Akira Ohyoshi

Thermal decomposition of cyclodextrins (α-, β-, γ-, and modified β-CyD) and of metal—(β-CyD) complexes in the solid phase

The thermal decomposition of solid cyclodextrins (CyDs) (natural CyDs are α-, β-, and γ-CyD; modified β-CyDs are triacetyl- (TAue5f8), triphenylcarbamoyl- (TCue5f8), and dimethyl—β-CyD (DMue5f8β-CyD)) and of metal—β-CyD complexed (metal = Ca, Zn, Cd) has been studied by thermal analysis under the same conditions (heating rate = 10 deg min−1; in He). Most of the water molecules are released below 100°C in natural CyDs. Other strongly bound (included) water molecules were found in both α-CyD and γ-CyD, from which the water molecules were liberated at 260–270°C. The decomposition temperature of the CyD ring is lowered in β-CyD because this ring is of lowest symmetry among the three natural CyDs. Although no difference could be found between the 50%-decomposition temperatures of the CyD rings, the final decomposition rate (up to 550°C) distinguished between α-CyD and γ-CyD (both 98%), and β-CyD (86%). The water contents of the modified β-CyDs are much smaller than the natural β-CyD, and TCue5f8β-CyD has only included water molecules. The decomposition temperature of the CyD ring after dehydration, both in TAue5f8 and DMue5f8β-CyD is higher by 20–60°C than that of the parent β-CyD. The thermal stability of modified β-CyDs increased in the order TCue5f8 < DMue5f8 < TAue5f8β-CyD. n nMetal—β-CyD complexes have been isolated. All complexes contain water molecules, but these are not tightly bound. Ethanol, which was used as a precipitation reagent, was included only in the Cdue5f8β-CyD complex. Complexation of a heavy metal ion to β-CyD leads to a depression of the thermal degradation of the β-CyD ring.

A kinetic study on reduction of nitric oxide over cobalt tetraphenylporphyrin supported on titanium dioxide

Abstract The catalytic reduction and decomposition of nitric oxide and nitrous oxide over cobalt tetraphenylporphyrin supported on TiO 2 (Co-TPP/TiO 2 ) were investigated kinetically and mechanistically in the reaction temperature range of 50 to 150 °C, and reveal a high catalytic activity brought about by supporting on titanium dioxide. The kinetic equation for the reduction of nitric oxide with hydrogen over Co-TPP/TiO 2 ( V = k × P NO −0.9 P H 2 0.6 ) suggested that the surface reaction between nitric oxide adsorbed strongly on the cobalt ion and hydrogen adsorbed dissociatively on the porphyrin ring is the rate-determining step. The selective formation of nitrous oxide in the initial stage of the reaction and its successive transformation to molecular nitrogen were explained in terms of the stronger adsorption of nitric oxide. Decomposition of nitric oxide and nitrous oxide also proceeded over this catalyst, producing nitrous oxide and molecular nitrogen, respectively. The residual oxygen produced on Co-TPP may be transferred to the support to a certain limit. The characteristic activity of (Co-TPP/TiO 2 ) can be ascribed to the drastic modification in the electronic configuration of the cobalt ion, as well as the porphyrin ring, induced by the electron transfer from the support.

Studies on actinide elements—VI: Photochemical reduction of uranyl ion in citric acid solution

Abstract The photochemical reduction of uranyl ion in citric acid solutions was studied in the presence of visible light. The rate of the reduction was found to be: rate = k obs [UO 2+ 2 ], where k obs is the apparent rate constant. The value of k obs was 1·63 × 10 −2 min −1 at [UO 2+ 2 ]: 9·5 × 10 −3 M, [citric acid]: 4·8 × 10 −2 M, pH 3·1, 30°C, and 4050–4360 A light irradiation. The quantum yield for U(IV) formation varied with the hydrogen-ion concentration of reaction medium from 0·03 (pH 1·0) to 0·99 (pH 3·5). The oxidation products of citric acid were identified to be acetone and carbon dioxide. The reaction seems to proceed predominantly through the intramolecular decomposition process of uranyl-citrate complex, i.e [UO 2 H 3 L] + + h v →r [UO 2 H 3 L +∗ →r U(V) + CO 2 ketocarboxylic acid, and ketocarboxylic acid →r acetone + 2CO 2 . This mechanism is different from those which involve two competing mechanisms in the case of uranyl-lactic acid system. This may be interpreted by assuming that the uranyl citrate is more stable than lactato complex and it forms a chelate ring to efficiently dissipate the absorbed photon energy.

