Koichiro Jitsukawa

STRUCTURAL AND SPECTROSCOPIC CHARACTERIZATION OF A MONONUCLEAR HYDROPEROXO- COPPER(II) COMPLEX WITH TRIPODAL PYRIDYLAMINE LIGANDS

A model for the key intermediate in copper oxygenase reactions, the Cu(II)-OOH complex, was prepared with the novel tripodal pyridylamine ligand, bis(6-pivalamide-2-pyridylmethyl)(2-pyridylmethyl)amine. The HOO- moiety is stabilized by hydrogen bonding to two amine H atoms (see structure on the right).

SOD activities of the copper complexes with tripodal polypyridylamine ligands having a hydrogen bonding site

Abstract As a structural mimic of the Arg 141 residue near copper site in native bovine Cu,Zn–superoxide dismutase (Cu,Zn–SOD), four mononuclear copper complexes with tris(2-pyridylmethyl)amine derivatives having a hydrogen bonding site (pivalamido, neopentylamino, or amino groups) at the pyridine 6-position, [Cu(tnpa)(OH)]ClO4 (1), [Cu(tapa)Cl]ClO4 (2), [Cu(tapa)(OH)]ClO4 (3), and [Cu(bppa)](ClO4)2 (4), and two analogous dinuclear copper complexes, [Cu2(tppen)(H2O)2](ClO4)4 (5) and [Cu2(tppen)Cl4] (6), were prepared, and the correlation between the coordination structures of the copper complexes and their superoxide dismutation activities were examined. Their structures in both solution and solid states were characterized by electronic absorption and ESR spectroscopic (for all the complexes) and by X-ray analytical methods (for 1, 2, 5 and 6), respectively. The coordination geometries around the copper ions were determined to be five-coordinate trigonal bipyramidal for 1, 2 and 3 and to be an intermediate of five-coordinate trigonal bipyramidal and square pyramidal for 5 and 6 in both crystal and solution phases, in contrast to four-coordinate square planar structure for 4 reported previously. The cyclic voltammetry measurement of the mononuclear complexes 1–4 showed quasi-reversible redox potentials (Cu(II)/Cu(I) couple) in the range between −330 mV (vs. NHE at pH 7; O2/O2 −) and +890 mV (vs. NHE at pH 7; O2 −/H2O2), which are in the range responsible for superoxide dismutation (SOD) reaction, although the dinuclear copper complexes, 5 and 6, gave only reduction potentials. The SOD activities of complexes 1, 2, and 3 were moderate and those of 5 and 6 were rather high, although 4 showed the lowest activity of all. Those of 1, 2 and 3 with a trigonal bipyramidal structure and hydrogen bonding interaction site are slightly high in comparison with that of the corresponding Cu(II) complex without hydrogen bonding site, [Cu(tpa)(H2O)](ClO4)2 (7). Relatively higher SOD activity observed in complexes 5 and 6 may be explained in terms of higher flexibility in the conformation and cooperativity by dinuclear copper ions.

Synthesis, Structure, and Spectroscopic Properties of [Feiii(tnpa)(OH)(PhCOO)]ClO4: A Model Complex for an Active Form of Soybean Lipoxygenase-1

The cis configuration between the hydroxo and the carboxylato and the three amino groups of the tetradentate, tripodal ligand tris(6-neopentylamino-2-pyridylmethyl)amine favors the formation of hydrogen bonds which stabilize the hydroxo-Feiii complex 1. Thus, its structure closely resembles that of the active center of Feiii -soybean lipoxygenase-1, which also contains a six-coordinate Feiii atom.

An infinite chiral single-helical structure formed in Cu(II)-l-/d-glutamic acid system

Abstract Reaction of Cu(ClO4)2·6H2O with l -glutamic acid ( l -glu) in 1:1 or 1:2 molar ratio at pH 5 gave only the complex [Cu( l -glu)-(H2O)]·H2O, whose crystal structure revealed that the copper atom was coordinated in square-planar geometry, with the amino nitrogen and the carboxylate oxygen of l -glu, the side-chain carboxylate oxygen of a neighboring l -glu, and the oxygen of a water molecule in the equatorial positions. Weak coordination of two additional glutamate oxygens to both axial positions complete a distorted octahedron. The [Cu( l -glu)(H2O)] units linked by coordination of the side-chain carboxylate group form an infinite left-handed single helix; the use of d -glu in place of l -glu gives a right-handed helix, indicating that the glu enantiomerism determines the helicity. Thermogravimetric and differential thermal analyses of the complex showed reversible desorption of just two water molecules at 95–130°C, whose behavior was examined by ESR and circular dichroism spectral and powder X-ray diffraction methods in solid state. The crystals obtained from the reaction of Cu(II) ion with dl -glu showed spontaneous resolution.

Reverse reactivity in hydroxylation of adamantane and epoxidation of cyclohexene catalyzed by the mononuclear ruthenium-oxo complexes with 6-substituted tripodal polypyridine ligands

Abstract The electronic character of the ruthenium complexes with tripodal polypyridine ligands, which is controlled by the substituted groups at pyridine 6-position, gives rise to differences in the reactivity for the ruthenium catalyzed hydroxylation of adamantane and epoxidation of cyclohexene with PhIO as an oxidant; Ru complexes containing electron-withdrawing groups ( 1 , 3 , and 5 ) promote the epoxidation, while those containing electron-donating groups ( 2 , 4 , and 6 ) promote the hydroxylation.

