Yasuo Nakabayashi

CH⋯Metal(II) axial interaction in planar complexes (metal = Cu, Pd) and implications for possible environmental effects of alkyl groups at biological copper sites

Intramolecular M(II)...H-C interactions (M(II)=Cu(II), Pd(II)) involving a side chain alkyl group of planar d8 and d9 metal complexes of the N-alkyl (R) derivatives of N,N-bis(2-pyridylmethyl)amine with an N3Cl donor set were established by structural and spectroscopic methods. The methyl group from the branched alkyl group (R=2,2-dimethylpropyl and 2-methylbutyl) axially interacts with the metal ion with the M...C and M...H distances of 3.056(3)-3.352(9) and 2.317(1)-2.606(1) A, respectively, and the M-H-C angles of 122.4-162.3 degrees . The Cu(II) complexes showing the interaction have a higher redox potential as compared with those without it, and the (1)H NMR signals of the interacting methyl group in Pd(II) complexes shifted downfield relative to the ligand signals. Dependence of the downshift values on the dielectric constants of the solvents used indicated that the M(II)...H-C interaction is mainly electrostatic in nature and may be regarded as a weak hydrogen bond. Implications for possible environmental effects of the leucine alkyl group at the type 1 Cu site of fungal laccase are also discussed.

Evaluation of osmium(II) complexes as mediators accessible for biosensors

Abstract The evaluation of Os(II) complexes as mediators accessible for biosensors was examined according to the determinations of the redox potentials of Os(II) complexes and the second-order rate constants of the reactions as shown in Eqs. (1) and (2). The mixed ligand (1) GOx red +2 Os(III) → k s ( g ) GOx ox +2 Os(II) +2 H + (GOx: glucose oxidase) (2) HRP ox +2 Os(II) +2 H + → k s ( h ) HRP red +2 Os(III) (HRP: horseradish peroxidase) Complexes of Os(II) were synthesized and the redox potentials of Os(III/II) complexes could be lowered by the use of 4,4′-dimethyl-2,2′-bipyridine, imidazole and chloride ion as ligands. The second-order rate constants of the reactions as shown in Eqs. (1) and (2) were greater than that for ferrocenecarboxylic acid (FcCOOH) as a mediator. It is consequently concluded that the mixed ligand complexes of Os(II) can be more efficient mediators than FcCOOH for the fabrication of glucose and hydrogen peroxide sensors.

Capillary isotachophoretic determinations of metal ions by use of complexation equilibria in acetone-water medium

The determination of metal ions by capillary isotachophoresis and the complexation equilibria between metal ions and polyaminopolycarboxylic acids has been investigated. A seven-component mixture of metal ions can be separated in 45% v/v acetone-water medium when EDTA or DCTA is used as the terminating ion. Linear calibration graphs are obtained for a standard mixture of Mn(+), Cu(2+), Zn(2+), Cd(2+), Pb(2+) and Fe(3+) in the range 0.5-5.0 nmole, with relative standard deviations of 1.0% or better. The effective mobilities of the Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes increase in parallel with the stability constants, except for the Cu(II) complexes. It is concluded that the abnormal behaviour of the Cu(II) complexes may be attributed to a difference in steric configuration.

Interactions of glucose oxidase with various metal polypyridine complexes as mediators of glucose oxidation

Abstract. The interaction between glucose oxidase (GOx) and a typical metal complex, which is chemically stable in both oxidized and reduced forms, has been investigated by a voltammetric method. The evaluation of an electron-transfer mediator useful for glucose oxidation is discussed from thermodynamic and kinetic points of view, i.e. the redox potentials of various metal complexes and the second-order rate constants for the electron transfer between GOx in reduced form and the metal complexes in oxidized form. No mediation of glucose oxidation by [Co(bpy)3]2+ (bpy=2,2′-bipyridine) or [Cu(bpy)2]2+ occurred, in spite of their appropriate redox potentials. This was attributed mainly to the lower electron-self-exchange rates of the mediator and the reaction with GOx. All three types of osmium(II) complexes, [Os(PP)n]2+ (n=2 or 3; PP=polypyridine), [OsL2(PP)2]2+ (L=imidazole and its derivatives), and [OsClL(bpy)2]+, acted as excellent electron-transfer mediators for the glucose oxidation. Mixed ligand complexes, [OsL2(PP)2]2+ and [OsClL(bpy)2]+, have been concluded to be more efficient electron-transfer mediators. The electron-transfer rates between the mediator and GOx have been found to be accelerated by intermolecular electrostatic interactions or hydrogen bonds.

Overall stability constants and thermodynamic parameters of various metal 8-quinolinethiolato complexes in nonaqueous solvents

Abstract The overall stability constants of various metal 8-quinolinethiolato complexes ([M(qt) 2 ]; M  Mn, Co, Ni, Cu, Zn, Cd, Hg) in DMSO have been obtained by a combination of the polarography of the sodium salt of 8-quinolinethiol and the potentiometry with a mercury electrode based on the determination of the position of exchange equilibria of the type [Hg(qt) 2 ] + M 2+ ⇌ [M(qt) 2 ] + Hg 2+ . The stability sequence of Mn(II) to Zn(II) complexes was in agreement with Irving—Williams series. Enthalpies and entropies of the complex formation have been also evaluated from the effect of temperature on the overall stability constants. Ethalpies of Mn(II) to Zn(II) complexes were dominated in relation to the overall stability constants and entropies were almost the same values. The overall stability constants of Zn(II), Cd(II), and Hg(II) complexes, however, were contributed to both parameters. Enthalpies of all complexes depended linearly on the softness of metal ions. A nearly linear relationship was found between the logarithmic overall stability constant of [Zn(qt) 2 ] and the donor numbers of the solvents.

