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Hitoshi Miyasaka

Publications and source records attributed to Hitoshi Miyasaka.

53 records · Page 3Linked to original sources
PubMed2003

Heterometallic hexanuclear cluster with an S = 8 spin ground state: MnII[MnII(hfac)2]3[NiII(pao)3]2 (hfac- = hexafluoroacetylacetonate, pao- = pyridine-2-aldoximate).

The heterometallic Mn(II)(4)Ni(II)(2) title compound has been synthesized and characterized by X-ray crystallography. The compound consists of a Ni-Mn-Ni linear moiety, [[Ni-(mu-NO)(3)](2)-Mn], linked by oximate bridges and three Mn(II) hfac terminal units attached by oximate oxygens in a di-mu-oxo fashion, forming a novel heterometallic cluster: Mn[Mn(hfac)(2)](3)[Ni(pao)(3)](2) (1). Magnetic measurements reveal the antiferromagnetic nature of the oximate pathway between Mn(II) and Ni(II) metal ions, which imposes an unusual high-spin ground state (S = 8) for 1.

Journal Article↗
PubMed2003

Structure and magnetic properties of the two-dimensional ferrimagnet (NEt4)[[Mn(salen)]2Fe(CN)6]: investigation of magnetic anisotropy on a single crystal.

The title compound, (NEt(4))[[Mn(salen)](2)Fe(CN)(6)] (1), was synthesized via a 1:1 reaction of [Mn(salen)(H(2)O)]ClO(4) with (NEt(4))(3)[Fe(CN)(6)] in a methanol/ethanol medium (NEt(4)(+) = tetraethylammonium cation, salen(2)(-) = N,N'-ethylenebis(salicylidene)iminate). The two-dimensional layered structure of 1 was revealed by X-ray crystallographic analysis: 1 crystallizes in monoclinic space group P2(1)/c with cell dimensions of a = 12.3660(8) A, b = 15.311(1) A, c = 12.918(1) A, beta = 110.971(4) degrees, Z = 2 and is isostructural to the previously synthesized compound, (NEt(4))[[Mn(5-Clsalen)](2)Fe(CN)(6)] (5-Clsalen(2-) = N,N'-ethylenebis(5-chlorosalicylidene)iminate; Miyasaka, H.; Matsumoto, N.; Re, N.; Gallo, E.; Floriani, C. Inorg. Chem. 1997, 36, 670). The Mn ion is surrounded by an equatorial salen quadridentate ligand and two axial nitrogen atoms from the [Fe(CN)(6)](3-) unit, the four Fe[bond]CN groups of which coordinate to the Mn ions of [Mn(salen)](+) units, forming a two-dimensional network having [[bond]Mn[bond]NC[bond]Fe[bond]CN[bond]](4) cyclic repeating units. The network is spread over the bc-plane of the unit cell, and the layers are stacked along the a-axis. The countercation NEt(4)(+) is located between the layers. Compound 1 is a ferrimagnet with T(c) = 7.7 K and exhibits hysteresis with a remnant magnetization of 13.44 cm(3).mol(-1) (M/N mu(B) = 2.4) at zero field and a coercivity of 1000 Oe when the powder sample was measured at 1.9 K. Magnetic measurements of a direction-arranged single crystal were also carried out. The orientation of the crystallographic axes of a selected single crystal was determined by X-ray analysis, and magnetization was measured when an external field was applied in the a*, b, and c directions. The magnetization in the a* direction increased more easily than those in the b and c directions below the critical temperature. No hysteresis was observed only for the measurement in the a* direction, indicating the presence of strong structural anisotropy with potential anisotropy on Mn(III) ions.

Journal Article↗
PubMed2003

CO2 response for expression of ribulose-1,5-bisphosphate carboxylase/oxygenase genes is inhibited by AT-rich decoy in the cyanobacterium.

The CO(2)-regulatory function of the AT-rich element in the promoter for ribulose-1,5-bisphosphate carboxylase/oxygenase (rbc) genes in the cyanobacterium Synechococcus sp. PCC7002 was analyzed using the transcription factor decoy approach. Double-stranded phosphorothioate AT-rich oligonucleotides with high affinity for a sequence-specific DNA-binding protein were successfully introduced into cyanobacterial cells in culture without any transfection reagent. The AT-rich decoy oligonucleotides interfered with CO(2) regulation of rbc expression by blocking the binding of the sequence-specific DNA-binding protein, indicating that the AT-rich element plays a critical role in CO(2) regulation for rbc genes. The decoy oligonucleotide approach to cyanobacteria provides a simple and excellent tool for investigating transcriptional regulation in vivo.

