrical isomer (cis or trans) was observed in the crystals; arguments are presented that both isomers are present in bulk samples. Calculations of molecular volumes for structurally related Cu(II) complexes containing non-fluorinated versus fluorinated ancillary ligands show that fluorine substitution does not significantly affect packing efficiency in the solid-state; however, solvent coordination decreases packing efficiency slightly. [Cu(tdf)(py)(μ-C3F7CO2)]2 (where tdf is the anion of 1,1,1,2,2,3,3,7,7,8,8,9,9,9-tetradecafluorononane-4,6-dionate), a derived impurity from preparations of Cu(tdf)2, was isolated in low yield. The copper coordination geometries in the centrosymmetric structure are intermediate between square pyramidal and trigonal bipyramidal, with two unsymmetrically bridging μ,η1:η1-C3F7CO2 ligands.

The indium-mediated Reformatsky reactions of 2,2-difluoro-2-halo-1-furan-2-yl ethanones in aqueous media

Abstract New 2,2-difluoro 2-halo-1-furan-2-yl ethanones (1a–c) were synthesized by two different methods. The Reformatsky reactions of 2,2-difluoro-2-halo-1-furan-2-yl ethanones with various aldehydes using indium metal in aqueous media gave α,α-difluoro-β-hydroxy ketones (4a–j).

Fibrillation mechanism of a model intrinsically disordered protein revealed by 2D correlation deep UV resonance Raman spectroscopy.

Understanding of numerous biological functions of intrinsically disordered proteins (IDPs) is of significant interest to modern life science research. A large variety of serious debilitating diseases are associated with the malfunction of IDPs including neurodegenerative disorders and systemic amyloidosis. Here we report on the molecular mechanism of amyloid fibrillation of a model IDP (YE8) using 2D correlation deep UV resonance Raman spectroscopy. YE8 is a genetically engineered polypeptide, which is completely unordered at neutral pH yet exhibits all properties of a fibrillogenic protein at low pH. The very first step of the fibrillation process involves structural rearrangements of YE8 at the global structure level without the detectable appearance of secondary structural elements. The formation of β-sheet species follows the global structural changes and proceeds via the simultaneous formation of turns and β-strands. The kinetic mechanism revealed is an important new contribution to understanding of the general fibrillation mechanism proposed for IDP.

Synthesis of fluorinated α-sila-β-diketones and their copper(II) complexes

Abstract Fluorinated α-sila-β-diketones, synthesized in good yields via the Claisen condensation of the esters of fluorinated acids or fluorinated acid fluorides and the lithium enolates of acetyltrialkylsilanes, were employed in the preparation of volatile copper complexes for copper metallization. The thermal properties of the corresponding copper(II) complexes were determined by TGA and DSC to evaluate the potential of these materials as copper metal–organic chemical vapor deposition (MOCVD) precursors; the new copper compounds have greater volatility and stability than the corresponding copper complexes of non-fluorinated α-sila-β-diketonates.

Facile synthesis of a novel class of organometalloid-containing ligands, the sila-β-diketones: preparation and physical and structural characterization of the copper(II) complexes, Cu[R′C(O)CHC(O)SiR3]2

Abstract The substitution of a carbon atom by silicon provides an attractive, novel approach to modification of the thermal stability and volatility of metal-organic chemical vapor deposition precursors supported by β-diketonate ancillary ligands. The low temperature reaction of the lithium enolates of acetyltrialkylsilanes with acyl chlorides affords the sila-β-diketones, R′C(O)CH 2 C(O)SiR 3 (R′=Me, Et, n -Pr, i -Pr, n -Bu, i -Bu, s -Bu, t -Bu; SiR 3 =SiMe 3 , SiEt 3 , SiMe 2 ( t -Bu), SiMe 2 ( t -hexyl), Si( i -Pr) 3 ), in good yields. Multinuclear NMR studies suggest that the sila-β-diketones exist as the enolic tautomer with a vinylsilane isomeric structure. Homoleptic Cu(II) sila-β-diketonate complexes were prepared in a first pass study to evaluate how precursor performance is affected by modulation of the peripheral substituents in the ligands. Thermal analyses, (TGA, DSC) show that the silylated Cu(II) precursors (SiR 3 =SiMe 3 ; R′= t -Bu or i -Bu) have greater volatility than the corresponding carbon analogues. Some of the new Cu(II) complexes exist as liquids or low melting solids, which are preferred states for industrial deposition processes. X-ray diffraction studies of selected copper complexes showed them to have typical, square planar geometry; calculations of molecular volumes suggest that packing in the solid-state is less efficient for the silicon-containing complexes than for the non-silylated analogues.

