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Takayuki Ishida

Publications and source records attributed to Takayuki Ishida.

At least 19 recordsLinked to original sources
PubMed2006

Strong ferromagnetic exchange couplings in copper(II) and nickel(II) complexes with a paramagnetic tridentate chelate ligand, 2,2'-bipyridin-6-yl tert-butyl nitroxide.

A paramagnetic ligand 6bpyNO (2,2'-bipyridin-6-yl tert-butyl nitroxide) is a newcomer in the field of metal-radical hybrid magnetic materials. Complexes [CuII(6bpyNO)Cl2] and [NiII(6bpyNO)2](PF6)2 having highly planar chelate rings showed considerably strong ferromagnetic exchange couplings J/kB = 202 and 192 K, respectively, across the direct radical oxygen coordination bonds (the spin Hamiltonian is defined as -2JSi.Sj).

Journal Article↗
PubMed2006

Double half-cubane copper(II) complexes available from copper(II) 1,1,1,5,5,5-hexafluoropentane-2,4-dionate dissolved in formamides.

Tetranuclear copper(II) complexes were obtained after simply dissolving [Cu(hfac)2] in formamide-methanol mixed solvents (Hhfac=1,1,1,5,5,5-hexafluoropentane-2,4-dione). X-Ray diffraction studies revealed that they possessed a tetranuclear double half-cubane core sandwiched with two trianionic ligands from 2,4,6-tris(trifluoromethyl)tetrahydropyran-2,4,6-triol (H3ttpt). Complexes [Cu4(ttpt)2(hfac)2(dmf)2.5], [Cu4(ttpt)2(tfa)2(def)4], and [Cu4(ttpt)2(hfac)2(H2O)4](fa) were prepared from N,N-dimethylformamide(dmf)-MeOH, N,N-diethylformamide (def)-MeOH, and formamide(fa)-MeOH (Htfa=trifluoroacetic acid), respectively. A possible mechanism is proposed where a templated aldol-type reaction takes place between hfac and 1,1,1-trifluoroacetonate. Magnetic measurements revealed the presence of antiferromagnetic interaction in the Cu4O6 core.

Journal Article↗
PubMed2006

Polymorphic alternating HNN-cobalt(II) chains both behaving as single-chain magnets (HNN = 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide).

Metal-radical alternating chains [Co(hfac)2HNN]n crystallized in two morphs containing repeating all-cis (alpha) and cis,cis,trans (beta) configurations with respect to the O(HNN)-Co-O(HNN) geometry (HNN = 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide). Both phases showed magnetization jumps with hysteresis at 2 K. The alpha phase has a relatively high activation energy of magnetization reorientation (193 K).

Cobalt↗
PubMed2006

[Development of computer-aided diagnostic system for detection of lung nodules in three-dimensional computed tomography images].

We have developed an automated computerized method for the detection of lung nodules in three-dimensional (3D) computed tomography (CT) images obtained by helical CT. In this scheme, a lung segmentation technique for the determination of the nodule search area is performed based on a gray-level thresholding technique. To enhance lung nodules, we employed the 3D cross-correlation method by using a 3D Gaussian template with zero-surrounding as a model of lung nodule. False positives are then eliminated by using a rule-base with 53 features. For further reduction of false positives, we performed linear discriminant analysis using these 53 features. The average number of false positives was 6.7 per case at a percent sensitivity of 85.0%. This computerized scheme will be useful to radiologists by providing a "second opinion" in case of possible early lung cancer.

Diagnosis, Computer-Assisted↗
PubMed2006

Oximate-bridged trinuclear Dy-Cu-Dy complex behaving as a single-molecule magnet and its mechanistic investigation.

Lanthanide ions are supposed to be promising candidates for the elements of single-molecule magnets (SMMs) because of the large magnetic momentum and anisotropy. We have established the [Dy2Cu] complex as a new SMM. A plausible mechanism for quantum tunneling of magnetization is proposed for the first time among the 4f-3d heterometallic SMMs. The magnetic coupling parameter between Dy and Cu ions was well-defined as -0.155 K.