AT Rich Sequence↗
PubMed2003

Maximization of hydrogen production ability in high-density suspension of Rhodovulum sulfidophilum cells using intracellular poly(3-hydroxybutyrate) as sole substrate.

Growth of and hydrogen production by wild-type (WT) Rhodovulum sulfidophilum were compared with those by one of its mutants lacking the poly(3-hydroxybutyrate) (PHB) biosynthesis ability (PNM2). During phototrophic growth under aerobic conditions with fixed illumination, changes in the extinction coefficient and PHB content of WT and PNM2 cells revealed interference of light penetration by PHB. WT cells synthesized PHB at an early stage of the cultivation. PHB degradation after exhaustion of acetate during the cultivation of WT resulted in a decrease of the extinction coefficient. The hydrogen production rate under anaerobic conditions with fixed illumination was examined in WT and PNM2 cell suspensions at different densities. The hydrogen production rate was determined not by the light penetration but by the kinds of hydrogen donors and the density of suspension. The highest value of the rate of hydrogen production from PHB, 33.0 ml/l/h, was improved compared with 26.6 ml/l/h, which was the highest value in hydrogen production from succinate. Under the same illumination, conversion to hydrogen from PHB is more efficient than that from succinate, which is one of the best substrates for hydrogen production. These results suggest that the hydrogen production rate can be maximized in the hydrogen production system based on PHB degradation, which is achieved in high-density suspension under external-substrate-depleted conditions after aerobic cultivation in the presence of an excess amount of acetate.

Alphaproteobacteria↗
PubMed2003

Regulation of phytochelatin synthesis by zinc and cadmium in marine green alga, Dunaliella tertiolecta.

Although Cd(2+) is a more effective inducer of phytochelatin (PC) synthesis than Zn(2+) in higher plants, we have observed greater induction of PC synthesis by Zn(2+) than Cd(2+) in the marine green alga, Dunaliella tertiolecta. To elucidate this unique regulation of PC synthesis by Zn(2+), we investigated the effects of Zn(2+) and Cd(2+) on the activities of both phytochelatin synthase (PC synthase) and enzymes in the GSH biosynthetic pathway. PC synthase was more strongly activated by Cd(2+) than by Zn(2+), but the difference was not very big. On the other hand, gamma-glutamylcysteine synthetase (gamma-ECS) and glutathione synthetase (GS) were activated by both heavy metals, but their activities were higher in Zn-treated cells than in Cd-treated cells. Dose-dependent stimulation of intracellular reactive oxygen species (ROS) production was observed with Zn(2+), but not Cd(2+) treatment. These results suggest that Zn(2+) strongly promotes the synthesis of GSH through indirect activation of gamma-ECS and GS by stimulating ROS generation. This acceleration of the flux rate for GSH synthesis might mainly contribute to high level PC synthesis.

Aminoacyltransferases↗
PubMed2003

Molecular characterization of glutathione peroxidase-like protein in halotolerant Chlamydomonas sp. W80.

A cDNA clone encoding a glutathione peroxidase (GPX)-like protein was isolated from the cDNA library from halotolerant Chlamydomonas W80 (C. W80) by a simple screening method based on the bacterial expression system. The cDNA clone contained an open reading frame encoding a mature protein of 163 amino acids with a calculated molecular mass of 18 267 Da. No potential signal peptide was found. The deduced amino acid sequence of the cDNA showed 40-63% and 37-46% homology to those of GPX-like proteins from higher plants and mammalian GPXs, respectively. The C. W80 GPX-like protein contained a normal cysteine residue instead of a selenocysteine at the catalytic site. However, it contained amino acid residues (glutamine and tryptophan) that are involved in three protein loops and are important for the catalytic activity in the mammalian GPX. Interestingly, the native and recombinant GPX-like proteins showed activities towards unsaturated fatty acid hydroperoxides, but not towards either H2O2 or phospholipid hydroperoxide. Transformed E. coli cells expressing the C. W80 GPX-like protein showed enhanced tolerance to 5% NaCl or 0.2 mM paraquat treatments. Accession number: The nucleotide sequence data reported have been submitted to the DDBJ, EMBL, and GenBank nucleotide sequence databases with the following accession number AB009083.

