Takeshi Yamamura

The Relation Between Catalytic Ability for Hydrogen Evolution Reaction and Characteristics of Nickel‐Tin Alloys

The relation between catalytic ability for hydrogen evolution reaction and characteristics of nickel-tin alloys prepared by electroplating was investigated. The catalytic ability was found to strongly depend on preparation conditions. Hydrogen overvoltage was drastically decreased with an increase of the width at half height of x-ray diffraction peaks which was related to the tin content. The nickel-arsenide-type structure and the initial high catalytic ability remained unchanged after an 800 day durability test, suggesting that the addition of the specific amount of tin, which itself had high overvoltage, enhanced the catalytic ability of nickel

Studies on the molecular structure of spinach ferredoxin. I. Comparison of two molecular species of ferredoxin

Abstract By hydrophobic chromatography on a Toyopearl HW-60F column, spinach ferredoxin was separated into the major (Fd-I) and minor (Fd-II) components in the native forms. These ferredoxins could be distinguished from each other as two different protein bands on a SDS-polyacrylamide gel electrophoresis in the presence of 4 M urea, but not in the absence of urea. Although both reduced ferredoxins exhibited the EPR spectra of rhombic symmetries having an identical gav value of 1.96 at 22 K, the anisotropy of the g-factors of Fd-II was slightly larger than that of Fd-I; gx = 1.890, gy = 1.955, and gz = 2.043 for Fd-I, and gx = 1.875, gy = 1.962, and gz = 2.049 for Fd-II. In the UV region, the absorption spectrum of Fd-I was subtly different from that of Fd-II. In the visible region, however, the absorption spectrum of Fd-I was essentially identical with that of Fd-II. In contrast, the CD spectra of both ferredoxins were different from each other mainly in the visible region. Upon addition of urea, the respective CD and absorption spectra of both ferredoxins changed in a similar manner. In addition, urea denaturations of both ferredoxins were found to consist of at least three processes from analyses of the time courses of the CD changes. The first and second processes of Fd-I were found to proceed faster than those of Fd-II, while the third process of Fd-I was found to occur slower than that of Fd-II. The iron-sulfur clusters decomposed during the third processes. These results lead to the conclusions that (1) the molecular structure of ferredoxin is maintained through the interaction between the iron-sulfur cluster and the protein moiety, and (2) the structural changes in the protein moiety of ferredoxin result in the geometrical alteration of the cluster.

Square planar nickel compounds with bulky thiols

Abstract Details of the syntheses and the results of X-ray structural analyses of square planar Ni compounds with aliphatic thiolato-sulfur ligands, [Ni(dpmep)2] (1) and [Ni(tpttd)] (2), where Hdmep and H2tpttd are the abbreviations for 2-(2,2-diphenyl-2-mercaptoethyl) pyridine and 2,2′,11,11′-tetraphenyl-1,5,8,12-tetrahiadodecane, respectively, are presented. Each of the thialato-sulfur atoms of these compounds is sterically protected by two benzene rings at the α carbon position to suppress dimerization upon synthesis. 1 · 1.5CH2Cl2 · MeCN crystallizes monoclinic P21/n with a = 18.362(3), b = 16.894(4), c = 13.273(4) A , β = 104.59(2)°, V = 3984(3) A 3 and Z = 4.2 · 1.5 MeCn crystallizes triclinic P 1 with a = 15.091(6), b = 15.661(3), c = 14.085(7) A , α = 96.00(2), β = 90.89(4), γ = 99.70(2)°, V = 3261(4) A and Z = 4. The Niue5f8S and Niue5f8N bond lenghts of 1 were compared with those of the nickel center in the A-cluster of carbon monoxide dehydrogenase.

