Shigeo Nakagawa

Synthesis and Effectively Reversible Oxygenation of Some “Picket Fence” Type Porphyrinatocobalt(II) Complexes

Abstract Some “picket fence” type meso-tetrakis(2-substitu-ted phenyl)porphyrinatocobalt(II) complexes were newly synthesized, which had different peripheral substituents in their numbers and/or geometrical dispositions to form “cavity” on the porphyrin plane. Their O2 affinities were determined with 1-methylimidazole as an axial base at various temperatures in solution, by visible spectral measurements. On the basis of thermodynamic quantities, four neopentylcarbonylamino groups were the most effective as a picket fence, and the thermodynamic values of the complex were nearly comparable to those of cobalt(II)myoglobin. It was found that O2 affinity decreased with an increase in ΔH°, regardless of ΔS°. In the case of using various amines as an axial base, imidazoles were effective to enhance O2 affinity rather than pyridines.

Phase transition and electrical properties of mono-, di-, tri- and tetraalkyl (or aryl) ammonium tetrahalogenocuprates(II)

Abstract The following four series of organoammonium tetrahalogenocuprates(II) were systematically prepared: (RNH 3 ) 2 CuX 4 , (R 2 NH 2 ) 2 CuX 4 , (R 3 NH) 2 CuX 4 and (R 4 N) 2 CuX 4 (where R = alkyl or aryl group; X = bromide or chloride ion). Their phase transitions and electrical properties were investigated by means of DTA, DSC, electrical conductivity measurements, and IR and UV spectrophotometries.

Cooperative dioxygen binding to the bi-bridged dimeric porphyrinatocobalt(II) complexes

Abstract Two types of bi-bridged dimeric porphyrinatocobalt(II) complexes, ‘picket fence’ type and ‘strapped’ type as a hemoglobin model, and the corresponding monomeric complexes were designed and synthesized. Their equilibrium constants for monodentate or bidentate axial ligands and their dioxygen affinities were measured in DMF. A strapped type dimer complex binds 1,2-bis(4-pyridyl)ethane to form a ‘sandwich’ structure and reveals the cooperative effect upon dioxygen binding. To explain such hemoglobin-like cooperativity, an intramolecular mechanism is postulated in keeping with the proposal of Perutzs stereochemical trigger mechanism.

Binding of nitric oxide to water-soluble iron(III) porphyrins

Abstract Binding equilibrium of NO to three water-soluble iron(III) porphyrins was examined spectrophotometrically in aqueous solution. Effects of electron-donor ability and hydrophobicity of porphyrin on the NO binding were discussed on the basis of the thermodynamic data for the binding. In aqueous and organic mixed solvents, NO binding to 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinatoiron(III) was found to be a two-step reversible reaction. With increasing the NO partial pressure, the Fe(III) complex firstly produces Fe(III)–NO species, followed by generation of Fe(II)–NO species. The results suggest that water would play an essential role in this phenomenon.

Effect of aromatic-aromatic interaction on ligand binding to zinc porphyrins

Abstract Two zinc porphyrins with a superstructure around the ligand binding sites have been prepared and characterized by 1 H NMR spectroscopy. The binding properties of amine ligands to the zinc porphyrins were analyzed by UV-Vis and 1 H NMR spectroscopy. The thermodynamic parameters for ligand binding to the zinc porphyrins were estimated and compared to those of zinc porphyrins with and without the superstructure. The binding of aromatic amines to the superstructured zinc porphyrins bearing phenyl groups was found to be strong compared to the binding of butylamine to the zinc porphyrins. The enhanced binding of aromatic ligands to the zinc porphyrins was discussed in terms of the relation between ligand geometries and the superstructure.

Syntheses and characterization of cobalt(II) complexes of dimeric ‘picket fence’ porphyrins

Abstract A series of dimeric picket fence porphyrinatocobalt(II) complexeses in which the length of the bridging chain controls the dioxygen affinity was newly derived from the coupling of two meso -mono- (β-o-aminophenyl)-tris-(α,α,α-o-pivaloylamidophenyl)- porphyrins with (CH 2 ) n (COCl) 2 ( n = 1, 3, 5 or 7). Some of the dimeric complexes form a unique ‘sandwich structure’ upon binding with certain bidentate ligands, and their dioxygen affinities are greatly increased compared with those for corresponding monomeric complexes. The relationship observed between the length of the bridging chain and the dioxygen affinity of the dimer complex having a sandwich structure is interpreted in terms of the displacement mechanism of the metal atom from a porphyrin plane.

