Safety evaluation of rechargeable cells with lithium metal anodes and amorphous V2O5 cathodes

Rechargeable cells with lithium metal anodes have a very large theoretical energy density and are a promising cell system. However, rechargeable lithium metal cells are not yet currently commercially available. One of the biggest problems with the cells is the poor safety aspect resulting from the high chemical reactivity of lithium. We have been studying a cell system consisting of an amorphous (a-)V2O5P2O5 (95:5 in molar ratio) cathode, a lithium (Li) metal anode and an organic electrolyte in fabricating an AA-size prototype. In this paper, we report recent progress on our rechargeable lithium metal cell focusing on its safety.     

Microwave-Hydrothermal Synthesis of Nanophase Ferrites

This paper reports the synthesis of technologically important ferrites such as ZnFe₂O₄, NiFe₂O₄, MnFe₂O₄, and CoFe₂O₄ by using novel microwave-hydrothermal processing. Nanophase ferrites with high surface areas, in the range of 72-247m²/g, have been synthesized in a matter of a few minutes at temperatures as low as 164°C. The rapid synthesis of nanophase ferrites via an acceleration of reaction rates under microwave-hydrothermal conditions is expected to lead to energy savings.     

Gas permeation properties of a composite membrane filled with poly(ethylene oxide) into a porous membrane

The permeability coefficients of O₂, N₂, and CO₂ gases at 25°C were examined for composite membranes that were prepared by filling poly(ethylene oxide)(PEO) with different molecular weights into a porous membrane. The permeability coefficients of O₂, N₂, and CO₂ were 2 × 10⁻¹⁰ – 4 × 10⁻¹⁰, 5 × 10⁻¹¹ – 9.5 × 10⁻¹¹, and 6 × 10⁻¹⁰ – 1 × 10⁻⁹ (cm³ STPcm/cm² s cmHg), respectively. The higher permeability coefficients of CO₂ are explained in terms of high solubility of CO₂ in filled PEO. The permeability coefficient of CO₂ was affected by the degree of crystallinity of PEO in the composite. On the other hand, there was little effect of crystallinity on O₂ and N₂ permeability coefficients. Some probable relationships between selectivities of O₂ to N₂ and CO₂ to N₂ and the degree of crystallinity of PEO were observed. The CO₂ gas permeability coefficients of the composite membrane for PEO50000 (M_w = 5 × 10⁴) showed a marked change due to melting or crystallization of PEO. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2733–2738, 1999     

Preparation of zinc ferrite in the presence of carbon material and its application to hot-gas cleaning

In order to develop an efficient absorbent of H₂S in coal gasification, zinc ferrite (ZnFe₂O₄) was prepared in the presence of carbon materials such as activated carbon (AC), activated carbon fiber (ACF), and Yallourn coal (YL). The absorption behavior of absorbents for H₂S was examined using a fixed-bed flow type reactor equipped with a quadrupole mass spectrometer.Carbon material-supported ZnFe₂O₄ exhibited larger desulfurization capacity for H₂S than unsupported ferrites. They could efficiently remove H₂S from 4000 ppm levels in a simulated coal gasification gas to less than 1 ppm at 500 °C. The absorption capacity of H₂S with ZnFe₂O₄/AC, ZnFe₂O₄/ACF, and ZnFe₂O₄/YL exhibited nearly 100% of stoichiometric amount of loaded metal species. They could be regenerated by an air oxidation in O₂-Ar (50 vol%) at 450 °C for 30 min. The regenerated ferrite can be used for repeated absorption of H₂S with a very slight decrease in the absorption capacity.     

Separation of aromatic components from light cycle oil by solvent extraction

To improve the versatility of light cycle oil (LCO), separation of aromatic compounds from LCO by solvent extraction was investigated. LCO was analyzed to identify 35 components: 19 aromatics and 16 alkanes. The batch liquid–liquid equilibrium extraction of LCO was performed using furfural, sulfolane, and methanol as extraction solvents. In each solvent, the aromatics present in LCO were selectively extracted relative to the alkanes. The separation selectivities of aromatics relative to alkanes were larger in sulfolane than in the other solvents. Among the aromatic components, di- and tricyclic compounds were selectively extracted relative to the monocyclic ones.     

