Hiroki Takahashi

Unusual Disordered Crystal Structure of a Racemate Exhibiting a Novel Enantiomeric Resolution: Preferential Enrichment

Simple recrystallization of racemic (±)-NC leads to preferential enrichment of one enantiomer in the mother liquor, which allows the efficient resolution of the two enantiomers. In the unique disordered crystal structure of the racemate, the two enantiomers form centrosymmetric dimers as the major component.

Water Transport during Ion Conduction in Anion-Exchange and Cation-Exchange Membranes

Water transport during ion conduction through an anion-exchange membrane AEM immersed in an aqueous solution of HNO3 and KOH was investigated. We have developed an apparatus to accurately measure small changes in volumes of the aqueous solution at each side of the membrane by capillary tubes during the passage of an electronic current through the membrane. In contrast to the previously reported apparatus, the present apparatus can be applied to an AEM in various aqueous solutions of electrolytes, and measurements under conditions close to those in actual solid alkaline fuel cells are therefore possible by using alkaline solutions. The water-transport number for AEM in HNO3 was larger than that in KOH, indicating the importance of selecting the appropriate aqueous solution of electrolytes. It is possible to determine whether anions or cations are conductors in electrolyte membranes with unknown properties. Fuel cells are expected to become important in the future for solving energy/environmental problems. By using fuel cells, it is possible to extract electric energies with high efficiency through the production of H2O from H2 and O2, with clean exhaust gases. These devices consist of two electrodes with catalysts usually Pt and an electrolyte membrane between them. Polymer electrolyte fuel cells PEFCs and solid alkaline fuel cells SAFCs use a protonconducting membrane and an anion-exchange membrane AEM

Ideal enantiomeric resolution by recrystallization of a racemic compound (part 4): Relationship between enantiomeric resolution phenomenon and crystal properties

A new example of a racemate showing unusual enantiomeric resolution phenomenon, in which simple recrystallization of the racemate leads to remarkable enantiomeric enrichment of either enantiomer up to 100% ee in the mother liquor, has been found. This compound is (±)-[2-[4-(3-ethoxy-2-hydroxypropoxy)phenylcarbamoyl]-ethyl]dimethylsulfonium p-nitrobenzenesulfonate [EtOCH2CH(OH)CH2OC6H4NHCOCH2CH2SMe2+O2NC6H4SO3−] [(±)-SN]. By repeating recrystallization of (±)-SN and the resulting deposited crystals successively and collecting the resulting enantiomerically enriched mother liquors with the same chirality sense, highly efficient enantiomeric resolution of the racemate into its separate enantiomers has been accomplished. The relationship between the occurrence of this enantiomeric resolution phenomenon and the crystal properties has been investigated with respect to SN and its aryl- and alkylsulfonate derivatives. The mode of enantiomeric resolution of (±)-SN was similar to that of para-substituted benzenesulfonate derivatives (±)-ST (4-MeC6H4SO3−) and (±)-SC (4-ClC6H4SO3−) previously reported, whereas the unsubstituted derivative (±)-SB (C6H5SO3−) and alkysulfonate derivatives (±)-SO (n-C8H17SO3−) and (±)-SM (CH3SO3−) did not show such an enantiomeric resolution phenomenon. The crystalline form of the former racemates that underwent the enantiomeric resolution was racemic compounds, while the latter were mixed crystals (solid solutions) composed of the respective optical antipodes. Chirality 9:220–224, 1997.