Charge Distribution and Amyloid Fibril Formation: Insights from Genetically Engineered Model Systems

The influence of electrostatic interactions on protein amyloidogenesis has been investigated using de novo designed repetitive polypeptides YEHK21 [GH6[(GA)3GY(GA)3GE(GA)3GY(GA)3GE]21GAH6] and YE8 [GH6[(GA)3GY(GA)3GE]8GAH6]. The beta-sheet forming polypeptides were designed with identical beta-strands but with variable substitution at the turns that enable precise location of charged residues (Topilina et al. Biopolymers 2007, 86 (4), 261-264; Topilina et al. Biopolymers 2010, submitted for publication; Topilina et al. Biomacromolecules 2006, 7 (4), 1104-11). Solubility, folding, and aggregation of YEHK21 and YE8 were shown to be controlled by charge distribution. Under those conditions favoring the development of charge, YEHK21 and YE8 have significant propensities to form intermolecular beta-sheet assemblies illustrating the potential of charged polypeptide chains to form ordered amyloid aggregates even in the absence of additional environmental factors such as the presence of polyelectrolytes, salts, and so on.

Indium-mediated allylation reaction of difluoroacetyltrialkylsilanes in aqueous media

Indium-mediated allylations of difluoroacetyltrialkylsilanes in aqueous media give homoallylic alcohols exclusively. The common Brook rearrangement C- to O-silyl group migration is totally suppressed with no detectable formation of enol silyl ethers. The influence of water on the allylation reaction is also described.

Reactions of novel mono- and difluoroacetyltrialkylsilanes with sulfur and phosphorus ylides

Abstract The reactions of difluoroacetyltrialkylsilanes with methylidene triphenylphosphorane and benzylidene triphenylphosphorane are affected by the nature of the silyl substituents giving either the enol silyl ether or normal Wittig product exclusively, or mixture of both. Reactions with Horner–Emmons type ylide gave only the alkene products. Reactions of mono- and difluoroacetyltrialkylsilanes with dimethylsulfoxonium methylide gave the enol silyl ether products exclusively. Conversion of an enol silyl ether to an epoxide was effected with m -CPBA.

Eutectic Mixtures of Ionic Liquids Electrolytes for Electric Double Layer Capacitors

Eutectic mixtures of oxygen-containing spirobipyrrolidiniumbased ionic liquids were investigated as prospective room temperature ionic liquid electrolytes (RTILs) for supercapacitor application. These in-house developed novel ionic liquids (IL) possess wide voltage window (6-7 V) and solubility (3-5.5 M) in conventional solvents, such as acetonitrile and propylene carbonate. The potential window of mixed RTIL was about 5.5 V (at 50 μA/cm threshold). The RTIL mixtures exhibit higher breakdown potential (> 4.6 V) as compared to conventional molecular solvent (acetonitrile)-based cells (~4.0 V) in supercapacitor tests. However, these RTIL mixtures (neat, i.e. w/o any solvent addition) lead to high equivalent series resistance (ESR) initiating around 3.9 V and lower capacitance. Cycling of the negative electrode at 4.6 V led to degradation of the active carbon material, while the positive electrode maintained its integrity.