Flexizymes: their evolutionary history and the origin of catalytic function

Transfer RNA (tRNA) is an essential component of the cell's translation apparatus. These RNA strands contain the anticodon for a given amino acid, and when "charged" with that amino acid are termed aminoacyl-tRNA. Aminoacylation, which occurs exclusively at one of the 3'-terminal hydroxyl groups of tRNA, is catalyzed by a family of enzymes called aminoacyl-tRNA synthetases (ARSs). In a primitive translation system, before the advent of sophisticated protein-based enzymes, this chemical event could conceivably have been catalyzed solely by RNA enzymes. Given the evolutionary implications, our group attempted in vitro selection of artificial ARS-like ribozymes, successfully uncovering a functional ribozyme (r24) from an RNA pool of random sequences attached to the 5'-leader region of tRNA. This ribozyme preferentially charges aromatic amino acids (such as phenylalanine) activated with cyanomethyl ester (CME) onto specific kinds of tRNA. During the course of our studies, we became interested in developing a versatile, rather than a specific, aminoacylation catalyst. Such a ribozyme could facilitate the preparation of intentionally misacylated tRNAs and thus serve a convenient tool for manipulating the genetic code. On the basis of biochemical studies of r24, we constructed a truncated version of r24 (r24mini) that was 57 nucleotides long. This r24mini was then further shortened to 45 nucleotides. This ribozyme could charge various tRNAs through very simple three-base-pair interactions between the ribozyme's 3'-end and the tRNA's 3'-end. We termed this ribozyme a "flexizyme" (Fx3 for this particular construct) owing to its flexibility in addressing tRNAs. To devise an even more flexible tool for tRNA acylation, we attempted to eliminate the amino acid specificity from Fx3. This attempt yielded an Fx3 variant, termed dFx, which accepts amino acid substrates having 3,5-dinitrobenzyl ester instead of CME as a leaving group. Similar selection attempts with the original phenylalanine-CME and a substrate activated by (2-aminoethyl)amidocarboxybenzyl thioester yielded the variants eFx and aFx (e and a denote enhanced and amino, respectively). In this Account, we describe the history and development of these flexizymes and their appropriate substrates, which provide a versatile and easy-to-use tRNA acylation system. Their use permits the synthesis of a wide array of acyl-tRNAs charged with artificial amino and hydroxy acids. In parallel to these efforts, we initiated a crystallization study of Fx3 covalently conjugated to a microhelix RNA, which is an analogue of tRNA. The X-ray crystal structure, solved as a co-complex with phenylalanine ethyl ester and U1A-binding protein, revealed the structural basis of this enzyme. Most importantly, many biochemical observations were consistent with the crystal structure. Along with the predicted three regular-helix regions, however, the flexizyme has a unique irregular helix that was unexpected. This irregular helix constitutes a recognition pocket for the aromatic ring of the amino acid side chain and precisely brings the carbonyl group to the 3'-hydroxyl group of the tRNA 3'-end. This study has clearly defined the molecular interactions between Fx3, tRNA, and the amino acid substrate, revealing the fundamental basis of this unique catalytic system.     

Enzymatic Analysis of Positional Distribution of Fatty Acids in Solid Fat by 1,3-Selective Transesterification with Candida antarctica Lipase B