Cloning and Tyrosine Phosphorylation of a Novel Invertebrate Immunocyte Protein Containing Immunoreceptor Tyrosine-based Activation Motifs

Immunoreceptor tyrosine-based activation motif (ITAM) plays an important role in signal transduction through mammalian T-cell and B-cell antigen receptors and Fc receptors. The ITAM has been found only in vertebrate immunocytes. Ascidians are intriguing invertebrates from the viewpoint of the evolution of immune systems because they are considered to be ancestors of the vertebrates. We have previously shown that the monoclonal antibody A74 inhibits cellular defense reactions of the ascidian. In the present studies, we found that the A74 antigen protein has two ITAMs and several motifs that are proposed to function in signal transduction. The A74 protein is tyrosine-phosphorylated and associated with other proteins in the initial stages of cellular defense reactions. The ITAMs of the A74 protein are tyrosine-phosphorylated by a c-Src kinase in vitro. The A74 protein provides a key to the understanding of the origin of vertebrate immune systems.

Ungewöhnliche fehlgeordnete Kristallstruktur eines Racemats als neues Phänomen bei der Racematspaltung: bevorzugte Anreicherung

Durch einfaches Umkristallisieren des Racemats (±)-NC findet eine bevorzugte Anreicherung eines Enantiomers in der Mutterlauge statt, was eine effiziente Racematspaltung ermoglicht. Das Racemat weist eine einzigartige fehlgeordnete Kristallstruktur auf, in der hauptsachlich zentrosymmetrische cyclische Dimere beider Enantiomere vorliegen.

Ca2+-binding properties and regulatory roles of lobster troponin C sites II and IV

Invertebrate troponin C typically contains Ca2+‐specific binding sites, sites II and IV, in the N‐ and C‐terminal domains, respectively. To investigate the roles of these sites for Ca2+‐dependent regulation of muscle contraction, we generated lobster troponin C mutants, and analyzed their Ca2+‐binding properties and regulatory effects on actomyosin–tropomyosin Mg‐ATPase activity. The results suggest that Ca2+ binding to site IV is responsible for regulation at relatively low Ca2+ concentrations, while site II has an essential role in full activation at higher Ca2+ concentrations.

Preferential enrichment : Mode of polymorphic transformation of a mixed crystal into a racemic compound crystal

Abstract A novel enantiomeric resolution phenomenon observed upon simple recrystallization of the racemates of ST, SC, SN and NNMe3 has been designated as “Preferential Enrichment” in the mother liquor. By the investigation of their crystal properties, it has been suggested that the presence of polymorphism and the resultant polymorphic transformation are responsible for the “Preferential Enrichment.” In this context, on the basis of the molecular alignment and intermolecular interactions in the crystals, a mode of the polymorphic transformation of a metastable mixed crystal (solid solution) of enantiomers into a stable racemic compound crystal is discussed.

Ion Conduction in Layered Oxide Solid Electrolyte

In the present study, membrane potential for concentration cell of NaOH was measured to seek inorganic materials with anion conduction for high-temperature-resistant fuel cells without noble-metal catalyst. We discovered the anion conduction in layered oxide NaCo2O4 and KCo2O4. Although LiCoO2 has the similar layered structure to NaCo2O4 and KCo2O4, this oxide showed cation conduction. Moreover, we succeeded in generating electricity by using NaCo2O4 electrolyte. The anion-conductivity is considered to be caused by reduction and hydration of NaCo2O4.

Anion Conduction in Solid Electrolytes Probed by Water Transport Measurement

Title Anion Conduction in Solid Electrolytes Probed by Water Transport Measurement Author(s) Takahashi, Hiroki; Takeguchi, Tatsuya; Yamanaka, Toshiro; Ueda, Wataru Citation ECS Transactions, 28(8): 83-86 Issue Date 2010 Doc URL http://hdl.handle.net/2115/48158 Rights

8,8′-Dialkyl-1,1′-biisoquinolines: preparation, absolute configuration and unexpected racemization behaviour†

A series of 8,8′-dialkyl-1,1′-biisoquinolines, in which methyl, ethyl and isopropyl groups are introduced for enhancing the transannular steric hindrance, are synthesized. The atropisomeric biisoquinolines are separated into both enantiomers, of which the absolute configurations and the optical stabilities are determined. Contrary to prior expectations, the racemization behaviour is inversely proportional to the steric size of the alkyl groups.