DNA Interaction and Cytotoxicity of Cyclometalated Ruthenium(II) Complexes as Potential Anticancer Drugs

To evaluate the anticancer activity of the cyclometalated ruthenium(II) complexes [Ru(bpy)2(C^N)]Cl, we have studied the interaction of these complexes using calf thymus DNA (CT-DNA) and cytotoxicity assays with two tumor (L1210 and HeLa) and a non-tumor (BALB/3T3 clone A31) cell lines. It is suggested that the complexes act as intercalators and/or DNA minor groove binders. Moreover, the complexes display favorable cytotoxicity activities with L1210 and HeLa, which in all cases were significantly more favorable than cisplatin. In contrast, the complexes exhibit appreciably lower cytotoxicity toward BALB/3T3 clone A31.

Electrode reactions of nickel(II)-, copper(II)- and zinc(II)8-quinolinethiolato complexes in N,N-dimethylformamide

Abstract Electrochemical studies of Ni(II)-, Cu(II)- and Zn(II)8-quinolinethiolato (qt) complexes in N,N-dimethylformamide have been carried out. The redox processes of these complexes, [M(qt)2] (M = Ni, Cu, Zn), have been examined by a variety of electrochemical techniques, i.e., polarography, cyclic voltammetry and controlled potential electrolysis. The existence of unusual lower oxidation states (I) or (0) for reduction in all the complexes was confirmed. Electrochemical oxidation of [M(qt)2] at the glassy carbon electrode did not produce the higher oxidation states (III) or (IV), but oxidation of the ligand to 8,8′-diquinolyldisulfide.

Electrode reactions of 8-mercaptoquinoline and manganese(II)-8-mercaptoquinolinato complexes in non-aqueous solvent

Abstract The electrode reactions of 8-mercaptoquinoline and manganese (II)-8-mercaptoquinolinato complexes at a dropping mercury electrode (DME) and a glassy, carbon electrode (GCE) have been studied in N,N-dimethylformamide (DMF). The sodium salt of 8-mercaptoquinoline (8-MQNa) undergoes a reversible one-electron oxidation wave (E1/2=−0.878 V vs. SCE) and an irreversible two-electron reduction wave (E1/2=−2.188 V vs. SCE) at the DME. The existence of bis- and tris-complexes of manganese (II), i.e. [Mn(8-MQ)2] and [Mn(8-MQ)3]−, has been established by analysing the polarograms and absorption spectra. These redox processes have been examined by polarography, cyclic voltammetry, controlled potential electrolysis, and spectrophotometry. These complexes undergo a one-electron oxidation wave at the GCE and a two-electron reduction wave at the DME. Manganese (II) compounds show complex behaviour for the oxidation waves at the DME. The proposed oxidation mechanisms at the DME are: [Mn(8-MQ)2]+Hg→Mn2++[Hg(8-MQ)2]+2 e− or 2[Mn(8-MQ)3]−+Hg ag2[Mn(8-MQ)2]+[Hg(8-MQ)2]+2 e− [Mn(8-MQ)2]+Hg→Mn2++[Hg(8-MQ)2]+2 e− and the reduction steps can be expressed by the following schemes: [Mn(8-MQ)2]+2 e−→[Mn(8-MQ)2]2− or [Mn(8-MQ)3]−+2 e−→[Mn(8-MQ)2]2−+(8-MQ)− (8-MQ)−+2 e−→(8-MQ)3− [Mn(8-MQ)3]− undergoes a single one electron oxidation step at the GCE: [Mn(8-MQ)3]− ag[Mn(8-MQ)3]+e− The oxidation mechanism of [Mn(8-MQ)2] at the GCE is also proposed.

Isotachophoretic separation of trivalent metal complexes of some polyaminopolycarboxylic acids in acetone-water solvent

The isotachophoretic separation of trivalent metal complexes of some polyaminopolycarboxylic acids in acetone-water solvent has been carried out. The variation of the qualitative index, RE, obtained by analysis of the isotachopherograms resulted in a classification into two groups: FeIII, CoIII, InIII and BiIII complexes, and AlIII, CrIII and GaIII complexes. The satisfactory separation of trivalent metal ions was accomplished by employing a polyaminopolycarboxylic acid as the terminating electrolyte. Linear calibration graphs were obtained in the range 2 × 10–5–2 × 10–4 mol dm–3, the injection volume being kept constant at 25 µl.

Syntheses and photodynamic properties of glucopyranoside-conjugated indium(III) porphyrins as a bifunctional agent

The glucopyranoside-conjugated porphyrins, H2TPP{p-O-(CH2)2-O-OAcGlc} (1), [InTPP{p-O-(CH2)2-O-OAcGlc}]NO3 (2), H2TPP{p-O-(CH2)2-O-Glc} (3), [InTPP{p-O-(CH2)2-O-Glc]-NO3 (4) and ZnTPP{p-O-(CH2)2-O-OAcGlc} (5) were synthesized, and characterized by 1H NMR, 13C NMR, ESI-MS, UV-vis spectroscopies and elemental analyses. In the 1H NMR spectrum of 2, two sets of signals were observed for H-atoms of the phenyl group of porphyrin, indicating that 2 has the axial chirality due to a NO3 ion coordinating to the indium atom. Abilities of the singlet oxygen production of these porphyrins, investigated by using 1,3-diphenylisobenzofuran (DPBF) as a quencher, were higher than those of the free-based and zinc porphyrins, reflecting the heavy atom effect. The photodynamic properties of these porphyrin derivatives were investigated against COLO 679. All of the glucopyranoside-conjugated porphyrins exhibited the high photocytotoxicity compared with Laserphyrin®. Above all, 4 exhibited the highest photocytotoxicity, coinciding with the high abilities of this complex for the singlet oxygen production and the cell permeability.