Boc-Glu-Thr-Ile-His-OMe/Zn2+ in terms of the zinc-binding sites of proteases

Abstract Reaction of Boc-Glu-Thr-Ile-His-OMe (Boc: butoxy carbonyl) (H 2 1 ), and Zn(ClO 4 ) 2 ·6H 2 O in N,N -dimethylformamide (DMF) was studied using NMR and mass spectrometry with respect to the active sites of proteases. The study of H 2 1/Zn 2+ = 1:1 mixture in DMF-d 7 revealed that Zn 2+ is bound to the His-imidazolyl group. The results of IR experiments on the 1:1 dried material suggested that the Glucarboxyl group still remains in the form of -COOH. Mass spectrometry showed that Zn 2+ in H 2 1 /Zn 2+ attracts water molecules under the ionization conditions of fast atom bombardment. The temperature ( T ) dependence of 1 H NMR of H 2 1 /Zn 2+ = 1:1 in DMF-d 7 , studied in the temperature range 218–323 K, revealed that the Zn 2+ unit undergoes protonation and hydration at low temperatures (below 253 K). The chemical shifts ( δ ) of the amide protons were nevertheless linearly dependent on temperature over the range 218–323 K, meaning that the 1:1 solution obeys the common reaction equilibrium and that the averaged main-chain folding of the peptide moiety is conserved. Based on this finding, the distance geometry and restrained molecular dynamics analyses were carried out using the distance information on 61 1 H— 1 H pairs, extracted from the rotating frame nuclear Overhauser effect spectroscopy experiment on this solution (300 K). These analyses revealed that the averaged main-chain folding of the Glu-Thr-Ile-His is just superimposed on that of the Zn 2+ binding sites of proteases forming a single helix with the Glu carboxyl group situated in the vicinity of the His imidazole group, or is directly but distally bound to Zn 2+ (in the case of γ-COO Glu − ). The hydrogen bond between γ-COO Glu − and the H 2 O on Zn 2+ was also found in comparatively higher energy area. Gel chromatography of the dried material obtained from H 2 1 /Zn 2+ = 1:1 mixture gave only [(H 1 ) 2 Zn] ( 2 ), as a discrete compound. The coordination atoms to Zn 2+ in 2 were assigned as Glu amide (N − ) and His imidazole nitrogens.

Synthesis and characterization of nickel(II) complexes containing ligands derived from disaccharides and 1,3-diaminopropane

The reaction of [Ni(tn)3]2+ ions (tn = 1,3-diaminopropane) with disaccharides having a glucose reducing terminal, i.e. maltose, lactose, cellobiose, and melibiose, in the presence of a catalytic amount of ammonium chloride gave blue, paramagnetic bis(N-D-aldosylpropane-1,3-diamine)nickel(II) complexes. The complexes were characterized by elemental analysis, magnetic susceptibilities, electronic absorption and circular dichroism spectroscopies, X-ray absorption and crystallographic analyses. The complex bis[N-(4-O-α-D-glucopyranosylglucosyl)propane-1,3-diamine]nickel(II) bromide dihydrate crystallizes in the hexagonal space group P6422, with a= 22.125(8), c= 21.464(9)A, and Z= 6. The structure was solved by Patterson methods and refined by full-matrix least-squares techniques to R= 0.080 and R′= 0.094. The complex cation has C2 symmetry and the central nickel atom is octahedrally co-ordinated by two tridentate glycosylamine ligands formed from maltose and tn. Each ligand is bonded through the oxygen atom of the hydroxyl group at C2 of maltose and through the two nitrogen atoms of the diamine in a meridional mode. The co-ordination behaviour of the glucose unit in the octahedral nickel(II) complexes has been established. In the crystal packing, the complex cation exists in a novel dimeric form supported by intermolecular hydrogen bonds, which might provide some fundamental information concerning sugar–sugar interactions in biological systems.

Photoelectrochemical behaviour of ruthenium(II) complex layers at a platinum electrode immobilized by the common-ion effect in aqueous electrolyte solution

The photoelectrochemical behaviour of multi-molecular layers of Ru(bipy)3(BPh4)2, where bipy = 2,2′-bipyridine, immobilized on a platinum electrode by the common-ion effect was studied under potentiostatic conditions in an aqueous electrolyte solution with no added redox agents. Upon illumination, anodic photocurrents were generally observed, the quantum efficiency being 3.5 × 10–4 at 480 nm with an applied potential of +150 mV (saturated calomel electrode). The effects of applied potential, light intensity, and pH were also examined. During each experiment, the surface layer stabilized by the common-ion effect was sufficiently stable to obtain reproducible data. The results are interpreted in terms of the reaction of a photo-generated ruthenium(III) complex with OH– ions.

Visible light-assisted electrochemical reduction of oxygen at a platinum electrode coated with surface active cobalt(II) and manganese(III) porphyrins

Visible light-assisted oxygen reduction with no applied potential was performed at a platinum electrode coated with surface active CoII and MnIII porphyrins.