Syntheses and characterization of porphyrins and their zinc complexes appending a multi-dentate ligand

Porphyrins with a multi-dentate ligand have been prepared by a covalent binding of nitrilotriacetic acid (NTA) to meso-mono (ortho- or para-aminophenyl)-triphenylporphyrin. The equilibrium between the porphyrins and Zn2+ has been analyzed by ultra violet–visible (UV–Vis) and 1H NMR spectroscopies and the porphyrins are found to form complexes with porphyrin/zinc ratios of 1:1 and 1:2. The zinc complexes with the porphyrin/zinc ratios of 1:1 and 1:2 have been prepared and characterized by UV–Vis, infrared (IR) and 1H NMR spectroscopies. An accelerated zinc incorporation reaction into the porphyrin appending NTA at its ortho-phenyl group is reported.

Modified picket fence porphyrin Fe(III) and Zn(II) complexes as a model for hemoglobin mutants

Abstract Zinc(II) and iron(III) complexes of three modified picket fence porphyrins in which one of the four pivalamido pickets was replaced by a meta -methyl, -amino, or -hydroxy benzoylamino picket were synthesized. The iron complex containing the phenolic OH on the picket fence mimics the abnormal active sites for a type of hemoglobin mutant, Hb M. Proton NMR and visible spectra for the zinc complexes have shown that the NH 2 or OH group on the picket fence does not coordinate to the central metal ion in CH 2 Cl 2 at room temperature. Contrary to this, coordination of the phenolic OH (or O − ) on the picket fence to form OFeO axial geometry was found for the iron complex by ESR measurements in CH 2 Cl 2 at 77 K. On the other hand, the ESR spectra for the three iron complexes with 1-methylimidazole under basic conditions have shown the presence of two regioisomers in OFeN axial geometry, because of the unsymmetrical distribution of the picket fences on the porphyrin plane.

Synthesis of Some Protic Picket Fence Porphyrinatocobalt(II) Complexes and Their Reactions with Dioxygen as Hydrogen-Bond Models in Oxy Hemoproteins

Abstract Some specific picket fence porphyrinatocobalt(II) complexes were newly synthesized and characterized. The complexes contain one protic substituent capable of forming intramolecular hydrogen bond with the dioxygen molecule coordinated to the central metal ion. Their reactions with dioxygen molecule were measured spectrometrically in solution containing an axial base, and the thermodynamic functions were determined. The results indicate that the protic groups promote the irreversible oxidation of Co(II) to Co(III). This effect may be ascribed to decreased electron density at the central Co(II) ion, which is resulted from shifted electron density toward the hydrogen atom of the protic group through the coordinated O2 molecule by hydrogenbond formation or the like. It is also found that the complexes prepared have lower O2 affinity than the corresponding complexes with no protic substituent and that the decreased binding energy −ΔH° of the dioxygen molecule to the complexes brings about the increased...

Synthesis and properties of water-soluble porphyrins bearing multidentate ligands

Water-soluble porphyrins bearing multidentate ligands were prepared by covalent binding of nitrilotriacetic acid to 5,10,15,20-tetrakis(4-aminophenyl)porphyrin or three atropisomers of 5,10,15,20-tetrakis(2-aminophenyl)porphyrin. The acid-base properties and monomer-dimer behavior of the porphyrins were affected by the positions of the multidentate ligands with respect to the porphyrin plane. Among the porphyrins, the porphyrin bearing multidentate ligands at the para position of the phenyl groups dimerized in an aqueous solution. The association constants of the porphyrins with various aromatic compounds were studied in water at pH 7.4 containing 10 mM HEPES at 25°C. These values varied with the structure and charges of both the porphyrins and the aromatic compounds. The association constants of the porphyrin bearing multidentate ligands at the 2-position of the phenyl groups were small compared to those of the porphyrin bearing multidentate ligands at the 4-position.