A protocol for the analysis of the positional distribution of fatty acids (FA) in solid triacylglycerols (TAG) was developed using sn-1(3) selective alcoholysis catalyzed by immobilized Candida antarctica lipase B (CALB). One part by weight of solid fat and ten parts by weight of ethanol (99.5 %) were warmed to liquefy the fat. After adding 0.44 parts by weight of CALB, the mixture was shaken at 50 °C for 10 min then at 30 °C for 2.8 h. The recovery of 2-MAG after the 3-h transesterification reaction was ca. 85 % of the maximum theoretical yield (33 mol%), with the loss of 15 % attributable to the acyl migration from sn-2 to sn-1(3). The recovery was similar to that of the solvent-free alcoholysis of structured lipids, 1,3-dipalmitoyl, 2-oleoyl glycerol and 1,3-dioleoyl, 2-palmitoyl glycerol, conducted at 30 °C for 3 h. In contrast, the acyl migration from sn-1(3) to sn-2 was hardly observed. Because the detected acyl migration was only in the direction of sn-2 to sn-1(3), and not vice versa, it is proposed to determine the FA composition of the sn-2 position of TAG by the gas chromatographic analysis of 2-MAG fraction recovered from the enzymatic reaction mixture, and the FA composition of sn-1(3) position by a mass balance using the FA composition of TAG and of the sn-2 position as inputs. The procedure was successfully applied to palm oil and shea butter, and docosahexaenoic acid (DHA)-rich single cell oil from Aurantiochytrium sp. KH105 for the first time.     

Immobilization of multicopper oxidase from Pyrobaculum aerophilum onto an electrospun-aligned single-walled carbon nanotube surface via a carbon-nanotube-binding peptide for biocathode

Biofuel cells (BFCs) that produce electrical energy from organic resources through enzymatic reactions have been attracting significant attention. Owing to the high electrical conductivity of carbon nanotubes (CNTs), their modification on the electrode surface of a BFC is expected to increase the current, and their high specific surface area may be useful in increasing the power output. Previously, we constructed a biocathode by immobilizing multicopper oxidase from Pyrobaculum aerophilum (McoP) with a carbon nanotube binding peptide (CBP) sequence on the CNTs. This resulted in higher current densities than when using enzymes without CBP sequences. However, owing to the randomly stacked CNTs on the surface of the electrodes, their conductive properties were impaired and performance as biocathodes was poor. Herein, we constructed a biocathode in which single-walled CNTs (SWCNTs) were oriented one-dimensionally and McoP is immobilized on the surface of an SWNCT via CBP. The current density was successfully increased by two-fold by orienting the CNTs and orienting and immobilizing McoP on their surfaces. This technology provides insights into the development of biodevices with controlled orientation of both the SWCNTs and enzymes immobilized on their surfaces.     

Optical resolution of racemic amino acid derivatives with chiral polyamides bearing glutamyl residue as a diacid component

Novel chiral polyamides with chiral environment in their main chains were obtained from aromatic diamine, 4,4′‐diaminodiphenylmethane (DADPM), and the D ‐isomer or the L ‐isomer of N‐α‐protected glutamic acid, such as N‐α‐benzyloxycarbonyl‐D ‐glutamic acid (Z‐D ‐Glu‐OH) or N‐α‐benzyloxycarbonyl‐L ‐glutamic acid (Z‐L ‐Glu‐OH), in the presence of triphenyl phosphite (TPP). Two types of newly prepared polyamide showed optical rotation, implying that there were asymmetric carbons in their main chains. Circular dichroism studies demonstrated that resulting chiral poly‐ amides took a helical structure. Optical resolution ability of those two types of polyamide was studied by adopting potential difference as a driving force for membrane transport. Membranes showed permselectivity toward racemic mixture of N‐α‐acetyltryptophan (Ac‐Trp). The permselectivity was dependent on the absolute configuration of diacid component. The permselectivity was expressed by diffusivity selectivity, which was determined by the presence of chiral helicity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Models for circular data from time series spectra

Circular data are those for which the natural support is the unit circle and its toroidal extensions. Numerous constructions have been proposed which can be used to generate models for such data. We propose a new, very general, one based on the normalization of the spectra of complex-valued stationary processes. As illustrations of the new construction's application, we study models for univariate circular data obtained from the spectra of autoregressive moving average models and relate them to existing models in the literature. We also propose and investigate multivariate circular models obtained from the high-order spectra of stationary stochastic processes generated using linear filtering with an autoregressive moving average response function. A new family of distributions for a Markov process on the circle is also introduced. Results for asymptotically optimal inference for dependent observations on the circle are presented which provide a new paradigm for inference with circular models. The application of one of the new families of spectra-generated models is illustrated in an analysis of wind direction data.