Journal Article↗
PubMed2005

Self-assembled meso-helicates of linear trinuclear nickel(II)-radical complexes with triple pyrazolate bridges.

Complexation of 3-nitronyl-nitroxide-substituted pyrazolate (pzNN) and 3-imino-nitroxide-substituted pyrazolate (pzIN) with nickel(II) gave [Ni3(pzNN)6] and [Ni3(pzIN)6], respectively. They were practically isomorphous and characterized as a linear trinuclear structure with neighboring nickel ions triply bridged by pyrazolate moieties. The space groups were P2(1)/n but the molecules have a pseudo three-fold axis. We found polymorphs in the crystals of [Ni3(pzIN)6] depending on the solvate molecules; another space group was a cubic Pa3[combining macron]. The opposite chirality around the inversion center at the central nickel(II) ion leads to a meso-helical symmetry in the whole molecule. The radical oxygen atoms participate in the 6-membered chelation at the terminal nickel(II) ions. Antiferromagnetic couplings were observed in both complexes, which are ascribable to interactions between the nickel and radical spins and between the nickel spins across the pyrazolate bridges.

Crystallography, X-Ray↗
PubMed2005

Trans-fused macrobicycle "betweenanene" around a planar Cu2(mu-CH3O)2 core showing remarkable antiferromagnetic interaction.

Complexation of 4,6-bis{3-(2-pyridyl)-1H-pyrazol-1-yl}pyrimidine (bppp) and copper(II) tetrafluoroborate in methanol gave a self-assembled [Cu2(CH3O)2(bppp)2]2+ ion having a betweenanene-type structure. Each bppp spans across the common Cu2O2 plane in a trans fashion to ligate each copper center. The antiferromagnetic interaction observed in the Cu2O2 core is ascribable to the superexchange along the Cu-O-Cu linkage and found to be one of the largest among the analogous compounds, owing to the large Cu-O-Cu angle perturbed with the two bppp molecular tweezers.

Journal Article↗
PubMed2005

Ameliorative and exacerbating effects of [pGlu(4),Cyt(6)]AVP((4-9)) on impairment of step-through passive avoidance task performance by group II metabotropic glutamate receptor-related drugs in mice.

To examine the effect of the arginine-vasopressin fragment, [pGlu(4),Cyt(6)]AVP((4-9)) (AVP4-9), on group II metabotropic glutamate receptor (mGluR2/3) agonist and antagonist induced impairment of passive avoidance (PA) task performance, AVP4-9 or phorbol 12-myristate 13-acetate (PMA) was administered in the presence of mGluR2/3-related drugs that induced the impairment of the step-through-type PA task performance. The PA task performance was evaluated in terms of the latency (the time that elapsed prior to entry into the dark compartment) at 24 h after the electrical stimulation. The subcutaneous injection of AVP4-9 at 1 mug/kg had the greatest facilitative effect on the performance, and the facilitative effect of AVP4-9 was inhibited by NPC-15437, a specific protein kinase C (PKC) inhibitor. The injection of AVP4-9 ameliorated PA task performance impairment induced by DCG-IV, an mGluR2/3 agonist. Intracisternal injection of PMA, a PKC activator, also ameliorated the DCG-IV-induced impairment. High doses of AVP4-9 exacerbated the PA task performance impairment induced by LY341495 (an mGluR2/3 antagonist), and PMA injection (1 mug) also exacerbated the impairment induced by the antagonist. These results suggest that an increase in the activity of the PKC-signaling pathway may not always facilitate PA task performance; therefore, AVP4-9 can either enhance or inhibit memory performance in mice.

Amino Acids↗
PubMed2005

Glutamate antagonists attenuate the action of NC-1900, a vasopressin fragment analog, on passive avoidance task performance in mice.