(Catecholato)iron(III) complexes with tetradentate tripodal ligands containing substituted phenol and pyridine units as structural and functional model complexes for the catechol-bound intermediate of intradiol-cleaving catechol dioxygenases

Abstract This paper reports the synthesis and structures of (catecholato)iron(III) complexes with tetradentate tripodal ligands (L R′,R″ ={2-hydroxy-3-R′-5-R″-phenyl-bis(2-pyridylmethyl)amine}) containing substituted phenol and pyridine units: [Fe III (L R′,R″ )(DBC)] ( 1a : R′,R″=H,H; 1b : R′,R″=Me,Me; and 1c : R′,R″=H,Cl, DBC=3,5-di- tert -butylcatecholato). X-ray structure analysis has revealed that the coordination arrangement around the iron atom of 1a is similar to that proposed for the active site of the catechol-bound intermediate of protocatechuate 3,4-dioxygenase (3,4-PCD). The series of complex 1 derivatives has been synthesized by two different methods: (i) reaction of [Fe III (L R′,R″ )(acac)] + ( 2a : R′,R″=H,H; 2b : R′,R″=Me,Me; and 2c : R′,R″=H,Cl, acac=acetylacetonato) with 1 equiv. of DBC and 1 equiv. of Et 3 N in N,N -dimethylformamide (abbreviated as DMF), and (ii) reaction of [Fe III (L R′,R″ )Cl 2 ] ( 3a : R′,R″=H,H; 3b : R′,R″=Me,Me; and 3c : R′,R″=H,Cl) with 2 equiv. of AgOTf (OTf=O 3 SCF 3 − ), 1 equiv. of the catechols, and 2 equiv. of Et 3 N in DMF. The exogenous acac ligand of 2 acts as a Lewis base like the Tyr447 ligand in the active site of 3,4-PCD in the formation of the catechol-bound intermediate. Complexes 1 , 2 , and 3 have been characterized by X-ray analysis, visible and EPR spectroscopies, and cyclic voltammetry. Oxygenation of the bound DBC on 1 in the presence of O 2 has also been investigated and is discussed based on the Lewis basicity of the tripodal ligand containing the substituted phenolato group which is introduced to mimic the Tyr408 ligand of 3,4-PCD.

Structures and electrochemical properties of the Co(III) ternary complexes containing NO3-type tripodal tetradentate ligands and amino acids: effect of the outer coordination sphere on the electrochemical properties

Abstract With a view to understanding the effect of the outer coordination sphere of metal complexes on the redox potential, the electronic absorption spectra, X-ray crystal structure and cyclic voltammograms were investigated of aqueous and ethanol solutions containing the complexes [Co(X)(aa)], where X denotes an NO3-type ligand such as bcmpa (N,N-bis(carboxymethyl)- l -phenylalanine), nta (nitrilotriacetic acid), bcmga (N,N-bis(carboxymethyl)- l -glutamic acid), bcmle (N,N-bis(carboxymethyl)- l -leucine), and aa is an amino acid. Examination of the solution and crystalline structures revealed that the outer coordination sphere of the Co(III) complexes did not exert any influence on the inner coordination sphere of the Co(III) ion. The Co(III) complex systems showed irreversible redox behavior in both the aqueous and ethanol solutions. This is discussed on the basis of the relationship between the hydrophobicity of the outer coordination sphere and the electron transfer reaction by use of reduction potentials.

Epoxidation activities of mononuclear ruthenium-oxo complexes with a square planar 6,6'-bis(benzoylamino)-2,2'-bipyridine and axial ligands

Abstract Some ruthenium complexes, [RuII(babp)(dmso)(L)], with a square planar ligand, H2BABP, and axial ligands, L (L=dmso, imidazole, or pyridine derivatives), have been prepared as catalysts for oxygen-transfer reactions. The catalytic activity and selectivity of the metal–oxo species derived from these complexes and PhIO have been affected by the axial ligands L, in which active species has been interpreted in terms of contribution of both characters of Ru(V)O and Ru(IV)O·.

Strukturelle und spektroskopische Charakterisierung eines einkernigen Hydroperoxo‐Kupfer(II)‐Komplexes mit tripodalem Pyridylaminliganden

Ein Modell fur die Schlusselintermediate bei der Reaktion von Kupferoxygenasen ist der Kupfer(II)-OOH-Komplex mit dem neuartigen, tripodalen Pyridylaminliganden Bis(6-pivalamid-2-pyridylmethyl)(2-pyridylmethyl)amin. Der HOO−-Rest wird hierin durch zwei Amin-H-Atome uber Wasserstoffbrucken stabilisiert (siehe Strukturbild rechts).

A novel amino acid-binding receptor based on weak non-covalent ligand-ligand interactions

Abstract The Co(III) complex with the (N)(O)3-type tripodal tetradentate ligand, bis-N,N-carboxymethyl- L -phenylalanine (BCMPA, H3bcmpa), can site-specifically coordinate a bidentate amino acid (AA, Haa) in the trans-N configuration rather than the cis-N form through the non-covalent weak interligand interactions of hydrogen bondings, steric repulsion, and electrostatic repulsion, on the basis of the 1H NMR spectroscopic data and X-ray crystallographic analysis. In addition, the [Co(bcmpa)(aa)]− complex with cis-N form isomerizes to the trans-N form, which confirms that the trans- N complex is thermodynamically more stable than the cis-N one. These interactions between the coordination sites of bcmpa and aa ligands are of interest as a molecular recognition model for the enzyme(bcmpa)-substrate(aa) complex.