Short-lived isotopes of lanthanum, cerium and praseodymium in neutron irradiated uranium☆

Abstract The separation of fission product La, Ce and Pr was performed within 90–180 sec by electromigration. As a supporting electrolyte, the solution of nitrilotriacetic acid ([NTA] = 3·7 × 10−3M, pH = 2·0, μ ∼ 0·05) was used. Rapid location of the zone on the paper strip reached after migration was obtained by color reaction of the carrier added to the irradiated uranyl nitrate solution. The γ-ray spectrum of each element was measured by a Ge(Li) detector connected with 512 channel pulse-height analyzer. In lanthanum fraction, at early times two prominent photopeaks at 395 keV ( T 1 2 = 40 ± 2 sec ) and 541 keV ( T 1 2 = 43 ± 3 sec ) were observed. From their decay rates, we presumed that they could be attributed to 144La ( T 1 2 = 41 sec ) whose γ-ray energies have not yet been reported. The two other photopeaks at 619 and 642 keV were assigned to the 14 min 143La and 92 min 142La. In Ce fraction, the photopeaks assigned to the 3 min 145Ce and to the 14 min 146Ce were observed, while no photopeaks could definetely be assigned to the 65 sec 147Ce. Some unreported γ-rays of 145Ce were found to be 233, 300, 429 and 915 keV. In Pr fraction, the 2·0 min 148Pr (γ-ray energy = 300 keV) and 12 min 147Pr (the photopeaks at 123 and 313 keV) were identified.

Rapid Separation of Fission-Product Rare Earths and Yttrium by Electromigration

The separation of fission-product La, Ce, Pr, Nd and Y was performed in 4 min by electro-migration. As complexing agent, nitrilotriacetic acid was used at two concentrations of the NTA ion selected so as to optimize mutual separation of the elements. Rapid location of the zone on the paper strip reached after migration was obtained by color reaction of the carrier added to the irradiated sample. The purity of the elements thus separated was checked by γ-ray spectrometry. At the higher concentration of NTA ([[NTA]=1.0×10−2M, pH=4.1) under which all of rare earths and Y migrate toward the anode, the elements were well separated from each other, although appreciable amounts of other F.P. were also found in each fraction. On the other hand, at the lower NTA concentration ([NTA]=4.0 × 10−3M, pH=2.0) where the F.P. all migrate toward the cathode, each zone contained the isotopes of the respective element almost exclusively, except for a few small photo-peaks attributable to other elements. In each fraction, the...

Synthesis and crystal structure of 1: 2 molecular complex between N,N′-(1,3-trimethylene)bis(2-oxy-1-naphthaldimine)copper(II) and 7,7′,8,8′-tetracyanoquinodimethane

Abstract The tetradentate Schiff base nickel(II) and copper (II) complexes with the condensation products of 2-hydroxy-1-naphthaldehyde and diamines such as trimethylenediamine and 1,2-diaminopropane were examined to determine whether the complex can form the molecular complex with TCNQ. The title compound was subjected to a single-crystal X-ray diffraction study. The crystals are monoclinic, space group C2/c, a = 37.343(8), b = 7.717(1), c = 13.888(2) A, β = 96.26(1)°, and Z = 4. The structure was solved by the heavy atom method and refined by the block-diagonal least-squares method to give an R factor of 6.9%. The crystal structure showed that the π-electron donors (naphthalene moieties of the complex) and acceptors (TCNQ) stack alternately, where the naphthalene ring overlaps just on one of the two neighbouring TCNQ molecules and partly on the other and the coordination geometry around the copper ion is pseudo-tetrahedron with the dihedral angle of 26.5° between the CuNO planes.