To examine the relationship between glutamate receptors and the action of NC-1900 on a step-through passive avoidance (PA) task in mice, MK-801, an NMDA receptor blocker, and (S)-4-carboxyphenylglycine (4CPG), a group I metabotropic receptor antagonist, were administered intraventricularly (i.c.v.) singly or as co-injections. The i.c.v. injection of MK-801 (0.8 microg) or 4CPG (2 microg) decreased the latency on the PA task. NC-1900 (1 ng/kg, subcutaneously (s.c.)) alone prolonged the latency on the retention trial in the PA task. MK-801 (0.2 and 0.8 microg) or 4CPG (0.5 and 2 microg) significantly inhibited the action of NC-1900, while the s.c. injection of NC-1900 did not affect latency in mice that received i.c.v. co-injection of MK-801 and 4CPG at any of the doses tested. These results suggest that glutamate receptors participate in the action of NC-1900 on learning and memory in PA task performance.

Animals↗
PubMed2004

Synthesis and characterization of dibenzodioxadiselenafulvalene.

Dibenzodioxadiselenafulvalene (DBOSF) was prepared and the cis and trans isomers were separated. X-ray crystallographic analysis revealed the presence of Se- - -H and O- - -H hydrogen bonds in both crystals. The electrochemical properties of cis- and trans-DBOSFs together with dibenzotetraoxafulvalene (DBTOF) and cis- and trans-dibenzodioxadithiafulvalenes were investigated by means of cyclic voltammetry and DFT calculation. The electron-donating ability and the stability of oxidized forms of DBOSFs are improved compared with those of DBTOF.

Journal Article↗
PubMed2004

Supramolecular triangular and linear arrays of metal-radical solids using pyrazolato-silver(I) motifs.

New chelating radical ligands pzNNH, pzINH, and pzbisINH (3-pyrazolyl nitronyl nitroxide, 3-pyrazolyl imino nitroxide, and pyrazole-3,5-diyl bis(imino nitroxide), respectively) were prepared. Complexation of these ligands with Ag+ gave [Ag(pzNN)]n, [Ag(pzIN)]6, and [Ag(pzbisIN)]n containing the corresponding anionic forms of the ligands. From the X-ray crystal structure analysis, [Ag(pzIN)]6 was characterized as a dimer of almost planar triangular moieties where the pyrazolate worked as a bridge, and metal-metal bonds brought about dimerization of triangles. [Ag(pzbisIN)]n was characterized as a uniform zigzag chain consisting of pyrazolate bridges and Ag ions with a cis-Npz-Ag-Npz coordination structure. Antiferromagnetic interactions observed could be analyzed based on the structures determined for both compounds. Ferromagnetic coupling was observed in [Ag(pzNN)]n, and a polymeric structure was assumed although the crystal structure could not be determined. Novel supramolecular architectures using pyrazolate-substituted imino nitroxides have been developed, using the unique coordinative versatility of the pyrazolate derivatives

Journal Article↗
PubMed2004

Effect of temporal subtraction images on radiologists' detection of lung cancer on CT: results of the observer performance study with use of film computed tomography images.

RATIONALE AND OBJECTIVES: To evaluate the effect of temporal subtraction images on the radiologists' detection of early primary lung cancer in computed tomography (CT) scans. MATERIALS AND METHODS: Fourteen cases with primary lung cancer and 16 normal cases were used for this study from a database of low-dose CT images, which were obtained from a lung cancer screening program in Nagano, Japan. Images were obtained with a single-detector helical CT scanner using 10 mm collimation and 2:1 pitch. Each case had both previous and current CT scans. Temporal subtraction images were obtained by subtracting the warped previous images from the current images. Seven radiologists, including four attendings and three residents, provided their confidence levels for the presence or absence of lung cancers with use of film CT images without and with temporal subtraction images. Receiver operating characteristic analysis was used to compare their performance without and with temporal subtraction images. RESULTS: The mean Az values (area under the receiver operating characteristic curve) of seven observers without and with temporal subtraction images were 0.868 and 0.930, respectively. Diagnostic accuracy was significantly improved by using temporal subtraction images (P = .007). Temporal subtraction images were especially useful when a nodule was present near the pulmonary hilum, where radiologists tended to overlook it. CONCLUSION: The temporal subtraction technique can significantly improve the sensitivity and specificity for detection of lung cancer on CT scans.

Adult↗
PubMed2004

[Challenge to RSNA].