Journal Article↗
PubMed2002

Evidence for single-chain magnet behavior in a Mn(III)-Ni(II) chain designed with high spin magnetic units: a route to high temperature metastable magnets.

We herein present the synthesis, crystal structure, and magnetic properties of a new heterometallic chain of MnIII and NiII ions, [Mn2(saltmen)2Ni(pao)2(py)2](ClO4)2 (1) (saltmen2- = N,N'-(1,1,2,2-tetramethylethylene) bis(salicylideneiminate) and pao- = pyridine-2-aldoximate). The crystal structure of 1 was investigated by X-ray crystallographic analysis: compound 1 crystallized in monoclinic, space group C2/c (No. 15) with a = 21.140(3) A, b = 15.975(1) A, c = 18.6212(4) A, beta = 98.0586(4) degrees , V = 6226.5(7) A3, and Z = 4. This compound consists of two fragments, the out-of-plane dimer [Mn2(saltmen)2]2+ as a coordination acceptor building block and the neutral mononuclear unit [Ni(pao)2(py)2] as a coordination donor building block, forming an alternating chain having the repeating unit [-Mn-(O)2-Mn-ON-Ni-NO-]n. In the crystal structure, each chain is well separated with a minimum intermetallic distance between Mn and Ni ions of 10.39 A and with the absence of interchain pi overlaps between organic ligands. These features ensure a good magnetic isolation of the chains. The dc and ac magnetic measurements were performed on both the polycrystalline sample and the aligned single crystals of 1. Above 30 K, the magnetic susceptibility of this one-dimensional compound was successfully described in a mean field approximation as an assembly of trimers (Mn...Ni...Mn) with a NiII...MnIII antiferromagnetic interaction (J = -21 K) connected through a ferromagnetic MnIII...MnIII interaction (J'). However, the mean field theory fails to describe the magnetic behavior below 30 K emphasizing the one-dimensional magnetic character of the title compound. Between 5 and 15 K, the susceptibility in the chain direction was fitted to a one-dimensional Ising model leading to the same value of J'. Hysteresis loops are observed below 3.5 K, indicating a magnet-type behavior. In the same range of temperature, combined ac and dc measurements show a slow relaxation of the magnetization. This result indicates the presence of a metastable state without magnetic long-range order. This material is the first experimental design of a heterometallic chain with ST = 3 magnetic units showing a "single-chain magnet" behavior predicted in 1963 by R. J. Glauber for an Ising one-dimensional system. This work opens new perspectives for one-dimensional systems to obtain high temperature metastable magnets by combining high spin magnetic units, strong interunit interactions, and uniaxial anisotropy.

Journal Article↗
PubMed2002

Tuning of spin density wave strengths in quasi-one-dimensional mixed-halogen-bridged nickel(III) complexes with strong electron correlation, [Ni(III)(chxn)(2)Cl(1-x)Br(x)](NO(3))(2).

This communication describes the syntheses of the quasi-one-dimensional mixed-halogen-bridged Ni(III) complexes with strong electron correlation [Ni(chxn)(2)Cl(1-x)Br(x)](NO(3))(2) and the tuning of the spin density wave strengths of these compounds. If the Cl 3p and Br 4p make one band in the compounds, we should observe a single peak in the electronic spectra. As a result, we should observe the single peak from 1.45 to 2.00 eV depending on the mixing ratios of Cl and Br ions. Therefore, the Cl 3p and Br 4p make one band. Then, we have succeeded in tuning the spin density wave strengths of the Ni(III) complexes with the strong electron correlation by mixing the bridging halogen ions successively.

Journal Article↗
PubMed2002

Enhancement of tolerance to heavy metals and oxidative stress in Dunaliella tertiolecta by Zn-induced phytochelatin synthesis.