A study of complexes with a polybasic acid: Am(III) citrate complexes

Abstract A method for the study of complex formation by a polybasic acid has been applied to the study of the Am(III) citrate complexes. The amount of free cation in equilibrium with the complexes was determined by an ion exchange method. At low pH, where the species H3Cit− and H2Cit2− both exist, a series of solutions containing a nearly constant amount of H3Cit−, which the H2Cit2− varied, was prepard. By using these solutions, it was found that complexes with H2Cit2−, AmH2Cit+ and Am(H2Cit)2− were formed while there was no evidence of complexes of the type, Am(H3Cit)x even when the pH is less than 2. At a pH of 6·56, complexes with HCit3−, AmHCit and Am(HCit)23− were found. The formation constants of the different complexes were determined.

Synthesis and characterization of imidazolate-bridged iron(III)-copper(II) and manganese(III)-copper(II) binuclear complexes

Imidazolate-bridged iron(III)–copper(II) and manganese(III)–copper(II) binuclear complexes [FeL1CuL2][BPh4](1) and [MnL1CuL2][BPh4](2) have been prepared and characterized, where H2L1 is 4-methyl-N,N′-bis(salicylidene)-4-azaheptane-1,7-diamine and H2L2 denotes the unsymmetrical quadridentate ligand 4-(6-methyl-8-oxo-2,5-diazanona-1,5-dienyl)imidazole. The magnetic susceptibility data indicated that the spin ground states of the complexes (1) and (2) are S= 2 and respectively, which are produced by antiferromagnetic interaction operating between high-spin iron(III)S1=5//2[manganese(III)S1= 2] and copper(II)S2=½ ions through the L2 imidazolate group. The Mossbauer spectrum of (1) measured at 4.2 K showed a doublet with Δ= 1.30 mm s–1 and δd= 0.49 mm s–1, consistent with high-spin iron(III). The e.s.r. spectrum of a powdered sample of complex (1) measured at 20 K showed no signals, while that of (2) showed several signals.

Synthesis and characterization of a new family of binuclear chelate ligands and their copper(II) complexes

Abstract A new family of binuclear copper(II) complexes with a flexible bridging group has been prepared by the electrophilic substitution reaction of N-salicylaldehyde-N-acetylacetoneethylenediiminocopper(II) with m-xylene disocyanate or hexamethylene diisocyanate. The de-metallation reaction of the copper(II) complexes with hydrogen sulfide gave the corresponding binuclear chelate ligands.

Gamma-Ray Energies and Half-Lives of Praseodymium-148 and -149

Rapid separation using NTA in paper electromigration was applied to the study of the γ-decay of 148Pr and 149Pr produced in the fission of 235U. The γ-ray spectrum was measured with a high-resolution Ge(Li) detector. The γ-transitions found to decay with half-lives shorter than 3 min were: 135, 162, 256, 300, 511, 614, 696, 868, 1,022 and 1,248 keV. Of these, the values of 300 keV, and of 135 and 162 keV were in fair agreement with those reported for 148Pr and 149Pr. The decay plot of the strong photopeak of 300 keV presented good linearity and the accurate half-life of 148Pr could be determined as 2.30±0.03 min, which is longer than the 1.98 min reported for 148Pr. Similar decay plots of both photopeaks at 135 and 162 keV gave a half-life of 2.9±0.1 min for 149Pr, which again is longer than the reported value of 2.3 min. Other low intensity photopeaks at 256, 696, 868 and 1,022 keV decaying with half-lives of 2.1∼2.4 min can possibly be attributed to 148Pr. The γ-transitions of 110, 578 and 742 keV repor...