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Bibliographies as Topic↗
PubMed2003

Molecular metamagnet [Ni(4ImNNH)(2)(NO(3))(2)] (4ImNNH = 4-imidazolyl nitronyl nitroxide) and the related compounds showing supramolecular H-bonding interactions.

A new chelating radical ligand 4ImNNH (2-(4-imidazolyl)-4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide) was prepared, and complexation with divalent transition metal salts gave complexes, [M(4ImNNH)(2)X(2)], which showed intermolecular ferromagnetic interaction in high probability (7 out of 10 paramagnetic compounds investigated here). The nitrate complexes (X = NO(3); M = Mn (1), Co (2), Ni (3), Cu (4)) crystallize isomorphously in monoclinic space group P2(1)/a. The equatorial positions are occupied with two 4ImNNH chelates and the nitrate oxygen atoms are located at the axial positions. Magnetic measurements revealed that the intramolecular exchange couplings in 1, 2, and 4 were antiferromagnetic, while that in 3 was ferromagnetic with 2J/k(B) = +85 K, where the spin Hamiltonian is defined as H = -2J(S(1).S(2) + S(2).S(3)) based on the molecular structures determined as the linear radical-metal-radical triads. The intramolecular ferromagnetic interaction in 3 is interpreted in terms of orthogonality between the radical pi and metal dsigma orbitals. Compounds 1-3 exhibited intermolecular ferromagnetic interaction ascribable to a two-dimensional hydrogen bond network parallel to the crystallographic ab plane. Complex 3 became an antiferromagnet below 3.4 K and exhibited a metamagnetic transition on applying a magnetic field of 5.5 kOe at 1.8 K. The complexes prepared from metal halides, [M(4ImNNH)(2)X(2)] (X = Cl, Br; M = Mn, Co, Ni, Cu), showed intramolecular antiferromagnetic interactions, which are successfully analyzed based on the radical-metal-radical system. The crystal structures determined here on 1-4, [Mn(4ImNNH)(2)Cl(2)], and [Cu(4ImNNH)(2)Br(2)] always have intermolecular hydrogen bonds of H(imidazole).X(axial ligand)-M, where X = NO(3), Cl, Br. This interaction seems to play an important role in molecular packing and presumably also in magnetic coupling.

Journal Article↗
PubMed2003

Ferro- and ferrimagnetic chains of hin-bridged copper(II) and manganese(II) and hnn-bridged manganese(II) complexes (hin = 4,4,5,5-tetramethylimidazolin-1-oxyl; hnn = 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide).

We have exploited potential utility of 4,4,5,5-tetramethylimidazolin-1-oxyl (hin) and 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide (hnn) as mu-1,4 and mu-1,5 bridging ligands, respectively, carrying an unpaired electron in development of metal-radical hybrid magnets. X-ray diffraction measurements of [Cu(hfac)(2)hin] (1), [Mn(hfac)(2)hin] (2), and [Mn(hfac)(2)hnn] (3) revealed one-dimensional metal-radical alternating chain structures, where hfac denotes 1,1,1,5,5,5-hexafluoropentane-2,4-dionate. Magnetic measurements of 1 indicate the presence of intrachain ferromagnetic coupling between copper and radical spins. The magnetic exchange parameter was estimated as 2J/k = 56.8 K based on an S = 1/2 equally spaced ferromagnetic chain model (H = -2J summation operator S(i).S(i+1)). This ferromagnetic interaction can be explained in terms of the axial coordination of the hin nitrogen or oxygen to Cu(II). The chi(m)T value of 2 and 3 increased on cooling, and the magnetic data could be analyzed by Seiden's ferrimagnetic chain model, giving 2J/k = -325 and -740 K, respectively. The antiferromagnetic interaction of 2 and 3 can be attributed to orbital overlap between the manganese and the oxygen or nitrogen magnetic orbitals. The exchange interactions between Cu-hin and Mn-hnn are larger than those of typical Cu- and Mn-nitronyl nitroxide complexes, indicating that the choice of small ligands is a promising strategy to bestow strong exchange interaction. Compound 3 became a ferrimagnet below 4.4 K, owing to ferromagnetic coupling among the ferrimagnetic chains.

Journal Article↗