The synthesis of phytochelatins (PCs) in a marine alga, Dunalliela tertiolecta, is strongly induced by Zn. Pretreatment of the cells with Zn enhances the tolerance toward toxic heavy metals such as Cd, Hg, Cu, Pb, and arsenate. Moreover, the pretreatment also increases the tolerance toward oxidative stress caused by hydrogen peroxide or paraquat. In vitro analysis shows that PC is a stronger scavenger of hydrogen peroxide and superoxide radical than glutathione. These results suggest that PCs inducibly synthesized by Zn treatment could play a role not only in detoxification of heavy metals but also in mitigation of oxidative stress.

Chelating Agents↗
PubMed2002

Dynamic insertion-deletion of introns in deuterostome EF-1alpha genes.

To test the validity of intron-exon structure as a phylogenetic marker, the intron-exon structure of EF-1alpha genes was investigated for starfish, acornworms, ascidians, larvaceans, and amphioxus and compared with that of vertebrates. Of the 11 distinct intron insertion sites found within the coding regions of the deuterostome EF-1alpha genes, 7 are shared by several taxa, while the remainder are unique to certain taxa. Examination of the shared introns of the deuterostome EF-1alpha gene revealed that independent intron loss or intron insertion must have occurred in separate lineages of the deuterostome taxa. Maximum parsimony analysis of the intron-exon data matrix recovered five parsimonious trees (consistency index = 0.867). From this result, we concluded that the intron-exon structure of deuterostome EF-1alpha has evolved more dynamically than previously thought, rendering it unsuitable as a phylogenetic marker. We also reconstructed an evolutionary history of intron insertion-deletion events on the deuterostome phylogeny, based on several molecular phylogenetic studies. These analyses revealed that the deuterostome EF-1alpha gene has lost individual introns more frequently than all introns simultaneously.

Amino Acid Sequence↗
PubMed2002

Translation initiation AUG context varies with codon usage bias and gene length in Drosophila melanogaster.

The relationship between the codon usage bias and the sequence context surrounding the AUG translation initiation codon was examined in 1100 Drosophila melanogaster mRNA sequences. The codon usage bias measured by the "codon adaptation index" (CAI), and the effectiveness of the AUG context for translation initiation assessed by the "AUG context adaptation index" (AUGCAI), showed a significant positive relationship (correlation coefficient: r = 0.34, p <0.0001), indicating that these two factors are evolutionally under a similar natural selection constraint at the translational level. The importance of each position of the AUG context in relation to codon usage bias was examined, and the preference for the nucleotide at the -13, -12, -11, -10, -7, -6, -5, -4, -3, -2, and -1 positions showed a significant positive correlation to the codon usage bias, suggesting the action of natural selection on these very specific positions of the Drosophila genome. The relationship between AUGCAI value and gene length was also examined, and a significant negative relationship was found (r = -0.15, p <0.0001), suggesting a general tendency of higher expressivity of shorter genes, and of lower expressivity of longer genes in D. melanogaster.

Animals↗
PubMed2002

Cloning and molecular analysis of poly(3-hydroxyalkanoate) biosynthesis genes in Pseudomonas aureofaciens.

Pseudomonas aureofaciens grown on octanoate or gluconate synthesized medium-chain-length polyhydroxyalkanoates (mcl-PHAs). To clone the PHA synthase gene(s) (phaC), the genomic library of P. aureofaciens was constructed using a cosmid vector. The recombinant cosmids that clone phaC were detected by the complementation with a PHA-negative mutant, P. putida GPp104. The resulting recombinant cosmid, named pVK6, contained a 13-kbp DNA insert. Genetic analysis of the pha locus in pVK6 revealed the presence of six ORFs, genes encoding two PHA synthases, 1 and 2 (phaC1 and phaC2), PHA depolymerase (phaZ), two PHA granule-associated proteins (phaF and phaI), and an unknown protein (phaD). The heterologous expression of pha genes from P. aureofaciens was confirmed. P. putida GPp104 regained the ability to accumulate PHA on introduction of pVK6. Wild-type strains P. oleovorans and P. fluorescens, which were unable to accumulate PHA when grown on gluconate, acquired the ability to accumulate PHA from gluconate when they possessed pVK6.

Acyltransferases↗
PubMed2002

CO(2) response element and corresponding trans-acting factor of the promoter for ribulose-1,5-bisphosphate carboxylase/oxygenase genes in Synechococcus sp. PCC7002 found by an improved electrophoretic mobility shift assay.

We analyzed the promoter of the genes encoding the ribulose-1,5-bisphosphate carboxylase/oxygenase (rbc) in the cyanobacterium Synechococcus sp. PCC7002 and localized the CO(2)-regulatory element. Cyanobacterial transformants were constructed with several DNA segments of the rbc promoter fused to the chloramphenicol acetyltransferase (CAT) gene, and their acetyltransferase activities were analyzed under 0.03% and 1% CO(2) conditions. We found that the AT-rich element localized from -262 to -291 relative to the rbc translation-starting site was required for CO(2)-dependent repression. Fluorescent-labeled oligonucleotide probes of identical sequence to the AT-rich element were reacted with protein extracts from cells cultured under conditions of low and high CO(2) atmospheric content. We detected a gel retardation complex of a strong signal intensity in extracts from cells cultured under 15% CO(2), but only a weak signal from cells cultured under 1% CO(2). Moreover, a DNA affinity precipitation assay identified a 16-kDa protein that bound to nucleotide sequences within the AT-rich element. The partial amino acid sequence of the protein was similar to the deduced protein sequences of ORF129 and ORF155 from Synechocystis 6803. Our findings suggest that the AT-rich element plays a role as a negative CO(2)-regulatory element and its trans-acting factor possibly regulates the rbc transcription in response to CO(2) levels.

Adenosine Triphosphatases↗
PubMed1998

Synthesis, Crystal and Network Structures, and Magnetic Properties of a Hybrid Layered Compound: [K(18-cr)(2-PrOH)(2)][{Mn(acacen)}(2){Fe(CN)(6)}] (18-cr = 18-Crown-6-ether, acacen = N,N'-Ethylenebis(acetylacetonylideneiminate)).

A hybrid layered compound [{K(18-cr)(2-PrOH)(2)}{Mn(acacen)}(2){Fe(CN)(6)}] has been prepared by the reaction of [Mn(acacen)(Cl)] with [K(18-cr)(H(2)O)(2)](3)[Fe(CN)(6)].3H(2)O in an ethanol/2-propanol mixed solvent (18-cr = 18-crown-6-ether, acacen = N,N'-ethylenebis(acetylacetonylideneiminate)). It crystallizes in the monoclinic space group P2(1)/a with cell dimensions of a = 13.272(3) Å, b = 15.768 (2) Å, c = 14.771(2) Å, beta = 105.64(1) degrees, Z = 2. It assumes a hybrid layered structure of alternating arrays of two types of layers. One of the layers is formed by the anionic part [{Mn(acacen)}(2){Fe(CN)(6)}](n)()(n)()(-), where [Fe(CN)(6)](3)(-) coordinates through its four cyanide groups on a plane to the axial sites of four [Mn(acacen)](+) entities. The two-dimensional layer consists of the cyclic octamer [-Mn-NC-Fe-CN-](4) having the Fe ions at the corners and the Mn ions on the edges of a deformed square. Another layer is formed by the cationic part [K(18-cr)(2-PrOH)(2)](+) that has a hexagonal-bipyramidal geometry about the metal with two 2-PrOH molecules at the apexes of the nearly planar [K(18-cr)](+). The anionic and cationic layers are combined by the hydrogen bond between the cyanide groups (free from coordination) of the anionic layer and the 2-propanol groups of the cationic layer with bond distance of N.O = 2.861(5) Å. Magnetic studies (magnetic susceptibility vs T, field-cooled magnetization vs T, saturation magnetization vs H) indicate that the compound is a metamagnet with a Néel temperature T(N) = 5.0 K, showing the onset of ferromagnetic ordering within the anionic layer and an antiferromagnetic interlayer interaction. Magnetization as a function of the applied magnetic field indicates a spin-flipping from antiferromagnetic arrangement to ferromagnetic arrangement between the layers around 1200 Oe and exhibits hysteresis behavior.

Journal Article↗
PubMed1998

The Synthesis and Characterization of Two-Dimensional Ferromagnetic Extended Structures Containing High-Spin (S = (5)/(2)) and Low-Spin (S = (1)/(2)) Iron(III) Bridged by Cyanide Groups.

The reaction of [Fe(salen)](+) and {A(3)[Fe(CN)(6)]} (A = NEt(4), K), depending on the countercation A(+) and on the reaction solvent, led to [(NEt(4)){Fe(salen)}(2){Fe(CN)(6)}](n)(), 4, and [{Fe(salen)}(3){Fe(CN)(6)}(MeOH)(2)](n)().3nH(2)O, 5 [NEt(4) = tetraethylammonium cation, salen = N, N'-ethylenebis(salicylideneiminato) dianion], displaying a similar extended 2D structure. Complex 5 crystallizes in the monoclinic, space group P2(1)/n, a = 13.495(7) Å, b = 14.220(9) Å, c = 33.137(5) Å, beta = 96.74(2) degrees, and Z = 4. It assumes a two-dimensional network layer structure consisting of cyclic octanuclear [-Fe(h.s.)-NC-Fe(l.s.)-CN-](4) units with [Fe(salen)(MeOH)(2)](+) located between the interlayer as a countercation. Complex 4 exhibits a metamagnetic behavior with a field-induced transition from an antiferromagnetic to a ferromagnetic-like state and a Neel temperature of ca. 6 K.

Journal Article↗
PubMed1997

Copper(II) Complexes of N,N'-Bis((2-substituted-imidazol-4-yl)methylene)-3,3'-diaminodi- propylamine (2-Substituent = H, Me): Delta and Lambda Enantiomorphs of the Protonated Complex and Helical Structure of the Deprotonated Complex Formed by Hydrogen Bonds.

Copper(II) complexes with the quinquedentate ligands H(2)L(n)() (n = 1, 2) of the 1:2 condensation products of 3,3'-diaminodipropylamine and each of 4-formylimidazole and 4-formyl-2-methylimidazole have been synthesized and characterized, where the complexes have the general formula of [Cu(H(2)L(n)())]X(2) and are abbreviated as 1X(2), and 2X(2) (n = 1, 2 for 2-substituent = H, Me; X = ClO(4), NO(3), Cl). X-ray crystal structures of 1(NO(3))(2), and 2(Cl)(2) were determined: 1(NO(3))(2), monoclinic, space group P2(1)/c (No. 14), a = 9.610(4) Å, b = 13.463(5) Å, c = 15.568(5) Å, beta = 98.12(3) degrees, and Z = 4; 2(Cl)(2), monoclinic, space group P2(1)/n (No. 14), a = 9.884(2) Å, b = 15.073(3) Å, c = 15.295(2) Å, beta = 98.57(2) degrees, and Z = 4. The complex assumes Delta or Lambda enantiomorphs due to the spiral arrangement of the quinquedentate ligand around the copper(II) ion, and these Delta and Lambda enantiomorphs of the cation for 1(NO(3))(2) and 2(Cl)(2) coexist as the racemic form in the crystals. When the protonated complexes were treated with NaOH, the mono-deprotonated complexes with the formula [CuHL(n)()]ClO(4), 1'ClO(4) (n = 1) and 2'ClO(4) (n = 2), were obtained. Crystal data for 1'ClO(4): Pbca (No. 61) with a = 13.211(3) Å, b = 25.387(3) Å, c = 10.939(3) Å, and Z = 8.; 2'.ClO(4), Pbca (No. 61) with a = 16.554(4) Å, b = 20.609(4) Å, c = 12.423(3) Å, and Z = 8. The structures consist of an electronically monopositive copper(II) complex involving a deprotonated imidazole moiety and a protonated imidazole moiety per molecular unit and a mononegative anion ClO(4)(-), where an imidazolate nitrogen atom N(2) of the copper(II) complex is hydrogen bonded to the imidazole nitrogen atom N(6) ( denotes the symmetry operation of (1)/(2) + x, (1)/(2) - y, -z) of the adjacent unit with the hydrogen bond distance of N(2).N(6) of 2.842(6) for 1'ClO(4) and 2.815(4) Å for 2'ClO(4) to give a one-dimensional helical structure running along the a-axis. Through the hydrogen bonds, the Delta isomer only aggregates with the Delta isomer and the Lambda isomer only aggregates with the Lambda isomer to give an extended helical chain structure described as DeltaDeltaDeltaDeltaDelta. or LambdaLambdaLambdaLambdaLambda., respectively.

Journal Article↗